Gross Anatomy of the Muscular System: Arm & Leg Muscles

Overview

This section covers the major muscles of the upper and lower limbs, focusing on their anatomical locations, actions, and key terminology relevant to the study of human anatomy and physiology. Understanding these muscles is essential for comprehending movement and function in the human body.

Main Regions of Limb Musculature

• Upper Arm

• Forearm

• Upper Leg/Thigh

• Lower Leg

Common Actions of Limb Muscles

Muscles in the limbs are responsible for a variety of movements, each defined by the direction and nature of the motion at a joint.

• Flexion: Decreases the angle between two body parts (e.g., bending the elbow or knee).

• Extension: Increases the angle between two body parts (e.g., straightening the elbow or knee).

• Abduction: Movement of a limb away from the body's midline.

• Adduction: Movement of a limb toward the body's midline.

• Plantar Flexion: Pointing the toes downward (as in standing on tiptoe).

• Dorsiflexion: Raising the toes upward toward the shin.

The Upper Arm Muscles

Muscles in the upper arm primarily move the elbow and forearm. Their origins and insertions determine their specific actions.

• Origins: Most upper arm muscles originate from the humerus.

• Insertions:

  • Triceps Brachii: Inserts at the ulna; responsible for extension of the elbow.

  • Biceps Brachii & Brachialis: Insert at the radius; responsible for flexion of the elbow.

Flexion vs. Extension

These are fundamental movements at synovial joints, especially in the limbs.

• Flexion: Decreases the angle between the origin and insertion of a muscle.

• Extension: Increases the angle between the origin and insertion of a muscle.

Example: Flexing the elbow brings the forearm closer to the upper arm (biceps contract), while extending the elbow straightens the arm (triceps contract).

Abduction vs. Adduction

• Abduction: Movement of a body part away from the midline (e.g., raising the arm sideways).

• Adduction: Movement of a body part toward the midline (e.g., lowering the arm to the side of the body).

Summary Table: Key Actions and Associated Muscles

Key Terms and Definitions

• Origin: The fixed attachment point of a muscle.

• Insertion: The movable attachment point of a muscle.

• Compartment: A group of muscles, nerves, and blood vessels surrounded by fascia, often sharing similar functions.

Study Tips

• Use tables to organize muscle names, origins, insertions, and actions.

• Focus on learning muscle compartments and their general functions to simplify memorization.

• Refer to lab handouts and diagrams for visual reinforcement.

Additional info: For a comprehensive understanding, students should also review muscles of the head, neck, and trunk as covered in previous labs, and consult lab handouts for detailed muscle lists and diagrams.