introduction to CNS, neuron

1. 28-10-2019

2. • Nervous system controls all the activities of
the body.
• It is quicker than other control system in the
body, namely endocrine system.
• Primarily, nervous system is divided into two
parts:
1. Central nervous system.
2. Peripheral nervous system.

3. Nervous System:
Central Nervous
System:
Peripheral Nervous
System:
Brain Spinal Cord
Spinal NerveCranial nerve
Origin Distribution
Autonomic Nerve Fiber Somatic Nerve Fiber
Sympathetic Division Parasympathetic Division

4. CENTRAL NERVOUS SYSTEM:
• It is formed by neurons and neuroglia (supporting cells).
• Structures of brain and spinal cord are arranged in two
layers, namely gray matter and white matter.
• Gray matter is formed by nerve cell bodies and the
proximal parts of nerve fibers, arising from nerve cell
body.
• White matter is formed by remaining parts of nerve
fibers.
In brain, white matter is placed in the inner part and
gray matter is placed in the outer part.
In spinal cord, white matter is in the outer part and gray
matter is in the inner part.

7. PERIPHERAL NERVOUS SYSTEM:
• Peripheral nervous system (PNS) is formed by
neurons and their processes present in all
regions of the body.
• It consists of:
A. cranial nerves, arising from brain
B. spinal nerves, arising from the spinal cord.
• It is again divided into two subdivisions:
1. Somatic nervous system
2. Autonomic nervous system.

10. • Neuron or nerve cell is defined as the structural and
functional unit of nervous system.
• Neuron is similar to any other cell in the body, having
nucleus and all the organelles in cytoplasm.
• However, it is different from other cells by two ways:
1. Neuron has branches or processes called axon and
dendrites
2. Neuron does not have centrosome so, it cannot undergo
division.
CLASSIFICATION OF NEURON:
A. Depending upon the number of poles.
B. Depending upon the function.
C. Depending upon the length of axon.

11. A. DEPENDING UPON
THE NUMBER OF POLES:
1- Unipolar Neurons.
• both axon and
dendrite arise.
• embryonic stage in
human beings.
2- Bipolar Neurons.
• Axon arises from
one pole and
dendrites arise
from the other
pole.
3- Multipolar Neurons.
• One of the poles
gives rise to axon
and all other poles
give rise to
dendrites.
B. DEPENDING UPON
THE FUNCTION:
1- Motor or Efferent
Neurons:
• Carry the motor
impulses from
central nervous
system to
peripheral effector.
2- Sensory or Afferent
Neurons:
• Carry the sensory
impulses from
periphery to central
nervous system.
C. DEPENDING UPON
THE LENGTH OF AXON:
1- Golgi Type I
Neurons:
• Have long axons.
(motor neuron)
2- Golgi Type II
Neurons:
• Have short axons.
(sensory neuron)

13. STRUCTURE OF NEURON:
• Neuron is made up of three parts:
1. Nerve cell body.
2. Dendrite.
3. Axon.
Form the processes of neuron.
Usually called nerve fiber.
• Cell body of neuron also known soma or perikaryon.
• Cytoplasm of cell body are called neuroplasm.
• Have cell membrane, large nucleus, nissl bodies, neurofbrils,
mitochondria and golgi apparatus.
• Axon are long processes.
• Longest axon is about 1 meter
• Cell membrane (axolemma), cytoplasm (axoplasm).
• Dendrites are Branched process
• Transmits impulses towards the nerve cell
body.

15. Organization of Nerve:
• Each nerve is formed by many bundles or groups
of nerve fibers.
• Each bundle of nerve fibers is called a fasciculus
Coverings of Nerve:
1. Epineurium: tubular sheath that covers the
whole nerve.
2. Perineurium: protective sheath that covers each
fasciculus.
3. Endoneurium: protective sheath that covers each
nerve fiber (axon).

17. MYELIN SHEATH:
• Myelin sheath is a thick lipoprotein sheath that
insulates the myelinated nerve.
• The area where myelin sheath is absent is called
node of Ranvier.
• Myelin sheath is responsible for white color of
nerve fibers.

18. Functions of Myelin Sheath:
1= Faster conduction:
• The impulses jump from one node to another
node, is called saltatory conduction.
2= Insulating capacity:
• Restricts the nerve impulse within single nerve fiber and
prevents the stimulation of neighboring nerve fibers.

19. NEURILEMMA:
• Neurilemma is a thin membrane, which surrounds
the axis cylinder It is also called neurilemmal
sheath or sheath of Schwann.
• It contains Schwann cells, which have flattened and
elongated nuclei.
• Cytoplasm is thin and modified to form the thin
sheath of neurilemma.
• In non-myelinated nerve fiber, the neurilemma
surrounds axolemma continuously.
• In myelinated nerve fiber, it covers the myelin
sheath.

20. Neurotrophins or neurotrophic factors:
• Neurotrophins or neurotrophic factors are the protein
substances, which play an important role in growth and
functioning of nervous tissue.
• Neurotrophins are secreted by many tissues in the body,
particularly muscles, neuroglial cells called astrocytes
and neurons.
1. 1. Facilitate initial growth and development of nerve
cells in central and peripheral nervous system.
2. Promote survival and repair of the nerve cells.
3. Play an important role in the maintenance of nervous
tissue and neural transmission.

22. Nerve fibers are classified by six different methods
1. DEPENDING UPON
STRUCTURE:
Myelinated Nerve Fibers Non-myelinated Nerve
Fibers
2. DEPENDING UPON
DISTRIBUTION:
Somatic Nerve Fibers
(supply skeletal muscle)
Visceral or Autonomic
Nerve Fibers (supply
internal organs )
3. DEPENDING UPON
ORIGIN:
Cranial Nerve Fibers (arising
from brain )
Spinal Nerve Fibers (arising
from spinal cord )
4. DEPENDING UPON
FUNCTION:
Sensory Nerve Fibers (carry
sensor impulses)
Motor Nerve Fibers (carry
motor impulses)
5. DEPENDING UPON
SECRETION OF
NEUROTRANSMITTER:
Adrenergic Nerve Fibers
(secretes noradrenaline)
Cholinergic Nerve Fibers
(secretes acetylcholine)
6. DEPENDING UPON
DIAMETER AND
CONDUCTION OF IMPULSE
(ERLANGER-GASSER
CLASSIFICATION) :

23. Properties of
Nerve Fibers

24. Properties: Description:
1- EXCITABILITY: Physiochemical change that occurs in a tissue when
stimulus is applied.
2- CONDUCTIVITY: The ability of nerve fibers to transmit the impulse
from the area of stimulation to the other areas
(usually one direction)
3- REFRACTORY PERIOD: The period at which the nerve does not give any
response to a stimulus.
4- SUMMATION: Is adding together one or more weak stimuli in order
to produce response.
5- ADAPTATION or
ACCOMMODATION:
The excitability of the nerve fiber is greater in the
beginning, later the response decreases slowly.
6- INFATIGABILITY: Nerve fiber can conduct only one action potential at a
time.
7- ALL-OR-NONE LAW: When a nerve is stimulated by a stimulus it gives
maximum response or does not give response at all.

25. Neuroglia

26. • Neuroglia or glia (glia = glue) is the supporting cell of
the nervous system.
• Neuroglial cells are non-excitable and do not
transmit nerve impulse (action potential).
• So, these cells are also called non-neural cells or glial
cells.
• When compared to the number of neurons, the
number of glial cells is 10 to 15 times greater.
• Neuroglial cells play an important role in the
reaction of nerve during infection.
• Most commonly, neuroglial cells constitute the site
of tumors in nervous system.

28. CLASSIFICATION OF
NEUROGLIAL CELLS:
o Astrocytes
o Microglia
o Oligodendrocytes.
o Ependymal cells
 Satellite cell
 Schwann cell.
CENTRAL NEUROGLIAL
CELLS:
PERPHRAL NEUROGLIAL
CELLS:

29. CENTRAL NEUROGLIAL
CELLS:
ASTROCYTES:
• Star-shaped neuroglial cells present in all the parts
of the brain.
• Two types:
1. Fibrous Astrocytes - Formation of blood-brain
barrier).
2. Protoplasmic Astrocytes - Supporting, maintain
the chemical environment of ECF around CNS
neurons, recycling of neurotransmitter).
MICROGLIA:
• Smallest neuroglial cells.
• Derived from monocytes and enter the tissues of
nervous system from blood.
• Changed to macrophage and migrate to the site of
infection or injury.

31. OLIGODENDROCYTES:
• Also called oligodendroglia.
• Oligodendrocytes have only few processes.
• Produce myelin sheath around the nerve fibers
in CNS.
• Provide support by forming a semi-stiff
between the neurons.
Ependymal cells
• Thin neuroectodermal lining of ventricular
system.
• Production of cerebrospinal fluid.
• Site where neuroregeneration take place

33. PERPHRAL NEUROGLIAL
CELLS:
SCHWANN CELLS:
• Major glial cells in PNS.
• Provide myelination (insulation) around the
nerve fibers in PNS.
• Phagocytic activity - Remove cellular debris during
regeneration.
SATELLITE CELLS:
• Present on the exterior surface of PNS neurons.
• Physical support to the PNS neurons.
• Regulation of chemical environment of ECF
around the PNS neurons.