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.

Muscle cells have a specialized endoplasmic reticulum called the sarcoplasmic reticulum. The sarcoplasmic reticulum regulates the calcium ion concentration in the cytoplasm of striated muscle cells, and so plays a significant role in muscle contraction and relaxation. The T-tubule is a specialized invagination of the sarcoplasmic reticulum, and the sarcomere is the single contractile unit of a muscle fibril. There is no muscle structure called the mycoplasmic reticulum.

The intervertebral disc articulate with the vertebrae via cartilaginous symphysis joints. These joints are amphiarthrotic, meaning that they allow for slight mobility. 

Synovial joints are all diarthrotic and characterized by a flexible joint capsule filled with synovial fluid. Synarthrotic joints have no movement - examples include the skull bones and the joints of the teeth to the jaw.

The head of the femur articulates with the acetabulum, a concave surface on the pelvis formed by the union of three bones: the ilium, the ischium, and the pubis. 

The obturator foramen is a large opening in the pelvis formed by the pubis and the ischium bilaterally. It does not form any joints but rather allows the passage of the obturator artery, nerve, and vein.

The glenoid fossa is the surface onto which the head of the humerus articulates in the shoulder, and the patella is a part of the knee.

Bursae are synovial fluid sac between bones and overlying tissues. They provide a cushion between the bone and tendons or musculature around them, allowing for reduced friction and painless movement.

A tendon is a connective tissue point of attachment of muscle to bone, while a ligament is a connective tissue attachment from bone to bone. A capsule is a fibrous, fluid filled structure surrounding a synovial joint.  

Bruxism, or involuntary tooth grinding, can cause inflammation and damage in the temporomandibular joint, which is the articulation between the condyle of the mandible and the temporal bone. 

The xiphisternal joint is between the xiphoid process and the body of the sternum. The intermetacarpal joints are formed between the metacarpal bones of the hand, and the pisotriquetral joint is between the pisiform and triquetrum of the wrist.

Movement along a sagittal plane that decreases the angle between bones is flexion. This is in contrast to extension, which is movement along a sagittal plane that increases the angle between bones. Adduction is movement that pulls a structure toward the midline of the body, while abduction moves a structure away from midline.

Circumduction is movement that produces a circular motion wth the distal end of a body part. True circumduction allows for a 360 degree range of movement. Of the joints listed, the only one capable of circumduction is the shoulder. 

Condyloid joints are a form of synovial joint in which a condyle rests in an ovoid cavity. Of the joints listed, the only condyloid joint is the metacarpophalangeal joints (the joint of the most proximal knuckle).

The acromioclavicular joint is a plane joint, while the glenohumeral and humeroradial joints are both ball and socket joints.

The only bone that the patella, or kneecap, articulates with is the femur, at the patellofemoral joint. The patella is a sesamoid bone, meaning it is fully embedded within a tendon. The patellar ligament joins the patella to the tibial tuberosity (but not the fibula).