The nerves that arise from the brain are called cranial nerves. In human body, there are 12 pairs of cranial nerves. Among these, 1st, and 2nd nerves are connected to the forebrain; 3rd and 4th nerves to midbrain; 5th, 6th, 7th and 8th nerves to pons and 9th. 10th, 11th and 12th nerves to medulla oblongata. Some of these nerves such as 1st, 2nd and 8th nerves are purely sensory while some others such as 3rd, 4th, 6th, 11th and 12th nerves are purely motor and the remaining ones i.e., 5th, 6th, 9th and 10th nerves of mixed type.
1st cranial nerve
It is also called olfactory nerve. It is a purely sensory nerve which carriers the sensation of smell from the receptor of smell in the nose to the limbic lobe of cerebrum. So it is the nerve for smell sensation.
2nd cranial nerve
Its name is optic nerve and it is also a sensory nerve. It carries visual sensation from the retiria-of eye to the brain.
3rd cranial nerve
It is called oculomotor nerve. Iit is a purely motor nerve. It contains both somatic and autonomic type of nerve fibers. The somatic fibers innervate some external ocular muscles and thereby control the movements of eyeball. The autonomic fibers of this nerve belong to the parasympathetic system. They innervate the smooth muscles present within the eyeball namely the ciliary muscles for increasing the curvature of lens during near vision, and the circular muscles of iris for constriction of pupil.
4th cranial nerve
It is called trochlear nerve which is also a motor nerve that innervates some external ocular muscles and controls eye movements.
5th cranial nerve
5th cranial nerve is called trigeminal nerve. It is a mixed nerve. Its sensory fibers carry the sensation of touch, pressure, temperature and pain from the mouth cavity, nasal cavity, cornea and iris of eye and skin of face to the brain. Its motor fibers control the movement of masticatory muscles and help in chewing.
6th cranial nerve
It is known as abducens nerve. It is a motor nerve supplying some external ocular muscles and controls eye movements.
7th cranial nerve
It is called facial nerve. It is a mixed nerve. Its sensory fibers carry the sensation of taste from the anterior two-third part of the tongue as well as general sensations from the skin of external ear. It contains somatic and autonomic motor fibers. Somatic motor fibers supply the facial muscles and control facial expressions. The parasympathetic fibres innervate salivary (submaxillary and sublingual) glands and lacrimal (tear) glands; thus, they control secretion of saliva and tear.
8th cranial nerve
It is known as auditory or vestibulo-cochlear nerve. It is a purely sensory nerve. It has two branches, vestibular and cochlear. The vestibular branch carries the information related to rotation of head originating from the vestibular apparatus of the internal ear. The cochlear division carries auditory sensations from the cochlea of the internal ear.
9th cranial nerve
The 9th cranial nerve is called glossopharyngeal nerve. It is a mixed nerve. Its sensory division carries conscious sensation of taste from the posterior one-third part of the tongue and sensation of touch and pressure from the pharynx. It also carries unconscious sensations related to blood flow, from the carotid sinus and carotid body receptors. Its motor division consists of somatic as well as parasympathtic fibers. The somatic motor fibers supply the pharyngeal muscles and help in swallowing. The parasympathetic fibers control secretion of salivary gland.
10th cranial nerve
Its name is vagus nerve. It is a mixed nerve and is most widely distributed among the cranial nerves. The sensory fibers of vagus nerve are distributed on pharynx, larynx, oesophagus, and various visceral organs present in chest and abdomen and carry different sensations from these organs. The motor fibers of vagus are mainly of parasympathetic type and are supplied to the muscles and glands of various thoracic and abdominal viscera. So, this nerve takes part in swallowing, voice production, movements of alimentary canal, secretion of digestive juices inhibition of heart etc.
11th cranial nerve
It is called spinal accessory nerve. It is a motor nerve having dual origin in medulla and upper five or six segments of spinal cord. Its cranial division controls the movements of larynx, pharynx and soft palate while the spinal division controls the muscles of neck. Thus, it controls voice production and movement of head.
12th cranial nerve
12th cranial nerve is known as hypoglossal nerve. It is a motor nerve supplying the voluntary muscles of tongue and thereby controls tongue movements.