This document summarizes several muscles of the head and neck region. It describes the origin, insertion, nerve supply and action of the temporalis, masseter, lateral pterygoid, medial pterygoid, mylohyoid, geniohyoid, sternohyoid, omohyoid, thyrohyoid, sternothyroid, trapezius, and sternocleidomastoid muscles. It also provides information on torticollis, listing four types: rheumatic, reflex, congenital, and spasmodic.

2. Muscles of mastication
Temporalis :
Origin: Temporal fossa and temporal fascia
Insertion: margin and deep surface of Coronoid process.
Nerve supply: deep temporal nerve.
Action : Elevation & protrusion of mandible and Side to
side grinding movement.

3. Origin:
Masseter:
Origin:
Superficial layer: anterior 2/3rd of lower border zygomatic arch
Middle layer: from anterior 2/3rd of deep surface & post. 1/3rd of
lower border of Zygomatic arch.
Deep layer: deep surface of zygomatic arch
Insertion
Superficial layer to lower part
Middle layer to middle part
Deep layer to upper part of lateral surface of mandible.
Nerve supply: masseteric nerve,
Action: Elevation of mandible during chewing.

4. Lateral pterygoid:
Origin of Upper head : Infratemporal surface and crest of greater wing of
sphenoid bone.
Origin of Lower head: Lateral surface of lateral pterygoid plate.
Insertion
I. Pterygoid fovea
II. Articular disc and capsule of TMJ
Nerve supply: Ant. division of mandibular nerve
Action: Depress and protrude the mandible, assist in grinding movement

5. Medial pterygoid:
Origin:
Superficial head from tuberosity of maxilla &
Deep head from medial surface of lateral pterygoid plate.
Insertion: medial surface of ramus of mandible.
Nerve supply: nerve to medial Pterygoid, br. Of main trunk
of mandibular nerve.
Action: elevation of mandible, grinding movement.

6. MylohyoidMylohyoid
O: Mylohyoid line on mandible
I; Body of hyoid bone and fibers from muscle on opposite
side
N: Mylohyoid nerve from inferior alveolar branch of
mandibular nerve
A: Support and elevation of floor of mouth; elevation of hyoid
Fixed mandible elevates and pulls hyoid bone forward; fixed
hyoid bone pulls mandible downward and in-ward

7. Geniohyoid
O: Inferior mental spine on inner surface of mandible
I; Anterior surface of body of hyoid bone
N: Branch from anterior ramus of C1 (carried along the hypoglossal
nerve)
A; Fixed mandible elevates and pulls hyoid bone forward; fixed hyoid
bone pulls mandible downward and in-ward

8. Sternohyoid
O; Posterior aspect of sternoclavicular joint and adjacent
manubrium of sternum
I; Body of hyoid bone medial to attachment of omohyoid
muscle
N; Anterior rami of C1 to C3 through the ansa cervicalis
A: Depresses hyoid bone after swallowing

9. Omohyoid
O; Superior border of scapula medial to suprascapular notch
I; Lower border of body of hyoid bone just lateral to
attachment of sternohyoid
N; Anterior rami of C1 to C3 through the ansa cervicalis
A; Depresses and fixes hyoid bone

11. Thyrohyoid
O; Oblique line on lamina of thyroid cartilage
I; Greater horn and adjacent aspect of body of hyoid bone
N; Fibers from anterior ramus of C1 carried along hypoglossal nerve
A; Depresses hyoid bone, but when hyoid bone is fixed raises larynx

12. Sternothyroid
O; Posterior surface of manubrium of sternum
I; Oblique line on lamina of thyroid cartilage
N: Anterior rami of C1 to C3 through the ansa cervicalis
A; Draws larynx (thyroid cartilage) downward

13. Trapezius
O ; Superior nuchal line; external occipital protuberance; ligamentum
nuchae; spinous processes of vertebrae CVII to TXII
I: Lateral one-third of clavicle; acromion; spine of scapula
N; Motor-accessory nerve [XI]; proprioception-C3 and C4
A: Assists in rotating the scapula during abduction of humerus above
horizontal; upper fibers-elevate, middle fibers-adduct, lower fibers-
depress scapula

14. Sternocleidomastoid muscle
O; Upper part of anterior surface of manubrium of sternum
I; Lateral one-half of superior nuchal line
O; Superior surface of medial one-third of clavicle
I : Lateral surface of mastoid process
N : Accessory nerve [XI] and branches from anterior rami of C2 to C3 (C4)
A: Individually-will tilt head to-wards shoulder on same side rotating head to turn face
to opposite side; acting to-gether, draw head forwards

16. Torticollis or wry neck- deformity in which the head bent to one
side and the chin points to the other side
1. Rheumatic torticollis- due to exposure to cold or draught
2. Reflex torticollis- due to inflamed or suppurating cervical
lymph nodes which irritate the spinal accessory nerve
3. Congenital torticollis- due to birth injury
4. Spasmodic torticollis- due to central irritation on CN-XI.

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