Muscles and Muscle Tissue: Structure, Function, and Types

Muscle Tissue Overview

Introduction to Muscle Tissue

Muscle tissue comprises nearly half of the body's mass and is essential for movement and force generation. Muscles transform chemical energy (ATP) into directed mechanical energy, enabling locomotion and manipulation of the environment.

• Types of muscle tissue: Skeletal, Cardiac, Smooth

• Characteristics of muscle tissue: Excitability, Contractility, Extensibility, Elasticity

• Muscle functions: Movement, posture, stabilization, heat generation

Types of Muscle Tissue

Terminology

Prefixes such as myo, mys, and sarco are commonly used in muscle-related terms. For example, sarcoplasm refers to the cytoplasm of a muscle cell.

Skeletal Muscle

Skeletal muscle tissue is organized into skeletal muscles, which are organs attached to bones and skin. These muscles are responsible for voluntary movements.

• Skeletal muscle fibers are the longest muscle cells and are striated (have stripes).

• Also called voluntary muscle because it can be consciously controlled.

• Contracts rapidly, tires easily, and is powerful.

• Key words: skeletal, striated, voluntary

Cardiac Muscle

Cardiac muscle tissue is found only in the heart and makes up the bulk of the heart walls. It is responsible for pumping blood throughout the body.

• Cardiac muscle is striated but involuntary (cannot be consciously controlled).

• Contracts at a steady rate due to the heart's own pacemaker, but the nervous system can increase the rate.

• Key words: cardiac, striated, involuntary

Smooth Muscle

Smooth muscle tissue is found in the walls of hollow organs such as the stomach, urinary bladder, and airways. It is essential for various involuntary movements within the body.

• Not striated

• Involuntary: cannot be consciously controlled

• Key words: visceral, nonstriated, involuntary

• Examples: Movement of food through the digestive tract, regulation of blood vessel diameter

Characteristics of Muscle Tissue

Four Main Characteristics

All muscle tissues share four fundamental properties that enable their function:

• Excitability (Responsiveness): Ability to receive and respond to stimuli

• Contractility: Ability to shorten forcibly when stimulated

• Extensibility: Ability to be stretched

• Elasticity: Ability to recoil to resting length after being stretched

Functions of Muscle Tissue

Major Functions

Muscle tissue performs several vital functions in the human body:

• Produce movement: Responsible for all locomotion and manipulation (e.g., walking, digesting, pumping blood)

• Maintain posture and body position

• Stabilize joints

• Generate heat as they contract, contributing to body temperature regulation

Summary Table: Comparison of Muscle Tissue Types

Feature	Skeletal Muscle	Cardiac Muscle	Smooth Muscle
Location	Attached to bones and skin	Heart walls	Walls of hollow organs
Striations	Present	Present	Absent
Control	Voluntary	Involuntary	Involuntary
Key Functions	Movement, posture	Pumping blood	Movement of substances (e.g., food, urine)

Key Terms and Definitions

• ATP (Adenosine Triphosphate): The primary energy carrier in cells, used for muscle contraction.

• Striations: Alternating light and dark bands seen in skeletal and cardiac muscle under a microscope.

• Voluntary muscle: Muscle that can be consciously controlled (skeletal muscle).

• Involuntary muscle: Muscle that cannot be consciously controlled (cardiac and smooth muscle).

• Sarcoplasm: The cytoplasm of a muscle cell.

*Additional info: The notes are based on lecture slides for a college-level Anatomy & Physiology course, focusing on the structure, function, and classification of muscle tissue. Expanded definitions and examples have been added for clarity and completeness.*