The muscles addressed in this chapter are the muscles of the head. These muscles can be divided into muscles of mastication (chewing), muscles of the scalp, and muscles of facial expression.

Mastication is the act of chewing. Therefore the muscles of mastication are those that attach to and are involved in movement of the mandible at the temporomandibular joints (TMJs). The four major muscles of mastication are the temporalis, masseter, lateral pterygoid, and medial pterygoid.

Muscles of the scalp and facial expression are superficial fascial muscles. The muscles of the scalp are involved in moving the scalp and the ear. Muscles of facial expression can be further subdivided into muscles of the eye, nose, and mouth. The contraction of these muscles is important for displaying emotions. Although some universality of facial expressions that display emotions are certainly apparent, variations are evident from one culture to another. Further, many of these muscles may act in concert with others to add to the spectrum of facial expressions. Some sources state that more than 1800 separate facial expressions can be created with combinations of the muscles of facial expression.

The companion CD at the back of this book allows you to examine the muscles of this body region, layer by layer, and individual muscle palpation technique videos are available in the Chapter 9 folder on the Evolve website.

OVERVIEW OF FUNCTION

The following general rules regarding actions can be stated for the functional groups of muscles of mastication at the TMJs:

 If a muscle attaches to the mandible and its other attachment is superior to the mandibular attachment, it can elevate the mandible at the TMJs.

 If a muscle attaches to the mandible and its other attachment is inferior to the mandibular attachment, it can depress the mandible at the TMJs.

 If a muscle attaches to the mandible and its other attachment is anterior to the mandibular attachment, it can protract the mandible at the TMJs.

 If a muscle attaches to the mandible and its other attachment is posterior to the mandibular attachment, it can retract the mandible at the TMJs.

 If a muscle attaches to the mandible and its other attachment is medial to the mandibular attachment, it can contralaterally deviate (do opposite side deviation of) the mandible at the TMJs.

 Reverse actions of the major muscles of mastication are unlikely because they would require movement of the entire head toward a fixed mandible (at the TMJs).

MUSCLES OF THE HEAD

Temporalis; Masseter

Pronunciation tem-po-RA-lis • MA-sa-ter

The temporalis and masseter are two of the four major muscles of mastication (chewing). The other two are the lateral and medial pterygoids discussed in the next layout. The temporalis and masseter are superficial muscles; the temporalis overlies the temporal bone and the masseter overlies the mandible (Figure 9-4). The masseter is usually divided into two layers: a superficial layer and a deep layer.

WHAT’S IN A NAME?

The name, temporalis, tells us that this muscle attaches onto the temporal bone.

The name, masseter, tells us that this muscle is involved with chewing.

* Derivation:

temporalis: L. refers to the temple

masseter: Gr. chewer

PALPATION

Both the temporalis and masseter are palpated with the client supine.

Temporalis

1. Place your palpating finger pads over the temporal fossa on the head (superior to the ear).

2. Ask the client to alternately contract and relax the temporalis; clenching the teeth and then relaxing the jaw will accomplish this. Feel for the contraction of the temporalis as the client clenches the teeth (Figure 9-5).

3. Once the contraction of the temporalis has been felt, palpate the entire muscle as the client continues to contract and relax it.

Masseter

1. Place your palpating finger pads between the zygomatic arch and the angle of the mandible.

2. Ask the client to alternately contract and relax the masseter; clenching the teeth and then relaxing the jaw will accomplish this. Feel for the contraction of the masseter as the client clenches the teeth (Figure 9-6).

3. Once the contraction of the masseter has been felt, palpate the entire muscle from the zygomatic arch to the angle of the mandible as the client continues to contract and relax it.

TREATMENT CONSIDERATIONS

 The temporalis muscle is deep to thick fibrous fascia called the temporalis fascia.

 A tight temporalis and masseter may be involved with tension headaches and with dysfunction of the temporomandibular joint (TMJ syndrome).

 The temporal fossa is much deeper in carnivores, allowing for a much thicker and stronger temporalis muscle, which contributes to the strength of a carnivore’s bite.

 Proportional to its size, the masseter is stated by many sources to be the strongest muscle in the human body.

MUSCLES OF THE HEAD: Pterygoid Group

Lateral Pterygoid; Medial Pterygoid

Pronunciation LAT-er-al TER-i-goyd • MEE-dee-al TER-i-goyd

The pterygoid group is composed of the lateral pterygoid and medial pterygoid muscles (Figure 9-7). The pterygoids are two of the four major muscles of mastication (chewing). The temporalis and masseter are the other two muscles and are discussed in the previous layout. Both pterygoids are deep to the mandible and best accessed from inside the mouth. The lateral pterygoid has two heads: a superior head and an inferior head.

WHAT’S IN A NAME?

The name, pterygoid, tells us that these muscles attach to the sphenoid bone (the pterygoid process). The lateral pterygoid is lateral to the medial pterygoid.

* Derivation:

pterygoid: Gr. wing shaped

lateral: L. side

medial: L. toward the middle

PALPATION

Both pterygoids are palpated with the client supine.

Lateral Pterygoid

1. Wearing either a glove or a finger cot, place your palpating finger inside the vestibule of the client’s mouth (between the cheeks and the teeth) and run along the external surfaces of the upper teeth until you reach the back molars. Then press posteriorly and superiorly into a little pocket in the tissue between the gum above the upper teeth and the condyle of the mandible. You will be on the internal surface of the lateral pterygoid (Figure 9-8).

2. Now ask the client to gently either protract the mandible at the TMJs or deviate contralaterally the mandible slowly and carefully (deviate it to the opposite side of the body). Feel for the contraction of the lateral pterygoid (Figure 9-9).

3. Once felt, palpate as much of the lateral pterygoid as possible, from the condyle of the mandible to the inside wall of the mouth (above the gum of the upper teeth).

Medial Pterygoid

1. From inside the mouth: Wearing either a glove or a finger cot, place your palpating finger along the internal surfaces of the lower teeth until you reach the back molars, then press posterolaterally until you reach the inside wall of the mouth.

2. Now ask the client to protract the mandible. Feel for the contraction of the medial pterygoid.

3. Once felt, palpate as much of the medial pterygoid as possible.

4. From outside the mouth: Curl your palpating fingers around to the inside surface of the angle of the mandible.

5. Ask the client to elevate the mandible at the TMJs by clenching the teeth. Feel for the contraction of the medial pterygoid (Figure 9-10).

TREATMENT CONSIDERATIONS

 The direction of fibers of the medial pterygoid is essentially identical to the direction of the fibers of the masseter; in fact, these two muscles occupy the same position. The difference is that the masseter is external (superficial) to the mandible, and the medial pterygoid is internal (deep) to the mandible.

 A tight lateral or medial pterygoid may be involved with dysfunction of the TMJ (TMJ syndrome).

 The lateral pterygoid functions to protract the mandible and the articular disc of the TMJ. It is important that the mandible and disc protract together when the jaw is opened. Therefore if the contraction of the lateral pterygoid is not precisely coordinated with the other muscles that move the mandible, the articular disc may become jammed between the two bones of the joint and dysfunction of the TMJ (TMJ syndrome) may occur.

Notes

MUSCLES OF THE HEAD: Muscles of the Scalp

Occipitofrontalis; Temporoparietalis; Auricularis Anterior; Auricularis Posterior; Auricularis Superior

Pronunciation ok-SIP-i-to-fron-TA-lis • TEM-po-ro-pa-RI-i-TAL-is • aw-RIK-u-la-ris an-TEE-ri-or • aw-RIK-u-la-ris pos-TEE-ri-or • aw-RIK-u-la-ris sue-PEE-ri-or

The muscles of the scalp are the occipitofrontalis (consisting of an occipitalis belly, a frontalis belly, and the intermediate galea aponeurotica), the temporoparietalis, and the three muscles of the auricularis group (auricularis anterior, auricularis posterior, and auricularis superior) (Figure 9-11). The occipitofrontalis and temporoparietalis are sometimes grouped together as the epicranius muscle. The muscles of the scalp are superficial fascial muscles.

WHAT’S IN A NAME?

The name, occipitofrontalis, tells us that this muscle lies over the occipital and frontal bones.

The name, temporoparietalis, tells us that this muscle lies over the temporal and parietal bones.

The name, auricularis, tells us that these muscles are involved with the ear. Anterior, superior, and posterior tell us their locations relative to the ear.

*Derivation:

occipitofrontalis: L. refers to the occiput and frontal bone

temporoparietalis: L. refers to the temporal and parietal bones

auricularis: L. ear

anterior: L. before, in front of

superior: L. upper, higher than

posterior: L. behind, toward the back

PALPATION

All three muscles and muscle groups are palpated with the client supine.

Occipitofrontalis

1. Place your palpating finger pads on the forehead of the client.

2. Ask the client to elevate the eyebrows. Feel for the contraction of the frontalis belly (Figure 9-12, A); once felt, palpate the entire frontalis.

3. Now palpate over the client’s occipital bone, and ask the client to elevate the eyebrows. Feel for the contraction of the occipitalis belly (Figure 9-12, B); once felt, palpate the entire occipitalis.

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