Anatomy and Muscle Function Study Guide

Terminology and Muscle Models

  • Terminology related to skeletal muscles is crucial for understanding muscle models.
  • Focus on concepts needed for the upcoming exam on muscle models.

Connective Tissue Layers of Skeletal Muscle

  • Skeletal muscles are enveloped by layers of connective tissue.
  • Illustration: A skeletal muscle cut in cross-section.
  • Example: Short head of the biceps brachii or rectus femoris.
  • Entire Muscle:
    • Surrounded by a connective tissue sheet called the epimysium.
    • Analogy: Epimysium is like the insulating layer on an electrical cord.

Muscle Fibers

  • Representation: Circles represent muscle fibers in cross-section, similar to fibers in a fiber optic cable.
  • Muscle fibers are skeletal muscle fibers.
  • Skeletal Muscle Fibers:
    • Long cells, approximately 10 to 12 inches in length.
    • Multinucleated: Containing hundreds of nuclei per fiber.
    • Striated: Exhibit light and dark banding patterns under a light microscope.
  • Muscle fiber cells are surrounded by the endomycin.

Fascicles and Connective Tissue Compartments

  • Fibers are divided into small compartments.
  • Connective tissue layer forms these compartments.
  • Perimysium: Connective tissue layer forming compartments.
  • Fascicles: Individual compartments within the muscle.

Fascicle Arrangements and Their Effects

  • Fascicles arrange in distinctly different manners.
  • Arrangement affects:
    • Power/tension generation during contraction.
    • Contraction speed.
    • Range of motion.
  • Responsibility: Know one example for each arrangement.

Parallel Muscles

  • Definition: Fascicles are parallel to the long axis of the muscle.
  • Example: Biceps brachii.
  • Tension/Power:
    • Depends on the number of myofibrils.
    • Myofibrils are lengthwise functional units within muscle fibers (cells).
    • The number of myofibrils activated during contraction determines strength.
  • Key factor: How many fiber cells activate during contraction.

Convergent Muscles

  • Fibers spread out at one end and converge to a narrow attachment.
  • Tendon: Connective tissue attachment of skeletal muscle to bone (usually a band).
  • Aponeurosis: Broad, flat sheet of connective tissue attaching muscle to bone.
  • Examples: Pectoralis major & minor
  • Functions: Fibers pull in different directions leading to multiple movements.

Origin and Insertion

  • Origin: Bony attachment at the non-movable part (e.g., sternum for biceps brachii).
  • Insertion: Point of attachment where movement occurs (e.g., greater tubercle of the humerus for biceps brachii).
  • Note: You are not responsible for specific points of origin and insertion.

Pennate Muscles

  • Fibers attach to the tendon at an angle.
  • Comparison: Compared to parallel muscles, pennate muscles generate less movement but more force.
  • Subtypes:
    • Unipennate: Fascicles on one side of the tendon.
      • Example: Extensor digitorum longus.
    • Bipennate: Fascicles on both sides of the central tendon.
      • Example: Rectus femoris (one of the quadriceps).
    • Multipennate: Tendinous branching.
      • Example: Deltoid.

Circular Muscles

  • Fibers are oriented circularly (sphincters).
  • Act as valves to control material flow, particularly in hollow organs.
  • Contraction reduces the diameter of the opening.
  • Example: Orbicularis oris (around the mouth).

Muscle Actions and Interactions

  • Origin: Fixed point of attachment where no movement occurs.
  • Insertion: Point of attachment where movement takes place; usually distal.
  • Abduction: Moving a body part away from the midline.
  • Agonists: Muscles that bring about a particular movement.
    • Example: Supraspinatus and deltoid during abduction of the humerus.
  • Antagonists: Muscles that produce the opposite movement.
    • Example: Pectoralis major is an antagonist to abduction, causing adduction.
  • Synergists: Muscles that assist the movement.
  • Fixators: Muscles that hold a joint steady so another movement can occur.

Movements

  • Flexion: Decreasing the angle between bones.
  • Extension: Increasing the angle between bones.
  • Abduction: Moving away from the midline.
  • Adduction: Moving towards the midline.
  • Rotation: Movement around an axis.
  • Medial/Lateral Rotation: Movement around the bone’s long axis (e.g., humerus).

Muscle Naming Conventions

  • By Region of Body:
    • Example: Rectus abdominis (abdomen) or brachialis (upper arm).
  • By Relative Position:
    • Example: Extrinsic vs. Intrinsic.
  • By Number of Divisions:
    • Example: Biceps brachii (two heads).
  • By Shape:
  • By Action:
    • Example: Flexor carpi radialis (flexion at the wrist).

Muscles of the Head and Neck

  • Identification: Primarily through photographs or diagrams.
  • Function: Knowledge of function in multiple-choice format.
  • Epicranial Aponeurosis (Galea Aponeurotica):
    • A broad, flat sheet of connective tissue.
  • Frontalis (Frontal Belly of Occipitofrontalis):
    • Located on the frontal bone.
  • Occipitalis (Occipital Belly of Occipitofrontalis):
    • Overlies a portion of the occipital bone.
  • Orbicularis Oris:
    • Sphincter muscle around the mouth.
  • Orbicularis Oculi:
    • Muscle around the eye.
      *Temporal Parietalis:
      *Superficial muscle.
      *Temporalis:
      *Underneath temporal parietalis.
  • Masseter:
    • Attaches to the zygomatic arch.
    • Elevates the mandible (closes the mouth).
  • Zygomaticus:
    • Originates from the zygomatic bone.
  • Buccinator:
    • Deep to the masseter with fibers running at a right angle.
  • Sternocleidomastoid:
    • Originates from the sternum and clavicle; inserts at the mastoid process.
    • Function depends on unilateral vs. bilateral contraction.
      • Bilateral contraction: Flexion of the head and neck (pulls the head forward)
        *Unilateral: Rotation to opposite side and lateral flexion to the same side.
  • Platysma:
    • A broad, large sheet of muscle in the neck.
    • Depresses the mandible.
  • Trapezius:
    • Large superficial muscle, trapezoid-shaped on posterior view.
  • Latissimus Dorsi:
    *Broad flat sheet from the posterior side.

Extrinsic Muscles of the Eye

  • Lateral Rectus
  • Superior Rectus
  • Medial Rectus
  • Inferior Rectus
  • Inferior Oblique
    *Superior Oblique
  • Trochlea: Ligamentous sling where the tendon for superior oblique comes through.