Download MBBS Nervous Tissue Lecture PPT

INTRODUCTION

? Nervous tissue--> Consists of two types of cells:

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neurons (nerve cells) and neuroglial cell.

? Nervous tissue has property of irritability and

conductivity.

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? Nerve cells are capable of receiving information from

external and internal environment.

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? 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.

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COMPOSITION OF NERVOUS TISSUE

1)Neuron (nerve cell)--Structural and functional units

of nervous system.

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2)Nerve cell processes--Many radiating processes

called dendrite and a single process called axon.

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3)Neuroglia--Supporting function for neurons and

their processes.
? NEURON--
? Functional cell of nervous tissue.

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? Consists of
Nerve Cell body -- Expanded portion.

Nerve cell processes-- Dendrite and axon,

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emerges from cell body.
? Nerve cell body--
? Contains:--
? Nucleus--large, spherical and centrally located.

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? Nissl bodies--large aggregations of rough

endoplasmic reticulum.

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? Melanin pigments--dark brown granules in

substantia nigra.

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Neurons (Nerve Cells)

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Figure 11.4b

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? Nerve cell processes--

? Elongated cytoplasmic processes originate from

the cell body

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? Two types ? Axon (single)
- Dendrite (multiple)
? Nerve fibre term used for nerve cell process

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(axon or dendrites).
? Dendrites--
? Multiple, short, branched and tapering processes

of nerve cell.

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? Receive information from other cells (input

portion of neuron).

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? Cytoplasm contains--Nissl bodies, microtubules,

microfilament and other organells.
? Axon--
? Single, long, cylindrical process of nerve cell.

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? Send information away from nerve cell body to

another cell.

? Axon hillock-- Conical origin of axon from cell body

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? Axon terminals are known as end bulbs (terminal

boutons).

? Axolemma--Plasma membrane of axon

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? Axoplasm-- Cytoplasm of axon.
? Nissl bodies is absent in axon.


Neurons (Nerve Cells)

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Figure 11.4b
DIFFERENCE BETWEEN AXON & DENDRITE

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AXON

DENDRITE

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SINGLE, LONG THIN PROCESS OF MULTIPLE, SHORT, THICK &

NERVE CELL

TAPERING PROCESSES OF NERVE

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CELL

TERMINATES AWAY FROM NERVE TERMINATES NEAR THE NERVE

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CELL BODY

CELL BODY

UNIFORM DIAMETER & SMOOTH NOT UNIFORM

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FREE OF NISSL GRANULES

CONTAIN NISSL GRANULES

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NERVE IMPULSE TRAVELS AWAY IMPULSE TRAVELS TOWARDS

FROM CELL BODY

CELL BODY

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CLASSIFICATION OF NEURONS

? BASED ON SHAPE OF CELL BODY & NUMBER OF CELL PROCESSES

? UNIPOLAR NEURONS--

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? Only one process (usually dendrite) extending from

cell body.

? Mesencephalic nucleus of trigeminal nerve.

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? PSEUDOUNIPOLAR NEURON--
? Has one process that divide into axon and dendrite.
? Dorsal root ganglion and cranial nerve ganglion.
? BIPOLAR NEURONS--

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? Has two processes(an axon and dendrite).
? Present in Retina.

? MULTIPOLAR NEURONS--
? Has many processes (an axon and many dendrite).

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? These are most common type of neurons
? Depending upon shape of cell bodies they are called

stellate (star shaped), purkinje (flask shaped) or

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pyramidal (triangular).

? Present in spinal cord, cerebrum & cerebellum.

? CLASSIFICATION BASED ON FUNCTION

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? SENSORY (AFFERENT)--
? Receives stimuli from receptor and conduct impulse

to CNS.

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? MOTOR (EFFERENT)--
? Conduct impulse from CNS to effector organs.

? INTERNEURON--

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? Located only in CNS .
? Small size, interconnect other neuron.
Synapses

? A junction that mediates information transfer

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from one neuron:

? To another neuron
? To an effector cell

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? Presynaptic neuron ? conducts impulses

toward the synapse

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? Postsynaptic neuron ? transmits impulses

away from the synapse

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Structure of synapse

Action

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potential

Neurotransmitter

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Na+

Ca2+

Axon terminal of

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1

presynaptic neuron

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Receptor

Postsynaptic

Mitochondrion

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membrane

Axon of

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Postsynaptic

presynaptic

membrane

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neuron

Ion channel open

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Synaptic vesicles

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containing

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neurotransmitter
molecules

Degraded

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2

neurotransmitter

Synaptic

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cleft

3

4

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Ion channel closed

Ion channel

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Ion channel (open)

(closed)

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Figure 11.18
Types of Synapses

? Axodendritic ? between the axon of one

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neuron and the dendrite of another.

Most common type.

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? Axosomatic ? between the axon of one

neuron and the soma of another.

? Axoaxonic- between one axon to other axon .

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NEUROGLIA

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? Neuroglia

? Provide structural and metabolic support for neurons.
? Segregate and insulate neurons.

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? Neuroglial cells in CNS

a)Astocytes

b)Ependymal cell

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c)Oligodendrocytes

d)Microglia

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? Neuroglial cells in PNS

a)Schwann cells

b)Satellite cells

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SIZE

LARGE

LARGE

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MEDIUM

SMALL

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NUCLEUS

OVAL

OVAL

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SPHERICAL

ELONGATED

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OCCURRENCE GREY MATTER

WHITE MATTER

WHITE MATTER

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GREY AND

WHITE MATTER

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FUNCTION

SUPPORTING,

MYELINATION

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PHAGOCYTOSIS

REPAIR AND

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BARRIER

ORIGINE

NEURONAL

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NEURONAL

MESODERMAL

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ECTODERM

ECTODERM
MYELIN SHEATH

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? Myelin is an insulating sheath surrounding axons

of central and peripheral nervous system.

? CNS-- Oligodendrocytes cells

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? PNS-- Schwann cells
? Between adjacent segment of myelin along each

axon, a gap occurs where axon is not covered by

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myelin.

? These gaps are called are called nodes of Ranvier.
? Myelin sheath increases the velocity of

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conduction of impulse.

? It provides insulating sheath surrounding fibres.