Nervous system introduction

2. THE NERVOUS
SYSTEM
INTRODUCTION

3. Definition
Nervous system and endocrine system are
the chief control centers in maintaining
body homeostasis.
The nervous system is a highly complex
part of an animal that coordinates its
actions and sensory information by
transmitting signals to and from different
parts of its body.

4. Terminology
Gray Matter –mostly nerve cell bodies.
White Matter –mostly myelinated
axons.
Nerve fiber –a single axon of a neuron.
Tract –a bundle of axons in the CNS.
Ganglion –a cluster of nerve cell bodies
in PNS
Nucleus –gray matter in CNS with
common function.
Nerve –a bundle of axons in the PNS.

5. Functions of the Nervous System
 Nervous system has 3major functions:
 Sensory input –sensory or afferent neutron
detect internal or external changes ( stimuli )
and send the message to the brain or spinal
cord.
 Integration–interneuronsin the brain or spinal
cord process and interpret the message from
the sensory neurons, and relay the massage
back to body parts.

6.  Motor output –motor or efferent neurons
receive the message from interneuron and
produce a response at the effector organ (
a muscle or a gland).

7. SUBDIVISION OF THE NERVOUS
SYSTEM

9. CELLS OF THE NERVOUS
SYSTEM
 There are two cells of the nervous system.
These are;
 Neuron
 Neuroglia

10.  The functional unit of the nervous system is
the nerve cell, or neuron
 Neuroglia or glial cells are supportive cells in
the nervous system that aid the function of
neurons

11. Neuron
• Basic functional cell
of nervous system
• Transmits impulses
(up to 250 mph)

12. Parts of a Neuron
• Dendrite – receive stimulus and carries it impulses
toward the cell body
• Cell Body with nucleus – nucleus & most of
cytoplasm
• Axon – fiber which carries impulses away from cell
body
• Schwann Cells- cells which produce myelin or fat
layer in the Peripheral Nervous System
• Myelin sheath – dense lipid layer which insulates
the axon – makes the axon look gray
• Node of Ranvier – gaps or nodes in the myelin
sheath

13. Classification of neurons
 Classification based on structure:
 a) unipolarneuron -a single nerve fiber is
extended from the some, and it divides into a
dendrite and an axon (sensory neurons that
conduct reflexes or detect various stimuli).
 b) bipolar neuron -a dendrite and an axon
extend from the soma independently (sensory
neurons involved in special senses such as
vision, olfaction, and hearing).

14.  c) multiple neuron -one axon and many
dendrites extend from the soma (interneurons
located inside the brain and spinal cord).

15. Classification based on
structure

17. Classification of neurons
 Classification based on function:
 o Sensory neurons – bring messages to CNS
 o Motor neurons - carry messages from CNS
 o Interneurons – between sensory & motor
neurons in the CNS

18. Classification based on
function

19. Nissl body
 A Nissl body, also
known as Nissl
substance and
Nissl material, is a
large granular body
found in neurons.

20.  These granules are of rough endoplasmic
reticulum (RER) with rosettes of free
ribosomes, and are the site of protein
synthesis.
 It was named after Franz Nissl, a German
neuropathologist who invented the Nissl
staining method

21. Axon hillock
 The axon
hillock is a
specialized part
of the cell body
(or soma) of a
neuron that
connects to the
axon.

22. Synapse
A synapse is the junction between two neurons,
or between a neuron and an effector organ
(muscle or gland).
Each synapse consists of:
 Presynapticneuron- that sends an impulse to
the synapse.
 Axon– the nerve fiber extends from the pres
synaptic neuron, that propagates the impulse
to the synapse
 Synaptic knobs - the round endings of the
axon

23.  Synaptic vesicles - membranous sacs that
contain a neurotransmitter (e.g. acetylcholine,
norepinephrine, dopamine), located in the
synaptic knobs.
 Synaptic cleft - a gap between the two
neurons in the synapse.
 Dendrite– the nerve fiber that continues to
propagate the nerve impulse to the second
neuron (postsynaptic neuron). Receptors on
this dendrite receive the neurotransmitter from
the axon.
 Postsynaptic neuron - the neuron that
receives the nerve impulse from the
presynaptic neuron, through the synapse.

25. NEUROGLIA (Glia)
 Glia, also called glial cells or neuroglia, are
non-neuronal cells in the central nervous
system (brain and spinal cord) and the
peripheral nervous system that do not produce
electrical impulses
 Neuroglia, or glia, are the supportive cells for
neurons

26. There are six types of supportive cells
 Four in the CNS
 Oligodendrocytes
 Ependymal cells
 Microglia
 Astrocytes
 Two in the PNS
 Schwann cells (Neurilemmocytes)
 Satellite cells

27. CNS Neuroglia
 Astrocytes
 Most numerous
 Repair damages neurons
 Control interstitial environment
 Blood brain barrier
 Surround capillaries to isolate the brain from
chemicals in the plasma

28.  Ependymal cells
 With capillaries produce cerebral spinal fluid
in the brain
 Oligodendrocytes
 Myelinateaxons in the CNS
 Works like insulation making actions potentials
travel down axons ~ 6 times faster
 Microglia
 Break down cellular waste and pathogens in
the CNS

29. PNS Neuroglia
 Schwann cells
 Myelinate axons in the PNS
 Satellite cells
 exchange waste/nutrients cell body &
extracellullar fluid

33. •Extensions of the soma form nerve such as
dendrites which conduct nerve impulses
toward the soma, and axon which conducts
nerve impulses away from the soma (to
another neuron, or to an effect or organ).
•The number of dendrites ranges from 1 ( in
unipolar and bipolar neurons) to thousands ( in
multipolar neurons).

34. •All neurons only contain 1axon.
•Longer axons are enclosed by a lipoprotein
substance called myelin sheath produced by
type of neuralgia cell celled schwann cells.

35. Myelination
It is a process by which:
Myelin is a lipid-rich (fatty) substance that
surrounds nerve cell axons (the nervous
system's wires) to insulate them and increase
the rate at which information (encoded as
electrical impulses) is passed along the axon

38. This myelin sheath insulates the axon against
depolarization, and forces action potential to
occur in the gaps (Node of Ranvier) in
between the myelin sheath

39. Mechanism of Myelination

40.  The myelin sheath insulates the axon leaving
only narrow gaps called Nodes of Ranvier to
allow action potential to occur.
 This type of nerve impulse propagation where
action potential jumps from one gap to the next
is referred to as "saltatory conduction"
(which increases the rate of impulse
transmission by 240 folds).

41. Gray and White Matter
 Axons enclosed by myelin sheath are called
myelinated axons which make up the white
matter in the nervous system;
 while axons that have no myelin sheath are
called unmyelinated axons which make up
the gray matter in the nervous system

42. Neuroglia vs. Neurons
 Neuroglia divide.
 Neurons do not.
 Most brain tumors are “gliomas.”
 Most brain tumors involve the neuroglia cells,
not the neurons.
 Consider the role of cell division in cancer!

43. Nerve Injury
Although there is DNA in the neuron, somehow
DNA replication and mitosis do not occur,
resulting in the neurons lack of ability to
reproduce or regenerate

45. Nerve Degeneration
 Loss of functional activity and trophic
degeneration of nerve axons and their
terminal arborizations following the destruction
of their cells of origin or interruption of their
continuity with these cells. The pathology is
characteristic of neurodegenerative diseases

46. You have to know yourselves
 SYMPATHETIC VS PARA SYMPATHETIC N S

47. কি বুঝকি ত োরো সবোই