NERVE TISSUE
AND THE
NERVOUS
SYSTEM
AUTHOR: JOELLE MANUELA KAPNANG
NOUKETCHEUSSI
OBJECTIVES
Introduction with the Central Nervous
System (CNS), Peripheral Nervous
System (PNS) and Neural Plasticity and
Regeneration

Introduction of the nerve tissue

Know the development of the nerves
tissue

Types of tissues in the CNS

Structure of a neuron

Meninges in the CNS

Function of synaptic communication

Define ganglia, gray matter, and
white matter


Role of neural plasticity and
regeneration
Enlist the names and function of
different types of neurons and
neuroglia

INTRODUCTION TO THE CENTRAL NERVOUS SYSTEM
(CNS)
Cerebrum, cerebellum
and the spinal cord are
the major structures of
the CNS
The human CNS is a
network of more than
100 billion of individuals
nerve cells
The CNS is covered by
connective tissue
layers, the meninges
The CNS contains few
collagen or similar
material making it
relatively soft and easily
damaged by injuries
affecting the
protectives skull or
vertebral bones
INTRODUCTION TO THE PERIPHERAL NERVOUS SYSTEM (PNS)
The majors
components of the PNS
are the nerves fibers,
the ganglia and the
nerves ending.
The PNS are linked to
the brain and the
spinal which are parts
of the CNS
The PNS is subdivided
into autonomic nervous
system and somatic
nervous system
INTRODUCTION TO NEURAL PLASTICITY AND
REGENERATION

The concept of brain plasticity covers all
the mechanisms involved in the capacity
of the brain to adjust and remodel itself in
response to environmental requirements,
experience, skills acquisition, and the new
challenges including the brain lesions.

Neural plasticity and reformation are
controlled by several growth factors
produced by both neurons and glial cells in
a family of proteins called neurotrophins.
NERVOUS SYSTEM
Sympathetic
division
(arousing)
Parasympathetic
division (calming)
Sensory
(afferent)
nervous system
Motor
(efferent)
nervous system
PERIPHERAL
NERVOUS
SYSTEM
Autonomic nervous system
which communicates with
Internal organs and gland
Somatic nervous system
which communicate with
sense organs and
voluntary muscles.
I- THE CENTRAL NERVOUS SYSTEM (CNS)
1.a) GRAY MATTER
1
- Gray matter consist
primarily of neuronal
cell bodies or soma,
dendrites astrocytes,
and microglial cells.
2
3
- Most synapse occurs in
this region
- Gray matter makes up
the thick cortex or
surface layer of both
the cerebrum and
cerebellum.
Mainly composed of myelinated
axons which are often grouped
together as tracts, and the myelin
producing oligodendrocytes.
Astrocytes and microglia are also
present but few neuronal cell bodies
It is found in deeper regions. Deep
within the brain are localized, variously
shaped darker areas which are called
cerebral nuclei, each containing large
numbers of aggregated neuronal cell
bodies.
2.b) WHITE
MATTER
c) ARRANGEMENT OF
WHITE AND GREY
MATTER IN THE BRAIN

Both gray and white
matter are sprayed
throughout the CNS :
the brain and the
spinal cord.

In cross section of the
spinal cord, the white
matter is peripheral
and the gray matter
forms a deeper Hshaped mass.
Cont.

Neuroscientists recognize six layers of
neurons in the folded cerebral cortex.
They all have different sizes and shapes.

The efferent pyramidal neurons is the
most conspicuous of those cells.
Neurons of the cerebral cortex function
in the integration of sensory information
and the initiation of voluntary motor
responses.

The cerebellar cortex coordinates
muscles activity throughout the body
and it is organized with three layers:
- thick outer molecular layers
- thin middle layer which have very
large amount of neurons called
Purkinje cells
- thick inner granular layer.

Gray matter
cont.
The gray matters have two anterior and
posterior projections:
- the anterior horn : contain cell
bodies of very large motor neurons
whose axons make up the ventral roots
of spinal nerves
- the two posterior horns: contains
interneurons which receive sensory
fibers from neurons in the spinal
ganglia.
Both Figure of the cerebral
cortex
A
B
P
P
C
e
r
e
b
r
a
l
c
o
rt
e
x
P
A
Cerebellum
ML
ML
GL
GL
P
M
M
A
B
C
P
Spinal
cord
A
B
2) THE MENINGES IN THE CNS

The skull and the vertebral column protect
the CNS, but between the bone and
nervous tissue are membranes of
connective tissue called the meninges

The meninges are series of membranes that
covers the CNS.

They consist of three layers: the dura mater,
the arachnoid mater and the pia mater.

These layers cover the brain and the spinal
cord with the primary function of protecting
and nourishing the CNS.
2.a) the dura mater

It is the a thick, durable membrane, and is closest to
the skull

It consists of dense irregular tissue organized as an
outer periosteal layer continuous with the periosteum
of the skull and an inner meningeal layer.

It is responsible for keeping the cerebrospinal fluid,
and for surrounding and supporting the Dural venous
sinuses that carry blood from the brain to the heart.

It is composed of two components:
- a sheet of connective tissue in
contact with the dura mater
- a system loosely arranged trabeculae
composed of collagen and
fibroblasts, continuous with the pia
mater layer.
2.b) the
Arachnoid
mater

Surrounding these trabeculae is a large,
sponge like cavity called the
subarachnoid space. It communicates
with the ventricles of the brain where
the CSF is produced.

The connective tissue of the arachnoid
is said to be avascular because it lacks
nutritive capillaries, but larger blood
vessels run through it where the
Cerebrospinal Fluid (CSF) is produced.
Cont.

Arachnoid granulations also known as
arachnoid villi are small protrusions of the
arachnoid mater into the cuter membrane
of the dura matter.

They protrude into the Dural venous sinuses
if the brain, and allow CSF to exit the
subarachnoid space and enter the blood
stream
2.c) the pia mater

It is the innermost layer of the meninges and envelops
and firmly attaches to the surface of the brain and
spinal cord.

It consists of flattened, mesenchymally derived cells
closely applied to the entire surface of the CNS tissue.

The pia mater contains bloods vessels and capillaries
that are responsible for nourishing the brain.
Picture of Meninges around the brain
3) THE BLOOD-BRAIN BARRIER (BBB)

BBB is a protecting structure which gives tight control
over the passage of substances moving from blood to
the tissues of the CNS. It is essential for ensuring the
specific nature of the neuronal microenvironment.

They are composed of capillary endothelium, in which
the cells are tightly sealed together and well-develop
occluding junctions, with little or no transcytosis
activity, and surrounded by the basement
membrane.

The BBB protects neurons and glia from bacterial
toxins, infectious agents, and other exogenous
substances.

It also helps maintaining the stable composition and
constant balance of ions in the interstitial fluid required
for normal neuronal function.
4) CHOROID PLEXUS

It consists of highly vascular tissue,
elaborately folded and projecting into
large ventricles of the brain.

It is found in the roofs of the third and
fourth ventricles and in parts of the two
lateral ventricular walls, all regions in
which the ependymal lining directly
contacts the pia mater.

It has for function to remove water from
blood and release it as the CSF.
II- PERIPHERAL NERVOUS SYSTEM (PNS)
1.a) Nerve Fibers

Nerve fibers are analogous to tracts in the CNS and
are containing axons enclosed within sheaths of glial
cells specialized to facilitate axonal function.

Axons are sheathed by Schwann cells in the
peripheral nerve fibers.

Depending on their diameter, the sheath may or
may nor form myelin around the axons.

The multiple layers of Schwann cell membrane unite
as a thick myelin sheath.
Cont.
Myelinated fibers are axons of large diameter growth
in the PNS, and they are engulfed along their length
by a series of differentiating neurolem-mocytes and
become myelinated fibers.
The major dense lines represents the fused, protein-rich
cytoplasmic surfaces of the Schwann cell membrane.
In the Unmyelinated fibers (UF), the glial cell does not
form the multiple wrapping of a myelin sheath.
• In the UF, each Schwann cell can enclose portions of many
axons with small diameter.
• Without the thick myelin sheath, nodes of Ranvier are not
seen along UF.
2.b) Nerve organization

Peripheral nerves have multiple layers of connective tissue surrounding
axons.

the endoneurium surrounding individual axons binding the fascicles into a
nerve, and perineurium binding axons into fascicles

Nerves fibers in peripheral nerves are wavy such that length of peripherical
nerve can be stretched to half again its length before tension is directly
transmitted to nerve fibers.

Nerve roots have much less connective tissue, and individual nerves within
the roots are straight leading to some vulnerability.

Peripheral nerves establish communication between centers in the CNS
and the sense organs and effectors (muscles, glands, etc.)
2.c) Ganglia

There are two types of ganglia: sensory ganglia and autonomic ganglia

Sensory ganglia receive afferent impulses that go to the CNS. Sensory ganglia are
associated with both cranial nerves (cranial ganglia) and the dorsal roots of the spinal
nerves (spinal ganglia).
- Sensory ganglia are supported by a distinct connective tissue capsule and an
internal framework continuous with the connective tissue layers of the nerves

Autonomic ganglia are small bulbous dilations in autonomic nerves, usually with
multipolar neurons. Some are located within certain organs, especially in the walls of
the digestive tract, where they constitute the intramural ganglia
-Autonomic ganglia nerves effect the activity of smooth muscle, the secretion of
some glands, heart rate, and many other involuntary activities by which the body maintains
a constant internal environment (homeostasis).
III. NEURAL PLASTICITY AND REGENERATION

Certain regions of the CNS, such as near the ependyma,
retain rare neural stem and progenitor cells that allow
some replacement of neurons throughout life; neural
plasticity involving formation and remodeling of synaptic
connections is also prevalent throughout life.

The complexity and distances of the neuronal and glial
interconnections with the CNS make regeneration and
restoration of function within this tissue after major injury
very difficult.

The more simply organized peripheral nerves have better
capacity for axonal regeneration, a process involving
reactivation of the perikaryon, Schwann cells, and
macrophages.
PART 2- DEVELOPMENT OF NERVE TISSUE

The nervous system develops
from the outermost of the
three early embryonic layers,
the ectoderm, beginning in
the third week of
development with signals
from the underlying axial
structure, the notochord,
ectoderm on the mid-dorsal
side of the embryo thickens
to form the epithelial neural
plate.
A- NEURONS

Neurons are the basic unit of the nervous system. All cells of the nervous system are
comprised of neurons. Neurons contains nerve processes which are "finger-like"
projections that extend from the nerve cell body. The nerve processes consist of axons
and dendrites which are able to conduct and transmit signals. Axons typically carry
signals away from the cell body. They are long nerve processes that may branch out to
convey signals to various areas. Dendrites typically carry signals toward the cell body.
They are usually more numerous, shorter and more branched than axons.

Axons and dendrites are bundled together into what are called nerves. These nerves send
signals between the brain, spinal cord, and other body organs via nerve impulses.
Neurons are classified as either motor, sensory, or interneurons. Motor neurons carry
information from the central nervous system to organs, glands, and muscles. Sensory
neurons send information to the central nervous system from internal organs or from
external stimuli. Interneurons relay signals between the motor and sensory neurons.

Structure of a neuron
A
“typical” neuron has three major parts:
(1) The cell body also called the perikaryon or soma is often
large, with a large, euchromatic nucleus and well-developed
nucleolus. The cytoplasmic contains basophilic Nissl substance
or Nissl bodies, which are large masses of free polysomes and
RER indicating the cell’s high rate of protein synthesis.

(2) Numerous short dendrites extend from the perikaryon,
receiving input from other neurons

(3)
A long axon carries impulses from the cell body and is
covered by a myelin sheath composed of other cells. The ends
of axons usually have many small branches (telodendria),
each of which ends in a knob-like structure that forms part of a
functional connection (synapse) with another neuron or other
cell.
Cont.
A
B
C
D
four main types of neurons:
A) Most neurons, including all motor
neurons and CNS interneurons, are
multipolar.
B) Bipolar neurons include sensory
neurons of the retina, olfactory
mucosa, and inner ear.
C) All other sensory neurons are
unipolar or pseudounipolar.
D) Anaxonic neurons of the CNS lack
true axons and do not produce
action potentials, but regulate
local electrical changes of
adjacent neurons.
\
B- SYNAPTIC COMMUNICATION

In the CNS, a synapse is a small gap at the end of a
neuron that allows a signal to pass from one neuron
to the next.

Synapses are found where nerve cells connect with
other nerve cells.

Synapses are key to the brain's function, especially
when it comes to memory
Cont.
Synapses are composed of three main parts:

The presynaptic ending that contains
neurotransmitters

The synaptic cleft between the two nerve cells

The postsynaptic ending that contains receptor sites

An electrical impulse travels down the axon of a
neuron and then triggers the release of tiny vesicles
containing neurotransmitters. These vesicles will then
bind to the membrane of the presynaptic cell,
releasing the neurotransmitters into the synapse. These
chemical messengers cross the synaptic cleft and
connect with receptor sites in the next nerve cell,
triggering an electrical impulse known as an action
potential.
C) Origin,
location and
principal
functions of
neuroglial cells.
Cont.
QUESTIONS

Which structure
contains trabeculae
around which
cerebrospinal fluid
(CSF) flows ?

Where is the white
matter found in the
CNS ?

What is the function of
Choroid plexus ?
REFERENCE

JUNQUEIRA’S BASIC HISTOLOGY, text and Atlas, 14th edition by Anthony L.
Mescher