Anatomy & Physiology of the Muscular System - Chapters 15, 16 & 17

INTRODUCTION

  • The human body contains more than 600 skeletal muscles.

  • Skeletal muscles constitute 40% to 50% of total body weight.

  • They, alongside the skeleton, shape the form and contour of the body.

GENERAL FUNCTIONS

  • Movement: Facilitates overall body movement or isolated movement of body parts.

  • Heat Production: Generates heat as a byproduct of muscle activity.

  • Posture: Maintains body position and stability.

CHARACTERISTICS OF SKELETAL MUSCLE CELLS

  • Excitability (Irritability): The capability to respond to nerve impulses.

  • Contractility: The ability to shorten and produce movement.

  • Extensibility: Allows muscles to stretch and return to resting length.

  • Muscle Cell Overview:

  • Muscle cells are referred to as fibers due to their threadlike structure.

  • Sarcolemma: The plasma membrane surrounding muscle fibers.

  • Sarcoplasmic Reticulum (SR): Responsible for calcium ion storage and release.

  • T tubules: Network within muscle fibers that assist in muscle contraction.

SKELETAL MUSCLE STRUCTURE (Size, Shape, and Fiber Arrangement)

  • Muscles widely vary in size, ranging from small to large.

  • Different shapes include:

  • Broad, narrow, long, tapering, short, blunt, triangular, quadrilateral, irregular, flat sheets, bulky masses.

  • Fiber Arrangement:

  • Can be parallel, converging to a narrow attachment, oblique, pennate, bipennate, or curved.

  • Direction of fibers affects muscle function.

ATTACHMENT OF MUSCLES

  • Origin: The attachment point that does not move during contraction.

  • Insertion: The attachment point that moves during muscle contraction.

  • Example: Sternocleidomastoid muscle.

MUSCLE ACTIONS

  • Movements are typically produced by the coordinated action of several muscles contracting and relaxing.

  • Prime Mover (Agonist):

  • The primary muscle performing a specific movement; example includes Brachialis assisting the biceps.

  • Antagonist:

  • Muscles that oppose the action of the prime mover, they relax while the prime mover contracts; for contraction control and precision, example: Triceps.

  • Synergists: Muscles that contract at the same time and assist the prime movers for efficient movement; for example, Brachioradialis.

  • Fixator Muscles: Stabilize joints and balance movement during contractions (type of synergist).

NAMING OF MUSCLES

  • Muscle names may come from Latin or English origins.

  • Features influencing names include:

  • Location (e.g., -alis), Function (e.g., levator, depressor), Shape (e.g., deltoid for triangle).

  • Direction of Fibers: Terms indicate orientation (e.g., rectus for straight, orbicularis for circular).

  • Number of Heads: Indicated with prefixes (biceps, triceps)

  • Points of Attachment: Origin and insertion points impacting the name (e.g., sternocleidomastoid).

  • Relative Size: Size indicators such as maximus (largest), minimus (smallest), longus (long), brevis (short).