Muscle Definitions and Functions: A&P Lab Final Review

Muscles of the Human Body

Overview of Major Muscles and Their Functions

This section provides definitions and functional descriptions of key muscles in the human body, focusing on their anatomical location and primary actions. Understanding these muscles is essential for comprehending movement, posture, and the musculoskeletal system in Anatomy & Physiology.

• Temporalis: Elevates the mandible for chewing. Example: Used when biting down on food.

• Masseter: Powerful jaw muscle; elevates the mandible. Example: Main muscle for mastication.

• Frontalis: Raises eyebrows; wrinkles forehead. Example: Expressing surprise.

• Orbicularis oculi: Closes eyelids; blinking. Example: Protects the eye from debris.

• Orbicularis oris: Closes lips; puckers lips. Example: Whistling or kissing.

• Zygomaticus: Smiling muscle; elevates corners of mouth. Example: Smiling.

• Depressor anguli oris: Depresses lip corners; frowning. Example: Expressing sadness.

• Buccinator: Compresses cheek; holds food between teeth during chewing. Example: Sucking or blowing.

• Sternocleidomastoid: Flexes neck and rotates head. Example: Turning head side to side.

• Deltoid: Abducts arm; forms shoulder contour. Example: Raising arm laterally.

• Pectoralis major: Flexes, adducts, and rotates arm medially. Example: Pushing movements.

• Latissimus dorsi: Extends, adducts, and medially rotates arm. Example: Pulling movements.

• Trapezius: Elevates, retracts, and rotates scapula. Example: Shrugging shoulders.

• Infraspinatus: Rotates arm laterally. Example: Throwing a ball.

• Teres major: Extends and adducts arm. Example: Pulling arm backward.

• Biceps brachii: Flexes elbow and supinates forearm. Example: Lifting objects.

• Triceps brachii: Extends elbow. Example: Pushing movements.

• Brachioradialis: Flexes forearm at elbow. Example: Hammering.

• Pronator teres: Pronates forearm. Example: Turning palm downward.

• Flexor carpi radialis: Flexes and abducts wrist. Example: Waving hand.

• Palmaris longus: Tenses palmar fascia. Example: Gripping objects.

• Transversus abdominis: Compresses abdomen. Example: Forced expiration.

• Internal/External obliques: Rotate trunk and compress abdomen. Example: Twisting torso.

• Rectus femoris: Extends knee, flexes hip. Example: Kicking a ball.

• Vastus lateralis: Extends knee. Example: Standing up from a chair.

• Vastus medialis: Extends knee. Example: Stabilizing patella.

• Tensor fasciae latae: Abducts thigh. Example: Moving leg sideways.

• Sartorius: Flexes thigh, rotates hip. Example: Crossing legs.

• Adductor longus: Adducts thigh. Example: Bringing legs together.

• Gracilis: Adducts thigh. Example: Stabilizing thigh during movement.

• Gluteus maximus: Extends thigh. Example: Climbing stairs.

• Gluteus medius: Abducts thigh. Example: Walking.

• Fibularis longus: Plantar flexion and eversion. Example: Standing on tiptoe.

• Tibialis anterior: Dorsiflexes and inverts foot. Example: Walking on heels.

• Extensor digitorum longus: Extends toes. Example: Lifting toes upward.

• Extensor hallucis longus: Extends big toe. Example: Pointing big toe upward.

• Flexor carpi ulnaris: Flexes and adducts wrist. Example: Moving hand toward body.

• Flexor digitorum superficialis: Flexes fingers. Example: Gripping objects.

• Extensor carpi radialis longus: Extends and abducts wrist. Example: Moving hand away from body.

• Extensor carpi ulnaris: Extends and adducts wrist. Example: Stabilizing wrist during hand movements.

• Extensor digitorum: Extends fingers. Example: Opening hand.

• Calcaneal tendon (Achilles tendon): Attaches calf muscles to heel. Example: Walking, running, jumping.

• Adductor magnus: Thigh adductor. Example: Stabilizing thigh during movement.

• Biceps femoris: Hamstring; knee flexion. Example: Bending knee.

• Semitendinosus: Hamstring; knee flexion. Example: Bending knee.

• Semimembranosus: Hamstring; knee flexion. Example: Bending knee.

Key Terms and Definitions

• Flexion: Decreasing the angle between two body parts.

• Extension: Increasing the angle between two body parts.

• Abduction: Movement away from the midline of the body.

• Adduction: Movement toward the midline of the body.

• Rotation: Movement around an axis.

• Pronation: Rotating the forearm so the palm faces downward.

• Supination: Rotating the forearm so the palm faces upward.

Muscle Group Classification

Muscles are often grouped by their location and function. For example, the hamstrings (biceps femoris, semitendinosus, semimembranosus) are located at the back of the thigh and are responsible for knee flexion. The quadriceps (rectus femoris, vastus lateralis, vastus medialis) are located at the front of the thigh and extend the knee.

Table: Major Muscles and Their Actions

Muscle	Location	Primary Action
Temporalis	Head	Elevates mandible
Deltoid	Shoulder	Abducts arm
Biceps brachii	Upper arm	Flexes elbow, supinates forearm
Triceps brachii	Upper arm	Extends elbow
Rectus femoris	Thigh	Extends knee, flexes hip
Gluteus maximus	Buttocks	Extends thigh
Gastrocnemius	Calf	Plantar flexes foot
Hamstrings	Thigh (posterior)	Flexes knee

Additional info: Muscle actions are often coordinated, with agonist and antagonist pairs controlling movement. For example, the biceps brachii (agonist) flexes the elbow, while the triceps brachii (antagonist) extends it.