The Names, Functions, and Locations of Cranial Nerves

Anatomy of the Brain

Cranial Nerves
The human cranial nerves and their areas of innervation. (Larger Image). Encyclopedia Britannica/UIG/Getty Images

The cranial nerves are nerves that arise from the brain and exit the skull through holes (cranial foramina) at its base rather than through the spinal cord. Peripheral nervous system connections with various organs and structures of the body are established through cranial nerves and spinal nerves. While some cranial nerves contain only sensory neurons, most cranial nerves and all spinal nerves contain both motor and sensory neurons.

Function

Cranial nerves are responsible for the control of a number of functions in the body. Some of these functions include directing sense and motor impulses, equilibrium control, eye movement and vision, hearing, respiration, swallowing, smelling, facial sensation, and tasting. The names and major functions of these nerves are listed below.

  1. Olfactory Nerve: Sense of smell
  2. Optic Nerve: Vision
  3. Oculomotor Nerve: Eyeball and eyelid movement
  4. Trochlear Nerve: Eye movement
  5. Trigeminal Nerve: This is the largest cranial nerve and is divided into three branches consisting of the ophthalmic, maxillary and mandibular nerves. Functions controlled include facial sensation and chewing.
  6. Abducens Nerve: Eye movement
  7. Facial Nerve: Facial expressions and sense of taste
  8. Vestibulocochlear Nerve: Equilibrium and hearing
  9. Glossopharyngeal Nerve: Swallowing, sense of taste, and saliva secretion
  10. Vagus Nerve: Smooth muscle sensory and motor control in throat, lungs, heart, and digestive system
  11. Accessory Nerve: Movement of neck and shoulders
  12. Hypoglossal Nerve: Movement of tongue, swallowing, and speech

Location

The cranial nerves consist of 12 paired nerves that arise from the brainstem. The olfactory and optic nerves arise from the anterior portion of the brain called the cerebrum. The oculomotor and trochlear cranial nerves stem from the midbrain. The trigeminal, abducens, and facial nerves arise in the pons. The vestibulocochlear nerve arises in the inner ears and goes to the pons. The glossopharyngeal, vagus, accessory and hypoglossal nerves are attached to the medulla oblongata.

Sensory Cranial Nerves

Snellen chart
Snellen chart test assesses visual acuity and optic nerve function. CentralITAlliance/iStock/Getty Images Plus

There are three sensory cranial nerves: olfactory (I), optic (II), and vestibulocochlear (VIII). These cranial nerves are responsible for our senses of smell, vision, hearing, and equilibrium. Medical professionals test cranial nerve I by having a person close their eyes and one nostril while inhaling a scent such as coffee or vanilla. An inability to recognize a scent may indicate problems with the sense of smell and cranial nerve I. Central and peripheral vision are under the control of optic nerve (II). Examiners test visual acuity using a Snellen chart.

Vestibulocochlear nerve (VIII) functions in hearing and can be assessed with the whisper test. The examiner stands behind the person and whispers a sequence of letters into one ear while the person holds a hand over the non-tested ear. The process is repeated with the opposite ear. Ability to repeat the whispered words indicate proper function.

Motor Cranial Nerves

Motor nerves function in movement of anatomical structures. Motor cranial nerves include the oculomotor (III), trochlear (IV), abducens (VI), accessory (XI), and hypoglossal (XII) nerves. Cranial nerves III, IV, and VI control eye movement. The oculomotor nerve controls pupil constriction and is assessed using a penlight. Light is briefly advanced from the outer edge of the eye to the center of the eye and pupil responses are observed. The trochlear and abducens nerves are often tested by having a person follow an examiner's finger movements with his or her eyes only.

The accessory nerve controls movement of the neck and shoulders. It is tested by having a person shrug his or her shoulders and turn their head from side to side against resistance from the the examiner's hand. The hypoglossal nerve controls movement of the tongue, swallowing, and speech. Assessment of this nerve involves asking the person to stick out his or her tongue to ensure that it is midline.

Mixed Cranial Nerves

Trigeminal nerve
 normaals/iStock/Getty Images Plus

Mixed nerves have both sensory and motor function. Mixed cranial nerves include the trigeminal (V), facial (VII), glossopharyngeal (IX), and vagus (X) nerves. The trigeminal nerve is the largest cranial nerve and is involved in facial sensation, chewing, and corneal reflex. Facial sensations are often checked by rubbing soft and blunt objects on various areas of the face. Chewing is typically tested by having the person open and close his or her mouth. The facial nerve controls facial expressions and is involved in taste sensation. This nerve is commonly tested by observing for facial symmetry. The glossopharyngeal nerve plays a role in swallowing, sense of taste, and saliva secretion. The vagus nerve is involved in smooth muscle sensory and motor control in the throat, lungs, heart, and digestive system. Cranial nerves IX and X are typically assessed together. The person is asked to say "ah" while the examiner observes movement of the palate. Swallowing ability and the ability to taste different foods are also tested.

Sources

  • "Facing Cranial Nerve Assessment." American Nurse Today, 17 May 2019, www.americannursetoday.com/facing-cranial-nerve-assessment/. 
  • Seladi-Schulman, Jill. "The 12 Cranial Nerves." Healthline, Healthline Media, www.healthline.com/health/12-cranial-nerves.