Animal movement is essential for all physiological processes, and muscle control, which is governed by soft tissue, is used to produce this motion in most animals. Physiological processes include movement at both the cellular level which depends on the cytoskeleton and motor proteins (i.e. intracellular transport) and the organismal level which depends on a collection of muscle cells (walking).
Muscle cells, also referred to as myocytes, are unique to animals and act as contractile cells. Animals possess two main types of muscle cells: these are known as striated muscle cells and smooth muscle cells. A striated muscle cell is made up of thick myosin filaments and thin actin filaments. These filaments are arranged into sarcomeres (basic muscle unit). These sarcomeres are organized in a parallel fashion and when muscles contract and relax these sarcomeres slide past each other.
Conversely, smooth muscle cells are not arranged into parallel sarcomeres. Instead, smooth muscle cells are made of one continuous and interconnected stretch of sarcomeres. This continuous stretch runs parallel along the length of the muscle.
The actual movement of both smooth and striated muscle depends on electrical signals. These electrical signals result from excitation-contraction coupling and get converted into physical changes, thus movement.
Animal movement varies greatly among different species and is also dependent heavily on the environments which organisms exist. Animals can swim in water, run or walk on land and jump or fly in air. Each of these movements varies in terms of their strengths and weaknesses.
For example, the size of an animal greatly influences the rate at which it moves, with larger animals being able to move faster than smaller ones. However, in water for instance, larger animals experience greater frictional drag, whereas smaller animals have more trouble dealing with the water viscosity. Evidently, the challenges faced are variable among different species.