Myology of the Head and Neck: Major Muscles, Origins, Insertions, and Functions

Myology: Head & Neck

Introduction

This study guide covers the major skeletal muscles of the head and neck, focusing on their origins, insertions, actions, and functional significance. Understanding these muscles is essential for comprehending facial expression, eye movement, mastication (chewing), and neck movement.

Etymology and Key Terms

Word Roots and Technical Terms

• -oid (G): form, shaped-like

• Capit-/caput- (L): head

• Colli (L): neck (as in "collar")

• Hyo- (G): U-shaped (also 'Y' shaped)

• Pharynx (G): throat

• Larynx (G): windpipe/throat

• Intrinsic: within, part of

• Extrinsic: outside, external but related

• Intra-: within, inside

• Extra-: outside, more, beyond, besides

• Inter-: between, among

Major Muscle Groups of the Head and Neck

Overview

• Muscles of Facial Expression

• Extrinsic Eye Muscles

• Muscles of Mastication (chewing)

• Neck Muscles (superficial anterior and deep vertebral)

Each group is specialized for distinct functions such as communication, eye movement, chewing, and head/neck movement.

Muscles of Facial Expression

General Features

• Move the highly mobile soft tissues of the face for communication and other functions (e.g., drinking, sucking).

• Typically attach to the skull at one end and to the skin at the other.

• Thin, delicate muscles with varied shapes (strap, circular, sheet-like).

• All are innervated by the Facial Nerve (Cranial Nerve VII).

Facial Muscles Near the Mouth

• Platysma: Covers the anterior neck; origin: fascia near clavicle; insertion: skin near mandible; action: tenses skin of neck.

• Orbicularis Oris: "Circular" muscle around the mouth; origin: maxilla and mandible; insertion: skin and mucous membrane of lips; action: compresses and protrudes lips (kissing muscle).

• Zygomaticus Major: Origin: zygomatic bone; insertion: modiolus (corner of mouth); action: draws corners of mouth upward and laterally (smiling).

• Buccinator: Origin: pterygomandibular raphe, alveolar processes of maxilla and mandible; insertion: blends with orbicularis oris; action: compresses cheek against teeth (important for chewing, not a muscle of mastication).

Facial Muscles Near the Eyes

• Occipitofrontalis (Epicranius): Two muscle bellies (frontalis and occipitalis) connected by an aponeurosis; action: raises eyebrows, wrinkles forehead.

• Orbicularis Oculi: Circular muscle around the eye; origin: medial margin of orbit; insertion: skin around eyelids; action: closes eyelids (blinking, wincing).

• Levator Palpebrae Superioris: Origin: sphenoid bone; insertion: upper eyelid; action: elevates upper eyelid (not innervated by facial nerve, but by oculomotor nerve).

Extrinsic Eye Muscles

Identification and Function

• Control the position and movement of the eyeball.

• Four rectus muscles (superior, inferior, medial, lateral) and two oblique muscles (superior, inferior).

• Most are innervated by the Oculomotor Nerve (CN III), except:

  • Superior Oblique: Trochlear Nerve (CN IV)

  • Lateral Rectus: Abducens Nerve (CN VI)

Primary Eye Movements

• Elevation: Superior rectus, inferior oblique

• Depression: Inferior rectus, superior oblique

• Abduction: Lateral rectus

• Adduction: Medial rectus

• Oblique muscles also contribute to complex movements such as intorsion and extorsion.

Muscles of Mastication

Overview

• Move the temporomandibular joint (TMJ) for chewing.

• All are innervated by the Trigeminal Nerve (Cranial Nerve V).

Major Muscles

Muscle	Origin	Insertion	Primary Action
Masseter	Zygomatic arch & bone	Lateral surface of mandibular ramus & angle	Elevation, protrusion, lateral deviation of mandible
Temporalis	Temporal lines/fascia, fossa	Coronoid process of mandible	Elevation, retraction, lateral deviation of mandible
Medial Pterygoid	Medial side of lateral pterygoid plate (sphenoid)	Medial surface of mandibular angle	Elevation, protrusion, lateral deviation of mandible
Lateral Pterygoid	Lateral side of lateral pterygoid plate	Medial surface of TMJ & neck of mandible	Protrusion, lateral deviation of mandible

Movements of the Mandible

• Elevation: Closing the mouth (masseter, temporalis, medial pterygoid)

• Depression: Opening the mouth (digastric, infrahyoid, suprahyoid muscles, gravity)

• Protrusion: Moving jaw forward (lateral pterygoid, superficial masseter, medial pterygoid)

• Retraction: Moving jaw backward (posterior temporalis, deep masseter)

• Lateral Deviation: Side-to-side movement (retractors of same side, protruders of opposite side)

Anterolateral Muscles of the Neck

Sternocleidomastoid

• Origin: Manubrium of sternum and medial clavicle

• Insertion: Mastoid process of temporal bone

• Action:

  • Unilateral: Laterally flexes neck to same side, rotates face to opposite side

  • Bilateral: Flexes lower neck, extends upper neck/head

• Innervation: Accessory Nerve (CN XI)

Suprahyoid and Infrahyoid Muscles

• Suprahyoid: Attach to hyoid and mandible/temporal bone; elevate hyoid (swallowing) or depress mandible (mastication)

• Infrahyoid: Attach to hyoid, thyroid cartilage, and sternum; depress hyoid and larynx during swallowing and speech

Scalene Muscles

• Located deep to sternocleidomastoid, lateral to vertebral column

• Origin: Transverse processes of cervical vertebrae

• Insertion: Ribs 1 and 2

• Action: Elevate ribs during forced inspiration, flex and rotate neck

Deep Neck Muscles of the Vertebral Column

Suboccipital Muscles

• Located deep and posterior to the atlas and axis, below the occipital bone

• Responsible for fine movements of the head at the atlanto-occipital ("yes" movement) and atlanto-axial ("no" movement) joints

Summary Table: Major Muscles of the Head and Neck

Muscle Group	Key Muscles	Innervation	Main Actions
Facial Expression	Orbicularis oris, zygomaticus major, buccinator, platysma, orbicularis oculi	Facial Nerve (CN VII)	Move facial skin for expression, communication
Extrinsic Eye	Superior/inferior/medial/lateral rectus, superior/inferior oblique	Oculomotor (CN III), Trochlear (CN IV), Abducens (CN VI)	Move eyeball in various directions
Mastication	Masseter, temporalis, medial/lateral pterygoid	Trigeminal Nerve (CN V)	Chewing, jaw movement
Neck	Sternocleidomastoid, scalene, suprahyoid, infrahyoid	Accessory (CN XI), cervical nerves	Head/neck movement, swallowing

Additional info:

• Some minor muscles and detailed anatomical variations are not assessed in introductory courses.

• For clinical testing of eye muscles, specific eye movements are used to isolate each muscle's function.