Muscles of the Human Body: Classification and Function (Chapter 11 Study Guide)

Muscles of Facial Expression

Overview

Muscles of facial expression are responsible for movements that convey emotions and facilitate nonverbal communication. These muscles are generally located in the subcutaneous tissue and attach to the skin, allowing for a wide range of facial movements.

• Occipitofrontalis: Raises eyebrows and wrinkles forehead.

• Orbicularis oculi: Closes eyelids; enables blinking and squinting.

• Orbicularis oris: Closes and protrudes lips; important for speech and eating.

• Depressor anguli oris: Depresses the corner of the mouth (frowning).

• Zygomaticus major: Elevates the corners of the mouth (smiling).

Muscles of Mastication

Overview

These muscles are involved in chewing and moving the jaw. They are essential for the mechanical breakdown of food.

• Masseter: Elevates the mandible; primary muscle for chewing.

Muscles that Move the Head and Neck

Overview

These muscles control movements such as flexion, extension, rotation, and lateral bending of the head and neck.

• Sternocleidomastoid: Flexes and rotates the head; important for turning the head side to side.

Muscles of Respiration

Overview

Muscles involved in breathing facilitate the movement of air into and out of the lungs.

• Diaphragm: Main muscle of inspiration; contracts to increase thoracic cavity volume.

• External intercostals: Elevate ribs during inspiration.

• Internal intercostals: Depress ribs during forced expiration.

• External oblique: Compresses abdomen; assists in forced expiration.

• Internal oblique: Compresses abdomen; assists in forced expiration.

• Transversus abdominis: Compresses abdominal contents.

Muscles that Move the Abdominal Region (Trunk)

Overview

These muscles support trunk movement, posture, and protect internal organs.

• Rectus abdominis: Flexes vertebral column; compresses abdomen.

• External oblique: Rotates and laterally flexes trunk.

• Internal oblique: Rotates and laterally flexes trunk.

• Transversus abdominis: Compresses abdominal contents.

Muscles that Move the Scapula

Overview

These muscles stabilize and move the scapula, allowing for shoulder mobility.

• Trapezius: Elevates, retracts, and rotates scapula.

Muscles that Move the Humerus at the Shoulder Joint

Overview

These muscles are responsible for movements of the upper arm, including abduction, adduction, flexion, and extension.

• Pectoralis major: Flexes, adducts, and medially rotates humerus.

• Deltoid: Abducts arm; assists in flexion and extension.

• Latissimus dorsi: Extends, adducts, and medially rotates humerus.

• Teres major: Assists in extension and medial rotation of humerus.

• Triceps brachii: Extends forearm; assists in arm adduction.

Muscles that Move the Forearm at the Elbow Joint

Overview

These muscles enable flexion and extension of the forearm at the elbow.

• Biceps brachii: Flexes elbow; supinates forearm.

• Brachialis: Primary flexor of the elbow.

• Triceps brachii: Extends elbow.

Muscles that Move the Hand at the Wrist Joint

Overview

Muscles in the forearm control movements of the hand and fingers at the wrist joint. Additional info: Specific muscles not listed in the notes, but generally include flexors and extensors of the wrist and fingers.

• Flexor group: Flexes wrist and fingers.

• Extensor group: Extends wrist and fingers.

Muscles that Move the Thigh at the Hip Joint

Overview

These muscles are responsible for movements such as flexion, extension, abduction, and rotation of the thigh.

• Iliopsoas: Flexes thigh at hip.

• Tensor fascia latae: Abducts and medially rotates thigh.

• Sartorius: Flexes, abducts, and laterally rotates thigh.

• Gluteus maximus: Extends and laterally rotates thigh.

• Gluteus medius: Abducts and medially rotates thigh.

• Gluteus minimus: Abducts and medially rotates thigh.

• Semimembranosus: Extends thigh; flexes knee (part of hamstrings).

• Semitendinosus: Extends thigh; flexes knee (part of hamstrings).

• Biceps femoris: Extends thigh; flexes knee (part of hamstrings).

Hamstrings group: Semimembranosus, Semitendinosus, Biceps femoris.

Muscles that Move the Leg at the Knee Joint

Overview

These muscles allow for extension and flexion of the leg at the knee.

• Sartorius: Flexes knee; assists in thigh movements.

• Rectus femoris: Extends knee; flexes thigh (part of quadriceps).

• Vastus lateralis: Extends knee (part of quadriceps).

• Vastus medialis: Extends knee (part of quadriceps).

• Vastus intermedius: Extends knee (part of quadriceps).

• Biceps femoris: Flexes knee (part of hamstrings).

• Semitendinosus: Flexes knee (part of hamstrings).

• Semimembranosus: Flexes knee (part of hamstrings).

Quadriceps group: Rectus femoris, Vastus lateralis, Vastus medialis, Vastus intermedius. Hamstrings group: Biceps femoris, Semitendinosus, Semimembranosus.

Muscles that Move the Foot at the Ankle Joint

Overview

These muscles control movements such as plantar flexion and dorsiflexion of the foot.

• Gastrocnemius: Plantar flexes foot; flexes knee.

• Soleus: Plantar flexes foot.

• Fibularis longus: Everts and plantar flexes foot.

Functional Groupings and General Principles

Overview

Muscles are often grouped by their location and function. For example, muscles in the anterior forearm generally flex the hand and/or digits, while those in the posterior forearm extend them.

• Anterior forearm muscles: Flexors of the hand and fingers.

• Posterior forearm muscles: Extensors of the hand and fingers.

Additional info: Understanding muscle groupings by location and function is essential for predicting movement and diagnosing injuries.