Transcript Nervous Tissues

Nervous Tissues
Department of
Biology
Introduction

Nervous tissues are formed of cell
specialized to receive external and internal
stimuli and to transmit them between different
parts of the body.

Coordination of the different activities of body
organs.
Introduction
Originate from the ectoderm.
 The cells become differentiated in one of 2 way:
1. Some ectodermal cell differentiated into
neuroblasts. Multiply actively and transform
gradually into nerve cells (neurons) do not
multiplication.
2. Other ectodermal cell differentiated into
spongioblasts. Continue modification forming
neuroglia cells (bind and protect the neurons)

Structure of the nerve cell
The nerve cell or Neuron consist of two parts:
 The cell body (Cyton).
 Cytoplasmic processes:
1. Dendrites, receive the stimuli and transmit the
impulses to the nerve cell body.
2. Axon, extend from the cell body and ends in a
number of small branches (terminal arborizations)
carry the nerve impulses from the nerve cell
outwards. The axons of several neurons collect
together to form Nerves.
Cell body (Cyton)



Located in certain nervous organs (brain,
spinal cord and nerve ganglia. From these
organs nerves extend to different tissues.
The cytons differ in size and shape, some
few microns and other hundreds microns
in diameter.
May be round, ovoid, spindle, star-shaped
Cell body (Cyton)



The cell body contain
central spherical
nucleus with one or
more nucleoli.
Cytoplasm contains:
Golgi apparatus,
mitochondria,
lysosomes as well as
other common
cytoplasmic organelles
and inclusions
No centriole.
Cell body (Cyton)
 Nissel bodies: granules,
found also in dendrites,
but not in axons, rich in
ribonucleic acid.
 Neurofibrils: fine threadlike structure, form
network, provide
pathway for the nerve
impulses within nerve
cells.
Nerve Fibers




Nerve fiber consists
of an axis cylinder
surrounded by
myelin sheath.
This layer covered
by neurilemma.
Node of Ranvier
Internode.
Nerve Fibers

Schwann’s cell,
responsible for the
formation of myelin
sheath and
neurilemma.
Nerve Fibers
The nerve fibers two types
1. Meduullated nerve fibers have myelin
sheath, found in cranial and spinal nerves.
2. Non -meduullated nerve fibers which lacks
myelin sheath. Found in the sympathetic
nerves.
Nerves
A nerve consist of bundles of myelinated
nerve fibers extend parallel to each other.
 Each nerve fiber appears circular in cross
section and the axon in the center
Endoneurium: Loose C.T.surround the nerve
fiber.
Perineurium: C.T. surround the nerve bundle.
Epineurium: C.T. surround the whole nerves

Peripheral Nerve (cross section) 40X
epineurium
perineurium
Spinal Cord



1.
2.
Surrounded by C.T., pia mater and has central canal.
Dorsal fissure above the central canal and ventral
fissure below it.
The substance of the cord is differentiated into:
Inner region Gray matter with 2 dorsal horns and 2
ventral horns. This region contains nerve cell bodies
and some dendrites all supported by neuroglia cells.
White matter surround the gray matter, composed of
myelinated nerve fibers supported by the neuroglia
projecting from the gray matter.