Unit 4: Lesson 1 – Muscle Tissue & Physiology

Learning Objectives

• Define terminology pertinent to the anatomy and physiology of muscle tissue.

• Identify the structural (anatomic) components of muscle tissue and their significance.

• Describe the function (physiology) of muscle tissue components.

• List and explain the steps in significant functional processes of muscle tissue.

• Understand the anatomy and physiology of muscle tissue through examples.

Introduction to Muscle Tissue

Types of Muscle Tissue

Muscle tissue consists of cells specialized for contraction, enabling movement and force generation in the body. There are three main types of muscle tissue:

• Skeletal Muscle: Forms the muscular system; responsible for voluntary movement of bones at joints and maintaining posture.

• Cardiac Muscle: Found only in the heart; responsible for involuntary contraction needed for pumping blood.

• Smooth Muscle: Located in hollow viscera walls and blood vessels; responsible for involuntary contraction needed for movement of substances, peristalsis, and vasoconstriction.

Functions of Skeletal Muscle

Major Functions

Skeletal muscle performs several essential functions in the human body:

• Movement: Facilitates locomotion and manipulation of the environment.

• Support: Maintains posture and stabilizes joints.

• Protection: Shields internal organs from injury.

• Heat Generation: Produces heat as a byproduct of contraction, aiding in temperature regulation.

• Nutrient Storage: Stores glycogen and other nutrients for energy.

• Blood Circulation: Assists in venous return through muscle contractions.

Structure of Skeletal Muscle

Connective Tissue Layers

Skeletal muscle is organized and protected by dense connective tissue, which forms three distinct layers:

• Epimysium: Outermost layer, surrounds the entire muscle.

• Perimysium: Surrounds bundles of muscle fibers called fascicles.

• Endomysium: Surrounds individual muscle fibers (cells).

Muscle Fiber Characteristics

• Each muscle cell is known as a muscle fiber or myocyte.

• Muscle fibers are long, cylindrical, and multinucleated.

Bundles Within Skeletal Muscle

Hierarchical Organization

Skeletal muscle is organized into bundles for efficient force generation:

• Muscle: Composed of bundles of fascicles.

• Fascicle: Composed of bundles of muscle fibers.

• Muscle Fiber: Contains bundles of myofibrils.

• Myofibril: Made up of bundles of myofilaments (actin and myosin).

Key Terms and Definitions

• Myofibril: Contractile organelle within muscle fibers, composed of repeating units called sarcomeres.

• Myofilament: Protein filaments (actin and myosin) that slide past each other to produce contraction.

• Sarcomere: The functional unit of muscle contraction, defined as the segment between two Z-lines.

• Epimysium, Perimysium, Endomysium: Connective tissue layers that organize and protect muscle tissue.

Example: Skeletal Muscle Structure

Consider the biceps brachii muscle: the epimysium surrounds the entire muscle, perimysium groups muscle fibers into fascicles, and endomysium encases each individual muscle fiber. Within each fiber, myofibrils are arranged in parallel, each containing sarcomeres responsible for contraction.

Additional info:

• Muscle contraction is initiated by the sliding filament theory, where actin and myosin filaments slide past each other, shortening the sarcomere and generating force.

• ATP is required for muscle contraction and relaxation.