Lecture 10: Tissues-Organs-Systems – Muscles: Structure & Function (Myology)

Introduction

This study guide summarizes the key concepts from ANAT1005 Lecture 10, focusing on the anatomical and physiological basis of skeletal muscle tissue, its structure, function, and terminology. The content is organized to support foundational understanding for Anatomy & Physiology students.

Skeletal Muscle Structure

Levels of Organization

Skeletal muscle is a complex organ composed of multiple tissue types and organized into hierarchical levels:

• Muscle Belly: The main body of the muscle, surrounded by epimysium (connective tissue).

• Fascicles: Bundles of muscle fibers within the muscle belly, each surrounded by perimysium.

• Muscle Fibers (Cells): Individual muscle cells within fascicles, each encased by endomysium.

• Myofibrils: Contractile threads within muscle fibers, composed of repeating units called sarcomeres.

Each muscle-tendon unit is an organ, containing:

• Muscle tissue (contractile)

• Connective tissue (supportive)

• Nerves (control)

• Blood vessels (nutrition and waste removal)

Myology is the study of muscles.

Functions of the Muscular System

Overview

Muscles perform several essential functions in the human body:

• Convert chemical energy into mechanical work:

• Cause/control movement: Movement of bones, blood, food, etc.

• Monitor movement: Proprioception (awareness of body position)

• Support: Stabilization of bony and soft tissues

• Protection: Guarding of orifices

• Body temperature regulation: Through heat production

• Nutrient store: Storage of glycogen and other nutrients

Main Types of Tissues in Organs

Classification

• Connective tissue: Supports, tethers, fills spaces, and provides fluids

• Muscle tissue: Contractile, produces force and movement

• Nervous tissue: Conducts electrochemical signals

• Epithelial tissue: Linings and glandular functions

Each organ is made up of different combinations of these tissues.

Sliding Filament Theory (Basics)

Contractile Units

The sarcomere is the fundamental contractile unit of skeletal muscle. Muscle contraction occurs when actin and myosin filaments slide past each other, shortening the sarcomere and thus the muscle fiber.

• Calcium release triggers contraction by enabling actin-myosin interaction.

• ATP is required for both contraction and relaxation.

Muscle Belly Attachment Concepts

Types of Attachments

Muscle bellies attach to bones or other muscles via three main types:

• Tendon: Rope-like or cord-like connective tissue transmitting force from muscle to bone or another muscle.

• Aponeurosis: Sheet-like tendon, providing broad attachment.

• Muscular attachment: Direct attachment of muscle fibers to bone or another muscle.

Origin: The fixed or stable attachment (usually proximal on limbs, inferior on torso).

Insertion: The attachment to the part being moved (usually distal on limbs, superior on torso).

Tendon vs Ligament

• Tendon: Connects muscle to bone or muscle; transmits force.

• Ligament: Connects bone to bone; stabilizes joints and prevents unwanted movement.

Muscle Biomechanics (Basics)

Moment Arm

The moment arm is the perpendicular distance from the axis of rotation (joint) to the line of action of the force (tendon). It affects the output force and efficiency of muscle movement.

• Changes in joint angle and tendon position alter the moment arm and thus the force produced.

Levers in the Musculoskeletal System

Muscles and bones form lever systems to facilitate movement. There are three classes of levers:

• First class: Fulcrum between effort and load (e.g., neck extension)

• Second class: Load between fulcrum and effort (e.g., standing on tiptoe)

• Third class: Effort between fulcrum and load (e.g., biceps flexing the forearm)

Muscle Contraction Types & Roles

Types of Contraction

• Isotonic: Muscle changes length to produce movement

  • Concentric: Muscle shortens

  • Eccentric: Muscle lengthens

• Isometric: Muscle length remains the same; no movement occurs

Roles of Muscles

• Agonist (Prime mover): Main muscle causing movement

• Antagonist: Opposes the action of the agonist

• Synergist: Assists the agonist

• Fixator: Stabilizes the origin of the agonist

Muscle Belly & Fibre Arrangements (Architecture)

Types of Muscle Fibre Arrangement

• Parallel: Fibers run parallel to the long axis of the muscle; allows greater range of motion

• Convergent: Fibers converge from a broad origin to a single insertion point

• Pennated: Fibers attach obliquely to a central tendon (feather-like); increases force production

  • Unipennate, bipennate, multipennate: Variations based on arrangement

• Circular: Fibers arranged in concentric rings; found around openings (e.g., orbicularis oris)

Physiological Cross-Sectional Area (PCSA): Indicates the total area of muscle fibers; larger PCSA means greater force-generating capacity.

Understanding Muscle Names

Etymology and Naming Conventions

Muscle names often reflect their characteristics, including:

• Action: Flexor, extensor, adductor, abductor, supinator, pronator

• Location: Body region (e.g., brachialis – arm, pectoralis – chest)

• Attachments: Named for bones or regions attached (e.g., sternocleidomastoid)

• Direction: Orientation of fibers (e.g., rectus – straight, obliquus – diagonal, transversus – transverse)

• Shape: Quadratus (square), rhomboid (diamond), trapezius (trapezoid)

• Size & Length: Maximus/major (large), medius (medium), minimus/minor (small), longus (long), brevis (short)

• Number of Heads: Biceps (2), triceps (3), quadriceps (4)

Understanding these roots aids in identifying muscle function and location.

Table: Comparison of Muscle Attachment Types

Table: Muscle Fibre Arrangements

Additional info:

• Some content inferred from standard anatomy textbooks to clarify fragmented points.

• Tables reconstructed to summarize key comparisons and classifications.