Nervous vs Hormone

8/2/2019 Nervous vs Hormone

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NERVOUS & HORMONALNERVOUS & HORMONAL

COMMUNICATIONCOMMUNICATION

Chapter 6Chapter 6


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Learning objectivesLearning objectivesi. Identify four different types of hormone classesii. Compare the mechanism of action of hormones

iii. Identify the endocrine glands and describe the actionsof their hormones

iv. Describe the processes involved in neural signaling

v. Describe the structure of neuron

vi. Explain how a neuron transmit impulsevii. Describe several types of nervous system in animals

viii. Identify the organization of a human nervous system

ix. Compare endocrine with nervous system function


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HormoneHormone

classesclasses

i. Fatty acid

derivatives Prostaglandins and

juvenile hormones of

insects Prostaglandins are

synthesized fromarachidonic acid a20 carbon fatty acid


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Hormone classesHormone classesii) Steroids

The natural steroidhormones aregenerally synthesizedfrom cholesterol in the

gonads and adrenalglands.

These forms ofhormones are lipids.


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Hormone classesHormone classes

iii) Amino acid derivatives

Synthesized from amino acids

Adrenaline and noradrenalline are

derived from the amino acid thyrosine


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Hormone classesHormone classes

iv) Peptides and protein

Peptide hormones are a class ofpeptides that are secreted into the blood

stream and have endocrine functions inliving animals


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Mechanism of actionMechanism of action Hormones are released by endocrine

glands into blood

Transported by blood, they will arrive atthe target cells where they shows differentmechanism of action

The mechanism can be divided intosteroid and peptide hormones

Steroid hormones are lipid soluble Peptide hormones are water soluble


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Mechanism of actionMechanism of action -- SteroidSteroid

Lipid soluble hormones are able to enter

cells.

This is because the lipid portion of the

plasma membrane does not act as abarrier to entry of lipophilic regulators.

Steroid hormones are lipid themselves and

thus they are lipophilic.


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Mechanism of actionMechanism of action -- SteroidSteroid Because these hormones are not water-

soluble, they are not able to dissolve in theplasma portion of the blood.

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 membraneof the cell.


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Some steroid hormones will combine with

receptors within the target cell cytoplasmand then move as a hormone receptorcomplex to the nucleus.

Others travel into the nucleus to encountertheir receptor protein.


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Mechanism of actionMechanism of action -- SteroidSteroid 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 thathappens outside the cell results in enzymes andother proteins that are able to carry out a

response to the hormonal signal.


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Mechanism of actionMechanism of action -- PeptidePeptide

Peptide hormones are hydrophilic.

Therefore, a peptide hormone cannotcross the target cell's plasma membrane

that is lipid soluble (consist of dwilayerlipid membrane)

The hormones include all the peptide and

glycoprotein hormones.


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Mechanism of actionMechanism of action -- PeptidePeptide Because these hormones are not able to

enter cells, they will bind to receptor proteinslocated on the surface of the plasmamembrane.

Once the hormone has bound to itsreceptor, a cascade of events will occurproducing secondary messenger molecules

that will allow the cell to properly respond tothe hormones message.


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Binding of a peptide hormone (first

messenger) caused formation of a secondmessenger, the cyclic AMP (cAMP).

These cascade of reactions are enzyme-mediated and results in a response of thecell to the hormonal action.


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Glands in the endocrine systemGlands in the endocrine system Vertebrate hormones regulate growth and

development, reproduction, salt and fluidbalance, many aspects of metabolism andfluid behavior.

Homeostasis depends on normalconcentrations of hormones.

Over or under-secrection of hormones willresult in endocrine disorders.


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Glands in theGlands in the

endocrineendocrinesystemsystem


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Pituitary glandPituitary gland Most endocrine activity is controlled either

directly or indirectly by the hypothalamus.

The pituitary glands hang by a stalk fromthe hypothalamus.


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Pituitary glandPituitary gland The pituitary gland can

be divided into two

parts, the anterior andposterior lobes.

The posterior lobe of

the pituitary glanddevelops from braintissue; therefore itcontains axons that

originate in cell bodieswithin thehypothalamus.


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Pituitary glandPituitary 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 terminals

until the neuron is stimulated.

Once it is stimulated, the axon content willdiffuse into the surrounding capillaries.


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Pituitary glandPituitary gland Oxytoxin stimulates

contraction of theuterus and stimulatesejection of milk by the

mammary glands.

ADH stimulates

reabsorption of waterby the kidney tubules.


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Pituitary glandPituitary gland Compared to the

posterior lobe, the

anterior lobedevelops fromepithelial cell rather

than neural cell. The anterior lobe

receives signal and

releases its hormoneinto the bloodvessels.


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Pituitary glandPituitary gland The anterior lobe of the pituitary gland

secretes growth hormone, prolactin andseveral tropic hormones (hormonesproduced at the anterior gland but

stimulates other endocrine glands).

The other tropic hormones are ACTH,

TSH, FSH and LH.


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Pituitary glandPituitary gland ACTH and TSH control the secretions

from the adrenal glands and thyroid glandsrespectively.

FSH and LH have essential roles ingamete formation and hormonalsecretions required in sexual reproduction

of animals.


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Pituitary glandPituitary gland


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Thyroid glandThyroid 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) and triiodothyronine (T3). In vertebrates, thyroid hormones are essential

for normal growth and development because

they stimulate the rate of metabolism.


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Thyroid glandThyroid gland


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Thyroid glandThyroid gland Regulation of thyroid

secretion depends mainly on

the secretion of the thyroidsecreting hormone (TSH)from the anterior lobe of thepituitary hormone.

When the concentration of thethyroid hormones in the bloodrises above normal, theanterior pituitary secretes less

thyroid-stimulating hormone(TSH).


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Thyroid glandThyroid gland The thyroid gland also

secretes calcitonin, a

peptide hormone thatmaintains a properlevel of calcium in theblood.

When blood calciumlevels rises, calcitoninis released to cause

calcium to bedeposited in thebones.


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Thyroid glandThyroid gland

The parathyroid gland islocated on the surface of

the thyroid gland. It secretes parathyroid

hormone (PTH), which

regulates the calciumconcentration bystimulating calcium release

from bones and increasingcalcium reabsorption in theintestine.


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CalcitoninCalcitonin vsvs PTHPTH


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Adrenal glandAdrenal gland The paired adrenal

glands are small,

yellow masses oftissue that lie incontact with the upperends of the kidneys.

Each gland consists ofa central portion, theadrenal medulla, and

the outer section, theadrenal cortex.


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Adrenal glandAdrenal gland Adrenal medulla is a neuroendocrine gland

that is controlled by the sympathetic nervoussystem.

The adrenal medulla secretes epinephrine andnorepinephrine, 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 musclecontraction. These hormones reroute blood toorgans needed for fight or flight.


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Adrenal glandAdrenal gland


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Adrenal glandAdrenal gland Adrenal cortex

The hypothalamus controls the activity in the

adrenal cortex by means of the ACTH (fromthe anterior lobe of the pituitary gland).

Two other hormones secreted by the adrenal

cortex arei. sex hormones precursors(covered in the reproductive

system)

ii. mineralcortisoids such as aldosteroneiii. glucocortisoids such as cortisol


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Adrenal glandAdrenal gland Aldosterone maintains a proper

balance of sodium and potassium ionsin the kidney tubules.

Cortisol promotes gluconeogenesis in

liver cells resulting in the conversion ofamino acids increasing level of glucosein the blood.

Thus during stress, the adrenal cortexensures adequate fuel supplies for thecells.


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PancreasPancreas--An endocrine organAn endocrine organ

Glucagon raisesblood glucose(glycogenolysis)while insulin

lowers theconcentration ofglucose in the

blood.


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Testes and ovariesTestes and ovaries Testes produce testosterone and ovaries

produce estrogen and progesterone.

Hypothalamus controls the secretion of thesehormones by means of the LH and FSHhormone.

Testosterone allows secondary growth in maleduring puberty.

Estrogen is necessary for egg development and

maturation and together with progesterone theyare 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 glandPineal gland Melatonin secreted by the pineal gland, which is

located in the brain influence our biological clockand the onset of sexual maturity.

We feel sleepy at night and awake in the daytime. This 24 hour cycle is called the circadianrhythm that is controlled by melatonin.

It also helps regulate sexual development.


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Hormones from other tissueHormones from other tissue Atrial natriuretic factor (ANF), which is secreted

by the atrium of the heart, promotes sodiumreabsorption thus lowering blood pressure.

Gastrin is secreted by the stomach thatstimulates release of gastric juice andsomastostatin inhibits secretion of gastric juice.

Secretin and cholecystokinin increase output ofpancreatic juice. The latter also stimulatesejection of bile salts from the gallbladder.

M lti d t h i iM lti g d m t m h i i


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Molting and metamorphosis inMolting and metamorphosis in

insectsinsects In invertebrates, hormones are secreted by

neuron rather than the endocrine glands.

These hormones regulate

i. Regeneration in hydras, flatworms and

annelidsii. Color changes in crustaceans

iii. Growth and development

iv. Metabolic ratev. Gamete production and reproduction

Molting nd met mor hosis inMolting and metamorphosis in


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insectsinsects As insects grow, their hardened exoskeleton

cannot fit them anymore.

Therefore, insects undergo a series of moltingprocess where they shed their old exoskeletonin a process called molting.

In an immature insect, paired endocrine glandscalled the corpora allata secrete juvenilehormone (JH).

This hormone suppresses metamorphosis at

each larval molt in order to ensure the larvaeincrease in size but remains in the larval(immature) state.



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insectsinsects 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

the production of the ecdysone from theprothoracic glands, which stimulates growth andmolting.

Therefore, metamorphosis in adult form occurs

when molting hormone acts in the absence ofjuvenile hormone.


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Neural signalingNeural signalingSensors Sensory receptors at the end of peripheral

nerves pick up information about the body'sinternal and external environment.

These receptors also detect changes that

occur. For example, when you feel pain whentouching a hot object, a sensory receptor ispicking up that information.

All sensory information is picked up in the

peripheral nervous system and sent to thecentral nervous system.


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Neural signalingNeural signalingIntegration

The integrative function takes place in the brainor spinal cord.

These organs receive sensory information andmake 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 painfulstimulus.


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Neural signalingNeural signalingEffectors 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 muscleor a gland; these are called effectors.


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Neural signalingNeural signaling


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NeuronNeuron Nervous tissue consistsof nerve cells or

neurons. Neurons are functional

units of the nervoussystem which arespecialized to receiveand send information ina form of electrical

signals called nerveimpulses.


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NeuronNeuron The largest/enlarged portion of the neuronis the cell body. It contains the nucleus,

the bulk of cytoplasm and most of theorganelles.

NN


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NeuronNeuron

There are two types of cytoplasmic extensionswhich project from the cell body

i. Dendrites Typically short and highlybranched. Numerous of them extend from thecell body. They functions in receiving stimuliand 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. Each neuron has a single axon leavingits cell body.

NeuronNeuron


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NeuronNeuron In vertebrates, the axons of many neurons are

surrounded by a myelin sheath that is made of Schwanncells. The nucleus of the Schwann cells can clearly beseen at the myelin sheath.

The gap between Schwann cells is known as the node ofRanvier. At this point, the axon is not insulated bymyelin.

They serve as points along the neuron for generating asignal.

NeuronNeuron


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NeuronNeuronThere are three types of neuronsi. Sensory neurons typically have a long dendrite

and short axon, and carry messages fromsensory receptors to the central nervoussystem.

ii. Motor neurons have a long axon and short

dendrites and transmit messages from thecentral nervous system to the muscles (or toglands).

iii. Interneurons are found only in the central

nervous system where they connect neuron toneuron.


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NeuronNeuron Neurons are supported structurally and

functionally by supporting cells called

neuroglia.

The neuroglia supplies the neurons with

nutrients; removes waste and also provideimmune function.


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NeuronNeuron Two of the most important kinds ofneuroglia in invertebrates are Schwann

cells and oligodendrocytes that producemyelin sheath.

Schwann cells produce myelin sheath inthe Peripheral Nervous System (PNS)whereas the oligodendrocytes produce

myelin sheath for the Central NervousSystem (CNS).


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Neuron transmission of impulseNeuron transmission of impulse A neuron that is not transmitting impulse is said

to be in the resting membrane potential state The plasma membrane of neurons always had

an 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 plasmamembrane.


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Neuron transmission of impulseNeuron transmission of impulse Biologists can measure the potential across themembrane by placing one electrode inside thecell and a second electrode outside the cell, andconnecting through a very sensitive voltmeter or

oscilloscope.


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Neuron transmission of impulseNeuron transmission of impulse 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 holdingopposite charges apart.

Neuron transmission of impulseNeuron transmission of impulse


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Neuron transmission of impulseNeuron transmission of impulse There are three factors that results in differences of

charges between the extracelullar fluid and inside theneurons.

i) These differences are due to ionic concentrations.Molecules such as proteins, carbohydrates, and nucleicacids that carry net negative charge are more abundantinside the cell. This is because they are too large to

diffuse out. These molecules are called fixed anions.



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pp

ii) The sodium-potassium pumps (Na+ / K+) activelypumps in two K+ ions for every three Na+ ionsthat it pumps out. These helps in maintaining aconcentration gradient where there is high K+ ionand low Na+ ion inside the cell whereas high Na+ion and low K+ ion outside the cell.



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Neuron transmission of impulseNeuron transmission of impulseiii) Ion leak channels are membrane proteins that

are more numerous for K+ than Na+. Thischannels functions in allowing little (Na+) to

diffuse in but allows more (K+) to diffuse out,leaving an excess of negative charge (from ionslike Cl-) inside themembrane.



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Neuron transmission of impulseNeuron transmission of impulse This charge difference is called a resting potential

and is measured in millivolts. The voltage potentialis 65 to -70mV (millivolts) of a cell at rest (resting

membrane potential). The negative sign indicatesthat the inside of the cell is negative compared tothe outside.



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The cell membrane of aneuron will respond to stimulisuch as heat, pressure, andchemicals by changing the

amount of polarization acrossits membrane.

As a stimulus is applied,within 2-3 msec, the voltagewill rise to a voltage at about

-50mV, which is called thethreshold potential.

Neuron transmission of impulse


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

increasing positive charge inside the membranetriggers the opening of more and more of Na+channels.



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Neuron transmission of impulseNeuron transmission of impulse As more and more Na+ moves in, the voltage will

soar to its peak to at about +35mV.

The peak voltage triggers the closing of the Na+channels while the K+ channels opens to allowrapid diffusion of K+ ions out of the membrane.



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The action potentials regenerate itself alongthe neuron.

The three parts shown in the figure belowshow movements of stimulus along theneuron

The first region shows the flow of Na+ intothe neurons membrane creating the

action potential.



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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 theregions where K+ leaving the axon.

The regeneration of action potential will carry the

stimulus to our central nervous system (spinalcord and the brain).


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NeuronNeuron

transmission oftransmission of

impulseimpulse


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pp The process that impulses jump from node to node

in myelinated axons is called salutatoryconduction.

An action potential is all or none event, eachthreshold depolarization produces either a fullaction potential due to the complete opening of

gated channels or none at all.



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Hyperpolarization

Some stimuli causes theinside of the membranebecame more negative bythe opening of gated K+

channels.

Usually did not generatean action potential



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Depolarization astimulation thatcauses the inside ofthe membrane tobecome less

negative

If it reached threshold it might cause an

action potential


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Neuron

transmissionof impulse



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

passed to a receiving cell across thesynapse.



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pp The neuron whose axon transmits action

potentials to the synapse is the presynaptic cell,while the cell receiving the signal on the other

cell is the postsynaptic neuron.



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Synapses can be either electrical or chemical.

In an electrical synapse, action potentialspossibly passed from one neuron to the otherwhere the receiving neuron is stimulated quicklyand at the same level. This is because itinvolves cytoplasmic connections formed by the

pre and postsynaptic neuron. In human, electrical synapses are common in

the heart and the digestive system because the

nerve signals need to maintain steady andrhythmic muscle contractions.



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Chemical synapses have a narrow gap

called the synaptic cleft that separates thesending neuron (presynaptic) from thereceiving neuron (postsynaptic).

The end of a presynaptic neuron isswollen and filled with numerous synapticvesicles that are packed with

neurotransmitters.



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pp

Arriving at a synaptic cleft, the action

potential (an electrical signal) will stimulatethe opening of gated Ca++ channels.These will lead to rapid entrance of Ca++

via diffusion. This serves as a stimulus for the fusion of

presynaptic neurons vesicle with its own

outer membrane cell.



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p

Therefore, the contents of the vesicles

which are in a form of neurotransmitter willbe released by exocytosis to the synapticcleft.

The released neurotransmitter moleculeswill diffuse across the cleft and bind toreceptors protein on the receiving

postsynaptic neurons plasma membrane.



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The binding openschemical sensitive

ion channelscausing ions todiffuse to the

receiving cellsmembrane andtrigger new actionpotentials.



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Neurotransmitters arevery important inhomeostasis becausetheir precise signalingamong neurons

enables the nervoussystem to coordinatethe activities at all part

of the body.



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Neurotransmitters can be divided into two,

i. Excitatory-They open Na+ channels, thustriggering the action potentials in the receivingcells. Excitatory neurotransmitters promotedepolarization.

ii. Inhibitory-Open membrane channels for ionslike Cl- that decreases the receiving cellstendency to develop action potentials. Thispromotes hyperpolarization because themembrane inside the receiving neuronbecomes more negatively charged.



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Neurotransmitters tend to be small molecules,some are even hormones. The time forneurotransmitter action is between 0.5 and 1millisecond.

Neurotransmitters are either destroyed byspecific enzymes in the synaptic cleft, diffuse outof the cleft, or are reabsorbed by the cell.

More than 30 organic molecules are thought toact as neurotransmitters.



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

AcH causes Na+ to diffuse inside the cell causing thepostsynaptic 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 thepostsynaptic membrane called acetylcholinesterasecleaves AcH into an inactive fragment.

Glycine and GABA are inhibitory neurotransmitters that

produce hyperpolarization at the postsynapticmembrane.

Nervous system in animalsNervous system in animals


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Some animals lack a nervous system;such as the sponges that do not have any

cell specialized for generating andtransmitting nervous signals.

Hydra is an animal that has the simplesttype of nervous system. Their nervoussystem is what we referred as a nerve net.

The nerve net is a web-like system ofneurons that extends throughout the body.



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This adaptation is adequate for the hydrabecause they are headless and have a radialsymmetry. Besides, their activity is limited where

they are usually stationary, attached tosubmerged plant stems or rocks.

Their nerve net is responsive to signals aboutfood or danger.



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Another animal with radial symmetry, theechinoderms have radial nerves that

extend through each arm from a centralnerve ring.



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Radially symmetricalnervous systems are

uncentralized unlike thebilaterally symmetricalanimals. These animals

have a head and a tailand have a tendency tomove head-first through

the environment.



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Two evolutionary hallmarks of bilateral

symmetricali. Cephalization Concentration of the

nervous system at the head end.

ii. Centralization The presence of acentral nervous system (CNS) distinctfrom the peripheral nervous system(PNS)



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The flatworm has a small brain composedof ganglia (masses of nerve cell bodies)

and two parallel nerve cords (bundles ofaxons and dendrites).

These elements are the worms CNS whilethe smaller nerves are the PNS.

The high degree of cephalization and

centralization in the squids nervoussystem give them a degree of intelligence.



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Organization of the nervous systemOrganization of the nervous system

Th h


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The humannervoussystem can

be dividedinto theCentral

NervousSystem andthePeripheral

NervousSystem



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The centralnervous system

(CNS) consists ofthe brain and thespinal cord

The peripheralnervous system isthe part outside thecentral nervous

system (PNS).

Organization of the nervous systemOrganization of the nervous system The PNS can be divided into


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The PNS can be divided intotwo subdivision, sensory(afferent) and motor (efferent)

pathways. Sensory divisions are nerve

fibers that carry informationfrom sensory receptors all overthe body to the CNS.

Sensory division keeps theCNS constantly informed of

events going on both inside andoutside the body.


The motor (efferent)


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The motor (efferent)division carries impulsesfrom the CNS to effector

organs, the muscles andthe glands that responsesto the stimulus sensed bythe sensory division.

The motor division can befurther subdivided into twosubdivisions, the

autonomic and somaticsystems.

Organization of the nervous systemOrganization of the nervous system The somatic nervous


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The somatic nervoussystem primarily allowsus to control and

coordinate, usuallyvoluntarily the skeletalmuscles, so it is mostinvolved with physical

activity. The autonomic nervoussystem control eventsinvoluntarily the blood

vessels, glands andinternal organs.


It i di id d i t t t th


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It is divided into two parts - theparasympathetic nervous system which

slows body functions, thus conservingenergy and the sympathetic nervoussystem which speeds body functions, thus

increasing energy use. These two divisions has opposing effect,

when one stimulate, the other inhibits.



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EndocrineEndocrine vsvs NervousNervous Both are systems of internal communication and


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Both are systems of internal communication andalso regulation

However the nature of the messages in the

endocrine system are in a form of chemicalsignal whereas the messages in the nervoussystem are electrical signal.

The speed of message in the endocrine systemis quite slow because it needs to be transportedby blood to specific target sites whereas in thenervous system the speed is really past due tosalutatory conduction

EndocrineEndocrine vsvs NervousNervous


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Eventhough message can arrive really fastto target sites in the nervous system, the

duration of effect is very short and promptas compared to the duration of effect inthe endocrine system

The speed of response in the nervoussystem is rapid whereas the speed ofresponse in the endocrine system is

slower

EndocrineEndocrine vsvs NervousNervous

The accuracy of message in the nervous system


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The accuracy of message in the nervous systemis precise but the accuracy of message in theendocrine system is more diffused

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Nervous vs Hormone