11.3 Axial Muscles of the Head, Neck, and Back

Facial and eye muscles are crucial for communication and vision. These muscles allow us to express emotions, blink, and move our eyes. They work together to create a wide range of facial expressions and precise eye movements.

Suprahyoid and infrahyoid muscles play key roles in swallowing and speech. Located above and below the hyoid bone, these muscles help elevate and depress the hyoid bone and larynx. They're essential for safe swallowing and clear speech production.

Facial and Eye Muscles

Facial expression muscles

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Top images from around the web for Facial expression muscles

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• Orbicularis oculi encircles the eye, closes eyelids, and is involved in blinking (winking) and squinting (narrowing eyes in bright light)
• Orbicularis oris encircles the mouth, closes and protrudes lips, and is involved in whistling, kissing (puckering), and speech articulation (rounding lips for "o" sound)
• Buccinator compresses cheeks against teeth, assists in chewing (keeping food between teeth) and whistling (pushing air through pursed lips)
• Zygomaticus major and minor elevate corners of mouth and create smiling expression (grinning, beaming)
• Risorius pulls corner of mouth laterally and contributes to grinning expression (smirking, sneering)
• Levator labii superioris elevates upper lip and contributes to snarling expression (sneering, disgust)
• Depressor labii inferioris depresses lower lip and contributes to pouting expression (frowning, sadness)
• Depressor anguli oris depresses corners of mouth and creates frowning expression (disappointment, disapproval)
• Frontalis raises eyebrows and wrinkles forehead, contributing to surprised (raised eyebrows) or worried expressions (furrowed brow)
• Corrugator supercilii draws eyebrows medially and downward, creating frowning (scowling) or concentrating expressions (focusing, thinking)
• These muscles are innervated by the facial nerve, which controls their movement and allows for various facial expressions

Extrinsic eye muscle functions

• Six extrinsic eye muscles control eyeball movement: four rectus muscles (superior, inferior, medial, lateral) and two oblique muscles (superior, inferior)
• Rectus muscle actions:
  1. Superior rectus elevates and slightly adducts eyeball (looking up and toward nose)
  2. Inferior rectus depresses and slightly adducts eyeball (looking down and toward nose)
  3. Medial rectus adducts eyeball (looking toward nose)
  4. Lateral rectus abducts eyeball (looking away from nose)
• Oblique muscle actions:
  1. Superior oblique depresses, abducts, and intorts eyeball (looking down and out, top of eye rotates medially)
  2. Inferior oblique elevates, abducts, and extorts eyeball (looking up and out, top of eye rotates laterally)
• Coordinated contraction and relaxation of these muscles allow for precise eye movements like saccades (rapid movements between fixation points), smooth pursuit (tracking of moving objects like following a ball), and vergence (inward or outward rotation for focusing at different distances like reading a book vs looking at a distant sign)

Suprahyoid and Infrahyoid Muscles

Suprahyoid vs infrahyoid muscles

• Suprahyoid muscles are located superior to hyoid bone and include digastric, stylohyoid, mylohyoid, and geniohyoid muscles. They elevate hyoid bone and larynx during swallowing (to prevent aspiration of food into trachea) and contribute to opening of mouth (jaw depression) and depression of mandible (chin tuck).
• Infrahyoid muscles are located inferior to hyoid bone and include sternohyoid, sternothyroid, thyrohyoid, and omohyoid muscles. They depress hyoid bone and larynx after swallowing (returning structures to resting position) and stabilize hyoid bone and larynx during speech (providing stable platform for precise larynx and vocal cord movements).
• Swallowing actions:
  1. Suprahyoid muscles elevate hyoid bone and larynx, helping prevent aspiration of food or liquid into trachea (choking, coughing)
  2. Infrahyoid muscles depress hyoid bone and larynx after swallowing, returning structures to resting position (relaxed state)
• Speech actions:
  • Suprahyoid and infrahyoid muscles work together to stabilize hyoid bone and larynx
    • Provides a stable platform for precise movements of larynx and vocal cords
    • Allows for proper phonation (voicing) and articulation (shaping sounds) during speech

Muscle Structure and Function

• Muscle fascicles are bundles of muscle fibers that contribute to the overall structure and function of muscles
• Origin and insertion refer to the attachment points of muscles, with the origin being the fixed point and the insertion being the movable point
• Muscle contraction occurs when muscle fibers shorten, generating force and movement
• Antagonistic muscle pairs work in opposition to each other, with one muscle contracting while the other relaxes to produce movement