Transcript THE NERVOUS SYSTEM I

THE NERVOUS SYSTEM
FUNCTIONS AND ORGANIZATION
FUNCTIONS
• collection of
sensory input
• integration
• motor output
The function of the nervous
system of all animals is to
detect changes in the:
External or Internal
environments.
So, it bring about
appropriate responses in
Muscles,
Organs and
Glands.
ORGANIZATION
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STRUCTURAL
CNS
PNS
FUNCTIONAL
sensory division
(Afferent)
motor division
(Efferent)
– autonomic
– somatic
Neurons
The basic structural (anatomical) , functional and embryological unit of
the nervous system is the nerve cell or neurone.
The human nervous system is estimated to contain about 1010.
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• The functions of the neuron are to receive and integrate incoming
information from sensory receptors or other neurons and to
transmit information to other neurons or effector organs.
• Neuronal structure is highly specialized to fulfill these functions.
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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 synaptic
specializations, sometimes many
thousands of them, through which
they receive information from other
neurons with which they make
contact.
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In sensory neurons, the dendrites may be specialized to detect changes in
the external or internal environment.
Olfactory
receptor
neurons
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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,
inducing changes in the membrane
potential.
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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 and
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 and 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 serving the upper
or lower limbs form the
brachial or lumbar plexus.
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Nerve cell bodies that are
aggregated within these
structures called ganglia.
Autonomic Nervous
System
• Neurones that detect
changes in, 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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• The autonomic nervous system is
divided into two anatomically and
functionally distinct parts:
• Sympathetic and parasympathetic
divisions.
• They generally have antagonistic effects
on the structures that they innervate.
• 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 and Interneuron
• Nerve cells that carry information from peripheral
receptors to the CNS are referred to as afferent
neurones .
• If the information they carry reaches a conscious level
they are also called sensory neurons.
• 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
REGIONS 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.
MAIN SENSORY AREAS OF THE CORTEX
• Somatic sensory area
is located in the parietal
lobe posterior to the
central sulcus
• Visual area in the
medial surface of the
posterior lobe
• Auditory sensations
are received in the
temporal lobe close to
the lateral sulcus
• Olfactory sensations
are received deep inside
the temporal lobe
olfactory
PRIMARY MOTOR AREA OF THE CORTEX
• Primary motor
area is located in
the frontal lobe,
anterior to the
central sulcus
• Body is
represented upside
down
• Axons of these
neurons form the
pyramidal tract
(corticospinal
tract)
TISSUE OF THE CEREBRAL HEMISPHERES
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Basal nuclei
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The outermost 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
Corpus callosum is a very
large fiber tract connecting
the 2 cerebral hemispheres
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.
THALAMUS
The thalamus is a relay station for sensory
impulses passing upward to the sensory cortex.
EPITHALAMUS
The epithalamus forms the roof
of the 3rd ventricle. It is made
from two parts: the pineal body
and the choroid plexus.
The choroid plexus produces
cerebrospinal fluid.
The pineal body is part of the
endocrine system.
HYPOTHALAMUS
The hypothalamus is an important center
for regulation of the autonomic nervous
system. It regulates body temperature,
water balance and metabolism.
It is connected to the pituitary gland, important for the regulation
of the endocrine system, and the mammillary bodies, reflex
centers involved in olfaction.
THE LIMBIC SYSTEM
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The hypothalamus is an important part of the limbic
system.
The hypothalamus has centers that regulate :
Appetite,
Thirst,
Sex,
Pain,
Pleasure
BRAIN STEM
The brainstem has three parts: midbrain,
Pons and medulla oblongata.
MIDBRAIN
The midbrain extends from the mammillary bodies to
the Pons. It has 3 parts: cerebral aqueduct, cerebral
peduncles and corpora quadrigemina.
MIDBRAIN
Corpora quadrigemina are reflex centers
involved with vision and hearing.
The cerebral aqueduct is a canal
connecting the 3rd and the 4th ventricle.
MIDBRAIN
The cerebral peduncles are two big
fiber tracts which carry ascending
and descending fibers.
PONS
The Pons is a rounded part of the
brainstem that contains mainly fiber
tracts. The reflex center regulating
breathing is also located there.
MEDULLA OBLONGATA
Medulla oblongata connects the brain with the
spinal cord. It contains many fiber tracts and the
centers that regulate heart rate, blood pressure,
breathing, swallowing and vomiting.
CEREBELLUM
Cerebellum has 2 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.
PROTECTION OF THE CNS
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THE CNS IS PROTECTED BY:
Skull & vertebral column (bone)
Meninges (membranes)
Cerebrospinal fluid (watery cushion)
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THERE ARE 3 LAYERS OF
MENINGES:
Dura mater (outer)
Arachnoid mater (middle)
Pia mater (inner)
MENINGES
DURA MATER
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Double-layered membrane
Outermost layer is attached to the inside surface of the skull bones (endostial
layer)
Internal layer (meningeal layer) covers the surface of the brain and the spinal
cord
The two layers are fused together, except in 3 places where they form
channels (dural sinuses) where venous blood from the brain is collected
in some places the inner dural membrane forms folds (falx cerebri) that
attaches the brain to the cranial cavity
ARACHNOID MATER
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looks like cobweb
has threadlike extensions (arachnoid villi) that attach it to the
innermost membrane (pia mater)
the arachnoid villi absorb cerebrospinal fluid
contains the subarachnoid space filled with cerebrospinal fluid
PIA MATER
thin, delicate membrane
attached to the surface of the brain
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 and the
cerebellum
 Cerebral aqueduct
connects the 3rd to the
4th ventricle
CEREBROSPINAL FLUID
CSF is constantly produced by the
choroid plexuses inside each ventricle.
Inside the brain, CSF flows from the
lateral ventricles in the 3rd and 4th
ventricle.
From the 4th ventricle, part of the CSF flows
down in the central canal of the spinal cord.
Most of the CSF drains from the 4th ventricle
in the subarachnoid space around the brain and
returns to the dural sinuses through the
arachnoid villi.
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