The cheek bones are formed by the zygomatic arches, which are part of the temporal bones of the face. The mental protuberance forms the chin, the styloid processes are just under the ears and serve as an attachment point for several muscles of the mouth and throat, and the pterion is the suture where the frontal, parietal, temporal, and sphenoid bones come together.

The cheek bones are formed by the zygomatic arches, which are part of the temporal bones of the face. The mental protuberance forms the chin, the styloid processes are just under the ears and serve as an attachment point for several muscles of the mouth and throat, and the pterion is the suture where the frontal, parietal, temporal, and sphenoid bones come together.

The costal cartilage of the ribcage is joined to the sternum, which is made up of three bony structures: the most superior is the manubrium, which articulates not just with the costal cartilage of the first rib but also with the clavicles. The body of the sternum is inferior to the manubrium, and articulates with the second through fifth ribs. The xiphoid process is a small protuberance just below the body of the sternum, at the point where the bottom of the ribcage meets the sternum. It is an attachment point for several muscles, including the diaphragm, the rectus abdominis, and the transverse abdominis. This is a common location for referred pain from gallbladder disease, GERD, or pain due to musculoskeletal injury or irritation.

The costal cartilage of the ribcage is joined to the sternum, which is made up of three bony structures: the most superior is the manubrium, which articulates not just with the costal cartilage of the first rib but also with the clavicles. The body of the sternum is inferior to the manubrium, and articulates with the second through fifth ribs. The xiphoid process is a small protuberance just below the body of the sternum, at the point where the bottom of the ribcage meets the sternum. It is an attachment point for several muscles, including the diaphragm, the rectus abdominis, and the transverse abdominis. This is a common location for referred pain from gallbladder disease, GERD, or pain due to musculoskeletal injury or irritation.

The smallest contractile unit in muscle tissue is the sarcomere. Myofibrils are made up of many sarcomeres attached end-to-end at a series of dark lines (hence the term "striated") called Z lines. Each sarcomere contains actin and myosin filaments, which pull together during contraction to shorten the sarcomere.

The smallest contractile unit in muscle tissue is the sarcomere. Myofibrils are made up of many sarcomeres attached end-to-end at a series of dark lines (hence the term "striated") called Z lines. Each sarcomere contains actin and myosin filaments, which pull together during contraction to shorten the sarcomere.

Cardiac muscle cells are striated, branching cells that are linked by structures called intercalated discs. These discs are composed of gap junctions, which allow the free passage of electrical signaling between heart cells, and very strong attachment points called desmosomes.

Cardiac muscle cells are striated, branching cells that are linked by structures called intercalated discs. These discs are composed of gap junctions, which allow the free passage of electrical signaling between heart cells, and very strong attachment points called desmosomes.

During a muscle cell action potential, calcium enters the cell via t-tubules, which are specialized invaginations of the sarcoplasmic reticulum. Calcium binds with troponin, which pulls the tropomyosin strand away from actin binding sites and allows myosin heads to bind. Neither sodium nor potassium bind to troponin, and ATP and ADP both bind to myosin, rather than troponin.

During a muscle cell action potential, calcium enters the cell via t-tubules, which are specialized invaginations of the sarcoplasmic reticulum. Calcium binds with troponin, which pulls the tropomyosin strand away from actin binding sites and allows myosin heads to bind. Neither sodium nor potassium bind to troponin, and ATP and ADP both bind to myosin, rather than troponin.