Chapter 10: The Muscular System – Skeletal Muscle Tissue and Muscle Organization

The Muscular System

Introduction to the Muscular System

The muscular system is essential for numerous physiological processes and dynamic interactions with the environment. Skeletal muscles are composed of elongated cells called muscle fibers, which contract along their longitudinal axis to produce movement.

• Muscle fibers: Specialized cells capable of contraction.

• Function: Enable movement, posture, and interaction with surroundings.

Types of Muscle Tissue

There are three primary types of muscle tissue, each with distinct functions and characteristics:

• Skeletal muscle: Pulls on bones to produce voluntary movements.

• Cardiac muscle: Pushes blood through arteries and veins via rhythmic, involuntary contractions.

• Smooth muscle: Moves fluids and solids along internal passageways (e.g., digestive tract) through involuntary contractions.

Properties of Muscle Tissue

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

• Excitability: Ability to respond to stimuli.

• Contractility: Ability to shorten and exert a pull or tension.

• Extensibility: Ability to contract over a range of resting lengths.

• Elasticity: Ability to rebound toward original length after contraction.

Functions of Skeletal Muscles

Major Functions

Skeletal muscles perform several vital functions in the human body:

• Produce skeletal movement: Pull on tendons to move bones.

• Maintain posture and body position: Stabilize joints to aid in posture.

• Support soft tissue: Support the weight of visceral organs.

• Regulate entering and exiting of material: Voluntary control over swallowing, defecation, and urination; encircle orifices of digestive and urinary tracts.

• Maintain body temperature: Some energy used for contraction is converted to heat, helping regulate temperature.

Anatomy of Skeletal Muscles

Gross Anatomy

Gross anatomy focuses on the overall organization of muscles and their associated structures:

• Organization: Arrangement of muscle fibers and connective tissue.

• Connective tissue: Provides support and structure.

• Nerves: Innervate muscles to control contraction.

• Blood vessels: Supply nutrients and oxygen to muscle tissue.

Connective Tissue Layers

Three layers of connective tissue surround and organize skeletal muscles:

• Epimysium: Dense tissue that surrounds the entire muscle.

• Perimysium: Dense tissue that divides the muscle into parallel compartments called fascicles.

• Endomysium: Dense tissue that surrounds individual muscle fibers; contains myosatellite cells that repair damaged muscle tissue.

Table: Connective Tissue Layers of Skeletal Muscle

Layer	Location	Function
Epimysium	Surrounds entire muscle	Protects and supports muscle; connects to tendons
Perimysium	Surrounds fascicles (bundles of fibers)	Provides pathways for nerves and blood vessels
Endomysium	Surrounds individual muscle fibers	Supports and repairs muscle fibers (via myosatellite cells)

Example: Muscle Fiber Organization

In the biceps brachii, the epimysium surrounds the entire muscle, perimysium divides it into fascicles, and endomysium wraps each muscle fiber, ensuring coordinated contraction and repair.

Additional info: The connective tissue layers also merge at the ends of muscles to form tendons, which attach muscles to bones, facilitating movement.