Axial Skeletal Muscles: Structure, Function, and Anatomy

Muscles of the Head and Face

Overview of Head and Facial Muscles

The muscles of the head and face are responsible for facial expression, mastication (chewing), and movements of the scalp and neck. These muscles are unique because many insert into the skin or other muscles rather than bones, allowing for a wide range of expressive movements.

• Muscles of Facial Expression: Include the orbicularis oculi, orbicularis oris, zygomaticus major and minor, buccinator, and platysma. These muscles control movements such as smiling, frowning, and blinking.

• Muscles of Mastication: The main muscles involved in chewing are the masseter, temporalis, and buccinator.

• Scalp Muscles: The epicranius (frontal and occipital bellies) moves the scalp and eyebrows.

Muscles Promoting Mastication and Tongue Movements

Mastication is primarily performed by the masseter and temporalis muscles, which elevate the mandible. The buccinator assists by holding food between the teeth during chewing.

• Masseter: Elevates the mandible, the main muscle for closing the jaw.

• Temporalis: Elevates and retracts the mandible.

• Buccinator: Compresses the cheek, aiding in chewing and blowing.

Muscles Used in Facial Expressions

Facial expression muscles allow humans to convey emotions nonverbally. Each muscle is responsible for a specific movement, such as raising the eyebrows or smiling.

• Zygomaticus major: Raises the corners of the mouth (smiling).

• Orbicularis oculi: Closes the eyelids.

• Orbicularis oris: Closes and protrudes the lips.

• Platysma: Tenses the skin of the neck and depresses the mandible.

Muscles of the Neck and Back

Superficial Muscles of the Thorax and Shoulder Acting on the Scapula and Arm

These muscles stabilize and move the scapula and upper arm. They are essential for shoulder movement and posture.

• Trapezius: Elevates, retracts, and rotates the scapula.

• Deltoid: Abducts the arm.

• Latissimus dorsi: Extends, adducts, and medially rotates the arm.

• Rhomboid major and minor: Retract the scapula.

• Levator scapulae: Elevates the scapula.

Muscles of the Neck and Vertebral Column That Move the Head and Trunk

These muscles are responsible for movements of the head, neck, and trunk, including flexion, extension, rotation, and lateral bending.

• Sternocleidomastoid: Flexes and rotates the head.

• Scalenes (anterior, middle, posterior): Elevate the first two ribs and flex and rotate the neck.

• Splenius capitis and cervicis: Extend and rotate the head.

• Erector spinae group (iliocostalis, longissimus, spinalis): Prime movers of back extension and lateral flexion.

• Semispinalis and quadratus lumborum: Assist in extension and lateral flexion of the vertebral column.

Muscles of the Abdominal Wall

Structure and Function

The abdominal wall is composed of four paired muscles that support and protect abdominal viscera, and promote movements such as flexion and lateral flexion of the vertebral column.

• Rectus abdominis: Flexes the vertebral column and compresses abdominal contents.

• External oblique: Flexes and rotates the vertebral column; compresses abdominal wall.

• Internal oblique: Same actions as the external oblique.

• Transversus abdominis: Compresses abdominal contents.

Muscles of Respiration

Intercostal Muscles

The intercostal muscles are located between the ribs and play a crucial role in breathing by aiding the expansion and contraction of the thoracic cavity.

• External intercostals: Elevate the ribs during inspiration, increasing thoracic volume.

• Internal intercostals: Depress the ribs during forced expiration.

Diaphragm

The diaphragm is the primary muscle of inspiration. It separates the thoracic and abdominal cavities and contracts to increase thoracic volume during inhalation.

• Central tendon: The insertion point for muscle fibers of the diaphragm.

• Openings: Allow passage of the aorta, esophagus, and inferior vena cava.

Summary Table: Major Axial Muscles and Their Functions

Muscle Group	Main Muscles	Primary Actions
Facial Expression	Orbicularis oculi, zygomaticus, platysma	Facial movements (smiling, frowning, blinking)
Mastication	Masseter, temporalis, buccinator	Chewing, jaw closure
Neck	Sternocleidomastoid, scalenes	Head flexion, rotation
Back	Erector spinae, trapezius, rhomboids	Extension, rotation, and stabilization of vertebral column
Abdominal Wall	Rectus abdominis, obliques, transversus abdominis	Trunk flexion, compression of abdominal contents
Respiration	Diaphragm, intercostals	Inspiration and expiration

Additional info: The axial muscles are essential for posture, breathing, and protection of internal organs. Dysfunction in these muscles can lead to clinical conditions such as hernias, back pain, and respiratory difficulties.