2. The nervous system is organized
to:
Receive, Store & Transmit
information.
Function of nervous system
3. Neurons
It is the building unit of nervous system.
Specialized conducting cell of the neurologic
system which receives, conducts and transmits
small electrical signals
.
4. Interneurons are a third type of Neurons that
form interconnections between other Neurons
5. Multiple Neurons are grouped into pathways
Nerves
Tract, fasciculus,
lemniscus and peduncle
6. Nerve fiber
A nerve fiber, also
called an axon, is a
long and slender
projection of nerve
cells (or neurons)
that carry electrical
impulses away from
the nerve cell body
A neuron typically has one nerve fiber emerging
from its cell body that transmits impulses to other
neurons, muscles or glands
• Dys-functioning of the nerve fibre can
cause major acquired and inherited
neurological disorders that affect both the
central nervous system and the peripheral
nervous system.
7. Important medical terms
• Synapse
Connections between Neurons in which they communicate via
chemical signals (Neurotransmitters)
• Neurologic Pathway: Chain of communicating Neurons
• Neuraxis Tract (or fasciculus, peduncle or lemniscus)
• Bundle of axons in a pathway within the Central Nervous
System (CNS)
• Nerve
• Bundle of axons in a pathway within the Peripheral Nervous
System
8. • Neural Nucleus
• Group of Neuron cell bodies (soma)
with attached group of axons (nerve tracts)
• Includes brain nuclei, Cranial Nerve nuclei, cerebellar
nuclei and spinal cord nuclei
• Ganglia are the Peripheral Nerve versions of the CNS
neural neuclei
9. Supporting cells
• Gliocytes
The cells which
support neurons in the
central nervous
system.
• Schwann cells
The cells which
support peripheral
nerves
10. Neuron is consisting of
(1) Cell body (soma)
(2) Cell Processes (axon and dendrites).
11. (1) Cell body
It contains cytoplasm,
nucleus and cell organelles.
It contains large number of
Nissl granules these
granules are the granular
endoplasmic reticulum of the
neuron. Their functions are
the synthesizing of proteins
and export it to the cell
processes.
There is no centrosome in
the
nerve cell.
The cell bodies are present mainly inside the CNS.
But some cell bodies are also found in the
autonomic and dorsal ganglia.
12. There are processes that emerge from the cell
body: -
(1) Dendrites
(2) Axon (nerve fibres) it arises from a conical part of
the cell called axon hillock.
The axon ends up in several terminal branches.
Each terminal ends in a disc-like expansion called
synaptic knob
Axon hillock
Cell processes are the nerve fibres which
makes
1. the peripheral nerves outside the CNS
2. the nerves tract inside the CNS.
(2) Cell processes
13. Axon
Dendrites
Transmit impulses away
from the cell body.
Transmit impulses from
around of the cell to the
cell body.
Increase the surface
area of the cell.
A neuron has only one
axon
A neuron could have
one or more dendrites
14. Axon:
• The nerve fibres are covered by a cell membrane called
axolemma.
• It is a three layered bilipid membrane that specifies what
transported in and out of the nerve cells.
• The cytoplasm of the nerve fibres is known as axoplasm, it
has a high concentration of microtubules, microfilaments
and mitochondria.
15. • Synaptic knobs are the end branches of a nerve fibre,
has swollen ends called axon terminals that join one
neuron to another forming a synaptic junction.
• A single nerve fibre with its multiple branches
innervates multiple parts of the brain and generates
multiple synaptic terminals
16. • The nerve fibres can be as small as a few millimetres or
can extend up to one-meter long.
• The longest nerve fibre of the human body is the sciatic
nerve that extends
from the spinal cord
to the big toes of both feet.
• The diameter of the nerve fibre
is also variable ranging from
about one micrometre to up to 20
µm.
17. The nerve fibres are covered
by a layer of insulating fatty
substance called myelin that is
composed of Schwann cells
and oligodendrocytes. Some of
the nerve fibres are
unmyelinated as well.
Nodes of Ranvier are short
unmyelinated segments
interspersed in the nerve fibre
that serve as the site of action
potential generation.
18. • The area from where the nerve fibres extend from the
body of the nerve cells is called axon hillock.
• The axon initial segment (AIS) is a separate
functional area of the nerve fibres that separates nerve
fibres from the rest of the neuron and also helps in
initiating action potentials.
19. What are the main functions of the
nerves?
Controls the voluntary and involuntary movement
of the body.
Maintains the balance of the body.
Maintains the homeostasis of the body by doing
functions such as thermal regulation, etc.
Responsible for sensing the stimuli, processing
them, and sending the appropriate response.
Release chemical regulators
20. Types of nerve fibres according to the presence or
absence of myelin sheath
Myelinated nerve
fiber: Covered by myelin
sheath which is
interrupted with gaps
called nodes of Ranvier
Non-Myelinated nerve
fiber Not covered by
myelin sheath
21. Myelinated nerve
fibers
Myelinated nerve
fibers
Axon
diameter
Large small
Myelin
sheath
Covered by many
layers of Schwann
cells
Surrounded by the
cytoplasm of Schwann
cells
Conduction Salutatory conduction Sweeping conduction
Channel Has a large number of
voltage gated Na
channel
Has a less number of
voltage gated Na
channel
Energy less great
22. Types of the nerves according to the diameter and velocity
of conduction
Group Functions Diameter
(u)
Velocity
Meter/sec
Spike
duration
Sensitive
to
A- Alpha (a) Somatic motor,
proprioception &
annulospiral ending
2-20 10-120 0.5m.sec pressure
A-Beta (b) Fine touch,
proprioception
10-20 60-120
A-Gamma
(g)
Motor to muscle
spindle
5-10 30-60
A-Delta (d) Temperature (cold),
crude touch and
pricking
3-5 15-30
B Myelinated autonomic
preganglionic fibres.
1-2 5-10 1 O2 lack
C Unmyelinated fibres Less than1 0.5-2 2 Local
anesthetic
23. Excitability
The nerve fibres are highly excitable structures that
respond to several stimuli and can also generate
electrical impulses.
Stimulus: it is the changes which occur in the
environment around the living organism.
Types of the stimulus:
Electrical stimulus: by using galvanic current and it is
preferred
Chemical stimulus: O2, Co2, H+, acids and alkali
Mechanical stimulus: pain and movements.
Physical stimulus: cold and hot.
Characters of nerve fibres:
24. Electrical stimulus is preferred because
We can control its onset
We can control its intensity
We can control its duration
It resembles the natural stimulus.
It leaves the stimulated tissue without
damage.
25. Conductivity
The electrical impulses generated in the
nerve fibers are propagated along its
entire length and to different neurons,
muscles and glands by synaptic
connections.
Refractory Period: The nerve fibers can
conduct one action potential at once, i.e.,
the excitability of the fibres is less during
conduction and hence a new electrical
impulse cannot be generated.
26. Not fatigued
The nerve fibers don’t fatigue when they are
stimulated continuously.
Explain why. the fatigue occur due to
1- exhaustion of neurotransmitter, which is
present in the synapse not in the nerve.
2- accumulation of waste production due to
metabolism which happens in muscle not in the
nerve)
All or None Response: A nerve fiber translates either
all of the impulse or none at all. If a stimulus is applied
up to a threshold level, an action potential will be
generated but increasing the strength of the stimulus
will not affect the action potential.
27. It is the ability of the nerve to adapt itself quickly to
the continuous stimulating agent.
It is of three types:
Slowly adapting: pain sensation
Moderately adapting: hot and cold sensation
Rapid adapting: touch sensation.
Adaptation
Summation: If a sub-
threshold stimulus is applied, it
cannot generate an action
potential. However, when
multiple sub-threshold stimuli
are applied in rapid
succession, an action potential
is generated
