Transcript THE NERVOUS SYSTEM I

THE NERVOUS SYSTEM
FUNCTIONS
• collection of sensory
input
• integration
• motor output
The function of the nervous
system is to detect changes in
the:
External or Internal
environments
So, it bring about appropriate
responses in
Muscles,
Organs and
Glands.
ORGANIZATION
•
•
•
•
STRUCTURAL
CNS
PNS
FUNCTIONAL
Sensory division
(Afferent)
Motor division
(Efferent)
– autonomic
– somatic
Neurons
What is neurone?
It is the basic structural (anatomical) , functional and embryological unit
of the nervous system.
The human nervous system is estimated to contain about 1010.
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• The functions of the neuron is to receive and integrate incoming
information from sensory receptors or from other neurons and to
transmit information to other neurons or effector organs.
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Information is passed
between neurons at
specialized regions called
synapses
In the synapses the
membranes of adjacent
cells are in close apposition
(contiguity not continuity).
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• There is wide diversity in the
shape and size of neurons in
different parts of the nervous
system.
• But all share certain common
characteristics.
• There is a single cell body
from which a variable
number of branching
processes emerge.
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Most of these processes
are receptive in function.
They are known as
Dendrites.
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The dendrites possess:
A variable number of shot
processes.
They form the receptive
element of the neurone.
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• One of the processes leaving the
cell body is called the axon which
carries information away from the
cell body.
• Axons are highly variable in length
and may divide into several
branches or collaterals through
which information can be
distributed to a number of
different destinations
simultaneously.
• At the end of the axon,
specializations called terminal
buttons occur.
• Here information is transferred to
the dendrites of other neurones.
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• Transmission of information
between neurons almost always
occurs by chemical rather than
electrical means.
• Action potential causes release of
specific chemical that are stored
in synaptic vesicles in the
presynaptic ending.
• These chemicals are known as
neurotransmitters and diffuse
across the narrow gap between
pre- and postsynaptic membranes
to bind to receptors on the
postsynaptic cell.
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Neuroglia
• Neuroglia, or glia cells constitute the other major cellular component of the nervous
system.
• It is a specialized connective tissue for the nervous system.
• Unlike neurones, neuroglia do not have a direct role in information processing but
they are essential for the normal functioning of nerve cells.
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Three main types of neuroglial cell are recognized:
1. Oligodendrocytes (oligodendroglia) they form the myelin sheath that
surrounds many neuronal axons, which increase the rate of conduction.
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2- Microglia have a phagocytic role in response to nervous
system damage.
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3. Astrocytes are thought to
form a selectively permeable
barrier between the circulatory
system and the neurons of the
brain and spinal cord.
• This is known as the
'blood-brain barrier' and
has a protective function.
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Central & peripheral
nervous systems
The nervous system is divided
into:
• 1- Central nervous system
(CNS).
• 2- Peripheral nervous system
(PNS).
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• The central nervous system
consists of the brain and the
spinal cord, lying within the
protection of the cranium and
vertebral column, respectively.
• This is the most complex part
of the nervous system.
• It contains the majority of
nerve cell bodies and synaptic
connections.
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• The peripheral nervous
system constitutes the link
between the CNS & structures
in the periphery of the body.
• It receives sensory information
from the body.
• It sends controlling impulses in
response to these information.
• The peripheral nervous system
consists:
• 1- Cranial nerves
• 2- Spinal nerves.
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• Spinal nerves supplying the
upper or lower limbs form
the brachial or lumbar
plexus.
•
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Nerve cell bodies that are
aggregated within the CNS
are called GANGLIA
Autonomic Nervous System
• Neurones that detect
changes and control
the activity of, the
viscera are collectively
referred to as the
autonomic nervous
system.
• Its components are
present in both the
central and peripheral
nervous systems.
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SYMPATHETIC & PARASYMPATHETIC
SYSTEMS
• The autonomic nervous
system is divided into
two anatomically and
functionally distinct parts:
• Sympathetic: Or
• Thoracolumbar outflow
• Parasympathetic: Or
• Craniosacral outflow.
• Sympathetic and
parasympathetic
divisions are generally
have antagonistic effects
on the structures that they
innervate.
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• The autonomic nervous
system innervates:
• Smooth muscle,
• Cardiac muscle,
• Secretory glands.
• It is an important part of
the homeostatic
mechanisms that control
the internal environment of
the body.
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Afferent, Efferent & Interneuron
• Nerve cells that carry
information from peripheral
receptors to the CNS are
referred to as afferent
neurones
• Efferent neurones carry
impulses away from the
CNS
• If they innervate skeletal
muscle to cause movement
they are also referred to as
motor neurons.
• The vast majority of
neurones, however, lies
entirely within the CNS and
are usually called
interneuron
PARTS OF THE BRAIN
• Cerebral
hemispheres
• Diencephalon
• Cerebellum
• Brain stem
CEREBRAL HEMISPHERES
FRONTAL
PARIETAL
TEMPORAL
OCCIPITAL
• The largest part
of the brain
• They have
elevations, called
gyri
• Gyri are
separated by
depressions
called sulci
• Each hemisphere
is divided into 4
lobes
• Lobes are
separated by
deeper grooves
called fissures or
sulci.
TISSUE OF THE CEREBRAL
HEMISPHERES
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Basal nuclei
•
The outer layer is the
gray matter or cortex
Deeper is located the
white matter,
composed of bundles
of nerve fibers,
carrying impulses to
and from the cortex
Basal nuclei are made
from gray matter and
are located deep within
the white matter
They help the motor
cortex in the regulation
of voluntary motor
activities
DIENCEPHALON
The diencephalon is located between
the 2 hemispheres and is linked to
them and to the brainstem.
The major structures of the
diencephalon are the thalamus,
hypothalamus and Epithalamus.
BRAIN STEM
The brainstem has three parts:
midbrain, Pons and medulla
oblongata.
CEREBELLUM
Cerebellum has 2 cerebellar hemispheres and a convoluted surface.
It has an outer cortex of gray matter and an inner region of white matter.
It provides precise coordination for body movements and helps maintain
equilibrium.
BRAIN VENTRICLES
• Brain is bathed by the
cerebrospinal fluid (CSF)
• Inside the brain, there are
spaces (ventricles) filled
with CSF
• There are 4 ventricles
 2 lateral ventricles:
are in the hemispheres
 3rd ventricle:
in the diencephalon
 4th ventricle:
between the Pons & the
cerebellum
 Cerebral aqueduct:
connects the 3rd to the
4th ventricle
CSF is constantly produced by the
choroid plexuses inside each ventricle.
Inside the brain, CSF flows
from the lateral ventricles to
the 3rd and 4th ventricles.
From the 4th ventricle, part of
the CSF flows down in the
central canal of the spinal cord.
CEREBROSPINAL FLUID
Most of the CSF drains from
the 4th ventricle in the
subarachnoid space around
the brain and returns to the
dural sinuses through the
arachnoids villi.