Obese cat sitting on the floor and meowing.

The Musculoskeletal System

The musculoskeletal system in mammals is responsible for locomotion, plus support and protection of vital internal organs. The components of this system include muscles, bones, and a variety of supportive structures, including ligaments, tendons, and cartilage.

Disorders of the musculoskeletal system can be quite debilitating to a dog or cat and be accompanied by a lot of pain.

Anatomy and Physiology

The type of muscle involved in skeletal locomotion is termed striated muscle. This type of muscle is in contrast to the cardiac muscle found in the heart, and the smooth muscle found in many of the internal organs, both of which are under involuntary control by the nervous system.

Striated muscle consists of interlocking bands of cells capable of contracting with great force, thereby achieving movement. Tendons are those tough, fibrous bands that anchor the striated muscle to bone and allow this movement to occur. A strain is said to have occurred on injury to a muscle or a tendon.

The axial skeleton of the cat consists of the skull, the vertebrae, and the ribcage. The appendicular skeleton consists of the bones making up the front and hind limbs, as well as the pelvis.

Each type is made up of a hard mineralized matrix with bone cells interspersed within. The centers of most bones are hollow and filled with soft bone marrow. This substance is an important component of the host immune system as the location for white blood cell production.

Red blood cells and platelets, those structures involved in the blood- clotting scheme, are also produced exclusively within the bone marrow.

Bone is a dynamic tissue, constantly being reabsorbed and regenerated throughout the life of the individual. Long bones grow in length by means of a special structure called an epiphyseal plate, located at the ends of the bones.

It is interesting to note that overall health and growth patterns of bony tissue are very dependent on proper nutrition; malnutrition and vitamin or mineral deficiencies can wreak havoc on the development and/or integrity of the skeletal system.

A ligament is different from a tendon in that it connects bone to bone, not muscle to bone. Injuries involving ligaments are properly termed sprains.

A joint is the site at which two bones meet. Not all joints are movable, such as those making up the skull. However, for purposes of discussion, the types of joints referred to most often are called synovial joints.

These joints, found throughout the body, allow for free movement between bones and also serve a shock-absorbing capacity.

Each synovial joint consists of ligaments, cartilage on which the ends of the bones move or articulate, joint fluid designed to lubricate the joint and provide nutrition to the articular cartilage, and a tough, fibrous capsule surrounding it all.

In addition, some synovial joints contain special pads of cartilage, called menisci, which act as super shock absorbers. The knee joint, or stifle, is a good example of such a joint.