Muscle Fiber Functionality

Que. 1 The relationship between distribution of muscle fiber type and performance

Generally, there are two types of muscle fibres; slow-twitch (type I) and fast-twitch (type II) muscle fibres. Type I fibres contracts and releases energy slowly and are required by the body during steady-state activities such as cycling, jogging and endurance swimming. Moreover, these muscle fibres are efficient in utilizing oxygen in order to generate energy in the form of ATP, and thus are resistant to fatigue. However, the distribution of these muscle fibres is high when the body is involved in endurance-type activities, since they are perfect in meeting immediate energy demands of the working muscles. For example, postural muscles of the neck have a high percentage of slow-twitch muscle fibres since they require in maintaining posture against gravity (McArdle, Katch & Katch, 2010).

On the other hand, fast-twitch muscle fibres contract quickly, release energy rapidly and usually fatigue since they are efficient in providing energy through anaerobic metabolism. The distribution of these fibres is high in muscles that are required to produce rapid, powerful, and explosive strengths, such as muscles in the arm and legs (McArdle, Katch & Katch, 2010).

How exercise training modify or change a person’s fiber-type distribution

However, exercise training contributes to the adaptation of each type of muscle fibre. For example, endurance type exercises causes hypertrophy of type I muscle fibres, increased size and number of mitochondria (facilitating efficient energy production), increased capillary supply (thus enhancing gaseous exchange and movement of nutrients and waste products), and significant increase of myoglobin content. Moreover, exercises such as weight-lifting and sprint track athletics enhances the hypertrophy of type II B fibres, lactic-acid tolerance, efficiency of ATP supply, and quick and forceful contraction of muscles (McArdle, Katch & Katch, 2010).

Que. 2 Mechanisms by which muscle glycogen is broken down to glucose for use in glycolysis

During heavy muscle exercises, the body derives almost 80% of glucose for use in glycolysis from glycogen that is stored in skeletal muscles. The process of breaking down the stored glycogen is referred as glycogenolysis. The initial mechanism involves breakdown of glycogen into gluco-1-phospate (G1P), through the activity of glycogen phosphorylase catalyst. This reaction is referred to as phosphorolysis since it uses phosphate ion to break glycogen polymer into small molecules, rather that the water molecule like in hydrolysis reactions. Moreover, this phosphate comes from coenzyme pyridoxal phosphate rather than from ATP, making the reaction to save cell energy. Consecutively, this catalyst only act on non-reducing ends of the glycogen chain, which is at least five glucose molecules away from a branch point, and this, prevents the glycogen molecule from leaving the muscle cell in this form (Richter et al. 2001).

Glycogen Debranching Enzyme (GDE) is then used to convert alpha (1-6) branches of glycogen into alpha (1-4) branches, leaving a single glucose at each 1,6 branch. This enzyme acts on glycogen branches that have reached their hydrolysis limit with glycogen phosphorylase catalyst. Therefore, the main products of glycogen breakdown are G1Pmolecule and glucose. Apparently, this glucose can proceed to the glycolysis pathway, as G1P molecule proceeds to be broken down into glucose units. The third mechanism of glycogenolysis involves the conversion of G1P into glucose-6-phosphate (G6P) by Phosphoglucomutase enzyme (Richter et al. 2001).

Que. 3 How nerve impulse is transmitted along the axon

The transmission of a nerve impulse along the axon involves a number of processes. The process starts when a stimulus is received by the dendrites, and then transmitted to the axon. At this point, this stimulus depolarizes the neurolemma (membrane of the nerve cell), in order to facilitate the transmission of the nerve impulse along the axon. The potassium and sodium gates at the nodes of Ranvier (the gaps between myelin sheath) opens such that sodium ions diffuses from the extracellular fluid into the neural, while potassium ions diffuse from the neuron into the extracellular fluid. This ion exchange causes an action potential (depolarization) to occur, which excite a response to the next node of Ranvier, such that the nerve impulse is propagated from one node to the other. Moreover, at the axon terminal, the nerve impulse stimulates the axon terminal bundles to release neural transmitters into the synaptic gap, which then binds with proteins of the next neuron that is about to receive the impulse (Popov, 2014). However, after the nerve impulse is propagated to the proceeding node, depolarization and hyperpolarization of the nerve cell occurs, until when sodium and potassium pumps restores concentrations (resting potential).

Que. 4 Advantages of fat over carbohydrate for fuel storage in the body

Stored fast can be used as an alternative source of fuel especially during situations such as fasting or during times of food scarcity. Most studies reveal that fats yield twice more energy compared to carbohydrates. For example, 1 gram of fats produces 9 kilocalories, while 1 gram of carbohydrates yields 4 kilocalories (Lutz, Mazur & Litch, 2014). Consecutively, fats help to provide body insulation against cold environmental temperatures.

Que. 5 Description of the primary structure of the heart

Human heart is a four-chambered organ that is sized and shaped like a clenched human fist. The four chambers include the right atrium, right ventricle, left atrium and left ventricle. The two atria are thin walled while both ventricles are thick walled. The thickness or thinness of these chambers is based on the amount of pressure that each is required to generate. The right atrium receives deoxygenated blood from the body tissues through the pulmonary vein. The right ventricle receives deoxygenated blood from the right atrium and pumps it to the lungs to be oxygenated through the vena cava. The left atrium receives oxygenated blood from the lungs through the pulmonary vein, while the left ventricle receives blood from the left atrium and pumps it to all body parts through the aorta (Iaizzo, 2009).

The heart also has tricuspid valve that prevents blood from flowing back to the right atrium when the right ventricle contracts, and bicuspid valve which prevents blood from flowing back into the left atrium when the left ventricle contracts. Moreover, semilunar valves prevent the blood from flowing back into the ventricles when these ventricles dilate (Iaizzo, 2009). Consecutively, the heart is made up of three layers. The outer layer is referred as the epicardium; center layer is myocardium, while the inner layer is endocardium.

The primary functions of blood

The blood has three main functions; it is responsible for the transportation of various chemicals such as carbon dioxide, oxygen, hormones, among others. In addition, the blood is responsible for the protection of individuals from various diseases and infections, since it contains platelets, white and red blood cells, and plasma (Iaizzo, 2009). Consecutively, blood is responsible for maintaining stable internal body environments, through regulating the body`s osmotic pressure and temperatures.

References

McArdle, W. D., Katch, F. I., & Katch, V. L. (2010). Exercise physiology: Nutrition, energy, and human performance. Baltimore, MD: Lippincott Williams & Wilkins.

Popov V., (2014). Transmission of nerve impulse along the axon, Retrieved from, http://www.answers.com/Q/How_does_a_nerve_impulse_get_transmitted_along_an_axon

Webb, F. S., & Whitney, E. N. (2013). Nutrition: Concepts & controversies. Belmont, Calif.: Wadsworth Cengage Learning.

Iaizzo, P. A. (2009). Handbook of cardiac anatomy, physiology, and devices. New York, NY: Springer.

Richter, E. A et al. (2001). Skeletal muscle glucose uptake during dynamic exercise in humans: role of muscle mass. Am. J. Physiol. 254: E555–E561.

Lutz, C., Mazur, E., & Litch, N. (2014). Nutrition and Diet Therapy. Philadelphia: F.A. Davis Company.