Biol+Sci+201+Ch+10

Skeletal Muscle Tissue

  • Information sourced from ehow.com

Chapter Overview

Objectives

  • Understand various functions of muscle

  • Identify macroscopic and microscopic arrangement of skeletal muscle

  • Learn how muscles attach to bones, including origins and insertions

  • Recognize types of skeletal muscle fibers

  • Understand muscular dystrophy

Functions and Characteristics of Skeletal Muscle

  • Produces Movement: Facilitates voluntary motion of the body.

  • Maintains Posture: Helps ensure stability and correct posture.

  • Joint Stability: Supports and stabilizes joints during various activities.

  • Generates Heat: Muscle contractions produce heat, important for temperature regulation.

  • Properties of Muscle Tissue:

    • Contractility: Ability to shorten and generate force.

    • Excitability: Capacity to receive and respond to stimuli.

    • Extensibility: Ability to be stretched without damage.

    • Elasticity: Ability to return to original shape after being stretched.

Types of Muscle Tissue

  • Skeletal Muscle:

    • Primarily involved in body movement under voluntary control.

  • Smooth Muscle:

    • Found in the walls of hollow visceral organs, operates involuntarily.

  • Cardiac Muscle:

    • Exclusive to the heart, functions involuntarily.

Structure of Skeletal Muscle

  • Macro to Micro:

    • Epimysium: Dense irregular connective tissue surrounding the entire muscle.

    • Fascicles: Bundles of muscle fibers wrapped by Perimysium.

    • Muscle Fibers (cells): Surrounded by Endomysium.

    • Myofibrils: Contractile elements within muscle fibers.

Microanatomy of Myofibril

  • Dark Band: Contains the A band (thick filaments).

  • Light Band: Recognized as the I band (thin filaments).

  • H Zone: Area of the A band where there is no overlapping of thin filaments.

  • Z Disc: Defines the boundaries of a sarcomere.

  • Titin: The largest protein in the body, stabilizing thick filaments and providing muscle elasticity.

The Sarcomere

  • Functional Unit of skeletal muscle.

  • Microfilaments:

    • Actin: Thin filaments arranged along with myosin components.

    • Troponin and Tropomyosin: Regulatory proteins associated with actin.

    • Myosin: Thick filaments with heads that contain two binding sites for actin and ATPase.

Innervation of Skeletal Muscle

  • Motor Neuron and Neuromuscular Junction:

    • Acetylcholine release stimulates an electrical impulse in the muscle cell membrane.

    • T Tubule: Conducts the electrical impulse into the cell's interior.

    • Sarcoplasmic Reticulum: Releases Ca2+ upon activation.

  • Myofibrils respond to the calcium release, triggering contraction.

Muscle Contractions

  • Concentric: Muscle shortens to cause movement.

  • Eccentric: Muscle lengthens while under tension.

Muscle Attachments

  • Types of Attachments:

    • Indirect: Muscles connect to bones via tendons merging with periosteum; includes aponeurosis (flat tendon).

    • Direct: Muscle connects to bone with minimal space, small gaps filled with collagen fibers; may attach to fascia or skin.

Origins and Insertions

  • Origin: Bony attachment that remains stationary during muscle contraction.

  • Insertion: Bony attachment that is more mobile.

  • Belly: Thick section of muscle between origin and insertion.

Types of Muscle Fibers

  • Slow-Oxidative Fibers (SO):

    • Thin red fibers with high myoglobin, suitable for endurance and aerobic activity.

  • Fast-Glycolytic Fibers (FG):

    • Thick white fibers with low myoglobin, designed for strength and short-duration contractions.

  • Fast-Oxidative Fibers (FO):

    • Intermediate fibers rich in myoglobin, having characteristics of both SO and FG fibers.

Disorders of Skeletal Muscle

  • Muscular Dystrophy:

    • An inherited disorder characterized by dysfunction in the protein dystrophin, leading to replacement of muscular tissue with fat and connective tissue.