Physiology of Muscle: Structure, Function, and Types

Topic 2.3 - Physiology of Muscle

Overview

This section covers the microscopic structure and physiology of muscle tissue, including skeletal, cardiac, and smooth muscle. Key concepts include muscle cell anatomy, mechanisms of contraction, neuromuscular junctions, contractile properties, muscle metabolism, and comparative features of muscle types.

General Features of Muscle Cells

Muscle Cell Terminology and Structure

• Muscle fibers: Elongated cells specialized for contraction.

• Terminology: Prefixes myo- and sarco- refer to muscle.

• Contraction depends on actin and myosin myofilaments.

Comparison of Muscle Types

The three main muscle types differ in location, structure, and function.

Feature	Cardiac Muscle	Skeletal Muscle	Smooth Muscle
Location	Only in heart	Attached to and covers bony skeleton	Walls of hollow, visceral organs
Striations	Striated	Striated	Nonstriated
Control	Involuntary; pacemaker sets rate	Voluntary	Involuntary
Contraction	Can contract rapidly; tires easily	Strong, adaptable; tires easily	Slow, sustained contractions

Muscle Functions and Characteristics

Functions of Muscle

• Generate movement: Locomotion, manipulation, blood pressure regulation, respiration, propulsion of food and urine.

• Maintain posture: Muscles work constantly against gravity.

• Joint stabilization: Stabilize joints during movement (e.g., shoulders, knees).

• Generation of heat: Maintains body temperature, especially by skeletal muscle (about 40% of body mass).

Functional Characteristics of Muscle

• Excitability (Irritability): Ability to receive and respond to a stimulus, usually a chemical (neurotransmitter, hormone). Response is an action potential along the sarcolemma, leading to contraction.

• Contractility: Ability to shorten forcibly when adequately stimulated.

• Extensibility: Ability to be stretched or extended.

• Elasticity: Ability to resume resting length after being stretched.