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Atrophy
Muscle atrophy refers to the loss of muscle tissue as a result of disease or lack of activity. The majority of muscle atrophy in the generally results from disuse. People with sedentary jobs and elderly people with low numbers of physical activity can lose muscle tone and experience atrophy. This type of atrophy is reversible with an increase in vigorous exercise. Deteriorating muscle can be significant in bed-ridden people. Two types of muscle atrophy result from disease, that resulting from damaged nerves in the muscles, and disease of the muscle itself. "Such diseases as poliomyelitis (polio), amyotrophic lateral sclerosis (ALS or Lou Gehrig's disease), and Guillain-Barre syndrome affect the nerves that control muscles. (Sheth)" Muscular dystrophy, myotonia congenita, and myotonic dystrophy as well as other congenital, inflammatory, or metabolic myopathies (muscle diseases) are examples of diseases that affect primarily the muscles. Minor muscle atrophy results in some loss of power or mobility. "Research has shown that during the first several days of muscle disuse, reduction in muscle protien synthesis initially causes atrophy. (Sheth)" After this beginning period of atrophy, latter atrophy occurs due to increased muscle protein breakdown. "Muscle atrophy resulting from prolonged muscle disuse occurs due to both a reduction in the rate of muscle protein breakdown. (Powers, Howley 153)" Muscle atrophy is not permanent and can be reversed by returning the muscle to normal use. Beginning a program of resistance training exercise is a rapid and effective means of restoring normal muscle size and function after a period of disuse atrophy. "Resistance training provides the muscle with an overload stimulus and promotes an increase in protein synthesis that results in both muscle hypertrophy and an increase in muscular strength. (Powers, Howley 153)"

Athletic Amenorrhea
"Amenorrhea is a condition where females do not have menstrual periods. Missed periods may be caused by rapid weight gain or loss, malnutrition, or vigorous exercise. (Powers,Howley 447)" "Primary amenorrhea is defined as not starting periods by age 16. Secondary amenorrhea is the absence of at least 3 to 6 consecutive periods in a female who has had periods. (UIHC)" Amenorrhea is more common in athletes than in the general population. Intense, vigorous participation in sports may delay the start of menstrual periods or cause periods to stop. This is called athletic amenorrhea. "Body fat decreases due to excessive exercise and poor eating habits. When it is too low, the ovaries stop making estrogen. (Robergs, Keteyian 202)" Estrogen is the key hormone for ovulation and menstruation. Bone loss is a result of low levels of estrogen, which can cause a risk for fractures. "If bone density is lost during youth, more serious problems can occur with menopause. (Powers, Howley 448)" Athletes require more calories, carbohydrates, and protein than those who are not as active. Yet they often eat poorly to maintain a certain weight. "1500 mg of calcium is recommended daily for athletes with amenorrhea. (UIHC)" This is needed because low estrogen can cause calcium levels to decrease. "Ovulation and periods will begin when food intake is increased, exercised is reduced to normal levels, and hormone levels are balanced. (Robergs, Keteyian 202)"

Axon
The functional unit of the nervous system is the neuron. There are 3 regions in which we can divide neurons: •	Cell Body -The center of operation for the neuron is the cell body or soma, which contains the nucleus. •	Dendrites- Cytoplasmic attachments extend from the cell body and are called dendrites. “Dendrites serve as a receptive area that can conduct electrical impulses toward the cell body. (Powers, Howley 119)” •	Axon- The axon, also called the nerve fiber, carries the electrical message away from cell body toward another neuron or effecter organ. The axon, also called the nerve fiber, carries the electrical message away from cell body toward another neuron or effecter organ. “Axons vary in length from a few millimeters to a meter. Each neuron has only one axon; however the axon can divide into several collateral branches that terminate at other neurons, muscle cells, or glands. (Powers, Howley 119)” Contact points between an axon of one neuron and the dendrite of another neuron are called synapse. In large nerve fibers like those innervating skeletal muscle, the axons are covered with an insulating layer of cells called Schwann cells. The membranes of Schwann cells contain a large amount of a lipid protein substance called myelin, which forms a discontinuous sheath that covers the outside of the axon. The gaps or spaces between the myelin segments along the axon are called Node of Ranvier and play an important role in neural transmission. “The larger the diameter of an axon, the greater the speed of neural transmission will be. (Powers, Howley120)” Axons with large myelin sheaths conduct impulse more rapidy than small non-myelinated fibers.