Cranial Nerves
Cranial nerves are sets of nerves that connect our brain to different parts of our head, neck and trunk. There are twelve cranial nerves which are named according to their function as well as structure. These are named using the Roman numerals based on their location in the body from the front to the back. These nerves are divided into two types based on their functions:
i)Sensory nerve or ii)motor nerve
Sensory nerves are the type of nerves which are connected with the sense organs such as hearing, smelling, touching, etc. While motor nerves are related to the controlling of movements and functions of muscles or glands.
The twelve types of cranial nerves are:
Olfactory Nerve
This nerve is related to ‘smell’. This nerve carries sensory information to our brain regarding the smells that we sense through our nose. The roof of the nasal cavity is called “olfactory epithelium”. It is the moist lining that dissolves the aromatic molecules or any kinds of particle that we inhale through our nose. It stimulates to generate the nerve impulses to the olfactory bulb, containing groups of nerve cells. Then these signals are sent to the part of the brain connected with memory or recognition of smells.
Optic Nerve
It is the sensory nerve that is connected with ‘vision’. When we see the light, i.e. when light enters into the eye, rods and cones receive the information and pass it from the retina to the optic nerve. Then through the optic tract, nerve impulses reach the visual cortex(located in the back part of the brain) which processes the information.
Oculomotor Nerve
It is the motor nerve that helps in the functioning of muscles as well as pupil response. These nerves provide motor functions to the muscles around the eyes. These help the eyes to move or focus on different objects at different distances. It responds to light by controlling the size of the pupil. This nerve stretches from the midbrain to the eye sockets.
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Trochlear Nerve
It controls our superior oblique muscle. This muscle helps in all kinds of eye movements like downward, outward as well as inward. It originates from the back part of mid-brain to the eye sockets.
Trigeminal Nerve
It is the largest cranial nerve that serves both the sensory and motor functions. It is divided into three parts:
Ophthalmic
It sends information sensory information from upper parts of the face like forehead, scalp and upper eyelids.
Maxillary
It sends information sensory information from middle parts of the face like cheeks, nasal cavity and upper lip.
Mandibular
It serves both the sensory as well as motor functions. It controls the movement of muscles between the jaw and ears.
Abducens Nerve
It controls the movement of another eye muscle known as the lateral rectus muscle. This muscle involves outward eye movement.
Facial Nerve
It provides both sensory as well as motor functions. It is responsible for facial expressions, providing a sense of taste through the tongue, transmitting glands in the head or neck area like salivary glands or tear-producing glands and carrying sensations from outer parts of the ear.
Vestibulocochlear Nerve
It has sensory functions like hearing and balance. It consists of mainly two parts- Cochlear and Vestibular portion. Both the portions of this nerve emerges from separate parts of our brain. Cochlear portion detects vibrations from the ear like that of sound’s loudness or pitch while the vestibular portion tracks both linear as well as rotational movements of the head.
Glossopharyngeal Nerve:
It also has both sensory and motor functions such as transmitting sensory information from the back of the throat, inner ear and providing a sense of taste for the back part of the tongue. It also stimulates voluntary movements. This nerve originates from the Medulla Oblongata.
Vagus Nerve
It is a diverse nerve having both sensory as well as motor functions like sending sensory information from chest and trunk organs like heart, etc. This nerve has the most extended pathway among all other cranial nerves. It stretches from the brain to the abdomen.
Accessory Nerve
It is a motor nerve that controls the muscles of the neck. It allows us to rotate, flex and extend our neck and shoulders. It is divided into two parts- spinal and cranial. Both the parts meet before the spinal region of the nerve moves to supply the muscles of the neck.
Hypoglossal Nerve
It is the twelfth cranial nerve, responsible for the movement of muscles of the tongue. It stretches from the medulla oblongata to the tongue.
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