Muscles of the Head

Muscles of Facial Expression

The muscles of facial expression are responsible for producing the wide variety of facial movements that convey emotion and facilitate communication. These muscles are generally attached to the skin and underlying bones of the face.

• Frontalis: Raises the eyebrows and wrinkles the forehead. Example: Expressing surprise.

• Orbicularis oculi: Closes the eyelid during squinting and blinking. Example: Protecting the eye from bright light or foreign objects.

• Orbicularis oris: Closes and protrudes the lips, as in speaking, kissing, and whistling. Example: Puckering the lips to whistle.

• Platysma: Tenses the skin of the neck. Example: Expressing tension or stress.

• Zygomaticus minor: Raises the upper lip. Example: Showing disdain or a sneer.

• Zygomaticus major: Raises the lateral corner of the mouth for smiling. Example: Smiling or laughing.

• Buccinator: Compresses the cheek while whistling, blowing, or chewing. Example: Blowing up a balloon or keeping food between teeth while chewing.

Muscles of Mastication

These muscles are involved in the movement of the jaw, allowing for chewing and grinding of food.

• Masseter: Elevates the mandible to close the jaw; also protrudes the mandible. Example: Biting into food.

• Temporalis: Elevates the mandible to close the jaw; retracts the mandible. Example: Chewing tough foods.

Muscles of the Neck

The neck muscles facilitate movement of the head and assist in swallowing and breathing.

• Sternocleidomastoid: Flexion and lateral flexion of the neck; rotates the head so that the face is turned superiorly and to the opposite side. Example: Turning the head to look over the shoulder.

• Suprahyoid muscles: Elevate the hyoid bone during swallowing and speaking. Example: Swallowing food or liquid.

• Infrahyoid muscles: Depress the hyoid bone; elevate the larynx. Example: Speaking or singing.

• Scalenes: Lateral flexion of the neck; elevate ribs 1 and 2. Example: Deep inhalation during heavy breathing.

Respiratory Muscles of the Thorax

These muscles are essential for the mechanics of breathing, altering the volume of the thoracic cavity to facilitate inspiration and expiration.

• Diaphragm: Increases the volume of the thoracic cavity by pulling the central tendon inferiorly. Example: Main muscle used during quiet breathing.

• External intercostals: Elevate the ribs during normal inspiration. Example: Expanding the chest during inhalation.

• Internal intercostals: Depress the ribs during forced expiration. Example: Blowing out candles or forceful exhalation.

Muscles of the Abdominal Wall

The abdominal wall muscles support the trunk, allow movement, and help maintain posture. They also play a role in increasing intra-abdominal pressure during activities such as forced expiration, defecation, and childbirth.

• Rectus abdominis: Flexion of the vertebral column; stabilizes the pelvis during walking; increases intra-abdominal pressure during forced expiration. Example: Performing a sit-up.

• External oblique: Rotation and lateral flexion of the trunk; increases intra-abdominal pressure during forced expiration. Example: Twisting the torso.

• Internal oblique: Same actions as the external oblique. Example: Bending sideways or rotating the trunk.

• Transversus abdominis: Increases intra-abdominal pressure during forced expiration. Example: Bracing the core during heavy lifting.

Deep Muscles of the Back

These muscles are primarily responsible for the extension, rotation, and stabilization of the vertebral column and head, maintaining posture and allowing complex movements of the back and neck.

• Splenius: Extension of the head and neck; lateral flexion and rotation of the head and neck. Example: Looking up or turning the head to the side.

• Erector spinae: Extension of the vertebral column and head; lateral flexion of the vertebral column and head; maintains normal curvature of the vertebral column. Example: Standing up straight after bending over.

• Transversospinalis: Extension and rotation of the vertebral column; stabilizes the vertebral column. Example: Maintaining posture during movement.

Summary Table: Major Muscle Groups and Actions

Additional info:

• The diaphragm is the primary muscle of respiration, separating the thoracic and abdominal cavities. Its contraction increases the vertical dimension of the thoracic cavity, allowing air to enter the lungs.

• The erector spinae group consists of three columns of muscles (iliocostalis, longissimus, and spinalis) running parallel to the vertebral column.

• Muscles of the abdominal wall work together to protect internal organs and assist in forced expiration, such as coughing or sneezing.