Muscular+System



Muscular System (1) What are the three types of muscles in the human body? (Describe and include pictures)

Smooth muscle has fibers which are spindle-shaped cells, forming sheets. It is involuntary and is found in the walls of hollow organs. Cardiac muscle makes up the walls of the heart. It is uninucleated like smooth muscle tissue and it is also involuntary. Skeletal muscle is voluntary and runs the length of parts of the skeleton.

(2) List and discuss the functions of muscles.

Muscles support the body, help bones move and help the body maintain a constant body temperature. They aid homeostasis in this way because muscle contraction causes ATP to break down which distributes heat throughout the body. Muscles also support movement in the cardiovascular and lymphatic vessels because pressure created by contraction keeps the blood moving. They lastly protect internal organs and support joints.

(3) Give an example that illustrates how muscles work in antagonistic pairs. (pictures good)

The bicep muscles and tricep muscles act as pairs.

(4) Describe the microscopic anatomy of muscle fiber and explain the sliding filament model of muscle contraction. (long answer)

A muscle fiber has a cytoplasm called the sarcolemma. Its endoplasmic reticulum is the sarcoplasmic reticulum and it has a T system that causes tubules of the sarcolemma to dip down into the cell. This dipping down causes expanded parts of the sarcoplasmic reticulum and thus forms calcium storage areas. The reticulum also has many myofibrils and contains glycogen and a red pigment called myoglobin.

The sliding filament model occurs when the muscle fiber contracts and a sarcomere shortens. Actin filaments slide past the myosin and come towards eachother. The Z line comes inward, the I band becomes shorter and the H zone nearly goes away.

(5) Describe the structure and function of the neuromuscular junction.

The neuromuscular junction is the part of the muscle fiber where the axon of a neuron nearly meets the sarcolemma. The small gap in between the two parts is called the synaptic cleft. At the junction, vesicles release a neurotransmitter called acetylcholine, which diffuses, across the cleft.

(6) Describe the events as myosin pulls actin toward the center of the sarcomere.

ATP is broken down by myosin filaments, which then attach to actin filaments. ADP is released and bridges formed change positions. The change in position causes actin filaments to pull toward the center of a sarcomere.

(7) Contrast a muscle twitch with summation and tetanus.

A muscle twitch occurs when a motor unit receives infrequent electrical impulses. A single contraction results. In a twitch, the muscle experienced a latent period, a contraction period and a relaxation period. Unlike a muscle twitch, in summation and tetanus, a maximum contraction of a muscle is achieved and lasts until the muscle fatigues. The muscle does not relax between stimuli of the motor unit.

(8) What is muscle tone, and how is it maintained?

Muscle tone is when motor units in a muscle are always contracted but not enough to cause the muscle to move. It is maintained by exercise.