Knes 259: Muscle Physiology

Page 1: Lecture Overview

• Course Title: KNES 259: Muscle Physiology

Page 2: Class Outline

1. Functions
2. Properties
3. Types
4. Skeletal Muscle Fibre Types
   • Structure Diagrams:
   • I band
   • A band (myosin)
   • H zone
   • M line
   • Z disc
   • Sarcomere Structure

Page 3: Functions of Muscle Tissue

• Overview of muscle functions.

Page 4: Functions of Muscular Tissue

• Producing Body Movements:
  • Skeletal muscles pull from their origin to attachment points across joints via tendons, creating movement.
  • Speed and force of movement depend on the number of muscle fibers recruited.

Page 5: Functions of Muscular Tissue

• Stabilizing Body Positions:
  • Muscles are activated to maintain posture.
  • Examples include:
  • Standing for prolonged periods
  • Keeping the head up while attending lectures
  • Muscles contract over sustained periods of time to fulfill this function.

Page 6: Functions of Muscular Tissue

• Storing and Mobilizing Substances:
  • Proteins in muscle tissue can be broken down into amino acids when dietary needs are unmet.
  • Liver converts amino acids into glucose to provide energy for other organs.

Page 7: Functions of Muscular Tissue

• Generating Heat:
  • Muscle contractions require energy, which releases heat as a byproduct.
  • Heat generated helps maintain body temperature (~37℃).

Page 8: Functions of Muscular Tissue

• Supporting Soft Tissues:
  • The abdominal wall and pelvic cavity floor consist of skeletal muscle layers.
  • These muscles support the weight of visceral organs and protect them from injury.

Page 9: Functions of Muscular Tissue

• Guarding Entrances and Exits:
  • Skeletal muscles encircle openings of the digestive and urinary tracts (sphincters).
  • Sphincters provide voluntary control over swallowing, defecation, and urination.

Page 10: Properties of Muscle Tissue

Page 11: Properties of Muscular Tissue

• Electrical Excitability:

  • Ability to respond to stimuli by producing electrical signals (e.g., action potentials).
  • Stimuli are typically electrical or chemical (hormones).
  • Skeletal muscles respond to electrical stimulation from the nervous system; cardiac and smooth muscles respond to both neural and hormonal inputs.

• Contractility:

  • Muscle cells can shorten (contract) when stimulated.
  • Shortening occurs as thick (myosin) pulls thin (actin) filaments toward the center of the sarcomere, exerting force on tendons.

Page 12: Properties of Muscular Tissue

• Extensibility:
  • Ability to stretch to normal resting length after contraction.
  • Example: Elbow extensor muscles must be stretched to allow elbow flexion.
  • Lack of extensibility is called spasticity.

Page 13: Properties of Muscular Tissue

• Elasticity:
  • Ability to recoil to original length after being stretched.
  • Muscle rebounds to its original length following contraction.

Page 14: Types of Muscle Tissue

Page 15: Three Types of Muscular Tissue

• Cardiac Muscle:
  • Cells are short, branching, with a single nucleus and light striations.
  • Intercalated discs join cardiac muscle cells.
  • Gap junctions allow ions to move easily between cells, facilitating action potential spread.
  • Enables rhythmic contractions of the heart; under involuntary control.

Page 16: Cardiac Muscle

• Cardiac muscle consists of sarcomeres arranged similarly to skeletal muscle but have intercalated discs and typically are uni-nucleated.
• Cardiac cell shape allows greater sarcomere lengthening and shortening during the cardiac cycle.

Page 17: Cardiac Muscle

• Intercalated Discs:
  • Contain desmosomes for strong cellular attachment, preventing separation during heartbeats.
  • Gap junctions permit action potentials spread across muscle fibers.

Page 18: Cardiac Muscle

• Cardiac muscle action potentials:
  • Slower, last longer, and have a greater refractory period than skeletal muscle.
  • Adaptations help prevent tetanus, reduce fatigue, and ensure adequate filling time for heart chambers.

Page 19: Cardiac Muscle

• Cardiac muscle cells rely on aerobic respiration, containing more mitochondria than skeletal muscle.
• Supports approximately 70,000 - 100,000 heartbeats daily to pump blood and deliver nutrients.

Page 20: Three Types of Muscular Tissue

• Smooth Muscle:
  • Cells are long, cylindrical, single-nucleated, without striations.
  • Common in the walls of hollow visceral organs (e.g., intestines, stomach, blood vessels).
  • Function is involuntary control.

Page 21: Smooth Muscle

• Unique appearance compared to cardiac and skeletal muscle.
• Thick in the middle and tapered at the ends, not striated.
• Arranged as single-unit or multi-unit fibers.

Page 22: Smooth Muscle

• Layers of smooth muscle line various body organs and tubes.
• Contractile function is not under voluntary control.

Page 23: Smooth Muscle

• Contractions start slower and last longer than those in skeletal and cardiac muscle.
• Capable of significant shortening and stretching.
• Fibers shorten in response to the stretching of the organ/vessel.

Page 24: Three Types of Muscular Tissue

• Skeletal Muscle:
  • Long, multi-nucleated, cylindrical, heavily striated (striped).
  • When referring to a muscle cell, the term "muscle fiber" is typically used.
  • Visible striations arise from the arrangement of contractile elements.
  • Under voluntary control, crucial for moving and positioning the body.

Page 25: Comparison of the Three Muscle Types

Page 26: Tension in Muscle Types

• Graphical Representation: Tension over time for Skeletal, Cardiac, and Smooth Muscle not detailed.

Page 27: Skeletal Muscle Fibre Types

Page 28: Skeletal Muscle Fibre Types

• Slow Twitch (Type I):
  • Darker (red) appearance due to higher myoglobin concentrations.
  • Primarily generate ATP through aerobic respiration.
  • High levels of mitochondria and capillaries.
  • Slow twitch contraction velocity; fatigue resistant, sustain contractions for hours.

Page 29: Skeletal Muscle Fibre Types

• Fast Twitch (Type IIb/x - Glycolytic):
  • Lighter (white/pale) appearance due to lower myoglobin concentrations.
  • Generate ATP primarily through anaerobic glycolysis (fermentation).
  • Low levels of mitochondria and capillaries.
  • Faster twitch contraction velocity; fatigue rapidly but provide power for short, explosive movements.

Page 30: Skeletal Muscle Fibre Types

• Fast Twitch (Type IIa - Oxidative-Glycolytic):
  • Red-pink appearance due to moderate myoglobin concentrations.
  • Generate ATP through both aerobic respiration and anaerobic glycolysis.
  • High levels of mitochondria and capillaries.
  • Moderate velocity and power twitch contractions; fairly fatigue resistant, suitable for sustained speed events (e.g., 400-800 m running).

Page 31: Comprehensive Comparison of Muscle Fiber Types

Page 32: Relationship of Muscle Fiber Composition

• Majority of skeletal muscles consist of a mixture of muscle fiber types; composition is genetically predetermined.
• Each motor unit innervates only one muscle fiber type.
• Overall muscle force depends on the recruitment pattern and fiber type proportions present in the muscle, which varies across the body.