human anatomy 2015
lecture three
Dr meethak ali ahmed
neurosurgeon
Nervous system
the nervous system is divided into two main parts , the central nervous
system , which consists of the Brain & spinal cord , & the Peripheral
nervous system , which consists of 12 pairs of cranial nerve & 31 pairs of
spinal nerves & their associated ganglia . functionly , the nervous system
may be further divided into the somatic nervous system , which controls
voluntary activities , & the autonomic nervous system , which control
involuntary activities .
central Nervous system
The CNSis composed of large number of nerve cells &their processes ,
supported by specialized tissue called neuroglia. the neuron is the name
given to the nerve cell & all its process . the nerve cell has two type of
processes called dendrites & an axon .the interior of the CNS is
organized into gray & white matter . gray matter consists of nerve cells
embedded in neuroglia . white matter consists of nerve fiber
(axon)embedded in neuroglia .
peripheral Nervous system PNS
P N S CONSISTS of the :
Cranial Nerves ; There are 12 pairs of crania l nerve that leave the
brain & pass through foramina in the skull.
Spinal Nerve ; there are 31 pairs of spinal nerves that leave the spinal
cord & pass through intervertebral foramina in the vertebral column; 8
cervical ,12 thoracic , 5 lumbar , 5 sacral & 1 coccygeal .
Each spinal nerve is connected to the spinal cord by two roots , the
anterior root &the posterior root . anterior root consists of bundles of
nerve fiber carrying nerve impulses away from CNS such nerve fibers are
called efferent fibers . those efferent fibers that go to skeletal muscle &
causes them to contract are called motor fiber their cells of origin lie in
the anterior gray horn of the spinal cord . the posterior root consist of
bundle of nerve fiber that carry impulses to the CNS & are called afferent
fibers are concerned with conveying information about sensation of
touch , pain temperature and vibration they are called sensory fiber ,.the
reference, snell clinical anatomy
human anatomy 2015
lecture three
Dr meethak ali ahmed
neurosurgeon
cell body of these nerve fibers are situated in a swelling on the posterior
root called the posterior root ganglion .At each intervertebral foramen
the anterior & posterior root unite to form a spinal nerve , here the
motor and sensory fiber become mixed together , so that a spinal nerve
is made up of mixture of motor & sensory fiber . On emerge from
foramen , spinal nerve divided into large anterior ramus & smaller
posterior ramus .posterior ramus passes posteriorly around the
vertebral column to supply the muscles & skin of the back . anterior
ramus continues antriorly to supply the muscle& skin over anterolateral
body wall & all muscles & skin of the limbs
Plexuses ; At root of the limbs , the anterior rami join one another to
form complicated nerve plexuses . the cervical & brachial plexuses are
found at the root of the upper limbs,& the lumber & sacral plexues are
found at root of the l
ower limbs
Autonomic Nervous System
Is the part of the nervous system concerned with innervations of
involuntary structures such as the heart , smooth muscle & glands
reference, snell clinical anatomy
human anatomy 2015
lecture three
Dr meethak ali ahmed
neurosurgeon
throughout the body . divided in to sympathetic & parasympathetic ,
sympathetic system prepare the body for an emergency . it accelerates
the heart rate ,causes constriction of peripheral blood vessels , & arises
the blood pressure .parasympathetic system aim at conserving and
restoring energy .
sympathetic system part of the Autonomic Nervous System
Efferent Nerve Fiber . ; the gray matter of spinal cord , form the
first thoracic segment to the second lumbar segment , possesses a lateral
horn , or column in which are located the cell body of the sympathetic
connector neuron .the myelinated axon of these cell leave the spinal
cord in the anterior nerve roots & then pass via th white rami
communicantes to the paravertebral gaglia of the sympathetic trunk
.Once the preganglionic fibers reach the ganglia in the sympathetic trunk
the may pass to the following destintion ; 1-may terminate in the
ganglion they have entered by synapsing with an excitor cell in the
ganglion .Asynapse may be defned as the site where two neurons com
into close proximity but not into anatomical continuity the gap between
the two neuron is bridged by aneurotransmitter substance ,
acetylcholine. these postganglionic fiber now pass to the thoracic spinal
nerves as gray rami communicantes & are distributed in the branches of
the spinal nerve to supply smooth muscle in the walls of blood vessels ,
sweat gland and arrecctor pili muscle of the skin.
2-those fibers entering the ganglia of the sympathetic trunk high up in
the thorax may travel up in the sympathetic trunk to the ganglia in the
cervical region . postganglionic nerve fiber leave the sympathetic trunk
as gray rami communicantes & most of them join the cervical spinal
nerve , many of the preganglionic fiber entering the lower part of the
sympathetic trunk from the lower thoracic & upper two lumbar segments
of the spinal cord travel down to gaglia in the lower lumbar & sacral
region .3-the preganglionic fibers may pass through the ganglia on
thethoracic part of the sympathetic trunk without synapsing . these
myelinated fiber from the splanchnic nerves , of which these are three.
the greater splanchnic nerves arise from the fifth to the ninth thoracic
reference, snell clinical anatomy
human anatomy 2015
lecture three
Dr meethak ali ahmed
neurosurgeon
ganglia , pierces the diaphragm ,& synapses with excitor cells in the
ganglia of the cliac plexus .The lesser splanchnic nerve arises from the
tenth & eleventh ganglia , pierces the diaphragm , & synapses with
exciter cells in the ganglia of the lower part of the celiac plexus . the
lowest splanchnic nerve (when present) arises from the twelfth thoracic
ganglion pierces the diaphragm , & synapses with excitor cell in the
ganglia of the renal plexus .
sympathetic trunks ; are two ganglionated nerve trunk that extend
the whole length of the vertebral column , There are 3 ganglia in each
trunk of the neck , 11 or 12 ganglia in the thoracic , 4 or 5 ganglia in the
lumbar , 4 or 5 in the pelvis . The two trunks lie closed to the vertebral
column & end below by joining together to form a single ganglion , the
ganglion impar.
Afferent Nerve Fiber
The afferent myelinated nerve fiber travel from the viscera
through the sympathetic ganglia with out synapsing. they enter spinal
nerve via the white rami communicantes & reach their cell bodies in the
posterior root ganglion of corresponding spinal nerve , the centeral
axons then enter the spinal cord and may form the afferent component
of local reflex arc. Others may pass up to higher autonomic center in the
brain.
The para sympathetic system part of the Autonomic Nervous
System
The connector cells of this part of the system are located in the brain &
the sacral segment of the spinal , those in the brain form parts of the
nuclei of origin of cranial nerve 3 , 7 ,9, 10, & the axons emerge from the
brain contained in the corresponding cranial nerves. The sacral connector
cells are found in the gray matter of the second, third, & fourthsacral
segments of the cord . these cells are not sufficiently numerous to form a
lateral gray horn. The myelinated axons leave the spinal cord in the
anterior nerve root of the corsponding spinal nerve they leave the sacral
nerve & form pelvic splanchnic nerve All the efferent fiber described so
reference, snell clinical anatomy
human anatomy 2015
lecture three
Dr meethak ali ahmed
neurosurgeon
far are preganglionic , & they synapse with excitor cells in peripheral
ganglia which usually situated close to the viscera they innervated . the
cranial preganglionic fiber relay in the ciliary , pterygopalatine ,
submandibular & otic ganglia. the preganglionic fiber in the pelvic
splanchnic nerve relay in the ganglia in the pelvic plexuses.
Afferent Nerve Fibers ; afferent myelinated fiber travel from the
viscera to their cell bodies located either in the sensory ganglia of the
cranial nerves to the cranial nerve or in the posterior root ganglia of the
sacral nerve s . the centeral axons then enter the spinal cord and may
form the afferent component of local reflex arc. Others may pass up to
higher autonomic center in the brain.
reference, snell clinical anatomy
human anatomy 2015
lecture three
Dr meethak ali ahmed
neurosurgeon
reference, snell clinical anatomy