Axial Muscles: Head, Neck, Vertebral Column, Abdomen, and Pelvis

Competency 5: The Muscular System

Overview of Axial Muscles

The axial muscles are essential for movement, support, and protection of the head, neck, vertebral column, and trunk. Understanding their gross and microscopic anatomy, as well as their physiological functions, is fundamental in Anatomy & Physiology.

• Axial muscles include those of the head, neck, vertebral column, thorax, abdomen, and pelvis.

• They are responsible for facial expression, mastication, respiration, posture, and stabilization of the trunk and pelvic floor.

Muscles of the Head and Neck

Muscles of Facial Expression

These muscles control movements of the face, allowing for expressions such as smiling, frowning, and blinking.

• Frontalis: Raises eyebrows and wrinkles forehead.

• Occipitalis: Tenses and retracts the scalp.

• Orbicularis oculi: Closes the eyelids.

• Zygomaticus major and minor: Elevate and retract the corners of the mouth (smiling).

• Risorius: Draws the corner of the mouth laterally.

• Depressor anguli oris: Depresses the corner of the mouth (frowning).

• Orbicularis oris: Compresses and purses the lips.

• Mentalis: Elevates and protrudes the lower lip.

• Buccinator: Compresses the cheek (as in blowing).

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

Muscles of Mastication

These muscles are involved in chewing and moving the jaw.

• Masseter: Elevates mandible (closes jaw).

• Temporalis: Elevates and retracts mandible.

• Medial pterygoid: Elevates mandible and moves it side to side.

• Lateral pterygoid: Depresses and protracts mandible, moves it side to side.

Muscles of the Neck

Neck muscles support the head and facilitate movement.

• Sternocleidomastoid: Flexes neck, bends head toward shoulder, rotates head.

• Platysma: Tenses skin of neck, depresses mandible.

Muscles of the Vertebral Column

Major Muscles and Actions

These muscles maintain posture and allow for movement of the spine.

• Erector spinae: Extends and laterally flexes the vertebral column.

• Splenius capitis: Together, extend the neck; alone, rotate and flex the neck.

• Semispinalis capitis: Together, extend the neck; alone, extend and flex the neck.

Muscles of Respiration

Primary Muscles

These muscles are essential for breathing by changing the volume of the thoracic cavity.

• Diaphragm: Major muscle of respiration; contracts to expand thoracic cavity for inhalation.

• External intercostals: Elevate ribs during inhalation.

• Internal intercostals: Depress ribs during forced exhalation.

Muscles of the Abdomen

Abdominal Wall Muscles

These muscles support the trunk, allow movement, and protect internal organs.

• Rectus abdominis: Flexes vertebral column, compresses abdomen; responsible for "six-pack" appearance.

• External oblique: Compresses abdomen, flexes and rotates vertebral column.

• Internal oblique: Compresses abdomen, flexes and rotates vertebral column; deeper than external oblique.

• Transversus abdominis: Compresses abdomen; deepest abdominal muscle, important for posture.

Note: The arrangement from superficial to deep is: external oblique, internal oblique, transversus abdominis.

Muscles of the Pelvic Floor

Pelvic and Urogenital Diaphragm

These muscles support pelvic organs and control openings of the urethra and anus.

• Levator ani: Supports pelvic viscera, elevates and retracts anus.

• Coccygeus: Flexes coccygeal joints, supports pelvic floor.

• Superficial transverse perineal: Stabilizes central tendon of perineum.

• External urethral sphincter: Closes urethra.

• External anal sphincter: Closes anal opening.

Muscles That Move the Eye (Extraocular Muscles)

Actions and Innervation

These muscles control eye movement and are innervated by cranial nerves.

Name	Action	Nerve
Lateral rectus	Moves eye laterally	VI (abducens)
Medial rectus	Moves eye medially	III (oculomotor)
Superior rectus	Elevates eye, turns it medially	III (oculomotor)
Inferior rectus	Depresses eye, turns it medially	III (oculomotor)
Inferior oblique	Elevates eye, turns it laterally	III (oculomotor)
Superior oblique	Depresses eye, turns it laterally	IV (trochlear)

Summary Table: Major Axial Muscles and Their Actions

Region	Muscle	Action
Head	Frontalis	Raises eyebrows, wrinkles forehead
Head	Occipitalis	Tenses and retracts scalp
Face	Orbicularis oculi	Closes eyelids
Jaw	Masseter	Elevates mandible
Neck	Sternocleidomastoid	Flexes neck, rotates head
Vertebral Column	Erector spinae	Extends vertebral column
Thorax	Diaphragm	Inhalation
Abdomen	Rectus abdominis	Flexes vertebral column
Pelvic Floor	Levator ani	Supports pelvic organs

Additional info:

• The study guide emphasizes the importance of reading the textbook and practicing with anatomical models for full mastery.

• Some muscle names and actions were inferred from standard anatomical knowledge and labeled diagrams.