i want 30 multiple choice questions with their model answer below each question that covers all of the following question: 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) IN
CNS.
•Peripheral 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.