SPH405

GOAL: Students will know the communicative functions associated with each of the twelve cranial nerves.

OBJECTIVES:
Students will demonstrate a satisfactory cranial nerve screening appropriate to the speech/language evaluation to the instructor's standards.
Students will relate the twelve cranial nerves to two communicative functions on the test at 90% accuracy.

Some of the cranial nerves have functions that do not relate directly to communication.

Vagus supplies, "General Visceral Efferent impulses to the cardiac muscles and to muscles of the esophagus, bronchi, lungs and intestines." (A. Foley, 1975).
These functions are important, but not to communication per se.
We are also interested in functions associated with swallowing.

Communicative functions of the cranial nerves can be grouped into efferent and afferent categories.
Efferent functions are mainly motor to bulbar musculature.

There are some glandular functions associated with digestion.
Also some visceral motor functions that can lead to reflux.

Afferent functions involve the special senses and muscle feedback.

Of these, vision and hearing are probably the most important.
All the motor nerves have afferent fibers that transmit impulses to the thalamus to coordinate with the actions of the other motor nerves

Testing or screening of Cranial nerves is a standard way to assess function of the speech mechanism.
Remember, we are not neurologists. Cranial nerve testing is beyond the scope of our professional responsibility.
We will not suggest we are testing cranial nerves. There are many functions of the cranial nerves that we have no professional need to test.
We use the only format of the cranial nerve screening to provide structure for examining the peripheral speech mechanism.
This structure is shared by other disciplines that work with our patients and who receive input from our evaluations: Internal Medicine, ENT, and Neurology

Thus, we are using a standard format, one that others use. We report our findings in order of the format, number one (olfactory) first and move on through number twelve (hypoglossal).

We can infer certain functional limitations or potentials from our knowledge of bulbar musculature functions, but must remember these are inferences. We do not infer that there is something wrong with the nerve. Indeed, there is usually nothing wrong with the nerve, but, rather, with the collection of CNS tracts that aggregate from various CNS components to impinge upon the peripheral cranial nerve.

Efferent functions of the cranial nerves involve the movements and sensations of the eyes, the control of the muscles articulation and swallowing and the control of the muscles facial expression. (we will cover each if these again in detail)

I is for smell (discuss communicative and swallowing function of smell. What is the communicative function of smell? Ask the patient if she has noticed any changes. Most often I skip this one, unless there is a good reason to ask the question. For managing deglutition problems, the sense of smell may be important. Remember, the olfactory sense is the only one that does not relay through the thalamus.

II is for vision. Is vision an asset to communication? Don't forget the importance of facial expression or other gestural means in communication, not to mention the role of vision in graphic communication. Once, again, we are interested here in vision as a sense, beyond cranial nerve function. We simply arrange our screening in order of the nerve arrangement in a caudal direction along the brainstem. If our patient has difficulty with vision, there are many etiologies apart from dysfunction of II that may be sources.

III; IV; VI control the orbital movements of the eye. III controls the intrinsic eye muscles as well as the medial rectus and the levator palpebrae superiorus muscle (the one that lifts the eyelid). IV and VI provide motor impulses for other extrinsic eye muscles. Nystagmus is the condition in which the movement of the eyes is not smooth. It can be voluntary or involuntary. It is tested by caloric means. Exophoria is when the eye deviates outward (to temporal half). Esophoria is when the eye deviates to nasal half. Vol. eye field is important for reading and tracking. Following movement is not the same as directed eye movement.

V motor function is the muscles mastication (except the buccinator). Especially muscles mandibular elevation and lateralization. Vowels and consonants that require elevation of the mandible.

VII facial expression. It's for labial phonemes and rounded vowels and Facial gestures.

VIII is the vestibulocochlear nerve. Its function is related to audition and to maintenance of balance sense and equilibrium. Function of this nerve may be screened by using a portable audiometer or the auditory pathways may be tested by an audiologist. Audiological evaluation is a thorough testing of auditory function. Neurologists test the equilibrium function.

IX is difficult to test. Its contribution to speech is minimal, but it has a role in deglutition. Since we can not isolate its function, we leave it out of our screening.

X and XI are tested together.

They are difficult to separate in the brainstem.

Aberrant fibers of XI join fibers of X . Accessory fibers provide motor innervation to the intrinsic muscles of the larynx.

Motor to the muscle pharynx; larynx, levator Veli Palatini; Swallowing; Phonation; /h/; //

Afferent fibers of X are sensory to the pharynx.

XII innervates intrinsic and extrinsic muscles of the tongue.

Intrinsic muscles elevate tip, fold blade.; apical consonants, high (near) front vowels.

Extrinsic muscles change the position of the tongue body.

1. Geniohyoid muscles originates inside the mandible and inserts in the inferior tongue.



2. Palatoglossus elevates back of tongue: / k/ /g/ and /N/.

What is the role of tongue mobility in deglutition?

Afferent functions are those interpreted by the patient.
These depend upon accurate and controlled stimulation. We can only infer that the patient has sensed the stimulus.
Anesthesia: loss of sensation
Paresthesia: Change in sensation perception.

V: Touch at the facial dermatomes and anterior 2/3 of the tongue.

VII: Taste on the anterior 2/3 of the tongue.

VIII: Naturally, the reception of sound-generated action potential is an asset to auditory/vocal communication. Need I say more? further, the sense of balance has an indirect effect on language development, since locomotion in one's environment is so important to cognitive maturation. Vestibular impulses are distributed to the skeletal muscles to help keep the individual balanced for exploration of the world.

IX and XI: Sensation at posterior tongue:

1. Gag reflex. (demonstrate) Why test gag?



2. Not the same as cough reflex. (From X)



3. Taste at posterior 1/3 of tongue

FYI: there are unconscious afferent impulses from nearly all the bulbar musculature. These are fusal impulses, and enable the complex intermingled network of muscles work together. Imagine how difficult it would be to scan a page visually if the extraocular eye muscles did not work smoothly together.

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E-mail Bill Culbertson at bill.culbertson@nau.edu
Call Bill Culbertson at (520) 523-7440

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