Myology - Pectoral Area and Superficial & Deep Neck

Text Reference

  • Seeley's Anatomy & Physiology

  • Chapter 10

Actions, Origins, and Insertions

  • Origin: Defined as the less movable attachment point; typically located at the proximal end of the muscle.

  • Insertion: Defined as the more movable attachment point; typically found at the distal end of the muscle.

Muscles of the Head

Muscles of the Scalp

  • Frontalis: Involved in raising the eyebrows and wrinkling the forehead.

  • Occipitalis: Assists in pulling the scalp backward.

Muscles of Mastication

  • Temporalis: A muscle that aids in closing the jaw when chewing.

  • Masseter: One of the primary muscles responsible for mastication, facilitating chewing movement.

Facial Expression Muscles

  • Zygomaticus: Responsible for elevating the corner of the mouth, smiling.

  • Buccinator: Aids in flattening the cheek to keep food between the teeth during chewing.

  • Platysma: A superficial muscle that draws down the lower lip; involved in facial expressions of surprise or fright.

  • Orbicularis oculi: Encircles the eye; functions to close the eyelids and assist in blinking.

  • Orbicularis oris: Encircles the mouth; involved in puckering and facial expressions.

  • Levator labii superioris: Raises the upper lip.

  • Depressor labii inferioris: Draws down the lower lip.

Anterolateral Neck Muscles

  • Sternocleidomastoid: Functions to rotate the head and flex the neck.

  • Scalenes: Group of muscles that assist in elevating the first rib and flexing the neck.

  • Trapezius: Elevates, retracts, and rotates the scapula; extends the neck.

Anterior Neck Muscles

Suprahyoid Muscles

  • Digastric: Consists of two muscle bellies; functions to elevate the hyoid bone and depress the mandible.

  • Mylohyoid: Forms the floor of the mouth; supports the hyoid bone and aids in swallowing.

  • Geniohyoid: Located above the mylohyoid; assists in hyoid elevation.

Infrahyoid Muscles

  • Sternohyoid: Depresses the hyoid bone.

  • Sternothyroid: Aids in depressing the thyroid cartilage.

  • Thyrohyoid: Elevates the thyroid cartilage and depresses the hyoid bone.

  • Omohyoid: Depresses the hyoid bone and aids in swallowing; consists of superior and inferior bellies.

Abdominal Wall Muscles

  • External Oblique: Contributes to the flexibility and stability of the abdomen; supports lateral bending and rotation.

  • Internal Oblique: Helps in compressing the abdominal cavity and aids in rotation.

  • Transverse Abdominis: Deepest abdominal muscle; acts as a stabilizer for the trunk and can compress the abdomen.

  • Rectus Abdominis: Known as the “abs”; compresses the abdomen and flexes the vertebral column.

  • Pectoralis Major: Covers the upper part of the chest; assists in shoulder movements.

  • Latissimus Dorsi: One of the largest muscles; involved in shoulder adduction and extension.

  • Serratus Anterior: Primary muscle for the protraction of the scapula.

Anatomical Landmarks

  • Linea Alba: Midline structure where the two sides of the rectus abdominis meet.

  • Linea Semilunaris: Curved line appearing on the lateral part of the abdomen.

  • Umbilicus: The center of the abdominal wall, often used as a guiding landmark.

  • Inguinal Ligament: Runs from the pubic bone to the anterior superior iliac spine, creating the base of the inguinal canal.

  • Inguinal Canal: Passage for structures that pass from the abdomen to the groin region.

  • Rectus Sheath: Encases the rectus abdominis muscle.

Breathing Muscles

  • Anterior Scalene: Elevates the first rib during inhalation.

  • Middle Scalene: Assists in elevating the first rib.

  • Posterior Scalene: Elevates the second rib during inhalation.

  • External Intercostals: Muscles located between the ribs; aid in inhalation by expanding the thoracic cavity.

  • Internal Intercostals: Positioned beneath the external intercostals; assist in forced exhalation.

  • Diaphragm: The primary muscle of respiration that separates the thoracic and abdominal cavities; its contraction increases thoracic volume and decreases thoracic pressure, allowing inhalation.

  • Transversus Thoracis: Found inside the thoracic cavity; aids in depress the ribs during exhalation.

Muscles of the Anterior Thorax and Back

  • Serratus Anterior: Functions to protract and stabilize the scapula.

  • Rhomboids: Assist in retracting the scapula.

  • Splenius: A muscle that aids in extending and rotating the head and neck.

Origin and Insertion of Anterior Neck Muscles

  • Digastric (2 bellies):

    • Origin: Lower margin of the mandible; mastoid process (temporal bone).

    • Insertion: Hyoid bone.

  • Mylohyoid:

    • Origin: Medial surface of the mandible.

    • Insertion: Hyoid bone.

  • Geniohyoid:

    • Origin: Mental tubercle of the mandible.

    • Insertion: Hyoid bone.

  • Sternohyoid:

    • Origin: Manubrium of sternum.

    • Insertion: Hyoid bone.

  • Sternothyroid:

    • Origin: Manubrium of sternum.

    • Insertion: Thyroid cartilage.

  • Thyrohyoid:

    • Origin: Thyroid cartilage.

    • Insertion: Hyoid bone.