Lab 16 Muscles of the Head and Neck

Endomysium

A thin sheet of loose connective tissue that surrounds each individual muscle fiber.

Perimysium

A thicker layer of connective tissue that wraps about 20 to 60 muscle fibers together into bundles called fascicles.

Epimysium

A thick fibrous sheath that surrounds the entire muscle.

Fascia

The most superficial and thickest sheet of connective tissue that separates muscle groups from each other.

Tendon

A straplike cord of connective tissue that attaches muscle to bone.

Intrinsic muscle

A muscle that acts upon and is contained entirely in the body region of interest.

Extrinsic muscle

A muscle that acts upon a body region of interest and is not completely contained in that body region.

Agonist (prime mover)

The muscle that is most responsible for producing a movement.

Antagonist

A muscle that opposes the agonist, usually found on the opposite side of the bone or body.

Synergist

A muscle that aids the agonist.

Parallel muscles

Muscles with fascicles arranged in parallel bundles of uniform width.

Fusiform muscles

Muscles that are thickest in the middle and taper on each end.

Circular muscles

Muscles with fascicles arranged in rings or circles around body openings.

Triangular (convergent) muscles

Muscles that are broad or wide at one end and converge to a narrower end.

Pennate muscles

Muscles that are feather shaped with three types: unipennate, bipennate, and multipennate.

Masseter

The strongest muscle responsible for elevating the mandible.

Temporalis

A large muscle that elevates the mandible and overlies the temporal bone.

Sternocleidomastoid

A muscle named for its attachment sites; it flexes the neck and can rotate the head.

Trapezius

A large muscle with multiple fiber directions, capable of various neck movements.

Scalenes

Three paired muscles in the neck that can flex the neck and elevate the rib cage.

Orbicularis oculi

A circular muscle around the eye responsible for closing the eyelids.

Orbicularis oris

A circular muscle around the mouth responsible for movements such as puckering.

Buccinator

A muscle that compresses the cheek against the teeth.

Platysma

A broad muscle in the neck responsible for depressing the lower lip.

Superior rectus

An extrinsic eye muscle responsible for elevating the eye.

Inferior rectus

An extrinsic eye muscle responsible for depressing the eye.

Lateral rectus

An extrinsic eye muscle responsible for moving the eye laterally.

Medial rectus

An extrinsic eye muscle responsible for moving the eye medially.

Superior oblique

An extrinsic eye muscle that rotates the eye down and laterally.

Inferior oblique

An extrinsic eye muscle that rotates the eye up and laterally.

Masseter: Origin, Insertion, and Action

• Origin: Zygomatic arch and maxilla.- Insertion: Lateral surface of mandibular ramus and angle.- Action: Elevates mandible (closes mouth).

Temporalis: Origin, Insertion, and Action

• Origin: Temporal fossa.- Insertion: Coronoid process and anterior border of mandibular ramus.- Action: Elevates and retracts mandible.

Sternocleidomastoid: Origin, Insertion, and Action

• Origin: Sternal head: manubrium; Clavicular head: medial third of clavicle.- Insertion: Mastoid process of temporal bone; Lateral half of superior nuchal line.- Action: Unilateral contraction rotates head to opposite side and flexes neck laterally; Bilateral contraction flexes neck.

Orbicularis oculi: Origin, Insertion, and Action

• Origin: Medial orbital margin; Lacrimal bone.- Insertion: Eyelids and skin around orbit.- Action: Closes eyelids (blinking, winking).

Example of Agonist, Antagonist, and Synergist muscles in elbow flexion

• Agonist (Prime Mover): Biceps brachii.- Antagonist: Triceps brachii (resists flexion).- Synergists: Brachialis and Brachioradialis (assist the biceps brachii).

Example of Intrinsic versus Extrinsic muscles

• Intrinsic muscle example: The lumbrical muscles of the hand, which originate and insert entirely within the hand.- Extrinsic muscle example: The biceps brachii, which acts on the forearm but originates in the shoulder region (outside the forearm).