NERVOUS SYSTEM

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NERVOUS SYSTEM

• DR WAHEEB AGGAD

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Nervous system

• 1-It is a system which monitor the changes in the
  external and internal environment and start
  dealing with them
• .2-It is formed of highly specialized nerve
  cells (neurons) which can
• receive stimuli (from receptors scattered all
  over the body)
• and deal with them
• and finally send the proper impulses to the
  effectors which could be muscles or glands.

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N.B

• 3)The C.N.S can't regenerate if injured.

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4) .The functional unit of the Nervous System is
the neuron.

• Neuron is the term given to the nerve cell and
  all its processes. It is formed of
• A) cell body has nucleus
• B) two types of processes,
• called an axon and dendrites.
• 1) the axon is, 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 forming the different
  nerves of the body
• 2)Dendrites are multiple ,the short processes of
  the cell body, which carry impulses to wards the
  cell body.

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Divisions of the Nervous System

• The nervous system is divided into
• two main parts
• 1) The central nervous system
• 2) The peripheral nervous system

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1-The central nervous system,

• 1-The central nervous system is the part of N.S
  which is protected by bones ,it is consists of
• a) The brain
• b) spinal cord

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A) The brain

• It is formed of
• a) cerebrum ( the 2 cerebral hemispheres the
  interbrain).
• b) Brain stem which includes
• Midbrain ( upper part)
• Pons (middle part)
• medulla oblongata (lower part)
• c)cerebellum

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A) The brain

• it is covered by 3 meninges
• 1-Dura (the outer layer )
• 2-arachnoid (the middle)
• 3-the pia (the inner) matters.
• It contains cavities (Ventricles).

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A) The brain

• In cross sections, it shows
• a)Grey matter dark areas which contains the
  cell bodies .
• The grey matter on the surface of the cerebrum is
  called the cerebral cortex .
• The term nucleus is used to describe any
  collection of cell bodies which perform the same
  function.
• b) White matter light areas which contain nerve
  fibers (axons) .
• The fibers run inside the C.N.S .as bundles or
  tracts.

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B) The spinal cord

• The spinal cord
• Covered by3 meninges like the brain.
• Contains cavity called the central canal .

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B) The spinal cord

• In cross section ,it shows
• a) Grey matter it is arranged in the shape of
  butter fly or like letter H.
• 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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B) The spinal cord

• The cord is divided into segments (31)
• a-cervical segments8.
• b-Thoracic segments 12.
• c-Lumber segments 5.
• d- Sacral segments 5.
• e- Single Coccygeal .
• NB. The right and left parts of the C.N.S. are
  connected together by nerve fibers called
  commissures.

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2-The peripheral nervous system

• The peripheral nervous system, It is not
  protected by bones ,
• It is divided functionally into
• a-Somatic nervous system carries sensations and
  controls skeletal muscles .
• b-Autonomic nervous system Controls smooth
  muscle ,heart glands .

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A-The Somatic nervous System

• The Somatic nervous System which formed of
• a) cranial nerves 12 pairs of nerves which
  arise from the brain.
• b) spinal nerves 31 pairs of nerves and their
  associated ganglia which arise from the spinal
  cord ,a pair arises from each segment.

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A-The Somatic nervous System

• a)Cranial Nerves
• There are 12 pairs of cranial nerves that leave
  the brain and pass through foramina in the skull.
  
• All the nerves are distributed in the head and
  neck except the Xth (vagus), which also supplies
  structures in the thorax and abdomen. ) .

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A-The Somatic nervous System

• B) Spinal Nerves
• A total of 31 pairs of spinal nerves leave the
  spinal cord and pass through intervertebral
  foramina in the vertebral column .
• The spinal nerves are named according to the
  region of the vertebral column with which they
  are associated
• 8 cervical,
• 12 thoracic,
• 5 lumbar,
• 5 sacral, and
• 1 coccygeal.
• ).

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A-The Somatic nervous System

• NB
• Q )There are eight cervical nerves and only seven
  cervical vertebrae and that there is one
  coccygeal nerve and four coccygeal vertebrae.
  WHY?
• A) During development, the spinal cord grows
  slowly than the vertebral column. In the adult,
  when growth STOPED, the lower end of the spinal
  cord reaches inferiorly only as far as the lower
  border of the first lumbar vertebra( L1

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B) Spinal Nerves

• Each spinal nerve is connected to the spinal cord
  by two roots
• A) the anterior root and
• B) the posterior root.

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B) Spinal Nerves

• 1)The anterior root (Efferent fibers )
• consists of Motor fibers, arises from the
  anterior horn of gray matter of the spinal cord.
  
• carrying motor impulses from the central nervous
  system to skeletal muscle and cause them to
  contract

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B) Spinal Nerves

• 2) The posterior root (Afferent fibers) consists
  of sensory fibers that are concerned with
  conveying information about sensations of( touch,
  pain, temperature, and vibrations ) to the
  central nervous system, so they are called
  sensory fibers ,and ends in the dorsal horn of
  the gray matter of the spinal cord .
• The cell bodies of these nerve fibers are
  situated in a swelling on the posterior root
  called the posterior root ganglion

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B) Spinal Nerves

• 3)posterior root ganglion each posterior root
  carries posterior root ganglion which contains an
  aggregation of cell bodies situated in a swelling.

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B) Spinal Nerves

• At each intervertebral foramen, the anterior and
  posterior roots unite to
• form a Trunk of spinal nerve Here, the motor
  and sensory fibers become mixed together, so that
  a spinal nerve is made up of a mixture of motor
  and sensory fibers .
• On emerging from the foramen, the spinal nerve
  divides into 2 rami
• .

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B) Spinal Nerves

• 1)Anterior ramus
• it is a large mixed nerve .
• The anterior ramus continues anteriorly to supply
  the muscles and skin over the anterolateral body
  wall and all the muscles and skin of the limbs.
• It supplies those either directly or after
  plexuses formation with neighbouring ventral
  rami .
• The ventral rami are connected to the
  sympathetic chain by rami communicantes

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B) Spinal Nerves

• 2)posterior ramus
• It is a smaller mixed nerve .
• The posterior ramus passes posteriorly around the
  vertebral column to supply the muscles and skin
  of the back.
• The dorsal rami do not form plexuses

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The Somatic nerve plexuses

• The Somatic nerve plexuses
• Most of the ventral rami of the spinal nerves
  have great tendency to form nervous networks in
  which the nerve fibers exchanged between the
  neighbouring ventral rami .
• At the root of the limbs, the anterior rami join
  one another to form complicated nerve plexuses.
• 1- cervical
• 2-brachial plexuses supply the skin muscles of
  the upper limbs.
• 3- lumbar
• 4-sacral plexuses supply the skin muscles of the
  lower limbs.
• N.B. the 12 thoracic ventral rami do not form
  plexus .

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Functionally, the nervous system can be further
divided into

• the somatic nervous system, which controls
  voluntary activities.
• the autonomic nervous system, which controls
  involuntary activities.
• The nervous system, together with the endocrine
  system, controls and integrates the activities of
  the different parts of the body.

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SUMARY TO N.S

• Central Nervous System
• The central nervous system is brain( cerebral
  hemisphere
• Brain stem cerebellum )spinal cord composed of
  large numbers of a) nerve cells and
• b) their processes,
• c) supported by specialized tissue called
  neuroglia.
• the peripheral nervous system can be further
  divided into
• a-the somatic nervous system, which controls
  voluntary activities.
• a) 12 pairs of cranial nerves and
• b)31 pairs of spinal nerves and their associated
  ganglia.
• b- the autonomic nervous system, which controls
  involuntary activities.
• The nervous system, together with the endocrine
  system, controls the activities of the different
  parts of body.

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2-Autonomic Nervous System
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2-Autonomic Nervous System

• 2-Autonomic Nervous System
• The autonomic nervous system is the part of the
  nervous system concerned with the innervation of
  involuntary structures such as the heart, smooth
  muscle , and glands throughout the body .
• It is distributed throughout the central and
  peripheral nervous system.

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2-Autonomic Nervous System

• The autonomic system
• divided into two parts
• 1)the sympathetic system .
• 2) the parasympathetic system.
• Both systems have antagonistic functions but
  they are complementary to each other . To control
  the muscles glands,

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2-Autonomic Nervous System

• The autonomic nervous system need 2 sets of
  neurons
• 1 - preganglionic neurons they carry the
  impulses from the CNS to ganglia out side the
  CNS .
• 2 - Postganglionic neurons they carry impulses
  from the ganglia to the smooth muscles and
  glands.
• A ganglia means a collection of neurons (cell
  bodies ) out side the CNS .
• .In the ganglia the pre Postganglionic neurons
  meet by making Synapse.

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1)the sympathetic system

• The Functions of the sympathetic part of the
  autonomic system
• prepare the body for an emergency,stress 3 f
  (fight ,freight,flight).
• accelerates the heart rate,
• causes constriction of the peripheral blood
  vessels, and raises the blood pressure.
• Redistribution of the blood so that it leaves
  the areas of the skin and intestine and becomes
  available to the brain, heart, and skeletal
  muscle.
• Dilatatios of the pupil.
• Stimulation of sphincters of gut .
• Erection of hairs .
• sweating

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Sympathetic System

• It is formed of
• 1) pre ganglionic fibers
• Arise from neurons of the lateral horn of the
  The gray matter of the spinal cord, in the
  following segment
• 1)all thoracic segment
• 2) the first and the second lumbar segment
  ,SO,the name thoraco lumber outflow

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the preganglionic fibers

• The axons of these cells leave the spinal cord in
  the
• anterior roots, nerve trunk ,ventral ramus of
  the corresponding spinal nerve .
• Finally ,the preganglionic fibers leave the
  ventral ramus as the white rami communicantes
  to the ganglia of the sympathetic chain.

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Once the preganglionic fibers reach the ganglia
in the sympathetic chain, they may pass to the
following destinations by dividing into

• a- Ascending group These are fibers W make
  synapses with the cell bodies of upper ganglia of
  the chain.
• b- Transverse group These are fibers W make
  synapses with the cell bodies of same level
  ganglia of the chain.
• c- descending group These are fibers W make
  synapses with the cell bodies of lower ganglia of
  the chain.
• N.B. SOME pre ganglionic fibers do not make
  synapse with sympathetic chain ,Instead ,they
  reach other distal sympathetic ganglia ,e.g.,
  Coeliac ganglion where they relay.

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2-The postganglionic nerve fibers

• The postganglionic nerve fibers they are the
  axons of the cell bodies of sympathetic ganglia
  .
• They pass from the sympathetic ganglia to reach
  different parts of the body by one of 3 methods
• 1) by rejoining the ventral dorsal rami to be
  distributed via them.
• The connection between the ganglia ventral rami
  are called gray rami communicantes .
• They are distributed in the branches of the
  spinal nerves to supply the smooth muscle in the
  walls of blood vessels, the sweat glands, and the
  erector pili muscles of the skin.
• 2)By passing along the blood vessels .
• 3)By reaching the viscera directly.

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3) Sympathetic chains

• . Sympathetic trunks are two ganglionated nerve
  trunks 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 thorax, 4 or 5 ganglia in
  the lumbar region, and 4 or 5 ganglia in the
  pelvis.
• The two trunks lie close to the vertebral column
  and end below by joining together to form a
  single ganglion, the ganglion impar.

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2) Parasympathetic System
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2) The Functions of the Parasympathetic System

• parasympathetic part of the autonomic system
  conserving and restoring energy. i.e.,
• rebuilding the body resources during rest
• They slow the heart rate
• increase peristalsis of the intestine and
  glandular activity, and open the sphincters.
• constriction of the pupil.
• NB .The hypothalamus of the brain controls the
  autonomic nervous system and integrates the
  activities of the autonomic and neuroendocrine
  systems, thus preserving homeostasis in the body

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2) Parasympathetic System

• It is formed of
• 1)The preganglionic fibers
• They arise from CNS in 2 sites
• with the cranial nerves number 10,9,7,3.
• From the neurons of the lateral horn of sacral
  spinal segments number 2,3,4.
• SO the name cranio -sacral outflow. leave the
  spinal cord in the anterior roots of the
  corresponding spinal nerves. They then leave the
  sacral nerves and form the pelvic splanchnic
  nerves.

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2) Parasympathetic System

• 2 -peripheral ganglia
• The preganglionic fibers synapse with cells in
  peripheral ganglia, which are usually situated
  close to the viscera they innervate.
• The cranial preganglionic fibers relay in (4
  cranial Para sympathetic ganglia )the ciliary,
  pterygopalatine, submandibular, and otic ganglia
  .
• The preganglionic fibers in the pelvic splanchnic
  nerves relay in ganglia in the hypogastric
  plexuses or in the walls of the viscera.

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3)The postganglionic fibers

• The post ganglionic Para sympathetic fibers (The
  axons of the cell bodies inside the ganglia )
  leave the ganglia to reach their targets.

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N.B.

• 1) peripheral nerves can regenerate if injured.
• 2) peripheral nerves are either
• a-Motor ( Efferent)if they carry orders ,e.g.,
  to a gland or muscle.
• b-Sensory (Afferent) if they carry sensations
  ,e.g., pain or touch.
• c- Mixed if they contain both motor sensory
  fibers .

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Clinical Notes

• Clinical Modification of the Activities of the
  Autonomic Nervous System
• Many drugs and surgical procedures that can
  modify the activity of the autonomic nervous
  system are available.
• For example, drugs can be administered to lower
  the blood pressure by blocking sympathetic nerve
  endings and causing vasodilatation of peripheral
  blood vessels.
• In patients with severe arterial disease
  affecting the main arteries of the lower limb.