Assessment of Muscles Innervated by Cranial Nerves: Jacqueline Montgomery



Assessment of Muscles Innervated by Cranial Nerves


Jacqueline Montgomery


This chapter describes the muscles innervated by motor branches of the cranial nerves and describes test methods of assessing muscles of the eyelid, face, jaw, tongue, soft palate, posterior pharyngeal wall, and larynx. It also covers the extraocular muscles. The tests are appropriate for patients whose neurologic deficits are either central or peripheral. The only requirement for the patient to participate in the test is the ability to follow simple directions.




Introduction to Testing and Grading


Muscles innervated by the cranial nerves are not amenable to the classic methods of manual muscle testing and grading. In many, if not most, cases they do not move a bony lever, so manual resistance as a means of evaluation of their strength and function is not always the primary procedure.


The therapist needs to become familiar with cranial nerve innervated muscles in normal people. Their appearance, strength, excursion, and rate of motion are all variables that are unlike the other skeletal muscles. As for the infant and young child, the best way to assess the gross function of their muscles is to observe the child while crying or sucking, for example. In any event, experience with assessment requires considerable practice with both normal people and a wide variety of patients with suspected and known cranial nerve motor deficits emanating from both upper and lower motor neuron lesions.


The issue of symmetry is particularly important in testing the ocular, facial, tongue, jaw, pharyngeal, and palate muscles. The symmetry of these muscles, except for the laryngeal muscles, is visible to the therapist. Asymmetry is more readily detected merely by observation in these muscles (in contrast to the limb muscles) and should always be documented.


In all tests in this chapter, the movements or instructions may not be entirely familiar to the patient, so each test should be demonstrated and the patient should be allowed to practice. In the presence of unusual or unexpected test results, the therapist should inquire about prior facial reconstructive (e.g., cosmetic) surgery, and in this era, Botox injections.






Extraocular Muscles


The six extraocular muscles of the eye (Figure 7-1 and Figure 7-2) move the eyeball in directions that depend on their attachments and on the influence of the movements themselves. It is usual that no muscle of the eye acts independently, and because these muscles cannot be observed, palpated, or tested individually, much of the knowledge of their function is derived from some variety of dysfunction. The extraocular muscles are innervated by cranial nerves III (oculomotor), IV (trochlear), and VI (abducent) (Figure 7-3).


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FIGURE 7-1

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FIGURE 7-2

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FIGURE 7-3





Eye Motions


The extraocular muscles seem to work as a continuum; as the length of one changes, the length and tension of the others are altered, giving rise to a wide repertoire of paired movements.2,3 Despite this continuous commonality of activity, the function of the individual muscles can be simplified and understood in a manner that does not detract from accuracy but simplifies the test procedure.


Conventional clinical testing assigns the following motions to the various extraocular muscles (Figure 7-5).1–3


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FIGURE 7-5 Extraocular muscles and their actions. The six extraocular muscles enable each eye to move in a circular arc, usually accompanied by head movements, though head position is static during testing. The traditional pairing of extraocular muscles is an oversimplification of their movement patterns. In any ocular rotation all six muscles change length. The reference point for description of the motions of the extraocular muscles is the center of the cornea.








Eye Tracking


Eye movements are tested by having the patient look in the cardinal directions (numbers in parentheses refer to tracks shown in Figure 7-6).2 All pairs in tracking are antagonists.


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FIGURE 7-6

Laterally (1) Upward and laterally (5)


Medially (2) Upward and medially (7)


Upward (3) Downward and medially (6)


Downward (4) Downward and laterally (8)


Ask the patient to follow the therapist’s slowly moving finger (or a pointer or flashlight) in each of the following tests. The object the patient is to follow should be at a comfortable reading distance. First, one eye is tested and then the other, covering the nontest eye. After single testing, both eyes are tested together for conjugate movements. Each test is started in the neutral position of the eye.


The range, speed, and smoothness of the motion should be observed, as well as the ability to sustain lateral and vertical gaze.2–4 The therapist will not be able to use these observational methods to distinguish movement deviations accurately because accuracy requires the sophisticated instrumentation used in ophthalmology. The tracking movements will appear normal or abnormal, but little else will be possible.








Muscles of the Face and Eyelids


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FIGURE 7-10


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FIGURE 7-11


The face should be observed for mobility of expression, and any asymmetry or inadequacy of muscles should be documented. A one-sided appearance when talking or smiling, a lack of tone (with or without atrophy), the presence of fasciculations, asymmetrical or frequent blinking, smoothness of the face, or excessive wrinkling are all clues to VII nerve involvement.


The facial muscles (except for motions of the jaw) convey all emotions via voluntary and involuntary movements.




Eye Opening (3. Levator palpebrae superioris)


Opening the eye by raising the upper eyelid is a function of the levator palpebrae superioris (see Figure 7-10). The muscle should be evaluated by having the patient open and close the eye with and without resistance. The function of this muscle is assessed by its strength in maintaining a fully opened eye against resistance.


The patient with an oculomotor (III) nerve lesion will lose the function of the levator muscle, and the eyelid will droop in a partial or complete ptosis. (A patient with cervical sympathetic pathology may have a ptosis but will be able to raise the eyelid voluntarily.) Ptosis is evaluated by observing the amount of the iris that is covered by the eyelid.


In the presence of a facial (VII) nerve lesion, the levator sign may be present.2 In this case, the patient is asked to look downward and then slowly close the eyes. A positive levator sign is noted when the upper eyelid on the weak side moves upward because the action of the levator palpebrae superioris is unopposed by the orbicularis oculi.




Criteria for Grading






0:


No eyelid opening.



image Peripheral versus Central Lesions of the Facial (VII) Nerve


Involvement of the facial nerve may result from a lesion that affects the nerve or the nucleus (i.e., a peripheral lesion). Motor functions of the face also may be impaired after a central or supranuclear lesion. These two sites of interruption of the VII nerve lead to dissimilar clinical problems.5


The peripheral lesion results in a flaccid paralysis of all the muscles of the face on the side of the lesion (occipitofrontalis, corrugator, orbicularis oculi, nose and mouth muscles). The affected side of the face becomes smooth, the eye remains open, the lower lid sags, and blinking does not completely close the eye; the nose is depressed and may deviate to the opposite side. The cheek muscles are flaccid, so the cheek appears hollow and the mouth is drawn to one side. Eating and drinking are difficult because chewing and retention of fluids and saliva are impaired. Speech sounds, especially vowels or sounds that require pursing of the lips, are slurred.


When the VII nerve is affected central to the nucleus, there is paresis of the muscles of the lower face but sparing of the muscles of the upper face. This occurs because the nuclear center that controls the upper face has both contralateral and ipsilateral supranuclear connections, whereas that which controls the lower face has only contralateral supranuclear innervation. For this reason, a lesion in one cerebral hemisphere causes paresis of the lower part of the face on the contralateral side and there is sparing of the upper facial muscles. This may be called a “central VII syndrome.”


One notable difference between peripheral and central disorders is that peripheral lesions often (but certainly not always) result in paralysis of all facial muscles; central lesions leave some function even of the involved muscles and are, therefore, notably weak but not paralytic.


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PLATE 8


Closing the Eye (4. Orbicularis oculi)


The orbicularis oculi muscle is the sphincter of the eye (Figure 7-13).1 Its lids are innervated by the facial (VII) nerve (temporal branch and zygomatic branch) (Figures 7-14 and 7-15). Its palpebral portion closes the eyelids gently, as in blinking and sleep. The orbital portion of the muscle closes the eyes with greater force, as in winking. The lacrimal portion draws the eyelids laterally and compresses them against the sclera to receive tears. All portions act to close the eyes tightly (Figure 7-16). Observation of the patient without specific testing will detect weakness of the orbicularis because the blink will be delayed on the involved side.


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FIGURE 7-13

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FIGURE 7-14

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FIGURE 7-15

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FIGURE 7-16




Manual Resistance:

Place the thumb and index finger below and above (respectively) each closed eye using a light touch (Figure 7-17). The therapist attempts to open the eyelids by spreading the thumb and index finger apart. REMINDER: NEVER PRESS ON THE EYEBALL FOR ANY REASON.


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FIGURE 7-17



Criteria for Grading







Frowning (5. Corrugator supercilii)


To observe the action of the corrugator muscle (Figure 7-18; see also Figure 7-14), the patient is asked to frown. Frowning draws the eyebrows down and medially, producing vertical wrinkling of the forehead.


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FIGURE 7-18




Raising the Eyebrows (1. Occipitofrontalis, frontalis part)


To examine the frontal belly of the occipitofrontalis muscle (Figure 7-21 and see Figure 7-14), the patient is asked to create an expression of surprise where the forehead skin wrinkles horizontally. The occipital belly of the muscle is not tested usually, but it draws the scalp backward.


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FIGURE 7-21




Nose Muscles


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FIGURE 7-24


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FIGURE 7-25


The three muscles of the nose are all innervated by the facial (VII) nerve. The procerus (Figure 7-24) draws the medial angle of the eyebrows downward, causing transverse wrinkles across the bridge of the nose. The nasalis (compressor nares) depresses the cartilaginous portion of the nose and draws the ala down toward the septum (see Figure 7-15). The nasalis (dilator nares) dilates the nostrils. The depressor septi draws the alae downward, constricting the nostrils.


Of the three nose muscles only the procerus is tested clinically. The others are observed with respect to nostril flaring and narrowing in patients who have such talent.




Muscles of the Mouth and Face


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FIGURE 7-28 Muscles of the head and neck. (From Williams PL, Warwick R, Dyson M, Bannister LH, eds. Gray’s Anatomy, 38th ed. New York: Churchill-Livingstone; 1995.)


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FIGURE 7-29 The disposition of the modiolus and orbicularis oris pars peripheralis and pars marginalis (on the left); the successively transected laminae of the direct labial tractors on both upper and lower lips (on the right). (From Williams PL, Warwick R, Dyson M, Bannister LH, eds. Gray’s Anatomy, 39th ed. New York: Churchill-Livingstone; 2005.)



image The Modiolus


The arrangement of the facial musculature often causes confusion and misunderstanding. This is not surprising since there are 14 small bundles of muscles running in various directions, with long names and unsupported functional claims. Of all the muscles of the face, those about the mouth may be the most important because they have responsibility for both ingestion of food and for speech.


One major source of confusion is the relationship between the muscles around the mouth. The common description until recently was of uninterrupted circumoral muscles. In fact, the orbicularis oris muscle is not a complete ellipse but rather contains fibers from the major extrinsic muscles that converge on the buccal angle, as well as intrinsic fibers.1,6,7 The authors and others do not describe complete ellipses, but most drawings illustrate such.6


The area on the face that has a large concentration of converging and diverging fibers from multiple directions lies immediately lateral and slightly above the corner of the mouth. Using the thumb and index finger on the outer skin and inside the mouth and compressing the tissue between them will quickly identify the knotlike structure known as the modiolus.8–10


The modiolus (from the Latin meaning nave of a wheel) is described as a muscular or tendinous node, a rather concentrated attachment of many muscles.8,9 Its basic shape is conical (though this is oversimplified); it is about 1 cm thick and is found in most people about 1 cm lateral to the buccal angle. Its shape and size vary considerably with gender, race, and age. The muscular fibers enter and exit on different planes, superficial and deep, with some spiraling, but essentially they constitute a three-dimensional complexity.


Different classifications of modiolar muscles exist, but basically 9 or 10 facial muscles are associated with the structure:9



















Levator anguli oris Levator labii superioris
Orbicularis oris Levator labii superioris alaeque nasi
Depressor anguli oris Zygomaticus minor
Zygomaticus major Mentalis
Depressor labii inferioris
Buccinator


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Frequently associated are the special fibers of the orbicularis oris (incisive superior, incisive inferior), platysma, and risorius (the latter is not a constant feature in the facial musculature).


The orbicularis oris and the buccinator form an almost continuous muscular sheet, which can be fixed in a number of positions by the zygomaticus major, levator anguli oris, and depressor anguli oris (the latter three being the “stays” used to immobilize the modiolus in any position).


When the modiolus is firmly fixed, the buccinator can contract to apply force to the cheek teeth; the orbicularis oris can contract against the arch of the anterior teeth, thus sealing the lips together and closing the mouth tightly.9 Similarly, control of the modiolar active and stay muscles enables accurate and fine control of lip movements and pressures in speech.


There are many muscles associated with the mouth, and all have some distinctive function, except perhaps the risorius. Rather than detail a test for each, only definitive tests will be presented for the buccinator and the orbicularis oris (the sphincter of the mouth). The function of the remaining muscles is illustrated, and individual testing is left to the therapist. All muscles of the mouth are innervated by the facial (VII) nerve.




Lip Closing (25. Orbicularis oris)


This circumoral muscle (Figures 7-28 and 7-29) serves many functions for the mouth. It closes the lips, protrudes the lips, and holds the lips tight against the teeth. Furthermore, it shapes the lips for such functional uses as kissing, whistling, sucking, drinking, and the infinite shaping for articulation in speech. (For innervation, see Figure 7-25.)



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Aug 25, 2016 | Posted by in RHEUMATOLOGY | Comments Off on Assessment of Muscles Innervated by Cranial Nerves: Jacqueline Montgomery

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