Download Central nervous system

by
Dr. Dalia Mohamed Ali
 The
nervous system (N.S) is
divided into two main parts:


1) The central nervous system(C.N.S)
2) The peripheral nervous
system(P.N.S)
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
-
It is formed of:
Cranial nerves arise from brain
Spinal nerves arise from spinal cord
 It
is divided functionally into :
 a-Somatic nervous
 controls skeletal muscles .
 b-Autonomic
system
system :
nervous
:Controls smooth muscle ,heart
&glands (sympathetic & parasympathetic) .
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1-somatic nervous system



The somatic nervous
system is concerned
with somatic functions.
It includes the nerves
supplying the skeletal
muscles.
Controls the voluntary
movements of the
body by acting on the
skeletal muscles .
2-Autonomic nervous
system
The autonomic nervous
system is concenrned
with regulation of
visceral or vegetative
functions.
 involuntary nervous
system.
 The autonomic nervous
system consists of two
divisions:
* sympathetic division
* parasympathetic
division.


It includes:
-Brain
-Spinal cord

It is formed of:
-Highly specialized nerve cells (neurons)
-Supporting cells (neuralgia)

The structures of brain and spinal cord are arranged in
two layers: the gray matter and white matter.

In brain the white matter is centrally placed and gray
matter is in the outer part.

In spinal cord white matter is in the outer part and
gray matter is in inner part.

Brain is situated in the skull.

It is continued as spinal cord in the vertebral canal
through the foramen magnum of the skull bone.

Brain and spinal cord are surrounded by three layers of
meninges:
•
•
•
the outer dura mater
middle arachnoid
inner pia mater.

The space between the arachnoid mater and pia mater
is known as subarachnoid space.

This space is filled with a fluid called cerebrospinal fluid

The brain and spinal cord are actually suspended in CSF.
(CSF).
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
It is formed of :
a) cerebrum ( the 2 cerebral hemispheres +
the interbrain).
b) Brain stem: which includes:

c)cerebellum


◦ Midbrain ( upper part)
◦ Pons
(middle part)
◦ medulla oblongata (lower part)
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

The functional & structural unit of the Nervous
System is the neuron.
Neuron is called the nerve cell
 Nerve
cell body:
 Irregular in shape
 mass of cytoplasm called neuroplasm
which is covered by a cell membrane.
 The cytoplasm contains a large nucleus,
Nissel bodies, neurofibrils, mitochondria
and Golgi apparatus.
 Nissel bodies and neurofibrils are found
only in nerve cell and not in other cell
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
It is different from other cells in:
-
It has branches or processes
-
It does not have centrosome (it cant divide)

two types of processes:
1) the axon the axons(nerve fibers) runs in
groups forming the different nerves of the
body.
2)Dendrites
1) Axon
•single
• the longest process of the cell body
•carries nervous impulses away from the cell body. out
side the CNS
• the axons(nerve fibers) runs in groups (fasciculus)
forming the nerves of the body
2)Dendrites
•are multiple
•the short processes of the cell body
•which carry impulses towards the nerve cell body
Organization of nerve :
 Many axons together form a bundle called
fasciculus.
 many fasciculi together form a nerve.
Myelin sheath



myelin sheath is a thick lipoprotein sheath that insulates
the nerve fiber.
it is absent at regular intervals.
myelin sheath is responsible for the white color of the
nerve fibers
-Myelinated nerve fiber
The nerve fibers which are insulated by myelin sheath.
-Nonmyelinated nerve fiber
The nerve fiber is not covered by myelin sheath.
Function of Myelin sheath:
1- Faster conduction  faster conduction of impulse
2- Insulating capacityrestricts the nerve impulse within
the single nerve fiber
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Classification of neuron
I- depending on number of poles:
1- unipolar neurons
have only one pole from which both the axon and
dendrite aries
2- Bipolar neurons
have two poles.axon arises from one pole and
dendrites aries from the other pole
3- Multipolar neurons
have many poles. One of the poles gives rise to
the axon and all the other poles give rise to
dendrites

II- depending on function:
1- Motor neurons (efferent)
 motor neurons or efferent nueurons which
carry the motor impulses from central
nervous system to the peripheral effector
organs like muscles,glands,blood vessels.
2- Sensory neurons (afferent)
 sensory neurons or afferent neurons which
carry the sensory impulses from periphery to
the central nervous system.
III-depending on length of axon:
1- Golgi type I neurons (long axons)
 have long axons.
 The cell body of these neurons is in central
nervous system and their axons reach the
remote peripheral organs.

2- Golgi type II neurons (short axons)
 have short axons.
 These neurons are present in cerebral cortex
and spinal cord.
I- depending on structure:
-Myelinated nerve fibers
-NonMyelinated nerve fibers
 II-depending on distribution
-somatic nerve fibers
-autonomic nerve fibers
 III-depending on origin:
-cranial nerve: arise from brain
-spinal nerve: arise from spinal cord

IV-depending on function:
1-sensory or afferent nerve fibers which carry
sensory impulses from different parts of the
body to the central nervous system
2-motor or efferent nerve fibers which carry
motor impulses from central nervous system to
different parts of the body.
 V-depending on neurotransmitter:
1. Adrenergic nerve fibers that secrete
noradrenaline
2. cholinergic nerve fibers that secrete
acetylcholine

 Excitability
 Conductivity
 Refractory
period: -absolute RP
-relative RP
 Adaptation
 Summation
 Infatigability
 Excitability
the physiochemical change that occurs in a
tissue when a stimulus is applied
 Conductivity
the ability of nerve fibers to transmit the
impulse from the area of stimulation to the
other areas
 Refractory
period
the period at which the nerve does not give any
response to a stimulus
-absolute RP
-relative RP
 Adaptation


While stimulating a nerve fiber
the excitability of the
nerve fiber is greater in the beginning.
continuous stimulation
Later the response decreases
slowly and finally the nerve fiber does not show any response
at all
 Infatigability

A nerve fiber cannot be fatigued, even if it is stimulated
continuously for a long time
 Summation


When one subliminal stimulus is applied
it does not
produce any response in the nerve fiber .
if two or more subliminal stimuli are applied within a short
interval
the response is produced
Neuroglia or glia cell is supporting cells
 It is nonexcitable not transmit impulses
 Classification:
1- central glia cells:
-astrocytes
-microglia
-oligodendrocytes
2- peripheral glia cells:
-schwan cells
-satellite cells

It is sensory nerve ending that terminate in
the periphery
 Classification:
 I- Exteroceptors:
-cutaneous receptors: pain, pressure, touch
-chemoreceptors: taste, smell
-telereceptors: vision, hearing
 II- Interoceptors:
-viscroceptors
-proprioceptors

are the receptors which give response to stimuli
arising from outside the body.
1_cutaneous receptor:
 The receptor situated in the skin
 also called mechanoreceptors
their response
to mechanical stimuli such as touch, pressure &pain.
2_chemoreceptors:
 The receptors which give response to chemical stimuli
are called to chemoreceptors.
3_telereceptos:
 Are the receptors that give response to stimuli arising
away from the body.

Are the receptors which give response to
stimuli arising from within the body
interoceptors are of 2 types:
1-visceroceptors:
 situated the viscera.
2-proprioceptors:
 Are the receptors which give to change in the
position of different parts of the body.

Exteroceptors
Chemoreceptors
Taste
Taste
buds
telereceptors
smell
Vision
Hearing
olfactory
receptors
rods and
cones in
retina
hair cells
in organ
of corti
cutaneous receptors
Touch
Meisnner's
Pressure
pacinian
corpuscle
Pain
free nerve
ending
nocicepto
r
Interoceptors
viscereoceptors
1-Stretch receptor
proprioceptors
1- muscle spindle
2- baroreceptors
2- Golgi tendon organ
3- chemoreceptors
3- pacinian corpuscle
4- osmoreceptors
4- free nerve ending
1-specificity of response
 2-adaptation


3-response to increase in strength of stimulus
4-sensory transduction
 5- receptor potential

1-specificity of response

the response given by a particular types of
receptor to a specific sensation.
2-adaptation

It is the decrease in the response when a
receptor is stimulated continuously with
constant strength.
3-response to increase in strength of stimulus

if the response given by the receptor is to be doubled
the strength of stimulus must be increased 100 times.
4-sensory transduction
 The process by which the energy (stimulus) is converted
into electrical impulses.
5- receptor potential
I.
Is a nonpropagated transmembrane potential
difference that develops when a receptor is
stimulated
II.
short lived
III.
transient
IV.
receptor potential is not action potential.
Synapse:
 It is the junction between the two neurons.
Classification:
I- Anatomical:
1-axaoaxnic synapse
 in which axon of one neuron terminates on axon
of another neuron.
2-axodendritic synapse
 in which axon of one neuron terminates on
dendrite of another neuron.
3-axosomatic synapse
 in which axon of one neuron ends on soma(cell
body)of another neuron.
II
Functional:
classified into 2 types:
1-electrical synapse:

Between the presynaptic and the postsynaptic neurons.

there is direct exchange of ions between the 2 neurons
though the gap junction.
2-chemical synapse:

Junction between a nerve fiber and a muscle fiber or between
2 nerve fibers

through which the signals are transmitted by the release of
chemical transmitter.
1-excitatory synapses which transmit the
impulses from one neuron to another.
2-inhibitory synapses inhibit transmission of
impulses.
- Postsynaptic inhibition
-presynaptic inhibition
-renshaw cell inhibition

Excitatory synapse transmits the impulses from
presynaptic neuron to postsynaptic neuron by
the development of excitatory postsynaptic
potential (EPSP).
Excitatory prostsynaptic potential:
 Excitatory postsynaotic potential (EPSP) is the
nonptopagated electrical potential that develops
during the process of synaptic transmission
 the common neurotransmitter in synapse is
acetylcholine.
Arrival of action potential in axon
terminal
Opening of calcium channels in
presynaptic membrane
Influx Calcium ions from ECF in to
The axon terminal
Formation of Ach-receptor complex
Opening of sodium channels and influx of sodium ions from ECF
Development of EPSP
Opening of sodium channels in initial segment of axon
Influx of sodium ions from ECF and development of action potential
Spread of action potential.
Inhibition of synaptic transmission is classified
into 3 types:
1-postsynaptic inhibition.
2-presynaptic inhibition.
3-renshaw cell inhibiton
1- postsynaptic inhibition

due to the release of an inhibitory neurotransmitter from
presynaptic
terminal
instead
of
an
excitatory
neurotransmitter.

the inhibitory nurotranmittrs are: gamma amino butyric acid
(GABA), dopamine and glycine.

the transmitter receptor complex opens the ligand gated
potassium channels instead of sodium channels.

now the potassium ions which are available in the cell body of
postsynaptic neuron move to ECF .

simultaneously chloride channels also opened.

the exit of potassium ions and influx of chloride ions cause
more negativity inside leading to hyperpolarization.
2- Presynaptic inhibition:
 It's the synaptic inhibition which occurs because
of the failure of presynaptic axon terminal to
release
the
excitatory
neurotransmitter
substance (indirect inhibition).
3- renshaw cell inhibition:
 It's the type of synaptic inhibition which is
caused by renshaw cells in spinal cord.
 the renshaw cell is stimulated
it sends
inhibitory impulses to a motor neurons so that
the discharge from a motor neurons is reduced.

the synaptic inhibition in CNS limits the
number of impulses going to muscles and
enables the muscles to act properly and
appropriately
1-one way conduction :
 Impulses are transmitted only in one direction
(from presynaptic neuron to postsynaptic neuron).
2-the synaptic delay:
 Synaptic delay is a short delay that occurs during
the transmission of impulses through the synapse
it's due to the time taken for:
i.
ii.
iii.
release of neurotransmitter.
passage of neurotransmitter from axon terminal
to postsynaptic membrane.
action of the neurotransmitter to open the ionic
channels in postsynaptic membrane.
3-fatigue:
 the fatigue at the synapse is due to the depletion of
neurotransmitter substance acetylcholine.
4-summation:
 it's
the progressive increase in the excitatory
postsynaptic potential(EPSP) in postsynaptic neuron
when:
* many presynaptic excitatory terminals are stimulated
simultaneously
* or when single presynaptic terminal is stimulated
repeatedly.
5-electricale property:
 The electrical properties of the synapse are the EPSP
and IPSP which are already.
Neurotransmitters:
 It is chemical substance that acts as the mediator
for the transmission of nerve impulse from one
neuron to another through synapse.
 Classification:
I- depending on chemical nature:
1- aminoacids
2- amines
3- others
II-depending on function:
1- excitatory neurotransmitters
2- inhibitory neurotransmitters
Excitatory
Inhibitory
1-acetylcholine.
2-histamine.
1-GABA.
2-glycine.
3-dopamine.
Excitatory and
inhibitory actions:
1-noradrenaline.
2-adrenaline.

It is the response to peripheral nervous stimulation that occurs
without our consciousness.
Reflex arc:
1-Receptor
 It is the end organ , which receives the stimulus
2-affrent nerve
 Afferent or sensory nerve transmits sensory impulses from the
receptor to the center
3-center
 The center is located in the brain or spinal cord
4-Efferent nerve
 Efferent or motor nerve transmits motor impulses from the center
the effectors organ
5- Effector organ
 The effector organ is the structure such as the muscle or gland
where the activity occures in response to the stimulus
 Classification
of reflexes:
I- depending on inborn or acquired
-unconditioned reflexes
-conditioned reflexes
II- depending on site of the center:
-cerebellar reflexes
-cortical reflexes
-midbrain reflexes
-Medullary reflexes
-spinal reflexes
III- depending on the purpose:
-protective reflexes
 The protective reflexes are the relaxes which protect the
body from nociceptic (harmful)
 the flexor muscles contract during these reflexes resulting
in flexion at joints
-antigravity reflexes
 The body against the gravitational force
 the extensor muscles contract during these reflexes
resulting in extension at joints
IV- depending on the number of synapse:
-monosynaptic reflexes
reflexes having only one synapse in the reflex arc are called
monosynaptic reflexes
-polysynaptic reflexes
Reflexes having more than one synapse in the reflex are
called polysynaptic reflexes.
V- depending on clinical base:
1- superficial reflexes
 Are the reflex which are elicited from the surface of
the body .
 superficial reflex are of 2 type mucous membrane
reflex and skin reflex
2-deep reflexes
 Are elicited from the deeper structures beneath the
skin like tendon
3-visceral reflex
 Arising from the pupil and the visceral organs.
4-pathological reflex
 Elicited only in pathological condition .
Superficial mucous membrane
Reflex
Stimulus
response
Pharyngeal reflex
Irritation of Pharyngeal
mucous membrane
gagging
Uvular reflex
Irritation of Uvular
Raising of Uvular
Deep reflex
Reflex
Stimulus
response
Jaw jerk
Tapping middle of the
chin
Closure of mouth
Knee jerk of patellar
tendon reflex
Percussion of patellar
ligament
Extension of leg
Covered by 3 meninges like the brain.
 Contains cavity called the central canal .

It is extends from foramen magnum where
it is continuous with medulla oblongata
 The cord is divided into segments (31):
a-cervical segments: 8
b-Thoracic segments :12
c-Lumber segments :5
d- Sacral segments :5
e- Single Coccygeal 1

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Spinal nerves
 The segments Of spinal cord correspond to
the 31 pairs of spinal nerves in a symmetrical
manner
Cervical spinal nerves = 8
Thoracic spinal nerves = 12
Lumbar spinal nerves = 5
Sacral spinal nerves = 5
Coccygeal nerves = 1
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
3 -In cross section ,it shows:
Grey matter:
it is arranged in the shape of butter fly or
like letter H.
a)



It projects as:
2 dorsal horns (contain sensory neurons )
&
2 ventral horns ( contain motor neurons) .
A third lateral horn is found only in the
segments which give autonomic outflow.
B) White matter : surrounds the grey matter
and contains nerve fibers which run as
tracts.

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63
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Tract in spinal cord
Tract of the spinal cord are collection of nerve fibers
passing through the spinal cord.
 Spinal tract are divided into two main groups :
1. Short tract
2. Long tract
Long tract two type :
 Ascending tract
which carry sensory impulses from the spinal cord to
brain
 Descending tract
which carry motor impulses from brain to spinal cord

Ascending tract of spinal cord
situation
Anterior
white
column
tract
1. Anterior
spinothalamic tract
2. Lateral
spinothalamic tract
function
Touch
Pain and
temperature
Descending tracts of spinal cord
 The descending Of the spinal cord are formed
by motor nerve fibers arising from brain and
descend in to the spinal cord
 The descending tracts of spinal cord are two
types :
 1-pyramidal tracts
 2- extrapyramidal tracts
Pyramidal tracts
These tracts of spinal cord and concerned with voluntary
motor activities of the body.
Function
 The pyramidal tract are concerned with voluntary
movement of the body.
 fibers of the pyramidal tract transmit motor impulses
from motor area of cerebral cortex to the anterior motor
neurons of the spinal cord .
 these two tract are responsible for fine, skilled
movements .
 The lesion in the neurons of motor cortex and the fibers
of pyramidal tract is called the upper motor neuron
lesion

Extrapyramidal tract
somatosensory system
somatosensory system is defined as sensory system associated with
different parts of the body.
sensations are of two type :
Somatic sensations
2.
Special sensations
Somatic sensation :
 Somatic sensation are sensations arising from skin , muscles,
tendons and joint .
 these sensation have specific receptors
Special sensation :
 Special sensation are the complex sensation ,
 sensation of vision ,hearing, taste and smell are the Special
sensation
1.
Epicretic sensation
 The mild or light sensations.

epicretic sensation are :
1.
Fine touch or tactile sensation
2.
Tactile localization
Protopathic sensation
 protopathic sensation are the crude sensation
protopathic sensation are :
1.
Pressure sensation
2.
Pain sensation
Deep sensation :
 Deep sensation are the sensation arising from the deeper
structures beneath the skin and the visceral organs .
The Sensory pathways are two types :
1. Pathways of somatosensory system
2. Pathways viscerosensory system
The Pathways of somatosensory system convey the
information from the sensory receptors in skin ,
skeletal muscles and joints.
 the pathways of viscerosensory system convey the
information from the receptors of the viscera


pyramidal tracts
extrapyramidal tracts
the extrapyramidal tracts are concerned regulation of tone, posture
and equilibrium .
upper motor neuron :
upper motor neuron are the neurons in the higher center of brain
,which control the lower motor neurons . there are three type of upper
motor neuron :
1.
motor neuron in the cerebral cortex
2.
neurons in basal ganglia
3.
neurons in the cerebellum

lower motor neuron :
lower motor neuron are the anterior gray horn in spinal cord and motor
neurons of the cranial nerve nuclei situated in brainstem which innervate
the muscles directly .
components of pain sensation:
A pain stimulus produces two pain sensation
1.fast pain
2. slow pain
 Fast pain is the first sensation whenever a pain
stimulus is applied.
 It is experienced as a bright, sharp and localized
pain .
 The receptors for both the components of pain are
the same
pathway of pain sensation from face
Carried by trigeminal nerve.
Definition:
 is the pain that is perceived at a site adjacent to
or away from the site of origin.
examples of referred pain
1. cardiac pain is felt at the inner part of left arm
and left shoulder.
2. pain in ovary is referred to umbilicus.
Dermatomal rule


According to dermatomal rule, pain is referred to a structure , which is
developed from the same dermatome from which the pain producing
structure.
A dermatome includes all the structures or parts of the body , which
are innervated by afferent nerve fibers of one dorsal root.
analgesia system

The pain control system.

the body has its own analgesia system in brain which provides a short
term relief from pain . it is also called endogenous analgesia.

The analgesia system has got its own pathway through which it blocks
the synaptic transmission of pain sensation in spinal cord and
suppresses the pain sensation.