Anatomy and Physiology - Muscular System Notes

Overview of the Muscular System

• The muscular system comprises skeletal muscles.

Muscle Attachments

• Connective Tissue Layers:

  • Epimysium: Outer layer surrounding the entire muscle.

  • Perimysium: Surrounds bundles of muscle fibers (fascicles).

  • Endomysium: Surrounds individual muscle fibers.

• At the muscle's ends, these layers merge to form tendons (attach muscle to bone).

• Aponeurosis: Flat, sheet-like tendon that can attach to bone, skin, or other muscles.

Muscle Contraction Concepts

• During muscle contraction:

  • One bone moves while the other remains fixed.

  • Origin: Less movable attachment.

  • Insertion: More movable attachment.

• Recent terminology changes:

  • For axial muscles:

    • Superior attachment (instead of insertion)

    • Inferior attachment (instead of origin)

  • For appendicular muscles:

    • Proximal attachment (instead of origin)

    • Distal attachment (instead of insertion)

Muscle Fiber Organization

• Fascicles (bundles of fibers) have various organizational patterns:

  • Circular Muscles: Fascicles arranged concentrically around an opening (e.g., sphincters).

  • Parallel Muscles: Fascicles run parallel to the muscle’s long axis.

  • Convergent Muscles: Fascicles converge toward a single attachment point.

  • Pennate Muscles: Fascicles are arranged at an angle relative to the tendon:

    • Unipennate: Fascicles on one side of the tendon.

    • Bipennate: Fascicles on both sides of the tendon.

    • Multipennate: Branching tendons within muscles with fascicles arranged around them.

Actions of Skeletal Muscles

• Agonists (Prime Movers): Muscles that contract to produce a movement (e.g., triceps brachii for forearm extension).

• Antagonists: Muscles that oppose the agonists, aiding in smooth movement (e.g., biceps brachii for forearm extension).

• Synergists: Muscles that help the agonist by stabilizing the origin or adding tension (e.g., the role of biceps brachii and brachialis in elbow flexion).

Muscle Naming Conventions

• Named based on:

  • Action: (e.g., flexor digitorum longus for finger flexion).

  • Body region: (e.g., rectus femoris near the femur).

  • Attachments: (e.g., sternocleidomastoid attaches at sternum/clavicle and mastoid process).

  • Orientation: (e.g., rectus abdominis for straight fibers).

  • Shape: (e.g., deltoid like a triangle).

  • Size: (e.g., gluteus maximus is the largest).

  • Number of Heads: (e.g., triceps brachii has three heads).

Muscles of Face and Expression

• Muscles of Facial Expression:

  • Mainly connect from bones to skin to move the skin.

  • Innervated by facial nerve (CN VII).

  • Key muscles include:

    • Occipitofrontalis: Raises eyebrows.

    • Orbicularis oculi: Closes the eye.

    • Zygomaticus major: Smiling.

    • Platysma: Tenses skin of the neck.

Muscles of the Eye

• Extrinsic Eye Muscles: Move the eye and attach to the sclera. Includes:

  • Rectus Muscles: Medial, lateral, inferior, and superior rectus.

  • Oblique Muscles: Inferior oblique and superior oblique for lateral movement and elevation/depression.

Muscles of Mastication (Chewing)

• Temporalis: Elevates and retracts the mandible.

• Masseter: Elevates and protracts the mandible.

• Medial and Lateral Pterygoid: Protractions and side-to-side movements.

Tongue Muscles

• Intrinsic Muscles: Adjust the shape of the tongue.

• Extrinsic Muscles: Move the tongue:

  • Genioglossus: Protracts tongue.

  • Hyoglossus: Depresses/retracts tongue.

  • Palatoglossus: Elevates posterior part of tongue.

Pharyngeal Muscles

• Aid in swallowing; include the superior, middle, and inferior pharyngeal constrictor muscles that push food into the esophagus.