Physiology of Muscle: Structure, Function, and Types

Topic 2.3 – Physiology of Muscle

Overview

This section covers the microscopic structure and function of muscle tissue, the mechanisms of muscle contraction, the neuromuscular junction, contractile properties, muscle metabolism, and a comparison of muscle types.

General Features of Muscle Cells

Muscle Cell Terminology and Structure

• Muscle fibers are elongated cells specialized for contraction.

• Common prefixes: myo- and sarco- refer to muscle.

• Muscle contraction depends on the interaction of actin and myosin myofilaments.

Comparison of Muscle Types

The three main types of muscle tissue are skeletal, cardiac, and smooth muscle. They differ in structure, control, 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; neural input can increase rate)	Voluntary	Involuntary
Contraction	Strong, rhythmic	Rapid, tires easily, adaptable	Slow, sustained

Functions and Characteristics of Muscle

Functions of Muscle

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

• Maintain posture: Constantly working against gravity to keep the body upright.

• Joint stabilization: Stabilizes joints, e.g., shoulders and knees during movement.

• Generation of heat: Maintains body temperature, especially via skeletal muscle (which makes up at least 40% of body mass).

Functional Characteristics of Muscle

• Excitability (Irritability): Ability to receive and respond to a stimulus, usually a chemical (neurotransmitter, hormone, pH change). The 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.