Muscular System Terminology, Tissue, and Mechanics

Module Four: Muscular System Terminology, Tissue, and Mechanics

Overview

  • This module covers essential terminology related to muscle tissues and mechanics of the muscular system.

Key Terminology

  • Myo or Miss: Refers to muscle, indicating a relationship with muscle cells.

  • Muscle Fibers: These are elongated muscle cells found in skeletal or smooth muscle types.

    • Cardiac Muscle Cells: Unlike skeletal muscle fibers, these cells are not elongated and are referred to as cardiac muscle cells.

Muscle Tissue Function

  • Muscle tissue uniquely converts chemical energy, specifically from adenosine triphosphate (ATP), into mechanical energy to exert force.

Types of Muscle Tissue

  1. Smooth Muscle

    • Structure: Relatively long fibers, not striated; uninucleate (single nucleus).

    • Location: Found in the walls of organs (e.g., bladder, intestines) and inside blood vessels.

    • Function: Contraction alters diameter of organs and facilitates peristalsis (wave-like motion for material movement).

    • Control: Involuntary control via the autonomic nervous system.

    • Innervation:

      • Single Unit Smooth Muscle: Generalized innervation affecting multiple cells.

      • Multiunit Smooth Muscle: Specific innervation to individual cells.

  2. Cardiac Muscle

    • Structure: Striated muscle cells, interwoven, not elongated like skeletal muscle.

    • Location: Exclusively found in the heart wall.

    • Function: Controls heart contractions through autorhythmicity – the ability to generate spontaneous action potentials.

    • Control: Involuntary, regulated by local electrical and chemical signals.

  3. Skeletal Muscle

    • Structure: Elongated, striated, and voluntary; attached to bones.

    • Function: Responsible for movement or resisting the movement of bones; consciously controlled.

    • Anatomy:

      • Levels of Muscle Organization:

      • Epimysium: Surrounds entire muscle.

      • Perimysium: Surrounds fascicles (bundles of fibers).

      • Endomysium: Surrounds individual fibers.

      • Sarcomeres: Contractile units of skeletal muscle comprising thick (myosin) and thin (actin) filaments.

      • Z-disc: Discs delineating sarcomeres.

    • Hypertrophy: Increase in size of muscle fibers through the addition of sarcomeres and muscle cells.

Muscle Functionality

  • Motor Unit: A single neuron and all muscle fibers it innervates.

    • Small motor units for fine control (e.g., in hands) vs. large motor units for force (e.g., in thighs).

  • Primary Functions of Muscle:

    • Movement production (primary function).

    • Stabilization of joints.

    • Maintenance of posture.

    • Heat generation (shivering reflex).

    • Protection of organs.

    • Regulation of substance passage (constriction/dilation).

Types of Muscle Attachments

  1. Direct Attachment:

    • Muscle fibers fuse at the epimysium with the periosteum of bone (e.g., intercostal muscles).

  2. Indirect Attachment:

    • Epimysium extends to form a tendon/aponeurosis that merges with periosteum (more common).

Muscle Mechanics
Types of Contractions

  1. Isometric Contraction:

    • Muscle generates tension with no movement; load equals force of contraction.

  2. Isotonic Contractions:

    • Concentric: Muscle shortens as it generates force; force exceeds load.

    • Eccentric: Muscle lengthens while generating tension; often against a force of gravity.

Factors Affecting Muscle Contraction Force

  • Number and Size of Muscle Fibers: More fibers means more force, larger fibers contribute to greater force due to additional sarcomeres.

  • Frequency of Nerve Stimulation: More frequent stimulation increases contraction count, boosting force until the limit is reached.

  • Degree of Muscle Stretch:

    • Optimal length maximizes contraction efficacy.

    • Too much stretch or shortening impairs force generation.

Muscle Attachments and Movements

  • Origin: Fixed attachment point of muscle.

  • Insertion: Movable point of attachment.

  • Action: Resulting effect on joints during muscle contraction.

    • E.g., Biceps brachii moves forearm closer to the arm.

  • Muscle Types:

    • Prime Mover (Agonist): Main muscle responsible for producing a movement.

    • Synergist: Assists the prime mover; supports actions.

    • Antagonist: Opposes a specific movement; typically relaxed when agonist acts.

Lever Systems in Muscle Mechanics

  • Components:

    • Lever: Rigid bar (bone) around a fulcrum (joint).

    • Effort: Force generated by muscle contraction.

    • Load: Resistance that effort must overcome (weight).

Types of Levers

  1. First Class Lever: Fulcrum between load and effort (e.g., seesaw).

  2. Second Class Lever: Load between fulcrum and effort (e.g., wheelbarrow).

  3. Third Class Lever: Effort between fulcrum and load (e.g., tweezers).

Naming of Muscles

  • Based on:

    • Location (e.g., intercostal, temporalis)

    • Shape (e.g., teres, trapezius)

    • Size (e.g., gluteus maximus/minimus)

    • Fiber Direction (e.g., rectus femoris)

    • Number of Origins (e.g., biceps, triceps)

    • Attachment Locations (e.g., sternocleidomastoid)

    • Muscle Actions (e.g., adductor longus)

Study Tips

  • Engage in lab participation for better learning outcomes.

  • Utilize resources like Primal Pictures (3D anatomical software) and YouTube (e.g., Anatomy Zone) for additional visual aids.

  • Recognize potential variation in anatomical terms across different resources; prioritize lecture notes for foundational knowledge.

Conclusion

  • Completion of Module Four, Part A discussions regarding the muscular system's terminology and mechanics. Engage with practical applications in upcoming modules for deeper understanding.