Vertebrate Anatomy Notes

Muscles and Internal Organs of the Rat

Muscle Basic Histology

  • Muscle Attachments

    • Tendons: Connect muscle to bone.
    • Ligaments: Connect bones to bones.

  • Structure of Muscle

    • Muscle: Composed of bundles of fascicles, protected by epimysium.
    • Fascicle: Contains bundles of muscle fibers covered by perimysium.
    • Muscle Fiber: Composed of bundles of myofibrils, protected by endomysium.
    • Myofibril: Composed of bundles of myofilaments; contractile elements in sarcomeres.
    • Myofilament: Interact to generate contraction.
Sarcomere Structure

  • Contractile Unit: Sarcomeres are the functional units of muscle bundles.

  • Composition: Skeletal muscle fibers consist of myofibrils arranged in rows of sarcomeres.

  • Boundaries:

    • Z disks (Z-lines) hold thin filaments in position.
    • M line holds thick filaments in position.

  • A Band: Region where thick (myosin) and thin (actin) filaments overlap, appears dark.

  • I Band: Light area where only thin filaments are present; bordered by Z lines.

  • Function: Z-disk movement pulls together to shorten muscle and contract.

Muscle Actions (Antagonist Pairing)

  • Extensors vs Flexors:

    • Extensors increase the joint angle; flexors decrease it.

  • Abductors vs Adductors:

    • Abductors move limbs away from midline; adductors move them towards.

  • Retractors vs Protractors:

    • Retractors move backward; protractors move forward.

  • Supinators vs Pronators:

    • Supinators turn palm/sole anterior; pronators turn them posterior.
Muscle Orientation

  • Origin: Fixed end of the muscle, often harder to determine (e.g., back muscles); usually nearest to midline.

    • In limbs: Proximal; in trunk: Medial.

  • Insertion: End that causes motion during contraction, typically farthest from midline.

    • In limbs: Distal; in trunk: Lateral.
Shapes and Arrangement of Muscle Fibers
  • Types of Muscle Fiber Arrangement:
    • Parallel (e.g., abdominal muscles).
    • Fusiform (e.g., biceps brachii).
    • Convergent (e.g., pectoralis).
    • Unipennate (e.g., digital extensor).
    • Bipennate (e.g., rectus femoris).
    • Multipennate (e.g., deltoideus).
    • Circular (e.g., orbicularis oculi).
Anatomical Orientation
  • Directional Terms:
    • Posterior: Back
    • Anterior: Front
    • Superior: Above
    • Inferior: Below
    • Medial: Towards the midline
    • Lateral: Away from the midline
    • Proximal: Nearer to the trunk or point of origin
    • Distal: Farther from the trunk or point of origin
    • Deep: Beneath the surface
    • Superficial: On or near the surface
    • Cranial: Towards the head
Dorsal Aspect Muscles
  • Trapezius Muscle: Divided into portions based on origins (Acromio-, Clavo-, Spino-).
    • These muscles cross the shoulder joint to move the arm, including:
    • Spinodeltoideus
    • Biceps Brachii
    • Latissimus Dorsi
    • Obliques: External and internal manage abdominal support.
    • Muscles crossing the hip joint include:
    • Tensor Fasciae Latae
    • Gluteus Maximus
    • Semitendinosus
    • Biceps Femoris
    • Gastrocnemius: Calf muscle that facilitates foot movement.
Lateral and Ventral Aspect Muscles
  • Lateral Aspect: Similar muscles to the dorsal aspect.
  • Ventral Aspect:
    • Sternohyoid: Used for swallowing.
    • Pectoral Muscles: Major and minor share origins and cross the shoulder joint.
    • Linea Alba: Connective tissue joining the right and left obliques.