according to PCI syllabus

1. SEMINAR ON NERVOUS
SYSTEM
By Ishika , Ragghee , Aeswarya , Shobhit

3. NEURONS
 These can be classified into 3 different methods
1. No. of poles – unipolar ,bipolar, multipolar
2. Function- motor and sensory neurons
3. Size of axon- Golgi type1 and Golgi type 2
 Neuron is made up of three parts:
 1. Nerve cell body
 2. Dendrite
 3. Axon.
 Dendrites are short processes and the
 axons are long processes. Dendrites and axons are
 usually called nerve fibers.
ORGANISATION OF NERVE ( In diagram )
 Neurotropin-play an important role in growth and
functioning of nervous tissue. It is secreted in astrocytes ,neurons , and many
tissues particularly muscles.
 Functions
 Neurotrophins -Facilitate initial growth and development of nerve
Promote survival and repair of the nerve cells
Maintenance of nervous tissue and neural transmission

4. NEUROGLIA
 Neuroglia or glia (glia = glue) is the supporting cell of
the nervous system.
 Neuroglial cells in CNS are of three types:
1. Astrocytes
2. Microglia
3. Oligodendrocytes
 Neuroglial cells in PNS are of two types:
1. Schwann cells
2. Satellite cells.

5. CLASSIFICATION OF NERVE FIBERS
Classification of nerve fibers
 1. Depending upon structure : myelinated and non-myelinated nerve fibers
 2. Depending upon distribution: somatic and autonomic nerve fibers
 3. Depending upon origin: cranial and spinal nerve fibers
 4. Depending upon function: sensory and motor nerve fibers
 5. Depending upon secretion of neurotransmitter: adrenergic and cholinergic nerve fibers
 6. Depending upon diameter and conduction of impulse (Erlanger Gasser classification) :
 Types of nerve fiber
Type Diameter(μ) Velocity of conduction(meter/second)
A alpha 12 to 24 70 to 120
A beta 6 to 12 30 to 70
A gamma 5 to 6 15 to 30
A delta 2 to 5 12 to 15
B 1 to 2 3 to 10
C < 1.5 0.5 to 2

6. PROPERTIES OF NERVE FIBRE
 „EXCITABILITY
 Excitability is defined as the physiochemical change
that occurs in a tissue when stimulus is applied.
 Chronaxie is an important parameter to determine the condition of
nerve fiber. Clinically, the damage of nerve fiber is determined by
measuring the chronaxie. It is measured by chronaxiemeter
 Response Due to Stimulation of Nerve Fiber
1. Action potential or nerve impulse
2. Electrotonic potential or local potential
Cathelectrotonic and Anelectrotonic Potentials

7. CONDUCTIVITY
 Conductivity is the ability of
nerve fibers to transmit the
impulse from the area of
stimulation to the other areas
 CONDUCTION THROUGH
MYELINATED NERVE FIBER
– SALTATORY CONDUCTION
Action potential in nerve fiber
Mode of conduction through nerve fibers
A. Non-myelinated nerve fiber: continuous conduction.
B. Myelinated nerve fiber: saltatory conduction (impulse jumps
from node to node). AP = Action potential

8.  REFRACTORY PERIOD
 Refractory period is the period at which the nerve does not give any
response to a stimulus.
 Refractory period is of two types:
1.Absolute Refractory Period
Absolute refractory period corresponds to the period from the time when firing
level is reached till the time when one third of repolarization is completed.
2.Relative Refractory Period
 Relative refractory period extends through rest of the repolarization period.
SUMMATION
 If two or more subliminal stimuli are applied within a short interval of about
0.5 millisecond, the response is produced. It is because the subliminal
stimuli are summed up together to become strong enough to produce the
response. This phenomenon is known as summation.

9.  ADAPTATION
While stimulating a nerve fiber continuously, the excitability of the nerve
fiber is greater in the beginning. Later the response decreases slowly and
finally the nerve fiber does not show any response at all.
 INFATIGABILITY
Nerve fiber cannot be fatigued, even if it is stimulated continuously for a
long time. The reason is that nerve fiber can conduct only one action
potential at a time. At that time, it is completely refractory and does not
conduct another action potential .
 ALL-OR-NONE LAW
All-or-none law states that when a nerve is stimulated by a stimulus it
gives maximum response or does not give response at all.
ELECTROTONIC POTENTIAL DOESN’T FOLLOW THIS LAW

12. In a neuron, as in a muscle fiber, the
concentration of sodium ions is higher in the
extracellular fluid than in the cytosol, and the
concentration of potassium ions is higher in the cytosol
than in the extracellular fluid. These gradients are
maintained (and to some degree even created) by the
ATP-consuming Na+>K+ pump, which brings two
potassium ions into the cytosol as it moves three sodium
ions into the extracellular fluid.

13. The Resting Membrane Potential

14. Action Potentials

17. Receptor, molecule, generally a protein, that receives signals for a cell. Small molecules, such as
hormones outside the cell or second messengers inside the cell, bind tightly and specifically to their
receptors.

18. SYNAPSES IN THE NERVOUS SYSTEM
WHERE NERVE IMPULSES ARE PASSED FROM
NEURON TO NEURON
In the central nervous system, 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.
History
The term synapse was first introduced in 1897 by physiologist Michael Foster in his "Textbook of
Physiology" and is derived from the Greek synapsis, meaning "conjunction."
There are two main types of synapses:
Chemical Synapse
Electrical Synapses

22. MENINGES
MADE UP OF CONNECTIVE TISSUE THAT
COVERS THE BRAIN AND SPINAL CHORD
Composed of three membraneous layers:

23. LAYERS OF MENINGES:
 Dura matter: made up of tough connective tissue, provides connection
between meninges to the skull and spinal cord.
 Archanoid matter: it is the middle layer present between dura matter
and pia matter. Provides a subarchanoid space for passage of blood
vessels and nerves.
 Pia matter: inner most layer, rich in blood vessels and contains choroid
plexus.

24. FUNCTION OF MENINGES:
 Protects & support the CNS.
 It connects the brain and spinal cord to the skull and spinal canal
 It produces CSF .

25. CHOROID PLEXUS:-
 It is a network of capillaries and specialized epithelial cell located in the
ventricular system.
 It produces cerebrospinal fluid.
 Also provides a toxin barrier to the brain and other parts of CNS.

26. CEREBROSPINAL FLUID
 CSF protects and nourishes CNS tissue by acting as a shock absorber,
by circulating nutrients and by getting rid of waste products.
 CSF is present in the subarchanoid space and ventricular system
around and inside the brain and spinal cord.
 About 125 ml of CSF is present at one time and about 500ml of CSF is
produced every day.

28. VENTRICULAR SYSTEM:
 Ventricular system is a set of communicating cavities that are surrounded by cells of
CHOROID PLEXUS responsible for the transportation of CSF around the cranial cavity
and removal of it.

30. BRAIN
 Largest organ in the body and coordinates all body activities.
 It is made up of more than 1000 billion neurons.

39. EXTERNAL STRUCTURE OF SPINAL CORD

40. INTERNAL STRUCTURE OF SPINAL CORD

42. GREY MATTER AND
WHITE MATTER• GREYMATTER
CONSISTS OF:
1.DENDRITES,NEURON
AL CELL,
NONMYLINATED
AXONS, AND
NEUROGLIA
• WHITE MATTER
CONSISTS OF:
2.BUNDLES OF

43. SIGNALS
ARE
TRANSMITT
ED TO
DIFFERENT
ORGANS OF
BODY.

44. FUNCTIONS OF SPINALCORD
CONDUCTION: bundles of fibres passing information up and
down spinal corde
LOCOMOTION: repetitive, coordinate actions of several muscles
groups. Central pattern generators are pools of neurons providing
control of flexors and extensors (walking).
REFLEXES: involuntary, stereotyped responses to stimuli
(removing hand from hot plate.) . Involves brain, spinal cord and
peripheral nerves.

47. TYPES OF REFLEXES
Based on Origin:
• Unconditioned and inborn reflexes: This reflexes are triggered immediately
after birth .
Example: Blinking eye when a strong light falls on it
• Conditioned reflexes: This reflexes are triggered by a stimulus other than the
one that usually initiates response.
Based on Anatomy and Physiology:
• Protective reflexes: This reflexes protect the animal from an injury by
withdrawal of the stimulated body part.
• Anti-gravity reflexes: It maintain equilibrium against gravitational force.
• Righting reflexes: Responsible for the adjustment of head to the surface of
earth followed by position of trunk w.r.t head and the of limb w.r.t the body.
Based on Control:
• Spinal reflex: Controlled by Spinal cord.
• Cerebral reflex: Controlled by brain.