Skeletal Muscle Tissue: Structure, Function, and Properties

Chapter 10: Skeletal Muscle Tissue

Introduction

Skeletal muscle tissue is a primary component of the human body, essential for movement, posture, and heat generation. This chapter explores the unique properties, terminology, and functions of muscle tissue, with a focus on skeletal muscle.

Objectives

• Identify the four functional properties that distinguish muscle tissue from other tissues.

• Compare and contrast skeletal, cardiac, and smooth muscle tissue.

• Describe the layers of connective tissue in and around skeletal muscle.

• Define muscle fascicles.

• Explain muscle attachment at origins and insertions.

• Describe the microscopic structure of skeletal muscle fibers and the arrangement of thick and thin filaments into sarcomeres and myofibrils.

• Describe the structure and functions of the sarcoplasmic reticulum and T tubules.

• Explain the sliding filament mechanism of muscle contraction.

• Describe the innervation of skeletal muscle fibers at neuromuscular junctions.

• Compare and contrast the three kinds of skeletal muscle fibers.

• Explain symptoms of muscular dystrophy.

• Describe embryonic development and regeneration capacity of skeletal muscle.

• Explain changes in skeletal muscle with aging.

Muscle Tissue Overview

Definition and Distribution

• The term muscle comes from the Latin word for "little mouse."

• Muscle is the primary tissue in the heart (cardiac muscle tissue), walls of hollow organs (smooth muscle tissue), and skeletal muscle.

• Skeletal muscle makes up nearly half the body's mass.

Functional Properties of Muscle Tissue

Contractility

• Contractility is the ability of muscle tissue to shorten forcefully.

• This property is due to contractile filaments composed of actin (thin filaments) and myosin (thick filaments).

Excitability

• Excitability refers to the ability of muscle cells to respond to stimuli by generating electrical impulses that travel along the plasma membrane.

Extensibility

• Extensibility is the ability of muscle tissue to be stretched by the contraction of opposing muscles or by substances within hollow organs (e.g., food in the stomach, urine in the bladder).

Elasticity

• Elasticity is the ability of muscle tissue to recoil to its original length after being stretched.

Terminology Specific to Muscle Tissue

• myo- and mys-: Prefixes meaning "muscle" (e.g., myofibril, endomysium).

• sacro-: Prefix meaning "flesh" (e.g., sarcolemma, sarcoplasm).

• Sarcolemma: The plasma membrane of muscle cells.

• Sarcoplasm: The cytoplasm of muscle cells.

Functions of Muscle Tissue

Produce Movement

• Skeletal muscle is attached to the skeleton and moves the body by moving bones.

• Smooth muscle squeezes fluids and other substances through hollow organs.

Open and Close Body Passageways

• Sphincter muscles function as valves to regulate the passage of substances through body openings.

• They contract to close passageways and relax to allow passage.

Maintain Posture and Stabilize Joints

• Muscle tone enables the body to remain sitting or standing and helps stabilize many synovial joints.

• Example: Weakness in muscles stabilizing the knee can lead to dislocation due to shallow patellar surfaces.

Heat Generation

• Muscle contractions produce heat, which helps maintain normal body temperature.

• Example: Shivering is a result of involuntary muscle contractions to generate heat.

Additional info: Muscle tone is the continuous and passive partial contraction of the muscles, which helps maintain posture and joint stability even when the muscle is not actively moving.