Collect the information about cranial nerves. Spinal nerves from the internet or from your school library. (AS4)

The nerves originate from central nervous system and connect either receptor or effector organs form peripheral nervous system. Those nerves which arise from brain are called cranial nerves and those which arise from spinal cord are spinal nerves.

Cranial nerves - They are named so because they pass through various foramina in the cranial bones . There are 12 pairs of cranial nerves present in man.

1) Olfactory nerve - Its nerve fibres arise in the olfactory epithelium of the nasal chamber. It is sensory nerve which carries impulse of smell from olfactory epithelium to brain.

2) Optic nerve - They originate in the retina of the eye and combine to form optic nerve. It is sensory and carries impulses of sight from the retina of the brain.

3) Oculomotor nerve - It arises from the floor of the midbrain. It innervates the eye muscles. It is a motor nerve and carries impulses from the brain to these muscles for controlling the movements of eye ball.

4) Trochlear nerve - It innervates an extrinsic eye muscle that loops a pulley-shaped ligament in the orbit. The trochlear nerve is the thinnest and smallest cranial nerve. It originates from the floor of the midbrain.

5) Trigeminal nerve - It is the largest cranial nerve. It arises from the ventral surface of the pond Varolii. It divides into three branches :

a) Ophthalmic nerve - It is the smallest branch of trigeminal nerve. It runs forward through the eye orbit and innervates the lacrimal glands , the conjunctiva , the forehead , the eyelids etc. It is sensory nerve and carries impulses of touch from the above mentioned areas to the brain.

b) Maxillary nerve - It innervates the cheek , the upper gums , the upper teeth and lower eyelids, etc. It us sensory branch and carries stimuli from these areas.

c) Mandibular nerve - It us the largest branch. It distribute nerve fibres to the teeth , gums of lower jaw , pinna of the ear , lower lip and the tongue. It is a mixed branch showing both sensory and motor functions.

6) Abducens nerve - It controls the extrinsic eye muscle that abducts the eyeball. It originates from pins Varolii. It is a motor nerve and controls the movements of the eyeball.

7) Facial nerve - It arises from a lower part of pins Varolii. It innervates the taste buds of the tongue and muscles of the face. It also innervates the salivary glands. It is a mixed nerve.

8) Auditory nerve - It arises from the internal ear. It is formed by two branches : cochlear nerve and vestibular nerve.

9) Gloss of pharyngeal nerve - It originates from the aide of medulla oblangata. It controls secretion of saliva, sense of taste and movement of the pharynx.

10) Vagus nerve - It is the longest cranial nerve. It arise from the aide of medulla oblangata. It is a mixed nerve. It controls the visceral sensations , movement, etc.

11) Accessory nerve - It originates from both the brain and spinal cord. It is a motor nerve which innervates the muscles of the pharynx ,larynx , neck and shoulder .

12) Hypoglossal nerve - It originates from the ventral side of medulla oblangata. It innervates the muscle of tongue and hyoid apparatus. It is a motor nerve which controls movement of the tongue.

Spinal nerves - 31 pairs of spinal nerves are named and numbered according to the vertebrae with which they are associated. It includes 8 pairs of cervical nerves , 12 pairs of thoracic nerves, 5 pairs of lumbar nerves, 5 pairs of sacral nerves and one pair of coccygeal nerves.

The spinal nerves are formed by the union of dorsal and ventral roots shortly after they leave the spinal cord. Each spinal nerve has afferent and efferent fibers. All spinal nerves are mixed nerves as they carry both sensory and motor impulses.