Facial Muscles Overview

Muscles of Facial Expression

• Superficial muscles of the face, head, and neck are responsible for facial expressions.
• Some cultures interpret facial expressions differently, but some are universal across cultures.

Orbital Group of Facial Muscles

• Occipitofrontalis (Epicranius)
  • Single muscle with two bellies:
    • Occipital Belly: Located at the back of the head
    • Frontal Belly: Located at the forehead
    • Connected by the Epicranial Aponeurosis, a flat sheet of connective tissue
  • Allows eyebrow elevation.
• Corrugator Supercilli: Wrinkles the eyebrows.
• Orbicularis Oculi:
  • Circles the eye (ocular area).
  • Allows forceful eye closure.

Oral Group of Facial Muscles

• Zygomaticus Major: Larger of the two.
• Zygomaticus Minor: Smaller of the two.
  • They work together, connecting from the zygomatic arch to the corner of the mouth.
• Risorius: Draws the corner of the mouth laterally.
• Levator Labii Superioris: Elevates the upper lip.
• Depressor Labii Inferioris: Depresses the lower lip.
• Depressor Anguli Oris: Depresses the corner of the mouth.
• Orbicularis Oris: Circles the mouth.
• Mentalis: Elevates and protrudes the lower lip.
• Buccinator: Compresses the cheek.
  • Also known as the trumpeter muscle.
• Platysma: Draws the lower lip inferiorly and posteriorly.

Facial Nerve (CN VII)

• Responsible for motor function of facial expression muscles.

Muscles of Mastication

• Masseter: Most important muscle for closing the jaw.
• Temporalis: Elevates the mandible, located over the temporal bone.
• Medial and Lateral Pterygoids:
  • Work together to protract the mandible.
  • Pull the mandible side to side.

Mastication Muscle Innervation

• Trigeminal Nerve (Cranial Nerve V)

Muscles of Tongue Movement

• Genioglossus: Protracts the tongue.
• Hyoglossus: Retracts and depresses the tongue.
• Styloglossus: Retracts the tongue.

Suprahyoid Muscles

• Located above the hyoid bone.
• All insert on the hyoid bone.
• Digastric:
  • Anterior belly originates on the mandible.
  • Posterior belly originates on the mastoid process.
  • Inserts on the hyoid bone.
• Stylohyoid:
  • Originates on the styloid process of the temporal bone.
  • Inserts on the hyoid bone.
• Mylohyoid:
  • Originates on the mylohyoid line of the mandible.
  • Inserts on the hyoid bone.

Infrahyoid Muscles

• Located below the hyoid bone.
• All insert on the hyoid or thyroid cartilage.
• Sternohyoid:
  • Originates on the manubrium of the sternum.
  • Inserts on the hyoid bone.
• Omohyoid:
  • Originates on the superior surface of the scapula.
  • Inserts on the hyoid bone.
• Thyrohyoid:
  • Originates on the thyroid cartilage.
  • Inserts on the hyoid bone.
• Sternothyroid:
  • Originates on the manubrium of the sternum.
  • Inserts on the thyroid cartilage.

Muscles of The Neck and Vertebral Column

• Sternocleidomastoid:
  • Originates on the manubrium and clavicle.
  • Inserts on the mastoid process.
  • Flexes, rotates, and laterally flexes the head.
• Scalenes:
  • Originate on the transverse processes of the cervical vertebrae.
  • Insert on the first two ribs.
  • Elevate the first two ribs and flex and rotate the neck.
• Splenius:
  • Extends and rotates the head.
• Semispinalis:
  • Three regions: capitis, cervicis, and thoracis.
  • Extends and rotates the head and vertebral column.
• Quadratus Lumborum:
  • Originates on the iliac crest.
  • Inserts on the transverse processes of the lowest ribs.
  • Laterally flexes and extends the lumbar spine.

Diaphragm

• The prime mover of inspiration (inhalation).

External Intercostals

• Aid in inspiration.

Internal Intercostals

• Aid in forceful expiration.

Muscles of Abdominal Wall

• Rectus Abdominis:
  • Originates on the pubic crest and symphysis.
  • Inserts on the xiphoid process and cartilage of ribs 5-7.
  • Surrounded by an aponeurosis called the rectus sheath.
  • Flexes and rotates the lumbar region.
• External Oblique:
  • Flexes and rotates the vertebral column.
• Internal Oblique:
  • Sits just deep to the external oblique.
  • Muscle angle runs opposite of the external oblique.
  • Flexes and rotates the vertebral column.
• Transversus Abdominis: Compresses the abdominal contents.

Muscles of The Pelvic Floor

• Levator Ani: Supports pelvic organs.
• Coccygeus: Supports pelvic organs.

Muscles of The Perineum

• Ischiocavernosus: Helps maintain erection of the penis or clitoris.
• Bulbospongiosus: Helps maintain erection of the penis or clitoris.

Muscles of The Upper Limbs

Muscle of The Anterior Thorax

• Serratus Anterior:
  • Protracts and superiorly rotates the scapula.
  • Known as the "boxer's muscle."
• Pectoralis Minor:
  • Originates on the anterior surface of ribs 3-5.
  • Inserts on the coracoid process of the scapula.
  • Protracts and depresses the scapula; elevates ribs if scapula is fixed.
• Subclavius: Helps stabilize and depress the pectoral girdle.
• Levator Scapulae: Elevates and retracts the scapula.
• Trapezius:
  • Originates on the occipital bone and spinous processes of C7-T12.
  • Inserts on the acromion, spine of the scapula, and lateral clavicle.
  • Elevates, depresses, retracts, and superiorly rotates the scapula; helps extend the head.

Rhomboid Major and Minor

- Stabilize, retract, elevate, and inferiorly rotate the scapula.

Muscles Crossing the Shoulder Joint: Anterior

• Pectoralis Major:
  • Originates on the clavicle, sternum, and ribs 1-6.
  • Inserts on the greater tubercle of the humerus.
  • Adducts and medially rotates the arm.
• Deltoid:
  • Originates on the clavicle, acromion, and scapular spine.
  • Inserts on the deltoid tuberosity of the humerus.
  • Abducts, flexes, and extends the arm.
• Coracobrachialis:
  • Originates on the coracoid process of the scapula.
  • Inserts on the medial humerus shaft.
  • Flexes and adducts the arm.

Muscles Crossing the Shoulder Joint: Posterior

• Teres Major: Extends, medially rotates, and adducts the arm.
• Latissimus Dorsi:
  • Originates on the spinous processes of T7-L5, iliac crest, inferior 3-4 ribs, inferior angle of the scapula.
  • Inserts on the intertubercular sulcus of the humerus.
  • Extends, adducts, and medially rotates the arm.