4. neuro anatomy 2010

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Neuro Anatomy

microscopis I

Bambang Soemantri



Nervous system

± Swift, brief responses to stimuli

Endocrine system ± Adjusts metabolic operations

± Directs long-term changes

Two organ systems coordinate

and direct activities of body



Anatomical Organization of the

Nervous system Central Nervous system :

± Brain

± Spinal cord Peripheral nervous system

± Ganglion

± Cranial nerves

± Spinal nerves



PNS further subdivided into:

± Sensory division and Motor division Motor division further subdivided into:

± Somatic and Autonomic

Autonomic further subdivided into: ± Sympathetic and Parasympathetic



Blue arrows: afferent signalsRed arrows: efferent signals



An Overview of the NervousSystem



Nervous system includes all

neural tissue in body Central Nervous System

± Brain and spinal cord

Peripheral Nervous System ± All neural tissue outside CNS



Functional divisions of nervous

system Afferent

± Sensory information from receptors to CNS

Efferent

± Motor commands to muscles and glands

± Somatic division

Voluntary control over skeletal muscle

± Autonomic division Involuntary regulation of smooth and cardiac muscle,

glands



Histology of Neural Tissue



Neurons

Cells in Nervous Tissue

Neuroglia



about half the volume of cells in the CNS

smaller than neurons

5 to 50 times more numerous

do NOT generate electrical impulses

divide by mitosis

Four types in the CNS

± Astrocytes

± Oligodendrocytes ± Microglia

± Ependymal cells

Neuroglia (Glia)



Neuroglia (Neuroglial Cells)Neuroglia (Neuroglial Cells)

Central NeurogliaCentral Neuroglia

Astrocyte Astrocyteprotoplasmic astrocyteprotoplasmic astrocyte

fibrous astrocytefibrous astrocyte

OligodendrocyteOligodendrocyteperineuronal satellite cellperineuronal satellite cell

interfascicular cellinterfascicular cell

MicrogliaMicroglia

Ependymal Cell Ependymal Cell

Peripheral NeurogliaPeripheral Neuroglia

Schwann Cell Schwann Cell

in peripheral nervein peripheral nerve

and ganglionand ganglion

Capsular (Satellite) Cell Capsular (Satellite) Cell

in ganglionin ganglion



Astrocyte Astrocyte OligodendrocyteOligodendrocyte MicrogliaMicroglia

CentralCentralNeurogliaNeurogliaCentralCentralNeurogliaNeuroglia



Largest of glial cells

Most numerous

Star shaped with many processes

projecting from the cell body

Help form and maintain blood-brain barrier

Provide structural support for neurons

Maintain the appropriate chemical

environment for generation of nerve impulses/action potentials

Regulate nutrient concentrations for neuron survival

Regulate ion concentrations - generation of action potentials by neurons

Take up excess neurotransmitters

Assist in neuronal migration during brain development

Perform repairs to stabilize tissue

Astrocytes



Astrocyte Astrocyte

Protoplasmic Astrocyte: Gray Matter Protoplasmic Astrocyte: Gray Matter

Fibrous Astrocyte: White Matter Fibrous Astrocyte: White Matter

Cell Body Cell Body µpotato¶ shape nucleus, scarse pale cytopasmµpotato¶ shape nucleus, scarse pale cytopasm

ProcessesProcesses

- - GFAP GFAP (glial fibroacidic protein):(glial fibroacidic protein): intermediate filament intermediate filament

- - Perivascular Feet Perivascular Feet (Foot Process, Vascular End (Foot Process, Vascular End- -Feet)Feet)

surrounding blood vesselssurrounding blood vessels

Specialized AstrocytesSpecialized Astrocytes

- - Bergmann¶s gial cell, Muller cell, pituicyteBergmann¶s gial cell, Muller cell, pituicyte



Oligodendrocytes

Most common glial cell

type

Each forms myelin

sheath around the

axons of neurons in

CNS

Analogous to Schwann

cells of PNS

Form a supportivenetwork around CNS

neurons

fewer processes than astrocytes round or oval cell body



Microglia

Small cells found near blood vessels

Phagocytic role - clear away dead cells protect CNS from disease through phagocytosis of

microbes

migrate to areas of injury where they clear away debris

of injured cells - may also kill healthy cells

few processes

derived from mesodermal cells

that also give rise to monocytes

and macrophages



Ependymal Cells

Form epithelial membrane lining cerebral cavities (ventricles) & central

canal - that contain CSF

Produce & circulate the cerebrospinal fluid (CSF) found in these

chambers CSF = colourless liquid that protects the brain and SC against

chemical & physical injuries, carries oxygen, glucose and other

necessary

chemicals from the blood to neurons and neuroglia

epithelial cells arranged in a

single layer

range in shape from cuboidal

to columnar



Flat cells surrounding PNS axons

Support neurons in the PNS

PNS: Satellite Cells



PNS: Schwann Cells

each cell surrounds multiple unmyelinated PNS axons with a

single layer of its plasma membrane

Each cell produces part of the myelin sheath surrounding an

axon in the PNS

contributes regeneration of PNS axons



Neurons

have the property of electrical excitability - ability to produce

action potentials or impulses in response to stimuli

what is the main defining characteristic of neurons?



Representative Neuron

1. cell body or soma-single nucleus with prominent nucleolus

- Nissl bodies

-rough ER & free ribosomes for protein

synthesis

-proteins then replace neuronal cellular

components for growth

and repair of damaged axons in the PNS

-neurofilaments or neurofibrils

give cell shape and support -

bundles of intermediate filaments

-microtubules move material

inside cell

-lipofuscin pigment clumps

(harmless aging) - yellowish

brown



2. Cell processes =

dendrites (little trees)

- the receiving or input

portion of the neuron

-short, tapering andhighly branched

-surfaces specialized

for contact with other

neurons

-cytoplasm contains

Nissl bodies &

mitochondria

Neurons



3. Cell processes = axons Conduct impulses away from cell body-

propagates nerve impulses to another

neuron Long, thin cylindrical process of cell

contains mitochondria, microtubules &

neurofibrils - NO ER/NO protein synth.

joins the soma at a cone-shaped

elevation = axon hillock first part of the axon = initial segment

most impulses arise at the junction of the

axon hillock and initial segment = trigger

zone

cytoplasm = axoplasm

plasma membrane = axolemma

Side branches = collaterals arise from

the axon

axon and collaterals end in fine

processes called axon terminals

Swollen tips called synaptic end bulbscontain vesicles filled with



Axonal Transport Cell body is location for most protein synthesis

± neurotransmitters & repair proteins

however the axon or axon terminals require proteins

± e.g. neurotransmitters

Axonal transport system moves substances

± slow axonal flow

movement of axoplasm in one direction only -- away from cell

body

movement at 1-5 mm per day

replenishes axoplasm in regenerating or maturing neurons ± fast axonal flow

moves organelles & materials along surface of microtubules

at 200-400 mm per day

transports material in either direction

for use in the terminals or for recycling in cell body



Components of Axonal (Axoplasmic) Transport Components of Axonal (Axoplasmic) Transport Components Velocity (mm/day) TransportingComponents Velocity (mm/day) Transporting

SubstancesSubstances

Anterograde Axonal Transport Anterograde Axonal Transport

Fast Transport Fast Transport 200 200- -400 400 synaptic vesicle, enzymesneurotransmitters

Mitochondrial Transport 5050--100100 mitochondria

Slow Transport Slow Transport

Slow Components a (SCa) 0.10.1 - - 1.0 1.0 tubulin, neurofilament

protein

Slow Comnponent b (SCb) 2 2 - - 6 6 actin, clathrine,calmodulins

spectrin, cytoplasmic

enzymes

Retrograde Axonal Transport Retrograde Axonal Transport 100 100- -200 200 prelysosomal vesicles,

recycled proteins, HRP,

neurotrophic viruses

Axonal (Axoplasmic) TransportAxonal (Axoplasmic) Transport



Mechanism of Mechanism of AxonalAxonal

TransportTransport

Fast Fast

Anterograde Anterograde

Axonal transport Axonal transport

andandRetrogradeRetrograde

Axonal transport Axonal transport



Functional Classification of Neurons

Sensory (afferent) neurons

± transport sensory information from skin, muscles,

joints, sense organs & viscera to CNS

Motor (efferent) neurons ± send motor nerve impulses to muscles & glands

Interneurons (association) neurons

± connect sensory to motor neurons

± 90% of neurons in the body



Afferent division of PNS

Deliver sensory information from sensory receptors to CNS

± free nerve endings: bare dendrites associated with pain, itching,

tickling, heat and some touch sensations

± Exteroceptors: located near or at body surface, provide informationabout external environment

± Proprioceptors: located in inner ear, joints, tendons and muscles,

provide information about body position, muscle length and tension,

position of joints

± Interoceptors: located in blood vessels, visceral organs and NS

-provide information about internal environment

-most impulses are not perceived ± those that are,

are interpreted as pain or pressure

Sensory Neurons



Sensory Neurons Sensory receptors cont«

± mechanoreceptors: detect pressure, provide sensations of touch,pressure, vibration, proprioception, blood vessel stretch,

hearing and equilibrium

± thermoreceptors: detect changes in temperature

± nociceptors: respond to stimuli resulting from damage (pain)

± photoreceptors: light

± osmoreceptors: detect changes in OP in body fluids

± chemoreceptors: detect chemicals in mouth (taste), nose (smell)

and body fluids

-analgesi a: relief from pain

-drugs: aspirin, ibuprofen ± block formation of prost a gl andins that

stimulate the nociceptors

-novocaine ± block nerve impulses along pain nerves

-morphine, opium & derivatives (codeine) ± pain is felt but not perceived in

brain (blocks morphine and opiate receptors in pain centers)



Efferent pathways

Stimulate peripheral structures

± Somatic motor neurons

Innervate skeletal muscle

± Visceral motor neurons

Innervate all other peripheral effectors

Preganglionic and postganglionic neurons

Motor Neurons

-both divisions

- irst neuron has

( re-ganglionic)

-second neuronganglion ( ost-g

-parasym

-cranial

-pregan

o the c-short p

-housek



Motor Units Each skeletal fiber has only ONE

NMJ

MU = Somatic neuron + all theskeletal muscle fibers it

innervates

Number and size indicate

precision of muscle control

Muscle twitch ± Single momentary contraction

± Response to a single stimulus

All-or-none theory

± Either contracts completely or not

at all

Muscle fibers of different motor units are intermingled so that net distribution of

force applied to the tendon remains constant even when individual muscle

groups cycle between contraction and relaxation.

Motor units in a whole muscle fire asynchronouslysome fibers are active others are relaxed

delays muscle fatigue so contraction can be sustained



Named for histologist that first described themor their appearance

Structural Classification of Neurons

Purkinje = cerebellum

Renshaw = spinal cord

others are named for shapes

e.g. pyramidal cells



Classification of neurons by cell

size

1. golgi type I :

± Neurons have a long axon and large soma

2. Golgy type II : ± Neurons have short axon undergoes

extensive terminal aeborization and small

soma



The Nerve Impulse

C ti S lt t



Continuous versus Saltatory

Conduction

Continuous conduction(unmyelinated fibers)

± An action potential spreads

(propagates) over the

surface of the axolemma

± as Na+ flows into the cell

during depolarization, the

voltage of adjacent areas is

effected and their voltage-gated Na+ channels open

± step-by-step depolarization

of each portion of the length

of the axolemma



Properties of axon

Presence or absence of myelin sheath

Diameter of axon

Rate of Impulse Conduction



MyelinMyelin

Conduction velocity Conduction velocity is proportional tois proportional to1. The Length of Internodal Segment 1. The Length of Internodal Segment

2. Thickness of Myelin2. Thickness of Myelin

3. Diameter of Nerve Fiber 3. Diameter of Nerve Fiber



Synaptic Communication



Synapse

± Site of intercellular communicationbetween 2 neurons or between aneuron and an effector (e.g. muscle)

Originates in the soma

Travels along axons

Permit communication between neuronsand other cells

± Initiating neuron = presynaptic neuron

± Receiving neuron = postsynapticneuron

Most are axodendritic axon -> dendrite

Some are axoaxonic ± axon > axon

Synapse



Tipes of synapses

Axodendritic:

± Between an axon and a dendrite

Axosomatic:

± Between an axon and a soma

Axoaxonic:

± Between two axon

Dendrodendritic:

± between two dendrites



Synaptic morphology

Presynaptic membrane:

± Contains metochondria, a few elements of

SER, and an abundance of synaptic vesicles.

Synaptic cleft

Postsynaptic membrane:

± Contains neorotransmitter receptors



SYNAPSESYNAPSE

Presynaptic Portion: Synaptic ButtonPresynaptic Portion: Synaptic Button-- synaptic vesiclesynaptic vesicle

-- mitochondriamitochondria-- presynaptic membrane: tubulinpresynaptic membrane: tubulin

Synaptic Cleft Synaptic Cleft

-- 2020--30 nm30 nm

Postsynaptic PortionPostsynaptic Portion

-- postsynaptic membrane: actin, fodrin, spectrinpostsynaptic membrane: actin, fodrin, spectrin

-- mitochondriamitochondria



SYNAPSESYNAPSE



Impuls transmission at synapse

can occur:

Electrically

Chemically



VIEW OF THE CHEMIC AL

SYNAPSE & FUNCTION



Neurotransmitters

Are signaling molecules that are released

at the presynaptic membranes and

activate receptors on postsynaptic

membranes.



More than 100 identified

Some bind receptors and cause channels to

open

Others bind receptors and result in a second

messenger system Results in either excitation or inhibition of the

target

Represented by three groups:

± Small molecules transmitters

± Neuropeptides

± Gases

Neurotransmitters



Small molecule neurotransmitter :

± Acetylcholine

± Amino acids : Glutamat, Aspartat, GABA

± Biogenic amines : modified amino acids Catecholamines : Epinephrine, NE, Dopamine

Serotonin Neuropeptides :

± Substane P; Opoid peptides (endorphine,enkephaline, dynorphines); hypothalamic releasing

hormones; hormones stored in and release fromneurohypophyse

Gases : NO and CO



Removal of Neurotransmitter

Diffusion

± move down concentration gradient

Enzymatic degradation

± acetylcholinesterase Uptake by neurons or glia cells

± neurotransmitter transporters

NE, epinephrine, dopamine, serotonin



Peripheral nervous system The PNS includes the peripheral nerves

and nerve cell bodies located outside

the CNS

Peripheral nerves are bundles of nerve

fibers (axons) located outside the CNSand surrounded by connective tissue

sheaths. These bundles (fascicles) may

be observed with the unaided eye.Usually, each bundles has both sensory

and motor components.



Peripheral NervePeripheral Nerve



Nerve Fiber Nerve Fiber

Myelinated Nerve Fiber Myelinated Nerve Fiber

Axon, Axon, Myelin sheathMyelin sheath, Schwann cell , Schwann cell

Unmyelinated Nerve Fiber Unmyelinated Nerve Fiber

Axon, Schwann cell Axon, Schwann cell

Connective Tissue SheathConnective Tissue Sheath

EndoneuriumEndoneurium

PerineuriumPerineurium ± ± blood vesselsblood vessels

EpineuriumEpineurium

Composition of Peripheral NerveComposition of Peripheral Nerve



Connective tissue investment

Connective tissue investments of

peripheral nerves include the:

± Epineurium

± Perineurium

± Endoneurium



Epineurium

Is the outermost layer

Is composed of dense irregular,

collagenous connective tissue

containing thick elastic fibers that

completely ensheathe the nerve. Collagen

fibers within the sheath are aligned and

oriented to prevent damage byoverstretching of the nerve bundle.



Perineurium

The middle layer of connective tissue

investments, covers each bundle of

nerve fibers (fascicle) within the nerve.

Composition:

± Dense connective tissue but is thinner

than epineurium.



Endoneurium

The innermost layer connective tissueinvestment of a nerve, surrounds

individual nerve fibers (axons).

Is a loose connective tissuecomposed of a thin layer of reticular

fibers (produced by Schwann cells),

scattered fibroblasts, macrophages, and

mast cells.

The endoneurium is in contact with the

basal lamina of the Schwann cells.



Somatic motor and autonomic

nervous systems

Functionally, the motor component is divided

into the somatic and autonomic nervous systems

The somatic nerves systems provides motor

impulses to the skeletal muscles The autonomic nerves systems provides motor

impulses to the smooth muscles of the viscera,

cardiac muscle and secretory cells of the

exocrine and endocrine glands.



Motor component of the somatic

nervous system

Motor innervation to skeletal muscle is

provided by somatic nerves from spinal

and selected cranial nerves.

The cell bodies of these nerve fibers

originate in the CNS



Autonomic nervous system = ANS

(involuntary , visceral)

Is generally defined as a motor system.

Controls the viscera of the body bysupplying the general visceral efferent

(visceral motor) component to smoothmuscle, cardiac muscle, and glands.

The autonomic nervous system possessestwo neurons between the CNS and theeffector organ.



Cell bodies of the first neuron lie in theC

NS and their axons are usuallymyelinated.

These preganglionic fibers (axons) seekan autonomic ganglion located outside

the CNS, where they synapse onmultipolar cell bodies of postganglionicneurons.

Postganglionic fibers usuallyunmyelinated although they always areenveloped by Schwann cells, exit theganglion to terminate on the effector organ.



The ANS is subdivided into two

functionally deferent divisions:

± The sympathetic nervous system

± The parasympathetic nervous system



Ganglia

Are aggregations of cell bodies of neurons

located outside the CNS, there are two

types of ganglia:

±Sensory

±Autonomic



Sensory ganglia

Sensory ganglia house cells bodies of sensory neurons.

Cell of the sensory ganglia are

pseudounipolar which enveloped bycuboidal capsule cells. These capsule

cells are surrounded by connective

tissue capsule composed of satellite

cells and collagen.



Autonomic ganglia

Autonomic ganglia house cells bodies of

postganglionic autonomic nerves.

Nerve cells bodies of autonomic ganglia

are motor in function.



Central nervous system

The CNS, composed of :

the brain and the spinal cord,

consist of :

white matter and gray matter without

intervening connective tissue elements ;

therefore, the CNS has the consistency of a

semifirm gel.

Continued



Continued

White matter is composed mostly of

myelineted fibers a long with someunmyelineted fibers and neoroglial cells.

Gray matter is consist of aggregation of

neuronal cells bodies, dendrites, andunmyelineted portion of axons as wellas neuroglial cells.

Gray matter in the brain is located at the

periphery (cortex) of the cerebrum andcerebellum. Whereas the white matter lies deep to the cortex and surroundsthe basal ganglia.

continued



continued

Spinal cord:

± White matter is located in the periphery,

whereas grey matter lies deep in the spinal

cord, where it forms an H shape in cross

section. ± Central canal lined by ependymal cells.



Meninges

Are three connective tissue covering the

brain and spinal cord.

Meninges consist of:

±Dura mater : the outermost layer

± Arachnoid : the intermediate layer

±P

ia mater : the innermost layer



D t



Dura mater The dura mater is the dense outermost layer

of the meninges. Cerebral dura:

± Is a dense, collagenous CT composed of two

layers that are closely apposed in the adult. ± 1. Periosteal dura mater , the outer layer, is

composed of osteoprogenitor cells, fibroblast

and collagen fibers. Periosteal dura mater

serves periosteum of the inner surface of theskull, and as such it is well vascularized.



Dura mater

Strongest

2 layers :

- Periosteal- Meningeal

Layers fuse

except at dural

sinuses



continued



continued

2. Meningeal dura :

± Inner layer of the dura is composed of fibroblastand collagen fibers.

± This layer contains small blood vessels

± Internally meningeal dura covered by a layer of

cells called border cell layer, is composed of fibroblast.

Spinal dura mater

Does not adhere to the walls of the vertebral canal.

The epidural space : the space between the dura

and the bony walls of the vertebral canal, is filled with

epidural fat and a venous plexus.



Arachnoid

Is the intermediate layer of the meninges. Is avascular although blood vessels course

through it.

It consist of fibroblast, collagen, and someelastic fibers.

Subdural space located between dura and

arachnoid, is a potential space because itappears only after injury resulting subdural

hemorrhage

continued



continued

In certain regions the arachnoid extend

through the dura to form arachnoid

villi, which protrude into the dural

venous sinuses. The function of the

arachnoid villi is transporting CSF fromthe subarachnoid spaces into the

venous system.



Arachnoid mater

* Arachnoid Villi

Projections through duraPass into superior sagittal

sinus

Passage of CSF

* Web-like attachments to pia



Arachnoid mater

Spaces

± Subdural

Between dura and arachnoid

Little CSF

± Subarachnoid

between arachnoid and pia

CSF and blood vessels



Pia mater

Is the innermost highly vascular layer of

the meninges, is in close contact with the

brain, following closely all of its contours.

The pia mater does not contact with the

neural tissue because a thin layer of

neuroglial processes is always interposed

between them.



Pia mater

* Delicate

* Vascular

* Clings to surface of brain



continued



These endothelial cells have relatively

few pinocytotic vesicles and vesicular traffic is almost completely restricted to

receptor mediated transport.

Ch id l



Choroid plexus

Are formed by folds of pia mater contain abundant of fenestrated

capillaries and invested by the

simple cuboidal (ependymal) liningextend into the third, fourth, and lateral

ventricles of the brain.

Are produced CSF.

Cerebrospinal fluid



Cerebrospinal fluid

Cerebrospinal fluid bathes, nourishes,and protects the brain and spinal cord.

Is produces by the choroid plexus.

CSF



CSF Contains

± Sodium

± Chloride

± Magnesium

± Protein

± Glucose

± Oxygen

Functions

± Cushion

± Waste

removal

± Nourish brain



Production of CSF

Formed in choroid

plexuses ± Rich capillary bedsin pia surrounded byependymal cells

Filtrate of bloodplasma fromcapillaries

Fl f CSF



Flow of CSF

Choroidplexus

Ventricles

Subarachnoidspace throughlateral andmedian

apertures of 4th ventricle

Blood of duralsinuses via

arachnoid villi

Cerebral cortex



Cerebral cortex

Is responsible for learning, memory,sensory integration, information

analysis, and initiation of motor

responses.

Is divided into six layers as follows:

1. Molecular layer : contains horizontal cells

and neuroglia

2. External granular layer : contains mostlygranule(stellate) cells and neuroglial cells

continued



3. External pyramidal layer : contains

pyramidal cells and neuroglial cells.

4. Internal granular layer contains small

granule cells (stelate cells), pyramidal

cells, and neuroglia.

5. Internal pyramidal layer contains larges

pyramidal cells and neuroglia

6. Multiform layer consist of variousshapes (Martinotti cells), and

neuroglia.

Cerebellar cortex



Cerebellar cortex

Is responsible for balance, equilibrium,muscle tone, and muscle coordination.

Is divided into three layers:

1. Molecular layer , lies directly below thepia mater.

2. Purkinje cell layer , contains the large,flask-shaped Purkinje cells, which arepresent only in the cerebellum.

3. Granular layer , consist of small cells andglomeruli (cerebellar islands).



Neural Regeneration

N ti



Nerve regeneration

Nerve cells, unlike neuroglial cells, cannot

proliferate but can regenerate their axons,

located in the PNS.

When a traumatic event destroy neurons,

they are not replaced because neurons

cannot proliferate ; therefore the damage

to the CNS is permanent.

continued



However, if a peripheral nerve fiber is

injured or transected, the neurons

attempts to repair the damage,

regenerate the process, and restore

function by initiating a series of structural and metabolic events,

collectively called the axon reaction.

A ti



Axon reaction

The reactions to the trauma are

characteristically localized in three

regions of the neurons:

1. Local changes: at the site of damage.

2. Anterograde changes: distal to the site of

damage

3. Retrograde changes: proximal to the site of damage.

Local reaction



Local reaction Local reaction to injury involves repair and

removal of debris by neuroglial cells. The severed ends of the axon retract away from

each other, and the cut membrane of each stumpfuses to cover the open end, preventing loss of

axoplasm. Macrophages and fibroblast infiltrate the

damaged area, secrete cytokines and growthfactors, and up-regulate the expression of receptors.

Macrophages invade the basal lamina andassisted by Schwann cells, phagocytose thedebris.

N l R ti



Human Anatomy, 3rd edition

Prentice Hall, © 2001

Neural Regeneration

Anterograde reaction



Anterograde reaction

In the anterograde reaction process,

that portion of the axon distal to aninjury undergoes degeneration andis phagocytosed

The axon undergoes anterogradechanges as follows:

1. The axon terminal becomeshypertrophied and degeneretes within

a week. Schwann cells prolivered andphagocitose the remnants of the axonterminal, and the newly formed Schwanncells occupy the synaptic space.

Continued



± 2. The distal portion of the axon undergoes

Wallerian degeneration, distal to the lesion,

the axon and the myelin disintegrate, Schwanncells dedifferentiate and myelin synthesis is

discontinued. Macrophages and Schwann cells

phagocytose the disintegrated remnants

± 3. Schwann cells proliferate, forming a

column of Schwann cells ( Schwann tubes )

enclosed by the original basal lamina of the

endoneurium.

Neural Regeneration



Retrograde reaction and regeneration

In these process, the proximal portion of the

injured axon undergoes degeneration followed bysprouting of a new axon whose growth is

directed by Schwann cells.

The portion of the axon proximal to the damage

undergoes the following changes :

± 1. the perikaryon of the damaged neuron becomes

hypertrophied, its Nissl bodies disperse, and its

nucleus is displaced ( these events called

chromatolysis). The soma is actively producing free

ribosomes and synthesizing proteins and various

macromolecule.

continued



± 2. Several ³sprouts´ of axon emerge

from the proximal axon stump, enter theendoneurium, and are guided by the

Schwann cells to their target cell. For

regeneration to occur, the Schwann cells,

macrophages, and fibroblasts as well asthe basal lamina must be present. These

cells manufacture growth factors and

cytokines and up-regulate the expression

for the seceptors of these signalingmolecules.

continued



± 3. the sprout is guided by the Schwann

cells that redifferentiate and either beginto manufacture myelin around the

growing axon or, in nonmyelinated axons,

form a Schwann cell sheath. The sprout

that reaches the target cell first form asynapse, whereas the other sprout

degenerate.



Regeneration in the CNS



Regeneration in the CNS

Injured cells within the CNS arephagocytosed by microglia, and the space

liberated by the phagocytosis is occupied by

proliferation of glial cells, which form a

cell mass called glial scar .

Regeneration



Limited ability in PNS

Severed peripheral nerve successfully

regenerates a fraction of the axons

± Function is permanently impaired ± Schwann cells participate

Wallerian degeneration

± Loss of axon distal to damage

Regeneration

Regeneration in CNS



More complicated than PNS regeneration

Far more limited

More axons involved

Astrocytes produce scar tissue preventing

axonal regrowth

Astrocytes release chemicals blocking

regrowth

Regeneration in CNS

Nerve ending ± nerve terminal



Nerve ending nerve terminal

Two structural type : ± 1. Motor ending terminal of axon )

Transmit impulses from the CNS to skeletal &

smooth muscle & to glands ( secretory ending)

± 2. sensory ending = sensory receptor =terminal of dendrites :

Perceive various stimuli and transmit this input

to the CNS

continued



These sensory receptor are classified

into three type depending on the sourceof the stimulus, and are components of

the general or special somatic and

visceral afferent pathway :

± Exteroceptors

± Proprioceptors

± interoceptors

Exteroceptors



Exteroceptors

Location : near the body surface Specialized to perceive stimuli from the

external environment

These receptors sensitive to :

± Temperature

± Touch

± Pressure and

± Pain

Are component of the general somatic

afferent

continued

S i l ti ff t



Special somatic afferent :

± Specialized for light ( sense of vision) andsound (sense of hearing)

Special visceral afferent modality :

± Specialized for smell and taste

Proprioceptors



Proprioceptors

Are specialized receptor located in jointcapsules, tendon and intrafusal

fibers within muscle.

These general somatic afferentreceptors transmit sensory input to the

CNS, which translated into information

that relates to an awareness of the body

in space and movement

continued



Vestibular (balance) mechanism,

located within the inner ear , arespecialized for receiving stimuli related

to motion vectors within the head.

Interoceptors



Interoceptors

Are specialized receptors that perceivesensory information from within organs

of the body.

Specialized peripheral receptors



Specialized peripheral receptors

Certain peripheral receptors,specialized to receive particular stimuli,

include mechanoreceptors,

thermoreceptor, and nociceptors

The dendritic ending located in various

regions of the body, including muscles,

tendons, skin, fascia and joint capsules

continued



These receptors are classified into three

types : ± Mechanoreceptors, which respond to

touch

± Thermoreceptors,which respond to coldand warmth

± Nociceptors, which respond to pain due

to mechanical stress, extremes

temperature differences and chemicalsubstance

Mechanoreceptors



Mechanoreceptors

Mechanoreceptors respond to

mechanical stimuli that may deform the

receptor or the tissue surrounding the

receptor. Stimuli that trigger the

mechanoreceptors are touch, stretch,

vibration and pressure

Nonencapsulated



mechanoreceptors

Are simple unmyelinated receptorspresent in the skin, connective tissues

and surrounding hair follicle

± Peritricial nerve ending, located in theepidermis of the skin, especially in the face

and cornea of the eye

± Merckel¶s disks, specialized for perceiving

discriminatory touch, located in non hairyskin and regions of the body more

sensitive to touch.

Encapsulated mechanoreceptors



Encapsulated mechanoreceptors

Encapsulated Mechanoreceptors exhibitcharacteristic structure and are present in specific

location

± 1. Meissner¶ corpuscles :

Specialist for tactile

Location : dermal papillae of the non hair portin

of the hand, eyelids, lip, tongue, nipples, skin of

the foot and forearm.

Each corpuscle is formed by three or four nerve

terminals and their associated Schwann cells,

all which are encapsulated by connective

tissue.

continued

2 P i i l



± 2. Pacinian corpuscles Location : in the dermis and hypodermis in the

digits of the hand, breast, connective tissue of the joint, periosteum and the mesentery

Spezialied to perceive pressure, touch andfibration

Morphology : ± ovoid & large receptor

± Single unmyelinated fiber as a core and itsSchwann cell

± Surrounded by approximately 60 layers of

modified fibroblast ± Each layer separated by a small fluid-filled

space

Ruffini¶s corpuscles



Ruffini s corpuscles

Location : in the dermis of skin, nailbeds, periodontal ligament and joint

capsules

Composition : ± branched nonmyelinated terminals

interspersed with collagen fibers

± Surrounded by four to five layers of

modified fibroblast

Krause¶s end bulb



Morphology : ± Spheris

± Unmyelinated nerve ending

Location : papilla dermis, joints,

conjunctiva, peritoneum, genitalregions, subendothelial c.t. of the oraland nasal cavities

F

unction : unknown, they were thoughtto be receptors sensitive to cold

Muscle spindles and Golgi tendon

organs



organs

Muscle spindles provide feedbackconcerning the changes and the rate

alteration of the muscle length

Golgi tendon organs monitor the tension

and the rate at which the tension is beingproduced during movement

Information from these two sensory structures

is processed at the unconscious level within

the spinal cord; the information also reachesthe cerebellum & cerebral cortex, so that

individual may sense muscle position.

Thermoreceptor



p

Which respons to temperaturedifferences of about 2° C, are three

types: warmth receptors, cold receptors

and temperature-sensitive nociceptors.

Specific receptors have not been

identified for warmth

Cold receptors are derived from naked

nerve ending in the epidermis

Nociceptors



Are receptors sensitive to pain caused by

mechanical stress, extreme of temperature,

and cytokines as bradykinin, serotonin and

histamin.

Are naked ending of myelinated nerve fibersthat branch freely in the dermis before

entering the dermis

Divided into three groups :

± Those that respond to mechanical stress or damage

± Those that respond to extremes in heat or cold

± Those that respond to chemical compound such

as bradykinin, serotonin and histamin



Afferent EndingsAfferent Endings

Encapsulated EndingsEncapsulated Endings

- - Meissner¶s CorpuscleMeissner¶s Corpuscle

- - Pacinian CorpusclePacinian Corpuscle

(Corpuscle of Vater (Corpuscle of Vater- -Pacini)Pacini)

- - Genital CorpuscleGenital Corpuscle

- - Ruffini¶s Ending Ruffini¶s Ending

- - End Bulb of KrauseEnd Bulb of Krause

-- Golgi tendon organ:Golgi tendon organ: Proprioceptor Proprioceptor



Receptor Receptor EndingsEndings

Free nerveFree nerve

ending ending

Expanded Expanded

tip ending tip ending

Encapsulated Encapsulated

ending ending



M eissner¶s CorpuscleM eissner¶s Corpuscle



pp

Pacini an CorpusclePacini an Corpuscle



pp

Efferent EndingsEfferent Endings



gg

Somatic Efferent EndingsSomatic Efferent EndingsNeuromuscular JunctionNeuromuscular Junction

(Myoneural Junction, Motor End (Myoneural Junction, Motor End

Plate)Plate)

Autonomic EfferentAutonomic Efferent

EndingsEndingsEndings on smooth muscleEndings on smooth muscle

and blood vesselsand blood vessels

Somatic Efferent EndingsSomatic Efferent EndingsNeuromuscular JunctionNeuromuscular Junction

(Myoneural Junction, Motor End (Myoneural Junction, Motor End

Plate)Plate)

Autonomic EfferentAutonomic Efferent

EndingsEndingsEndings on smooth muscleEndings on smooth muscle

and blood vesselsand blood vessels



NeuromuscularNeuromuscularJunctionJunction

( My oneur al Junction,( My oneur al Junction,

M otor End P l ate)M otor End P l ate)

NeuromuscularNeuromuscularJunctionJunction

( My oneur al Junction,( My oneur al Junction,

M otor End P l ate)M otor End P l ate)

NMJNMJNMJNMJ

MM

NN



Autonomic Efferent EndingsAutonomic Efferent EndingsAutonomic Efferent EndingsAutonomic Efferent Endings



Neuromuscular SpindleNeuromuscular Spindle



Neuromuscular SpindleNeuromuscular Spindle

Both receptor and effector Both receptor and effector

StructureStructure

1. Capsule1. Capsule

2. Intrafusal Muscle Fibers2. Intrafusal Muscle Fibers

- - Nuclear Bag Fiber Nuclear Bag Fiber

- - Nuclear Chain Fiber Nuclear Chain Fiber

3. Receptor and Effector Nerve3. Receptor and Effector NerveEndingsEndings

- - Afferent Ending Afferent Ending

- - Efferent Ending Efferent Ending



NB: nuclear bag fiber NB: nuclear bag fiber IF: intrafusal muscle fiber IF: intrafusal muscle fiber

CA: capsuleCA: capsuleEF: extrafusal muscleEF: extrafusal muscle

fiber fiber

4. neuro anatomy 2010

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