Chapter 6 Hormone Nervous System Student

7/30/2019 Chapter 6 Hormone Nervous System Student

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CHAPTER 6:Nervous & Hormonal

Communication

Siti Noorfahana Mohd Idris, CFS UiTM


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Learning Objectives

i. Identify four different types of hormone classesii. Compare the mechanism of action of hormones

iii. Identify the endocrine glands and describe the

actions of their hormones

iv. Describe the processes involved in neural signaling

v. Describe the structure of neuron

vi. Explain how a neuron transmit impulse

vii. Describe several types ofnervous system in animals

viii. Identify the organization of a human nervous system

ix. Compare endocrine with nervous system function


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Overview: The Bodys Long-

Distance Regulators

Animal hormones are

chemical signals that are

secreted into the circulatory

system and communicateregulatory messages within the

body

Hormones reach all parts of the

body, but only target cells havereceptors for that hormone

Insect metamorphosis is

regulated by hormones


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Overview: The Bodys Long-

Distance Regulators

Two systems coordinate communicationthroughout the body: the endocrine system andthe nervous system

The endocrine system secretes hormones thatcoordinate slower but longer-acting responsesincluding reproduction, development, energymetabolism, growth, and behavior

The nervous system conveys high-speedelectrical signals along specialized cells calledneurons; these signals regulate other cells


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Hormone classes

i) Fatty acid derivatives Prostaglandins and juvenile

hormones of insects

Synthesized from arachidonic acid (a

20 carbon fatty acids)

ii) Steroids

The natural steroid hormones are

generally synthesized from cholesterol

in the gonads (sex hormones) andadrenal cortex (mineralcortisoids and

glucocortisoids).

These forms of hormones are lipids.


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Hormone classes

iii) Amino acid derivatives

Synthesized from amino acids

Adrenaline, noradrenalline

(cathecolamnies) and thyroxine are

derived from the amino acid

thyrosine.

iv) Peptides and proteins

Peptide hormones shorter in length

Protein hormones are one or morepolypeptide.

Synthesized in ER Golgi

Packed in vesicles store/release


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Hormone classes

Peptide hormones oxytoxin, calcitonin, parathyroid

hormone (PTH), Antidiuretic hormone

Protein hormones - Insulin, glucagon, growth hormone

(GH), FSH, LH, prolactin

Lipid-soluble hormones (steroid hormones) pass easily

through cell membranes, while water-soluble hormones

(polypeptides and amines) do not.

The solubility of a hormone correlates with the location of

receptors inside or on the surface of target cells.


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Mechanism of action

Hormones are released by endocrine glands

into blood

Transported by blood, they will arrive at the

target cells where they shows differentmechanism of action

The mechanism can be divided into steroid and

non steroid hormones

Steroid hormones are lipid soluble

Non steroid hormones are water soluble


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Mechanism of action

Water and lipid soluble hormones differ in theirpaths through a body

Water-soluble hormones are secreted by

exocytosis, travel freely in the bloodstream,and bind to cell-surface receptors

Lipid-soluble hormones diffuse across cellmembranes, travel in the bloodstream bound to

transport proteins, and diffuse through themembrane of target cells


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Water-soluble Vs Lipid-soluble


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Water-soluble Vs Lipid-soluble


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Mechanism of action Steroid

(Lipid-soluble)

Lipid soluble hormones are able to enter cells.

This is because the lipid portion of the plasma

membrane does not act as a barrier to entry of

lipophilic regulators. Steroid hormones are lipid themselves and thus

they are lipophilic.

Because these hormones are NOT watersoluble, they are not able to dissolve in the

plasma portion of the blood (need transport

protein in blood)


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Mechanism of action -

Steroid

Therefore, they are carried in the

blood attached to a protein carrier.

When the hormones arrive at their

target cells, they dissociate from

their carriers and pass through the

plasma membrane of the cell.

Some steroid hormones (steroids,

thyroid hormones, and the hormonal

form of vitamin D) will combine with

receptors within the target cell

cytoplasm and then move as a

hormone receptor complex to the

nucleus.

Others travel into the nucleus to

encounter their receptor protein.


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Mechanism of action -

Steroid

The hormone-receptor complex that is

activated may able to bind to specific

regions in the DNA.

This may activate or repress

transcription of gene regions into

messenger RNA.

Translation of the mRNA transcripts

that happens outside the cell results in

enzymes and other proteins that are

able to carry out a response to the

hormonal signal.

* Protein alter the activity of cell.
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Mechanism of action - Steroid

For example, estrogen is a

steroid hormone necessary

for female.

In female birds and eggs,

estradiol (a form of estrogen)

has specific receptor on liver

cells.

Binding of this hormone to

the receptor activates

transcription of the gene for

protein vitellogenin.

Vitellogenin is secreted and

transported to the blood,

where it is used to produce

egg yolk.


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Mechanism of action- Peptide

hormones (Water-soluble)

Peptide hormones are hydrophilic.

Therefore, a peptide hormone cannot cross the

target cell's plasma membrane that is lipid

soluble (consist of dwilayer lipid membrane) The hormones include all the peptide and

glycoprotein hormones.

Because these hormones are not able to entercells, they will bind to receptor proteins located

on the surface of the plasma membrane.


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Mechanism of action-

Peptide hormones

(Water-soluble)

Once the hormone has bound to its

receptor, a cascade of events will occur

producing secondary messenger

molecules that will allow the cell to

properly respond to the hormones

message. Binding of a peptide hormone (first

messenger) caused formation of a

second messenger, the cyclic AMP

(cAMP).

These cascade of reactions are

enzyme mediated and results in aresponse of the cell to the hormonal

action.


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The hormone epinephrine has multiple effects

in mediating the bodys response to short-term

stress

Epinephrine binds to receptors on the plasmamembrane of liver cells

This triggers the release of messenger

molecules that activate enzymes and result in

the release of glucose into the bloodstream


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Multiple Effects of Hormones

The same hormone may have different effects

on target cells that have

Different receptors for the hormone

Different signal transduction pathways


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Endocrine Tissues and Organs

In some tissues, endocrine cells are grouped

together in ductless organs called endocrine

glands.

Endocrine glands secrete hormones directly into

surrounding fluid.

These contrast with exocrine glands, which have

ducts and which secrete substances onto body

surfaces or into cavities


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Endocrine Vs Exocrine

Exocrine glands have ducts to carry hormones, while endocrineglands are ductless.

Examples of exocrine glands are sweat, saliva and mammary

glands, as well as oil and enzymes. There are glands which function

as both endocrine and exocrine glands.

Exocrine hormones are released into the external environment, oroutside of the body. Endocrine hormones are released into the

internal environment, or inside of the body.

Endocrine response is slower because hormones travel through the

blood.

The duration in endocrine transmission is prolonged becausekidneys have to filter the blood


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Glands in the endocrine system

Vertebrate hormones regulate growth and

development, reproduction, salt and fluid

balance, many aspects of metabolism and fluid

behavior. Homeostasis depends on normal concentrations

of hormones.

Over or under-secretion of hormones will result

in endocrine disorders.


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Pituitary gland

Most endocrine activity is controlled either directly or indirectly bythe hypothalamus.

The pituitary glands hang by a stalk from the hypothalamus.

The pituitary gland activity is

regulated by the integration of

the nervous and endocrine system

(neuroendocrine gland)

Because it controls the activity of

several other endocrine glands,

pituitary gland is said to be the

master gland of the body.


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Pituitary gland

The pituitary gland can

be divided into two

parts, the anteriorand

posterior lobes.

The posterior lobe ofthe pituitary gland

develops from brain

tissue; therefore it

contains axons thatoriginate in cell bodies

within the

hypothalamus.


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Pituitary gland


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Posterior Pituitary gland

This neuroendocrine gland secretes two peptide

hormones, oxytoxin and antidiuretic hormone

(ADH).

These hormones are enclosed within vesicles. They are transported down the axons into the

posterior lobe of the pituitary gland.

The vesicles are stored in the axon terminalsuntil the neuron is stimulated.

Once it is stimulated, the axon content will

diffuse into the surrounding capillaries.


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Posterior Pituitary gland

Oxytoxin stimulates

contraction

of the uterus and

stimulates ejection of

milk by the mammaryglands.

ADH stimulates

reabsorption of water

by the kidney tubules.

The posterior pituitary

stores and secretes

hormones that are made in

the hypothalamus


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Anterior Pituitary gland

Compared to the posterior lobe,

the anterior lobe develops from

epithelial cell rather than

neural cell.

The anterior lobe receivessignal and releases its hormone

into the blood vessels.

The anterior pituitary makes

and releases hormones underregulation of the hypothalamus


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The anterior lobe of the pituitary gland secretes growthhormone, prolactin and several tropic hormones

(hormones produced at the anterior gland but stimulates

other endocrine glands).

The other tropic hormones are ACTH, TSH, FSH and

LH.

Prolactin stimulates the mammary glands to produce

milk.

Melanocyte-stimulating hormone (MSH) regulates

skin color in amphibians, fish, and reptiles by controlling

pigment distribution in melanocytes.

In mammals, MSH plays additional roles in hunger and

metabolism in addition to coloration.


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Growth hormone (GH/somatotropin) is a hormone that

promotes tissue growth by promoting protein synthesis.

GH stimulates the liver to produce insulin-like growth

factors (IGFs), which promotes skeletal and tissue

growth. An excess of GH can cause gigantism, while a lack of

GH can cause dwarfism

ACTH and TSH control the secretions from the adrenal

glands and thyroid glands respectively. FSH and LH have essential roles in gamete formation

and hormonal secretions required in sexual reproduction

of animals.


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Thyroid gland

The thyroid gland is located in the neck region,

in front of the trachea and below the larynx (Adams

apple).

The thyroid gland secretes thyroid hormones, thyroxine

(T4) = four iodine atoms and triiodothyronine (T3) =three iodine atoms.

In vertebrates, thyroid hormones

are essential for normal growth

and development because they

stimulate the rate of metabolism.


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Thyroid gland

Regulation of thyroid

secretion depends mainly

on the secretion of the TSH

(thyroid secreting hormone)

from the anterior lobe ofthe pituitary gland.

When the concentration of

the thyroid hormones in the

blood rises above normal,the anterior pituitary

secretes less thyroid-

stimulating hormone (TSH).


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Di d f Th id F ti


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Disorders of Thyroid Function

and Regulation

Hypothyroidism, too little thyroid function, can

produce symptoms such as

Weight gain, lethargy, cold intolerance

Hyperthyroidism, excessive production of thyroid

hormone, can lead to

High temperature, sweating, weight loss,

irritability and high blood pressure Malnutrition can alter thyroid function

Di d f Th id F ti


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Disorders of Thyroid Function

and Regulation

Graves disease, a form of hyperthyroidism

caused by autoimmunity, is typified by protruding

eyes

Insufficient dietary iodine leads to an enlarged

thyroid gland, called a goiter


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Thyroid gland: Control of Blood

Calcium

The thyroid gland also secretes calcitonin, a

peptide hormone that maintains a proper level

of calcium in the blood.

When blood calcium levels rises, calcitonin is

released to cause calcium to be deposited in

the bones.


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Calcium

The parathyroid gland is

located on the surface of the

thyroid gland.

It secretes parathyroid

hormone (PTH), which

regulates the calcium

concentration by

stimulating calciumrelease from bones and

increasing calcium

reabsorption in the

intestine.


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Th id l d C t l f Bl d


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Calcium

PTH increases the level of blood Ca2+

It releases Ca2+ from bone and stimulates

reabsorption of Ca2+ in the kidneys

It also has an indirect effect, stimulating thekidneys to activate vitamin D, which promotes

intestinal uptake of Ca2+ from food

Calcitonin decreases the level of blood Ca2+

It stimulates Ca2+ deposition in bones andsecretion by kidneys


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Adrenal gland

The paired adrenal

glands are small,

yellow masses of

tissue that lie incontact with the upper

ends of the kidneys.

Each gland consists of

a central portion, theadrenal medulla, and

the outer section, the

adrenal cortex.


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Adrenal gland

Adrenal medulla is a neuroendocrine gland that is

controlled by the sympathetic nervous system.

- The adrenal medulla secretes epinephrine and

norepinephrine, the hormones help the body cope

with stress.

- Epinephrine and norepinephrine help the body to

respond to danger by increasing the heart rate,

metabolic rate and the strength of muscle

contraction. These hormones reroute blood toorgans needed for fight or flight.


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Adrenal gland


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Adrenal gland

Adrenal cortex

The hypothalamus controls the activity in the

adrenal cortex by means of the ACTH (from the

anterior lobe of the pituitary gland). Two other hormones secreted by the adrenal

cortex are

i. mineralcortisoids such as aldosterone

iii. glucocortisoids such as cortisol


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Adrenal gland

Aldosterone maintains a proper balance of

sodium and potassium ions in the kidney

tubules.

Cortisol promotes gluconeogenesis in liver

cells resulting in the conversion of amino

acids increasing level of glucose in the blood.

Thus during stress, the adrenal cortex ensures

adequate fuel supplies for the cells.


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Pancreas- An endocrine system In addition to secreting

digestive enzymes, thepancreas is an important

endocrine gland.

Its hormones, insulin and

glucagon, are secreted bycells that occur in little

clusters called the islets of

Langerhans.

The islets consist mainlyofbeta cells, which

secrete insulin, and

alpha cells, which

secrete glucagon.


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Pancreas- An endocrine system

Glucagon raises blood glucose (glycogenolysis) while

insulin lowers the concentration of glucose in the blood.

Insulin reduces blood glucose levels by

Promoting the cellular uptake of glucose

Slowing glycogen breakdown in the liver

Promoting fat storage, not breakdown

Glucagon increases blood glucose levels by

Stimulating conversion of glycogen to glucose in theliver

Stimulating breakdown of fat and protein into

glucose


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Diabetes Mellitus

Diabetes mellitus is perhaps the best-

known endocrine disorder

It is caused by a deficiency of insulin or a

decreased response to insulin in targettissues

It is marked by elevated blood glucose

levels


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Diabetes Mellitus

Type I diabetes mellitus (insulin-dependent) is an

autoimmune disorder in which the immune system

destroys pancreatic beta cells

Type II diabetes mellitus (non-insulin-dependent)

involves insulin deficiency or reduced response of targetcells due to change in insulin receptors


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Testes and ovaries

Testes produce testosterone and ovaries

produce estrogen and progesterone.

Hypothalamus controls the secretion of these

hormones by means of the LH and FSHhormone.

Testosterone allows secondary growth in male

during puberty.

Estrogen is necessary for egg development and

maturation and together with progesterone they

are responsible for the menstruation cycle.


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Thymus

Thymus gland is located beneath the sternum. It secretes thymosin that is responsible forlymphocyte

(white blood cells) maturation.


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Pineal gland

Melatonin secreted by the pineal gland, which is

located in the brain that influence the onset of

sexual maturity and our biological clock.

We feel sleepy at night and awake in the daytime.

This 24 hour cycle is called the circadian

rhythm that is controlled by melatonin.

It also helps regulate sexual development.


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Hormones from other tissue

Atrial natriuretic factor(ANF), which is

secreted by the atrium of the heart, promotes

sodium reabsorption thus lowering blood

pressure. Gastrin is secreted by the stomach that

stimulates release of gastric juice and

somastostatin inhibits secretion of gastric juice.

Secretin and cholecystokinin increase outputof pancreatic juice. The latter also stimulates

ejection of bile salts from the gallbladder.


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Review


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Molting and metamorphosis in


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insect

In invertebrates, hormones are secreted by

neuron rather than the endocrine glands.

These hormones regulate

i. Regeneration in hydras, flatworms andannelids

ii. Color changes in crustaceans

iii. Growth and developmentiv. Metabolic rate

v. Gamete production and reproduction



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insect

As insects grow, their hardened exoskeleton cannot fitthem anymore.

Therefore, insects undergo a series of molting process

where they shed their old exoskeleton in a process

called molting. In an immature insect, paired endocrine glands called

the corpora allata secretejuvenile hormone (JH).

This hormone suppresses metamorphosis at each larval

molt in order to ensure the larvae increase in size butremains in the larval (immature) state.



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insect

When the concentration of JH decreases,metamorphosis occurs and the larvae transformed into

pupae.

Prior to molting, neuroendocrine cells in the insect brain

secrete brain hormone (BH). BH stimulates theproduction of the ecdysone from the prothoracic glands,

which stimulates growth and molting.

Therefore, metamorphosis in adult form occurs when

molting hormone acts in the absence of juvenilehormone.


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Overview: Lines of Communication

The cone snail kills preywith venom that disablesneurons.

Neurons are nerve cellsthat transfer informationwithin the body

Neurons use two types ofsignals to communicate:electrical signals (long-distance) and chemicalsignals (short-distance)


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Neural signaling

Sensors Sensory receptors at the end of peripheral

nerves pick up information about the body's

internal and external environment.

These receptors also detect changes that

occur. For example, when you feel pain when

touching a hot object, a sensory receptor is

picking up that information. All sensory information is picked up in the

peripheral nervous system and sent to the

central nervous system.


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Neural signaling

Integration

The integrative function takes place in the brain

or spinal cord.

These organs receive sensory informationand make decisions regarding the

information.

The decision making is the integrative function.

For example, if you feel pain your brain might

decide you need to move away from the painful

stimulus.


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Neural signaling

Effectors

Once the CNS makes a decision, it then carries

out a motor function.

The motor function is the stimulation of a muscle(skeletal, smooth or cardiac muscle) or a gland.

When a motor function is carried out, neurons in

the CNS carry an impulse along a peripheral

nerve to either a muscle or a gland; these are

called effectors.


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Nervous tissue consists of nerve cells orneurons.


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Neurons are functional units of the nervous system which are

specialized to receive and send information in a form of electrical

signals called nerve impulses.


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Neuron

The largest/enlarged portion of the neuron is the cellbody. It contains the nucleus, the bulk of cytoplasm and

most of the organelles.


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Neuron

There are two types of cytoplasmic extensions which project fromthe cell body:

i. Dendrites

Typically short and highly branched. Numerous of them extend

from the cell body.

They functions in receiving stimuli and sending signals to the

cell body. Can be found at one end of the cell body.

ii. Axon

Conducts nerve impulses away from the cell

body to another neuron, a muscle or a gland. Eachneuron has a single axon leaving its cell body.

The cone-shaped base of an axon is called the axon hillock.

Information is transmitted from a


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Information is transmitted from a

presynaptic cell (a neuron) to a

postsynaptic cell (a neuron, muscle, or

gland cell)

Most neurons are nourished or

insulated by cells called glia.

In vertebrates the axons of many neurons are


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In vertebrates, the axons of many neurons are

surrounded by a myelin sheath that is made of

Schwann cells. The nucleus of the Schwann cells can

clearly be seen at the myelin sheath. The gap between Schwann cells is known as the node

of Ranvier.At this point, the axon is not insulated by

myelin.

They serve as points along the neuron forgenerating asignal.


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Neuron

Neurons are supported structurally and functionally by supportingcells called neuroglia.

The neuroglia supplies the neurons with nutrients; removes waste

and also provide immune function.

Two of the most important kinds of neuroglia in invertebrates are

Schwann cells and oligodendrocytes that produce myelinsheath.

Schwann cells produce myelin sheath in the Peripheral Nervous

System (PNS) whereas the oligodendrocytes produce myelin sheath

for the Central Nervous System (CNS).

N


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Neuron

There are three types of neurons

i. Sensory neurons typically have a long dendrite and

short axon, and carry messages from sensory

receptors to the central nervous system.

ii. Motor neurons have a long axon and short dendrites

and transmit messages from the central nervous

system to the muscles (or to glands).

iii. Interneurons are found only in the central nervous

system where they connect neuron to neuron.

N


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Neuron

N t i i f i l


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Neuron transmission of impulse

Every cell has a voltage (difference in electricalcharge) across its plasma membrane called a

membrane potential

The resting potential is the membrane potential

of a neuron not sending signals

Changes in membrane potential act as signals,

transmitting and processing information

N t i i f i l


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The plasma membrane of neurons always hadan unequal distribution of electrical charges

between the two sides of the membrane.

(Electrical Gradient).

This electrical gradient is called potential

difference that exists at every cells plasma

membrane.

N t i i f i l


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Biologists can measure the potential across themembrane by placing one electrode inside the cell and a

second electrode outside the cell, and connecting

through a very sensitive voltmeter oroscilloscope.

N t i i f i l


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The fluid outside of the membrane has a positivecharge while the cytoplasm inside has a

negative charge.

Opposite charges are usually attracted to eachother, the membrane stores energy by holding

opposite charges apart.

N t i i f i l


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There are three factors that results in differences ofcharges between the extracelullar fluid and inside the

neurons.

i) These differences are due to ionic concentrations.Molecules such as proteins, carbohydrates, and

nucleic acids that carry net negative charge are

more abundant inside the cell. This is because they

are too large to diffuse out. These molecules are calledfixed anions.

N t i i f i l


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ii) The sodium-potassium pumps (Na+ / K+) activelypumps in two K+ ions for every three Na+ ions that it

pumps out. These helps in maintaining a concentration

gradient where there is high K+ ion and low Na+ ion

inside the cell whereas high Na+

ion and low K+ ionoutside the cell.

N t i i f i l


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iii) Ion leak channels are membrane proteins that are morenumerous for K+ than Na+. This channels functions in allowing little

(Na+) to diffuse in but allows more (K+) to diffuse out, leaving an

excess of negative charge (from ions like Cl-) inside the

membrane.

N t i i f i l


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This charge difference is called membrane potential and ismeasured in millivolts.

When a cell at rest (resting membrane potential) where it does not

transmit any impulse, the voltage potential is - 65 to -70mV. The

negative sign indicates that the inside of the cell is negative

compared to the outside.

N t i i f i l


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N t i i f i l


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The cell membrane of aneuron will respond to stimuli

such as heat, pressure, and

chemicals by changing the

amount of polarization across

its membrane.

As a stimulus is applied,

within 2-3 msec, the voltage

will rise to a voltage at about-50mV, which is called the

threshold potential.

Ne ron transmission of imp lse


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The stimulus triggers the opening of the Na+ channel.Once the threshold is reached, the increasing positive

charge inside the membrane triggers the opening of

more and more of Na+ channels.



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As more and more Na+ moves in, the voltage will soar to its peak toat about +35mV.

The peak voltage triggers the closing of the Na+ channels while

the K+ channels opens to allow rapid diffusion of K+ ions out of

the membrane.



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The first region shows the flow of Na+ into the neuronsmembrane creating the action potential.

The action potentials regenerate itself along the neuron.

The three parts shown in the figure below show movements of

stimulus along the neuron.

As the action potential moves to the next region, K+ will diffuse

out of the neuron. At this time Na+ channels are closed (Almost

like domino effect).

Action potential are propagated in only one direction along the axon

due to the fact that action potential cannot be regenerated in the

regions where K+ leaving the axon.

The regeneration of action potential will carry the stimulus to our

central nervous system (spinal cord and the brain).

Neuron transmission

of impulse


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of impulse

At the site where the action

potential is generated, usually theaxon hillock, an electrical currentdepolarizes the neighboring regionof the axon membrane

Action potentials travel in only

one direction: toward the synapticterminals

Inactivated Na+ channels behindthe zone of depolarization preventthe action potential from travelingbackwards



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Action potentials are conducted without decrement,thus, the last action potential at the end of the axon is

just as large as the first action potential.

Myelinated axons conduct impulses more rapidly than

nonmyelinated axons because the action potentials innonmyelinated axons are only produced at the nodes of

Ranvier.

The process that impulses jump from node to node in

myelinated axons is called salutatory conduction. An action potential is all or none event, each threshold

depolarization produces either a full action potential due

to the complete opening of gated channels or none at all.



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Hyperpolarization

Some stimuli causes the

inside of the membrane

became more negative by

the opening of gated K+

channels.

Usually did not generate

an action potential



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Depolarization astimulation that

causes the inside of

the membrane to

become less negative

If it reached threshold

it might cause an

action potential


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Neuron

transmission of

impulse

Generation of Action

Potentials:

A Closer Look


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A Closer Look


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During the refractory period after anaction potential, a second action potential

cannot be initiated

The refractory period is a result of a

temporary inactivation of the Na+ channels


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Neuron transmission of impulse:


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Synapse

Wheneveraction potentials arrive at the endof a neurons axon, the information will be

passed to a receiving cell across the synapse.

The neuron whose axon transmits action

potentials to the synapse is the presynaptic

neuron, while the cell receiving the signal on the

other cell is the postsynaptic neuron.



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Synapse

Synapses can be eitherelectricalorchemical.

In an electrical synapse, action

potentials possibly passed from

one neuron to the other where the

receiving neuron is stimulated

quickly and at the same level. Thisis because it involves cytoplasmic

connections formed by the pre and

postsynaptic neuron.

In human, electrical synapses are

common in the heart and thedigestive system because the

nerve signals need to maintain

steady and rhythmic muscle

contractions.



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Synapse

Chemical synapses have a narrow gap called thesynaptic cleft that separates the sending neuron

(presynaptic) from the receiving neuron (postsynaptic).

The end of a presynaptic neuron is swollen and filled

with numerous synaptic vesicles that are packed withneurotransmitters.

Arriving at a synaptic cleft, the action potential (an

electrical signal) will stimulate the opening of gated

Ca++ channels. These will lead to rapid entrance ofCa++ via diffusion.

This serves as a stimulus for the fusion of presynaptic

neurons vesicle with its own outer membrane cell.



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Synapse

Therefore, the contents of the vesicles which are in aform ofneurotransmitter will be released by

exocytosis to the synaptic cleft.

The released neurotransmitter molecules will diffuseacross the cleft and bind to receptors protein on the

receiving postsynaptic neurons plasma membrane.

The binding opens chemical sensitive ion channelscausing ions to diffuse to the receiving cells

membrane and trigger new action potentials.

1. An action potentialarrives, depolarizing the

presynaptic membrane.

2. The depolarization opens

voltage-gated channels,


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g g ,

triggering an influx of

Ca++.

3. The elevated Ca++

concentration causes

synaptic vesicles to fusewith the presynaptic

membrane, releasing

neurotransmitter into the

synaptic cleft.

4. The neurotransmitter

binds to ligand-gated ion

channels in the

postsynaptic membrane.

In this example, bindingtriggers opening, allowing

Na+ and K+ to diffuse

through.



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Synapse

After release, the neurotransmitter May diffuse out of the synaptic cleft

May be taken up by surrounding cells

May be degraded by enzymes

Neurotransmitters are very important in homeostasis

because their precise signaling among neurons enables

the nervous system to coordinate the activities at all part

of the body.

Neurotransmitter


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Neurotransmitter

Neurotransmitters can be divided into two,i. Excitatory-They open Na+ channels, thus triggering

the action potentials in the receiving cells. Excitatory

neurotransmitters promote depolarization.

ii. Inhibitory- Open membrane channels for ions like

Cl- that decreases the receiving cells tendency to

develop action potentials. This promotes

hyperpolarization because the membrane inside thereceiving neuron becomes more negatively charged.

Neurotransmitter


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Neurotransmitter

Neurotransmitters tend to be small molecules, some areeven hormones. The time for neurotransmitter action is

between 0.5 and 1 millisecond.

Neurotransmitters are either destroyed by specific

enzymes in the synaptic cleft, diffuse out of the cleft, orare reabsorbed by the cell.

More than 30 organic molecules are thought to act as

neurotransmitters.

There are five groups: acetylcholine, biogenic amines,amino acids, neuropeptides, and gases

Neurotransmitter


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Neurotransmitter

Neurotransmitter: Acetylcholine


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Neurotransmitter: Acetylcholine

Acetylcholine is an example of a neurotransmitter. AcHcrosses the synapse between a motor neuron and a

skeletal muscle.

AcH causes Na+ to diffuse inside the cell causing the

postsynaptic membrane to become depolarized. Because the postsynaptic cell is a skeletal muscle cell,

the action potential stimulates muscle contraction.

To stop muscle contraction, an enzyme in the

postsynaptic membrane called acetylcholinesterasecleaves AcH into an inactive fragment.

Neurotransmitter: Amino Acids


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Neurotransmitter: Amino Acids

Amino acid neurotransmitters are active in the CNS andPNS

Known to function in the CNS are

Glutamate

Gamma-aminobutyric acid (GABA)

Glycine

Glycine and GABA are inhibitory neurotransmitters

that produce hyperpolarization at the postsynaptic

membrane.

Neurotransmitter: Biogenic Amines


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Neurotransmitter: Biogenic Amines

Biogenic amines include Epinephrine

Norepinephrine

Dopamine Serotonin

Dopamine and serotonin affect sleep, mood,

attention and learning.

They are active in the CNS and PNS

Neurotransmitter: Neuropeptides


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Neurotransmitter: Neuropeptides

Several neuropeptides, relatively short chainsof amino acids, also function asneurotransmitters

Neuropeptides include substance P and

endorphins, which both affect our perception ofpain

Opiates bind to the same receptors asendorphins and can be used as painkillers

Neurotransmitter: Gases


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Neurotransmitter: Gases

Gases such as nitric oxide and carbon monoxideare local regulators in the PNS

For example, during sexual arousal, certain

neurons in human male releases NO into the

erectile tissue of the penis.

This causes the blood vessel to dilate and fill the

spongy erectile tissue with blood.

How Drugs Affect

N t itt ?


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Neurotransmitter?

Drugs can interfere with just about every step in the work ofneurotransmitters.

More specifically, drugs can:

- Stop the chemical reactions that create neurotransmitters.

- Empty neurotransmitters from the vesicles where they're normally stored

and protected from breakdown by enzymes.

- Block neurotransmitters from entering or leaving vesicles.

- Bind to receptors in place of neurotransmitters.

- Prevent neurotransmitters from returning to their sending neuron (the

reuptake system).

- Interfere with second messengers, the chemical and electrical changes

that take place in a receiving neuron.

Nervous system in animals


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Some animals lack a nervous system; such as thesponges that do not have any cell specialized for

generating and transmitting nervous signals.



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Hydra is an animal that has the simplest typeof nervous system. Their nervous system is

what we referred as a nerve net.

The nerve net is a web-like system of

neurons that extends throughout the body.

This adaptation is adequate for the hydrabecause they are headless and have a

radial symmetry. Besides, their activity is

limited where they are usually stationary,

attached to submerged plant stems or rocks.

Their nerve net is responsive to signalsabout food or danger.



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e ous sys e a a s

Another animal with radial symmetry, theechinoderms have radial nerves that extend

through each arm from a central nerve ring.



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y

Radially symmetrical nervous systems areuncentralized unlike the bilaterally symmetrical

animals. These animals have a head and a tail and

have a tendency to move head-first through the

environment.



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y

Two evolutionary hallmarks ofbilateralsymmetrical:

i. Cephalization Concentration of the

nervous system at the head end.

ii. Centralization The presence of a central

nervous system (CNS) distinct from the

peripheral nervous system (PNS)

The flatworm has a small brain composed of

ganglia (masses of nerve cell bodies) and two

parallel nerve cords (bundles of

axons and dendrites).

These elements are the worms CNS while thesmaller nerves are the PNS.

The high degree of cephalization and

centralization in the squids nervous system

give them a degree of intelligence.



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y

Annelids and arthropods have segmentallyarranged clusters of neurons called ganglia.


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Organization of the nervous system


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g y

In vertebrates The CNS is composed of the brain and spinal cord

The per ipheral nervous system(PNS) is

composed ofnerves and ganglia

Central Nervous System


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y

The spinal cord conveys information from and to the brain The spinal cord also produces reflexes independently of the brain

A reflex is the bodys automatic response to a stimulus

For example, a doctor uses a mallet to trigger a knee-jerk

reflex



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y

Invertebrates usuallyhave a ventral nerve

cord while vertebrates

have a dorsal spinal

cord

The spinal cord and

brain develop from the

embryonic nerve cord

The nerve cord givesrise to the central canal

and ventricles of the

brain



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y



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y

The central canal of the spinal cord and the ventricles ofthe brain are hollow and filled with cerebrospinal fluid

The cerebrospinal fluid is filtered from blood and

functions to cushion the brain and spinal cord as well as

to provide nutrients and remove wastes The brain and spinal cord contain

Gray matter, which consists of neuron cell bodies,

dendrites, and unmyelinated axons

White matter, which consists of bundles ofmyelinated axons



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y



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y

Glia are present throughout the vertebrate brain and spinal cord. Glia have numerous functions to nourish, support, and regulate

neurons:

i. To surround neurons and hold them in place,

ii.To supply nutrients and oxygen to neurons,

iii.To insulate one neuron from another,

iv.To destroy pathogens and remove dead neurons.

Embryonic radial glia form tracks along which newly formed

neurons migrate. Astrocytes induce cells lining capilaries in the CNS to form tight

junctions, resulting in a blood-brain barrier and restricting the entry

of most substances into the brain

Astrocytes: Enable the

neurons to obtain oxygen

and glucose more quickly.



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Ependymal cells line the

ventricles and have cilia that

promote circulation of the

cerebrospinal fluid.

Microglial: Immune

cells that protect

against pathogens.

Peripheral Nervous System


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y

The PNS transmits information to and from theCNS and regulates movement and the internal

environment

The PNS can be divided into two subdivision,

sensory (afferent) and motor (efferent)

pathways.

Afferent neurons transmit information to the

CNS and efferent neurons transmit informationaway from the CNS



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Sensory divisions are nerve fibers that carryinformation from sensory receptors all over

the body to the CNS.

Sensory division keeps the CNS constantly

informed of events going on both inside and

outside the body.



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The motor(efferent)division carries impulses from

the CNS to effector organs,

the muscles and the glands

that responses to the stimulussensed by the sensory division.

The motor division can be

further subdivided into two

subdivisions, the autonomicand somatic systems.


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The somatic nervous system (Motor System) primarilyallows us to control and coordinate, usually voluntarily

the skeletal muscles, so it is most involved with

physical activity.

The autonomic nervous system control eventsinvoluntarily the blood vessels, glands and internal

organs.



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Autonomic nervous system is divided into two parts theparasympathetic nervous system which slows body

functions, thus conserving energy (rest and digest) and

the sympathetic nervous system which speeds body

functions, thus increasing energy use (fight-or-flight

response).

These two divisions has opposing effect, when one

stimulate, the other inhibits.

The enteric division controls activity of the digestive

tract, pancreas, and gallbladder


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Nervous system disorders


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Disorders of the nervous system includeschizophrenia, depression, drug addiction,

Alzheimers disease, and Parkinsons disease

Genetic and environmental factors contribute to

diseases of the nervous system

Schizophrenia


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About 1% of the worlds population suffers fromschizophrenia

Schizophrenia is characterized by hallucinations,

delusions, and other symptoms

Available treatments focus on brain pathways

that use dopamine as a neurotransmitter

Depression


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Two broad forms of depressive illness areknown: major depressive disorder and bipolar

disorder

In major depressive disorder, patients have a

persistent lack of interest or pleasure in most

activities

Bipolar disorderis characterized by manic

(high-mood) and depressive (low-mood) phases Treatments for these types of depression include

drugs such as Prozac

Alzheimers Disease


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Alzheimers disease is a mental deterioration

characterized by confusion and memory loss Alzheimers disease is caused by the formation of

neurofibrillary tangles and amyloid plaques in the brain

There is no cure for this disease though some drugs are

effective at relieving symptoms

Parkinsons Disease


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Parkinsons disease is a motor disordercaused by death of dopamine-secreting

neurons in the midbrain

It is characterized by muscle tremors,flexed posture, and a shuffling gait

There is no cure, although drugs and

various other approaches are used tomanage symptoms

Endocrine vs Nervous


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Both are systems of internal communication and alsoregulation

However the nature of the messages in the endocrine

system are in a form ofchemical signal whereas themessages in the nervous system are electrical signal.

The speed of message in the endocrine system is quite

slow because it needs to be transported by blood tospecific target sites whereas in the nervous system the

speed is really fast due to salutatory conduction



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Even though message can arrive really fast to targetsites in the nervous system, the duration of effect is very

short and prompt as compared to the duration of effect

in the endocrine system

The speed of response in the nervous system is rapid

whereas the speed of response in the endocrine system

is slower

The accuracy of message in the nervous system is

precise but the accuracy of message in the endocrine

system is more diffused



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THE END

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Chapter 6 Hormone Nervous System Student