MS by System

7/31/2019 MS by System

1/44

Cells

Definition

Cells are the smallest unit or the building block of all living things.

Anatomy of a Cell

Basic parts of a cell consist of:

1. Nucleus2. Cytoplasm3. Plasma membrane

The nucleus is located at the most central part of a cell which is surrounded by a semi fluid component ofa cell called a cytoplasm. The cytoplasm is enclosed by the outer cell boundary called the plasma

membrane.

The Headquarters: Nucleus

The control center of a cell is the nucleus. This part of a cell contains the genetic material called DNA

(deoxyribonucleic acid) which is encloses all data of instruction for building a persons protein and cell

production.


2/44

Parts of a nucleus

1. Nuclear Membrane (nuclear envelope)a double membrane barrier that binds the nucleus. It hasa selective permeability.

2. Nucleoplasma jelly-like fluid that is enclosed by the nuclear membrane. It is in this part wherethe nuclear components are floating.

3. Nucleolismall, dark-staining round bodies. It is in this area where ribosomes are broughttogether. Ribosomes are the actual site of protein synthesis.

4. Chromatinloose network of bumpy threads that is dispersed throughout the nucleus. When celldivision occurs, the chromatin forms the chromosomes.

The Factory Area: Cytoplasm

The cytoplasm is the area where cellular activities take place. It is

located outside the nucleus and inside the plasma membrane.

Major elements of a cytoplasm

1. Cytosolsuspends the other elements in cytoplasm.2. Organellesthe metabolic machinery of a cell.3. Inclusionsstored nutrients or stored cell products.

Cytoplasmic Organelles

Mitochondriareferred as the powerhouse of the cell as it supplies ATP. It is a sausage-shapedorganelle that is composed of a double membrane situated in each side.

Ribosomesactual site of protein synthesis. Endoplasmic Reticulumit carries substances (mostly protein) from one part of the cell to

another.

1. Rough Endoplasmic Reticuluman organelle that builds materials of cellular membranes.This structure is also referred as the cells membrane factory and it is studded with

ribosomes.2. Smooth Endoplasmic Reticulumbasically functions in lipid metabolism and the clearing of

drugs and pesticides. It is essential in cholesterol and fat synthesis and breakdown. Liver

cells contain a large amount of smooth endoplasmic reticulum.


3/44

Golgi apparatussituated close to the nucleus. It is involved in the modification and packagingothe proteins from the rough ER through the transport vehicles.

Lysosomescontains digestive enzymes. These enzymes are formed by the ribosomes andpackaged by the Golgi apparatus.

Peroxisomescontains oxidase enzymes that utilize molecular oxygen to cleanse harmful andpoisonous substances (e.g. alcohol and formaldehyde). More importantly, it is responsible forconverting free radicals to hydrogen peroxide then to water with the presence of the enzymecatalase.

Cytoskeletondetermines the shape of the cell and provides support to other organelles. Centriolesdirect the formation of the mitotic spindle during cell division.

Plasma Membrane or Cell Membrane

The cell membrane separates the cells from the surrounding and contains all the cellular components or

materials. Its structure consists of the following:

Phospolipids Cholesterol Polar heads of phospholipid molecules Bimolecular lipid containing proteinsthe proteins are responsible for the specialized function o

the cell membrane. Proteins in plasma membrane could be:

1. Enzymes2. Glycoprotein or sugar-proteins = determines blood type, serves as receptors of certain bacteria,

viruses and toxins. It also plays a role in cell-to-cell communication or interaction.

Most proteins that are found on the area of plasma membrane have to do with transport functions. Water

or small water-soluble molecules or ions can move through cells as proteins gather together to form tinypores from protein channels. Other proteins are responsible for attaching to a substance and transport it

towards the cell through the membrane.

Nonpolar tails of phospholipids moleculesA plasma membrane has two common specializations namely:

Microvilli Membrane junctions

Microvilli are the minute finger-like projections of the plasma membrane that is responsible for

increasing the cells surface area for absorption making the process occurring more quickly. Themembrane junctions, on the other hand, vary structurally depending on their roles:

Tight junctionsthese are resistant junctions that fuse cells together into impermeable structurethat will prevent the substances from passing through the extracellular space between the cells.

Desmosomesprevent cells from mechanical stress. For instance, skin cells are prevented frombeing pulled apart (mechanical stress) because of the presence of desmosomes.


4/44


5/44

Physiology of a Cell

The cells internal structure performs various functions such as:

Metabolism (using nutrients to build new cell material, break down substances and make ATP)

Digestion Excretion (dispose wastes) Reproduction Growth Movement Irritability (response to a stimulus)

Two major period of cell cycle:

Interphase or Metabolic phase Cell division

Cell Division

Functions of cell division:

1. Promote growth by producing more cells.

2. Repair processes

Before cell division takes place the genetic materials are duplicated precisely. DNA replication occurs

towards the end of interphase period. The following processes take place chronologically:

DNA helix uncoils and slowly divides its nucleotide chains. Individual nucleotide contains a setof instruction or serves as template for building another nucleotide strand.

Nucleotides unites in complementary ways such as the following:1. Adenine (A) ALWAYS bonds to thymine (T)

2. Guanine (G) ALWAYS bonds to cytosine (C)

Identical DNA molecules are formed from the original DNA helix. Each DNA consists one old and one newly constructed nucleotide strand.

Events of Cell Division:

1. Mitosis: division of the nucleus

2. Cytokinesis: division of cytoplasm


6/44

MITOSIS

The division of the nucleus is termed as mitosis. This event occurs after DNA replication takesplace. When the nucleus divides, the daughter cells contain the same genetic information as the

original mother cell.

Stages during mitosis are as follows:

Prophasestage where nuclear envelope and nucleoli have broken down and disappeared.Chromosomes in during this time have joined the spindle fibers through the centromeres.

Detail of event:

During this period, the chromosomes appear due to the coiling and shortening of the chromatinthreads. Each chromosome is made up of a pair of chromatid which is held together by a

centromere (small button like body). Mitotic spindle is brought together by separation and movin

of the centrioles to the opposite side of the cell.

Metaphasechromosomes have gathered together during this period and are lined up at the centeof the spindle midway between the centrioles (metaphase plate).

Anaphasechromatids that are held together split (now called chromosome again) and begins tomove gradually apart from each other to the opposite ends of the cells. This phase ends when the

chromosome movement ends.

Telophasethe reverse of prophase.

CYTOKINESIS

The division of the cytoplasm begins during the late anaphase period and ends or is alreadycompleted during the telophase stage.


7/44

Muscular SystemMuscles

machines of the body Muscle make up nearly half the bodys mass. The essential function of muscle is contraction

or shortening. This unique characteristic setsmuscle apart from other tissues in the body.

All body movements depend on the muscles.

Thus, muscles can be viewed as themachines of the body.

Functions of the muscles

1. Produces movement. All movements of thehuman body are result of muscularcontraction.

2. Maintaining posture. The skeletal muscles inthe body maintain posture.

3. Stabilizing joints. Presence of muscletendons reinforces and stabilizes joints that

have poorly fitting articulating surfaces.4. Generating heat. Heat is a by-product of

muscle activity. This heat is essential in

maintaining normal body temperature.

Types of muscles

Skeletal muscles

Also called: voluntary muscle, striated muscle This type of muscle attaches to the bodys skeleton. Because of their attachment to the bony

part of the body smoother contours of the body are formed. Skeletal muscle fibers are cigar-shaped, multi-nucleate cells and are the largest of the muscle fiber types. This is the only

muscle type that can be controlled consciously, thus it is a voluntary muscle. Since its fibersappear to be striped it is known as striated muscle.

Summary of the characteristic of Skeletal Muscles:

1. Subject to conscious control.2. Multinucleated.3. Cigar-shaped.4. Attaches to the bodys skeleton5. Soft and fragile.6. Its tissue can rapidly contract and with great force.7. Tires easily.8. Contraction is abrupt and rapid.


8/44

What is the reason why skeletal muscles are not ripped apart as they exert effort?

Skeletal muscles do not rip apart after exerting effort because thousands of skeletal musclefibers are bundled together by connective tissues which are responsible for providingstrength and support to the muscle as a whole.

Structure or Parts of Skeletal Muscle

1. Endomysium a delicate connective tissue sheath that encloses each skeletal muscle fiber.2. Perimysium a coarse fibrous membrane that wraps the sheathed muscle fibers.3. Fascicle bundle of fibers formed from group of sheathed muscle fibers wrapped by

perimysium.4. Epimysium a tough overcoat of connective tissue that bounds together fascicles. This is the

connective tissue that covers the entire muscle.

5. Tendons these are cordlike structures that are formed from epimysia. These are composedof mostly collagenic fibers that can cross rough bony projections. Aside from anchoringmuscles, tendons are very important in providing durability.

6. Aponeuroses these are sheet like structures that attaches muscles indirectly to bones,cartilages or connective tissue coverings of each other.

Smooth Muscles

Also called: visceral muscles, non-striated muscles,involuntary muscles

Smooth muscles, unlike skeletal muscles, have nostriations. It is controlled involuntarily, meaning to

say individuals cannot consciously regulate it. If

skeletal muscles are found in the bones, smoothmuscles are found on the walls of hollow visceralorgans such as the stomach, urinary bladder and

respiratory passages. The main function of smooth

muscles is to propel substances along a definitetract or pathway within the body. These muscleshave only one nucleus and are spindle-shaped.

Summary of the characteristics of smooth muscles

1. Involuntary control.2. Found on the walls of the hollow visceral organs.3. Have no striations.4. Propels substances along a fixed tract inside the body.5. Spindle-shaped.6. Have a single nucleus.7. Arranged in layers or sheets. Most often, it is arranged in two layers, one circular the other

longitudinal.

8. Alternately contracts and relaxes to change the shape and size of an organ.9. Contraction of these muscles is slow and sustained.


9/44

Cardiac Muscle

Unlike the other two types of muscles mentioned above, cardiac muscle is only found in oneplace in the body the heart. The function of the heart as the pump propelling blood intothe blood vessels and to all tissues of the body, is carried out because of the presence ofcardiac muscle. This muscle has similarities to skeletal muscles as it is striated and smooth

muscles as it is involuntary and cannot be controlled consciously. Cardiac muscle fibers arebranching cells joined together by special junctions called intercalated discs.

Summary of the characteristics of cardiac muscle

1. Only found in the heart.2. Striated.3. Involuntary control.4. Cushioned by small amounts of soft connective tissue.5. Arranged in spiral or figure 8-shaped bundles.6. Contracts at a steady rate set by the hearts pacemaker.

Types of Muscles in the BodyCharacteristic Skeletal Smooth Cardiac

Location in the body Attached to bones Located in the walls ofthe hollow visceral

organs with the

exception of the heart

Walls of the heart

Muscle fiber shape and

appearance

Single, cigar shaped,

very long, cylindrical,

striated, multinucleatedcells

Single, no striations,

fusiform, cells have

single nucleus

Branching cell chains,

uninucleate, with

striations, intercalateddiscs

Regulation ofcontraction

Voluntary Involuntary Involuntary

Speed of contraction Slow to fast Very slow Slow

Rhythmic contraction No Yes, in some Yes


10/44

Gross anatomy of Skeletal Muscles

Muscles in the head and neck

Facial Muscles

1. Frontalis covers the frontal bone. This muscleruns from the cranial aponeurosis to the skin ofthe eyebrows where it inserts. Frontalis muscleallows a person to raise his or her eyebrows and

wrinkle ones forehead.2. Orbicularis Oculi the muscle fibers of this

muscle run in circles around the eyes. It is the

presence of this muscle that an individual isable to close his or her eyes, squint, blink andwink.

3. Orbicularis Oris also called the kissing muscle.This circular muscle runs around the mouth.This is responsible for closing and protrudingones mouth.

4. Buccinator this muscle runs across the cheekand inserts into orbicularis oris. This muscleplays a vital role during chewing. It is listed as achewing muscle as it compresses the cheek to

hold the food between the teeth duringchewing. When a person is whistling andblowing a trumpet this muscle flattens the cheek.

5. Zygomaticus this muscle is referred to as the smiling muscle as it raises the corners ofthe mouth upward.

6. Chewing muscles aside from buccinators which is described above, chewing musclesinclude the masseter and the temporalis muscle. Masseter is the muscle covering the lowerjaw and is responsible for closing the jaw when chewing by elevating the mandible. Thetemporalis muscle, a fan-shaped muscle, inserts into the mandible and acts as a synergist othe masseter in closing the jaw.

7. Neck muscles muscles in the neck are the platysma and sternocleidomastoid. Platysma isthe sheet like muscle that covers the neck anterolaterally. Its action is to pull the corners ofthe mouth inferiorly which produces downward sag of the mouth. The other muscle of the

neck, the sternocleidomastoid, is found on each side of the neck. The sternocleidomastoidmuscles are two-headed muscles. Of the two heads of each muscle, one arises from the

sternum and the other arises from the clavicle. When the sternocleidomastoid musclescontract together, the neck flexes. If only one muscle of the sternocleidomastoid musclecontracts, the head is rotated toward the opposite side.

Trunk Muscles

Anterior Muscles

1. Pectoralis major this muscle is a large fan-shaped muscle covering the upper part of thechest. The adduction and the flexion of the axilla is the action of this muscle. It forms the

anterior wall of the axilla.


11/44

2. Intercostals muscles these muscles are located deep between the ribs. The externalintercostals muscles help raise the rib cage for breathing air in, making it a vital structure inbreathing. The internal intercostals ribs, on the other hand, help air to move out the lungs

when an individual exhales forcibly.

3. Muscles of the abdominal girdle muscles of the abdominal girdle are subdivided into twocategories the anterior and posterior abdominal muscles. The anterior muscles serve as

reinforcement of the body trunk. Both of these muscles are suitable for containing andprotecting the abdominal contents.

Anterior Abdominal Muscles

Rectus abdominis muscle this paired strap-like muscle is the most superficial muscle of theabdomen. The MAIN FUNCTION of the rectus abdominis muscle is to flex the vertebralcolumn. During defecation and childbirth, this muscle compresses the abdominal contents.Aside from that, it is also involved in forced breathing.

External Oblique muscle this paired muscle makes up the lateral walls of the abdomen. ThMAIN FUCNTION of this muscle is to flex the vertebral column like the rectus abdominismuscle. However, they also rotate the trunk and bend it laterally.

Internal oblique muscle this paired muscle serves the same function as that of the externaoblique muscles.

Posterior Muscles

1. Trapezius muscles these muscles are the mostsuperficial muscles of the posterior and uppertrunk. They serve as the antagonists of thesternocleidomastoids and they can elevate,

depress, adduct ad stabilize the scapula. When

seen together, the trapezius muscle forms adiamond or kite-shaped muscle mass.

2. Latissimus Dorsi muscle this is a large and flatpair of muscle that covers the entire lower back.Latissimus dorsi muscle extends and adducts thehumerus. This muscle plays a vital role in bringing

down the arm in a power stroke when swimming

or striking a blow.3. Erector Spinae muscle this group of muscle is a prime movers of back extension. Aside

from acting as powerful back extensors, erector spinae muscle also helps control the action

of bending over at the waist. When an injury to back structure occurs, these muscles go intospasms which are a common source of lower back pain. Each erector spinae muscle iscomposed of three muscle columns that cover the entire length of the vertebral column. The

three muscle columns are longissimus, iliocostalis and spinalis.

4. Deltoid muscles these are fleshy and triangle-shaped muscles that form the round shape othe shoulders. They are bulky and have been the most common and most favorite injectionsite. The deltoid muscles are the prime movers of arm abduction.


12/44

Muscles of the Upper Limb

Muscles of the upper limbs are divided into three groups.

1. First group muscles arising from the shoulder girdle and cross the shoulder joint to insertinto the humerus. These muscles move the arm.

2. Second group muscles that encloses the humerus and insert on the forearm bones. Thesemuscles cause movement at the elbow joint.

3. Third group includes muscles of the forearm that cause their movement.Muscles of the Humerus that Act on the forearm

1. Biceps Brachii this muscle bulges when the elbow is flexed. It is a powerful prime mover fothe flexion of the forearm and acts to supinate the forearm.

2. Brachialis this muscle plays an essential in elbow flexion. It lies deep to the biceps muscle3. Brachioradialis this is a fairly weak muscle. It arises on the humerus and inserts into the

distal forearm.

4. Triceps brachii this is the only muscle fleshing out the posterior humerus. It is the powerfuprime mover of elbow extension. Other term for this muscle is the boxers mucle as it candeliver a straight arm knock-out punch. This muscle is also the antagonist of the biceps

brachii muscle.

Muscles of the Lower Limb

Characteristic of the muscles of the lower limb:

1. These muscles cause movement at the hip, knee and foot joints.2. They are one of the largest and strongest muscles in the body.3. These muscles play a vital role in walking and balancing the body.

Muscles causing movement at the hip joint

1. Gluteus Maximus Muscle this is a superficial hip muscle that shapes the buttocks. Gluteusmaximus muscle is a very powerful hip extensor that is responsible in bringing the thigh to a

straight line.

2. Gluteus medius Muscle this is a hip abductor muscle. Gluteus medius muscle is veryimportant in stabilizing the pelvis when an individual is walking. When more than 5 ml of

medication is administered intramuscularly, the gluteus medius muscle is used. However, th

medial part of each buttock overlies the large sciatic nerve, hence; this area must be usedcarefully. Because of this reason, the fleshy gluteus maximus would be a better choice. Incases, where the gluteus medius is used for IM injection, the nurse should divide the

buttocks into four equal parts mentally. The upper outer quadrant is a very safe site for an

IM injection.

3. Iliopsoas this muscle is composed of two muscles the iliacus and psoas major. Iliopsoasis a prime mover of hip flexion and it also acts to keep the upper body from falling backwardwhen a person is standing erect.

4. Adductor muscles as their name indicate, these muscles adduct or press the thighstogether. However, since gravity does most of the work for them, these muscles tend tobecome flabby very easily.


13/44

Muscles causing movement at the knee joint

1. Hamstring group these muscles form the muscle mass of the posterior thigh. This group iscomposed of three muscles the biceps femoris, semimembranosus and semitendinosusmuscles.

2. Sartorius this thin and strap-like muscle is not very significant because it is a very weakflexor of the thigh. However, this muscle is the most superficial muscle of the thigh. TheSartorius muscle is often referred to as the tailors muscle because it acts as a synergist tobring about the cross-legged position in which old-time tailors is often shown.

3. Quadriceps group four muscles compose this muscle group. Namely, the rectus femoris anthe three vastus muscles. These muscles flesh out the anterior thigh. Quadriceps group actsto extend the knee powerfully.

Muscles causing movement at the ankle and foot

1. Tibialis anterior this is a superficial muscle of the anterior leg that acts to dorsiflex andinvert the foot.

2. Extensor digitorum longus this muscle inserts into the phalanges of toes 2 to 5. It is aprime mover of toe extension and a dorsiflexor of the foot.3. Fibularis muscles there are three fibularis muscles namely, the longus, brevis and tertius.These muscles are found on the lateral part of the leg and working as a group, they are

responsible for the plantar flexion and the eversion of the foot.

4. Gastrocnemius this muscle forms the curved half of the posterior leg. It is a prime moverfor plantar flexion of the foot.

5. Soleus this muscle lies deep to gastrocnemius. It has no effect on knee movement but it isa string plantar flexor of the foot.


14/44

Nervous SystemDefinition

The nervous system is an organ system that contains a network of specialized cells called neurons. This i

the master controlling and communicating system of the body. It coordinates the action of an animal and

transmits signals between the different parts of the body. Every thought, movement and emotions reflectthe activity of the nervous system.

Functions of the NERVOUS SYSTEM

1. To monitor changes that takes place inside and outside the body. The nervous system utilizesthe million sensory receptors to carry out this function. Any changes or stimuli occurring are

noted by the nervous system and the gathered data is now called a sensory input.2. Another important function of the nervous system is to process and interpret the sensory input

or gathered data. It is the working of this system to make decision about what should be done at

each moment. This is the process known as INTEGRATION.3. As the nervous system has reached a decision of what response and appropriate action to be done

in response to the stimuli, it then effects a response by activating muscles or glands through

motor output.

Structural Classification of the Nervous system

Structurally, the nervous system is classified into the central nervous system and the peripheral nervous

system.

Central nervous system. The CNS consists of the brain and the spinal cord. These organs occupythe dorsal body cavity and act as the INTEGRATING and COMMAND CENTERS of the

nervous system. It is the CNS that interprets an incoming sensory information and sends andinstruction basing on the past experience and current condition.

Peripheral Nervous System. The PNS is consisting of the nerves that extend from the brain andthe spinal cord. It is the part of the nervous system outside the CNS. There are varieties of nervesThe spinal nerves carry impulses to and from the spinal cord. The cranial nerves, on the other

hand, carry impulses to and from the brain. These nerves serve as the communication lines of the

body.

Functional Classification of the Nervous System

The functional classification of the nervous system is only concerned about the structures of the

peripheral nervous system (PNS). The PNS in this classification is divided into two principal

subdivisions:

Sensory or afferent division. This subdivision is composed of the nerve fibers that conveyimpulses to the central nervous system (CNS) from the sensory receptors. These sensory receptorare located in the different parts of the body. With the presence of these sensory fibers the CNs is

constantly informed of the events going on both inside and outside the body.


15/44

1. The fibers responsible for delivering impulses from the skin, skeletal muscles and joints are calledthe somatic sensory fibers.

2. Fibers that transmit impulses from the visceral organs are called the visceral sensory fibers. Motor or efferent division. This division is responsible for carrying impulses from the CNS to the

effector organs, muscles and glands. In response these impulses, activate muscles and glands andthey effect a motor response. The two classification of motor or efferent division are:

1. Somatic nervous system. This subdivision is also referred as the voluntary nervous system. Thesomatic NS allows a person to consciously or voluntarily control a persons skeletal muscles.

2. Autonomic nervous system (ANS). The ANS regulates the events that are automatic orINVOLUNTARY such as the activity of the smooth and cardiac muscles and glands. The two partof the ANS are the sympathetic and the parasympathetic systems.

Function and Structure of the Nervous System

If you think of the brain as a central computer that controls all bodily functions, then the nervous system

is like a network that relays messages back and forth from the brain to different parts of the body. It does

this via the spinal cord, which runs from the brain down through the back and contains threadlike nervesthat branch out to every organ and body part.

The nervous system derives its name from nerves, which are cylindrical bundles of fibers that emanatefrom the brain and central cord, and branch repeatedly to innervate every part of the body. Even though i

is complex, nervous tissue is made up of two principal types of cells namely, the supporting cells and the

neurons.

SUPPORTING CELLS

The supporting cells in the CNS are lumped together as NEUROGLIA or GLIAL CELLS. GlialCells are non-neuronal cells that provide support and nutrition, maintain homeostasis, form myelin andparticipate in signal transmission in the nervous system. In the human brain, it is estimated that the

total number of glia roughly equals the number of neurons, although the proportions vary in different

brain areas.

The functions of glial cells are:

1. to support neurons and hold them in place2. to supply nutrients to neurons3. to insulate neurons electrically4. to destroy pathogens and remove dead neurons5. to provide guidance cues directing the axons of neurons to their targets


16/44

Characteristics of Glial Cells:

1. Lumped together.2. Not able to transmit impulses.3. Never lose their ability to divide.

The CNS glia include:

Astrocytes. These are star-shaped cells that accountnearly half of the neural tissue. Astrocytes form a

living barrier between capillaries and neurons and play

a role in making exchanges between the two. This is toprevent harmful substances in the blood from entering

the neurons. Aside from that, astricytes are also

important in controlling the chemical environment in

the brain. This is done by picking up excess ions andrecapturing released neurotransmitters.

Microglia. These are spiderlike phagocytes thatdispose debris including dead brain cells and bacteria.

Ependymal cells. These cells line the cavities of the brain and the spinal cord. Aside from liningthe cavities of certain organs, these cells are very important in helping the CSF through their cilia

to circulate and fill those cavities and form a protectivecushion around the CNS.

Oligodendrocytes. These are glial cells that wrap their flatextensions tightly around the nerve fibers, producing fatty

insulating coverings called myelin sheaths.

NEURONS

Anatomy of the Neuron

The nervous system is defined by the presence of a special type of

cellthe neuron (sometimes called neurone or nerve cell).

Neurons can be distinguished from other cells in a number of ways,but their most fundamental property is that they communicate with

other cells via SYNAPSES, which are membrane-to-membrane

junctions containing molecular machinery that allows rapid

transmission of signals, either electrical or chemical. Many types ofneuron possess an AXON, a protoplasmic protrusion that can

extend to distant parts of the body and make thousands of synaptic

contacts. Axons frequently travel through the body in bundles called nerves.


17/44

Cell bodythe metabolic center of the neuron. This part of neuron contains the usual organellesexcept for the centrioles. It contains a nucleus and cytoplasm. Where it is most distinct from cells

of other types is that out of the cell body, long threadlike projections emerge. Over most of the

cell there are numerous projections that branch out into still finer extensions. This is wellprotected and is located in the bony skull or vertebral column and is essential to well-being of the

nervous system. The cell body carries out most of the metabolic functions of a neuron. Nissl substance and Neurofibrilsfound in the cell body that is essential in maintaining cell

shape.

Dendritesneuron processes that covey incoming messages TOWARD the cell body. Axonsneuron processes that generate nerve impulses AWAY from the cell body. Axon hillocka cone-like region of the cell body where the axon arises. Axon terminals- located at the terminal end of the axons that contains tiny vesicles or

membranous sacs that contains chemicals called neurotransmitters. When impulses reach the axo

terminals, they stimulate the release of neurotransmitters into the extracellular spaces.

Synaptic clefta tiny gap that separates axon terminal from the next neuron. Myelina whitish, fatty material that covers long nerve fibers. It has a waxy appearance that

protects and insulates the fibers and increases the rate of nerve impulses.

Schwann cellsmyelinates the axon outside the nervous system. Schwann cells are specializedsupporting cells that enclose themselves tightly around the axon jelly-roll fashion.

Myelin sheatha tight coil of wrapped membranes created after the Schwann cells enclose theaxon.

Neurilemmapart of the Schwann cell external to the myelin sheath. Nodes of Ranviergaps or indentations between the myelin sheaths.

Classification of Neurons

Functional Classification of Neurons

Even in the nervous system of a single species such ashumans, hundreds of different types of neurons exist,

with a wide variety of morphologies and functions.

These include SENSORY NEURONS that transmute

physical stimuli such as light and sound into neuralsignals, and MOTOR NEURONS that transmute neural

signals into activation of muscles or glands; however in

many species the great majority of neurons receive all oftheir input from other neurons and send their output to

other neurons. An ITERNEURON is always found

completely within the CNS and conveys messages

between parts of the system

In addition to neurons, nervous tissue contains glial cells such as the Schwann cells covering the neuronswith sheath. These cells maintain the tissue by supporting and protecing the neurons. They also provide

nutrients to neurons and help to keep the tissue free of debris. The neurons require a great deal of energy

for the maintenance of the ionic imbalance between themselves and their surrounding fluids, which is

constantly in flux as a result of the opening and closing of channels through the neuronal membranes.


18/44

Structural Classification of Neurons

Multipolar neuronsThese are several processes extending from the cell body. All motor andassociation neurons are multipolar and this is the most common structural type.

Bipolar neuronsThese are neurons with two processesan axon and a dendrite. Bipolarneurons are rare in adults and are only found in some special sense organs such as the eye or nosewhere they act in sensory processing as receptor cells.

Unipolar neuronsThese neurons have single process emerging from the cell body. it is veryshort and divides almost immediately into proximal (central) and distal (peripheral) processes.

Neurons are dynamically polarized, so that information flows from the fine dendrites into the main

dendrites and then to the cell body, where it is converted into all-or-none signals, the action potentials,which are relayed to other neurons by the axon, a long wire-like structure. The neuron is actually a very

poor conductor; the signal drops to 37% of its original strength in only about 0.15 mm. Thus it needs

amplification all along its length in the form of sodium-potassium pumps and gates.

Sodium ions rush into the neurons from the extracellular fluid, resulting in a transient change in the

voltage difference between the neuron and the surrounding environment. The action potential travels like

a wave from the cell body down the neuron via the repeating amplifications. Thus, the action potentialenables the neuron to communicate rapidly with other neurons over sizable distances, sometime more

than a meter away with a speed from 20 -200 m/sec. When the action potential reaches an axon terminal,

it causes the terminals to secrete a chemical messenger (neurotransmitter), generally an amino acid or itsderivative, which binds to receptors in the post-synaptic neurons on the far side of the synaptic cleft.

When the postsynaptic potential has reached a specific value an action potential is triggered and the

signal is passed to the next neuron.

THE CENTRAL NERVOUS SYSTEM

The Central Nervous System (CNS) is composed of the brain and spinal cord. The CNS is surrounded bybone-skull and vertebrae. Fluid and tissue also insulate the brain and spinal cord. During embryonic

development, the brain first forms as a tube, the anterior end of which enlarges into three hollow

swellings that form the brain, and the posterior of which develops into the spinal cord.


19/44

Anatomy of the CNS

Brain

When a message comes into the brain from anywhere in the body, the brain tells the body how to react.

For example, if you accidentally touch a hot stove, the nerves in your skin shoot a message of pain to

your brain. The brain then sends a message back telling the muscles in your hand to pull away. Luckily,this neurological relay race takes a lot less time than it just took to read about it. Considering everything i

does, the human brain is incredibly compact, weighing just 3 pounds. Its many folds and grooves, though

provide it with the additional surface area necessary for storing all of the bodys important information.

The four main regions of the brain are:

Cerebral hemispheres Diencephalon Brain stem Cerebellum

Cerebral Hemispheres

The paired cerebral hemispheres are the most superior part of the brain and are collectively calledthecerebrum.

1. Gyri or gyrus (singular)elevated ridges of tissue found on the entire surface of the cerebralhemisphere.

2. Sulci or sulcus (singular)shallow grooves that separates the gyri.3. Fissuresdeeper groves which separates the larger regions of the brain. The cerebral hemisphere

are separated by a single deep fissure called the LONGITUDINAL FISSURE.

The cerebrum, the largest part of the human brain, is divided into left and right hemispheres connected to

each other by the corpus callosum. The hemispheres are covered by a thin layer of gray matter known as

the cerebral cortex, the most recently evolved region of the vertebrate brain. The cortex in each

hemisphere of the cerebrum is between 1 and 4 mm thick. Folds divide the cortex into four lobes:occipital, frontal, parietal and temporal. No region of the brain functions alone, although major functions

of various parts of the lobes have been determined.


20/44

The occipital lobe (back of the head) receives and processes visual information. The temporallobereceives auditory signals, processing language and the meaning of words. The parietal lobe is

associated with the sensory cortex and processes information about touch, taste, pressure, pain, and heat

and cold. The frontal lobe conducts three functions:

1.

motor activity and integration of muscle activity2. speech3. thought processes

Language comprehension is found in Wernickes area. Speaking ability is in Brocas area. Damage toBrocas area causes speech impairment but not impairment of language comprehension. Lesions inWernickes area impair ability to comprehend written and spoken words but not speech. The remaining

parts of the cortex are associated with higher thought processes, planning, memory, personality and other

human activities.

Diencephalon

The diencephalon or interbrain sits atop the brainstem and is enclosed by the cerebral hemispheres. The

major structures of the diencephalon are:

1. ThalamusThe thalamus is a relay station for sensory impulses passing upward the sensorycortex.

2. HypothalamusPlays a role in body temperature regulation, water balance and metabolism. It isalso the center for many drives and emotion such as thirst, appetite, sex, pain and pleasure. Aside

from that, the hypothalamus regulates the pituitary gland and produces two hormones of its own.

3. EpithalamusThe epithalamus contains the pineal body and the choroid plexuses. The choroidplexuses form the cerebrospinal fluid.Brain Stem

The brain stem is about the size of a thumb in diameter and is approximately 3 inches long. It provides a

pathway for ascending and descending tracts. The structures of the brain stem are:


21/44

1. MidbrainThe midbrain, located underneath the middle of the forebrain, acts as a mastercoordinator for all the messages going in and out of the brain to the spinal cord. It is composed

primarily of two bulging fiber tracts called the cerebral peduncles, which convey ascending and

descending impulses.2. Ponsthe pons have an important nuclei in the control of breathing.3.

Medulla oblongata

most inferior part of the brain stem. It contains many nuclei that regulatevital visceral activities. The medulla oblongata contains centers that control heart rate, BO,

breathing, swallowing, vomiting and others.

4. Reticular Formationthe neurons of the reticular formation are involved in the motor control ofthe visceral organs. A special group of reticular formation neurons, the reticular activating system(RAS) plays a role in consciousness and the awake/sleep cycles.

Cerebellum

The cerebellum is the third part of the hindbrain, but it is not considered part of the brain stem. Functions

of the cerebellum include fine motor coordination and body movement, posture, and balance. This regionof the brain is enlarged in birds and controls muscle action needed for flight.

Spinal Cord

The spinal cord runs along the dorsal side of the body and links the brain to the rest of the body.

Vertebrates have their spinal cords encased in a series of (usually) bony vertebrae that comprise the

vertebral column.

The gray matter of the spinal cord consists mostly of cell bodies and dendrites. The surrounding white

matter is made up of bundles of interneuronal axons (tracts). Some tracts are ascending (carrying

messages to the brain), others are descending (carrying messages from the brain). The spinal cord is alsoinvolved in reflexes that do not immediately involve the brain.

Nerves divide many times as they leave the spinal cord so that they may reach all parts of the body. The

thickest nerve is 1 inch thick and the thinnest is thinner than a human hair. Each nerve is a bundle of

hundreds or thousands of neurons (nerve cells). The spinal cord runs down a tunnel of holes in yourbackbone or spine. The bones protect it from damage. The cord is a thick bundle of nerves, connecting

your brain to the rest of your body.


22/44

Peripheral Nervous System

The Peripheral Nervous System contains only nerves andconnects the brain and spinal cord (CNS) to the rest ofthe body. The axons and dendrites are surrounded by a

white myelin sheath. Cell bodies are in the centralnervous system (CNS) or ganglia. Gangliaare collections of nerve cell bodies. Cranial nerves in the

PNS take impulses to and from the brain (CNS). Spinal

nerves take impulses to and away from the spinal cord.There are two major subdivisions of the PNS motor

pathways: the somatic and the autonomic.

Two main components of the PNS:

1. sensory (afferent) pathways that provide input from the body into the CNS.2. motor (efferent) pathways that carry signals to muscles and glands (effectors).

Most sensory input carried in the PNS remains below the level of conscious awareness. Input that doesreach the conscious level contributes to perception of our external environment.

Autonomic Nervous System


23/44

The Autonomic Nervous System is that part of PNS consisting of motor neurons that control internalorgans. It has two subsystems. The autonomic system controls muscles in the heart, the smooth muscle in

internal organs such as the intestine, bladder, and uterus. TheSympathetic Nervous System is involved

in the fight or flight response. TheParasympathetic Nervous System is involved in relaxation. Each ofthese subsystems operates in the reverse of the other (antagonism). Both systems innervate the same

organs and act in opposition to maintain homeostasis. For example: when you are scared the sympatheticsystem causes your heart to beat faster; the parasympathetic system reverses this effect.

Motor neurons in this system do not reach their targets directly (as do those in the somatic system) but

rather connect to a secondary motor neuron which in turn innervates the target organ.

Somatic Nervous System

The Somatic Nervous System (SNS) includes all nerves the muscular system and external sensoryreceptors. External sense organs (including skin) are receptors. Muscle fibers and gland cells are

effectors. The reflex arc is an automatic, involuntary reaction to a stimulus. When the doctor taps yourknee with the rubber hammer, she/he is testing your reflex (or knee-jerk). The reaction to the stimulus isinvoluntary, with the CNS being informed but not consciously controlling the response. Examples of

reflex arcs include balance, the blinking reflex, and the stretch reflex.

Sensory input from the PNS is processed by the CNS and responses are sent by the PNS from the CNS to

the organs of the body.

Motor neurons of the somatic system are distinct from those of the autonomic system. Inhibitory signals,

cannot be sent through the motor neurons of the somatic system.


24/44

Respiratory SystemOverview

Cells in the body require oxygen to survive. Vital functions of the body are carried out as the body i

continuously supplied with oxygen. Without the respiratory system exchange of gases in the alveoli

will not be made possible and systemic distribution of oxygen will not be made possible. Thetransportation of oxygen in the different parts of the body is accomplished by the blood of the

cardiovascular system. However, it is the respiratory system that carries in oxygen to the body andtransports oxygen from the tissue cells to the blood. Thus, cardiovascular system and respiratory

system works hand in hand with each other. A problem in the cardiovascular system would affectthe other and vice versa.

Functional Anatomy of the Respiratory System

Nose

The nose is the only external part of the respiratory system and is the part where the air passes

through. During inhalation and exhalation, air enters the nose by passing through the external nareor nostrils. Nasal cavity is found inside the nose and is divided by a nasal septum. The receptors forthe sense of smell, olfactory receptors are found in the mucosa of the slit-like superior part of the

nasal cavity which is located beneath the ethmoid bone. Respiratory mucosa lines the rest of thenasal cavity and rests on a rich network of thin-walled veins that warms the air passing by.

Important information about nose is the presence of the sticky mucus that is produced by the

mucosas gland. This important characteristic moistens the air and traps the incoming bacteria andother foreign debris passing through the nasal cavity. Cells of the nasal mucosa are ciliated and it

creates a gentle current that moves the contaminated mucus posteriorly towards the throat, whereit is swallowed and digested by stomach juices.

In cases where the temperature of the environment is cold, the cilia become sluggish. Thus, moremucus are allowed to accumulate in the nasal cavity and to dribble outward through the nostrils.This is the main reason why a runny nose is noted during a cold day.

Conchae these are three mucosa-covered projections or lobes that greatly increase the surface

area of the mucosa exposed to the air. Aside from that, conchae increase the air turbulence in thenasal cavity.

Palate a partition that separates the nasal cavity from the oral cavity. Anteriorly, the palate thatis supported by a bone called the hard palate and the one which is unsupported is the soft palate.

Paranasal Sinuses these are structures surrounding the casal cavity and are located in the

frontal, sphenoid, ethmoid and maxillary bones.

Pharynx


25/44

The pharynx is a 13 cm long muscular tube that is commonly called the throat. This muscularpassageway serves as a common food and air pathway. This structure is continuous with the nasalcavity anteriorly via the internal nares.

Parts of pharynx:

1. Nasopharynx the superior portion of the pharynx. The pharyngotympanic tubes that drainthe middle ear open in this area. This is the main reason why children who have otitis media

may follow a sore throat or other tyoes of pharyngeal infections since the two mucosae of

these regions are continuous.2. Oropharynx middle part3. Laryngopharynx part of pharynx that enters the larynx.

When food enters the oral cavity, it travels to the oropharynx and laryngopharynx. However, instea

of entering the larynx, the food is directed into the esophagus and not to the larynx.

Tonsils clusters of lymphatic tissues found in the pharynx.

Types of Tonsils:

1. Palatine tonsils tonsils found at the end of the soft palate.2. Pharyngeal tonsils lymphatic tissues located high in the nasopharynx. This is also called

adenoid.3. Lingual tonsils located at the base of the tongue.

Larynx

The larynx is the one that routes the air and food into their proper channels. Also termed as thevoice box, it plays an important role in speech. This structure is located inferior to the pharynx andis formed by:

1. Eight rigid hyaline cartilages2. Spoon-shaped flap of elastic cartilage, which is called the epiglottis.

Thyroid cartilage this is the largest hyaline cartilage that protrudes anteriorly in males and isreferred to as the Adams apple.

Epiglottis this is a flap of tissue that serves as a guardian of the airways as it protects thesuperior portion of the larynx. The epiglottis does not restrict passage of air into the lower

respiratory passages when a person is not swallowing. However, when a person swallows food, theepiglottis tips and forms a lid or blocks the opening of the larynx so that food will not be directed tothe lower respiratory passages. The food will be then routed to the esophagus and in cases where it

enters the larynx, a cough reflex is triggered to expel the substance and prevent it from continuinginto the lungs. This protective reflex does not work when a person is unconscious that is why it isnot allowed to offer or administer fluids to an unconscious client.

Vocal folds a pair of folds which is also called the true vocal cords that vibrate when air is


26/44

expelled.

Glottis the slit-like passageway between the vocal folds.

Trachea

Also called the windpipe, the trachea is about 10 to 12 cm long or about 4 incheas and travels dwonfrom the larynx to the fifth thoracic vertebra. This structure is reinforced with C-shaped rings ofhyaline cartilage and these rings are very important for the following purposes:

1. The open parts of the rings abut the esophagus that allows the structure to expand anteriorlwhen a person swallows a large size of food.

2. The solid portions of the C-rings are supporting the walls of the trachea to keep it patent oropen even though pressure changes during breathing.

The trachea is lined with ciliated mucosa that primarily serves for this purpose: To propel mucus

loaded with dust particles and other debris away from the lungs towards the throat where it caneither be swallowed or spat out.

Main Bronchi

The main bronchi, both the right and the left, are both formed by tracheal divisions. There is a sligh

difference between the right and left main bronchi. The right one is wider, shorter and straighter

than the left. This is the most common site for an inhaled foreign object to become lodged. When areaches the bronchi, it is already warmed, cleansed of most impurities and well humidified.

Lungs

The lungs are fairly large organs that occupy the most of the thoracic cavity. The most central partof the thoracic cavity, the mediastinum, is not occupied by the lungs as this area houses the heart.

Apex the narrow superior portion of each lung and is located just below the clavicle

Base the resting area of the lung. This is a broad lung area that rests on the diaphragm.

Divisions of the Lungs

The lungs are divided into lobes by the presence of fissures. The left lung has two lobes while theright lung has three.

Pleural Layers

Visceral pleura also termed as the pulmonary pleura and covers each surface of the lings.

Parietal pleura covers the walls of the thoracic cavity.

Pleural fluid a slippery serous secretion that allows the lungs to slide along over the thorax wallduring breathing movements and causes the two pleural layers to cling together.


27/44

Bronchioles smallest air-conducting passageways.

Bronchial tree or respiratory tree a network formed due to the branching and rebranching of therespiratory passageways within the lungs.

Alveoli air sacs. This is the only area where exchange of gases takes place. Millions of clustered

alveoli resembles bunches of grapes and these structures make up the bulk of the lungs.

Respiratory Zone this part includes the respiratory bronchioles, alveolar ducts, alveolar sacs,alveoli.

Physiology of Respiration

The respiratory primarily supplies oxygen to the body and disposes of carbon dioxide through

exhalation. Four events chronologically occur, for respiration to take place.

1. Pulmonary ventilation this process is commonly termed as breathing. With pulmonaryventilation, air must move out into and out of the lungs so that the alveoli of the lungs arecontinuously drained and filled with air.

2. External respiration this is the exchange of gases or the loading of oxygen and theunloading of carbon dioxide between the pulmonary blood and alveoli.

3. Respiratory gas transport this is the process where the oxygen and carbon dioxide istransported to the and from the lungs and tissue cells of the body through the bloodstream.

4. Internal respiration in internal respiration the exchange of gases is taking place betweenthe blood and tissue cells.

Mechanics of Breathing

Breathing, also called pulmonary ventilation is a mechanical process that completely depends on thvolume changes occurring in the thoracic cavity. Thus, a when volume changes pressure alsochanges, and this would lead to the flow of gases equalizing with the pressure.

Inspiration also called inhalation. This is the act of allowing air to enter the body. Air is flowinginto the lungs with this process. Inspiratory muscles are involved with inspiration which includes:

1. The diaphragm2. External intercostals

These muscles contract when air is flowing in and thoracic cavity increases. When the diaphragmcontracts it slides inferiorly and is depressed. As a result the thoracic cavity increases. The

contraction of the external intercostal muscles lifts the rib cage and thrusts the sternum forward.This increases the anteroposterior and lateral dimensions of the thorax.

Expiration also called expiration. It the process of breathing out air as it leaves the lungs. This

process causes the gases to flow out to equalize the pressure inside and outside the lungs. Undernormal circumstances, the process of expiration is effortless.


28/44


29/44

OLFACTORY RECEPTORS AND THE SENSE OF SMELL

Chemoreceptors are those that respond to chemicals in solution for taste and olfaction. The olfactoryreceptors are believed to be sensitive to a much wider range of chemicals. Thousands of olfactory

receptors occupy a postage stamp-sized area in the roof of each nasal cavity. These are the receptors for

the sense of smell.

Air entering the nasal cavities must make a hairpin turn to enter the respiratory passageway below which

causes more air to flow superiorly across the olfactory receptors, thus, intensifying the sense of smell.Olfactory receptor cells are special neurons that are equipped with olfactory hairs. Olfactory hairs are

long cilia that protrude from the nasal epithelium and are continually bathed by a layer of mucus secreted

by underlying glands.

When the receptors are stimulated by chemicals that are dissolved in the mucus, they transmit impulses

along the olfactory filaments, which collectively make up the olfactory nerve (cranial nerve I) to the

olfactory complex of the brain. It is in the brain that the interpretation of the odor occurs. The olfactorypathways are closely tied into the limbic system, the emotional-visceral part of the brain. Hence, olfactor

impressions are long lasting and are very much part of our memories and emotions.

The olfactory receptors are extremely sensitive. Only a few molecules are required to activate them.

Olfactory neurons tend to adapt rather quickly when they are exposed to unchanging stimulus of odor.This is the main reason why a woman stops smelling her own perfume but quickly picks up the scent of

another persons perfume.

Gustatory (taste)

TASTE BUDS AND SENSE OF TASTE

The tongue is a versatile organ with specialized functionslike taste and speech. Beneath a cover of taste buds, the

tongue is almost entirely made up of muscle. The muscles

of the tongue are essential for its bodily movement andintrinsic manipulations, required for actions like speech,

articulation, deglutition or swallowing, whistling, licking,

kissing and even cleaning teeth.

Taste is the brains interpretation of chemicals that triggerreceptors on the tongue, which are housed in the taste

buds. The basic chemical components, are found in foods,toxins, and other ingested matter. Unappealing tastes areusually associated with toxins, as this is a defense

mechanism preventing consumption. The chemicals bind

their particular receptors and initiate signaling that travelsthrough the nerves to the brain, where they are interpreted.


30/44

Taste Buds

The taste buds are specific receptors for the sense of taste which are widely distributed in the oral cavity.Of the 10,000 taste buds that humans have, most are located in the tongue. Few are found on the soft

palate and inner surface of the cheeks.

Papillaesmall peg-like projections that covers the dorsal surface of the tongue. These peg-like

projections are of three types namely:

Sharp filiform papillae Rounded fungiform papillae Circumvallate papillae

Taste buds are found on the sides of the circumvallate papillae but are more numerous on the fungiform

papillae. When a person eats something, the specific cells that respond to the chemical dissolved inthe saliva are epithelial cells called gustatory cells. Gustatory cells are surrounded by supporting cells in

the taste bud. Their long microvilli, the gustatory hairs, protrude through the taste pore and when they ar

stimulated, they depolarize and impulses are transmitted to the brain. To carry the taste impulses threecranial nerves transports it to the gustatory cortex namely:

Cranial nerve VII Cranial nerve IX Cranial nerve X

Auditory (hearing)

Overview

Hearing is one of the major senses and like vision is important for distant warning and communication. It

can be used to alert, to communicate pleasure and fear. It is a conscious appreciation of vibration

perceived as sound. In order to do this, the appropriate signal must reach the higher parts of the brain.

Functions of the ear

The ears are paired sensory organs comprising the auditory system, involved in the detection of sound,

and the vestibular system, involved with maintaining body balance or the equilibrium. The ear divides

anatomically and functionally into three regions: the external ear, the middle ear, and the inner ear. Allthree regions are involved in hearing. Only the inner ear functions in the vestibular system.

1. SOUND DETECTION. The function of the ear is to convert physical vibration into an encodednervous impulse. It can be thought of as a biological microphone. Like a microphone the ear is

stimulated by vibration: in the microphone the vibration is transduced into an electrical signal, in

the ear into a nervous impulse which in turn is then processed by the central auditory pathways ofthe brain.


31/44

2. MAINTAINING BODY BALANCE or EQUILIBRIUM. The prime function of the vestibularsystem is to detect and compensate for movement. This includes the ability to maintain optic

fixation despite movement and to initiate muscle reflexes to maintain balance.

Anatomy of the Ear

The ear is divided into three major areas: the outer or external ear, the middle ear and the inner or interna

ear. The outer and middle ear are involved with hearing only whilst the inner ear functions both

equilibrium and hearing.

OUTER (EXTERNAL) EAR

The outer ear collects sound waves in the air and channels them to the inner parts of the ear. The outer eaalong with its canal has been shown to enhance sounds within a certain frequency range. That range just

happens to be the same range that most of the characteristics of humanspeech sounds fall into. This

allows the sounds to be boosted to twice their original intensity. Parts of the outer ear are the following:

1. PinnaAlso called the auricle. It is the part which protrudes from the side of the skull made ofcartilage covered by skin. The pinna collects sound and channels it into the ear canal. The pinnasshape enables it to funnel sound waves into the external auditory meatus. The various folds in the

pinnas structure amplify some high frequency components of the sound. They also help in the

localization of sound in the vertical plane. As sounds hit the pinna from above and below, their

paths to the external auditory meatus vary in length. This means that they take different times toreach the meatus.

2. External acoustic meatus or external auditory canalthis is a short chamber about 1 inch lonby inch wide. It is carved into the temporal bone of the skull. The canal has bends in both thevertical and horizontal planes. This means that it is difficult for anything poked into the meatus to

hit the drum. Any trauma is likely to be to the walls of the canal. In its skin-lined walls are

the ceruminous glands, which secrete a waxy yellow substance, called earwax orcerumen.


32/44

Sound waves entering the external auditory canal eventually hit the tympanic membrane or eardrum andcause it to vibrate. The canal ends at the eardrum, which separates the outer ear from the middle ear.

MIDDLE EAR

The middle ear or tympanic cavity is an air filled space within the temporal bone. It transforms theacoustical vibration of the sound wave into mechanical vibration and passes it onto the inner ear. The

three tiny bones of the middle ear act as a lever to bridge the eardrum with the oval window. Incoming

forces are magnified by about 30 %. This increased force allows the fluid in the cochlea of the inner earto be activated.

The tympanic cavity is spanned by the three smallest bones in the body, the ossicles which transmit thevibratory motion of the eardrum to the fluids of the inner ear. These bones, named for their shape, are the

following:

Hammer or malleus Anvil or incus Stirrup or stapes

When the eardrum moves the hammer moves with it and transfers the vibration to the anvil. In response

to this, the anvil passes it on to the stirrup which in turn presses on the oval window of the inner ear. Themovement of the oval window sets the fluids of the inner ear into motion, eventually exciting the hearing

receptors.

The Eustachian tube is a canal that links the middle ear with the throat area. This tube helps to equalize

the pressure between the outer ear and the middle ear. Having the same pressure allows for the proper

transfer of sound waves. The eustachian tube is lined with mucous, just like the inside of the nose andthroat.

Inner Ear

The inner ear consists of a maze of fluid-filled tubules running through the temporal bone of the skull.The bony tubes, the bony labyrinth, are filled with a fluid called perilymph. Within this bony labyrinth i

a second series of delicate cellular tubes, called the membranous labyrinth, filled with the fluid called

endolymph. This membranous labyrinth contains the actual hearing cells, the hair cells of the organ of

Corti.

There are three major sections of the bony labyrinth:

1. The front portion is the snail-shaped cochlea, which functions in hearing2. The rear part, the semicircular canals, helps maintain balance3. Interconnecting the cochlea and the semicircular canals is the vestibule, containing the sense

organs responsible for balance, the utricle and saccule.


33/44

The bony cochlea is so called because it is shaped like a snail shell It has two and a half turns and housesthe organ of hearing known as the membranous labyrinth surrounded by fluid called the perilymph. The

cochlea has a volume of about 0.2 of a millilitre. In this space lie up to 30,000 hair cells which transduce

vibration into nervous impulses and about 19,000 nerve fibers which transmit the signals to and from thebrain.

The inner ear has two membrane-covered outlets into the air-filled middle earthe oval windowand

the round window. The oval window sits immediately behind the stapes, the third middle ear bone, and

begins vibrating when struck by the stapes. This sets the fluid of the inner ear sloshing back and forth.The round window serves as a pressure valve, bulging outward as fluid pressure rises in the inner ear.

Nerve impulses generated in the inner ear travel along the vestibulocochlear area (cranial nerve VIII),

which leads to the brain. This is actually two nerves, somewhat joined together, the cochlear nerve for

hearing and the vestibular nerve for equilibrium.

How Do We Hear?

The range of audible sound is approximately 10 octaves from somewhere between 16 and 32 Hz (cycles

per second) to somewhere between 16,000 and 20,000 Hz. The sensitivity is low at the extremes but

becomes much more sensitive above 128 Hz up to about 4,000 Hz when it again becomes rapidly lesssensitive. The range of maximum sensitivity and audibility diminishes with age.

What Do We Hear?

All sounds (music, voice, a mouse-click, etc.) send out vibrations, or sound waves. Sound waves do nottravel in a vacuum, but rather require a medium for sound transmission, e.g. air or fluid. What actually

travels are alternating successions of increased pressure in the medium, followed by decreased pressure.

Hearing starts with the outer ear. When a sound is made outside the outer ear, the sound waves, or

vibrations, travel down the external auditory canal and strike the eardrum (tympanic membrane). The

eardrum vibrates. The vibrations are then passed to three tiny bones in the middle ear called the ossicles.

The ossicles amplify the sound and send the sound waves to the inner ear and into the fluid-filled hearingorgan (cochlea).

Once the sound waves reach the inner ear, they are converted into electrical impulses which the auditory

nerve sends to the brain. The brain then translates these electrical impulses as sound.

The mechanism of hearing is summarized below:

1. Sound2. Pinna collects the sound heard3. External auditory canal4. Vibration in the ear drum is produced5. Amplified by the ossicular chain. The sound is then transmitted to the inner ear.6. The cochlea converts the sound vibration to electrical impulses. Within the cochlear duct, the

endolymph-containing membranous labyrinth of the snail-like cochlea is the organ of Corti, whic

contains the hearing receptors or hair cells. The chambers above and below the cochlear duct


34/44

contain perilymph. Sound waves that reach the cochlea through vibrations of the eardrum,ossiscles and oval window set cochlear fluids into motion.

7. The hair cells transmit impulses along the cochlear nerve or auditory nerve (a division of cranialnerve VIIIthe vestibulocochlear nerve) to the auditory cortex in the temporal lobe.

8. Auditory cortex interprets the sound, or hearing occurs.Since sound usually reaches the two ears at different times, a person can hear in stereo, whichfunctionally helps humans differentiate where sounds are coming from the environment. In cases where

the sounds or tones keep reaching the ears, the auditory receptors tend to adapt or stop responding tothese sounds, thus the person becomes no longer aware of them. Important information about hearing is

the fact that it is the last sense to leave the awareness when a person falls asleep or receives anesthesia or

dies. As a person awakens from sleep, it is the first sense to return.

Vision (sight)

Overview

A persons sense of sight is very important to humans. Vision is arguably the most used of the 5 senses

and is one of the primary means that we use to gather information from our surroundings. The human eye

is the organ which gives us the sense of sight, allowing us to observe and learn more about thesurrounding world than we do with any of the other four senses.

People use their eyes in almost every activity they perform, whether reading, working, watching

television, writing a letter, driving a car, and in countless other ways. Most people probably would agree

that sight is the sense they value more than all the rest. The eyes are at work from the moment a person iswake up to the moment he or she closes them to go to sleep.

This special organ takes in tons of information about the world around you shapes, colors, movement


35/44

and more. Then they send the information to your brain for processing so the brain knows whats goingon outside of your body.

Anatomy of the Eye

External and Accessory Structures

The adult eye is a sphere-shaped organ that measures about 1 inch or 2.5 cm in diameter. However, onlyone sixth (1/6) of the eyes surface can normally be seen and the rest is enclosed and protected by acushion of fat and the walls of the bony orbit.

The accessory structures of the eye are the following:

Extrinsic eye muscles. The extrinsic muscles of the eye come from the bones of the orbit and aremovable due to broad tendons in the eyes tough outer surface. There are six extrinsic eye musclethat function to MOVE the eye in various directions:

1. Superior rectus musclerotates the eye upward and toward the midline

2. Inferior rectus musclerotates the eye downward and toward the midline3. Medial rectusrotates the eye toward the midline4. Lateral rectusrotates the eye away from the midline5. Superior obliquerotates the eye downward and away from the midline6. Inferior obliquerotates the eye upward and away from the midline Eyelids. The eyelids protect the eyes anteriorly which meet at the medial and the lateral corners o

the eye. From the border of each eyelid are the EYELASHES. The eyelashes help filter out

foreign matter, including dust and debris, and prevent it from getting into the eye. Eyelid edges


36/44

associate with modified sebaceous glands make up the TARSAL GLANDs. These glands producan oily secretion that lubricates the eye. Between the eyelashes, modified sweat glands called

ciliary glands are found.

Conjunctiva. The conjunctiva is a mucous membrane that begins at the edge of the cornea andlines the inside surface of the eyelids and sclera, which serves to lubricate the eye. It is the thin,transparent tissue that covers the outer surface of the eye. This structure is nourished by tiny

blood vessels that are nearly invisible to the naked eye. The conjunctiva is composed of 3

sections:

Palpebral Conjuctivacovers the posterior surface of the eyelids Bulbar Conjuctivacoats the anterior portion of the eyeball Fornixthe transition portion, forming the junction between the posterior eyelid and the eyeball

NOTE: Although the palpebral conjunctiva is moderately thick, the bulbar conjunctiva is very thin. The

latter also is very movable, easily sliding back and forth over the front of the eyeball it covers. Since it i

clear, blood vessels are easily visible underneath it.

Within the bulbar conjunctiva are goblet cells, which secrete mucin. This is an important componen

of the pre-corneal tear layer that protects and nourishes the cornea.

Lacrimal Apparatus. The lacrimal apparatus consists of the lacrimal gland and a number ofducts that drain the lacrimal secretions into the nasal cavity. Located above the lateral end of each

eye are the lacrimal glabds that continually release a dilute salt solution, known as tears, onto the

anterior surface of the eyeball through several small ducts. The flow of tears flush across the

following structures orderly:

1. Eyeball2. Lacrimal canals medially3. Lacrimal sac4. Nasolacrimal duct that empties into the nasal cavity.

Lacrimal secretion contains antibodies and an enzyme that destroys bacteria known as lysozyme. Hence,

tears cleanse and protect the eye surface as it moistens and lubricates it. in cases when lacrimal secretion

substantially increases, tears spill over the eyelids and fill the nasal cavities. This causes congestion and

the sniffles. When eyes are irritated by foreign objects or chemicals and when a person is emotionally

upset lacrimal secretion is stimulated and increased.

Internal Eye structures

The Eyeball


37/44

The eye, commonly called the eyeball, is a hollow sphere and is composed of:

3 tunics or coats Humorsthe interior filled with fluids that help maintain the shape of the eye Lensthe main focusing apparatus of the eye. This structure is supported within the eye cavity

dividing it into two chambers.

TUNICS of the EYEBALL

Fibrous Tunicthis is the outermost tunic and is also known as the sclera, the thick and whiteconnective tissue. The fibrous tunic (sclera) is seen anteriorly as the white part of the eye. The

central portion of this tunic is modified so that it is crystal clear. The cornea is the transparent

window through which light enters the eye and is well supplied with nerve endings. This is the

main reason why blinking and increased tearing occur when the cornea is touched because most

nerve endings found here are pain fibers.

Vascular tunicthis is the middle coat of the eyeball and has three distinguishable regionsnamely:

1. Choroidthis is located posteriorly and lies between the sclera and the retina. It contains theblood vessels that provide nourishment to the outer layers of the retina. It is composed of layers o

blood vessels that nourish the back of the eye. The choroid is opaque and deeply pigmented

with melanin to absorb excessive light; else internal reflection would form multiple images on theretina. It is less vascular where the retina is thin. The choroid connects with the ciliary body

toward the front of the eye and is attached to edges of the optic nerve at the back of the eye.


38/44

2. Ciliary Bodythe ciliary body is made up of ciliary muscles and ciliary processes. It lies just behindthe iris. This is the structure to which lens are attached by a suspensory ligament called the ciliary zonule

and then the iris. The pigmented iris has a rounded opening, the pupil, through which light passes.

Nourishment for the ciliary body comes from blood vessels which also supply the iris. Ciliary processesare short, black tissues arranged radially. They secrete aqueous humour.

One function of the ciliary body is the production of aqueous, the clear fluid that fills the front of the eye

It also controls accommodation by changing the shape of the crystalline lens. When the ciliary body

contracts, the zonules relax. This allows the lens to thicken, increasing the eyes ability to focus up closeWhen looking at a distant object, the ciliary body relaxes, causing the zonules to contract.

3. Sensory Tunicthis is the innermost tunic of the eye and is called the retina. This structure extendsanteriorly only to the ciliary body. It converts images into electrical impulses that are sent along the optic

nerve to the brain where the images are interpreted. The retina can be compared to the film of a camera. I

contains millions of receptor cells, the rods and cones. Rods and cones are called photoreceptors because

they respond to light.

The rods and cones are not distributed evenly in the retina. The rods are most dense at the periphery or

edge of the retina and decrease in number as the center of the retina is approached. It is more numerous,some 120 million, and are more sensitive than the cones. However, they are not sensitive to color. The 6

to 7 million cones provide the eyes color sensitivity and they are much more concentrated in the central

yellow spot known as the macula. In the center of that region is the fovea centralis a 0.3 mm diameterrod-free area with very thin, densely packed cones. Consequently, this is the area of greatest visual acuity

or the point of sharpest vision and anything we wish to view critically is focused on the fovea centralis.

The photoreceptor cells are distributed over the entire retina, except where the optic nerve leaves the

eyeball. This is the site called the optic disc or blind spot. When light from an object is focused on the

optic disc, it disappears from our point of view and we cannot see it.

LENS

The crystalline lens is located just behind the iris. Light entering the eye is focused on the retina by the

lens. The nucleus, the innermost part of the lens, is surrounded by softer material called the cortex. The

lens is encased in a capsular-like bag. It is held upright in the eye by a suspensory ligament, the ciliaryzonule, attached to the ciliary body. Together, the lens and the ciliary body help control fine focusing of

light as it passes through the eye. The lens is divided into two segments namely:

1. Anterior (aqueous) segmentlocated anterior to the lens and contains a clear wayetry fluid calledaqueous humor. The aqueous humor helps to nourish the cornea and the lens. It is continually

produced by the ciliary body.

2. Posterior (vitreous) segmentlocated posterior to the lens and is filled with a gel-like substancecalled the vitreous humor or the vitreous body. The vitreous is a thick, transparent substance that

fills the center of the eye. It is composed mainly of water and comprises about 2/3 of the eyes

volume, giving it form and shape. The viscous properties of the vitreous allow the eye to return toits normal shape if compressed. The vitreous humor helps maintain the shape of the eye.


39/44

image courtesy of health.allrefer.com, medical-dictionary.thefreedictionary.com, walgreens.com,genericlook.com, medicalook.com, health.howstuffworks.com,umm.edu

Tissues

Definition

Body tissues are groups of cells that are similar in structure and function.EPITHELIAL TISSUES

Epithelial tissues are the tissues that lines or covers the body. It is the lining, covering and theglandular tissue of the body. Primarily, epithelial tissues functions include:

1. Protection2. Absorption3. Filtration4. Secretion

In general, the epithelium has the following distinct characteristics:

1. Forms continuous sheet by fitting together closely with the exception of glandular tissues.2. Have one free surface or edge in the membranes called an apical surface.3. Has a basement structure where the lower surface of the epithelium rests.4. Have no blood supply.


40/44

5. Depends on diffusion from the capillaries in the underlying connective tissue for food andoxygen.

6. Regenerates themselves if well nourish.The epithelium is classified into simple and stratified epithelium. The classification is based on the cell

arrangements.

Simple Epithelium

This type of epithelium is very thin. It functions for absorption, secretion and filtration. Protection is not

one of their specialties.

Simple squamous epitheliumforms the membranes where filtration or exchange of substancesby rapid diffusion takes place.

Simple cuboidal epitheliumthis is one layer of cuboidal cells which lies on the basement of themembrane. It forms the walls of the tubules in the kidney and the one that covers the surface ofthe ovaries in females.

Simple columnar epitheliumthis is one layer of columnar cells (tall cells) that fits closelytogether. It covers the entire area of the digestive tract from the stomach to the anus. In this typeof epithelium, goblet cells are found. Goblet cells are the one which produce lubricating mucus.

Pseudistratified Columnar Epitheliumthis type of epithelium gives the impression that it isstratified. The main function of this epithelium is on absorption and secretion.

Stratified Epithelium

This epithelium consists of two or more layer of cells. These epithelia mainly functions for protection. Itis more durable than the simple epithelia making it possible to carry out its function of protection.

Stratified squamous epitheliumthis is the most common stratified epithelium in the body whichconsists of several layers of cells. Cells located at the outer portion or edge area are squamous

cells while those that are located near the basement are either cuboidal or columnar. This type of

epithelium is located in sites where a good deal of abuse or friction is occurring in the body.These areas are the esophagus, mouth and the outer portion of the skin.

Stratified columnar epitheliumin this type of stratified epithelium the cells are columnar.However the basal cells are in various sizes and shapes. This is a rare epithelium in the bodywhere it is just found in the ducts of the large glands.

Stratified cuboidal epitheliumlike the stratified columnar epithelium these cells are also rare inthe body and are only found in the ducts of the large glands in the body. Typically, this type of

stratified epithelium has at least two layers of cells with the surface cells becoming cuboidal inshape.

Transitional epitheliumthis epithelium forms the lining of few organs such as the urinarybladder, the ureters and part of the urethra. With a transitional epithelium, cells located at the basare either cuboidal or columnar while those at the free surface are varying in their appearance.

Thus, it is a highly modified and stratified squamous epithelium. The transitional cells has the

ability of stretching by sliding past one another and changing their shape thus allowing stretching


41/44

of the organ to take place.

Glandular Epithelium

The main function of glandular epithelium is for secretion. A gland is composed of one or more cells that

makes and secretes a particular product or secretion. This secretion contains molecules in a water basedfluid. Two glands in the body are developed from the epithelial sheets namely:

Endocrine glandsthese are the ductless glands which secrete hormones that directly diffuse intothe blood that intertwines through the glands. Endocrine glands include the thyroid, adrenals and

the pituitary.

Exocrine glandsare the glands that carry out their function of secretion through their ducts tothe epithelial surface. Included in this classification are the sweat and oil glands, the liver and thepancreas.

CONNECTIVE TISSUES

Connective tissues are located everywhere in the body. Based on its name, it is responsible forconnecting body parts. The functions of these tissues are the mainly the following:

1. Protecting2. Supporting3. Binding together other body tissues

Connective tissues have the following distinct characteristics:

Connective tissues have variations in their blood supply. Some connective tissues are poor bloodsupply such as the tendons and ligaments while the other have no blood supply at all (avascular)

such as the cartilage. However, most connective tissues have a good blood supply (vascular).

All structures of a connective tissue heal very slowly.


42/44

It is composed of an extracellular matrix that enables the connective tissue form a soft packingtissue around other organs allowing the tissues to bear weight and to withstand stretching and

other abuses such as abrasion that no other tissue could have endured. This makes connective

tissue different from other tissues in the body.

Types of connective tissue:

1. Bonethis is the most rigid connective tissue in the body which is also called osseous tissue. It iscomposed of lacunae which are bone cells that are sitting in cavities. The lacunae are thensurrounded by layers of a very hard matrix that is comprised of calcium salts plus the large

amount of collagen fibers. The bone has an outstanding ability to protect and support other body

organs because of its rocklike hardness.2. Cartilagenext to the bone, cartilage is less hard but is more flexible. Though found in only few

areas of the body the most widespread is the hyaline cartilage which contains a large amount of

collagen fibers. The cartilage is the one that forms the supporting structures of the larynx. Aside

from that it is the one responsible for attaching the ribs to the breastbone and covers the ends ofthe bones where they form the joints. The fibrocartilage is the cushion-like discs that are located

in between the vertebrae. Another type of cartilage is the elastic cartilage that supports the

external ear and is located in areas where elasticity is desired.3. Dense Connective tissuethis connective tissue forms the tendons and the ligaments. It is also

called dense fibrous tissue where its main matrix is the collagen fibers. In the collagen fibers are

the fibroblasts that produce the building elements of the fibers. Tendons are responsible for

attaching muscles to the bone whilst ligaments are responsible for connecting bones to bonejoints. Aside from tendons and ligaments, dense connective tissue makes up the dermis which is

the lower layer of the skin.

4. Loose connective tissuethese are softer tissues containing more cells and fewer fiber. Areolartissue is under this type which is the most widespread tissue of its kind. Adipose tissues also

called fat is an areolar tissue where fat cells are predominating. Reticular connective tissues

resemble fibroblasts which form the stroma that supports many free blood cells in the lymphoid

organs in the body such as the lymph nodes, spleen and the bone marrow.5. BloodBlood is considered a connective tissue which is composed of blood cells that are

surrounded by a fluid matrix called blood plasma. It is also termed as vascular tissue where the

fibers it contains are soluble protein molecules that become visible only when the blood clots.

MUSCLE TISSUE

Muscle tissues produce movement in the body by their ability to shorten and contract.


43/44

Types of Muscle Tissues

Skeletal Muscle Tissue

Skeletal muscle tissues are muscles that can be consciously or voluntarily controlled. Thesetissues are attached

Documents

MS by System