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Peripheral Nervous System & Autonomic Nervous System

Peripheral Nervous System


Nervous System:
Is an organ system in charge of sending message to & form the brain & spinal cord to & from all the part of body.
The nervous system detects & responds to changes inside & outside the body.
It consists of brain and spinal cord, also including peripheral nerves.

Two groups: CNS (Central Nervous System): Brain & Spinal cord.
PNS (Peripheral Nervous System): Include all nerves outside of Brain & spinal cord.

Peripheral nervous system:
• The main function of the PNS is that connects the CNS nervous system to the limbs or organs.
• PNS is not protected by the bone of spine or skull.
• PNS comprises paired cranial & sacral nerves (Somatic Nerves) & ANS:
o Some of these are sensory (afferent) transmitting impulses to the brain.
o Some of nerves are motors (efferent) transmitting the impulses from the CNS.
o Mixed nerves- outside the spinal cord, when sensory & motor nerves are enclosed within the same sheath of connective tissue.
• It is useful to considered two functional parts:
o Sensory division
o Motor division
In motor division subdivided into 2 parts:
Somatic Nervous System: Control voluntary movement.
• Autonomic Nervous System: Control the involuntary movements Eg: Heart beats, Paristalsis.
Subdivided: Sympathetic
Parasympathetic

Classification of Peripheral nervous system:

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Peripheral Nerves System:
➢ Consist of two i.e. Somatic Nervous System and Autonomic Nervous System

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a) Somatic nervous system:
• Has both sensory function & motor function.
• Responsible for carrying information to the CNS & motor information from
the CNS.
• Responsible for sensory information as well as for voluntary movements.
Two major types of neurons:

  1. Sensory neurons (Afferent)
  2. Motor neurons (efferent)
  1. Subdivided into two parts:
  2. 12 pairs of Cranial nerves
  3. 31 pairs of spinal nerves
    Cranial Nerves (12 pairs):
    • Originating from nuclei in the inferior surface of the brain (some are sensory, some are motors or mixed)
    • Nerves that emerged directly from the brain, in contrast to spinal nerves, which emerge from segments of the spinal cord.
    • 12 pairs emerge from the cerebrum; the remaining 10 pairs emerge from the brain stem. They are numbered using Roman numerical according to the order they connect to the
    brain.
    I Olfactory nerve (Sensory): It is nerve of smell.
    II Optic nerve (Sensory): nerve of vision.
    III Oculomotor nerve (motor): Supplies the muscles of eye movement.
    IV Trochlear nerve (motor): supplies the muscles of eye movement.
    V Trigeminal nerve (mixed): Sensory fibers to the face & forehead.
    VI Abducens nerve (motor): It supplies the muscles of the eye ball & movement.
    VII Facial nerve (mixed): It supplies the muscles of Facial expression.
    VIII Auditory nerve (sensory): Cochlear nerve: nerve of hearing, &

Vestibulocochlear nerve: nerve of equilibrium and balance
IX Glossopharyngeal nerve (mixed): Sensory to tongue & motor to the pharyngeal muscles.
X Vagus nerve (mixed): distributed to pharynx, Larynx, lungs, heart, stomach & intestine.
XI Accessory nerve (motor): supplies pharynx & larynx, muscles of neck.
XII Hypoglossal nerves (motor): supplies the muscles of the tongue.

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Spinal Nerves (31 pairs):
Spinal Nerves or nerves roots branch off spinal cord & pass out through a hole in each of the vertebrae called the foramen. These nerves carry information from the spinal cord to the rest of the body & from body back to the brain.
They are named & grouped according to the vertebrae with which they are associated-

  1. 8 cervical (C1-C8)
  2. 12 thoracic (T1-T12)
  3. 5 Lumber (L1-L5)
  4. 5 sacral (S1-S5)
  5. 1 Coccygeal (C0)

The lower ends of spinal cord terminate in a bunch of nerves called as ‘Cauda equina’.
There are only seven vertebrae; there are 8 cervical nerves because 1st pair leaves the vertebral canal between the occipital bone & atlas (1st cervical vertebrae) & 8th pair leaves below the last cervical vertebrae.
The spinal nerves are formed within a few centimeters of the spine on each side. Some groups of spinal merge each other to form a large plexus. Some spinal nerves divided into smaller branches
without forming a plexus.
A plexus is a group of nerves that combine with each other. There are 5 main plexi formed by the spinal nerves.

  1. Cervical Plexus: Composed of spinal nerves C1 through C5, these divide into smaller nerves that carry sensory messages & provide motor control to the muscles of the neck &
    sholders.
  2. Branchial Plexus: Formed by the merging of spinal nerve C5 through T1, These plexus branches into the nerves that carry sensory messages & provide motor control to the arm
    and upper back. Subdivided:
    • Axillary nerves
    • Radial nerves
    • Musculocataneous nerve
    • Median nerves
    • Ulnar nerves
    • Medial cutaneous nerves
  3. Lumbar Plexus: Spinal nerves L1 through L4 converge to form the lumbar plexus. This plexus splits into nerves that carry sensory messages and provide motor control to the
    muscles of the abdomen and leg. Subdivided:
    • Iliohypogastric nerves
    • Ilioinguinal nerves
    • Genitofemoral
    • Lateral cutaneous nerves of thigh
    • Femoral nerves
    • Obturator nerves
    • Lumbosacral nerves
  4. Sacral Plexus: Spinal nerves L4 through S4 join together, and then branch out into nerves that carry sensory messages and provide motor control to the muscles of the legs.
    Subdivided:
    • Sciatic nerve
    • Tibial nerve
    • Common peroneal nerve
    • Pudendal nerve
  5. Coccygeal Plexus: Composed of the merging of nerves S4 through Co1, this plexus supplies motor and sensory control of the genitalia and the muscles that control defecation.
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Autonomic Nervous System


(Autonomus system/ Visceral/ Vegetative or Involuntary)
• ANS widely distributed throughout the bodies.
• The ANS control the homeostasis, Cardiovascular; digestive, respiratory function as well
as salivation, pupil diameters, etc.
• In general nerve impulses from one division of the ANS stimulate the organ to increase its activity (excitation), and another part inhibit the organs activity (inhibition).
Structurally, ANS includes:
✓ autonomic sensory neurons (afferent)
✓ integrating centers in the CNS
✓ autonomic motor neurons (efferent)
• The ANS consist of two division
 Sympathetic (Thoracolumbar Outflow)
 Parasympathetic (Craniosacral outflow)
Sympathetic has thoracolumbar outflow that means the neurons begin at the thoracic & Lumbar (T1-L2) of the spinal cord. Parasympathetic division has Craniosacral outflow that means neurons begin at the cranial nerves (CN3, CN7, CN9 & CN10) and sacral nerves (S2-S4) of spinal cord.

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The ANS generally has Efferent or visceral efferent fibers that create motor repose due to afferent or visceral efferent fiber stimulation.
• Efferent pathways consist of 2 neurons:
1st neuron is stored in the brain stem or spinal cord, which also referred as preganglionic neurons.
2nd neuron is stored in ganglia or in the body itself and referred to as Post-ganglionic neurons.
Cell body of the Preganglionic neurons
(Brain stem or spinal cord)
Its axon terminals synapse with the cells body of the post ganglionic neurons
In the autonomic ganglion outside the CNS Cell body of the post ganglion which is in the autonomic ganglion.
The post-ganglionic neuron conducts impulses to the effector organ.
Anatomically, both the sympathetic & parasympathetic nervous system consist of:

  1. A preganglionic nerves:
    a. The cell body located within the gray matter of the CNS (brain or spinal cord)
    b. Its myelinated axon exits the CNS.
    c. The pre-ganglionic axon passes from the CNS in the spinal or cranial nerve.
    d. The pre-ganglionic axon terminates in a ganglion.
  2. A ganglion
    Is a collection of nerve cell bodies located in a specific site within the body but outside the CNS
  3. A post ganglionic nerves
    a. Cell body located in an autonomic ganglion.
    b. Location of the ganglion is dependent upon the division of the ANS to which the neurons belongs & which organ it will innervate.
    c. Axon of post-ganglia is unmylinated fibers.
    d. Axon passes from the ganglion to effector (cardiac muscles, smooth muscles, or gland) is either stimulated or inhibited.
    e. Because of location of ganglia Sympathetic post ganglionic fibers are relatively long while parasympathetic postganglionic fibers are short.
  4. An effector organs which the nerves supplies.
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Sympathetic nerves:

  1. Preganglionic fibers:
    a. They are arises from the lateral horn cell of the spinal cord. They pass through anterior nerves roots of spinal nerves.
    b. Then they run for a shorter distance in the spinal nerve.
    c. Myelinated.
  2. Sympathetic Gangalion:
    The cells in these ganglia send long processes to the organ supplied.
    Types- Sympathetic Chain or Prevertibral gangalia & Paravertibral ganglia
  3. Postganglionic fibers:

They are formed by the ‘grey rami communicans’(each nerves receive a branch) which form ganglia of sympathetic chain.

4. Receptors


The receptors present at the post ganglionic sympathetic nerves ending are called adnergic receptors.
  • ➢ Alpha receptor- action on which is excitatory (except intestinal)
    ➢ Beta receptor- action on which is inhibitory (except heart)
    Neurotransmitter (Chemical substance of messages) in the Preganglionic sympathetic nerves
    is ‘Acetylcholine [(Ach): Function; contract smooth muscles, increase bodily secretion & slow down heart rate]’ which is liberated at the ganglion. And in postganglionic sympathetic nerves ending is ‘Nor-adernaline’ [(NA): Function; increase the force of skeletal muscles
    contraction, forced in contraction of heart]
    Parasympathetic Nervous Sytem:
  • Preganglionic fibers:
    Fibers of parasympathetic arises from cells present in the
    -midbrain
    -medulla
    -sacral portion of spinal cord
    All these nerves end in a ganglion
  • Parasympethetic ganglion (terminal ganglia):
    Lies near the organ supplied & hence have short postganglionic process.
  • Postganglionic fibers: They arise from the ganglia and then reach the structure which
    these nerves supply.
  • Receptors: 1. Nicotinic & 2. Muscarinic
    The Neurotransmitter of both Preganglionic & Paraganglionic in Parasympathetic nervous system in liberated ‘Acetylcholine’.
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