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BIO 100 Week 7

Integration and control of the body

The nervous system

Sense organs

171 !ervous Tissue

The nervous system is divided into the central nervous

system" consisting of the brain and s#inal cord" and the

#eri#heral nervous system" consisting of nerves that

carry messages to and from the central nervous system

The nervous system contains t$o ty#es of cells% neurons

and neuroglia

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Ty#es of !eurons and !euron Structure

There are three classes of neurons% sensory neurons"

interneurons" and motor neurons

&ll neurons have three #arts% a cell body" dendrites" and

an a'on

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(yelin Sheath Some a'ons are covered by a #rotective

myelin sheath The myelin sheath serves as an e'cellent

insulator and #lays an im#ortant role in nerve

regeneration

The !erve Im#ulse

The nature of a nerve im#ulse can be characteri)ed by

voltage changes

*esting +otential When the a'on is not conducting an

im#ulse" the inside is negatively charged" and the outside

is #ositively charged There is a##ro'imately a ,- m.

#otential di/erence across the membrane This charge

di/erence is due to the action of the sodium#otassium

#um# that actively trans#orts sodium out of and

#otassium into the a'on

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&ction +otential

&n action #otential is a ra#id change in #olarity across an

a'onal membrane as the nerve im#ulse occurs It is an

allornone #henomenon

Sodium ates O#en When the action #otential begins" the

gates of the sodium channels o#en and sodium 2o$s into

the a'on The membrane #otential changes from ,- m.to 340 m.

+otassium ates O#en Second" the gates of the

#otassium channels o#en" and #otassium 2o$s outside

the a'on This re#olari)es the a'on 5onduction of an

&ction +otential

The action #otential travels do$n an a'on one small

section at a time

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Transmission &cross a Syna#se

6very a'on branches into many ne endings" each ti##ed

$ith an a'on terminal 6ach terminal lies very close to

either the dendrite or cell body of another neuron This is

called a chemical syna#se 5ommunication bet$een the

t$o neurons is carried out by molecules called

neurotransmitters that are stored in syna#tic vesicles inthe a'on terminals and released $hen nerve im#ulses

reach the a'on terminal

Syna#tic Integration

& neuron is on the receiving end of many e'citatory and

inhibitory signals Syna#tic integration is the summing u#

of these signals

!eurotransmitters&t least 8- di/erent neurotransmitters have been

identied Once a neurotransmitter has been released

into a syna#tic cleft and initiated a res#onse" it is

removed from the cleft

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178 The 5entral !ervous SystemThe s#inal cord and the brain make u# the central

nervous system 95!S: The S#inal 5ord The s#inal cord

e'tends from the base of the brain through a large

o#ening in the skull and into the vertebral canal

Structure of the S#inal 5ord

The s#inal nerves #ro;ect from the cord bet$een the

vertebrae

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The 5erebrum

The cerebrum is the largest #ortion of the brain It is the

last center to receive sensory in#ut and carry out

integration before commanding voluntary motorres#onses The cerebrum carries out the higher thought

#rocesses re=uired for learning and memory and for

language and s#eech

The 5erebral >emis#heres

The cerebrum is divided into the left and right cerebral

hemis#heres Shallo$ grooves divide each hemis#here

into lobes

The cerebral corte' is a thin but highly convoluted outer

layer of gray matter that covers the cerebral

hemis#heres

+rimary (otor and Sensory &reas of the 5orte'

The #rimary motor area is located in the frontal lobe The

#rimary somatosensory area is located in the #arietal

lobe

&ssociation &reas

&ssociation areas are #laces $here integration occurs

+rocessing 5enters

+rocessing centers of the corte' receive information from

the other association areas and #erform higherlevel

analytical functions

5entral White (atter

(ost of the rest of the cerebrum beneath the cerebral

corte' is com#osed of $hite matter Basal !uclei (asses

of gray matter located dee# $ithin the $hite matter are

called basal nuclei

The ?ience#halon

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The hy#othalamus and the thalamus are in the

dience#halon The hy#othalamus is the integrating center

that hel#s maintain homeostasis by regulating hunger"

slee#" thirst" body tem#erature" and $ater balance Thethalamus integrates sensory in#ut from the visual"

auditory" taste" and somatosensory systems The #ineal

gland is located in the dience#halon

The 5erebellum

The cerebellum receives sensory in#ut from the ;oints"

muscles" and other sensory #ath$ays about the #resent

#osition of body #arts It also receives motor out#ut from

the cerebral corte' about $here these #arts should be

located The cerebellum maintains balance and #osture

The Brain Stem

The brain stem contains the midbrain" the #ons" and the

medulla oblongata The medulla oblongata contains anumber of re2e' centers for regulating heartbeat"

breathing" and blood #ressure 6lectroence#halograms

The electrical activity of the brain can be recorded in the

form of an electroence#halogram 966:

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17@ The Aimbic System and >igher (ental

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The limbic system is a com#le' net$ork of tracts and

nuclei that incor#orates #ortions of the cerebral lobes"

the basal nuclei" and the dience#halon The hi##ocam#us

and the amygdala are im#ortant for learning and memoryand emotions such as anger and fear

>igher (ental

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174 The +eri#heral !ervous System

The #eri#heral nervous system is com#osed of nerves

and ganglia !erves are bundles of a'ons anglia are

collections of cell bodies Somatic System The #eri#heral

nervous system is subdivided into the somatic system

and the autonomic system

The somatic system serves the skin" skeletal muscles"

and tendons Some actions in the somatic system are due

to re2e'es" $hich are automatic res#onses to a stimulus

The *e2e' &rc

*e2e'es are #rogrammed" builtin circuits that allo$ for

#rotection and survival They re=uire no conscious

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thought !erve im#ulses travel from the sensory neuron

to the s#inal cord and back to the motor neuron

&utonomic System

The autonomic system regulates the activity of cardiacand smooth muscle and glands The system is com#osed

of the sym#athetic and #arasym#athetic divisions These

divisions function automatically and usually in an

involuntary manner" innervate all internal organs" and

utili)e t$o motor neurons that syna#se at a ganglion

Sym#athetic ?ivision

The sym#athetic division is es#ecially im#ortant during

emergency situations

+arasym#athetic ?ivision

The #arasym#athetic division is sometimes called the

housekee#er division because it #romotes all the internal

res#onses $e associate $ith Crest and digestD

17- ?rug &buse

In general" drugs either im#act the limbic system or

a/ect the action of a #articular neurotransmitter at the

syna#se

Some S#ecic ?rugs of &buse

!icotine

!icotine causes a release of e#ine#hrine It induces both

#hysiological and #sychological de#endence &lcohol

96thanol:

6thanol in2uences the action of &B& and glutamate It

damages the liver and is able to cross the #lacenta and

harm the unborn fetus

(ari;uana

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(ari;uana is rich in tetrahydrocannabinol 9T>5: that

binds to rece#tors for a neurotransmitter in the brain that

is im#ortant for shortterm memory #rocessing

5ocaine and 5rack5ocaine #revents the syna#tic u#take of do#amine

5ocaine causes e'treme #hysical de#endence >eroin

>eroin binds to rece#tors meant for endor#hins" natural

neurotransmitters that kill #ain and #roduce a feeling of

tran=uility

C5lubD ?rugs 6cstasy" rohy#nol" and ketamine are drugs

that are abused by teens and young adults $ho attend

nightlong dances called raves or trances

(etham#hetamine C(ethD or CcrankD is a #o$erful 5!S

stimulant

17, ?isorders of the !ervous System

?isorders of the Brain

&l)heimer disease is the most common cause of

dementia

+arkinson disease is characteri)ed by a gradual loss of

motor control

(ulti#le sclerosis is the most common neurological

disease that aEicts young adults (S is an autoimmune

disease in $hich the #atients o$n immune system

attacks the myelin of the nervous system

& stroke results in disru#tion of the blood su##ly to the

brain

(eningitis is an infection of the meninges

Several brain diseases are caused by #rions including

5reut)feldtFakob disease and mad co$ disease

?isorders of the S#inal 5ord

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S#inal cord in;uries may result from trauma Aittle or no

nerve regeneration is #ossible in the 5!S" so any

resulting disability is usually #ermanent

&myotro#hic lateral sclerosis is a devastating conditionthat a/ects the motor nerve cells of the s#inal cord

?isorders of the +eri#heral !erves

uillainBarre syndrome is an in2ammatory disease that

causes demyelination of #eri#heral nerve a'ons

(yasthenia gravis is an autoimmune disorder in $hich

the body reacts against the acetylcholine rece#tor at the

neuromuscular ;unction of the skeletal muscles

Sensory !euron!eurons $hich takes messages to the 5!SInterneuron!eurons $hich receive in#ut from theneurons before they communicate $ith

motor neurons(otor !euron!eurons $hich takes messages a$ay fromthe 5!S to an e/ectorSch$ann 5ells& neuroglia $hich makes the myelinsheath in the +!SOligodendroglial 5ells& neuroglia $hich makes the myelinsheath in the 5!S

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ray (atter& nervous tissue $hich contains cellbodies and short" nonmyelinated bers

White (atter& nervous tissue $hich containsmyelinated a'ons that run together inbundles called tracts

!erve Im#ulse

The nervous system uses these im#ulsesto convey information*esting +otential

The #eriod $hen the a'on is notconduction an im#ulseSodium#otassium +um#s

5arrier #roteins $hich actively trans#ort!a3 out of and G3 into the a'on&ction +otential& ra#id change in #olarity across ana'onal membrane as the nerve im#ulseoccursH based on allornone #henomenon

ThresholdWhen a stimulus that causes the a'onalmembrane to de#olari)e to a certain level?e#olari)ation

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When the charge inside the a'on changesfrom negative to #ositiveH !a3 movesinside the a'on

*e#olari)ationWhen the inside of the a'on resumes anegative charge as G3 e'its the a'on*efractory +eriod& #eriod $hich the sodium gates areunable to o#en

!eurotransmitterStored syna#tic vessels in the a'onterminalSyna#tic Integration

The summing u# of e'citatory andinhibitory signals

The central nervous system5ontains the s#inal cord and brain(eninges5overing of the brain and s#inal cord5erebros#inal

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5erebrumThe largest #ortion of the brain in humansHlast center to receive sensory in#ut andcarry out integration before commanding

voluntary motor res#onses5erebral >emis#heres

T$o halves of the cerebrum5or#us 5allosum& bridge of $hite matter $hich divides thecerebrum

5erebral 5orte'& thin but highly convoluted outer layer ofgray matter that covers the cerebralhemis#heres+rimary (otor &rea.oluntary commands to skeletal muscles

begin in the #rimary motor areaH control ofthe versatile human hand takes u# anessentially large #ortion of the #rimarymotor area+rimary Somatosensory &reaSensory information from the skin andsketeal muscles arrive here

&ssociation areas+laces $here integration occurs+refrontal &rea

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& #rocessing center in the frontal lobe$hich receives information from the otherassociation areas and uses it to reasonand #lan our actions

Wernickes &rea

The area $hich hel#s us understand boththe $ritten and s#oken $ord and sendsthe information to Brocas areaBrocas &rea

The area $hich adds grammatical

renements and directs the #rimary motorarea to stimulate the a##ro#riate musclesfor s#eakingBasal !uclei(asses of gray matter located dee# in$hite matter $hich integrate motorcommands" ensuring that #ro#er muscle

grou#s are activated or inhibited?ience#halon$here the thalamus and thehy#othalamus are located>y#othalamus&n integrating center that hel#s maintain

homeostasis by regulating hunger" slee#"thirst" body tem#erature" and $aterbalanceH manufactures hormones andcontrols the #ituitary glandH serves as alink bet$een the nervous and endocrinesystem

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ThalamusWhere the sensory in#ut from the visual"auditory" taste" and somatosensory

systems arrive at the thalamus via thecranial nerves and tracts from the s#inalcord5erebellumSe#erated from the brain stem by thefourth ventricleH receives sensory in#utfrom the ;oints" muscles" and other

sensory #ath$ays about the #resent#osition of body #arts