micro 11.1 pt 3

Division of anterior neck muscles

Divided into suprahyoid muscles (above the hyoid bone) and infrahyoid muscles (below the hyoid bone).

Primary function of suprahyoid muscles

Elevate the hyoid bone during swallowing and speaking.

Suprahyoid muscle group

Composed of digastric, geniohyoid, mylohyoid, and stylohyoid.

Unique feature of the digastric muscle

Has two bellies (anterior and posterior) connected by an intermediate tendon.

Actions of the digastric muscle

Elevates the hyoid bone and depresses the mandible.

Action of the geniohyoid muscle

Elevates the hyoid bone.

Action of the mylohyoid muscle

Elevates the hyoid bone and raises the floor of the mouth.

Muscular floor of the mouth

Formed by the mylohyoid muscle.

Action of the stylohyoid muscle

Elevates the hyoid bone and lengthens the floor of the oral cavity during swallowing.

Primary function of infrahyoid muscles

Depress the hyoid bone or thyroid cartilage after swallowing.

Infrahyoid muscle group

Consists of omohyoid, sternohyoid, sternothyroid, and thyrohyoid.

Action of the omohyoid muscle

Depresses the hyoid bone and helps fix the hyoid during mouth opening.

Action of the sternohyoid muscle

Depresses the hyoid bone.

Action of the sternothyroid muscle

Depresses the thyroid cartilage of the larynx after swallowing.

Action of the thyrohyoid muscle

Depresses the hyoid bone and elevates the thyroid cartilage during swallowing.

Infrahyoid muscles that anchor the hyoid

Omohyoid, sternohyoid, and thyrohyoid help anchor the hyoid for the digastric to depress the mandible.

Main action of the anterolateral neck muscles

Flex the neck.

Primary anterolateral neck muscles

Sternocleidomastoid and the three scalene muscles.

Attachment of the sternocleidomastoid

From the sternum and clavicle to the mastoid process.

Effect of contracting both sternocleidomastoid muscles

The neck flexes.

Effect of contracting one sternocleidomastoid muscle

Laterally flexes the neck and rotates the head to the opposite side.

Head rotation caused by left sternocleidomastoid contraction

Head rotates to the right.

Actions of the scalene muscles

Flex the neck and elevate the first and second ribs during forced inhalation.

Primary function of posterior neck muscles

Extend the neck.

Superficial muscle that helps extend the neck

Trapezius.

Neck extension and same-side head rotation

Contracting splenius capitis and splenius cervicis extends the neck bilaterally and rotates the head to the same side unilaterally.

Actions of the longissimus capitis muscle

Bilaterally extends the neck; unilaterally rotates the head to the same side.

Muscles in the suboccipital muscle group

Obliquus capitis superior, obliquus capitis inferior, rectus capitis posterior major, rectus capitis posterior minor.

Action of the obliquus capitis muscles

Turn the head to the same side.

Action of rectus capitis posterior major and minor muscles

Extend the neck.