Muscular System Study Notes

Muscular System

Objectives

  • Identify three types of muscle tissue

    • Skeletal Muscle
      • Voluntary muscle attached to bones.
      • Striated appearance due to sarcomeres.
      • Multi-nucleated cells.
    • Cardiac Muscle
      • Involuntary muscle found in the heart.
      • Striated like skeletal muscle but includes intercalated discs.
      • Single nucleus per cell.
    • Smooth Muscle
      • Involuntary muscle found in the walls of hollow organs (e.g., intestines, blood vessels).
      • Non-striated appearance.
      • Single nucleus per cell.

  • Compare the structure of the whole muscle and the structure of a single muscle fiber

    • Whole Muscle:
      • Composed of multiple muscle fibers grouped together.
      • Encased by connective tissue layers (epimysium).
    • Single Muscle Fiber:
      • A long, cylindrical cell containing myofibrils.
      • Myofibrils are comprised of sarcomeres, which are the functional units of muscle contraction.

  • Describe the sliding filament mechanism of muscle contraction

    • Explains how muscle fibers contract.
      • Involves the sliding of actin (thin filaments) over myosin (thick filaments).
      • Shortening of the sarcomere occurs when the cross-bridges form and pull the actin filaments toward the center of the sarcomere.

  • Explain the role of calcium and adenosine triphosphate (ATP) in muscle contraction

    • Calcium
      • Released from the sarcoplasmic reticulum in response to nerve impulses.
      • Binds to troponin, causing a change that allows myosin to bind to actin.
    • ATP
      • Provides the energy for the myosin head to perform the power stroke.
      • Required for detaching the myosin head from actin after contraction.

  • Describe the relationship between skeletal muscles and nerves

    • Motor Unit
      • A motor neuron and all the muscle fibers it innervates.
      • Functions together to produce movement.
    • Neuromuscular Junction
      • The synapse where the motor neuron communicates with the muscle fiber.
      • Neurotransmitter released (usually acetylcholine) initiates muscle contraction.

  • Discuss single-fiber and whole-muscle responses

    • Define twitch and tetanus
      • Twitch: A single contraction and relaxation cycle in a muscle fiber.
      • Tetanus: Sustained muscle contraction due to repetitive stimulation without relaxation.
    • Identify the sources of energy for muscle contraction
      • ATP, creatine phosphate, and anaerobic respiration initially.
      • Long-term energy sourced from aerobic respiration.
    • Trace the sequence of events from nerve stimulation to muscle contraction
    1. Nerve impulse reaches the neuromuscular junction.
    2. Acetylcholine is released into the synaptic cleft.
    3. Muscle fiber depolarizes, leading to calcium release from the sarcoplasmic reticulum.
    4. Calcium binds to troponin, exposing binding sites for myosin on actin.
    5. Myosin heads bind to actin, perform power stroke, and sarcomeres shorten.

  • Define muscle terms, and state the basis for naming muscles

    • Muscles are often named based on:
      • Location (e.g., rectus abdominis),
      • Shape (e.g., deltoid),
      • Size (e.g., gluteus maximus),
      • Direction of fibers (e.g., external oblique),
      • Number of origins (e.g., biceps brachii).

  • Identify and list the actions of the major muscles

    • Major actions include:
      • Flexion, extension, abduction, adduction, rotation, and circumduction.
    • Specific muscles perform specific actions (e.g., biceps brachii for elbow flexion).