Muscle Groups of the Head, Neck, Thorax, and Abdomen: Origins, Insertions, and Actions

Muscles That Cause Facial Expressions

Overview

Facial expression muscles are responsible for the wide range of human emotions displayed on the face. These muscles are unique in that they insert into the skin, allowing for subtle movements.

• Epicranius: Includes the occipitalis and frontalis muscles, connected by the epicranial aponeurosis. Action: Raises eyebrows, wrinkles forehead.

• Orbicularis oris: Encircles the mouth. Origin: Maxilla and mandible. Insertion: Lips. Action: Closes and purses lips ("kissing muscle").

• Zygomaticus major: Origin: Zygomatic bone. Insertion: Angle of mouth. Action: Raises angle of mouth (smiling muscle).

• Zygomaticus minor: Origin: Zygomatic bone. Insertion: Upper lip. Action: Elevates upper lip.

• Buccinator: Origin: Alveolar processes of maxilla and mandible. Insertion: Fibers of orbicularis oris. Action: Compresses cheek ("trumpeter's muscle").

• Platysma: Origin: Superior thorax. Insertion: Mandible and skin of cheek. Action: Tenses skin of neck and depresses mandible.

• Risorius: Origin: Fascia around parotid salivary gland. Insertion: Angle of mouth. Action: Draws corners of mouth to the side.

• Corrugator supercilii: Origin: Frontal bone. Insertion: Eyebrow. Action: Wrinkles eyebrows.

• Orbicularis oculi: Origin: Medial margin of orbit. Insertion: Skin around the eyelids. Action: Closes eyes.

Example

Smiling involves the coordinated action of the zygomaticus major and minor, while frowning uses the corrugator supercilii and platysma.

Muscles Involved in Mastication

Overview

Mastication (chewing) is performed by several muscles that move the jaw and assist in grinding food.

• Masseter: Origin: Zygomatic arch. Insertion: Mandibular ramus. Action: Elevates mandible.

• Temporalis: Origin: Temporal bone. Insertion: Coronoid process of mandible. Action: Elevates mandible.

• Pterygoids (Medial and Lateral): Origin: Sphenoid and palatine plates. Insertion: Mandibular condyle. Action: Elevates, protrudes, and moves jaw side to side.

• Digastric (Posterior and Anterior): Origin: Mastoid process and mandible. Insertion: Hyoid bone. Action: Depresses mandible and elevates larynx.

• Mylohyoid: Origin: Mandible. Insertion: Hyoid bone. Action: Depresses mandible.

Example

The masseter is one of the strongest muscles in the body relative to its size, allowing for powerful jaw closure during chewing.

Muscles of the Anterior Neck Region

Overview

Neck muscles stabilize and move the head and cervical spine, and assist in swallowing and breathing.

• Sternocleidomastoid: Origin: Sternum and clavicle. Insertion: Mastoid process. Action: Flexes neck; rotates head.

• Scalenes: Origin: Transverse processes of C2-C7. Insertion: Superior surface of ribs 1 and 2. Action: Elevates ribs 1 and 2; flexes neck.

Example

Turning the head to the side involves contraction of one sternocleidomastoid muscle.

Muscles That Move the Vertebral Column

Overview

These muscles are essential for posture, movement, and stabilization of the spine.

• Spinalis Muscles: Action: Extend the neck and vertebral column.

• Longissimus Muscles: Action: Extend neck and vertebral column; lateral flexion.

• Iliocostalis Muscles: Action: Extend neck and vertebral column; lateral flexion.

Example

Standing upright after bending forward uses the spinalis and longissimus muscles.

Intercostal Muscle Group

Overview

Intercostal muscles are located between the ribs and are vital for respiration.

Muscle	Origin	Insertion	Action
External Intercostals	Inferior border of each rib	Superior border of adjacent inferior rib	Elevation of ribs (inhalation)
Internal Intercostals	Superior border of each rib	Inferior border of adjacent superior rib	Depression of ribs (exhalation)

Example

During inhalation, the external intercostals contract to lift the rib cage and expand the thoracic cavity.

Abdominal Muscle Group

Overview

Abdominal muscles support the trunk, allow movement, and hold organs in place by regulating internal abdominal pressure.

• Rectus abdominis: Origin: Superior surface of pubis. Insertion: Xiphoid process and costal cartilage of ribs 5-7. Action: Flexes vertebral column and depresses ribs.

• Transversus abdominis: Origin: Lumbar fascia, ribs 7-12, iliac crest. Insertion: Linea alba. Action: Compresses abdomen.

• Internal oblique: Origin: Iliac spine and crest. Insertion: Inferior surface of ribs and adjacent processes. Action: Compresses abdomen and depresses ribs.

• External oblique: Origin: Outer surface of lower eight ribs. Insertion: Iliac crest and linea alba. Action: Compresses abdomen and depresses ribs.

Example

Sit-ups primarily engage the rectus abdominis, while twisting movements use the oblique muscles.

Additional info:

These notes cover key muscle groups relevant to the study of the muscular system in Anatomy & Physiology, including their anatomical origins, insertions, and primary actions. Understanding these muscles is essential for comprehending movement, posture, and physiological functions such as breathing and facial expression.