Cranial Nerves & The Special Senses

Cranial nerves are the pathways to perception of

•Olfaction

•Taste

•Visual system

•Hearing and balance

 

Cranial nerves reside in throughout the brain: cerebrum, and brain stem (midbrain, pons, and medulla oblongota). PTs will screen and assess gross cranial nerve function through observation of involuntary movement and simple motor commands.

Brainstem: connects spinal cord to brain; integration of reflexes necessary for survival

By Patrick J. Lynch, medical illustrator (Patrick J. Lynch, medical illustrator) [CC-BY-2.5 (http://creativecommons.org/licenses/by/2.5)], via Wikimedia Commons

 

Cranial nerves (CN): part of peripheral nervous system which arises directly from brain. Two pairs of CN arise from cerebrum; ten pairs arise from brainstem. Indicated by

Roman numerals I-XII from anterior to posterior. CNs may have one or more of three functions

• Sensory (special or general)

• Somatic motor (control of skeletal muscles)

• Parasympathetic (regulation of glands, smooth muscles, cardiac muscle)

 

Subdivisions and Associated Cranial Nerves

Brain Subdivision	Associated Cranial Nerve	Major Function
cerebrum	I: Olfactory	Smell and taste
thalamus	II: Optic	Vision
midbrain	III: Oculomotor IV: Trochlear	Eye movements (adduction, elevation, depression) and motor for eyelid
pons	V: Trigeminal VI: Abducens VII: Facial VIII: Vestibulocochlear(part)	Face sensation and motor Lateral eye movement Face sensory and motor, taste   Hearing and balance
medulla oblongata	VIII: Vestibulocochlear (part) IX: Glossopharyngeal X: Vagus   XI: Spinal Accessory XII: Hypoglossal	Hearing and balance   Taste posterior third of tongue and sensory/motor in throat Autonomic functions for viscera, (BP, HR, RR), speech, breathing Motor to SCM and trapezius Motor function for tongue

 

 

Cranial Nerve Tests and Measures

The Wayne State Tutorial is highly detailed and includes a section on "interpretation" which is outside of the PTA scope of practice. We have narrowed the focused of the tutorial by linking the procedures for testing in the table below.

Any patient who reports and/or demonstrates new signs and symptoms of cranial nerve dysfunction may be experiencing a medical emergency.

A PTA should be able to select and perform tests for cranial nerve function. Specific cranial nerve testing procedures are linked below:

Cranial Nerve	Procedures	Video Demo of Normal Function
I - Olfactory	Testing Smell	Smell test video
II - Optic	Testing Visual Fields	Visual field test demo
III, IV, VI - Eye control	Tracking Saccades Convergence Divergence	Eye motor control test demo
V - Trigeminal	Testing face sensation	Face sensation and motor test demo
VII- Facial	Testing face muscles	Facial motor testing and taste demo
VIII - Vestibulocochlear	Testing hearing function Testing vestibular function	Hearing function test demo
IX, X - Gag Reflexes	Testing gag reflex Testing vocal motor function	Gag reflex testing demo
XI - Spinal Accessory	Testing Trapezius and SCM function	Manual muscle testing demo
XII - Hypoglossal	Testing tongue movements	Tongue strength and motion testing demo

 

For your reference, you can link to the full Wayne State Cranial Nerve Tutorial

 

 

Abnormal Cranial Nerve Tests and Measures

Abnormal Cranial Nerve II

Recall that visual fields are dependent on individual eye function as well as convergence of both eyes on an object/image. Damage to central visual processing systems can result in visual disturbances or field cuts.

Full Visual Field - Binocular Vision	Left Visual Field Cut

http://en.wikipedia.org/wiki/Visual_field

 

 

The video provides an example of a patient with a R visual field cut.. No sound

 

Abnormal CN V Sensory Exam

This patient demonstrates unilateral sensory dysfunction in the Trigeminal nerve. Recall that the the Trigeminal nerve is the primary nerve anesthetized during dental procedures.

 

Abnormal CN VII: Note the asymmetry in facial muscles

 

Abnormal CN XII (Hypoglossal)

The tongue will deviate toward the affected (weaker) side when the patient is prompted to stick out their tongue

 

Cranial nerve coordination examination

Sample of Normal VOR

The VOR is also referred to as the "Doll's Eye's" reflex. The examiner (sound only) is assessing both eye motor function and coordination of eye and head motions which includes CN VIII

 

 

 Safety Considerations

Examples of possible safety considerations for patients with CN deficits include:

• placing yourself and transfer surfaces within the patients's intact visual field; securing call bell within visual and sensory fields
• orienting the patient to engage in compensatory strategies to accommodate for losses in vision, sensation, etc.
• checking swallowing precautions prior to offering any patient with a neurological condition food/drink
• obtaining a second person for assistance as needed when there is a balance disorder
• applying/utilizing adaptive equipment during therapy based on deficits (eye patch, written/visual instructions (e.g., with hearing loss), soft-restraint to prevent injury to self, positioning/splinting to challenge or rest affected structures.

 

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