Muscle System and Muscle Tissue

Muscle System and Muscle Tissue

Overview

  • Chapters Covered: Chapters 10 & 11
  • Key Topics: Functions, connective tissue associations, microscopic anatomy, coordinated action, neuromuscular junction, muscle metabolism, different muscle types.

Objectives

  • Describe structure and function of muscle types.
  • Describe the functional roles of microscopic skeletal muscle components.
  • Explain how skeletal muscle is able to contract.
  • Explain how muscle cells are stimulated.
  • Define a motor unit.
  • Describe differences between twitch and muscle gradation.
  • Differentiate between types of muscle contraction.

Muscle Facts

  • Muscles make up approximately 50% of body weight.
  • Applications: Used in physical therapy and intramuscular injections.
  • Classified into three muscle types: skeletal, cardiac, and smooth.
  • Muscles convert energy from ATP to mechanical movement.

Functions of Muscles

  • Movement:
    • Move body parts and contents such as during breathing, circulation, and digestion.
    • Involved in communication through speech, writing, and nonverbal expression.
  • Stability:
    • Maintain posture and stabilize joints.
  • Control of Body Openings and Passages:
    • Control food intake, movement of materials, and elimination of waste.
    • Regulate admission of light to the eye.
  • Heat Production (Thermogenesis):
    • Skeletal muscles produce 20% to 30% of body heat at rest, up to 85% during exercise.
  • Glycemic Control:
    • Skeletal muscles absorb, store, and utilize a significant amount of glucose, influencing its blood concentration.

Characteristics of Muscles

  1. Excitability (Responsiveness): Responds to chemical signals, stretch, and electrical changes across the plasma membrane.
  2. Conductivity: Local electrical excitation initiates a wave of excitation traveling along the muscle fiber.
  3. Contractility: Ability to shorten when stimulated.
  4. Extensibility: Capability of being stretched between contractions.
  5. Elasticity: Returns to its original resting length after being stretched.

Muscle Trivia

  • Largest Muscle: (info not provided in transcript)
  • Smallest Muscle: (info not provided in transcript)
  • Longest Muscle: (info not provided in transcript)
  • Strongest Muscle by Weight: (info not provided in transcript)

Types of Muscle Tissue

Smooth Muscle

  • Characteristics: No striations, located in walls of hollow organs (e.g., blood vessels and visceral organs).
  • Functions: Push content through body cavities, peristalsis, regulating pressure and flow of blood and air.
  • Control: Involuntary.

Cardiac Muscle

  • Location: Found in heart walls.
  • Characteristics: Striated, involuntary.
  • Function: Contracts without nervous stimulus; regulated by the pacemaker (sinoatrial or SA node).
  • Control: Nervous system can affect heart rate.

Skeletal Muscle

  • Muscle Fiber Definition: Myofibril represents a skeletal muscle cell.
  • Attachment: Skeletal muscles attach to and surround the skeleton.
  • Characteristics: Long cells with striations; voluntary, but can also act involuntarily; contributes to body mobility; possesses a rich blood supply; includes approximately 600 skeletal muscles in the human body.

Skeletal Muscle Connective Tissues

  • Epimysium: Surrounds an entire muscle.
  • Perimysium: Bundles muscle fibers into fascicles; contains larger nerves and blood vessels and stretch receptors.
  • Endomysium: Surrounds each muscle fiber, providing space for innervation and nourishment.

Skeletal Muscle Connective Tissues Visuals

  • Visuals associated with perimysium and endomysium, showing muscle fiber and fascicle structures in cross section and longitudinal section.

Fascicle Orientation and Muscle Classification

  • Importance: Orientation of fascicles affects strength and direction of pull.
  • Types of Muscles by Orientation:
    • Fusiform Muscles: Thick in the middle with fascicles converging at both tapered ends.
    • Parallel Muscles: Uniform width and parallel fascicles.
    • Triangular (Convergent) Muscles: Broad at one end with fascicles converging at the other, narrower end.
    • Pennate Muscles: Feather-shaped; fascicles attach obliquely on a tendon that runs the length of the muscle. Types:
    1. Unipennate: Fascicles attach from one side.
    2. Bipennate: Fascicles attach from both sides.
    3. Multipennate: Bunches of feathers converge to a single point.
    • Circular Muscles (Sphincters): Fascicles form rings around body openings and passages.

Muscle Attachments

  • Definitions:
    • Origin & Insertion: Refers to stationary and moving ends of muscles; can be proximal vs. distal or superior vs. inferior.
    • Direct Attachment: Muscle fused to periosteum.
    • Indirect Attachment: Muscle fibers attach to tendons, which attach to periosteum and bone matrix.
    • Aponeurosis: A broad, flat tendon.
    • Retinaculum: A connective band through which tendons pass under.

Functional Groups of Muscles

  • Intrinsic vs. Extrinsic Muscles:
    • Intrinsic Muscle: Entirely contained within a region.
    • Extrinsic Muscle: Acts on a designated region but arises from another region; examples found in tongue, larynx, back, hand, foot.
  • Muscle Actions:
    • Prime Mover: Produces the most force in a movement; example: brachialis flexes elbow.
    • Synergist: Aids the prime mover; example: biceps brachii assists brachialis.
    • Antagonist: Opposes the prime mover; example: triceps brachii extends elbow.
    • Fixator: Prevents movement of a bone; example: rhomboid muscles stabilize scapula when biceps contract.

Types of Muscle Movements

  • Flexion and Extension
  • Abduction and Adduction
  • Medial and Lateral Rotation
  • Pronation and Supination
  • Elevation and Depression
  • Dorsiflexion and Plantar Flexion

Innervation and Blood Supply

  • Contraction Origins: Triggered by a stimulus.
  • Anatomy of Nerve-Muscle Relationships: Important for diagnosis.
  • Cranial Nerves: Nerves from the base of the brain to skull foramina that innervate muscles of head and neck (CN 1 – CN 12).
  • Spinal Nerves: Innervate muscles below the neck, passing through intervertebral foramina.
  • Blood Supply: Extensive branching of capillaries through the endomysium supplies every muscle fiber; higher energy demand increases blood supply.
  • Cardiac Output Changes: At rest, cardiac output to the muscle system is 25% (1.24 L/min), which increases to up to 75% (11.6 L/min) during heavy exercise.

Muscle Fiber Structure

  • Muscle Fiber Characteristics: Large cells with multiple nuclei (30 to 80 per millimeter for fiber repair).
  • Organelles:
    • Glycogen: Stored for energy.
    • Glycosomes: Contain glycogen and glycolytic enzymes, compartmentalizing glycolysis.
    • Myoglobin: A red pigment structurally similar to a hemoglobin subunit with a single heme group.

Specialized Structures in Muscle Fibers

  • Sarcolemma: The excitable plasma membrane of muscle fibers.
  • Transverse (T) Tubules: Tubular infoldings of the sarcolemma associated with terminal cisterns.
  • Sarcoplasmic Reticulum: Smooth endoplasmic reticulum network acting as a calcium reservoir.
  • Myofibrils: Long protein cords making up most of the muscle fiber; composed of myofilaments (thick, thin, elastic).
  • Functional Unit: Sarcomere represents the functional or contractile unit of skeletal muscle, situated between Z disks, where actin and myosin filaments interpose each other during contraction.