Muscles That Move the Head, Neck, and Face

Overview

The muscles of the head, neck, and face are responsible for facial expressions, mastication (chewing), and movements of the head and neck. These muscles are essential for communication, eating, and positioning the head.

• Masseter: Closes the jaw and elevates the mandible. Example: Chewing food.

• Orbicularis oculi: Closes the eyes; produces blinking and squinting. Example: Protecting the eyes from bright light.

• Orbicularis oris: Closes lips; purses and protrudes the lips, as in kissing and whistling.

• Sternocleidomastoid: Flexes the neck forward; acting independently, rotates the head toward the opposite shoulder.

Muscles of the Abdominal Wall and Trunk

Overview

These muscles support the trunk, allow movement, and help with breathing by changing the volume of the thoracic cavity.

• Diaphragm: Main muscle of respiration; contraction causes flattening during inspiration, thus expanding the thoracic cavity. Example: Breathing in deeply.

• Rectus abdominis: Flexes the vertebral column. Example: Performing a sit-up.

Muscles That Move the Shoulder and Arm

Overview

These muscles are responsible for the movement and stabilization of the shoulder joint and upper arm.

• Deltoid: Abduction of the arm. Example: Raising the arm to the side.

• Pectoralis major: Adducts the arm. Example: Bringing the arm toward the body.

• Latissimus dorsi: Arm/shoulder extension. Example: Pulling the arm backward.

Muscles That Move the Forearm

Overview

These muscles control the flexion and extension of the forearm at the elbow joint.

• Biceps brachii: Forearm flexion. Example: Lifting a weight.

• Triceps brachii: Extension of the forearm. Example: Straightening the arm.

Muscles That Move the Hip and Knee

Overview

The muscles of the hip and knee are essential for locomotion, posture, and stability. They include groups that flex, extend, and stabilize these joints.

• Adductor magnus: Adducts the thigh.

• Gluteus maximus: Powerful thigh/hip extensor. Example: Rising from a sitting position.

• Hamstring muscles: Extend the thigh; flex the leg.

Quadriceps Femoris Group

The quadriceps femoris is a group of four muscles located at the front of the thigh. They are the main extensors of the knee.

• Rectus femoris: Extends the leg and flexes the thigh at the hip.

• Vastus lateralis: Extends the leg and stabilizes the knee.

• Vastus medialis: Extends the leg.

• Vastus intermedius: Extends the leg.

Muscles That Move the Ankle/Foot

Overview

These muscles control movements such as plantar flexion and dorsiflexion, which are important for walking, running, and balance.

• Gastrocnemius: Plantar flexes the foot. Example: Standing on tiptoe.

• Soleus: Plantar flexes the foot.

• Tibialis anterior: Dorsiflexes the foot. Example: Lifting the foot upward.

Summary Table: Major Muscles and Their Actions