The musculoskeletal system (also known as the locomotor system) is an organ system that gives animals the ability to physically move using the muscles and skeletal system. The musculoskeletal system provides form, stability, and movement to the human body. It consists of the body's bones (which make up the skeleton), muscles, tendons, ligaments, joints, cartilage, and other connective tissue. The term "connective tissue" is used to describe the tissue that supports and binds tissues and organs together. Its chief components are elastic fibers and collagen, a protein substance.(reword)

Human Musculoskeletal System

Hydrostatic Musculoskeletal System

Among others, cnidarians and annelids, have a hydrostatic skeleton . Hydrostatic skeletons consist of fluid-filled chambers. These closed chambers use internal pressures generated by muscle contractions causing locomotion for the arm, as well as maintaining the shape of the animals. Animals such as the earthworm and the sea anemone use these hydrostatic skeletons to change their body shape as they move forward. The sea anemone has one set of longitudinal muscles in the outer layer of the body, and a layer of circular muscles in the inner layer of the body. The anemone can elongate or contract its body by contracting one or the other set of muscles. Arthropodas have their muscles attached to an exoskeleton.

Muscle Contraction Initiation

In mammals, when a muscle contracts, a series of reactions occur. Muscle contraction is stimulated by the motor neuron sending a message to the muscles from the somatic nervous system. Depolarization of the motor neuron results in neurotransmitters being released from the nerve terminal. The space between the nerve teminal and the muscle cell is called the neuromuscular junction. These neurotransmitters diffuse across the synapse and bind to specific receptor sites on the sarcolemma (cell membrane of the muscle fiber). When enough receptors are stimulated, an action potential is generated and the permeability of the sarcolemma is altered. This process is known as initiation.

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