Skeletal Muscle Anatomy and Nomenclature

Muscle fiber: Possesses the ability to contract and conduct impulses.
Blood vessels: Deliver $O_2$ and remove $CO_2$ during muscle reactions.
Nerves: Transmit nerve impulses that control skeletal muscle activity.
Connective tissue: Surrounds specialized muscle fibers for protection and structure.

There are $5$ layers/levels of muscle structure: - Entire muscle: Covered by the epimysium (outer layer). - Fascicles: Bundles of fibers surrounded by the parium (middle layer). - Muscle fiber (myofiber): Individual cells covered by the endomysium (inner layer). - Myof fibral: Specialized internal structure surrounded by the psychop plasmic reticulum. - Myofilaments: Final layer containing active contractile proteins.

Psychop plasmic reticulum: A network of canals and tubes that store and regulate calcium for contraction.
Terminal system sist: Sacs that store and release calcium.
T tubules: Pathways that transmit electrical signals deep into the myof fibral.
Thick filament (misin): Contains active heads that movement to create a pulling mechanism.
Thin filament (actin): Consists of the actin molecule (binding sites), tropis (blocks binding sites/stabilizes), and the troponin complex (reacts with calcium to move tropis).
Saramy: The single repeating pattern/unit of muscle fiber arrangement. - A bands: Dark bands where misin is present. - I bands: Light bands where misin is absent. - Zed dis: A protein that anchors thin filaments; its movement shortens or lengthens the saramy.

Location: Named after body regions, such as the brachle region (e.g., bicep brachy, tricep brachy, brachialis).
Shape: E.g., the deltoid, named after the triangular Latin symbol Delta.
Size: Maximus (biggest), medius (middle), and minimus (smallest); or longus (long) and brevis (short).
Fiber direction: Rectus (vertical), transverse (horizontal), and oblique (diagonal/diagonal).
Action: Terms include flexor, extensor, adductor, abductor, supernates, pronates, levada (elevation), and depressor.
Number of Origins: Biceps ( $2$ heads) and triceps ( $3$ heads).

Circular: Found around orifices (e.g., obicularis orus).
Convergent: Features a broad origin and narrow insertion (e.g., pectoralis major).
Parallel: Strap-like muscles that move quickly (e.g., artorius).
Fusiform: Spindle-shaped with a thick belly (e.g., biceps).
Pennate: Fibers attach to a central tendon; includes uni penate, bipennate, and multi penate.

Capillary beds: Microscopic vessels that allow blood to seep through for exchange.
Muscle Regeneration: Possible if blood supply is present; otherwise, scar tissue forms.
Agonist (Prime mover): The primary muscle responsible for a movement.
Hypertrophy: Increase in the cross-sectional area of muscle fibers.
Atrophy: Decrease in the cross-sectional area of muscle fibers.
Hyperplasia: Rare increase in the actual number of muscle fibers.
Myostatin: A hormone that inhibits muscle growth.

Q: What is the agonist for shoulder flexion? A: Deltoid.
Q: What is the agonist for shoulder extension? A: Deltoid and latissimus dorsy.
Q: What is the agonist for scapula retraction? A: Rhomboids.
Q: What is the agonist for scapula protraction? A: Sadus anterior.
Q: What is the agonist for shoulder elevation? A: Trapezius.
Q: What is the agonist for elbow flexion? A: Bicep brachy and brachialis.
Q: What is the agonist for shoulder abduction? A: Deltoid and supraspinatus.
Q: What is the agonist for shoulder adduction? A: Pectoralis major and latissimus dorsy.
Question Regarding multiple agonists: The lead agonist depends on the angle and specific part of the movement range; for simplicity, both are listed as agonists.