Muscle and Nervous Tissues

Muscle and nervous tissues are considered excitable tissues. They are capable of transmitting electrical signals across their cell membranes by altering the membrane potential, the charge difference between the inside and outside of the cell. This electrical impulse is called an action potential and occurs when the inside of the cell becomes more positive and then negative by moving ions across the cell membrane. In muscle tissue, the electrical impulse sets off a series of events that leads to force generation within muscle cells. In nervous tissue, the electrical impulse can travel long distances and is used as a form of communication.

Muscle tissue is an excitable tissue that generates force leading to voluntary and involuntary movements of the body. Muscle tissue is divided into three types based on location and function: skeletal, cardiac, and smooth. The three types have cellular differences that are important for carrying out their distinct functions. Skeletal muscle is attached to bones and skin. The contraction of skeletal muscle allows the body to stand upright, walk, run, and perform other voluntary movements. Skeletal muscle fibers are multinucleated and rod-shaped with striations. These cells have multiple nuclei because cells fuse together during skeletal muscle development. When viewed microscopically, stripes called striations are visible. Striations result from the alignment of sarcomeres, the structural units of muscle fibers that facilitate contraction.

Cardiac muscle is a striated muscle type located in the walls of the heart. Contraction of cardiac muscle is under involuntary control. Cardiac cells (cardiomyocytes) are uninucleate and branched. An intercalated disc connects cardiac muscle cells and supports cardiac muscle contraction by allowing the electrical impulse to travel more rapidly.

Smooth muscle is located in the walls of internal organs and blood vessels. It is responsible for involuntary movements including those of the digestive, urinary, and reproductive systems. Smooth muscle cells are narrow and spindle-shaped with a single central nucleus and no striations. Smooth muscles contain the same contractile proteins as skeletal and cardiac muscle fibers, but they are not aligned to appear striated. Nervous tissue is excitable tissue that transmits electrical and chemical signals throughout the body by means of specialized cells called neurons. This tissue makes up the brain, spinal cord, and all of the nerves. A neuron is a cell in the nervous tissue that transmits electrical and chemical signals throughout the body. Neurons are associated with several types of cells called neuroglia that support the function of the neurons. The nervous tissue receives stimuli from the internal and external environment, processes information, and coordinates the functions of the body. Neurons have a distinct shape suited for sending and receiving signals over long distances. The neuron has a large cell body with branches called dendrites that receive signals from other cells and bring them to the cell body. Another extension, a long tail, or axon, sends signals from the neuron to other cells at the axon terminal. One type of neuroglia forms the myelin sheath, which allows axons to transmit signals more rapidly. Other neurogliabind neurons together and facilitate nutrient exchange by binding blood vessels to neurons.