i want 20 mcq with their model answer below each question about : NERVOUS TISSUE Nerve cells (neurons) Cell body
Structure: Cell body (Perikaryon)
It is part of neuron containing nucleus and surrounding cytoplasm.
*Size: varies from 4 um as in granular cells in cerebellar cortex to
100um as in motor neurons
*Shape: depends on number of cell processes;
unipolar have globular shape.
Bipolar have fusiform shape.
Multipolar are stellate, pyramidal or pyriform.
Nucleus: large spherical, euchromatic with a prominent nucleolus
(active cell)The cytoplasm:
1.It contains highly developed REr & numerous
polyribosomes appears under L.M as
basophilic granular areas called Nissl bodies.
varies
according to
neuronal
function.
2.Golgi complex present around nucleus.
3.Mitochondria are scattered
throughout the cytoplasm.
4. Neurofilaments (intermediate filaments
with a diameter of 10nm) are abundant in Perikaryon &
processes. visible by L.M (stained brown by Ag).
They provide structural support.5. Microtubules (20-28 nm in diameter)arranged in parallel bundles in Perikaryon & processes.They are involved in axonal transport of neurotransmitter substances, enzymes 6. Centrioles cannot be seen as neurons cannot divide. 7. Inclusions in form of ; ►Lipofuscin pigment is golden brown.It is a residue of undigested material by lysosomes. increases with aging. ►Melanin pigment dark brown or black is found in neurons of substantia nigra of mid brain. ►Lipid droplets in cytoplasm represent energy reserve or products of abnormal metabolism.Processes
Both dendrites & axon have mitochondria, neurofibrils & microtubules
Axon
Dendrites
1. Usually numerous
2. Short.
3.
Thick.
4. Branching like a tree. Branches arise at acute angle
5. Become thinner as they subdivide into branches.
contain Nissl granules.
6.
7.Covered by spine like processes called dendritic spines
that for synaptic contacts
f
r
o
m
8.
Carries nerve impulses to the cell body.
1. Single
2. Long
3. Thin.
4. Not branching except at the end.
arise at right angle
5. has aconstant diameter.
6. Does not Contain Nissl bodies.
7.No spines
8.Carry nerve impulses away the cell
body.Classification of neurons:
A-They are classified according to number of processes into:
1.Unipolar : have a single process that is close to the Perikaryon and divides into 2 branches to form a T shape, with one branch extending to a peripheral ending to act functionally as a dendrite
It is found in the spinal ganglia and mesencephalic nucleus of trigeminal nerve.
2.Bipolar: have(1)dendrite &(1)axon.-in cochlear & vestibular G. in ear, retina in eye & olfactory in nose .
3. Multipolar: have one axon and many dendrites. They take different forms: ► Stellate anterior horn cells in spinal cord. ► Pyramidal  pyramidal cells in cerebral cortex. ► Pyriform as purkinje cells in cerebellar cortex.Classification of neurons:
B- According to function:
1. Sensory (afferent) neurons
receive sensory stimuli as cells of
dorsal root ganglion.
2.Motor (efferent) neurons control
effector organs such as M.& glands
as anterior horn in spinal cord.
3.Interneurons connect nuerons as
in retina and spinal cord.Classification of neurons:
C- According to length of axon:
1.Golgi type I: neurons have long axon that
leaves grey matter & enters white matter as
motor neurons in spinal cord, pyramidal cells
in cerebral cortex and purkinje cells in cerebellar
cortex.
2.Golgi type II:neurons have short axon that
does'nt leave grey matter as interneuron in
cerebral & cerebellar .Golgi
Length of Axon
Type I
(pyramidal cells of cerebral cortex)
Golgi Type II
(granular cells of cerebellum)
sensory neuron
receptor
Interneuron
motor neuron
Function
effectorNerve fiber
►A nerve fibre consists of
an axon.
►The axon is covered by
axolemma and contains
cytoplasm called axoplasm.
►It arises from a conical
extension of the cell body
called axon hillock.Types of nerve fibres:
1. Unmyelinated nerve fibres: have no
myelin sheath. It is subdivided into:
• Unmyelinated fibres without sheath of Schwann cells
(neurolemma) -as in gray matter (Naked).
• Unmyelinated nerve fibres with sheath of Schwann cells as in
sympathetic post ganglionic fibres.
2. Myelinated nerve fibres:
have myelin sheath. It is subdivided into:
• Myelinated nerve fibres without sheath of Schwann cells as
in white matter.
• Myelinated nerve fibres with sheath of Schwann cells as in
peripheral nerve fibres.The sheath of Schwann
• It consists of flattened cells
with flattened nuclei that form a
thin chain around myelin of a
nerve fiber.
• Functions:
1.Formation of myelin sheath in
the peripheral nerves .
2.Electric insulation.
3.Regeneration where axon
grows from the proximal stump
along the path formed by
Schwann cells.Myelin Sheath:
Structure Formed of many layers of modified cell membranes with higher lipids than cell membrane. • L.M Lipoprotein so dissolves after routine fixation and Can be stained black by osmic acid •E/Mappears as fused spiral laminae of plasmalemma. •It shows gaps called nodes of Ranvier that represent the spaces between adjacent sheath cells. •sheath of myelin is thus divided into segments by the nodes which are called internodal segments. •Each Schwann cell wraps around one segment of a single axon in PNS while each oligodendroglia cell warps around one segment of many axons (10-60) INPeripheral Nervous System
It consists of Nerves, ganglia and nerve endings.Peripheral Nerve
Epineurium The nerve is covered by dense connective tissue Perineurium The nerve fibers are arranged in the form of bundles . Endoneurium Inside the bundle the nerve fibres are connected by (sheath of Henle). It consists of reticular fibres formed by Schwann cells. It is formed of flattened epithelium like cells
joined by tight junctions. This forms a barrier to protect the nerve fibres.Ganglia
They are collection of nerve
cells outside the central
nervous system.
They are of 2 types;
sensory (spinal) &
autonomic (sympathetic
and parasympathetic).Spinal Ganglion
1)Covered by a thick C.T. Capsule.
2) Contains no synapses
3) Contains unipolar neurons
4) Nerve cells are small, medium-
sized or large(15-100 um).
5) Nerve cells are rounded
Sympathetic Ganglion
1) Covered by a thin C.T. capsule
2) Contains synapses
3)Contains multipolar stellate neurons
4) Nerve cells show a uniform size
(25 um).
5) Nerve cells are stellateSpinal Ganglion
6) Nerve cells are arranged in group
of rows, separated by nerve and C.T
7) Nerve cells are capsulated by the
satellite cells
8) Nerve fibres may become
convoluted forming glomeruli.
9) Nerve fibres are myelinated
10) Poor blood supply
Sympathetic Ganglion
6) Nerve cells are scattered.
7) Satellite cells are only found in
large ganglia.
8) No glomeruli are formed by the
nerve fibres.
9) non myelinated
10) Rich blood supply.Synapse
Histologically: it is formed of;
1.Presynaptic
side rich
vesicles
of
in
mitochondria and
chemical transmitter (in chemical synapse).
It shows separate zones of dense cytoplasm.
2.Synaptic cleft: 20-30 nm in width.
It shows delicate fibres or granules.
3.Postsynaptic side that has receptors for the chemical
transmitter.
It shows a continuous zone of dense cytoplasm which is
associated with a network of filaments called synaptic web.NEUROGLIA
Glial cells are 10 times more abundant in the
mammalian brain than neurons.
They surround the cell bodies and processes.Astrocytes (Macroglia):
•large Star shaped cells with
multiple processes.
•They have large pale nucleus.
•They have Centrioles so can
divide &form tumors.
•By E/M, they show bundles of
intermediate filaments that keep
their shape.
•They are ectodermal in origin.
•In grey matter and white matter.Astrocytes (Macroglia):
••Functions:
1.They have processes with
expanded end feet linked to
endothelium of blood capillaries so
can control metabolic exchanges
between nerve cell and blood.
2.Blood brain barrier.
3.Structural support.
4.Repair process by formation of
scar tissue.
There are 2 types;Fibrous astrocytes
In white matter.
Cytoplasm is fibrillary.
Few long processes.
Cytoplasmic astrocytes
In grey matter.
Cytoplasm is granular.
Many short processes.Oligodendrocytes
•They are medium sized cells which
have few processes.
•medium dark nucleus.
 They have Centrioles.
 Dense dark cytoplasm
rich
in
endoplasmic reticulum, Golgi
body, ribosomes and mitochondria.
 Ectodermal in origin.
Present in both grey and white matter.
There are 2 types;Interfasicular Oligodendrocytes
Satellite Oligodendrocytes
In white matter in between bundles of axons
Formation of myelin sheath and electric insulation
In Grey matter
closely associated with the cell body of neurons
Support nerve cells.