Muscular+Ssytem+hw-+kat

(1) What are the three types of muscles in the human body? (Describe and include pictures) Three types of muscles in the human body are **smooth muscles**, **cardiac muscles**, and **skeletal muscles**.Smooth muscles are located in our organs and sustain prolonged contractions. Cardiac muscles are for involuntary contractions, like the heart muscle. Skeletal muscles are located along our bones and sustain voluntary contractions like moving our arms or legs.

(2) List and discuss the functions of muscles. The functions of our muscles are to make the bones in our bodies to move, support our bodies, maintain a constant body temperature, and protect internal organs and stabilize joints.

(3) Give an example that illustrates how muscles work in antagonistic pairs. (pictures good) When the bicep brachii contracts it raises the forearm. When the tricep brachii contracts it extends the forerm.

(4) Describe the microscopic anatomy of muscle fiber and explain the sliding filament model of muscle contraction. (long answer)
 * Sarcolemma**: Plasma membrane of a muscle fiber that forms T-tubules.
 * Sacroplasm**: Cytoplasm of a muscle fiber that contains the oragnelles, including myofibrils.
 * Glycogen**: A polysaccharide that stores energy for muscle contraction.
 * Myoglobin**: A red pigment that stores oxygen for muscle contraction.
 * T-tubule**: Extension of the sarcolemma that extends into the muscle fiber and conveys impulses that cause Ca2+ to be released from the sarcoplasmic reticulum.
 * Sarcoplasmic** **reticulum**: The smooth ER of a muscle fiber that stores Ca2+.
 * Myofibril**: A bundle of myofilaments that contracts.
 * Myofilament**: Actin filaments or myosin filaments, whose structure and functions account for muscle striations and contract.

(5) Describe the structure and function of the neuromuscular junction. Muscle fibers are stimulated to contract by motor neurons whose axons are in nerves. Te axon of one motor neuron can stimulate from a few to several muscle fibers of a muscle because each axon has several branches. Each branch of an axon ends in an axon terminal that lies in close proximity to the sarcolemma of a muscle fiber. A small gap, called a synpatic cleft, separates the axon terminal from the sarcolemma. The entire region is called a **neuromuscular joint**.

(6) Describe the events as myosin pulls actin toward the center of the sarcomere. Threads of tropomyosin wind about an actin filament, and troponin occurs at intervals along the threads. When calcium ions are released from the sarcoplasmic reticulum, they combine with troponin, and this causes the tropomyosin threads to shirt their position, exposing myosin binding sites. Myosin can now bind to actin.

(7) Contrast a muscle twitch with summation and tetanus. A **muscle twitch** is when a motor unit is stimulated by infrequent electrical impulses, a single contraction occurs that lasts only a fraction of a second.

(8) What is muscle tone, and how is it maintained?
 * Muscle tone** is when some motor units are always contracted but not enough to cause movement, the muscle is firm and solid. It is maintained by exercise.