Unit 7: The Muscular System

This unit provides an overview of the muscular system, focusing on skeletal muscle structure and function, as well as the anatomy and actions of major muscle groups in the human body. The following study notes summarize the key concepts and objectives for this unit.

Types of Muscle Tissue

There are three primary types of muscle tissue in the human body, each with distinct structures and functions:

• Smooth Muscle: Involuntary, non-striated muscle found in the walls of internal organs (e.g., digestive tract, blood vessels). Responsible for movements such as peristalsis and vasoconstriction.

• Cardiac Muscle: Involuntary, striated muscle found only in the heart. Specialized for continuous rhythmic contraction to pump blood.

• Skeletal Muscle: Voluntary, striated muscle attached to bones. Responsible for body movement, posture, and heat production.

Location in the Body:

• Smooth muscle: walls of hollow organs (stomach, intestines, blood vessels)

• Cardiac muscle: heart

• Skeletal muscle: attached to bones throughout the body

Muscle Origin and Insertion

Muscles attach to bones at two main points:

• Origin: The fixed attachment point of the muscle, usually proximal (closer to the trunk).

• Insertion: The movable attachment point, usually distal (further from the trunk). When a muscle contracts, the insertion moves toward the origin.

Example: The biceps brachii muscle originates at the scapula and inserts on the radius. When it contracts, it flexes the forearm at the elbow.

Structure and Function of Tendons

• Tendons are strong, fibrous connective tissues that connect muscle to bone.

• They transmit the force generated by muscle contraction to the skeleton, enabling movement.

• Tendons are composed primarily of collagen fibers, providing high tensile strength.

Major Muscles of the Anterior and Posterior Thorax

The thorax contains several important muscles involved in movement and respiration. Key muscles include:

• Pectoralis Major: Large, fan-shaped muscle of the chest. Action: Adducts and medially rotates the arm; flexes the shoulder.

• Pectoralis Minor: Thin, triangular muscle beneath pectoralis major. Action: Stabilizes the scapula by drawing it anteriorly and inferiorly.

• Intercostals: Muscles located between the ribs. Action: Aid in respiration by elevating or depressing the rib cage.

• Trapezius: Large, triangular muscle of the upper back. Action: Elevates, retracts, and rotates the scapula; extends the neck.

• Latissimus Dorsi: Broad, flat muscle of the lower back. Action: Extends, adducts, and medially rotates the arm.

• Levator Scapulae: Muscle at the back and side of the neck. Action: Elevates the scapula.

Major Muscles of the Anterior and Posterior Upper Arm

The upper arm contains muscles responsible for movements at the shoulder and elbow:

• Biceps Brachii: Anterior upper arm muscle. Action: Flexes the elbow and supinates the forearm.

• Triceps Brachii: Posterior upper arm muscle. Action: Extends the elbow.

• Brachialis: Lies beneath the biceps. Action: Flexes the elbow.

• Coracobrachialis: Assists in flexion and adduction of the arm at the shoulder.

Summary Table: Types of Muscle Tissue

Key Formula:

• Muscle force transmission:

Additional info: The above notes expand on the learning objectives by providing definitions, examples, and a summary table for clarity and exam preparation.