Transcript THE NERVOUS SYSTEM I

THE NERVOUS SYSTEM I:
CNS
FUNCTIONS
• collection of
sensory input
• integration
• motor output
ORGANIZATION
STRUCTURAL
• Central nervous
system (CNS)
• Peripheral nervous
system (PNS)
FUNCTIONAL
• sensory division
• motor division
– autonomic
– somatic
REGIONS OF THE BRAIN
CEREBRAL HEMISPHERES
• they are the largest
part of the brain
• they are paired
• they have ridges of
tissue, called gyri
• the gyri are separated
by grooves called
sulci
• large regions of the
brain are called lobes
• Lobes are separated
by deeper sulci
TISSUE OF THE CEREBRAL HEMISPHERES
• the outermost layer is called
gray matter or cortex
• deeper is located the white
matter, composed of fiber
tracts (bundles of nerve
fibers), carrying impulses to
and from the cortex
• corpus callosum is a very
large fiber tract connecting the
cerebral hemispheres
• the 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 activies
CEREBELLUM
The cerebellum has 2 hemispheres and a
convoluted surface. It has an outer cortex made from
gray matter and an inner region of white matter. It
provides precise coordination for body movements
and helps maintain equilibrium.
Spinal cord
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Long 42 cm
It is a two-way conduction pathway to the brain
It is a major reflex center
Extends from foramen magnum to L2 vertebra
Gives rise to 31 pairs of spinal nerves
Has 2 enlargements: cervical and lumbar
Does not reach to end of the vertebral canal
Has cauda equina (collection of spinal nerves at the
end of the spinal cord)
Gray matter of the spinal cord :
• 2 posterior dorsal horns  dorsal root
• 2 anterior (ventral) horns  ventral roots
• Central canal
• Dorsal root ganglion: contains bodies of sensory neurons
• Ventral horns: contain bodies of motor neurons
• Dorsal and ventral roots fuse to form the spinal nerves.
White matter of the spinal cord :
• 3 columns: posterior, lateral, anterior.
• They contain tracts (axons)
• Sensory (afferent) tracts
• Motor (efferent) tracts
PROTECTION OF THE CNS
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THE CNS IS PROTECTED BY:
the skull and the vertebral column (bone)
meninges (membranes)
cerebrospinal fluid (watery cushion)
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THERE ARE 3 LAYERS OF MENINGES:
dura mater (outside membrane)
arachnoid mater (middle membrane)
pia mater (inner membrane)
MENINGES
DURA MATER
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doule-layered membrane
the outermost layer is attached to the inside surface of the skull bones
(periosteal layer)
the 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 fromthe 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
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 the
CSF flows down in the central canal of
the spinal cord.
Most of the CSF drains from the 4th
ventricle in the subarachoid space around
the brain and returns to the dural sinuses
through the arachnoid villi.
NERVOUS SYSTEM II:
PNS
CRANIAL NERVES
12 pairs
• 4 pairs are mixed
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• trigeminal n. (5th)
• facial n. (7th)
• glossopharyngeal n. (9th)
• vagus n. (10th)
• 5 pairs are motor:
• occulomotor n. (3rd)
• trochlear n. (4th)
• abducent n. (6th)
• accessory n. (11th)
• hypoglossal n. (12th)
• 3 pairs are sensory:
• olfactory n. (1st)
• optic n. (2nd)
• vestibulocochlear n. (8th)
Spinal Nerves and Nerve Plexuses
• 31 pairs of spinal nerves
• named for the region of the
spinal cord from which they
arise
• each spinal nerve is attached
by two roots: dorsal (sensory)
& ventral (motor)
• each spinal nerve divides
into a dorasl and ventral
ramus
• The rami contain both
sensory and motor fibers
• the
dorsal rami are
distributed individually
innervate the skin and
muscles of the
posterior body trunk
• the ventral rami
form plexuses (except
in thoracic region
where they form the
intercostal nerves), and
supplythe anterior part
of the body
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