1.1
Temporalis
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Surface anatomy : Superficial, wide, and thin muscle. Easily palpable with teeth clenching.
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Origin : Temporal fossa of the parietal bone.
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Insertion : Wide spread to the parietal, frontal, maxilla, and mandibular bone.
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Function : Mastication by elevation and retraction of the mandible.
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Motor point (MP) 1 : Three MPs. Draw a line (AB) from the tragus (A) to the lateral cantus (B), then move the line AB (A is the center) upward about 30 degrees (MP1). Move the line AB (now B is the center) upward about 30 degrees (MP2). Draw a vertical line (XY) upward (XY = AB length) from the midpoint of the AB (MP3). MP3 is relatively diffuclt to be identified than MP1 and MP2.
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Injection tip : The muscle is thin. If needle hits the skull, then pull the needle back. Anterior part of the muscle (MP1) is the strongest and thickest part of the muscle (because the muscle fibers run vertically), and the posterior part of the muscle (MP2) is weakest part for mastication but important function for side to side jaw movement with lateral pterygoid muscle. 2 All MPs are located in the most prominent portion of the muscle when teeth are clenched.
1.2
Masseter
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Surface anatomy : Superficial muscle. Easily palpable with teeth clenching.
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Origin : Zygomatic process and arch of the maxilla.
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Insertion : Angle and ramus of the mandible.
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Function : Mastication by elevation and protrusion of the mandible.
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Motor point (MP) : The first MP (MP1) is midpoint between the maxillary process of the zygomatic bone (A) and mandibular angle (B). The second MP (MP2) is the midpoint between the zygomatic bone (A) and the distal end of ear lobule (C).
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Injection tip : For MP1, using thumb and the middle finger, localize the point A and B. Then place the index finger in the midpoint of the line AB. The index finger points the MP1. To avoid puncturing oral cavity, insert injection needle slowly from superficial to deep. For MP2, using thumb and the middle finger, localize the point A and C. Then place the index finger in the midpoint of the line AC. The index finger points the MP2.
1.3
Medial pterygoid
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Surface anatomy : Very difficult to palpable extraorally.
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Origin : The medial side of the lateral pterygoid plate (behind of upper last molar).
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Insertion : Internal surface of the ramus and angle of the mandible.
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Function : Close the jaw with elevation of the mandible.
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Motor point (MP) : It is very difficult to be localized extraorally. Transoral approach is recommended. The MP in the picture shows the needle entry point to the left medial pterygoid muscle.
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Injection tip : At neck hyperextension and mouth opening (the most important part of the approach), localize the pterygomandibular raphe (soft tissue band connecting mandible and maxilla at the end of the last lower and upper molars). Place injection needle lateral to the upper part of the raphe and push the needle posteriorly with 30 degrees upward (toward zygomatic process) slowly. With electrical stimulation, jaw is closed if the needle is in the right place. 1,3 A long injection needle and tongue depressor are needed.
1.4
Lateral pterygoid
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Surface anatomy : Located deep under the zygomatic arch and difficult to palpate.
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Origin : Great wing of sphenoid and pterygoid plate.
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Insertion : Condylar process of the mandible (just distal to the temporomandibular joint).
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Function : Protrusion and depression the mandible and the mandible side to side movement.
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Motor point (MP): Localize the temporomandibular joint (A, most prominent area) with index finger while opening and closing the mouth, and then palpate the zygomatic maxillary process with the ring finger (C). Place middle finger (B) at the midpoint of line AC. Point B is the portal of the MP of the lateral pterygoid.
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Injection tip : Extraoral approach is much easier than transoral approach. Ultrasound is useful to identify the TM joint and the muscle (Inset). For transoral approach, place an injection needle through the mucobuccal fold (junction of gingiva and oral mucosa) of the maxillary second molar toward to the TM joint. 1,4
1.5
Semispinalis capitis
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Surface anatomy : Deep to the upper trapezius and splenius capitis in the posterior neck area, but superficial at the occipital area (See inset; 1. multifidus, 2. semispinalis cervicis, 3. semispinalis capitis, 4. splenius capitis, 5. splenius cervicis, 6. upper trapezius at C 6 level).
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Origin : Lower cervical spines and transverse processes of the upper thoracic spines.
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Insertion : Occipital bone medial part (just lateral to inion).
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Function : Extension the head.
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Motor point (MP) : Midpoint between inion (A) and the point just lateral to the C7 spinous process (B) and in deep (deep to the upper trapezius and splenius capitis).
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Injection tip : Keep head flexion as much as possible during the injection. Neck extension muscles are small and thin. They are so closely layered that it is very difficult to identify each muscle.
1.6
Semispinalis cervicis
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Surface anatomy : The second deepest and the second most medial to the midline muscle of the posterior neck (see Inset; 1. multifidus, 2. semispinalis cervicis, 3. semispinalis capitis, 4. splenius capitis, 5. splenius cervicis, 6. upper trapezius at C 6 level).
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Origin : Transverse process of the upper thoracic (T1–6).
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Insertion : Spinous process of the upper and mid cervical spine (C2–6).
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Function : Extension the head and lateral flexion ipsilaterally.
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Motor point (MP) : 1 finger breath lateral to the C7 or T1 spinous process (A, medial to the splenius cervicis MP, see 1–8).
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Injection tip : MP is located in deep. Insert needle 45 degrees toward to the junction of lamina and spinous process of C7 or T1. Neck extension muscles are small and thin. They are so closely layered that it is very difficult to identify each muscle.
1.7
Splenius capitis
