It takes more than just bones for a cat to move. Overlying the skeletal framework is a complex network of muscles, 517 total, that gives the cat it’s powerful and graceful movement and its lithe body shape. It is what allows the cat to leap up to five times its own height, keep its balance, and land safely. The cat also moves in a contralateral fashion where the right front leg and left back leg move together and the same goes for the left front leg and right back leg.
The way in which the muscles and bones have developed in species of the cat family clearly indicates the variety of lifestyles found. For example, the cheetah, who spends most, if not all, of its time on the ground running, has narrow and deep muscle attachments on its shoulder blades. However, the leopard, who prefers climbing rather than running, has shallow and broad muscle attachments.
As the largest body system, the muscles account for about half the weight of a cat. Each individual muscle is composed of many cells held together by connective tissue. All muscle fibers receive their own nerve impulses, which trigger various motions (contraction and relaxation). When a signal or an impulse travels down the nerve to the muscle, the fiber changes chemical energy into mechanical energy, resulting in muscle contraction.
This is how muscles contract. In a muscle fiber are myofilaments, chains of two types of protein: actin and myosin. Although other proteins can be a part of a myofilament, it is the interaction between actin and myosin that ultimately brings about muscle contraction. When the two proteins bond, it releases energy and the muscle filament contracts.
There are three basic categories of muscles: smooth (or non-striated), cardiac, and voluntary (striated).
As the name implies, Smooth non-striated muscles lack visible striations under a microscope. It is the only muscle of this type, making it easy to identify. Smooth muscles carry out muscular functions not under the cat’s control. In order words, they are involuntary muscles that control the internal body systems such as the digestive system (i.e. intestines) and circulatory system (i.e. blood vessels). It is stimulated by involuntary neurogenic impulses and has slow, rhythmical contractions associated with the movement of internal organs.
One particular smooth muscle is cardiac muscle. They are only found in the heart, densely packed, and make up the bulk of the heart’s mass. These specialized muscle fibers are self-contracting and automatically regulated as they must continue to rhythmically contract to pump blood around the body through a network of arteries and veins. When the cardiac muscle contracts, it squeezes blood out of the heart, and when it releases, it fills the heart with blood.
Unlike other muscle types, the cardiac muscle has developed the ability to quickly spread electrochemical signals so all cells can contract together. Each cell is connected with three to four other cells due to its branched shape, creating a giant network from end to end. At the ends of each cell are intercalated disks, overlapping finger-like extensions of the cell membrane. These form tight junctions between the cells to ensure they will not separate while pumping blood and quickly passing electrochemical signals.
The last muscle type is the voluntary, striated, or skeletal muscles and are the most abundant type in the body. These are attached to bones with connective tissue tendons. When muscles contract, they pull on the tendons, when then pull on the bones, causing the limb to move. Muscle groups include biceps, triceps, quads, calves, abdominal just to name a few.
Voluntary muscles can only contract and pull. Because they were unable to push, these muscles work in pairs that flex and extend. Extensor muscles straighten the limbs and attach to the bones, so the bones act as levers. Flexor muscles, which bend the joints, act to pick up the limb. When one muscle type contracts, the other will contract afterwards as the first one begins to relax.
Muscle Related Diseases:
- Congenital muscular disorders: Congenital, inherited diseases of the muscles are extremely rare in cats. Congenital myotonia has been seen in the cat. This disease of skeletal muscle is characterized by involuntary active contraction of a muscle that persists after some sort of voluntary effort or stimulation of the muscle.
- Feline polymyositis: This disease is believed to be an immune-mediated inflammation of multiple muscles throughout the body. It causes muscle weakness, lethargy, decreased appetite, bizarre gait abnormalities and lameness.
- Myositis ossificans: This is a rare, progressive disease associated with cartilage and bone formation in skeletal muscles. Signs include firm masses in the affected muscles and adjacent soft tissues, limb weakness, stiffness, decreased range of motion of joints, muscle pain and immobility.
- Myositis caused by infections: Infectious agents such as bacteria, protozoa and some parasites may cause localized or generalized inflammation of the muscles.
- Feline polymyopathy: This disorder occurs when potassium levels fall to a dangerously low level within the body. Potassium is needed for normal muscle function, and low potassium causes widespread muscle weakness, inability to hold the head up, reluctance to walk and possible muscle pain.
- Neoplasia: Primary cancer lesions of muscles are rare and usually occur in adult or older animals.
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