3.7 Musculoskeletal System

The musculoskeletal system consists of two systems—the skeletal system and the muscular system—working together to allow movement and providing support to the body. This system includes all the bones, muscles, joints, tendons, and cartilage found in the animal’s body. The purpose of this system is to support the body, allow a wide range of movement, and protect the internal organs.

Some resources show the muscular and skeletal systems as separate; however, for the purposes of this book, they are combined in order to provide a basic overview of their components, functions, and pathologies.

Within the bones is bone marrow that functions to form the red blood cells, white blood cells, and platelets. Muscles contract to allow the animal to move which also results in the production of heat to keep the body warm.

Fish, frogs, reptiles, birds, and mammals are called vertebrates, a name that comes from the bony column of vertebrae (the spine) that supports the body and head. The rest of the skeleton of vertebrates (except fish) also has the same basic design, with a skull that houses and protects the brain and ribs that protect the heart and lungs. All four limbs have a similar bony organization as well (Lawson, 2024).

Bones

Bones are made of hard, dense connective tissue, and the number of bones varies between species. The purpose of bones is to assist with movement, support the body, protect the organs, and produce blood cells. Bones are in a constant state of building and repairing. 

Muscles

Muscles are one of the four primary tissue types of the body. The body contains three kinds of muscle tissue: skeletal muscle, cardiac muscle, and smooth muscle.

The main function of the muscular system is to assist with movement. Muscles work in pairs; as one muscle contracts, the opposing muscle relaxes. This contraction pulls on the bones and assists with movement.  Contraction is the shortening of the muscle fibres, whereas relaxation lengthens the fibres. This sequence of relaxation and contraction is influenced by the nervous system.

Types of Muscle

Skeletal muscles are closely associated with the skeletal system. Also known as striated muscles, they are responsible for voluntary muscle movement, such as running. 

Smooth muscles are mainly associated with the walls of internal organs. Also known as visceral muscles, they are responsible for involuntary muscle movement such, as breathing.

Cardiac (heart) muscle, also known as myocardium, is responsible for pumping blood; this pumping creates the heartbeat.

 

(Molnar & Gair, 2021)

Joints are any place where adjacent bones or bone and cartilage come together to form a connection; also known as articulation.

Cartilage is an elastic connective tissue found at the ends of bones as well as in other locations, such as the tip of the nose.

Tendons are dense, fibrous connective tissues that anchor muscle to bone.

Ligaments are tough, elastic connective tissues that connect bone to bone.

Arthritis: Inflammation of a joint.

Ataxia: A neurological sign consisting of a lack of voluntary coordination of muscle movements.

Dislocation: The displacement of bones in a joint from their normal alignment; also called luxation (Anspaugh et al., 2022).

Fracture: A break in a bone.

Hip dysplasia: a developmental trait characterized by an instability of the hip joint.

Intervertebral disc disease (IVDD): Refers to several pathological processes involving the discs located between the vertebrae that are used for cushioning; common in dogs, especially in dachshunds.

Osteoarthritis: Inflammation of the bones and joints.

Sprain: Abnormal stretching or tearing of a ligament that supports a joint (Anspaugh et al., 2022).

Strain: Abnormal stretching and tearing of a muscle or tendon (Anspaugh et al., 2022).

Tendonitis: Inflammation of a tendon.

Arthroscopy: The visual examination of a joint

Internal/external fixation: The process of stabilizing an injury (often a fractured bone). This may be accomplished internally (e.g., placing a rod within both parts of the broken bone) or externally (e.g., connecting both parts of the broken bone externally).

Musculoskeletal radiography: An image produced on a sensitive plate or film by X-rays, gamma rays, or similar radiation, and typically used in medical examination of the bones and joints. Radiography is used to identify fractures or tumours, monitor healing, or identify abnormal structures.

Onychectomy: An operation to remove an animal’s claws surgically by means of the amputation of all or part of the distal phalanges, or end bones, of the animal’s toes; also known as declawing.