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Cranial Nerves and their functions

The cranial nerves are the 12 pairs of nerves that leave the brain via their own individual apertures in the skull.


List of the Cranial Nerves

  1. I Olfactory (Smell)
  2. II Optic (Sight)
  3. III Oculomotor (Moves eyelid and eyeball and adjusts the pupil and lens of the eye)
  4. IV Trochlear (Moves eyeballs)
  5. V Trigeminal (Facial muscles incl. chewing; Facial sensations)
  6. VI Abducens (Moves eyeballs)
  7. VII Facial (Taste, tears, saliva, facial expressions)
  8. VIII Vestibulocochlear (Auditory)
  9. IX Glossopharyngeal (Swallowing, saliva, taste)
  10. X Vagus (Control of PNS e.g. smooth muscles of GI tract)
  11. XI Accessory (Moving head & shoulders, swallowing)
  12. XII Hypoglossal (Tongue muscles - speech & swallowing)


More information about the names, numbers and functions of the 12 cranial nerves is summarized in the following table.

Cranial Nerve

Function(s) of Cranial Nerve

1.

I olfactory

Smell

2.

II optic

Vision, also called eyesight. (Each optic nerve contains approx. a million nerve fibres that receive information from the rod and cone cells of the retina.)

3.

III oculomotor

Moves the eyeball and eyelid, adjusts the lens of the eye for near vision and also constricts the pupil of the eye via motor fibres distributed to muscles located in and around the eye.

Parasympathetic fibres
adjust the size of the pupil and the shape of the lens of the eye.

Fibres outside the eye
extend to the upper eye-lid and the extrinsic muscles that turn the eyeball in different directions, (incl. the superior rectus, medial rectus, inferior rectus and inferior oblique muscles).

4.

IV trochlear

Moves the eyeballs by sending nerve impulses to the superior oblique muscles which are among the group of muscles that rotate the eyeballs in their sockets. (The action of this nerve is coordinated with those of the oculomotor and abducens nerves i.e. cranial nerves III and VI.)

5.

V trigeminal

This is largest cranial nerve and splits into the following 3 divisions, each of which includes both motor and sensory fibres.

  1. Ophthalmic nerve
  2. Maxillary nerve
  3. Mandibular nerve

The motor fibres of all 3 divisions control the facial muscles involved in chewing. The sensory fibres convey sensations of touch, pain and temperature from the front of the head including the mouth and also from the meninges.

6.

VI abducens

Moves the eyeballs outwards by sending nerve impulses to the lateral rectus muscles.

7.

VII facial

Sensory fibres are concerned with taste via the taste buds at the front of the tongue.
Motor fibres control secretion of tears via the lacrimal glands and saliva via the sublingual salivary glandsas well as facial expressions via some of the muscles of facial expression.
A branch of the facial nerve regulates the tension on the ear ossicles.

8.

VIII vestibulocochlear

Two branches: Vestibular nerve (senses equilibrium) and Cochlear nerve (hearing)

Vestibular nerve:
Aids equilibrium by carrying impulses from the semicircular canals - providing info about posture, movement and balance

Cochlear nerve:
Carries impulses from the cochlea, so is known as the nerve of hearing.

9.

IX glossopharyngeal

Motor Fibres

  • Modulate swallowing via supply to muscles of the throat (pharynx) area
  • Parasympathetic control of secretion of saliva (via supply to the parotid salivary glands)

Sensory Fibres

  • Monitors blood pressure
  • Monitors levels of oxygen and carbon dioxide in blood
  • Coordination of some muscle activity e.g. in some swallowing muscles
  • Sensations of taste, touch, pain and temperature from posterior third of the tongue and tissues of the soft palate

10.

X vagus

Motor Fibres:

  • Under conscious control
    Stimulates voluntary muscles that effect swallowing, coughing and speech.
  • Under unconscious control
    • Stimulates the contraction and relaxation of smooth muscle in the gastrointestinal tract (GI, also called the alimentary canal)
    • Can trigger reduction (slowing) of heart-rate
    • Stimulates secretion of digestive fluids

Sensory Fibres:

  • Monitors blood pressure
  • Monitors levels of oxygen and carbon dioxide in blood
  • Sensations of touch, pain and temperature from thoat area
  • Sensations from visceral organs in thorax and abdomen

11.

XI accessory

Arises from two roots, cranial and spinal.

Cranial parts: Controls swallowing movements because nerve fibres (from the cranial root of cranial nerve XI) join the vagus nerve to form the recurrent laryngeal nerve which supplies the internal laryngeal muscles.

Spinal Parts: Governs movement of the head and shoulders by supplying the sternocleidomastoid and trapezius muscles in the (anterior and posterior) regions of the neck.

12.

XII hypoglossal

Supplies the muscles of the tongue - responsible for the tongue movements involved in speech and swallowing


See also information about the main parts of the brain and the parts (divisions) of the nervous system.

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