The Structure and Cellular Makeup of the Brain

7/25/2019 The Structure and Cellular Makeup of the Brain

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Functional Divisions of the Nervous System

Nervous system can be divided into two parts.

1. Central Nervous System (CNS)brain andspinal cord.

2. Peripheral Nervous System (PNS)cranial andspinal nerves.

PNS can be divided into two parts:

1. Sensory component provides input toCNS.

2. otor components relay output !rom CNSto

periphery.

"wo parts to the otor output:

1. #nvoluntary visceral motor system includesthree divisions:

Sympathetic ($%ht or &i%ht)

Parasympathetic (rest and rela')

nteric (in&uences %astric motility andsecretion)

2. oluntary somatic motor system.*oth o! these control e+ectors.

PNSnerve cells (neurons) are in clustered into ,-N,#-

axons %rouped into N/S

CNSneuronsare in either sheetscalled C0/"#CS or in clusterscalled NC#

axonsare %rouped into "/-C"S


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Direction of Neural Information Flow

Afferentinformation is

sensory information coming

into the CNS (incoming

information).

Efferentinformation is

information leaving the CNS(outgoing information).


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Finding Your Way Around the Brain (art ! of ")

Brain#Body $rientation

Because of the curvatureof the CNS in humans,

positional terms for thebrain are useddifferently.

%ostral & to'ard the nose

Caudal & to'ard the ac

of the head

Dorsal & to'ard the to* of

the head

(also called su*erior)

+entral & to'ard the ,a'

(also called inferior)

-oriontal Animals and

S*inal Cord of -umans/

%ostral & to'ard the head

(also called anterior in animals)

Caudal & to'ard the tail

(also called *osterior in animals)

Dorsal & to'ard the ac

(also called *osterior in humans) +entral & to'ard the elly

(also called anterior in humans)

S*atial $rientation 0erms/

1edial & to'ard the middle 2ateral & to'ard the side

3*silateral & same side

Contralateral & o**osite side

ro4imal (lims) & to'ard the center

Distal (lims) & to'ard the *eri*hery

Su*erficial & near the surface Dee* & to'ard the center


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Finding Your Way Around the Brain (art " of ")

Anatomical $rientation

Medialmeans toward the

middle of the brainand lateraltoward the side.

When brains are sectioned for analysis, slices are typically made in oneof three planes: coronal, sagittal or horizontal.


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Surface Features of the Brain

5yrus (*l. gyri)

A small *rotrusion or

um* formed y the

folding of the cereral

corte4.

Sulcus (*l. sulci)

A groove in rain matter6

often found in theneocorte4 or cereellum.

Fissure

A very dee* sulcus.


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C7%7B%A2 -713S-7%7S are

HIGHLY INVAGINATED8allo's for more

surface area to e *aced into sull

5Y%3 (singular/ gyrus)8ridges

S92C3 (singular/ sulcus)8valleys

F3SS9%7S8dee* valleys

2AND1A%:S S7A%A07 0-7 2$B7S/

C7N0%A2 S92C9S

se*arates F%$N0A2 (most rostral) from the

A%370A2 (more caudal)

2A07%A2 F3SS9%7

se*arates F%$N0A2 from 071$%A2

2$N5309D3NA2 F3SS9%7

se*arates left hemis*here from right

A%370$#$CC330A2 S92C9S

se*arates A%370A2 from $CC330A2

%7$CC330A2 N$0C-

se*arates $CC330A2 from 071$%A2

%7C7N0%A2 5Y%9S;(1$0$% C$%07


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Internal Features of the Brain: the Ventricles

Four +entricles (t'o lateral6 third and fourth/ cavities in the rain that containcereros*inal fluid (CSF)) made y the cells of the C-$%$3D 27


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1eninges/ 0hree layers of *rotective tissue located ,ust elo' the sull. Dura mater

=hard mother>? tough outer layer of firous tissue.

Arachnoid layer

lie a =s*ider@s 'e>? thin sheet of delicate connective tissue.

Suarachnoid s*ace filled 'ith cereral s*inal fluid (CSF).

ia mater

=soft mother>? moderately tough inner layer that clings to the rain@s

surface.B2$$D +7SS72S traverse

throughout the arachnoid

0rauma8such as a lo' to the head

8can cause leeding here.

S9BA%AC-N$3D -71$%%-A57

or

S9BD9%A2 -71A0$1A.


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5ray 1atter

Areas of the nervous system *redominately com*osed of cell odies and lood vessels

White 1atter Areas of the nervous system rich in fat#sheathed neural a4ons

Cor*us Callosum

Fier system connecting the t'o cereral hemis*heres

3nternal Features of the Brain/ 1acrosco*ic

Coronal sectionsof my rain

mae me smile


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Internal Features of the Brain: Microscopic

0'o main ty*es of cells/

Neurons

Carry out the rain@s ma,or functions.A**ro4imately ! illion.

5lial cells

Su**ort cells aid and modulate neuronal activity.A**ro4imately illion.

5lia/ Neuron ratio is /!. 0hin chocolate chi* cooie.


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5rou*s of a4ons running together form either nerves(NS) or tracts(CNS)

3nside the CNS

Nucleus: a grou* of

neurons.

Tract: a undle ofa4ons.

$utside the CNS

Ganglion/ a grou* of

neurons.

Nerves:a undle of

a4ons.


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Sies of Some Neural Structures and the 9nits of 1easure and 1agnification

9sed in Studying 0hem

3f;! cm (sie of human rain)

& miles

then;

. nm & !E! inch


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0he 1a,or arts of the Neuron Input zone8receives

information from other cells

through enrites!

Integration zone8cell

"o#(or soma) and a4on

hilloc;region 'here in*uts

are summed.

$onuction zone8single

a%on(or nerve fi"er)

conducts out*ut information

a'ay from the cell ody as

an electrical im*ulse.

&utput zone8a%on

terminalsat the end of the

a4on communicate activity

to other cells.


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Neurons Can Be Classified y Sha*e

Multipolar neurons

8one a4on6 many

dendrites? mostcommon ty*e.

Bipolar neurons8

one a4on6 one ma,or

dendrite.

'nipolar neurons8

a single e4tension

ranches in t'o

directions6 formingan in*ut one and an

out*ut one.


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Syna*ses


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$ells of the Nervous S#stem

0o understand nervous system6 it is im*ortant to e ale to loo at the function of individual cells.

(Bottom#u* a**roach.)

9ntil "th century6

0'o cam*s8

First cam*/ Camillo 5olgi develo*ed a method that stained only a small numer of nerve cells8ut

stained them in their entirety. 5olgi thought that nervous system 'as a reticulum of interconnect

nerve cells (a =nerve net>).

Second cam*/ Santiago %amon y Ca,al used 5olgi@s method to loo at cells in the

rain and concluded that cells 'ere all se*arate. -e thought that

individual neurons 'ere the units of rain function.

0urned out he 'as right.

3rony85olgi develo*ed the stain that *roved Ca,al@s theory.

(0hey still shared the Noel *rie in !GH8the first time that t'o scientists shared a *rie.)


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T#pes of Neurons

Sensory Neurons Carry information toward

the central nervous system (afferent).

74am*les/

Bi*olar neurons in the retina convey information aout light and dar to

the rain from the eye.

Somatosensory neurons convey information aout touch and *ressure to

the rain from the surface of the sin. Sensory neurons leading from muscle

detect muscle length and

relay that information to the

s*inal cord.


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T#pes of Neurons

3nterneurons(aa Association Neurons) 2in u* sensory and motor activity

withinthe central nervous system.74am*le/

Neurons in the s*inal cord that cou*le the

afferent input 'ith the efferent outputin the nee#,er refle4.


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T#pes of Neurons

1otor Neurons Carry information away from

the central nervous system (efferent)

to muscles.74am*le/

Al*ha motor neuron that leads from the s*inal cord and causes

contraction of muscles in the nee ,er refle4.


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Five T#pes of Glial $ells (supporting cells

for neurons)

!. 7*endymal Cells Small6 ovoid? found in the

'alls of the ventricles.

1ae and secrete

cereros*inal fluid (CSF).

-ydroce*halus (='ater on the rain>)

Build#u* of *ressure in the rain and s'elling of the head caused'hen the flo' of CSF is loced.

Can result in retardation in children. 9sually caused y tumors6

hemorrhages6 or congenital malformations.

0reatment of hydroce*halus ty*ically involves the

insertion of a shunt (a hollo' fle4ile tue) into the

ventricular system of the rain 'hich then diverts the

flo' of cereros*inal fluid into another region of the

ody (often the adominal cavity or a chamer of theheart) 'here it can e asored.


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Five T#pes of Glial $ells

". Astrocyte Star sha*ed. Structural su**ort for

neurons. 0hey act liescaffolding holding neurons in

*lace. 7nhance rain activity y

*roviding fuel to active rainregions;'hen neurons areactive6 astrocytes conveyinformation to lood vesselsto dilate and allo' more loodflo' to those active neurons.


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Brain is se*arated from lood su**ly.

3m*ortant ecause rain may e *articularly

susce*tile to to4ins that may e in the lood.

3n the rest of the ody6 molecules in lood *ass

through s*aces et'een endothelial cells that mae

u* the ca*illary 'all.

Foot *rocesses on astrocytes trigger tight ,unctionformation on lood vessels *reventing *assage of

molecules et'een lood and rain.

$ne dra'ac of BBB###thera*eutic drugs cannot

enter rain via venous in,ection/ they must e in,ected

into CSF or directly into rain.

0he Blood#Brain Barrier8another role for astrocytes


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. 1icrogliaScavenge

deris (e.g.6

dead cells).


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. $ligodendroglia CellI 5lial cell in the

central nerou! !y!temthat myelinates a4ons.1yelination allo's for faster

signal conduction in a4ons

(7ach myelinates multi*le neurons)


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. Sch'ann Cell

5lial cell in the

peripheral nerou! !y!temthat

myelinates a4ons(7ach myelinates a single neuron)

Figure at right sho's ho' oligodendrocytes

and Sch'ann cells differ in the 'ay they 'ra* a4ons.

$ligodendroglia Cell


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5lial coating thatsurrounds a4ons. Coating that allo's

signal to ,um* fromnode to node (thinside'al cracs).

1ulti*le Sclerosis

(1S)Autoimmune

disease associated'ith loss of myelin.

1yelin


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Sch'ann cells *lay an im*ortant role in neuronal cell regeneration


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0he *eri*heral nervous system consists ofnerves* or undles of a4ons.

Motor nerves transmit information froms*inal cord and rain to muscles and glands.

Sensor# nerves convey information from the

ody to the CNS.

$ranial nerves8connected to the rain.

Spinal nerves8also called !omatic nere!6connected to the s*inal cord.

+utonomic nerves8connected to rain and s*inalcord and control glands and internal organs.

eri*heral nervous system has three *arts/


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$ranial nerves8!" *airs

Three are purel# sensor# pathwa#s to the

rain/ $lfactory (3)8smell

$*tic (33)8vision

+estiulocochlear (+333)8hearing and alance


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Five are purel# motorpathwa#sfrom therain/

$culomotor (333)8eyemovement

0rochlear (3+)8eyemovement

Aducens (+3)8eyemovement

S*inal Accessory (


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Spinal $or

Controls most ody movements.

Can act inde*endently of the rain.

S*inal refle4/

Automatic movement.

-ard to *revent (rain cannot ea!ilyinhiit)

74am*le/ nee#,er (myotatic) refle4.

di id d i t di ti t i0h i l d


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can e divided into distinct regions.

Spinal nerves8! *airs

7ach s*inal nerve consists of a grou* of motor fiers that *ro,ect from the s*inal cord and a grou* ofsensory fiers that enter the s*inal cord.

S*inal nerves are named for the segment of s*inal cord they are connected to/

$ervical (nec)8J segments

Thoracic (trun)8!" segments

,um"ar(lo'er ac)8 segments

Sacral(*elvic)8 segments

$occ#geal (ottom)8! segment

0he s*inal cord


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Spinal Nerves

Dorsalfiers are afferent/ they

carry information from the ody@ssensory rece*tors.

Ventralfiers are efferent/ they

carry information from the s*inal

cord to the muscles.

0he myotatic (nee ,er) refle4 does not involve the rain


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0he myotatic (nee#,er) refle4 does not involve the rain


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0he autonomic nervous s#stemis the main system for controlling

the ody@s organs.

0'o ma,or divisions/

S#mpathetic nervous s#stem has a4ons that innervate the!ympathetic ganglia6 small clusters of neurons outside the CNS.

o Sym*athetic innervation *re*ares the ody for action8

0he =fight#or#flight> system.

-aras#mpathetic nervous s#stemo arasym*athetic neurons run from the CNS to the

para!ympathetic ganglia.

o arasym*athetic activity hel*s the ody to rela46 recu*erate6

and *re*are for future action 0he =rest and digest> system.

0he sym*athetic and *arasym*athetic nervous systems have different effects on

organs due to different neurotransmitters.


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reganglionic neurons are short.

ostganglionic neurons are longer (sym*athetic ganglionic chain is close to s*inal cord).


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reganglionic neurons are long.

ostganglionic neurons are shorter (*arasym*athetic ganglia are close to organs).

asor*tion


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+isualiing the 2iving -uman Brain

A measure of


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Strong magnets cause *rotons in rain

tissue to line u* in *arallel.

A *ulse of radio 'aves is used to noc

*rotons over.

rotons then reconfigure themselves6

emitting radio 'aves.

Different tissue densities emit different

signals.

Advantages/ higher resolution than C0

scan. Doesn@t use 4#rays.

Disadvantage/ taes longer to do.

htt*s/EE'''.youtue.comE'atchLv&!C5#n+Hg


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Detects the difference in lood flo' to different *arts of the rain during an activity.

Advantage/ can detect s*ecific areas that are more active than others during a tas.

Disadvantage/ inter*retation of results can e eKuivocal. S'ing voters sho'n the

'ords Democrat or %e*ulican had their amygdala light u*8sho'ing high emotion.But 'hat emotionL Disgust or *leasureL


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Advantage/ Su,ects can move their heads

around during recordings (e.g.a oo can

e read to see 'here the activity is during

reading).

Disadvantages/ lo'er resolution than f1%36

uses radioactive dyes.

1etaolic activity can e detected

as measured y glucose utiliation

more glucose means more

active areas of the rain.

$cci*ital loe0em*oral loe

arietal loe Frontal loe

htt*s/EE'''.youtue.comE'atchLv&5-2BcCvrK

Develo*ment of the Nervous System in the -uman 7mryo and Fetus


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e e o* e t o t e e ous Syste t e u a yo a d etus

-uman emryo develo* three

cell layers8endoderm6

mesoderm6 and ectoderm.

.ctoerm8outer layer6

ecomes the nervous system.

0hicening cell layers form a

groove 'hich ecomes the

neural *late.

0he neural tu"eforms from the

neural ridges.

0he anterior *art of the neural

tue has three sudivisions8the

fore"rain6 the mi"rain6 and the

hin"rain!

+ideo ". Brain Develo*ment


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0he Si4 Stages of Neural Develo*ment


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Brain develo*ment in H stages6

mostly in *renatal life/

". Neurogene!i!#mitosis

*roduces neurons fromnonneuronal cells.

$. %ell migration8cells move to

estalish distinct nerve cell

*o*ulations.

&. %ell differentiation8cells

ecome distinctive neurons or

glial cells.

'. (ynaptogene!i!8estalishment

of syna*tic connections.

). Neuronal cell death8selective

death of many nerve cells.*. (ynap!e rearrangement8loss

or develo*ment of syna*ses6

fine#tuning.

Animation !. Stages of Neuronal Develo*ment


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A 1odel for the Action of Neurotro*hic Factors


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Chemoaffinity hy*othesis


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The Structure and Cellular Makeup of the Brain

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