Peripheral and Autonomic nervous system

Peripheral nervous system

The nerves arising from the central nervous system constitute peripheral nervous system.  It includes cranial and spinal nerves.

Cranial nerves: the nerves arising from brain are called cranial nerves. There are 12 pairs of cranial nerves. Cranial nerves are sensory, motor and mixed. They are as follows:

        I.             Olfactory nerves- sensory in relation to smell

      II.            Optic nerves- sensory in relation to sight

    III.            Oculomotor nerves-motor ,control movements of eye , lens, iris, eyeball

    IV.            Trochlear or pathetic  nerves- motor, control rotation of eye

      V.            Trigeminal nerves

1.       Ophthalmic nerves-sensory, links with eyelid,conjunctiva,facial skin, forehead

2.       Maxillary nerves-sensory, links with cheeks, upper jaw and lower eyelid

3.       Mandibular nerves-mixed, linked with lower jaw, lower lip,tongue,pinna

    VI.            Abducent nerves-motor, control horizontal movement of eyeball.

  VII.            Facial nerves-mixed nerve to taste bud, motor to facial muscle for facial expression

VIII.           Auditory nerves

1.       Vestibular nerves-sensory, maintain body posture and balance

2.       Cochlear nerves-sensory, associated with hearing

    IX.            Glossopharyngeal nerves-mixed, linked with pharynx,paritod gland,tongue,tonsil

      X.            Vagus nerves-mixed, linked with pharynx,larynx,trachea,heart,oesophagus,intestine,liver,spleen.gall bladder,pancrease,kidney,ureter,blood vessels, stomach and larynx

    XI.            Accessory nerves- motor, linked with pharyngeal, neck and laryngeal muscle

  XII.            Hypoglossal nerves-motor, linked with hyoid bone, tongue, movement of larynx and tongue.

Spinal nerves: the nerves arising from spinal cord are termed as spinal nerves. There are 31 pairs of spinal nerves. They are named after name of vertebra. They are:

1.       Cervical-8 pairs

2.       Thoracic- 12 pairs

3.       Lumbar- 5 pairs

4.       Sacral- 5 pairs

5.       Coccygeal- 1 pair

Each spinal nerve carries both motor and sensory impulses hence they are mixed nerves. Each arises from spinal cord by two roots i.e. dorsal and ventral.

Autonomic nervous system

The nerve fibre that innervates smooth muscles, cardiac muscles, epithelium etc constitutes ANS. It includes sympathetic and parasympathetic nerves

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Sympathetic nerves: sympathetic nerves innervate visceral organs like heart, lungs, kidney, glands etc.  These release nonadrenaline or adrenaline as a neurotransmitter.

Parasympathetic nerves: these are nerves originated from 3, 7, 9 and 10 cranial nerves and 2, 3, 4 sacral nerves. They release acetylcholine as a neurotransmitter.

Working of ANS: the sympathetic and parasympathetic nerves supply the same organs but their effects are usually opposite. In general, sympathetic nerves stimulates organ for action while parasympathetic stimulates to calm down the organ. Example if sympathetic nerves increase the heart rate and blood pressure, then parasympathetic slows down the heart rate and blood pressure. Sympathetic and parasympathetic performs also the action of adrenaline and non adrenaline hormones.