Muscle Anatomy and Fascicle Arrangement

Muscle fibers are oriented parallel to each other, contracting along the direction of the fascicles.
Fascicle arrangement influences muscle shape and functional capabilities, including power and range of motion.
Longer muscle fibers yield a greater range of motion, while a higher number of fibers in a given cross-sectional area generates more power.
Muscle power depends on cross-sectional area, not muscle length.

Circular:
- Concentric ring formation.
- Surrounds body openings and closes these openings upon contraction.
- Example: sphincters like the orbicularis oris (mouth) and orbicularis oculi (eye).
Convergent:
- Broad origin converging to a single tendon of insertion.
- Triangular or fan-shaped, allowing for strong contractions.
- Example: pectoralis major (chest muscle).
Parallel:
- Fibers run parallel to the muscle's long axis.
- Allows greatest shortening during contraction.
- Can be strap-like or spindle-shaped with an expanded belly.
- Example: sartorius (thigh) and biceps brachii (upper arm).
Pennate:
- Short fibers attaching obliquely to a tendon, resembling feathers.
- Unipennate: Fibers insert on one side of a tendon (e.g., extensor digitorum longus).
- Bipennate: Fibers insert on both sides of a tendon (e.g., rectus femoris).
- Multipennate: Fibers insert from multiple directions (e.g., deltoid).

Most skeletal muscles span at least one joint and connect to bones at two points.
Muscle contractions apply force through tendons, moving the distal bone toward the proximal bone.
Example: gastrocnemius (calf muscle) illustrates these mechanics.

Ligaments: Connect bones, composed of collagen fibers, often attaching to the periosteum at joints.
Tendons: Fibrous tissue linking the muscle belly to bone.
Aponeurosis: Broad, flat connective tissue linking muscle to bone, covering a larger area than tendons.
Raphe: Line of fibrous tissue joining two separate muscles, generally providing long attachment to bone.

Skeletal muscles are voluntary, contracting in response to nerve activation.
Contractions can result in muscle length changes or remain isometric.
Isometric:
- Muscle length remains constant with no movement.
- Muscle force increases to resist external forces.
- Example: plank position.
Concentric:
- Muscle shortens along the direction of fascicles during contraction.
- Example: raising a barbell.
Eccentric:
- Muscle lengthens in the direction of fascicles during controlled relaxation.
- Example: lowering a barbell.

Muscles collaborate or oppose to generate movement efficiently.
Prime Mover:
- Main muscle responsible for producing a specific movement via concentric contraction.
- Example: biceps brachii in elbow flexion.
Synergist:
- Assists the prime mover by adding force or stabilizing against unwanted movement.
- Example: brachialis in elbow flexion.
Antagonist:
- Opposes the action of the prime mover using eccentric contraction, regulating speed.
- Example: triceps brachii during elbow flexion.
Fixator:
- Stabilizes the proximal limb while enabling movement in the distal portion.
- Example: rotator cuff muscles during elbow flexion.

Location: Name reflects anatomical location, e.g., temporalis (temporal region).
Shape: Descriptive of form, e.g., trapezius (trapezoidal shape).
Size: Comparisons in size, e.g., maximus (largest), longus (long), brevis (short).
Number of Origins: Indicates the number of heads, e.g., biceps has two heads.
Attachments: Highlights the origins and insertions, e.g., sternocleidomastoid connects sternum and clavicle (origin) to mastoid process (insertion).