AsturiaNOTES Lecture 2: Neurohistology · 2016-08-13 · Nucleus contains dark-staining nucleolus The nucleus is vesicular (pale-staining) 1 When a structure is said to be chromatic,

Lecture 2: Neurohistology Neuroscience 1: Neurohistology

AsturiaNOTES by RAsturiano UST-FMS A-2019: #TheElusiveDoktora August 20, 2015. Lecturer: Dr. A. Baroque—downloadable (for free!) at: www.theelusivedoktora.wordpress.com

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Cells of the Nervous System

Nervous tissue is one of the 4 types of tissues present in the human body. The other three are:

o Epithelial tissue

o Muscular tissue o Connective tissue

CNS o Neurons

Functions: 1 Receive information

a Sensory information b External information via skin, muscle, or other visceral

organs

2 Integrate/Process information a The “translation” of the information in a language

that can be interpreted by the nervous system—

electrical impulses 3 Transmit information

a Once the information has been “translated”, it is

transmitted to the next neuron b If transmission is successful, there is release of

chemicals called neurotransmitters (NT)

i The activity of NTs makes us: Hear See

Taste Move Feel

Emote/React Neurons are excitable ALL the time

1 Only cell in the body that is endowed with the ability to produce

electricity In the CNS:

1 Periphery—neurons

2 Middle—axons (white matter) a However, the reverse is true in spinal cord tissue

i Middle—gray horn (neurons)

ii Peripheral—axons (either ascending or descending, white matter)



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Fully mature neurons are incapable of mitosis 1 They rest in a permanent G0 phase

2 Thus, in cases when there is CNS injury, the cells die and they do not regenerate except in the following:

a Hippocampal areas

b Amygdaloid areas c Olfactory neurons

o Neuroglia

Are NOT excitable Neuroglia fill in the gaps between neurons

1 They serve as cushion, matrix Provide the nutrients required for normal neuron activity

Take care of the waste products generated by neuron metabolism Maintain electrochemical environment of the excitable neurons

PNS o Ganglion Cells o Satellite Cells

Shuttle nutritive molecules from blood vessels to neurons such as: 1 Glucose 2 ATP

Remove waste products Maintain electrochemical surroundings

1 Critical for the neuronal function (Proper generation of Action

Potentials) In early development of CNS, Satellite Cells guide developing neurons

to their correct location In adult CNS, Satellite Cells provide structural support

Table 1. CNS and PNS cell types

CNS PNS

Impulse Conducting cells Neuron Ganglion cells

Supporting cells Neuroglia or Glial Cells Schwann cells and Satellite Cells

STRUCTURE OF NEURONS Cell Body/Soma

o Contains the characteristic FISH-EYE Nucleus

Nucleus contains euchromatin 1 Euchromatin is reflective of the neuron’s highly active

metabolic status. 2 The euchromatin may be dispersed

3 The other chromatin structure—heterochromatin—are visible when the cells divide.



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a Which is why mature neurons will never exhibit the heterochromatin structure because they do not divide

Nucleus contains dark-staining nucleolus The nucleus is vesicular (pale-staining)

1 When a structure is said to be chromatic, it is dark-staining

o The soma processes/integrates information that are received o Contains Nissl’s Bodies

Dendrites—AKA Nerve Processes o Receives signals from other neurons

This feature of dendrites is termed to be cellulipetal—moving toward the cell body

1 If the direction of the signal/impulse is moving away from the cell body it is—cellulifugal

o The dendrites receive signals/information through physical contacts termed to

be synapses o Dendrites are shorter than axons o Dendrites are more abundant than axons

o Dendrites contain Gemmules AKA Dendritic Spines Functions:

1 Increase the surface area for synaptic connections Within the gemmules, organellar structures can be seen:

1 Microtubules and Neurofilaments

a Thin cytoskeletal elements b Located in the distal part of the dendritic branch

2 Nissl’s Bodies—AKA Nissl’s Substance a It consists of rosettes of polysomes and

endoplasmic reticulum i Therefore, it has a function in protein

synthesis

3 Endoplasmic Reticulum 4 Polyribosomes 5 Free ribosomes

a 2 to 5 are located in the proximal part of the dendritic branch

Axon o Functions in transmission of nerve impulses in a cellulifugal manner o Devoid of housekeeping organelles (Mitochondria, Endoplasmic Reticulum,

etc). The organelles contained are: Only CYTOSKLETON

1 Microtubules—biggest cytoskeleton a 25 nm in diameter



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b Composed of 13 protofilaments i Each protofilaments are made up of alternating

alpha- and beta-tubulin 2 Neurofilaments

a 10 nm in diameter

b Composed of helix of polymers—it is a tetramer i Each monomer is intertwined to become a

dimer. Then two dimers intertwine to become

tetramers. Then these tetramers become the protofilament. And the final aggregation of these protofilaments become the neurofilament.

3 Microfilaments—smallest cytoskeleton a 7 nm in diameter b 2 strands of G-actin monomers

NO Nissl’s bodies NO Gemmules WITH Mitochondria

Fewer branching as compared with dendritic branchings o Longer than dendrites

Consists of axon collaterals and branching

The axon length may either be myelinated or unmyelinated 1 If it is myelinated, determine first where in the nervous

system is that axon (neuron) located.

a PNS?—Then the cell responsible for myelinating the axon is the Schwann Cell

i 1 schwann cell can myelinate 1 axonal area Therefore, several schwann cells are

needed to myelinate the whole axonal length

ii In between Schwann cells, there are Nodes of

Ranvier which are sites for saltatory conduction

b CNS?—Then the cell responsible for myelinating the

axon is the Oligodendroglia/Oligodendrocyte i 1 Oligodendrocyte can myelinate many

axons

c If the axon is myelinated, then that axon belongs to a nerve classified as Type A fibers (alpha-A, beta-A, and delta-A)

i These Type A fibers carry signals that will be responsible for:

Light Touch

Position sense



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Vibration 2 If it is unmyelinated, then the axon belongs to nerve fibers

classified as Type C fibers. a Type C fibers still have myelin except that there is

only 1 schwann cells myelinating several axons

i This kind of myelin ensheathment does NOT allow:

Presence of Nodes of Ranver

o Therefore, these axons are continuous

Saltatory Conduction

o Hence, Type C fibers are slowly-conducting fibers

ii Type C fibers carry:

Pain impulses Temperature

3 Myelin Sheath Pathology

a Myelin sheath pathology decreases the magnitude of the signals that are being transmitted:

i Demyelination—acquired myelin disease

ii Dismyelination—congenital myelin disease o Axonal length originates from Axon Hillock o Axonal Transport

Function: Mediates the intracellular of secretory proteins, organelles, and cytoskeletal elements.

Makes use of the cytoskeletal elements + proteins Dynein and

Kinesin 1 Dynein—responsible for Retrograde (backward) transport

(from axon to be transported to the soma) 2 Kinesin—responsible for Anterograde/Orthograde

(forward) transport (from soma to axon terminal) a Mnemonic:

i DR KA? (Doctor ka?)

DR=Dynein-Retrograde KA=Kinesin-

Anterograde/Orthograde

Axonal transport is inhibited by Colchicine—depolymerizes microtubules

Types of Axonal Transport:

1 Fast Anterograde Axonal Transport a It is responsible for the transport of:

i All newly synthesized membranous organelles

(packaged in vesicles) ii Precursors of Neurotransmitters



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b This process occurs in the human body at the rate of 200-400 millimeters/day

c Mediated by: i Neurotubules ii Kinesin

d Fast Anterograde Axonal Transport is neurotubule-dependent

2 Slow Anterograde Axonal Transport

a It is responsible for the transport of: i Fibrillar cytoskeletal ii Protoplasmic elements

b This process occurs in the human body at the rate of

1-5 millimeters/day 3 Fast Retrograde Transport

a It is responsible for the backward transport (from

axon terminal to the cell body) of: i Used materials for:

Degradation

And Recycling b Rate: 100-200 millimeters/day c Transports:

i Nerve Growth Factors (NGF) ii Neurotropic Viruses and toxins:

Herpes Simplex

Rabies virus o Rabies virus enters the spinal

cord via retrograde transport.

When it enters the nervous system, it replicated and spreads through the entire CNS to give

rise to behavioral symptoms. Then via anterograde transport, the virus becomes present in the

saliva. Poliovirus Tetanus toxin

o AKA Tetanospasmin o From Clostridium tetani

d Mediated by:

i Neurotubules ii Dynein

e *Thus, the clear disadvantage of these transport

mechanisms is that infections can reach the CNS Loss of axonal transport mechanisms can result to:



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1 Wallerian Degeneration a Anterograde degeneration characterized by

disappearance of axons and myelin sheaths and the secondary proliferation of Schwann cells

b Occurs both in the CNS and PNS

2 Chromatolysis a It is the result of the retrograde degeneration in

the neurons in the CNS and PNS

b There is a loss of Nissl bodies after axotomy 3 Mnemonic: Loss of Axonal Transport kasi WA-CR (WAlang

CR) a WA=Wallerian-Anterograde transport loss

b CR=Chromatolysis-Retrograde transport loss o Axons may be capped at the distal portion by terminal boutons (boutons

terminaux)

o At the end of the axonal length, there are only two organs that are possibly innervated:

Muscles—for movement

Glandular Tissue—for secretions (salivary glands, etc)

Pigments and Inclusions in Neurons

o Lipofuscin Granules (Lay-poh-fyuu-sin NOT lay-poh-fyuu-SHIN pls) Are pigmented cytoplasmic inclusions that commonly accumulate

with aging

Are considered to be residual bodies from that are derived from lysosomes

o Melanin (Neuromelanin) Blackish intracytoplasmic pigments

Found in: 1 Substantia Nigra 2 Locus Ceruleus

These pigments disappear in the nigral neurons of patients with Parkinson’s Disease

o Lewy Bodies

Neuronal inclusions that are characteristic of Parkinson’s Disease o Negri Bodies

These intracytoplasmic inclusions are pathognomic of rabies

They are found in the: 1 Pyramidal cells of the hippocampus 2 Purkinje cells of the cerebellum

o Hirano Bodies Intraneuronal, intracytoplasmic, eosinophilic, rod-like inclusions that

are found in the: 1 Hippocampus of patients with Alzheimer’s Disease



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o Neurofibrillary Tangles Consist of intracytoplasmic degenerated neurofilaments

Seen in patients with Alzheimer’s Disease o Cowdry Type A Inclusion Bodies

Are intranuclear inclusions that are found in the neurons AND glia

of patients with Herpes Simplex Encephalitis TYPES OF NEURONS

A. Types of Neurons According to Number of Processes

This classification scheme is due to the disposition AND the number of the extruding limbs emanating from the soma.

Pseudounipolar neuron—AKA Dendraxon o Two processes which are fused to become one (resembling a T- or a Y-

shaped process)

o With an afferent and efferent limb o Found in:

Dorsal Root Ganglion (in Spinal Cord)

Cerebrospinal Ganglion Sensory Ganglia of Cranial Nerves:

1 5

2 7 3 9 4 10

Bipolar neuron—interneuron o With axons pointing two opposite directions (North- and Southward) o Found in sense organs:

Retina

Organ of Corti Taste buds Olfactory neuroepithelium

Cochlear/Vestibular Ganglia (Cranial Nerve 8) Olfactory Ganglia (Cranial Nerve 1)

Multipolar neuron—motor neurons (most of our neurons (90%) in the CNS are Multipolar)

o With dendrites (shorter emanations) and the axon (being the longer

emanation) o Found in:

Anterior Gray Horn of Spinal Cord

Autonomic Nervous System Pyramidal Cells of Cerebral Cortex Purkinje Cells of Cerebellum



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B. According to Length of Processes (Length of Axon)

Golgi Cell Type 1—AKA Projection Neurons o Very long axons, so long, that the axon synapses with structures very far

from the soma

o Examples: Purkinje Cell, Pyramidal cell, Anterior gray horn cell Golgi Cell Type 2—AKA Interneurons/Local Circuit

o Neurons with very short (or absence of) axons o Example: Granule Cell

C. According to Functional Characteristics

Afferent Neuron o Neurons that conduct signals from the periphery toward CNS (PNSCNS) o A sensory neuron

Efferent Neuron o Neurons that conduct signals from the CNS toward periphery (CNSPNS) o A motor neuron

Mnemonic: “So confusing naman coz it sounds the SAME!” (SensoryAfferent;MotorEfferent)

D. According to Neurotransmitter Released Dopaminergic

Cholinergic Adrenergic Glutamatergic

Glutaminergic Serotonergic GABAergic

Types of Synapses Formed by Neurons Three Types Based on Physical Connections

o Axosomatic The axon lodges NTs on a soma Example is the neuromuscular/myoneural junction

o Axodendritic

The axon lodges NTs on a dendrite o Axoaxonic

The axon lodges NTs on another axon

Two Types Based on Mechanism of Impulse Processing

o Electrical Synapse

Does NOT make use of NTs



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Makes use of a current (electrotonic) Has low resistance to ion flow

Occurs via gap junctions Faster in impulse conduction as compared to the chemical synapse

o Chemical Synapse Makes use of NTs Most common form of synapse in the nervous system

Slower in conduction of impulses compared to the Electrical Synapse Parts of a Synapse

o Pre-synaptic Neuron

Has synaptic vesicles which contain the neurotransmitter o Synaptic Cleft

20-50 nanometers in length

o Post-synaptic Neuron Contains the receptors where NTs will lodge Also contains post-synaptic web to maintain cohesion of the

synapsing surfaces

In synapses, there are dense filaments in pre- and post-synaptic terminals.

The subsynaptic/postsynaptic web maintains the cohesion of the two synapsing structures. And the action potential reaches the synaptic cleft via:

1. Presynaptic membrane is depolarized

2. Action potential is generated and travels through the length of the axon 3. Upon AP’s arrival at the distal end of the axon length, voltage-gated Ca2+ are

opened 4. Ca2+ ions are influxed

5. Ca2+ promotes exocytosis of vesicles containing the neurotransmitters 6. NTs are released 7. NTs combine with the receptors (receptors in the sarcolemma if it’s a muscle)

8. Cause efflux of ions and activation of post-synaptic terminal

The phenomenon of Transduction—electrical energy being “transduced” to

become chemical energy again being “transduced” to become electrical energy. This phenomenon is used by neurons capable of transmitting electrical impulses.

Characteristics of a Synapse o Unidirectionality

NTs are only found in the pre-synaptic neuron making retrograde

transfer of neuronal impulses impossible o The magnitude of NT’s effect on the post-synaptic membrane is variable

and dependent on the amount of NT released



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Therefore, more NT released? The greater the effect on the post-synaptic membrane

Types of Synapse

Table 2. Type of Synapses

ACh (Acetylcholine) Type of Synapse GABA Type of Synapse

Wider Narrower

Dense material is only found in the post-

synaptic membrane

Dense material is found both on the pre-

and post-synaptic membranes With round and large vesicles Oval/flattened, various shapes of vesicles

The Neuromuscular/Myoneural Junction

o Is an axosomatic type of synapse wherein the post-synaptic membrane is the muscle cell

o The muscle membrane forms secondary invaginations which increases the

surface area for the NT to combine with the receptors Diseases involving NT

o MYASTHENIA GRAVIS

Disease wherein there are antibodies that are destroying the receptors found at the post-synaptic terminal/membrane.

1 So: Even if there is enough ACh, if the receptors are destroyed,

there will be no transmission of impulse. 2 Thus: Patients have muscle weakness

a Usually, the extraocular muscles are the ones

affected. b In the morning, the patients are generally OK but

throughout the day, ptosis can be observed o PARKINSON’S DISEASE

Dopamine is the NT affected The substantia nigra is normally rich in Dopamine

1 However, in Parkison’s Dse, the dopamine deposits are low

resulting to: a Rigid stand b Difficulty in starting movement

c Tremors d Involuntary movement

i All these clinical symptoms are associated with

deficiency of dopamine It has been found that Parkinson’s Dse is likely to develop with

individuals who are exposed to contact sports



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ORGANIZATION OF NEURONS IN THE NERVOUS SYSTEM

In the CNS Nucleus—a cluster of functionally related nerve cell bodies

o Example: Hypoglossal nucleus, Nucleus Solitarius In the Cerebral Cortex neurons form 6 layers. And in the Cerebellar Cortex,

neurons form 3 layers.

o Layer/Lamina/Strata—nerve cell bodies arranged in a layer o In the cerebral cortex—there is a perpendicularly-oriented group of cell

bodies that are related by: Function

And the stimulus that drives them In the Spinal Cord, neurons form a functional COLUMN like the Dorsal Gray

Column

o Columns—nerve cell bodies arranged in columnar groups o In the spinal cord—there is a longitudinally-oriented group of

functionally relayed cells that extend for part or all of the length of the

brainstem Bundles of axons form tracts that are found in the outer white matter of Spinal

Cord

o Tracts/Fasciculus(i)/Lemniscus(i)—bundles of axons related by function

Funiculus—group of several tracts/fasciculi

Since the CNS has NO CONNECTIVE TISSUE, Neuroglia supports the

neurons in the CNS.

Types of Neuroglia Glial cells are the non-neural cells of the nervous system. Therefore, these cells are not capable of producing, propagating, and transmitting electric

impulses. Macroglia—two types of MacrogliaThe Astrocytes and Oligodendroglia

o Astrocytes—most numerous neuroglia in the CNS. Star-like in shape. Fibrous Astrocytes—predominant in the white matter Protoplasmic Astrocytes—predominant in the gray matter

Mnemonic: “Si FAW ay mahilig magPAGpag” 1 FAW=Fibrous AstrocytesWhite matter 2 PAG=Protoplasmic AstrocytesGray matter

Functions of Astrocytes: 1 They project foot processes that envelop the basement

membrane of capillaries, neurons, and synapses.



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a The perivascular foot of astrocytes helps establish the Blood-Brain Barrier (BBB)

2 They form the external and internal glial-limiting membranes of the CNS

3 They play a role in the metabolism of certain NTs:

a GABA b Serotonin c Glutamate

4 They buffer the potassium concentration of the extracellular space.

a After a wave of depolarization, wherein there are a lot of K+ in the vicinity, they remove the excess K+ and

shuttle it back to the circulation to bring back the environment of neurons to homeostasis

5 They form glial scars in damaged areas of the brain

(astrogliosis) 6 They contain glial fibrillary acidic protein (GFAP) which is a

marker for astrocytes

7 They contain glutamine synthetase, another biochemical marker for astrocytes

a This enzyme recycles glutamate by combining

Glutamate with Ammonia to form Glutamine. i In this way, levels of ammonia will be lessened

as glutamate is recycled

8 They may be identified with monoclonal antibodies such as (A2B5)

9 Responsible for clearing excitatory amino acids in the synaptic cleft

a Astrocytes therefore do not allow excess of NT i Once the NTs are released, they attach to their

respective receptors in the post-synaptic

membranes and the excel will be engulfed by the astrocytes to maintain the environmental milieu of the neuron

o Oligodendroglia AKA Oligodendrocytes They are the myelinating cells of the CNS

1 Can myelinate up to 40 internodes and as many as 30 axons at the same time

Ependymal Cells

o Ciliated cells that line the central canal and the ventricles of the brain o They also line the luminal surface of the choroid plexus o These cells produce Cerebrospinal Fluid (CSF)



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Microglia o They are the main immune cells of the CNS

o They act as a scavenger/macrophage Therefore, they are capable of phagocytosis

1 They phagocytose:

a Cellular waste b Pathogens

o In times of stress directed to the CNS (Injury, infection, trauma), microglia

proliferate o They arise from monocytes

Mnemonics: “CNS Glial cells came from MOA and EDSA”

MOA=Microglia, Oligodendroglia, and Astrocytes E of EDSA=Ependymal Cells

The Blood-Brain Barrier (BBB) o It consists of the tight junctions of non-fenestrated endothelial cells +

the perivascular foot processes of the astrocytes

o Infarction of brain tissue destroys the tight junctions of endothelial cells and results in vasogenic edema

Vasogenenic edema is due to the infiltration of plasma into the

extracellular space The Blood-CSF Barrier (BCB)

o It consists of the tight junctions between the cuboidal epithelial cells of the choroid plexus

o The barrier is permeable to some circulating peptides and plasma proteins: Circulating peptides: Insulin

Plasma proteins: Pre-albumin Meninges

The Dura, Arachnoid, and the Pia Matter o Dura

Toughest of the three meningeal layers

Contains granules called arachnoid granulations 1 Absorb excess CSF

o Arachnoid

Contains a space beneath it called the subarachnoid space 1 In the subarachnoid space is where the CSF is

o Pia Matter

Underneath the Pia Matter is the brain parenchyma Leptomeninges = Arachnoid + Pia Matter

o Subarachnoid infiltration by microbial invasion can produce meningitis or more appropriately, leptomeningitis



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Diseases Affecting the CNS

Astrocytoma/Glioblastoma multiforme o Neurons are terminally differentiated cells which do NOT undergo further

division. In contrast, astrocytes RETAIN the ability to proliferate all

throughout life making them the primary source of tumors in the CNS Sometimes, the tumor that they produce when discovered is already

on the late stage and prognosis is very bad.

o Most common form of brain tumor Alzheimer’s Disease

o Affects individuals of 40 years and up

o Accelerated neuron degeneration It is a neurodegenerative disease

o In a normal individual, the Gyri=Full, Sulci=Thin

In patients with Alzheimer’s disease, there is thinning of the gyri especially in the parahippocampic areas and sulci are very wide

1 This accounts for the severe memory loss and behavioral

problems In the PNS

Ganglion—collection of neuronal cell bodies that may either be:

o Sensory

Dorsal root Cranial Nerve

o Motor Visceromotor

Autonomic Rami/Roots—collection of axons Satellite Cells/Schwann cells—supporting cells

The DORSAL ROOT GANGLION AKA Spinal Root Ganglion

Rounded cell body With pseudounipolar neurons contaning fish-eyes nucleus wit very fine Nissl

bodies that are uniformly distributed

NUMEROUS satellite cells with epithelioid cells surrounding the cell body in the form of a capsule—these cells are the satellite cells/amphicytes

Associated with the thick myelinated fibers

SENSORY in function NO synapses because their process is both a 1. Dendrite and an 2. Axon

(Dendraxon) The AUTONOMIC GANGLION



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Multipolar cells with intermediate Nissl bodies and mass at the peripheral region

FEWER satellite cels Associated with Unmyelinated fibers MOTOR in function

o For The innervation of the: Smooth muscles Cardiac muscle

Glandular tissues WITH synapses because of the presence of pre- and post-synaptic terminals The SCHWANN CELLS

The myelinating cells of the PNS with a myelinating ratio of 1 schwann cell:1 axon

Myelin is needed for faster conduction in the PNS

o Two types of impulse conduction: Saltatory conduction Continuous conduction—Unmyelinated fibers allow the impulse to

travel through the entire length axon o In preparations, myelin has a foamy/bubbly keratin network because it

has been washed off during the preparation

Schidmt-Lantermann Lines o Areas of the schwann cell cytoplasm separating the myelin o Presence of this line is indicative of a myelinated peripheral nerve

Nerve coverings: o Endoneurium (innermost)

Covers one nerve fiber o Perineurium

Covers a bundle (fascicle) composed of several nerve fibers This is the site of the Blood-Nerve Barrier (BNB)

o Epineurium (outermost)

Covers the entire nerve trunk composed of several nerve bundles Made up of robust bundles of collagenous fibers

Nerve Injury

When a patient has injury to the CNS (like stroke), it would leave a space on the

area of injury. And this space would be filled up with proliferation of astrocytes that is now called an astrocytic scar. However, the proliferation is in a random, unorganized fashion—it is not designed to establish nerve function. Therefore, it is

just a spatial filler. On the other hand, when the patient suffers from a PNS Nerve Injury (like a

compression injury wherein the soma/perikaryon is retained, soma will try to



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regenerate and this regenerative function is made possible by the Schwann Cells.

Schwann cells would proliferate and form bands called bands of Bungner which would guide the proximally growing stumps to anastomose with the distally growing stumps.

o If the anastomosis is successful, reinnervation is acieved and muscle regains normal diameter.

o If the anastomosis is unsuccessful, it ends as blind stumps called neuroma

Changes seen during the nerve injury: Nucleus is eccentrically located as compared to the normal neuron with central

nucleus

Chromatolysis is observed Atrophy of muscle being supplied

-end- References 1. Lecture notes from Dra. Lumitao’s lecture on Neurohistology (HISTOLOGY) by Anna Dominique Py Castro (A-2013) 2. Lecture notes by RAsturiano (A-2019) from the lecturer 3. Transcription notes by Carmella Agcaoili (A-2019) 4. High-Yield Neuroanatomy (4th Edition) by James D. Fix Downloadable for free at: www.theelusivedoktora.wordpress.com For any corrections you may find, content or otherwise, email me at: [email protected]

-THANKS-

AsturiaNOTES By RAsturiano

#TheElusiveDoktora

http://www.theelusivedoktora.wordpress.com/

mailto:[email protected]

Documents

AsturiaNOTES Lecture 2: Neurohistology · 2016-08-13 · Nucleus contains dark-staining nucleolus The nucleus is vesicular (pale-staining) 1 When a structure is said to be chromatic,