1 A Exercise Sciences - Muscle Anatomy & Physiology

• Deltoid --> clavicle, scapula, and humerus

• Pectoralis major --> humerus

• Biceps brachii --> radius and coracoid process of scapula

• Rectus abdominis --> pubic crest and ribs 5-7

• Brachialis --> ulna and humerus

• External oblique --> ribs and iliac crest

• Brachioradialis --> radius and humerus

• Finger flexors --> ulna and phalanges

• Adductor longus --> femur and pubic crest

• Gracilis --> tibia and body of pubis

• Sartorius --> iliac crest (ASIS) and tibia

• Rectus femoris --> Iliac spine and patella

• Vastus lateralis --> femur and patella

• Vastus medialis --> femur and patella

• Tibialis anterior --> tibia and metatarsal bone 1

• Trapezius --> vertebral column c1-6, c7-t3, clavicle, spine of scapula

• Infraspinatus --> scapula and humerusTeres major --> scapula and humerus

• Triceps brachii --> long head -> scapula and ulna, medial and lateral head -> humerus and ulna

• Finger extensors --> humerus and metacarpals 2-5?

• Gluteus maximus --> pelvis (surface of coccyx and sacrum) and femur

• Semitendinosus --> pelvis and tibia

• Biceps femoris --> femur and head of fibula

• Semimembranosus --> pelvis and tibia

• Gastrocnemius --> femur and calcaneus

• Soleus --> head of fibula and calcaneus

Each skeletal muscle is an organ that contains muscle tissue, connective tissue, nerves, and blood vessels. The epimysium (fibrous connective tissue) covers the body's more than 430 skeletal muscles.

The epimysium is contiguous with the tendons at the ends of muscle. The tendon is attached to bone periosteum.Under the epimysium the muscle fibers are grouped in bundles, fasciculi, which may consist up to 150 fibers.

Each bundle is surrounded by a layer called perimysium.Each muscle fiber is surrounded by connective tissue called endomysium. That is contiguous with the sarcolemma, fiber's membrane.

Myofibrils dominate the the sarcoplasm. Myofibrils contain the apparatus that contracts the muscle cell.

The muscle cell consists of two types of myofilaments, myosin and actin. The globular head of a myosin filament protrudes away from the filament and a pair of myosin filaments forms a cross-bridge (formed when myosin heads attach to actin during muscle contraction)

Both filaments are organized longitudinally in the smallest contractile unit of skeletal muscle, the sarcomere. Myosin filaments are anchored to each other at the M-bridge in the center of the sarcomere.

Actin filaments are aligned at both ends of the sarcomere and are anchored at the Z-line. Six actin filaments surround each myosin filament, and each actin filament is surrounded by three myosin filaments.

• The A-band of the sarcomere corresponds with the myosin filaments.

• The I-band corresponds with the areas in two adjacent sarcomeres than only contain actin filaments.

• The Z-line is in the middle of the I-band and runs longitudinally through the I-band.

• The H-zone is the area in the center of the sarcomere where only myosin filaments are present.

Both filaments are organized longitudinally in the smallest contractile unit of skeletal muscle, the sarcomere.

Myosin filaments are anchored to each other at the M-bridge in the center of the sarcomere.

Actin filaments are aligned at both ends of the sarcomere and are anchored at the Z-line.

Six actin filaments surround each myosin filament, and each actin filament is surrounded by three myosin filaments.

The A-band of the sarcomere corresponds with the myosin filaments.

The I-band corresponds with the areas in two adjacent sarcomeres than only contain actin filaments.The Z-line is in the middle of the I-band and runs longitudinally through the I-band.

The H-zone is the area in the center of the sarcomere where only myosin filaments are present.Surrounding each myofibril is the sarcoplasmic reticulum which is responsible for storing and releasing calcium into the body.

T-tubules run perpendicular to the sarcoplasmic reticulum and terminate in the vicinity of the Z-line between two vesicles. Due to how the T-tubules run between outlying myofibrils and are contiguous with the sarcolemma at the surface of the cell, discharge of an action potential arrives simultaneously from the surface to all depths of the muscle fiber.

the sliding filament theory states that the actin filaments at end of each sarcomere slide inward on myosin filaments. This pulls the Z-lines toward the center of the sarcomere and thus shortening the muscle fiber. As actin filaments slide over myosin filaments, the H-zone and I-band shrink. The action of myosin crossbridges pulling on the actin is responsible for the movement of the actin filament.The resting phase: little calcium is present in the myofibril. Few crossbridges are formed. Actin and myosin still interact in a weak bond, which becomes strong when muscle tension is produced and after the release of stored calcium.Excitation-Contraction Coupling Phase: Before crossbridges can flex, they have to attract the actin filaments. When calcium is released it binds with troponin. This causes a shift to occur in tropomyosin. The myosin crossbridge now attaches much more rapidly to the actin filament. This allows force to be produced. The amount of force produced by a muscle at any time is directly related to the number of myosin crossbridges bound to actin at any instant in time.Contraction phase: the energy for power stroke comes from hydrolysis of ATP to ADP and phosphate. This reaction is catalyzed by the enzyme myosin adenosine triphosphatase (ATPase). Another molecule of ATP must replace the ADP on the myosin crossbridge so the globular head can detach from the active actin site and return to its original position. This allows contraction to continue as long as calcium is available to bind with troponin or the muscle relaxes if there is no calcium available.Recharge phase: Muscle shortening transpires only when this sequence of events occurs: binding of calcium to troponin, coupling of the myosin crossbridges with actin, power stroke, dissociation of actin and myosin, and resetting of the myosin head position is repeated over and over again. This occurs as long as calcium is available, ATP is available to assist in uncoupling the myosin from the actin, and sufficient ATPase to catalyze the breakdown of ATPRelaxation phase: This occurs when the stimulation of the motor nerve stops. Calcium is pumped back into the sarcoplasmic reticulum, which prevents the link between the actin and myosin.