Cranial Nerve Injury

The cranial nerves are nerves that run from the base of the brain into different parts of the head. They can commonly be involved in traumatic injury which also includes injury to the brain itself. Unlike injuries to nerves and other parts of the body, injuries to the cranial nerves can also involve alteration or destruction of some of our senses themselves. Treating physicians also refer to cranial nerves by their number. There are twelve below which are described and represented by roman numerals.

I. Olfactory

Special Sensory – Sensation of smell

II. Optic

Special Sensory – Sensation of vision

III. Oculomotor

Somatic Motor – Movement of the eyes and eyelids
Visceral Motor – Parasympathetic control of pupil size

IV. Trochlear

Somatic Motor – Movement of eyes

V. Trigeminal

Somatic Sensory – Sensation of touch to the face
Somatic Motor – Movement of muscles of mastication (chewing)

VI. Abducens

Somatic Motor – Movements of the eye

VII. Facial

Somatic Sensory – Movement of muscles of facial expression
Special Sensory – Sensation of taste in anterior two-thirds of the tongue

VIII. Auditory- vestibular

Special Sensory – Sensation of hearing and balance

IX. Glossopharyngeal

Somatic Motor – Movement of muscles in the throat (oropharynx)
Visceral Motor – Parasympathetic control of the salivary glands
Special Sensory – Sensation of taste in posterior one-third of the tongue
Visceral Sensory – Detection of blood pressure changes in the aorta

X. Vagus

Visceral motor – Parasympathetic control of the heart, lungs, and abdominal organs

XI. Spinal accessory

Somatic motor – Movement of muscles in the throat and neck

XII. Hypoglossal

Somatic motor – Movement of the tongue

One of the most commonly injured cranial nerves is cranial nerve I the olfactory nerve, which controls the sense of smell. Because our sense of taste depends primarily on smell, our sense of taste might be altered as well. Terms used to describe problems in this include:

Dysnosmia – impaired sense of smell
Ansomia – Complete lost of smell
Prosmia – Sensation of smell without cause
Cosmia – Smelling an offensive odor that does not exist
Generally cranial nerves are not injured in cases of mild TBI. However, it is well document that cranial nerve 1 can be disrupted in the context of a mild TBI.

The optic (cranial nerve II) plays a critical role in human sight. Approximately 5 % of patients with TBI receive optic nerve injury. Injury to the optic nerve can cause the pupil to loose its reactivity to light, visual acuity, or visual fields can be affected. Examination must be done to differentiate between effects of optic nerve damage versus damage to non-nerve related areas to the visual system.

It should be remembered that, like the brain, cranial nerve can recover from a traumatic injury. The cranial nerve is stretched or bruised. Function can recover for up to a year. Post trauma. During that time there may be tingling or sporadic enervation, both of which are uncomfortable, but also show signs of recovery of that nerve.