ANATOMI SISTEM SARAF DAN INDERA

BAMBANG SOEMANTRI

Anatomical Organization of the Nervous system

• Central Nervous system :

– Brain

– Spinal cord

• Peripheral nervous system

– Ganglion

– Cranial nerves

– Spinal nerves

Nervous system includes all neural tissue in body

• Central Nervous System

– Brain and spinal cord

• Peripheral Nervous System

– All neural tissue outside CNS

• Neurons

Cells in Nervous Tissue

• Neuroglia

Neuroglia (Neuroglial Cells)

Central Neuroglia Astrocyte protoplasmic astrocyte

fibrous astrocyte

Oligodendrocyte perineuronal satellite cell

interfascicular cell

Microglia

Ependymal Cell

Peripheral Neuroglia

Schwann Cell

in peripheral nerve

and ganglion

Capsular (Satellite) Cell

in ganglion

Neurons

•have the property of electrical excitability - ability to produce

action potentials or impulses in response to stimuli

•what is the main defining characteristic of neurons?

Representative Neuron

1. cell body or soma -single nucleus with prominent nucleolus

-Nissl bodies

-rough ER & free ribosomes for protein

synthesis

-proteins then replace neuronal cellular

components for growth

and repair of damaged axons in the PNS

-neurofilaments or neurofibrils

give cell shape and support -

bundles of

intermediate filaments

-microtubules move material

inside cell

-lipofuscin pigment clumps

(harmless aging) - yellowish

brown

2. Cell processes =

dendrites (little trees)

- the receiving or input

portion of the neuron

-short, tapering and

highly branched

-surfaces specialized

for contact with other

neurons

-cytoplasm contains

Nissl bodies &

mitochondria

Neurons

3. Cell processes = axons • Conduct impulses away from cell body-

propagates nerve impulses to another neuron

• Long, thin cylindrical process of cell

• contains mitochondria, microtubules & neurofibrils - NO ER/NO protein synth.

• joins the soma at a cone-shaped elevation = axon hillock

• first part of the axon = initial segment

• most impulses arise at the junction of the axon hillock and initial segment = trigger zone

• cytoplasm = axoplasm

• plasma membrane = axolemma

• Side branches = collaterals arise from the axon

• axon and collaterals end in fine processes called axon terminals

• Swollen tips called synaptic end bulbs contain vesicles filled with neurotransmitters

Functional Classification of Neurons

• Sensory (afferent) neurons

– transport sensory information from skin, muscles, joints, sense organs & viscera to CNS

• Motor (efferent) neurons

– send motor nerve impulses to muscles & glands

• Interneurons (association) neurons

– connect sensory to motor neurons

– 90% of neurons in the body

• Afferent division of PNS

• Deliver sensory information from sensory receptors to CNS – free nerve endings: bare dendrites associated with pain, itching, tickling,

heat and some touch sensations

– Exteroceptors: located near or at body surface, provide information about external environment

– Proprioceptors: located in inner ear, joints, tendons and muscles, provide information about body position, muscle length and tension, position of joints

– Interoceptors: located in blood vessels, visceral organs and NS

-provide information about internal environment

-most impulses are not perceived – those that are,

are interpreted as pain or pressure

Sensory Neurons

• Efferent pathways

• Stimulate peripheral structures

– Somatic motor neurons

• Innervate skeletal muscle

– Visceral motor neurons

• Innervate all other peripheral effectors

• Preganglionic and postganglionic neurons

Motor Neurons

-both divisions use two neurons and one ganglion

-first neuron has its cell body within the CNS

(Pre-ganglionic)

-second neuron has its cell body within the

ganglion (Post-ganglionic)

-sympathetic division:

-preganglionic fibers arise from middle

of the cord and are very short

-long post-ganglionic neurons

-flight or fight response

-NT = norepinephrine

-parasympathetic division:

-cranial nerves: vagus

-preganglionic fibers arise from bottom

of the cord and are very long

-short post-ganglionic neurons

-housekeeper division - relaxed state

e.g. pupil dilation, food digestion, slows

heartbeat

- NT = acetylcholine

Motor Units • Each skeletal fiber has only ONE NMJ

• MU = Somatic neuron + all the skeletal muscle fibers it innervates

• Number and size indicate precision of muscle control

• Muscle twitch

– Single momentary contraction

– Response to a single stimulus

• All-or-none theory

– Either contracts completely or not at all

• Muscle fibers of different motor units are intermingled so that net distribution of force applied to the tendon remains constant even when individual muscle groups cycle between contraction and relaxation.

• Motor units in a whole muscle fire asynchronously

some fibers are active others are relaxed

delays muscle fatigue so contraction can be sustained

Structural Classification of Neurons

• Based on number of processes found on cell body

– multipolar = several dendrites & one axon • most common cell type in the brain and SC

– bipolar neurons = one main dendrite & one axon • found in retina, inner ear & olfactory

– unipolar neurons = one process only, sensory only (touch, stretch) • develops from a bipolar neuron in the embryo - axon and dendrite fuse and

then branch into 2 branches near the soma - both have the structure of axons (propagate APs) - the axon that projects toward the periphery = dendrites

• Named for histologist that first described them or their appearance

Structural Classification of Neurons

•Purkinje = cerebellum

•Renshaw = spinal cord

• others are named for shapes

e.g. pyramidal cells

Classification of neurons by cell size

• 1. golgi type I :

– Neurons have a long axon and large soma

• 2. Golgy type II :

– Neurons have short axon undergoes extensive terminal aeborization and small soma

Synaptic Communication

Synapses

• Are the sites of impulse transmission between the presynaptic and post synaptic

• Impuls transmission at synapse can occur:

– Electrically

– chemically

Electrical synapse

• Uncommon in mammals

• They are present in the brain stem, retina and cerebral cortex

• Electrical synapses are usually represented by gap junction that permit free movement of ion from one cell to another

• Impulse transmission is much faster across electrical synapse than across chemical synapse

Chemical synapse

• Most common mode of communication between two nerve cells

• Presynaptic membrane release one or more neurotransmitters into synaptic cleft

• Neurotransmitter diffuses across the synaptic cleft to ion-channel receptor on the postsynaptic membrane

• Binding of the neurotransmitter to the receptors initiates the opening ion channels, which permits the passage of certain ions, altering the permeability of the postsynaptic membrane and reversing its membrane potentials

Tipes of synapses

• Axodendritic:

– Between an axon and a dendrite

• Axosomatic:

– Between an axon and a soma

• Axoaxonic:

– Between two axon

• Dendrodendritic:

– between two dendrites

Synaptic morphology

• Presynaptic membrane:

– Contains metochondria, a few elements of SER, and an abundance of synaptic vesicles.

• Synaptic cleft

• Postsynaptic membrane:

– Contains neorotransmitter receptors

Nerve ending – nerve terminal

• Two structural type :

– 1. Motor ending ( terminal of axon )

• Transmit impulses from the CNS to skeletal & smooth muscle & to glands ( secretory ending)

– 2. sensory ending = sensory receptor = terminal of dendrites :

• Perceive various stimuli and transmit this input to the CNS

continued

• These sensory receptor are classified into three type depending on the source of the stimulus, and are components of the general or special somatic and visceral afferent pathway :

– Exteroceptors

– Proprioceptors

– interoceptors

Exteroceptors

• Location : near the body surface

• Specialized to perceive stimuli from the external environment

• These receptors sensitive to :

– Temperature

– Touch

– Pressure and

– Pain

• Are component of the general somatic afferent

continued

• Special somatic afferent :

– Specialized for light ( sense of vision) and sound (sense of hearing)

• Special visceral afferent modality :

– Specialized for smell and taste

Proprioceptors

• Are specialized receptor located in joint capsules, tendon and intrafusal fibers within muscle.

• These general somatic afferent receptors transmit sensory input to the CNS, which translated into information that relates to an awareness of the body in space and movement

continued

• Vestibular (balance) mechanism, located within the inner ear, are specialized for receiving stimuli related to motion vectors within the head.

Interoceptors

• Are specialized receptors that perceive sensory information from within organs of the body.

Mechanoreceptors

• Mechanoreceptors respond to mechanical stimuli that may deform the receptor or the tissue surrounding the receptor.

• Stimuli that trigger the mechanoreceptors are touch, stretch, vibration and pressure

Nonencapsulated mechanoreceptors

• Are simple unmyelinated receptors present in the skin, connective tissues and surrounding hair follicle – Peritricial nerve ending, located in the

epidermis of the skin, especially in the face and cornea of the eye

– Merckel’s disks, specialized for perceiving discriminatory touch, located in non hairy skin and regions of the body more sensitive to touch.

Encapsulated mechanoreceptors

• Encapsulated Mechanoreceptors exhibit characteristic structure and are present in specific location

– 1. Meissner’ corpuscles :

• Specialist for tactile

• Location : dermal papillae of the non hair portin of the hand, eyelids, lip, tongue, nipples, skin of the foot and forearm.

• Each corpuscle is formed by three or four nerve terminals and their associated Schwann cells, all which are encapsulated by connective tissue.

continued

– 2. Pacinian corpuscles • Location : in the dermis and hypodermis in the

digits of the hand, breast, connective tissue of the joint, periosteum and the mesentery

• Spezialied to perceive pressure, touch and fibration

• Morphology :

– ovoid & large receptor

– Single unmyelinated fiber as a core and its Schwann cell

– Surrounded by approximately 60 layers of modified fibroblast

– Each layer separated by a small fluid-filled space

– 3. Ruffini’s corpuscle

• Location : in the dermis of skin, nail beds, periodontal ligament and joint capsules

• Composition :

– branched nonmyelinated terminals interspersed with collagen fibers

– Surrounded by four to five layers of modified fibroblast

– 4. Krause’s end bulb • Morphology :

– Spheris – Unmyelinated nerve ending

• Location : papilla dermis, joints, conjunctiva, peritoneum, genital regions, subendothelial c.t. of the oral and nasal cavities

• Function : unknown, they were thought to be receptors sensitive to cold

Muscle spindles and Golgi tendon organs

• Muscle spindles provide feedback concerning the changes and the rate alteration of the muscle length

• Golgi tendon organs monitor the tension and the rate at which the tension is being produced during movement

• Information from these two sensory structures is processed at the unconscious level within the spinal cord; the information also reaches the cerebellum & cerebral cortex, so that individual may sense muscle position.

ANATOMI SISTEM SARAF DAN INDERA B

The Special Senses

BAMBANG SOEMANTRI

The Five Special Senses:

• Smell and taste: chemical senses (chemical transduction)

• Sight: light sensation (light transduction)

• Hearing: sound perception (mechanical transduction)

• Equilibrium: static and dynamic balance (mechanical transduction)

The Chemical Senses: Taste and Smell

• The receptors for taste (gustation) and smell (olfaction) are chemoreceptors (respond to chemicals in an aqueous solution)

• Chemoreception involves chemically gated ion channels that bind to odorant or food molecules

Taste

3 Types of Lingual Papillae

1. Filiform papillae:

– provide friction

– do not contain taste buds

2. Fungiform papillae:

– contain 5 taste buds each

3. Circumvallate papillae:

– contain 100 taste buds each

Location of Taste Buds

• Located mostly on papillae of tongue

• Three of the types of papillae: – fungiform – Circumvallate – Filiform

Taste Buds

• Each papilla contains numerous taste buds

• Each taste bud contains many gustatory cells

• The microvilli of gustatory cells have chemoreceptors for tastes

The Five Basic Tastes

• Sweet: sugars, alcohols, some amino acids, lead salts

• Sour: H+ ions in acids

• Salty: Na+ and other metal ions

• Bitter: many substances including quinine, nicotine, caffeine, morphine, strychnine, aspirin

• Umami: the amino acid glutamate (“beef” taste)

Gustatory pathway

• Facial nerve (anterior 2/3 of tongue) & Glossopharyngeal nerve (posterior 1/3 of tongue)solitary nucleus of medulla (initiate PsNS reflexes to trigger saliva & gastric secretion)thalamusgustatory cortex of parietal lobes – Fibers also project to the

hypothalamus & limbic system (enjoyment)

Influence of Other Sensations on Taste

• Taste is 80% smell

• Thermoreceptors, mechanoreceptors, nociceptors also influence tastes

• Temperature and texture enhance or detract from taste

Smell

Both smell and taste use chemoreceptors. Of all the senses, only smell and taste have fibers that run to both cortical areas And the limbic system.

Smell

• Olfactory epithelium = primary sensory organ

– Found on roof of nasal cavity

– Olfactory receptors are one of the few neurons to renew thru adult life (replaced ~every 60 days)

– Covered w/mucus to dissolve airborne odor molecules

Location of Olfactory (Odor) Receptors

Odor Receptors

• Bipolar neurons

• Collectively constitute cranial nerve I

• Unusual in that they regenerate (on a ~60 day replacement cycle)

Olfactory receptors

• Smell is difficult to research

• At least 1000 ‘smell genes’ active only in the nose

• Extremely sensitive

• Nasal cavity also contains pain receptors (ammonia, chili peppers, menthol, etc)

Olfactory receptors are bipolar neurons. •Are replaced throughout lifetime, but lost at the rate of about 1 % per year. •The cilia, or olfactory hairs are the sensitive portions •Chemical must be dissolved in watery mucus to stimulate the receptor. •Combinations of primary scents allow us to recognize thousands of different odors.

Olfactory pathway

• Olfactory nerve (axons of receptor cells) synapse in olfactory bulb (on cribriform plate)olfactory tract (w/in bulb)

– 1. Thalamusolfactory cortex (frontal lobe) where smells consciously interpreted and identified

– 2. (subcortical) hypothalamus/amygdala/limbic system to elicit emotional responses to odors

• Danger (fight or flight), appetizing (GI stimulation), reflexes such as sneezing/choking/breathing (ammonia)

Odors

• Very complicated

• Humans can distinguish thousands

• More than a thousand different odorant-binding receptor molecules have been identified

• Different combinations of specific molecule-receptor interactions produce different odor perceptions

Transduction of Smell

•

• Binding of an odorant molecule to a specific receptor activates a G-protein and then a second messenger (cAMP)

• cAMP causes gated Na+ and Ca2+ channels to open, leading to depolarization

68

Anosmia: absence of the sense of smell – Trauma

– Colds or allergies producing excessive mucus

– Polyps causing blockage

– 1/3 are from zinc deficiency

Vision

Overview of the Eye

• Eye acts much like a camera

– Lens of eye adjusts to bring object into focus

– Pupil of eye constricts to allow less light to enter in bright setting or dilates to allow more light to enter in darker setting

– Through bending of light rays, image reaches retina

• Sensitive nerve cell layer of eye

• Image is transmitted to brain for interpretation

Surface Anatomy of the Eye

• Eyebrows divert sweat from the eyes and contribute to facial expressions

• Eyelids (palpebrae) blink to protect the eye from foreign objects and lubricate their surface

• Eyelashes detect and deter foreign objects

Conjunctiva

• A mucous membrane lining the inside of the eyelids and the anterior surface of the eyes

– forms the conjunctival sac between the eye and eyelid

• Forms a closed space when the eyelids are closed

• Conjunctivitis (“pinkeye”): inflammation of the conjunctival sac

The Lacrimal Apparatus

• Lacrimal Apparatus:

– lacrimal gland

– lacrimal sac

– nasolacrimal duct

• Rinses and lubricates the conjunctival sac

• Drains to the nasal cavity where excess moisture is evaporated

Internal Anatomy of the Eye--Tunics

• Fibrous tunic: sclera & cornea

• Vascular tunic: choroid layer

• Sensory tunic: retina

Figure 17–4b

3 Layers of the Eye

Internal Anatomy of the Eye

• Anterior Segment contains the Aqueous Humor – Iris

– Ciliary Body

– Suspensory Ligament

– Lens

• Posterior Segment contains the Vitreous Humor

Figure 17–4c

3 Layers of the Eye

Autonomic Regulation of the Iris

Pupil Constricts

Pupil Dilates

The Two Layers of the Retina

• Outer pigmented layer has a single layer of pigmented cells, attached to the choroid tunic, which absorbs light to prevent light scattering inside

• Inner neural layer has the photosensory cells and various kinds of interneurons in three layers

Neural Organization in the Retina

• Photoreceptors: rods (for dim light) and cones (3 colors: blue, green and red, for bright light)

• Bipolar cells are connecting interneurons

• Ganglion cells’ axons become the Optic Nerve

Neural Organization in the Retina

• Horizontal Cells enhance contrast (light versus dark boundaries) and help differentiate colors

• Amacrine cells detect changes in the level of illumination

The Optic Disc

• Axons of ganglion cells exit to form the optic nerve

• Blood vessels enter to serve the retina by running on top of the neural layer

• The location of the “blind spot” in our vision

• Light must cross through the capillaries and the two layers of interneurons to reach the photoreceptors, the rods and cones

Micrograph of the Retina

Light

Opthalmoscope Image of the Retina

• The Macula Lutea (“yellow spot”) is the center of the visual image

• The Fovea Centralis is a central depression where light falls more directly on cones providing for the sharpest image discrimination

• Light bouncing off RBCs’ hemoglobin causes “red eye” in flash photos

Auditory sensations and Equilibrium

Hearing and equilibrium rely on mechanoreceptors The ear is divided into three parts: • Outer ear • Middle ear • Inner ear

Anatomy of Ear

HEARING

ONLY

HEARING

&

BALANCE

Figure 8.15

Hearing

Within Cochlear duct,

membranous labyrinth is

Spiral Organ of Corti –

hearing receptors or “hair

cells”

Sound waves > eardrum > ossicles >

oval window > set fluid in motion >

vibrations stimulate “hair cells” > cochlear

nerve transmits impulse to midbrain >

auditory cortex of temporal lobe

•The ossicles (malleus, incus, and stapes)transmit the vibratory motion from the eardrum to the oval window. The auditory tube allows pressure to be equalized on both sides of the eardrum. These structures are also involved with sound transmission only.

INNER EAR : Bony chambers

• Cochlea – hearing

• Vestibule – static equilibrium

• Semicircular canals – dynamic equilibrium

•The bony labyrinth contains perilymph and membranous sacs filled with endolymph. Within the membranous sacs of the vestibule and semicircular canals are equilibrium receptors. Hearing receptors are found within the membranes of the cochlea.

• Hair cells of the organ of Corti (the receptor for hearing within the cochlea) are stimulated by sound vibrations transmitted through air, membranes, and fluids

• Deafness is any degree of hearing loss. Conduction deafness results when the transmission of sound vibrations through the external and middle ears is hindered. Sensorineural deafness occurs when there is damage to the nervous system structures involved in hearing.

• Receptors of the semicircular canals (cristae) are dynamic equilibrium receptors, which respond to angular or rotational body movements. Receptors of the vestibule (maculae) are static equilibrium receptors, which respond to the pull of gravity and report on head position. Visual and proprioceptor input are also necessary for normal balance.

• Symptoms of equilibrium apparatus problems include involuntary rolling of the eyes, nausea, vertigo, and an inability to stand erect.

Equilibrium – Balance

Static equilibrium – maintenance of body posture relative to gravity while the body is still.

Dynamic equilibrium – maintenance of the body posture (mainly the head) in response to sudden movements. Tracking a moving object.

Static Equilibrium

•Inside the vestibule are two chambers : utricle and saccule.

•Regions of hair cells and supporting cells called maculae.

•Otoliths – “ear rocks”

Dynamic Equilibrium

•Semicircular canals

•In ampulla is the crista ampullaris – contains hair cells and supporting cells covered by a gelatinous mass called the cupula.

•Neurological connections between eyes and semicircular canals – for tracking

•Nystagmus

Dynamic Equilibrium • Receptors found in semicircular canals

• Respond to angular or rotatory movements

• Oriented in 3 planes

• Ampulla, Crista Ampullaris, Cupula

• Movement constant rate, adapts

Figure 8.14