111 Ch. 28

end of a muscle attached to a more movable structure (keep in mind: the insertion moves toward the origin).

end of a muscle attached to a less movable structure.

the work accomplished when the muscle fiber contract.

• 1. Masseter muscle
• 2. Temporal muscle
• 3. Medial pterygoid muscle
• 4. Lateral pterygoid muscle
• * 5th nerve(trigeminal nerve) has 3 arches V1,V2,V3
• * V3 (mandibular division) of the 5th nerve. Controls the muscles.
• * The blood supply comes from the maxillary artery, which is a branch of the external carotid artery. 

• * Probably the most powerful of the muscles of mastication.
• * It takes its origin from two areas of the zygomatic arch.
• 1. Superficial head from the inferior border of the anterior 2/3 of zygomatic arch.
• 2. Deep head from the inferior border of the posterior 1/3 of the zygomatic arch.
• * Insertion into the angle of the mandible on the lateral side.
• * When the masseter muscle contracts, it elevates the mandible (closing the mouth).

• * Also called the temporalis muscle.
• * Origin-temporal fossa.( Very wide origin area)
• * Insertion into the coronoid process of the mandible and sometimes run down the anterior border of the ramus of the mandible as far as the 3rd molar.
• * If the entire muscle contracts it elevates the mandible (closing the mouth).
• * If the posterior fibers contract it pulls the mandible backward also known as retruding the mandible.

• * Origin- has 2 origins from 1) the large pterygoid plate and fossa and a tiny area of the palatine bone. 2) Smaller origin just behind the Maxillary 3rd molar.
• * Insertion-onto the medial side of the angle of the mandible (inside of the mandible) (tongue side).
• * Opposite the masseter insertion.
• * When the muscle contracts, it elevates the mandible and closes the mouth.

• * Has 2 separate origins
• 1) Top muscle- the smaller, superior origin arises from the infratemporal crest of the greater wing of the sphenoid bone. 
• 2) Bottom muscle- the larger, inferior origin arises from the lateral side of the
• pterygoid plate. This is just opposite the origin of the medial pterygoid muscle.
• * Pulls the condyle forward and helps protude and depress the mandible only if both left and right funtion together.
• * If only one lateral pterygoid contract, there will be a lateral excursion to the opposite side of the contracted muscle. Eg. Contract the RIGHT lateral pterygoid muscle and the mandible moves to the LEFT.
• * Involved in power stroke (action of biting).
• * As other muscles are pulling posteriorly, the upper head of the lateral pterygoid is relaxing and controlling that movement.

• * Involves opening of the mouth and retrusion of the mandible.
• * These muscles either open (depress) the mandible or elevate the hyoid bone.
• * 2 groups
• * 1) Suprahyoid group (above the hyoid bone) these muscles either open (depress) the mandible or elevate the hyoid bone.
• * 2) Infra hyoid group (below the hyoid bone) these muscle either open the mandible of depress the hyoid bone.
• - Hyoid is a horseshoe shaped bone suspend beneath the mandible. 
• - Not directly connected to any other bone, only connected to bone by muscle and ligament.

• 1. Digastric muscle (when contracting causes retruding) (backward pull) 
• 2. Mylohyoid muscle (forms the floor of the mouth) 
• 3. Geniohyoid muscle 
• 4. Stylohyoid muscle

• 1. Has 2 nerve supplies
• * V3 5th nerve (trigeminal nerve) Anterior part of muscle.
• * 7th nerve (facial nerve) Posterior part of muscle.
• 2. Origin at digastric notch (behind ear).
• 3. Insertion at digastric fossa (inferior surface of the mandible).
• 4. Blood supply lingual artery.
• 5. If the mouth is close, and the digastric muscle contracts, it elevates the hyoid bone.

• 1. Nerve V3 of 5th (trigeminal nerve).
• 2. Blood supply is a branch of the inferior alveolar artery.
• 3) Origin-Mylohyoid line on the medial surface of the mandible on each side.
• 4) Insertion- hyoid bone.

fusion of muscle at midline of the neck. Ex. Mylohyoid muscle

• * Origin- mental spine of the mandible. 
• * Inserts into the hyoid bone by the midline.
• * 1st cervical nerve in the neck.
• * Blood supply branch of the lingual artery.
• * Lies deep to the Mylohyoid muscle.

• * Origin- styloid process of the base of the skull. 
• * Insertion- posterior part of the hyoid bone.
• * Pulls the hyoid bone back and up.
• * Nerve- Branch of the facial nerve (7th).
• * Blood supply- Facial and occipital arteries.

• 1) Omohyoid muscle
• 2) Sternohyoid muscle
• 3) Sternothyroid muscle
• 4) Thyrohyoid muscle

• * When it contracts it pulls the hyoid bone down.
• * Nerve supply 2nd and 3rd cervical nerves.
• * Blood supply the lingual and superior thyroid arteries.
• * Arises from the Scapula (shoulder blade) and hyoid bone.

• * Origin- upper sternum
• * Insert- front part of hyoid bone.
• * Contracts pull hyoid bone down.
• * Nerve supply 2nd and 3rd cervical nerves.
• * Blood supply the lingual and superior thyroid arteries.

• * Origin- upper sternum
• * Insert- onto to an oblique line on the side of the thyroid cartilage of the larynx.
• * Contracts- pull the larynx down.
• * Nerve supply 2nd and 3rd cervical nerve.
• * Blood supply the superior thyroid artery.

• * Origin-oblique line on the lateral side of the thyroid cartilage.
• * Insert- into the hyoid bone.
• * Contracts- it either lifts the thyroid cartilage or raises the larynx or helps depress the hyoid bone.
• * Nerve supply 1st cervical nerve.
• * Blood superior thyroid artery.

Lateral pterygoid muscles acting together produce mandibular protrusion.

one of the lateral pterygoid muscles acting by itself

the medial pterygoid, masseter and temporal muscles

the inferior head of the lateral pterygoid muscle plus the hyoid muscles (this includes the Suprahyoid and Infrahyoid muscles). Once the Infrahyoid muscle contract and pull down the hyoid bone, the Suprahyoid muscles contract to pull the mandible down

the posterior or horizontal fibers of the temporal muscle, as well as the digastric muscle

• (These are not all the muscles involved but the important ones)
• The hyoid bone is pulled slightly up by the contraction of the Suprahyoid muscles. The Thyrohyoid muscle contract, elevating the thyroid cartilage of the larynx and, along with the contraction of the muscles attached to the epiglottis and the backward movement of the tongue, this moves the epiglottis over the opening of the larynx allowing the swallowed material to enter the esophagus.

• * Upon extra oral exam palpate beneath posterior border to check for enlargement of lymph nodes.
• * Origin- upper border of the sternum and the medial 1/3 of the clavicle.
• * Insertion- into the mastoid process of the temporal bone.
• * Action involves tilting and rotating head.
• * Nerve 11th cranial nerve (accessory nerve).
• * Blood supply is branch of external carotid artery.

• * Origin- external occipital protuberance on the occipital bone and from the bony ridges, the superior nuchal lines, which runs lateral from that. Also originates from spinous process of the cervical and thoracic vertebrae.
• * Insertion- into the spine of the scapula (back blade), the acromion process of the scapula, and the lateral 1/3 of the clavicle (collar bone).
• * Its function is to adduct (to move toward midline) and elevate the scapula(back blade) as well as slightly rotate it.
• * EXAMPLE: Shrugging of the Shoulder.
• * Typing at an improper height can cause pains in the trapezius from holding the arms in a raised position while doing work.

involuntarily contraction of the sternomastoid and trapezius muscles. Some malocclusions can also cause such spasms.

the SCM and trapezius get nerve supply from the 2nd,3rd,4th cervical nerves, which are in close approximation to the lower part of the trigeminal nerve nucleus in the upper spinal chord. This can at times causes pain to emanate from the area of the TMJ. To find problem anesthetize sternomastoid and trapezius to see if problem disappears.