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Cranial Nerves List and Functions: A Practical Reference

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The cranial nerves list is an orderly grouping of the twelve pairs of nerves that traverse the cranium (bony enclosure of the brain) and which exit through small holes in the skull known as foramina (pl. for foramen). 

The sequence of the cranial nerves list is by number. Each cranial nerve has a number as well as a name which denotes at least in part, its function(s), structure, or location. The number for each nerve is in the form of a roman numeral.  The list begins with Roman numeral I and ends with Roman numeral XII.  A list that is most helpful to learners is one that includes the number, name, and function of each nerve. 

What are the cranial nerves?    

Cranial nerves are the axons of clusters of neuron cell bodies from which they originate.  Some received signals from parts of the body. Others send them.  Some do both.  Those that receive signals are sensory cranial nerves.  Those that send signals are motor cranial nerves.  Mixed cranial nerves are those that have both sensory and motor fibers.

Motor cranial nerves   

Motor cranial nerves are efferent fibers, in that they effect actions. They have different modalities (modes of cranial nerves listaction) based on the type of nerve fibers and the body parts they supply. One mode of action is the movement of skeletal muscles and other muscles under voluntary control.  Somatic motor refers to the voluntary control of these types of muscles.  Another mode of action is the movement of smooth muscles, which are those not under voluntary control.  Yet, another mode of action is the stimulation of special groups of cells to release substances such as enzymes and hormones.  Finally, some fibers cause parts of viscera, other than smooth muscle, to perform some other vital functions.  Autonomic motor is the term for this type of involuntary control by cranial nerves.  It is an action of the parasympathetic nervous system. 

Cranial nerve fibers that govern voluntary muscle actions arise from clusters of cell bodies in the brainstem and/or brain, depending on the function(s).  These groups of cell bodies are termed cranial nerve nuclei (pl. for nucleus). They are the axons of multipolar neurons which tend to be in medial locations. Cranial nerve fibers that control involuntary motor activity, on the other hand, are axons of unipolar neurons that arise from one or more of four pairs of ganglia within the skull but outside of the CNS, except for those of cranial nerve X that supply viscera.  The latter arise from nests of cell bodies situated near or within the organs they connect with and send activating signals to.

Sensory cranial nerves  

There are also sensory cranial nerve nuclei, all of which are in the brainstem except for those of cranial nerves I and II, which are in the brain.  It bears noting however, that the cell bodies of sensory cranial nerves are not in the nuclei. They are in clusters within the cranium but outside of the CNS, much like those of the autonomic motor fibers.  The name for these structures is cranial nerve ganglia (pl. for ganglion).

Sensory cranial nerves otherwise have some similarities as well as differences to motor ones.  They have different modes of function, depending on the nerve.  Those modes are sensory, special sensory and autonomic sensory. The sensory axons of these structures connect centrally and send impulses to the brain by way of the sensory nuclei.  These sensory nuclei tend to be in the lateral portions of the brain and brainstem.

Mixed cranial nerves

Mixed cranial nerves have at least two different nuclei.  At least one is sensory and at least one is motor.  In some cases different cranial nerves will share a common nucleus.  The two nerves involved in taste is an example.  More specifically, cranial nerve IX does not have a nucleus of its own. It shares two nuclei with nerves VII and X. 

Cranial nerves and their functions

The table below is the list of 12 cranial nerves by number and name.  It also provides information about their mode(s) of action and their actual function(s).

#

Cranial Nerve Name

Modality

Function(s)

I

Olfactory

Special Sensory

Conveys smell

II

Optic

Special Sensory

Mediates eyesight by receiving signals for vision from rod and cone cells in the retina, and then sending them through other parts of the optical pathway to the calcarine cortex which processes them into vision

III

Oculomotor

Somatic Motor


Autonomic Motor
    1. Controls most movement of the eyeball by supplying four of the six eyeball muscles
    2. Raises and retracts the upper eyelid

    1. Constricts the pupil and decreases the amount of light entering the eye (light reflex) by stimulating the pupillary constrictor muscle when light entry increases or while maintaining focus as an object moves closer to the eye
    2. Causes changes in the shape of the lens of the eye to maintain focus when an object becomes closer (accommodation) by stimulating the ciliary muscle

IV

Trochlear

Somatic
Motor

Rotates the top of the eyeball inward and to a lesser extent downward by sending nerve impulses to the superior rectus muscle

V

Trigeminal

Somatic Motor

Sensory


Controls muscles of mastication (chewing)


Conveys general sensation (i.e. touch, pain and temperature perception) to the upper, mid and lower face as well as the gums and teeth; Consists of three branches:

    1. Ophthalmic branch
    2. Maxillary branch
    3. Submandibular branch

VI

Abducens

Somatic Motor

Causes abduction (i.e. outward or lateral movement) of the eyeball by sending nerve signals to the lateral rectus muscle

VII

Facial

Somatic Motor

Autonomic
Motor


Special Sensory

Sensory
Activates the muscles of facial expression

Causes production of tears by the lacrimal glands; saliva by salivary glands except the parotid gland; and mucus by mucous glands in the nose, mouth and throat regions via parasympathetic stimulation of them

Conveys taste to the anterior two thirds of the tongue


Provides general sensation to a small area of skin behind the ear and the external passage of the ear leading from the outside to the tympanic membrane (eardrum), as well as the outer surface of the tympanic membrane

VIII

Vestibulocochlear

Special Sensory

Has two branches; cochlear branch transmits hearing; vestibular branch senses equilibrium and helps maintain balance

IX

Glossopharyngeal

Somatic Motor

Autonomic
Motor

Sensory


Special Sensory

Autonomic Sensory


Activates the stylopharyngeus and superior constrictor muscles of the pharynx involved in swallowing; with the vagus nerve, it is involved in the gag reflex

Through parasympathetic stimulation, causes the parotid gland to produce amylase-rich secretions

Bestows general sensation to the posterior and lateral aspects of the pharynx as well as the middle ear, an area of skin behind the ear, the internal surface of the tympanic membrane, and the posterior one-third of the tongue

Provides taste to the posterior one-third of the tongue


1. Receives signals from baroreceptors in the carotid sinus when changes in blood pressure occur and thus participates in blood pressure regulation
2. Receives signals from chemoreceptors in the carotid sinus when significant changes in pH, CO2 or O2 occur, thus initiating compensatory measures

X

Vagus

Somatic Motor

Autonomic
Motor






Autonomic Sensory



Sensory
Activates muscles of the pharynx and larynx and one of the tongue muscles used during speaking, swallowing and coughing

Provides parasympathetic stimulation to most viscera producing such effects as:
  • Constriction of large airways in the lungs
  • Secretion of mucus by goblet cells of the respiratory tract and digestive tract
  • Slowing of the heart rate
  • Contraction and relaxation of smooth muscle in the gastrointestinal tract
  • Secretion of digestive fluids by the digestive tract and its accessory glands

    1. Receives signals from baroreceptors in the aortic arch when changes in blood pressure occur and thus participates in blood pressure regulation
    2. Receives signals from chemoreceptors in the aortic arch when significant changes in pH, CO2 or O2 occur, thus initiating compensatory measures

    Supplies general sensation to the throat area and visceral organs of the thorax and abdominal cavity
  • XI

    Spinal Accessory

    Somatic Motor
    Controls the trapezius muscle used for shoulder shrugging, and sternocleidomastoid muscle used for contralateral head rotation and ipsilateral head flexion

    XII

    Hypoglossal

    Somatic MotorSends nerve impulses to all but one of the tongue muscles, allowing movement, including that which is necessary for speaking and swallowing
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