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Course Code: HHP:2100
Course Title: Human Anatomy
Topic: Muscle Tissue and Organization
Subtopic: Gross Anatomy of Skeletal Muscle

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Lecture Overview:

  1. Overview of Muscle Tissue
  2. Gross Anatomy of Skeletal Muscle
    • Structural Hierarchy
    • Connective Tissues
    • Muscle Attachments
  3. Skeletal Muscle Fiber Orientation

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1. Overview of Muscle Tissue

  • There are over 700 skeletal muscles in the human body that together form the muscular system.
  • More generally, there are three types of muscle tissue:
    1. Skeletal muscle
    2. Cardiac muscle
    3. Smooth muscle

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1. Overview of Muscle Tissue Properties

  • All muscle tissues exhibit five key properties:
    1. Excitability
    2. Conductivity
    3. Contractility
    4. Extensibility
    5. Elasticity

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1. Overview of Muscle Tissue Properties

  • Detailed explanations of muscle tissue properties:
    • Excitability: The ability to respond to stimuli.
    • Conductivity: The ability to transmit electrical events along the cell membrane.
    • Contractility: The capability to generate tension and shorten cell length.
      • Note: The sliding of contractile proteins in muscle cells leads to body movements and other muscle functions.
    • Elasticity: The ability to return to resting length after shortening or lengthening.
    • Extensibility: The capability to be stretched beyond resting length.

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1. Overview of Muscle Tissue

Skeletal Muscle Characteristics
  • Each skeletal muscle is considered an organ.
  • Each muscle (e.g., biceps brachii) contains all four tissue types:
    • Epithelial tissue
    • Connective tissue
    • Muscle tissue
    • Nervous tissue
  • Muscles are usually attached to bones, and they vary in shape and size.

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1. Overview of Muscle Tissue

Skeletal Muscle Functions
  • Functions of skeletal muscle include:
    • Body movement: Enables physical movements.
    • Maintenance of posture: Helps in stabilizing positions.
    • Protection and support: Provides structural support and protects internal organs.
    • Regulating elimination of materials: Utilizes sphincters at orifices.
    • Heat production: Generates heat as a byproduct of muscle metabolism.

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2. Gross Anatomy of Skeletal Muscle

Structural Hierarchy
  • The organization levels of skeletal muscle include:
    • Whole muscle
    • Muscle fascicle
    • Muscle fiber
    • Myofibrils
    • Myofilaments

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2. Gross Anatomy of Skeletal Muscle

Structural Hierarchy
  • Individual muscle fibers contain myofibrils.
  • Myofibrils are composed of myofilaments.

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Table 10.1: Organizational Levels of Skeletal Muscle
Appearance and Description
  • Myofibril:
    • Description: Long, cylindrical contractile elements within muscle fibers; as long as the muscle fiber itself; composed of myofilaments; exhibits striations.
  • Myofilaments:
    • Thin Filament (Actin molecules): Short contractile proteins of two types:
      • Thick (composed of myosin)
      • Thin (composed of actin, tropomyosin, and troponin).
    • Thick Filament: Heads of myosin molecules.

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2. Gross Anatomy of Skeletal Muscle

Connective Tissues
  • Muscles have multiple layers of connective tissue within and around them.
    • Structure: Connective tissue layers are composed mostly of collagen and elastic fibers.
    • Functions:
      • Provide protection.
      • Serve as sites for blood vessel and nerve distribution.
      • Facilitate attachment to the skeleton.

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Connective Tissues
  • Endomysium: Innermost layer surrounding individual muscle fibers.
  • Perimysium: Middle layer surrounding groups of muscle fibers (fascicles).
  • Epimysium: Outermost layer that encases the entire muscle.
Anatomy Illustration:
  • Depiction of muscle fiber structures, including arteries, veins, nerves, and connective tissue layers (epimysium, perimysium, endomysium).

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2. Gross Anatomy of Skeletal Muscle

Muscle Attachments
  • Tendon: Connects muscle to bone.
  • Aponeurosis: A broad, flat tendon-like structure.
  • Deep Fascia: Surrounds muscles and compartments of muscles.
  • Most muscles extend over a joint and attach to bones on either side of the joint.
    • Muscle contraction typically causes one bone to move while the other remains fixed.

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3. Skeletal Muscle Fiber Orientation

Organization
  • Muscle fibers are organized into fascicles.
Pattern of Muscle Fascicle Arrangements
  • Four patterns exist:
    1. Circular
    2. Parallel
    3. Convergent
    4. Pennate:
      • Unipennate
      • Bipennate
      • Multipennate

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Skeletal Muscle Architecture
Description of Patterns
  • Circular:
    • Fibers arranged concentrically around an opening; functions as a sphincter to close a passageway or opening (examples: orbits, mouth, anus).
  • Parallel:
    • Fascicles are parallel to the long axis of the muscle; the body of the muscle increases in diameter with contraction; exhibits high endurance but is not very strong.
  • Convergent:
    • A triangular muscle with a common attachment site; allows for changing the direction of pull; does not pull as hard as equal-sized parallel muscle.
  • Pennate:
    • The muscle body has one or more tendons; fascicles are at an oblique angle to the tendon; pulls harder than a parallel muscle of equal size.
      • Unipennate: All muscle fibers on the same side of the tendon.
      • Bipennate: Muscle fibers on both sides of the tendon.
      • Multipennate: Tendon branches within the muscle.

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Learning Outcomes

Upon completion of this lecture, you should be able to:

  1. List the three types of muscle tissue.
  2. Describe five properties common to all types of muscle tissue.
  3. List five functions of skeletal muscle in the body.
  4. Describe the structural hierarchy of whole muscle.
  5. Name five types of connective tissue associated with skeletal muscle and describe their locations and/or functions.