Muscle Structure Quiz

Skeletal Muscle Structure

• Organized skeletal muscle contains muscle bundles, known as fascicles, held together by fascia, a collagenous connective tissue.
• Each fascicle consists of numerous muscle fibers (muscle cells) surrounding a plasma membrane called the sarcolemma.
• Muscle fibers contain multiple nuclei and are filled with sarcoplasm, which houses the endoplasmic reticulum, known as the sarcoplasmic reticulum, functioning as a calcium ion reservoir.
• Myofibrils, abundant in muscle fibers, are composed of filaments that display light and dark bands; the light bands (I-band) are made of actin, while dark bands (A-band) consist of myosin.

Myosin and Actin Interaction

• Myosin filaments are assembled from polymerized proteins called meromyosins, characterized by a globular head (heavy meromyosin) and a tail (light meromyosin).
• The globular head serves as an ATPase enzyme with binding sites for ATP and actin.
• Muscle contraction operates via the sliding filament theory, where thin filaments (actin) slide over thick filaments (myosin).
• Contraction is initiated by signals from the central nervous system (CNS) through motor neurons at the neuromuscular junction.

Rib Structure and Function

• Ribs are thin, flat bones attached posteriorly to the vertebral column and anteriorly to the sternum, featuring two articulation surfaces on their dorsal ends.
• True ribs (first seven pairs) connect directly to the sternum via hyaline cartilage; false ribs (8th, 9th, 10th pairs) connect indirectly while floating ribs (11th and 12th pairs) lack anterior attachment.
• The rib cage is formed by thoracic vertebrae, ribs, and sternum.

Appendicular Skeleton

• Comprises the limbs and girdles, with each limb consisting of 30 bones.
• Forelimb (hand) includes the humerus, radius, ulna, carpals (8), metacarpals (5), and phalanges (14).
• Hind limb (legs) includes the femur (longest bone), tibia, fibula, tarsals (7), metatarsals (5), and phalanges (14).
• Patella (knee cap) is a cup-shaped bone protecting the knee joint.

Girdles and Joint Function

• Pectoral girdle consists of the clavicle and scapula, facilitating upper limb articulation with the axial skeleton.
• Scapula is a triangular bone located between the second and seventh ribs, featuring the acromion for humeral articulation.
• Pelvic girdle is made of two coxal bones formed by the fusion of ilium, ischium, and pubis, including the acetabulum for femur articulation.

Joints and Movement

• Joints enable movement by serving as points of contact between bones or between bones and cartilages, acting as fulcrums for muscle-generated forces.
• Joints are classified as fibrous (no movement, e.g., skull sutures), cartilaginous (limited movement, e.g., vertebrae), and synovial (considerable movement, e.g., knee).
• Examples of synovial joints include ball-and-socket (shoulder), hinge (knee), pivot (between atlas and axis), gliding (carpals), and saddle (thumb).