Muscle Tissue Overview

Overview of Muscle Tissue

• Multiple muscle types exist with differing functions and structures.
• Skeletal Muscle: Voluntary, striated, multinucleate, moves bones and facial features.
• Cardiac Muscle: Involuntary, striated, uninucleate, pumps blood in the heart.
• Smooth Muscle: Involuntary, non-striated, uninucleate, found in hollow organs.

Key Terms

• Muscle Fiber: Individual muscle cell.
• Microfilaments: Actin and myosin proteins forming myofibrils.
• Endomysium: Connective tissue surrounding each muscle fiber.
• Perimysium: Connective tissue surrounding fascicles (muscle fiber bundles).
• Epimysium: Connective tissue encasing the entire muscle.
• Fascia: Connective tissue around muscles and groups of muscles.
• Aponeuroses: Flat tendons attaching muscles to bones.

Functions of Muscles

• Movement: Enables skeletal motion and expressions.
• Posture Maintenance: Stabilizes the body for upright posture.
• Joint Stabilization: Preserves joint integrity.
• Heat Generation: Produces body heat via contraction.

Microscopic Anatomy of Skeletal Muscle

• Sarcolemma: Muscle cell membrane.
• Myofibril: Long structures in muscle fibers, comprised of sarcomeres (contractile units).
• Sarcoplasmic Reticulum: Stores calcium ions for contraction.

Skeletal Muscle Activity

• Irritability: Muscle cell's ability to respond to stimulation.
• Contractility: Ability to shorten and generate force.
• Motor Unit: Motor neuron and all fibers it controls. Affects muscle control and force production.
• Synaptic Cleft: Gap between nerve and muscle fiber. Neurotransmitters pass signals across.
• Neurotransmitters (e.g., Acetylcholine): Chemical messengers initiating muscle contraction.
• Transmission Process: 1. Nerve signals travel, 2. Acetylcholine released, 3. Binding to muscle receptors, 4. Calcium release, 5. Muscle contraction initiated.
• Sliding Filament Theory: Thin actin filaments slide past thick myosin filaments, causing muscle shortening. Myosin heads attach to and pull actin.

Contraction of Skeletal Muscle as a Whole

• "All or None" Concept: Entire muscle fiber contracts fully or not at all, responding to nerve impulses.
• Graded Responses: Varying degrees of muscle contraction based on frequency of stimulation.
• Twitch: Brief, single contraction and relaxation.
• Summation: Accumulation of contractions from repeated stimuli.
• Tetanus (Incomplete/Complete): Sustained contraction with/without muscle relaxation between stimuli.
• Energy Pathways: Direct phosphorylation, aerobic respiration, and anaerobic glycolysis provide energy for muscle contraction.
• Oxygen Debt: Extra oxygen consumed to recover from intense exercise due to replenishing energy resources and clearing lactic acid.
• Isotonic Contraction: Muscle length changes during contraction (e.g., lifting).
• Isometric Contraction: Muscle tension increases, but length remains unchanged (e.g., holding a heavy object).
• Muscle Tone: Constant, slight tension in muscles, maintaining posture, preparedness for action.

Muscle Movements

• Origin and Insertion: Origin is stationary; insertion is the moving attachment.
• Muscles and Bone Movement: Muscle contraction pulls tendons, moving bones at joints.
• Five Golden Rules of Skeletal Muscle Activity: Muscles cross at least one joint, bulk is proximal, have at least two attachments, pull not push; insertion moves toward origin.
• Effects of Exercise: Increased strength, endurance, hypertrophy (growth), efficiency.
• Common Body Movements (e.g., Flexion, Extension, Abduction, Adduction, Circumduction): Types of movements produced by muscles.
• Special Body Movements (e.g., Dorsiflexion, Plantar Flexion, Inversion, Eversion, Supination, Pronation, Opposition): Detailed specialized movements.
• Muscle Types: Prime mover, antagonist, synergist, fixator.

Naming of Skeletal Muscles

• Naming criteria: Direction of fibers, size, location, number of origins, location of attachments, shape, and action.

Skeletal Muscles Identification

• Head and Neck Muscles: Examples: Frontalis, Masseter, Sternocleidomastoid.
• Trunk and Arms Muscles: Examples: Deltoid, Biceps Brachii, Pectoralis Major.
• Pelvis and Thigh Muscles: Examples: Gluteus Maximus, Quadriceps, Hamstrings.
• Lower Leg Muscles: Examples: Gastrocnemius, Tibialis Anterior.