2.02 Muscular System

Key Sections

• Types of Muscles

  • Skeletal Muscles: Found on bones, characterized by a striated appearance, voluntary control, and multinucleation. Named based on location, size, direction, number of origins, and actions (e.g., flexor and extensor).

  • Cardiac Muscles: Found only in the heart, striated and branched, involuntary. Cells are fused, enabling synchronized contractions to create the heartbeat.

  • Smooth Muscles: Found in organs and blood vessels, also known as visceral muscles, and are involuntary.

  • Sphincter Muscles: Special circular muscles that open and close to allow passage of substances. Found in the digestive and urinary systems.

• Structures of the Muscular System

  • Connective Tissue: Includes tendons (connect muscles to bones) and fascia (fibrous sheets wrapping around muscle bundles).

• Characteristics of Muscles

  • Extensibility: Ability to stretch or extend.

  • Contractibility: Ability to shorten or pull.

  • Elasticity: Ability to return to the original state.

  • Excitability: Ability to respond to stimuli.

  • Muscle Tone: Tension in muscles.

  • Atrophy: Decrease in muscle size due to disuse.

  • Hypertrophy: Increase in muscle size due to strength training.

  • Muscle Fatigue: Decrease in maximal force or power production.

• Muscles of the Body

  • Head and Neck: Includes muscles like frontalis (moves eyebrows), masseter (chewing), orbicular oculi (closes eyelids), and sternocleidomastoid (rotates head).

  • Torso/Trunk: Includes external intercostals (assist lungs), diaphragm (aids in breathing), rectus abdominus (abs), and latissimus dorsi (lower back).

  • Upper Extremities: Includes trapezius (supports arm), deltoid (lifts upper arm), pectoralis major (chest), biceps brachii (lifts forearm), and triceps brachii (straightens arm).

  • Lower Extremities: Includes gluteus medius/maximus (hip movement), vastus lateralis (extends knee), gastrocnemius (calf muscle), and tibialis anterior (dorsiflexes foot).

• Functions of the Muscular System

  • Movement: Result of muscle contraction and relaxation.

  • Posture: Maintained by musculoskeletal system.

  • Body Heat: Generated by muscle contractions.

• Movement Types

  • Includes rotation, extension, circumduction, supination, pronation, flexion, abduction, and adduction.

• Disorders of the Muscular System

  • Fibromyalgia: Causes muscle pain, fatigue, sleep disorders; mostly affects women.

  • Hernia: Organ pushes through a muscle opening; often occurs in the abdomen or groin.

  • Muscle Spasms: Sudden involuntary contractions; caused by overuse or dehydration.

  • Strain: Muscle tear or tendon damage; treated with RICE and NSAIDs.

  • Tendonitis: Inflammation of tendons; common in shoulders and elbows.

  • Muscular Dystrophy: Group of diseases causing progressive muscle weakness; mostly affects boys.

  • Tetanus: Serious illness caused by Clostridium bacteria; prevented by vaccine.