NEUROANATOMY 1

Neurohistology

CELLS OF THE NERVOUS SYSTEM  Lipofuscin: wear and tear

CNS PNS  Nissl bodies

Neurons Ganglion cells  Characteristic of nerve cells

Neuroglia Schwann cells  Consists of rosettes of polysomes and rough

endoplasmic reticulum
 Absent in axons
 More in motor nerves
NEURONS
 When the nerve cell is injured, or fatigued
 Neuron - Structural & functional unit of nervous system
Nissl bodies disappears, and the process is
 It is an excitable cell which is concerned with the
known as Chromatolysis
receiving information from the environment or other
 Functions
nerve cells, process information, send information to
1. Protein synthesis
other neurons or effector
2. Maintains continuous axonal flow
 Neurons are known for
 No mitosis
Axon
 No proliferation
 Arise from either the cell body or the dendrite
 High metabolic activity
 Originate from the Axon Hillock (Point of generation
of electric impulse)
STRUCTURE OF NEURON
 Transmit impulses away from the cell body
 Neuron consists of
 Has a long central core of cytoplasm  Axoplasm
 Nerve cell body/Soma/Perikaryon
 Covered by Axolemma (continuation of cell
 Processes of two kinds
membrane)
o Dendrites
 Axoplasm with axolemma is called axis cylinder of
o Axons
nerve fiber
 Apart from the usual organelles like Nucleus &
 Axolemma is surrounded by
Mitochondria, Neuron contains Neurofibrils,
 CNS  Oligodendrocytes
Neurotubules & Nissl bodies
 PNS  Schwann cells (Neurilemma or Sheath
of Schwann)
Nerve cell body/Soma/Perikaryon
 Nissl bodies are absent in the axon, so the necessary
 Cell membrane
proteins are synthesized in the soma & transmitted
 Like other cells
to the axon via axonal flow
 Trilaminar – 75 A˚
 Axons of some nerve fibers are insulated by myelin
 Nucleus
sheath  Myelinated nerve fibers
 Central, large, vesicular, prominent nucleolus
 Have branches (collaterals) that further divide &
 At Eccentric position in injury, fatigue, healthy
terminate in swellings called synaptic knobs or
sympathetic ganglion
terminal buttons
 Mitochondria
 End distally in terminal boutons in synapses with
 Golgi apparatus
neurons, muscle cells, and glands
 Lysosomes
 Neurofibrils
Myelin Sheath
 Arranged in plexiform manner in the cell body
 Thick lipoprotein sheath that insulates the
and extends in all processes.
axons of myelinated nerve fibers
 Crowded at axon hillock
 Imparts white color to the myelinated nerve
 Pigments
fibers
 Lipochrome - gives yellow color to neuron,
 It is not continuous & the areas where it is
Abundant in old age
absent are called – Nodes of Ranvier
 Melanin - Dopamine synthesis, Substantia
 Segment of nerve fiber between two nodes is
Nigra of mid brain
called Internode
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Neurohistology

 Formed of  One process divides in ‘T’ shaped

o Concentric layers of proteins manner into dendrite and axon.
Pseudo Unipolar
o Alternating with phospholipids  Eg: dorsal root ganglia of all spinal
(cholesterol, lecithin & cerebroside – nerves
sphingomyelin)  Contains only one process i.e. axon
 Functions  Found in lower animals
Unipolar
1. Faster conduction  Eg: Mesencephalic nucleus of
2. Insulating capacity (which restricts nerve trigeminal nerve
impulse within the nerve fiber & prevents  Axon & dendrite arise from 2
stimulation of neighboring nerve fibers) different poles
 Myelinogenesis Bipolar  Spindle shaped
o Formation of myelin sheath  Eg: Olfactory cells, Ganglion cell of
o It is formed by auditory nerve, some cells of Retina
- In the peripheral nerves  by  One pole gives rise to axon & other
Schwann cells in neurilemma Multipolar poles gives rise to dendrites
- In the CNS  by Oligodendrocytes  Eg: Motor neurons
o Schwann cells wrap up & rotate around
Depending on the Function
the axis cylinder in many concentric
layers, which fuse to produce the myelin Motor Neurons Sensory Neurons
sheath (efferent nerve cells) (afferent nerve cells)
o Outermost membrane of Schwann cells  Carry motor impulses  Carry the sensory
remains as neurilemma from CNS to peripheral impulses from
o Nucleus of these cells remains in between effector organs like periphery to the CNS
myelin sheath & neurilemma muscles, glands etc.  They have short axons &
 They have long axons & long dendrites
Dendrites short dendrites
 Branched processes that transmit impulses towards Depending upon the Length of the Axon
the nerve cell body (receptive)
 Contain cytoplasm similar in composition to that of Golgi type 1 Golgi type 2

the cell body Arrangement: Cell bodies in Arrangement: Have Short

 Golgi apparatus is not present CNS, with long axons axons
Eg: Reach peripheral Eg: Cerebral cortex, Spinal
organs cord

Anaxonic Neurons
 Small, stellate (star-shaped) cells with processes
that all look alike with no apparent axon
 Can be found in CNS, Retina, and Adrenal Medulla

CLASSIFICATION OF NEURONS

Depending upon the Number of Poles

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Neurohistology

Lining
cavities of
Neural
Ependymal cell CNS central
tube
nervous
system
Macropha
Bone
Microglia CNS gic
marrow
activity
Myelin
productio
Neural
Schwann cell PNS n
tube
Electric
insulation
Protects
Neural
Satellite Cells PNS neuron
tube
cell bodies

NEUROGLIA
 Non-neuronal cells of the CNS and the PNS
 Arise from the neural tube and neural crest
 Capable of cell division throughout life
 Best revealed with gold and silver impregnation stains NERVE FIBERS
 Consist of axons, dendrites, and their glial investments
CLASSIFICATION OF NEUROGLIA

Glial Cell Type Origin Location Functions ORGANIZATION OF NERVES

Myelin Many axons together form a bundle called Fasciculus


productio
Neural Many fasciculi together form a Nerve
Oligodendrocyte CNS n
tube
Electric
Connective Tissue Coverings
insulation
 Each fasciculus is covered by Perineurium (more
Astrocytes
fibroblasts)
Fibrous Astrocytes: Neural Structural
 Whole nerve is covered by Epineurium (a fibrous
Contains Gliofibrils tube support
dense connective tissue with adipocytes and blood
which extend into Repair
vessels)
processes processes
 Each nerve fiber is covered by Endoneurium (loose
Situated in white Blood–
CNS connective tissue with reticular fibers and
matter of CNS brain
fibroblasts)
Protoplasmic barrier
Astrocytes: Metabolic
Lack Gliofibrils exchanges
Situated in grey
matter of CNS

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Neurohistology

ending; touch, pressure

Pain & cold receptors; some touch
III Aδ
receptors
Dorsal
IV Pain, temperature & other receptors root
C
Physio-Clinical Classification
Susceptibility Most Least
Intermediate
to Susceptible Susceptible
Hypoxia B A C
Pressure A B C
Local
C B A
anesthetics
CLASSIFICATION
Depending on Presence or Absence of Myelin Sheath
Erlanger – Gasser Classification Myelinated Nerves Unmyelinated Nerves
Based on diameter of nerve fibers & conduction of
Schwann cell membrane is Axons are buried in the
Fiber coiled many times around Schwann cell, Myelin –
Conduction
Diamete axon – multiple layers absent
Type Velocity Function
r Eg: Preganglionic fibers of Eg: Post ganglionic fibers of
(m/s)
(m) ANS ANS
Proprioception; Faster conduction Slower conduction
Aα 12 - 20 70 - 120
Somatic motor More number of voltage Less number of voltage
Aβ 5 - 12 30 - 70 Touch, Pressure gated Na channels gated sodium channels
Motor to
Aγ 3-6 15 - 30
Muscle spindles
Pain, cold,
Aδ 2-5 12 - 30
Touch GANGLIA
Pre-ganglionic  Are aggregations of the neuronal cell bodies in PNS
B <3 3 - 15
autonomic  Ovoid structures surrounded by a capsule
C  2 types
Pain, 1. Sensory ganglia
Temperature,  Two types
Dorsal root 0.4 - 1.2 0.5 - 2 some mechano- i. Cranial ganglia (associated with cranial
reception, reflex nerves)
responses ii. Spinal ganglia (dorsal root ganglia)
Postganglionic 2. Autonomic ganglia
Sympathetic 0.3 – 1.3 0.7 – 2.3
Sympathetics  Consists of
 A & B fibers are Myelinated; C fibers are unmyelinated  Neuronal cell bodies
 Velocity of conduction ∞ thickness of the fibers  The nerve fibers leading to and from them
 Satellite cells
Numerical Classification
 Connective tissue
Fiber
Number Origin
Type
Spinal or Sensory or Autonomic or Sympathetic
Muscle spindle, Annulo-spiral Dorsal Root Ganglia Ganglia
Ia Aα
ending
Surrounded by thick Surrounded by thin capsule
Ib Golgi tendon organ Aα capsule
II Muscle spindle, flower-spray Aβ Peripherally arranged big Irregularly arranged

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Neurohistology

round pseudo unipolar Multipolar neurons - star  Outer White

neurons shaped of varying sizes in  Inner Gray
sections  Central (H shaped) horizontal bar of this
Each neuron is enveloped Few satellite cells H is an opening
by a layer of small cuboidal incompletely surround the  Central canal - a remnant of the lumen of
Spinal Cord
cells - satellite cells cell body the embryonic neural tube.
Neurons in groups Neurons widely spaced &  Limbs / horns of the H forms the anterior
separated by bundles of separated by axons / horns (ventral motor)
nerve fibres dendrites which pass  Arms forms the posterior horns (dorsal
through without being sensory)
involved in synapse
 Have three layers
Regularly arranged nerve Nerve fibers are irregularly
1. An outer molecular layer
fibers entering and leaving scattered
2. Central layer of large Purkinje cells
the ganglion
3. Inner granule layer
No synapse Synopsis is present
1. Molecular Layer
Ex: dorsal roots of the Ex: sympathetic ganglia
 Few cells and few Myelinated fibers; more
spinal nerves, sensory along sympathetic chain,
dendrites
ganglia of cranial nerves V, otic ganglion, ciliary
 Stellate cells (superficial) & basket cell
VII, IX, X ganglion, Submandibular
(deep)
ganglion
 Reason for the sparseness of nuclei
2. Purkinje or Middle Ganglionic Layer
SYMPATHETIC GANGLION CELLS
 Conspicuous cell body and their dendrites
 Multipolar neurons that reside entirely within the
Cerebellum are highly developed, assuming the aspect
PNS in sympathetic chain ganglia and “pre-aortic”
(Cerebellar of a fan
ganglia Cortex) 3. Granular Layer
 Closely packed chromatic nuclei
PARASYMPATHETIC GANGLION CELLS resembling lymphocytes, irregular light
 Multipolar neurons that also reside entirely within spaces that constitute the “islands” or
the PNS in the wall of the innervated organ “glomeruli”
 Granule Cells: Small, Multipolar cells with
HISTOLOGY OF CNS 3 or 4 dendrites, have unmyelinated axons
 Golgi Type II cell: Vesicular nuclei and
 Myelinated axons and the myelin-producing chromophilic bodies
White Oligodendrocytes  Mossy fibers: thick fibers and synapse
matter  Does not contain neuronal cell bodies with the granular layer
 Present in more central regions  Climbing Fibers: granular layer to
 Contains neuronal cell bodies, dendrites terminate of Purkinje cell
 Initial unmyelinated portions of axons and
Gray Glial cells  Composed of six layers
matter  Region at which synapses occur prevalent at Cerebrum 1. Molecular or Plexiform - Composed of
the surface of the cerebrum and cerebellum (Cerebral horizontal cells of Cajal & Golgi type II
 Forms the cerebral and cerebellar cortex Cortex) 2. Outer / External Granular Layer - Small
pyramidal or triangular cells whose
dendrites terminate on the molecular layer
3. Outer / External Pyramidal Layer
 Composed of typical well-formed
pyramidal neurons
 2 sub layers

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Neurohistology

o Superficial layer of medium sized Hirano Bodies

pyramidal cells: horizontal  Intraneuronal, eosinophilic, rod like inclusions that
Myelinated fibers are found in the hippocampus of patients with
o Deep layer of large pyramidal cells Alzheimer disease
4. Internal Granular Layer
 Composed of stellate cells Neurofibrillary Tangles
 Interspersed within the layer are  Consist of intracytoplasmic degenerated
horizontal myelinated fibers forming neurofilaments
external band of Baillarger (thalamo-  Seen in patients with Alzheimer disease
cortical ramifications)
5. Internal Pyramidal or Ganglion Layer Cowdry Type A Inclusion Bodies
 Giant Pyramidal cells of Betz (origin of  Are intranuclear inclusions that are found in
the pyramidal tract) neurons and glia in herpes simplex encephalitis
 Interspersed are granule cells and cells
of Martinotti, and horizontal fibers
forming the internal band of Baillarger
6. Multiform or Fusiform Layer
 Contains spindle-shaped cells, granule
cells, Martinotti cells, and stellate cells
 The layer is pervaded by fiber bundles

PIGMENTS AND INCLUSIONS

Lipofuscin (Lipochrome) Granules
 Pigmented cytoplasmic inclusions that commonly
accumulate with aging
 They are considered residual bodies that are
derived from lysosomes.

Neuromelanin (Melanin)
 Blackish intracytoplasmic pigment found in the
substantia nigra and locus ceruleus
 It disappears from nigral neurons in patients who
have Parkinson disease

Lewy Bodies
 Neuronal inclusions that are characteristic of
Parkinson disease

Negri Bodies
 Intracytoplasmic inclusions that are pathognomonic
of rabies
 Found in the pyramidal cells of the hippocampus
and the Purkinje cells of the cerebellum.

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 NEUROANATOMY 7
Neurohistology

5. Oligodendrocytes are important in –Kerala 01,

Mcq’s DNB 09
A. Blood brain barrier
CELLS OF THE NERVOUS SYSTEM B. Myelin formation
C. Phagocytosis
D. Chemotaxis
Ans:- B i.e. Myelin formation
Ref:- BDC 4/e vol III p - 300, Gray's Anatomy 39/e
NEURONS
p- 50-52
1. The myelin sheath in the peripheral nervous system is
Explanation:-
formed by which of the following cells listed below
A. Schwann’s cells Mn: "1SPM - 50CMO" i.e., Schwann cell Mylinate
B. Oligodendrocytes peripheral nervous system in 1:1 basis; and Central
C. Astrocytes nervous system is mylinated by Oligndendrocyte in
D. Microglia 1:50 basis.

A Gray’s Anatomy 38/e, p. 951

6. Pseudeounipolar neurons are seen in-DNB 06
A. Olfactory
B. Celiac ganglion
2. Neurilemmal sheath to the axonas of a peripheral
C. Spinal dorsal root ganglion
nerve is provided by
D. Cochlea
A. Golgi complexs
Ans:- C i.e., Spinal dorsal root ganglion
B. Cell membrane
Ref: BDC 4/e vol 111 p - 300, Gray's Anatomy 39/e
C. Schwan cell
p- 44, 59, 235, 391
D. Satellite cell. Explanation:-

C Gray’s Anatomy 39/e, p. 56-57 Pseudo-unipolar neurons is seen in dorsal spinal nerve root
\ ganglion

3. Which of the following is/are true with synapses? 7. Myelin sheath of nerve fibres of CNS is
A. Synapse is composed of a presynaptic membrane formed by
of a nerve cell, a synaptic gap and a postsynaptic A. Schwann cells
membrane of another nerve cell. B. Astrocytes
B. Synaptic gap ois about 200 A and synaptic vessels
0 C. Oligodendrocytes
contain neurotransmitter D. Microglia
C. Presynapitic terminal contains several mitochondria
C Ref: Gray’s Anatomy 38/e, p. 940
D. All of the Above

D Gray’s Anatomy 39/e, p. 44-47

NEUROGLIA

1. Gitter cells are-DNB 08, Kerala 01

4. Myelin sheath in CNS is synthesized by-DNB 04,
A. Microglia
AP 90
B. Modified macrophages
A. Microglia
C. Astrocytes
B. Schwann cell
D. Neutrophils
C. Oligodendroglia
Ans:- A i.e. Microglia
D. All
Ref:- Di Fiore's histology 7/e p-290
Ans:- C i.e. Oligodendroglia
Explanation:-

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Neurohistology

Gitter or Hortega cell is a lipid laden microglial cell Ref:- IBS Embryology 7/e P-312-14; Langman's 9/e P- 443; IBS
commonly seen at the edge of healing brain infarcts. Histology 4/e p-164
It phagocytize lipid from necrotic or degenerating Explanation:-
brain cells. It is also known as compound granule Dorsal root ganglion or spinal ganglion are unipolar or
cell, gitterzelle (lattice or wire-net), mesoglia or pseudounipolar & Sympathetic or autonomic ganglion
perivesicular glial cell. is mulitpolar on section.
2. Following cells are responsible for the nourishment of Dorsal root (Sensory/Spinal) ganglion Autonomic
CNS (Sympathetic) ganglion
A. Astrocytes Consists of pseudo unipolar Q neuron Consists of
B. Oligodendrocytes multipolar neuron
C. Schwann cells -Has cell bodies of afferent neuron
D. Microglia -Neurons arranged in groups Q separated by nerve fibres
lying in group -Has cell bodies of efferent
Essentials of Human Anatomy, 3/e, A.K neurons
A
Datta vol 4, p. 23 -Neurons & nerve fibres are scattered
Large rounded cell body with central nucleus & a prominent
nucleolus Cell body is smaller & irregular with
eccentric nucleus and a prominent nucleolus
NERVE FIBERS
- Neurons of sensory (dorsal /posterior) spinal nerve root
1. Connective tissue surrounding nerve fibre is called ganglion, sympathetic (autonomic) ganglion & sensory
A. Epineurium, ganglion of 5th, 7th, 8th, 9th & 10th cranial nerve are
B. Perineurium, derived from neural crest.
C. Endoneurium - Some dorsal root ganglion cells contain small clumps
D. None of the above lipofuschin pigment.
HISTOLOGY OF CNS
C Gray’s Anatomy 39/e, p. 56

GANGLIA 1. White matter of central nervous system contains.

1. Following are the peculiarities of sensory ganglion A. Oligodendrites
except; B. Microglial cells
C. Myelinated nerve fibre
A. The ganglion cells are unipolar D. All of the Above
B. The cell has a prominent nucleus and a nucleolus
C. The nuclei of satellite cells from a complete capsule C Gray’s Anatomy 39/e, p. 43
around each neuron
D. The cells are scattered among the fascicles of nerve
2. Following cells types are present in the granular layer
fibres
of cerebellar cortex except;
A. Golgi cells
D Gray’s Anatomy 39/e, p.58-59
B. Basket cells
C. Granular cells
2. All the following features are seen in neurons from D. Monodendritic cells of brush
dorsal root ganglia,except-AI 2002
A. They have centrally located nuclei Essentials of Human Anatomy, 3/e, A.K
B
B. They are derived from neural crest cells Datta p.162
C. They are multipolar
D. They contain, lipofuscin granules 3. Following cell types are present in the granular layer
Ans:- C i.e. They are multipolar of cerebellular cortex except;

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 NEUROANATOMY 9
Neurohistology

A. These are synaptic complexes in the granular layer C. Internal pyramidal cell layer (ganglionic layer)
of cerebellar cortex D. Multiform layer
B. At the center is a mossy fibre terminal
C. Mossy fibre terminal synapses with dendrites of Essentials of Human Anatomy, 3/e, A.K
C
granular golgi cells Datta vol 4 p.54
D. Axons of baskets cells also form synapses with
mossy fibre terminals at the glomerulus.

8. A typical granular cortex appears in the following

Essentials of Human Anatomy, 3/e, A.K
A parts of cerebral cortex except
Datta vol 4 p.162
A. Post central gyrus
B. Striate cortex
C. Striate cortex
4. Following fibres are present in the molecular layer of D. Cornu ammonius
cerebellar cortex except;
A. Mossy fibres Essentials of Human Anatomy, 3/e, A.K
D
B. Dendrities of the purkinje cells Datta vol 4 p.55-92
C. Dendrities of golgi neuron
D. Dendrities and axons of baskets cells.

9. Betz cells’ are predominantly present in the following

Essentials of Human Anatomy, 3/e, A.K
C part of cerebral cortex?
Datta vol 4 p.162
A. Precentral gyrus
B. Postcentral gyrus
C. Hippocampus
5. Following neurons of cerebellum form inhibitory D. Occipital cortex
synapses with purkinje cells except;
A. Golgi cells Essentials of Human Anatomy, 3/e, A.K
A
B. Basket cells Datta vol 4 p.55
C. Granule cells
D. Satellaite cells
PIGMENTS AND INCLUSIONS
Essentials of Human Anatomy, 3/e, A.K
C
Datta vol 4 p.163-64 1. Osmic acid stain is used for staining the following
part of a nerve fibre;
6. Following part of limbic lobe of cerebrum has A. Neurilemma sheath
trilaminar structure except; B. Myelin sheath
A. Dentate gyrus C. Schwann cell
B. Cornu ammonis D. Axon of a nerve fibres
C. Subiculum
D. Parahippocampal gyrus B Gray’s Anatomy 39/e, p.56-57

Essentials of Human Anatomy, 3/e, A.K

D
Datta vol 4 p.92

7. Inner band of baillarger is present in the following

layer of cerebral cortex?
A. External granular layer
B. Internal granular layer
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Neurohistology

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