Skeletal Muscles Physiology

Skeletal Muscles Physiology

Functions

• Movement: contraction and relaxation of muscles to facilitate movement
• Support: maintenance of posture and stability
• Protection: protection of internal organs and bones
• Regulation: regulation of body temperature

Structure

• Muscle fiber: functional unit of skeletal muscle, composed of:
  • Myofibrils: contain contractile proteins (actin and myosin)
  • Sarcoplasm: cytoplasm of muscle fiber, contains mitochondria and myoglobin
  • Sarcolemma: plasma membrane of muscle fiber
• Motor unit: group of muscle fibers innervated by a single motor neuron

Muscle Contraction

• Sliding filament theory: actin and myosin filaments slide past each other to produce contraction
• Excitation-contraction coupling: process by which a muscle action potential leads to muscle contraction
  • Depolarization of sarcolemma
  • Release of calcium ions from sarcoplasmic reticulum
  • Binding of calcium to troponin and tropomyosin
  • Sliding of actin and myosin filaments

Muscle Types

• Slow-twitch (Type I): high endurance, low force, aerobic respiration
• Fast-twitch (Type II): high force, low endurance, anaerobic respiration
• Intermediate (Type IIa): combination of type I and II characteristics

Neural Control

• Motor neurons: transmit signals from central nervous system to muscle fibers
• Motor end plate: specialized region of muscle fiber that receives neurotransmitters from motor neuron
• Neuromuscular transmission: process by which motor neuron stimulates muscle contraction

Muscle Fatigue

• Metabolic fatigue: accumulation of lactic acid and decreased ATP availability
• Neural fatigue: decreased neural transmission and muscle activation

Skeletal Muscles Physiology

Functions

• Facilitate movement through contraction and relaxation
• Maintain posture and stability through support
• Protect internal organs and bones
• Regulate body temperature

Structure

Muscle Fiber

• Composed of myofibrils, sarcoplasm, and sarcolemma
• Myofibrils contain contractile proteins (actin and myosin)
• Sarcoplasm contains mitochondria and myoglobin
• Sarcolemma is the plasma membrane of the muscle fiber

Motor Unit

• A group of muscle fibers innervated by a single motor neuron

Muscle Contraction

Sliding Filament Theory

• Actin and myosin filaments slide past each other to produce contraction

Excitation-Contraction Coupling

• Depolarization of sarcolemma leads to muscle contraction
• Release of calcium ions from sarcoplasmic reticulum
• Binding of calcium to troponin and tropomyosin
• Sliding of actin and myosin filaments

Muscle Types

Slow-Twitch (Type I)

• High endurance, low force, aerobic respiration

Fast-Twitch (Type II)

• High force, low endurance, anaerobic respiration

Intermediate (Type IIa)

• Combination of type I and II characteristics

Neural Control

Motor Neurons

• Transmit signals from the central nervous system to muscle fibers

Motor End Plate

• Specialized region of the muscle fiber that receives neurotransmitters from the motor neuron

Neuromuscular Transmission

• Process by which the motor neuron stimulates muscle contraction

Muscle Fatigue

Metabolic Fatigue

• Accumulation of lactic acid and decreased ATP availability

Neural Fatigue

• Decreased neural transmission and muscle activation

Learn about the functions and structure of skeletal muscles, including movement, support, protection, and regulation. Understand the composition of muscle fibers and their role in physiology.