muscle system

Overview of Muscle Types

  • Muscle Types:

    • Cardiac Muscle:

    • Involuntary muscle found in the heart.

    • Controlled automatically, brain does not command heart contractions directly.

    • Striated muscle, capable of generating contraction autonomously.

    • Initiated by signals from the lymph nodes.

    • Contains a complex electrical system for coordination of heart activity.

    • Skeletal Muscle:

    • Voluntary muscle found in organs and limbs, responsible for movement.

    • Not striated and allows for conscious control.

Functions of Muscles

  1. **Motion: **

    • Muscles are responsible for body movements.

  2. Posture:

    • Muscles help maintain upright posture and body alignment.

  3. Protection:

    • Muscles provide protective barriers to organs (e.g., rib cage protects the heart and lungs).

  4. Thermogenesis:

    • Muscle contractions produce heat, helping in thermoregulation.

  5. A Vascular Pump:

    • Muscles aid in circulation, particularly of venous blood, through contractions which assist blood flow in the veins.

Muscle Naming and Classification

  • Muscle Naming Basics:

    • Names can provide information about:

    1. Number of heads:

      • Example:

        • Biceps (two heads) vs. Triceps (three heads).

    2. Location:

      • Example: Biceps femoris (hamstrings region of thigh).

    3. Function:

      • Example:

        • Flexors (muscles that flex a joint) versus Extensors (muscles that extend a joint).

Important Muscle Properties

  1. Extensibility:

    • Ability to stretch without damage.

  2. Elasticity:

    • Ability to return to original shape after stretching.

  3. Excitability:

    • Ability to respond to stimuli (electrical signals).

  4. Conductivity:

    • Ability to propagate electrical signals along the muscle fibers.

Muscle Structure

  • Muscle Layers:

    • Epimysium:

    • Covers the entire muscle.

    • Perimysium:

    • Surrounds bundles of muscle fibers (fascicles).

    • Endomysium:

    • Surrounds individual muscle fibers (cells).

Muscle Fibers and Activation

  • Myofibrils:

    • Within muscle fibers, composed of repeating units called sarcomeres.

  • Sarcomeres:

    • Basic contractile units of muscle, consisting of thick (myosin) and thin (actin) filaments.

  • Neuromuscular Junction (NMJ):

    • Connection between motor neuron and muscle fiber, where electrical signals initiate contraction.

    • Acetylcholine (ACh) is the primary neurotransmitter involved in muscle contraction.

Types of Muscle Contractions

  1. Isometric Contraction:

    • Muscle contracts without changing length (e.g., holding a plank).

  2. Isotonic Contraction:

    • Muscle changes length while contracting.

    • Concentric:

      • Muscle shortens (e.g., lifting a weight).

    • Eccentric:

      • Muscle lengthens (e.g., lowering a weight).

Muscle Fibers Types

  • Slow Twitch Fibers:

    • Resistant to fatigue.

    • Rely on aerobic energy, suitable for endurance activities (e.g., jogging).

  • Fast Twitch Fibers:

    • Fatigue quickly but provide rapid bursts of speed and power.

    • Rely on anaerobic energy, suitable for sprinting activities.

Muscle Groups in the Upper Limb

Anatomical Classifications:

  • Intrinsic Muscles:

    • Originate and insert within the upper limb.

  • Extrinsic Muscles:

    • Originate outside the upper limb but insert within it.

  • Rotator Cuff:

    • A group of four muscles (SITS):

      • Supraspinatus:

      • Initiates shoulder abduction.

      • Infraspinatus:

      • Lateral rotation of the upper limb.

      • Teres Minor:

      • Assists in lateral rotation.

      • Subscapularis:

      • Medial rotation of the upper limb.

Muscle Actions

  • Agonist:

    • The muscle primarily responsible for a specific movement.

  • Antagonist:

    • Muscle that opposes the action of the agonist.

  • Synergists:

    • Assist the agonist during movement.

Muscles of the Forearm and Hand

  • Flexor Compartment Muscles:

    • Originate from the medial epicondyle, allowing wrist and finger flexion.

  • Extensor Compartment Muscles:

    • Originate from the lateral epicondyle, allowing wrist and finger extension.

  • Naming Convention:

    • Muscles are often identified based on:

    • Action (e.g., flexor, extensor).

    • Target structure (e.g., carpi, digitorum).

    • Orientation (e.g., longus, brevis).