The Neuron (bigger slides)

8/9/2019 The Neuron (bigger slides)

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he Neuronhe Living NerveCell


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What is a Neuron?

,Neurons nerve cells or neurones is a special typeof cell that is found in the bodies of most

( ,animals all members of the group Eumetazoa to-be precise this excludes only sponges and a few

).other very simple animals They exhibit different shapes but all have a cell

.body and one or more processes Neurons are electrically excitable cells that

process and transmits information by electrical

, ,and chemical signalling the latter via synapses.specialized connections with other cells


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The Parts of a Neuron


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a Typical Neuron


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A Typical Neuron

:The Main Parts of a Typical Neuron Cell Body or soma he cell body or the soma is a

ucleated body that receives input.rom dendrites It is usually,ompact round and a centrally.ocated structure A cell body,ontains DNA controls proteinanufacturing and directsetabolism but have no role in.eural signaling


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A Typical neuron

he cell body of a neuron isupported by a complex meshwork oftructural proteins calledeurofilaments which are resembled.nto larger neurofibrils Someeurons also contain pigment, -ranules such as neuromelanin a, (rownish pigment byproduct of

)ynthesis of catecholamines and( -ipofuscin yellow brown pigment).hat accumulate with age


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A typical neuron

:The Dendrites endrites are short extensions of theell body that provide an increasedurface for receipt of incoming .mpulses fro m a number of axonsendrites often extend for hundredsf microns and branching multipleimes giving rise to a complex

.endritic tree


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A typical neuron

:The dendritic growth Mature neurons generally cannot

divide but new dendrites can grow

to provide room for more connections.to other neurons New connections.are basis for learning


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A typical neuron

:The axon

,he longest process distinguishedy the absence of Nisslmaterials( ).ite of high protein synthesisn axon is a special cellularilament that arises from theell body at a swelling calledxon hillock and travels for aistance as far as 1metres in .umans or more in other species

cell body may give rise to,umerous dendrites but never to.ore than one axon


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A typical neuron

:Axon Hillock esides being an anatomical,tructure axon hillock is also

he part of the neuron that has-he greatest density of voltage.ependent sodium channels This-akes it the most easily excitedart of the neuron and the spike:nitiation zone for the axon ineurological terms it has theost negative action potential.hreshold


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A typical neuron

:he myelin sheath he myelin sheath is the white.atty casing on axon It acts as

.n electrical insulator Theyelin sheath is not present ,hen present it increases thepeed of neural signals down the

.xon


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Structural classification of

neurons

:Polarity Most neurons can be anatomically

:characterized as :Unipolar or pseudounipolar dendriteand axon emerging from the same

.process :Bipolar axon and single dendrite on

.opposite ends of the soma : .Multipolar more than two dendrites


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Structure classification of

neurons

Multipolar structured neurons can:be divided into two types

-Golgi I -neurons with long

;projection axonal processes ,examples are pyramidal cellsPunkinje cells and anterior horn

.cells

-Golgi II neurons whose axonal;process projects locally the best

.example is the granule cells


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The kinds of Neurons

:ensory Neuronsv re typically classified as theeurons responsible for convertingxternal stimuli from the environment

.nto internal stimuliv hey are activated by the sensory input( , , , .),ision touch hearing etc and sendrojections into the central nervousystem that convey the sensorynformation to the brain or spinal.ordv nlike neurons of the central nervous,ystem whose input come from other,eurons sensory neurons are activated,y physical modalities such as light, .ound and temperature


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The kinds of neurons

otor Neuronsv otor neurons are classified into threeroad categories according to their:arget namely. omatic Motor Neurons. pecial Visceral Motor Neurons. eneral Visceral Motor Neurons


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The somatic motor neurons

the somatic neurons are further dividedinto two types: alpha efferent neuronsand gamma efferent neurons.(both

types are called efferent to indicatethe flow of information from thecentral nervous system to theperiphery.

Alpha motor neurons- innervateextrafusal muscle fibers(typicallyreferred to simply as muscle fibers)located throughout the muscle.

Gamma motor neuron- innervate


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NERVOUS SYSTEM

BRAINSTHE ZOMBIES


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BRAIN

Portion of central nervous systemcontained within the skull.

Control center for movement andemotions.

1.3 kg mass

Protective membrane between thebrain and cranium: dura meter,

arachnoid layer and pia mater.


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ANATOMY

CEREBRUM Cerebral cortex

Longitudinal fissures

CEREBELLUM Vermis Cerebral peduncles

THALAMUS AND HYPOTHALAMUS

BRAIN STEM

Pons Medulla oblongata

Reticular formation midbrain


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SUBDIVISIONS OFCEREBRUM

1. FRONTAL LOBE voluntary controlof skeletal muscles

- Personality (with limbic system)- Intellectual processes (concentration,

planning, decision making)

- Verbal communication


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2. PARIETAL LOBE

- somatesthetic interpretation (cutaneous andmuscular senstaions)

- understanding and utterance of speech(wermckes area)

3.TEMPORAL LOBE

- interpretation of auitory sensations - auditory and visual memory4. OCCIPITAL LOBE

- visual center - integration of eye movmts, correlation of

visual images with previous experience, conciousseeing


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SUBDIVISION OF BRAIN AND MAJOR COMPONENTS

SUBDIVISIONS CHIEF COMPONENTS

RHINECEPHALON

TELENCEPHALON

CEREBRALHEMISPHERELATERALVENTRICLESPROSENCEPHALO

N EPITHALAMUS

DIENCEPHALON THALAMUSHYPOTHALAMUS

THIRD VENTRICLE


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SUBDIVISIONS COMPONENTS

TECTUM

MESENCEPHALON TEGMENTUM

CEREBRALAQUEDUCT

CEREBELLUM

METENCEPHALON TEGMENTUM4TH VENTRICLE

RHOMBENCEPHALON MYELENCEPHALO

NMEDULLAOBLAGATA4TH VENTRICLE


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DIENCEPHALON

EPITHALAMUSPineal- club-shaped of knoblike organ.

:lampreys- photoreceptor :gnathostomes-endocrine organ

that is stimulated in part by light that firstenters the body through the retina

:absent in few vertebrate

:large in primates and hagfishesParapineal- constant features of bonyfishes of the Devonian and ofancestral amphibians and reptiles,serves as parietal eye

:present in few fishes,lampreys, larval and adult


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HABENULAE : largest in sharks and bloodhounds : inconspicuous in most birds : developed permanently in mammals

THALAMUS :hidden in amniotes

HYPOTHALAMUS : optic chiasma- cephalic boundary of

diencephalon where optic nerves reach thebrain.

: saccus vasculosus- vascularized thin-walled

ventral evagination of the diencephalon floor ofelasmobranch and ray-finned fish

THIRD VENTRICLE - continuous caudal with cerebral

aqueduct of the


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CHONDRICHTHYES

* forebrain a. cerebral hemispheres have the large

olfactory tracts that extends to the olfactorylobe b. diencephalon bears the pineal body

dorsally

- bears the infundibulum ventrally to whichthe hypophysis is attached. * midbrain a. optic lobes paired, large lobes


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OSTEICHTHYES

* forebrain

a. cerebral hemispheres b. olfactory lobe c. diencephalon * optic lobe and cerebellum larger *spinal nerves extends through trunk vert. *cranial nerves 10 pairs


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AMPHIBIANSAMPHIBIANS a. telencephalon -largest lobe

-seat of memory, reasoning, intelligence -bears the olfactory lobe b. diencephalon -relay center for sensory information

c. mesencephalon -round lobes -visual center


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d. metencephalon

-muscular coordination and equilibrium e. myencephalon

-cardio-vascular and respiratory central

(heart, lungs, blood vessels)

-glandular secretion*cranial nerves 10 pairs

*spinal nerves 1 pair in each intervertebral discs

*spinal cord terminates in the anterior part of theurostle


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REPTILES

a. telencephalon -largest lobe and larger than amphibian

-has two long olfactory lobes b. optic lobe -behind the olfactory lobes -oval in shape -optic tracts and optic nerves c. metencephalon -pear-shaped posterior to optic lobes -larger than amphibians


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d. myelencephalon

-spread laterally below the cerebellum and narrows into the spinal nerve cord

* Cranial nerves 12 pairs

* Spinal nerves 1 pair each somite


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AVES

Brain is proportionately larger than in reptiles,and is short and broad.

a. Telencephalon-large and smooth-intelligence, memory, reasoning-olfactory lobes small - poor olfactory sense

b.Optic lobes -in the midbrain, conspicuously developed

(keen sight)


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Cerebellum

- has increased surface and has manysuperficial folds

- many activities of motor coordination

d. Metencephalon - behind cerebellum

*cranial nerves - 12 pairs

*spinal nerves 1 pair each somite


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MAMMALS

a.Telencephalon

- Largest lobe with olfactory lobes

- Sensory and motor activities,reasoning, memory, intelligence,instinctual and limbic (emotional)functions.


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. Diencephalon 1. THALAMUS relay center for sensory

impulses 2. HYPOTHALAMUS F center 3. PITUITARY GLAND regulation of endocrine

glands

- RH and IHc. Mesencephalon - corpora quadrigemina 1. SUPERIOR COLLICULUS- visual reflexes

2. INFERIOR COLLICULUS auditory reflexes 3. CERBRAL PEDUNCLES coordinating

reflexes, with many motor fibers


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. Metencephalon

1. CEREBELLUM equilibrium and motorcoordination 2. PONS relay center, respiratory nuclei-

depth of respiratione. Myelencephalon * medulla oblongata - relay center -visceral autonomic center *RR

*HR *Dilation & constriction of blood

vessels


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ranial nervesranial nerves:FUNCTIONS

D ire cts se n se im p u lse s.th rou g h ou t th e b od y

E q u ilib riu m

,E ye m ov e m en t visio nFa cia l se n sa tio n

;H e a rin g P h o n a tio n

R e sp ira tio n;S a liva tio n S w a llo w in g

S m e ll

Ta ste

The cranial or cerebral nerves arethe peripheral nerves of the headthat are related to the brain.Twelve pairs of cranial nerveshave been distinguished in human

anatomy.


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A n am n io te s h av e 1 0 p airs of,cra n ia ln e rve s a m n io te s h a ve

.1 2, ,N e rve s I III V III a re p u re ly sse n so ry

,to th e o lfa cto ry e p ith e liu m re tin a.a n d m e m b ra n o u s la b yrin th

, ,N e rve s III IV V I su p p ly th em yo tom al m u scle s of th e

.e ye b a ll

, , ,N e rve s V V II IX X su p p ly th ep h a ryn g e a la rch e s w ith m o to r

.a n d se n sory in n e rva tio n s


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:unctionSmellNerve I

i l i a o l f a c to r as the discreteundles oflfactory nerve.ibers omeronasalerve is theeparate

ubdivision ofhe olfactoryerve in .etrapodsts cell bodiesre located inhe olfactory

.pithelium
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Nerve I

he number oflfactoryibers in birdsnd platypus is.malln sharks andome teleostshe sac ontaining thelfactory pithelium isistant fromhe olfactory.ulb

n mammals thelfactorypithelium isn the upperart of the .asal passage

n marineammals thelfactory nerve.s vestigial


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Nerve I

-erminal nerveies close tohe olfactory .ulb and tractn lower ertebrates itas been mplicated inriggeringexual .esponses

erminal nerves also called .s nerve 0
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N II


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Nerve II:unctionSight he nerve emergesrom the rear ofhe eyeball andxtends to the,ptic chiasma/eyond w c it is

ermed the optic.racthe cell bodies ofhe optic nerveibers are in the.etina he term opticerve is from thembryological,iewpoint a

isnomer since theetina arises fromhe paired opticesicles thatever separate.rom the forebrain

he term tract is aundle of nerve/ibers w n theentral nervous


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Nerve III

:unctionupplies thextrinsicyeball musclesnd certainther myotomaluscles of the.yes

rises entrally fromhe .esencephalont containsisceral motoribers that endn the ganglionf theutonomic

Nerve IV


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Nerve IV:unctionupplies theuperior.blique t emergesentrally athe anteriornd of the.indbrain

ne of themallest of the,ranial nervesaving the .ewest fibersne of themallest of the,ranial nervesaving the .ewest fibershe cell bodiesf all fibersn these nerves

re in nuclei/n the central

Nerve V


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Nerve Vivided intohree:ivisions ,phthalmic,axillary and.andibularhis nerve is aensory foreneralensation tohe skin of the,ntire headncluding the

onjunctiva of,he eye theining of the,ar canal andhe ectodermal .f the eardrum

Nerve V


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Nerve V

he cell bodiesor all sensoryibers in theerve are alln the rigeminal.anglionhe mandibularerve is motoro the muscles.f the jawsll branchesontain sensory.ibers

Nerve VI


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Nerve VI

his nerveupplies thexternal.ectus t emergesentrally andnterior end of.he hindbrainne of themallest of the,ranial nerveaving the

.ewer fibers

Nerve VII


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Nerve VIIrises from thenterior end ofhe hindbrainn close ssociationith the fifth

.ervet is sensoryo the euromastrgans on theead of fishesnd aquaticmphibians and.o taste buds

erve VII ofishes containsensory fibersor general.ensation ,n mammals itontains

Nerve VIII


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Nerve VIIIhe estibulocochlearerve innervateshe hair celleceptors of the.nner ear Itarries vestibularnformation to the

rain from theemicircular, ,anals utricle andaccule providinghe sense of.alance It alsoarries informationrom the cochlearoviding the sense.f hearing Thisranial nerveranches into theestibular branch

Nerve IX


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Nerve IXn sharks it hashree major,ranches retrematic thatnters the arch inront of the first,ill slit osttrematic

ontrols theuscles that entersnside it and.haryngeal

he lossopharyngealerve innervates(he pharynx upper ),art of the throathe soft palate and-he posterior onehird of the.ongue It carriesensory information( , ,ouch temperature)nd pressure fromhe pharynx and

.oft palate It

Nerve X


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t is h e l o n g e s tra n i a l n e r v ennervating manytructures in the,hroat including theuscles of the vocal,ords thorax and.bdominal cavity Itrovides sensory( ,nformation touchemperature and)ressure from thexternal auditory

( )eatus ear canal andportion of the.xternal ear Itarries tasteensation from taste.uds in the pharynxt also rovides

Nerve X

Nerve XI


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Nerve XI

he spinal accessoryerve has two.ranches The cranialranch providesomatic motornnervation to somef the muscles in thehroat involved in.wallowing Thisranial branch is ,ccessory to CN Xriginating in theaudal nucleus,mbiguous with theibers of the cranialoot traveling theame extracranialath as the branchial

otor component of.he va us nerve The

Nerve XII


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Nerve XII

he hypoglossalerve providesomatic motornnervation to theuscles of the.ongue This pureotor nerveriginates from theypoglossal nucleusocated in theegmentum of the

.edulla

AUTONOMIC NERVOUS SYSTEM


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AUTONOMIC NERVOUS SYSTEM- is the part of the nervous systemof the higher life forms that is not

consciously controlled.-part of nervous system thatinnervates glands and smooth andcardiac muscles.

-it is entirely a visceral motor

system.2 motor neurons:1. Preganglionic neuron- invisceral efferent nucleus incentral nervous system.

2. Postgangloic neuron- is inan autonomic ganglion.

-it is composed of (1) asympathetic system-thoraculumbar system,emerges from the cord viamost of the spinal nerves of

the trunk and (2) aparasympathetic(craniosacral) system thatemerges from the brain vianerves III, VII, IX, X, andXI.

Autonomic ganglia are classifiedin three categories: paravertebral,colateral, and terminal.


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epresentativeomponents of theutonomic nervous .ystem of a mammal



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Sympathetic nervous systemPromotes a "fight or flight" response, corresponds with arousal and energy generation, inhibitsdigestion:Diverts blood flow away from the gastro-intestinal (GI) tract and skin via vasoconstriction.Blood flow to skeletal muscles, the lung is not only maintained, but enhanced (by as much as1200%, in the case of skeletal muscles).Dilates bronchioles of the lung, which allows for greater alveolar oxygen exchange.Increases heart rate and the contractility of cardiac cells (myocytes), thereby providing amechanism for the enhanced blood flow to skeletal muscles.Dilates pupils and relaxes the lens, allowing more light to enter the eye.

Parasympathetic nervous systemPromotes a *rest and digest" response; promotes calming of the nerves and return to regularfunction, enhances digestion.Dilates blood vessels leading to the GI tract, increasing blood flow. This is important followingthe consumption of food, due to the greater metabolic demands placed on the body by the gut.The parasympathetic nervous system can also constrict the bronchiolar diameter when the needfor oxygen has diminished.

During accommodation, the parasympathetic nervous system causes constriction of the pupiland lens.The parasympathetic nervous system stimulates salivary gland secretion, and acceleratesperistalsis, so, in keeping with the rest and digest functions, appropriate PNS activity mediatesdigestion of food and indirectly, the absorption of nutrients.Is also involved in erection of genitals, via the pelvic splanchnic nerves24.




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1. Paravertebralganglia are

interconnected bylongitudinal strands ofautonomic fibers to formsympathetic trunk close tothe vertebral column.

It is connected by two smallbranches, a white ramuscommunicans and a gray

ramus communicans.

The white rami carry pregangloicfibers from the spinal nerve to the

ganglion. It conducts visceral afferentfibers enroute to the spinal cord.Cervical and sacral nerve lack whiterami.

Gray rami conduct postganglionicfibers from the ganglion to the spinalnerve for distribution to the skin.

Branches to collateral ganglia usuallyjoin those from adjacent paravertebralganglia to form discrete autonomicnerves such as the splanchnicand andcardiac nerves that supply the heartwith a sympathetic innervation.



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Autonomic plexuses are

entwined around bloodvessels, the vertebral columnand other structures aroundthe neck and trunk.

2.Collateral ganglia are present in head

(ciliary, submandibular, sphenopalatine andotic) and in the abdomen at the base of themajor branches of the abdominal aorta.

3. Terminal ganglia found only in the trunk,

and are embedded in the walls of the organsthey innervate-heart, lungs, stomach, andurinary bladder.

3. Terminal ganglia found only in the trunk,and are embedded in the walls of the organs

they innervate-heart, lungs, stomach, andurinary bladder.

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