What are Cranial Nerves?
“Nerves that extend throughout the body on both sides emerging directly from brain and brain stem are called cranial nerves.”
Cranial nerves carry information from the brain to all parts of the body, primarily to the head and neck. These nerves are paired and present on both sides of the body. They are mainly responsible for facilitating smell, vision, hearing, and movement of muscles.
Cranial nerves are concerned with the head, neck, and other facial regions of the body. Cranial nerves arise directly from the brain in contrast to spinal nerves and exit through its foramina. Most of the cranial nerves originate in the brainstem and pass through the muscles and sense organs of head and neck.
Traditionally, there are twelve cranial nerves which are numbered using Roman numerals according to the order in which they emerge from the brain (from front to back).
Cranial nerves are considered as a part of the peripheral nervous system, although olfactory and optic nerves are considered to be part of the Central nervous system. Most of the cranial nerves belong to the somatic system. Some of the cranial nerves are sensory and motor nerves as they contain only sensory fibres and motor fibres. Others are mixed nerves because they include both sensory and motor fibres.
Only cranial nerves I and II are purely sensory, and function as the sense of smell and vision. The rest of the cranial nerves contain both afferent and efferent fibres and are therefore referred to as the mixed cranial nerves. However, the vagus nerve has branches to most of the internal organs and is the part of the autonomic nervous system.
Also Read: Nerves
Cranial Nerves List
Cranial nerves are basically named according to their structure and functions. Olfactory and optic nerves emerge from the cerebrum and all other 10 nerves emerge from the brain stem. Cranial nerve functions include all five senses and muscle movements.
The below table provides the complete list of cranial nerves along with their location and functions.
|Olfactory (I)||Cribriform plate||Sensory||Smell|
|Optic (II)||Optic foramen||Sensory||Vision|
|Oculomotor (III)||Superior orbital fissure||Motor||Eye movement|
|Trochlear (IV)||Superior orbital fissure||Motor||Eye movement|
|Trigeminal (V)||Superior orbital fissure||Mixed||Facial sensation|
|Abducens (VI)||Superior orbital fissure||Motor||Eye movement|
|Facial (VII)||Internal auditory canal||Mixed||Facial expression|
|Vestibulocochlear (VIII)||Internal auditory canal||Sensory||Hearing and balance|
|Glossopharyngeal (XI)||Jugular foramen||Mixed||Oral sensation and taste|
|Vagus (X)||Jugular foramen||Sensory||Vagus nerve|
|Accessory (XI)||Jugular foramen||Motor||Shoulder elevation and head-turning|
|Hypoglossal (XII)||Hypoglossal||Motor||Tongue movement|
Functions of Cranial Nerves
Following is the cranial nerves list along with the important functions they perform:
Olfactory nerve: This nerve helps to feel the sense of smell. This is the primary nerve that is responsible for the smell. Damage to this nerve may result in distortion of smell and taste.
Optic nerve: The optic nerve is the agent of vision. This transmits visual information for eyes to the brain and vice versa. Any damage to this nerve results in problems related to sight and vision.
Oculomotor nerve: Oculomotor nerve helps in the movement of the eye. Damage to this nerve leads to distortion in vision or double vision and even problem in the coordination of eyes.
Trochlear and Abducens nerves: These nerves also help in eye movement. Damage to the Trochlear nerve might cause inability to move eyeball downwards and damage to abducens nerve might result in diplopia.
Trigeminal nerve: This nerve helps you to have facial sensation. This nerve comprises of three parts namely ophthalmic, maxillary and mandibular.
Facial nerve: This nerve is responsible for facial expression. Due to the damage to this nerve, it might cause the inability to move face parts on one or more sides.
Vestibulocochlear: Vestibulocochlear is responsible for hearing and balance. This helps eyes to keep track of moving objects while your head is stable. The sensation of spinning and dizziness are the symptoms of damage to this nerve.
Glossopharyngeal: Oral sensation and taste are stimulated by this nerve. Damage to this nerve leads to the inability to recognize the taste and so on.
Vagus nerve: This nerve monitors the level of oxygen and helps us to feel the sensation of heat or cold near the throat area. Damage to this nerve leads to the inability to swallow. Major damage to the vagus nerve might result in hypertension or high blood pressure and heart attack.
Accessory nerve: This nerve arises from two roots namely the cranial and spinal bones. This nerve controls swallowing movements and helps in the movement of head and shoulders.
Hypoglossal nerve: This nerve facilitates the movement of the tongue and helps to talk, swallowing etc.
Read more about Nervous System Diseases
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