The Differences and Similarities Between Voluntary and Reflex Nerve Actions - Assignment Example

Biology Describe the differences and similarities between voluntary and reflex nerve actions. Our body carries out mainly 2 types of actions and they are voluntary actions, involuntary actions or reflex actions. Both the actions involve stimuli, impulse, neurons and effector organs. Voluntary action is nothing but an anticipated, may or may not be conscious, goal oriented movement. It is initiated in the cerebral cortex of the brain and the impulse passes into the motor area of the cerebral cortex and then to the spinal cord. From here, impulse is passed to motor neuron and then to the muscle making it contract (Barrett, 2010). Example of voluntary action is waving hand at a friend. The brain sends impulse to the muscles of the hand and makes the hand wave at the friend. Thus voluntary action is under the control of the will of the individual. Reflex action is involuntary. It is initiated by the stimulation of the receptor and the impulse passes through the dendrite and then the axon of the neuron through synapse. It then relays on the neuron of the grey matter in the spinal cord and the impulse is passed to motor neuron which then sends the impulse to the muscle. The muscle then contracts and produces action. Example of reflex action is running away on seeing a snake. The action occurs without the conscious of the individual. The control of actions is mainly at the spinal cord level. It is an instantaneous movement. Voluntary impulse passes over to the opposite side of the body, whereas reflex impulse does not. Voluntary reflex is slow because of longer pathway. Reflex impulse is quicker because it involves only 2 synapses (Barrett, 2010). Briefly outline the structure and function of each endocrine organ Endocrine organs are those organs which have specialized glands that produce and secrete chemical substances called hormones that regulate the growth, metabolism, development and function of the body. The major endocrine glands are pituitary, hypothalamus, thyroid, adrenals, parathyroids, reproductive organs and pineal body. The pineal body is located in the middle portion of the brain and secretes melatonin which regulated the wake-sleep cycle of the body. Hypothalamus releases several hormones that control the stimulation and suppression of hormones secreted by the pituitary gland. One of the important hormone released by hypothalamus is stomatostatin which stops the release of secretion of growth hormone by pituitary gland. Hypothalamus is secreted in the lower central part of the brain. The pituitary gland is located beneath the hypothalamus at the base of the brain. It is attached to the base of the brain by a stalk. It secretes several hormones which control the functions of other endocrine glands. The gland is divided into 2 parts, the anterior lobe and the posterior lobe. Most of the anterior pituitary hormones have a diurnal rhythm. The hormones of the anterior lobe are regulated by the hypothalamus. They are growth hormone which stimulates the growth of tissue and bone, thyroid stimulating hormone which stimulates the thyroid to produce and secrete thyroid hormones, adrenocorticotropin hormone which stimulates the adrenal glands to produce steroid hormones, prolactin which stimulates the production of milk in women and follicular stimulating and luteinizing hormones which control the functioning of sexual organs and production of sex hormones. Growth hormone is secreted by the pituitary gland. It is an anabolic hormone. It stimulates the growth of various types of tissues of the body especially the bone and the skeletal muscle. Growth hormone stimulates synthesis of proteins, causes mobilization of fat and inhibits the uptake and metabolism of glucose. In creased secretion of this hormone causes gigantism and decreased secretion causes dwarfism. The posterior lobe of the pituitary gland produces vasopressin which controls water loss through kidneys and oxytocin which stimulates milk production and contracts uterus during childbirth (Tortora & Derrickson, 2010). The thyroid gland is located in the front of the neck and produces thyroid hormones. They are critical for the metabolism in the body. They have a major role to play in the growth and development of various tissues in the body including the nervous tissue. The follicles of the thyroid store thyroglobin from which thyroid hormone is derived. Hypersecretion of thyroid hormone causes Grave's disease and hyposecretion leads to hypothyroidism, an extreme form of which is known as cretinism. The hormones also help maintain normal blood pressure and heart rate in the body. On the surface of the thyroid gland are 2 pairs of parathyroid glands which release parathormone. This hormone regulates the calcium metabolism in the bone and blood. The pancreas in located in the abdomen behind the stomach. It has both endocrine and exocrine parts. The endocrine part secretes glucagon and insulin that control glucose levels in the blood. There are 2 adrenal glands, each of which is located on the top of each kidney. They are triangular shaped and have outer cortex and inner medulla. The outer part reduces corticosteroids which regulate metabolism and control salt and water in the body. The medulla secretes catecholamines which maintain heart and blood pressure and cope with emotional and physical stress. The reproductive glands secrete sex hormones. The male testicles, which are located in the scrotum, secrete androgens like testosterone. These hormones are responsible for the growth and development of sexual characteristics in males. In females, the female hormones are secreted by ovaries which are located on either side of the uterus. They produce estrogens and progesterone which are responsible for female characteristics and are also involved in reproductive functions (Tortora & Derrickson, 2010). There are several or endocrine organs in the body which have clusters of endocrine cells that secrete various hormones. Some such examples are atrial natriuretic peptide secreted by heart, gastrin secreted by gastrointestinal tract, pregnancy hormones by placenta, renin by kidneys, cholecalciferol by skin and leptin by adipose tissue (Tortora & Derrickson, 2010). Reference Barrett, K.E. (2010). Ganong Review Of Medical Physiology. NewYork: Tata McGraw-Hill Education. Tortora, G.J., and Derrickson, B.H. (2010). Principles of Anatomy and Physiology. 12th Edition. NewYork: John Wiley Sons. Read More