mammalian physio unit 1 organized notes

8/10/2019 Mammalian Physio Unit 1 Organized Notes

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Prof Notes

Homeostasis

• Coined by Walter Cannon to describe the relative constancy of the chemical composition of the

blood despite considerable variations in external conditions

o External environment (variable) | integument (skin) |internal environment (relatively

constant)o Provides stable conditions for body cells

• Internal and external environments separated by some form of integument

o mammals the skin and mucous membranes

!he skin and the mucous membranes form the barrier bet"een the internal and

external environments limiting the transfer of biological materials bet"een the

t"o milieus and provide a first line of defense against infectious agents

#kin is also used to regulate temperature by forming an insulation layer that

limits the loss of heat E that is generated during cellular metabolism$ liver is a

key heat producer% &ot only heats but also cools the body in mammals "ith no

fur through the production of s"eat enabling the loss of excess heat thus cooling

the blood

o 'istinction proposed by Claude ernard a rench physiologist in the *+th

century• ,elative constant internal environment (blood- extracellular fluid) in vertebrates allo"s the levels

of cellular metabolism to be tightly regulated "ithin optimal ranges

• .rgans/systems are essential for maintaining the constancy of the internal environment

o 0ungs$ .1 in - C.1 and 21. out

o 3idneys$ urea- salts- and 21. out

o 4I tract$ nutrients and "ater in- "aste products out

o Cardiovascular$ circulated blood

o integument$ heat out

• .ther systems are not so closely related to homeostasis but are involved indirectly

o 5usculo$skeletal system allo"s the ac6uiring and consumption of "ater and food-

predator avoidance- extreme climate avoidance and reproductiono 7ll these processes are integrated "ith the other systems

• ,egulations !emperature- "ater- electrolyte- nutrient- excretory product- p2- .1 and C.1 etc%

o Involves the use of multiple systems that constantly measure and monitor levels of

specific aspects of blood chemistry (8blood glucose9) and may initiate a corrective

response if the levels go outside the optimal range (normal physiological range)

• !"o systems are primarily involved in the regulating process

o &ervous system

5ultiple roles providing the rapid sensory information- regulating the processing

of sensory information and generates a response triggering a target organ fast

Primary role in complex behavioural processing that maintain homeostasis and

reproductive functions (avoidance and group avoidance eg% :ocali;ation) and

other instinctual animal behaviour o Endocrine system

7long "ith other locally acting chemical messengers regulate most aspects of

metabolism- tissue gro"th and reproduction

:ery closely linked to the nervous system and have complementary roles

Endocrine system responds usually to various stimuli rapidly and slo"ly over an

extended period of time



#ome hormones have residual effects that alter function of different tissues long

after circulating levels of hormones decrease or increase%

Cells of the Nervous System

t"o main cell typeso neurons "hich conduct electrical signals and release chemical signals to other cells

(neurotransmitters across synapses or nerurohormones into circulation)

o glia cells "hich support the neurons and neuronal processes

&eurons

o are organi;ed into circuits throughout the nervous system controlling virtually every

activity of the body including the endocrine system via neuroendocrine secretions

o &eurons receive info from sensory receptors or other neurons integrate the information

and pass it on to the synapses via 7P

o &eurons typically are either anaxonic (no obvious axon in the C&#)- unipolar (one axon)

bipolar (t"o axons) or multipolar (dendritic tree receiving information and one main

output axon)

o #ensory receptors are speciali;ed cells that are able to sense and detect stimulus and areable to convert the stimulus to an 7P in the neurons (pressure$<Pacinian corpuscles)

4lial Cells

o Come in four main types each "ith a specific function in the system

.ligodendrocytes "hich provide the myelin insulation sheath around the nerve

fibres in the brain and spinal cord

#ch"ann cells "hich do the same but in the P&# (motor neurons)

7strocytes guide neurons to position during development- establish blood$ brain

barrier and provide critical gro"th factor and metabolic support to neurons in the

adult C&#

5icroglia are mobile cells that form the C&# defences against infection and

other damages (immune system cells cannot penetrate the blood$brain barrier)o !here are =*>> billion neurons in the adult human C&#- "ith larger numbers of glial

cells

Neurotransmission

#ignalling by neurons involve electric potentials(EP) (voltage differences) "hich are measured by

electrodes on the skull (electroencephalogram or EE4)

Possible to measure EP differences across the plasma membrane of individual cells

&eural transmission is achieved through transient charges in the membrane potential

7ll types of healthy cells have a membrane potential because of differences in the ions present

inside and outside the cells

.nly in neurons do they use this property utili;ing as a "ay of transmitting information

Membrane Potential

resting membrane potential results from a combination of factors

o semi$permeable properties of the plasma membrane

o presence of non$diffusible negatively charged molecules inside the cell

o action of sodium potassium pumps "hich maintain a steep concentration gradient of

sodium ions across the cell membrane

7s a result the inside of the cell is negatively charged compared to the outside



'ifference in charge or potential difference is the membrane potential

2ealthy resting neurons have the inside of the cell more negative than the outside and is about

$?> m:

Cellular proteins and phosphate groups of 7!P and other organic molecules are negatively

charged at the p2 of cell cytoplasm

&egative ions (anions) are fixed "ithin the cell because they cannot penetrate the plasmamembrane

7s a result anions attract positively charged inorganic ions (cations) from the EC fluid that are

small enough to diffuse through membrane pores

#mall inorganic cations (P- &a- and Ca) are distributed bet"een the ultra$cellular(@C) and

extracellular (EC) compartments and thus influenced by negative charged fixed ions "ithin the

cell

Plasma membrane more permeable to 3A than other cations- 3A accumulated "ithin the cell

more than others and as a result electrical attractions for the fixed anions

Instead of being distributed bet"een the @C and the EC compartments 3 becomes concentrated

"ithin the cell

Intracellular 3 concentration is *B> mEg/0 in the human body compared to an EC concentration

of B mEg/0

7s a result of une6ual distribution of charges bet"een in and out- each cell acts as a tiny battery

"ith the positive pole outside the plasma membrane and the negative pole inside the cell

5agnitude of the differences in charge is very small (less than a tenth of a :) critical importance

in physiological processes as muscle contractions- the regulation of heart beat- generation of

nerve impulses%

EQBM Membrane Potentials

• Extent to "hich each ion contributes to the potential differences across the plasma membrane or

membrane potential depends on

o Concentration gradient

o 5embrane permeability

• Plasma membrane is usually more permeable to 3 than other ions and membrane potential is

usually determined primarily by 3 concentration gradients

• If the membrane "as only permeable to 3 it "ould distribute according to the &E,#!

E@7!I.&

• ixed anions "ould cause intracellular 3 concentrations to become higher than EC concentrations

• 2o"ever- once the concentration gradient reached a particular value (ratio 8inside9 and 8outside9)

net movement of 3 "ould stop

• 5ore 3 entering the cell due to electrical attraction "ould cause the same amount to leave the

cell by net diffusion

• #tate of e6bm "ould be reached "here the 83A9 remained stable

• 5embrane potential that "ould stabili;e the 83A9 is kno"n as the 3A e6bm potential

• 4iven the normal 3A concentration gradient "here the 3A concentration is D>x higher inside than

out- value of E3 is $+> m: (sign indicates the polarity inside the cell)

o 5embrane potential of $+> m: is needed to produce e6bm in "hich the 3A

concentrations are *B> m5 inside and B m5 outside

o Intracellular and extracellular concentrations are kept stable

o Is the value "ere more negative it "ould dra" 3A into the cell

o If the value "ere less negative 3A "ould diffuse out of the cell



• In reality the cell membrane is never entirely impermeable to ions only =D> of 3 channels are

open in the cells at rest and many ions are slo"ly leaking across the membrane

• ,esting membrane potential is not E3 but ranges from =$FB to $GB m: (=$?> in most neurons at

rest)

Action Potential

4raded potentials caused by mechanical or ligand gated ion channels open in response to stimuli%

4raded potentials become large enough to cause voltage$gated &aA channels to open

!hreshold value "hen this occurs is usually about $BB m:

When the threshold in reached &a rushes into the cell and the membrane potential suddenly

reverses so it moves to"ards resting membrane potential of &a

4iven that I& concentrations of sodium are only about one tenth of those outside the cell (=*1

m: vs% *HB m5 EC)

&ernst e6uation indicates they potential of AFFm: (&a e6bm potential- E&a) "ould be needed to

stabili;e the &a concentrations across the membrane (pos% inside cell because pos% IC charger

"ould be needed to keep the sodium ion gradient in place "ith the &a channels open

7t =AD> m: the &a channels close again- voltage gated 3A channels are no" open- membrane

potentials shoot back belo" the normal resting potential- close to the 3 e6bm potential ($+> m:)o relative refractory period "hen cell is still excitable but it take more current to bring it

back to the threshold for other 7P

&a/3 7!P dependent pumps no" pump the excess &a out of the cell replacing it "ith 3- restoring

the ion gradients that existed before the 7P started%

Propagation of the AP

&eurons "hen an 7P is initiated at the axon hillock the adJacent sections of the axon membrane

are depolari;ed belo" the threshold because the spread of current "hich triggers an 7P here as

"ell

!his is continued se6uentially do"n the axon each section being depolari;ed by its neighbour

until eventually the 7P runs to the end of the axon%

7P canKt go back"ards up the axon because of the refractory period "hich immediately follo"smaking the section of the axon that the 7P has Just passed relatively refractory to conduction

Conduction in muscle fibres is fairly similar (not cardiac)

#keletal muscles- the 7P is caused by rapid opening of sodium channels but the resting membrane

potential and recovery are driven largely by chloride permeability

'efects in chloride channels can give rise to myotonia associated "ith a failure of the muscle to

relax after contraction

5yelinated axons have a relatively slo" side"ays spread of current needed to conduct action

potentials in non$myelinated axons is circumvented by insulating the axon in a myelin sheath

created by the #ch"ann cells

5yelinated axons depolari;ing current can Jump bet"een nodes of ,anvier speeding up

transmission dramatically as much as *>>x faster than in unmyelinated axons

7dditional benefit is the total ion flux across the membrane is much less in myelinated axons

saving the E re6uired by the &aA/3A 7!P dependent exchange pumps to bring back to the resting

state after an 7P has passed%

Summary

Important to be able to ientify components of a homeostatic feebac! loop an give

e"amples of pos# an neg# feebac! loops

Important to reali$e that each cell in a mammal e"hibits a resting membrane potential



%e"tboo! Notes

Homeostasis an &eebac! Control

,egulatory mechanisms of the body that are a single shared function maintaining constancy of

the internal environment and are maintained by negative feedback loops

!here are also positive feedback loops but that is for other functions than maintaining internal

environment consistency

Negative feebac! loops

o In order for the internal constancy to be maintained changes in the body must stimulate

sensors that can send information to an integrating center% !his allo"s the integratingcenter to detect changes from a set point%

o or each homeostatic mechanism there is a set point and is different for each mechanism

o !he integrating center is often located in the brain or spinal cord- but it can also be

located in endocrine glands as a group of cells

o 7 number of different sensors may send information to a particular integrated center

"hich can then integrate this information and direct the responses of effectors$ generally

muscles or glands%

o Integrating center may cause an increase or decrease in effector action to counter the

deviations from the set point and defend homeostasiso 7ctivity of the effectors is influenced by the effects they produce an because this

regulation is in the negative or reverse direction this type of control is kno"n as a

negative feedback loop

o Essential something is triggered to be added to the system that brings the system back to

homeostasis

o &egative feedback loops are continuous- ongoing processes- thus a particular nerve fibre

that is part of an effector mechanism may al"ays display some activity and a particularhormone that is part of another effector mechanism may al"ays be present in the blood%

o &erve activity and hormone concentration may decrease in response to deviations of the

internal environment in one direction or they may increase in response to deviation in the

opposite direction

o Changes from the normal range in either in effector direction are thus compensated forthe reverse changes in effector activity

o &egative feedback loops respond after deviations from the set point have stimulated

sensors- the internal environment is never absolutely constant%

o 2omeostasis is best conceived as a state of dynamic constancy in "hich conditions are

stabili;ed above and belo" the set point%

o Conditions can be measured 6uantitatively in degrees (Celsius for body temp- or mg/d0

for blood glucose etc%)

o #et point can be taken as an average value "ithin the normal range of measurements

Antagonistic effectors

o 5ost factors in the internal environment are controlled by several effectors that often

have antagonistic actions%o Control by antagonistic effectors is sometimes described as Lpush$pullM "here the

increasing activity of one effector is accomplished by decreasing activity of an

antagonistic effector

o !his allo"s a finer degree of control that Just by s"itching one effector on and off

o !he normal body temperature is maintained at a set point of around D?NC by the

antagonistic effects of s"eating- shivering- and other mechanisms

o 4lucose concentrations in the blood as "ell as Ca and other substances are regulated "ith

a negative feedback loops involving hormones that promote opposite effects%



Insulin lo"ers blood glucose and glucagon increases blood glucose

o In the heart the stimulation of one group of nerve fibres increase heart rate "hile the

stimulation of another group of nerve fibres "ill slo" the heart rate%

Quantitative measurements

o &ormal ranges and deviations from the set point must be kno"n 6uantitatively in order to

study physiological mechanisms

o uantitative measurements are basic to the science of physiology

7n example of this and antagonistic effectors is maintaining homeostasis% (ig%

*%B$ demonstrates that negative feedback mechanisms acted to restore

homeostasis in the experiment% !hese mechanisms involve the action of

hormones "hose effects antagonistic to that of insulin$ that is they promote the

secretion of glucose from the liver)

Positive feebac!

o !he action of effectors amplifies those changes and stimulated the effectors%

o 7n everyday example of positive feedback "ould be a thermostat that increases

temperature in response to a rise in temperature%

o 2omeostasis ultimately must be maintained by negative not positive feedback

mechanismso Effectiveness of some negative feedback loops can be increased by positive feedback

mechanisms that amplify the actions of the negative feedback response

lood clotting$ cascade of clotting factors are 7''E' to the system to

'EC,E7#E and prevent further blood loss

o !"o other examples of the positive feedback are exclusively in female reproductive

systems

!he cascade of hormones that affect the ovary "hich triggers ovulation

Contractions of the uterus during childbirth

Neural an enocrine regulation

o 2omeostasis is maintained by t"o general categories of regulatory mechanisms

Intrinsic$ built into the organs being regulated (molecules in : that allo" for

contraction and dilation)

Extrinsic$ regulation of the organ via the nervous and endocrine systems

o !he nervous and the endocrine system "ork closely together in regulating and integrating

body processes and maintaining homeostasis%

o !he nervous system controls the secretion of many endocrine glands and some hormones

in turn effect the function of the nervous system

o !ogether they regulate the activities of most of the other systems of the body

o ,egulation of the endocrine system is achieved by the secretion of chemical regulators

called hormones into the blood- "hich carries the hormones to all organs in the body%

o .nly certain organs can respond to certain hormones- thus the organ of a specific

hormones is kno"n as the target organ%

o &erve fibres are said to innervate the organs that they regulate% When stimulated thesefibres produce electrochemical nerve impulses that are conducted from the origin of the

fibre to its terminals in the target organ innervated by the fibre% !hese target organs can

be muscles or glands that function as effectors in the maintenance of homeostasis%

o or example

&egative feedback loops that help maintain homeostasis of arterial P in part by

adJusting the heart rate% If everything else is e6ual P is lo"ered by a decrease

heart rate and raised by an increased heart rate% 7ccomplished by regulating the

activity of the autonomic nervous system% 7 fall in P produced daily as "e go



from a lying position to a standing position$ compensated by a faster heart rate%

7s a conse6uence of this negative feedback loop our heart varies as "e go

through our day- speeding up and slo"ing do"n- so that "e can maintain

homeostasis of blood pressure and keep it "ithin normal limits%

Membrane Potentials

'ue to the permeability properties of the plasma membrane- the presence of nondiffusiblenegatively charged molecules inside the cell and the action of the &a/3 pump there is an une6ual

distribution of charges across the membrane%

!he inside of the cell is negatively charged compared to the outside

'ifference in charge or potential difference is kno"n as the membrane potential

5embrane potential is effected by permeability of the plasma membrane to specific ions

!he &a/3 pump goes against the gradient- this action alone creates and amplifies the difference in

concentration of these ions moving across the plasma membrane% !here is another reason "hy is

happens%

Cellular proteins and the phosphate groups of 7!P and other organic molecules are negatively

charged at the p2 of the cell cytoplasm

7nions "ithin the cell cannot penetrate the plasma membrane and attract cations from the ECfluid that can pass though the ion channels in the plasma membrane

7nions($ve ions- Cl$) "ithin the cell influence the distribution of cations (Ave- &aA- 3A- CaA)

bet"een the EC and IC compartments

Plasma membrane is more permeable to 3 than any other cations- 3 accumulates "ithin the cell

more than others as a result of the electrical attraction for the fixed anions

Instead of being distributed bet"een the IC and EC compartments- 3 becomes more highly

concentrated "ithin the cell

Intracellular 3 concentration is *B>mE6/0 in the human body compared to an EC concentration

of B mE6/0 (mE6/0 millie6uivalents- millimolar concentration multiplied by the valence of ion)

@ne6ual distribution of charge occurs bet"een the inside and outside of the cells%

Potential difference is the magnitude difference in charge- measured in voltage

E'bm potentials

o 5any inorganic ions in the IC and EC fluid "hat are maintained at specific

concentrations

o Extent to "hich ion contributes to the potential difference across the plasma membrane or

membrane potential depends on

Its concentration gradient

5embrane permeability

o ecause the plasma membrane is usually more permeable to 3 than any other ion- the

membrane potential is usually determined primarily by the 3 concentration gradient

o If the membrane "as only permeable to 3O

ixed ions "ould cause the IC 3 concentration to be higher than the EC 3

concentration- once the concentration gradient reached a particular value netmovement of 3 "ould cease% If more entered the cell because of electrical

attraction- the same amount "ould leave the cell by net diffusion% 7 state of e6bm

"ould be reached "here the concentration of 3 remained stable- the membrane potential that "ould stabili;e the 3 concentration is kno"n as 3 e6bm potential

(Ek)

o 7 sign is placed in front of the voltage to indicate the polarity of the inside of the cell



o 7 membrane potential of $+> m: is needed to produce an e6bm in "hich the 3

concentrations are *B> m5 inside and B m5 outside the cell

o 7t $+> m: these IC and EC concentrations are kept stable

If this value "ere more negative it "ould dra" 3 into the cell- if it "ere less

negative 3 "ould diffuse out

If the membrane "as only permeable to &aO

&a e6bm potential

Nernst e'uation

o 'iffusion gradients depend on the difference in concentration of the ions- therefore the

value of e6bm potential must depend on the ratio of the concentrations of the ions on the

t"o side of the membrane%

o &ernst e6uation allo"s for theoretical e6bm potential to be calculated for a particular ion

"hen its concentration are kno"n%

o Ex (F*/;)l log (8o9/8i9)

Ex e6bm potential in m: for ion

o concentration of the ion outside the cell

i concentration of the ion inside the cell

Q valance of the ion (A* for &a and 3)o !he e6bm potential for a cation has a negative value "hen i is greater than o

o #ay that the e6bm potential for 3 "as $+> m:% !hat mean the membrane potential of +>

m: "ith the inside of the cell negative- "ould be re6uired to prevent the diffusion of 3

out of the cell%

o &a has a higher concentration outside the cell than inside- thus in order to oppose the

diffusion the membrane potential inside the cell "ould need a positive polarity (AFF m:)

(esting membrane potential

o 5embrane potential of a real cell is not producing impulses is kno"n as the resting

membrane potentialo If the plasma membrane "ere only permeable to &a- its resting membrane potential

"ould e6ual the E &a of AFF m: if it "ere only permeable to 3 its resting membrane

potential "ould e6ual the Ek of $+> m:

o 7 real resting cell is more permeable to 3 than to &a- but it is not completely

impermeable to &a

o ,esting membrane potential is close to the Ek but some"hat less negative due to the

slight in"ard diffusion of &a

o !he resting membrane potential is less negative than the Ek thus there is also a slight

out"ard diffusion of 3 leakages are countered by the constant activity of the &a/3 pumps

o 7ctual value of the resting membrane potential depends on

!he ration of concentrations (o/i) of each ion on the t"o side of the plasmamembrane

#pecific permeability of the membrane to each different ion

o 5any ions including 3- &a- Ca- and Cl contribute to the resting membrane potential-

individual contributions are determined by the differences by the differences in their

concentrations across the membrane and by their membrane permeabilityKs

or any given ion a charge in its concentration in the EC fluid "ill change the

resting membrane potential but only that the membrane is permeable to that ion-



because the resting membrane is most permeably to 3 a change in the EC

concentration of 3 has the greatest effect on the resting membrane potential%

Change in membrane permeability to any given ion "ill change the membrane

potential% 5ost often it is the opening and closing of &a and 3 channels that are

involved but gated channels for Ca and Cl are also very important

(ole of Na)*+) pumps

o ,esting membrane potential is less negative than Ek- some 3 leaks out of the cell- thus

the cell is not in e6bm- "ith respect to 3 and &a concentrations

o !he concentrations of &a and 3 are maintained constant because of the constant

expenditure of E in active transport by the &a/3 pump

o &a and 3 pumps act to counter the leaks and thus maintain the membrane potential

o &a /3 pump does more than simply "ork against ion leaks because it transports D&a out

for every 13 that it moves in- net effect of contributing to the negative IC charge

o Electrogenic effect of the pumps adds approximately D m: to the membrane potential as

a result of all of these activities% 7 real cell has

7 relatively constant IC concentration of &a and 3

Constant membrane potential (in the absence of stimulation) in nerves and

muscles of $FB m: to $GB m:

Neurons an Supporting Cells

&ervous system is composed of neurons- "hich produce and conduct electrochemical impulses

and supporting cells "hich assist the functions of neurons% &eurons are classified functionally

and structurallyR the various types of supporting cells perform speciali;ed functions%

&ervous system in divided into central nervous system (brain and spinal cord) and the peripheral

nervous system (cranial nerves- arising from the brain and the spinal nerves arising from thespinal cord)

#ystem is broken do"n into t"o principle types

o &eurons

asic structural and functional units of the nervous system%

#peciali;ed to respond to physical and chemical stimuli- conduct electrochemical

impulses and release chemical regulators7ctivities through the neurons enable the perception of sensory stimuli- learning-

memory- and the control of muscles and glands

5ost neurons cannot divide by mitosis- although can regenerate a severed part or

sprout a ne" branch under certain conditions

o #upporting cells

7id in the functions of neurons and are Bx more abundant

In the C&# supporting cells are collectively called neuroglia or glial cells% @nlike

neurons- glial cells divide mitotically% ("hy tumors in the brain are glial cells

rather than neurons)

Neuronso although neurons vary considerably in si;e and shape they generally have three principle

regions

cell body

enlarged portion of the neuron that contains the nucleus

nutritional center "here macromolecules are produced



along "ith larger dendrites (but not axons) contain &issl bodies "hich

are dark staining granules composed of large stacks of rE, needed for

the synthesis of membrane proteins

"ithin the C&# are fre6uently clustered in groups called nuclei (not like

the nucleus)

"ithin the P&# usually occurs in clusters called ganglia

dendrites

thin branched processes off the cytoplasm of the cell body

provide a receptive area that transmits graded electrochemical impulses

to the cell body

axon

longer process that conducts impulses called 7P a"ay from the cell body

vary in length from mm to m or more in length (C&# to foot$ very long)

the origin of the axon near the cell body is an expanded region of called

the axon hillock it is "here the 7P originates from

side branches are called axon collaterals may extend from the axon

because they are 6uite long- special mechanisms are re6uired to transport

organelles and proteins from the cell body to the axon terminals

axon transport is energy dependant and is often divided into

fast component (1>> $H>> mm/day)

o mainly transports membranous vesicles (important for synaptic

transmission)

slo" component (>%1$* mm/day)

o transports microfilaments and microtubules of the cytoskeleton

slo" component (1 S G mm/day) transports over 1>> different proteins-

including critical synaptic function proteins

o the slo" components appear to transport their cargo in fast bursts "ith fre6uent pauses so

that the overall rate of transport is much slo"er than the fast component

o axonal transport may occur from the cell body to the axon and dendrites- the direction iscalled anterograde transport and involves molecular motors of kinesin proteins that move

cargo along the microtubules of the cytoskeleton

o kinesin motors move synaptic vesicles- mitochondria- and ion channels from the cell

body through the axons

o anterograde transport occurs in the dendrites as kinesin$ moves postsynaptic receptors for

neurotransmitters and ion channels along the microtubules in the dendrites

o in contrast axonal transport in the opposite direction that is along the axon and dendrites

to"ards the cell body is kno"n as retrograde transport- and involves molecular motor

proteins of dyneins

o dyneins move membranes- vesicles- and various molecules along the microtubules of the

cytoskeleton to"ards the cell body of the neuron

o retrograde transport can be responsible for movement of herpes virus- rabies- and tetanus

toxin from the nervous terminals into the cell bodies

o dendrites and axons can be referred to generally as processes or extensions of the cell

Classification of neurons an nerves

o &eurons can be classified according to their functions or structures

o unctional classification is based on the direction in "hich they conduct impulses

#ensory or afferent neurons conduct impulses from sensory receptors into the

C&#



5otor or efferent neurons conduct impulses out of the C&# to the effector organs

(muscles or glands)% !"o types of motor neurons

#omatic

o ,esponsible for both reflex and voluntary control of skeletal

muscles

7utonomic

o Innervate (send axons to) the involuntary effectors$ smooth

muscles- cardiac muscles- and glands

o !he cell bodies that innervate these organs are located outside

the C&# in autonomic ganglia

o !"o divisions

#ympathetic

Parasympathetic

o !he division together "ith their central control centers constitute

the autonomic nervous system

7ssociate neurons or interneurons are located entirely "ithin the C&# and serve

the associative or integrative functions of the nervous system

o the structural classification of neurons is based on the number of processes that extendfrom the cell body of the neurons

o pseudounipolar neurons have a single short process that branches like a ! to form a pair

of longer processes- they originate "ith t"o processes- during development they fuselater

sensory neurons are pseudounipolar- one of the branched processes receives

sensory stimuli and produces nerve impulses- the other delivers these impulses to

the synapse "ithin the brain or spinal cord

anatomically the part of the processes that conducts impulses to"ards the cell

body can be considered a dendrite and the part that conducts impulses a"ay from

cell body can be considered an axon

functionally the branched process behaves as a single- long axon that

continuously conducts 7P (nerve impulses)

only the small proJections at the receptive end of the process function as typical

dendrites rather than 7Ps

o bipolar neurons have t"o processes one at either end- found in the eye

o multipolar neurons the most common type- has several dendrites and one axon extending

from the cell bodyR motor neurons good ex

o &erve bundle of axons located outside the C&#

o 5ost nerves are composed of both motor and sensory fibres and are called mixed nerves

#ome of the cranial nerves contain sensory fibres only these are the nerves that

serve the special sense of sight- hearing- taste- and smell

o undle of axons in the C&# is called a tract

mammalian physio unit 1 organized notes

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