Download MBBS (Bachelor of Medicine and Bachelor of Surgery) Latest Nervous Tissue Lecture PPT
INTRODUCTION
? Nervous tissue--> Consists of two types of cells:
neurons (nerve cells) and neuroglial cell.
? Nervous tissue has property of irritability and
conductivity.
? Nerve cells are capable of receiving information from
external and internal environment.
? About 10 million neurons in human beings.
? Size of neuron 10 um to 120 um
? Neurons do not divide after birth, so their number
does not increases during lifetime.
COMPOSITION OF NERVOUS TISSUE
1)Neuron (nerve cell)--Structural and functional units
of nervous system.
2)Nerve cell processes--Many radiating processes
called dendrite and a single process called axon.
3)Neuroglia--Supporting function for neurons and
their processes.
? NEURON--
? Functional cell of nervous tissue.
? Consists of
Nerve Cell body -- Expanded portion.
Nerve cell processes-- Dendrite and axon,
emerges from cell body.
? Nerve cell body--
? Contains:--
? Nucleus--large, spherical and centrally located.
? Nissl bodies--large aggregations of rough
endoplasmic reticulum.
? Melanin pigments--dark brown granules in
substantia nigra.
Neurons (Nerve Cells)
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Figure 11.4b
? Nerve cell processes--
? Elongated cytoplasmic processes originate from
the cell body
? Two types ? Axon (single)
- Dendrite (multiple)
? Nerve fibre term used for nerve cell process
(axon or dendrites).
? Dendrites--
? Multiple, short, branched and tapering processes
of nerve cell.
? Receive information from other cells (input
portion of neuron).
? Cytoplasm contains--Nissl bodies, microtubules,
microfilament and other organells.
? Axon--
? Single, long, cylindrical process of nerve cell.
? Send information away from nerve cell body to
another cell.
? Axon hillock-- Conical origin of axon from cell body
? Axon terminals are known as end bulbs (terminal
boutons).
? Axolemma--Plasma membrane of axon
? Axoplasm-- Cytoplasm of axon.
? Nissl bodies is absent in axon.
Neurons (Nerve Cells)
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Figure 11.4b
DIFFERENCE BETWEEN AXON & DENDRITE
AXON
DENDRITE
SINGLE, LONG THIN PROCESS OF MULTIPLE, SHORT, THICK &
NERVE CELL
TAPERING PROCESSES OF NERVE
CELL
TERMINATES AWAY FROM NERVE TERMINATES NEAR THE NERVE
CELL BODY
CELL BODY
UNIFORM DIAMETER & SMOOTH NOT UNIFORM
FREE OF NISSL GRANULES
CONTAIN NISSL GRANULES
NERVE IMPULSE TRAVELS AWAY IMPULSE TRAVELS TOWARDS
FROM CELL BODY
CELL BODY
CLASSIFICATION OF NEURONS
? BASED ON SHAPE OF CELL BODY & NUMBER OF CELL PROCESSES
? UNIPOLAR NEURONS--
? Only one process (usually dendrite) extending from
cell body.
? Mesencephalic nucleus of trigeminal nerve.
? PSEUDOUNIPOLAR NEURON--
? Has one process that divide into axon and dendrite.
? Dorsal root ganglion and cranial nerve ganglion.
? BIPOLAR NEURONS--
? Has two processes(an axon and dendrite).
? Present in Retina.
? MULTIPOLAR NEURONS--
? Has many processes (an axon and many dendrite).
? These are most common type of neurons
? Depending upon shape of cell bodies they are called
stellate (star shaped), purkinje (flask shaped) or
pyramidal (triangular).
? Present in spinal cord, cerebrum & cerebellum.
? CLASSIFICATION BASED ON FUNCTION
? SENSORY (AFFERENT)--
? Receives stimuli from receptor and conduct impulse
to CNS.
? MOTOR (EFFERENT)--
? Conduct impulse from CNS to effector organs.
? INTERNEURON--
? Located only in CNS .
? Small size, interconnect other neuron.
Synapses
? A junction that mediates information transfer
from one neuron:
? To another neuron
? To an effector cell
? Presynaptic neuron ? conducts impulses
toward the synapse
? Postsynaptic neuron ? transmits impulses
away from the synapse
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Structure of synapse
Action
potential
Neurotransmitter
Na+
Ca2+
Axon terminal of
1
presynaptic neuron
Receptor
Postsynaptic
Mitochondrion
membrane
Axon of
Postsynaptic
presynaptic
membrane
neuron
Ion channel open
Synaptic vesicles
5
containing
neurotransmitter
molecules
Degraded
2
neurotransmitter
Synaptic
cleft
3
4
Ion channel closed
Ion channel
Ion channel (open)
(closed)
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Figure 11.18
Types of Synapses
? Axodendritic ? between the axon of one
neuron and the dendrite of another.
Most common type.
? Axosomatic ? between the axon of one
neuron and the soma of another.
? Axoaxonic- between one axon to other axon .
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NEUROGLIA
? Neuroglia
? Provide structural and metabolic support for neurons.
? Segregate and insulate neurons.
? Neuroglial cells in CNS
a)Astocytes
b)Ependymal cell
c)Oligodendrocytes
d)Microglia
? Neuroglial cells in PNS
a)Schwann cells
b)Satellite cells
SIZE
LARGE
LARGE
MEDIUM
SMALL
NUCLEUS
OVAL
OVAL
SPHERICAL
ELONGATED
OCCURRENCE GREY MATTER
WHITE MATTER
WHITE MATTER
GREY AND
WHITE MATTER
FUNCTION
SUPPORTING,
MYELINATION
PHAGOCYTOSIS
REPAIR AND
BARRIER
ORIGINE
NEURONAL
NEURONAL
MESODERMAL
ECTODERM
ECTODERM
MYELIN SHEATH
? Myelin is an insulating sheath surrounding axons
of central and peripheral nervous system.
? CNS-- Oligodendrocytes cells
? PNS-- Schwann cells
? Between adjacent segment of myelin along each
axon, a gap occurs where axon is not covered by
myelin.
? These gaps are called are called nodes of Ranvier.
? Myelin sheath increases the velocity of
conduction of impulse.
? It provides insulating sheath surrounding fibres.
This post was last modified on 30 November 2021