Dog Muscle Anatomy
Dog Muscle Anatomy Introduction:
Anatomy refers to the study of physical structure of animals. When we look at a dog, much of what we see is the result of the growth of the bones, muscles, joints, ligaments and tendons. The bones and muscles give the dog its general conformation or shape. In puppies we frequently use such terms as ‘leggy,’ meaning Muscles are what give your dog movement.
There are a lot of other systems that also contribute, but it is the contraction and relaxation of muscle that gives mechanical movement to the skeletal system, allowing dogs to walk, run, wiggle their noses, etc If the legs appear longer than normal; or ‘squatty,’ suggesting short legs. In any event, these non-scientific terms attempt to describe how the young animal’s bones and muscle tone have developed, or how they are developing.
Dog Muscle Anatomy – Muscles in Canines:
The primary function of muscles is to bring about movement to all or a part of the dog’s body. There are three types of muscles which make up dog muscle anatomy:-
Smooth – Smooth muscles are found within the internal organs such as the intestines, stomach, and bladder. These are not subject to voluntary or conscious control by the individual. They function automatically to satisfy the body’s needs.
Striated – Striated muscles are predominately attached to the skeleton. All of their movements are under the conscious control of the individual. They are involved with such things as walking, eating, tail wagging, eye movement, etc.
Dog Anatomy graphic created by Matt Beswick for Pet365. Click below to see the full size version.
Dog Muscle Anatomy – Cardiac Muscle
The Cardiac muscle in dogs is just what it sounds like. This is heart muscle which has well-developed cross-striations throughout the muscle. Heart muscle beats rhythmically on its own due to Pacemaker Cells in the Myocardium which discharge and cause the involuntary heartbeat as these fall under the category of involuntary muscles. The Myocardium is just the thickest middle layer of the heart wall and Pacemaker Cells are just cells that set and keep a pace within the heart synchronised properly.
Dog Muscle Anatomy Skeletal muscle
Made up of individual muscle fibers, taken together, form the muscle structure. Each muscle fiber runs in a parallel line between the tendons, and most muscle fibers both begin and end at the tendons. The way that these muscle fibers are arranged makes the contractile force additive, that is, when contraction occurs, the force along the line of muscle adds up as more force occurs.
There are three main proteins that make up the contractile mechanism in skeletal muscle:
- Tropomyosin- Tropomyosin is further made up of three subunits.
Skeletal muscle is made up of thin filaments and thick filaments. The contraction of muscle occurs when the thin filaments slide past the thick filaments. The so called “power stroke” occurs by what I would call a lever action. A lever from the thin filament detaches from the thick filament, moves down the thick strand, re-attaches, then flexes and pulls the strand shorter. The distance moved is just a few nanometers, but when hundreds or thousands of these lever actions occur all along the muscle filaments, considerable shortening of the muscle occurs.
There are two types of muscle fibers in the dog’s body:
Type I – Red muscle is mostly made up of Type I fibers and is darker, respond slowly and have long latency, and are responsible for maintaining posture. These are long, slow contractions.
Type II fibers – White muscles contain mostly Type II fibers and are responsible for fine and skilled movements. They have short twitch durations.
The different fiber types are found in different types of muscle.
One last titbit about muscle is that dog skeletal muscle has the ability to exert 3 to 4 kilograms of tension per square centimeter of cross-sectional area. This is also true for human skeletal muscle.
Dog Muscle Anatomy Characteristics:
The dog’s ancestral skeleton provided the ability to jump and leap. Their legs can propel them forward rapidly, leaping as necessary to chase and overcome prey. Consequently, they have small, tight feet, walking on their toes (thus having a digitigrades stance and locomotion); their rear legs are fairly rigid and sturdy; the front legs are loose and flexible, with only muscle attaching them to the torso.
All dogs (and all living Canidae) have a ligament connecting the spinous process of their first thoracic (or chest) vertebrae to the back of the axis bone (second cervical or neck bone), which supports the weight of the head without active muscle exertion, thus saving energy. This ligament is analogous in function (but different in exact structural detail) to the nuchal ligament found in ungulates. This ligament allows dogs to carry their heads while running long distances, such as while following scent trails with their nose to the ground, without expending much energy.
Although selective breeding has changed the appearance of many breeds, all dogs retain the basic ingredients from their distant ancestors. Dogs have disconnected shoulder bones (lacking the collar bone of the human skeleton) that allow a greater stride length for running and leaping. They walk on four toes, front and back, and have vestigial dewclaws on their front legs and sometimes on their rear legs. When a dog has extra dewclaws in addition to the usual one on each front leg, the dog is said to be “double De-clawed”.
There is some debate about whether a dewclaw helps dogs to gain traction when they run because, in some dogs, the dewclaw makes contact when they are running and the nail on the dewclaw often wears down in the same way that the nails on their other toes do, from contact with the ground. However, in many dogs the dewclaws never make contact with the ground; in this case, the dewclaw’s nail never wears away, and it is then often trimmed to keep it to a safe length.
The dewclaws are not dead appendages. They can be used to lightly grip bones and other items that dogs hold with the paws. However, in some dogs these claws may not appear to be connected to the leg at all except by a flap of skin; in such dogs the claws do not have a use for gripping as the claw can easily fold or turn.
In addition, for those dogs whose dewclaws make contact with the ground when they run, it is possible that removing them could be a disadvantage for a dog’s speed in running and changing of direction, particularly in performance dog sports such as dog agility.
The dog’s ancestor was about the size of a Dingo, and its skeleton took about 10 months to mature. Today’s toy breeds have skeletons that mature in only a few months, while giant breeds such as the Mastiffs take 16 to 18 months for the skeleton to mature. Dwarfism has affected the proportions of some breeds’ skeletons, as in the Basset Hound.