Muscles of Head, Neck Trunk_6c7586c125dff04c8f95a36cad3333b3

Muscles of Head, Neck & Trunk

Objectives

  • At the end of the session, students should understand the following muscle groups:

    • Muscles of facial expression

    • Muscles of mastication

    • Muscles of the neck

    • Muscles of the trunk

    • Superficial Musculoaponeurotic System (SMAS)

Muscles of Face

  • General Characteristics

    • Muscles originate from bone or fascia with insertions into the skin.

    • Functions mainly as facial expression muscles, sphincters, and dilators of facial orifices (orbits, nose, mouth).

    • Innervated by the facial nerve (CN VII).

  • Classification

    • Orbital Group

    • Nasal Group

    • Oral Group

    • Additional Muscle Group

Muscle Details

Orbital Group

  • Orbicularis Oculi

    • Parts: Palpebral and orbital

      • Palpebral: Medial palpebral ligament to lateral palpebral raphe; closes eyelids gently.

      • Orbital: Nasal part of frontal bone; closes eyelids forcefully and may cause forehead wrinkles.

    • Corrugator Supercilii: Skin of eyebrows; pulls eyebrows medially and downward.

Nasal Group

  • Nasalis

    • Transverse Part: Compresses nasal aperture.

    • Alar Part: Draws nasal cartilage downwards, opening nostril.

    • Procerus: Draws down medial angle of eyebrows, creating transverse wrinkles.

    • Depressor Septi: Pulls nose inferiorly.

Oral Group

  • Depressor Anguli Oris: Skin at corner of mouth; draws mouth corner downwards and laterally.

  • Depressor Labii Inferioris: Blends with orbicularis oris. Draws lower lip downwards.

  • Mentalis: Raises and protrudes lower lip; wrinkles skin on chin.

  • Orbicularis Oris: Closes and protrudes lips; forms ellipse around the mouth.

  • Buccinator: Presses cheek against teeth and aids mastication; expulses air from cheeks.

Other Facial Muscles

  • Anterior Auricular: Draws ear forward.

  • Occipitofrontalis: Frontal belly raises eyebrows; Occipital belly draws scalp backward.

Platysma

  • Large, thin muscle in superficial fascia of neck. Tenses neck skin and can lower the lip corners.

SMAS (Superficial Musculoaponeurotic System)

  • Organized fibrous network including the platysma muscle and parotid fascia.

  • Supports facial rejuvenation techniques like facelifts.

Botulinum Toxin (Botox)

  • Injectable toxin preventing muscle movement, smoothing facial wrinkles.

Muscles of Mastication

  • Masseter: Elevates mandible; originates from zygomatic arch.

  • Temporalis: Elevates and retracts mandible; originates from temporal fossa.

  • Medial Pterygoid: Elevates mandible; has deep and superficial heads.

  • Lateral Pterygoid: Protrudes mandible and assists with side-to-side movement.

Neck Anatomy

  • General Description: Connecting the head to the trunk, organized into four compartments.

    • Visceral compartment: Digestive and respiratory system

    • Vertebral compartment: Spinal cord and vertebrae

    • Vascular compartments: Major blood vessels; vagus nerve

Triangles of Neck

  • Anterior Triangle: Bounded by the midline, sternocleidomastoid, and mandible.

  • Posterior Triangle: Bounded by the trapezius and sternocleidomastoid.

Cervical Fascia

  • Superficial Fascia: Contains the platysma.

  • Deep Cervical Fascia: Organized into layers encapsulating various structures. Types include:

    • Investing layer

    • Prevertebral layer

    • Pretracheal layer

    • Carotid sheaths

Major Neck Muscles

  • Sternocleidomastoid

    • Origin: Manubrium and clavicle; Inserts: Mastoid process.

    • Function: Rotates head, tilts towards shoulder.

Supra Hyoid Muscles

  • Muscles: Stylohyoid, Digastric, Mylohyoid, Geniohyoid.

  • Function: Elevate hyoid bone and assist in mouth opening.

Infra Hyoid Muscles

  • Muscles: Sternohyoid, Omohyoid, Thyrohyoid, Sternothyroid.

  • Function: Depress hyoid bone and larynx.

Muscles of the Back

  • Group Organization: Superficial, Intermediate, Deep.

    • Superficial muscles: Trapezius, latissimus dorsi, etc.

    • Intermediate muscles: Serratus posterior groups.

    • Deep muscles: Rotators and extensors of vertebral column and neck.

Important Muscles to Learn

  • Know Origin, Insertion, Action, Nerve Supply: Sternocleidomastoid, Digastric, Trapezius, Latissimus dorsi.

  • Know Nerve Supply & Action: Orbicularis oculi, orbicularis oris, platysma, buccinator, mastication muscles, rhomboids, levator scapulae.