In order to achieve its function, the nervous system is divided into two major parts i.e. The Central Nervous System (CNS) and Peripheral Nervous System (PNS). The central nervous system is basically made up of the brain and spinal cord and has the main function of receiving information from the body and sending out instructions. While the brain is protected by the skull, the spinal cord is guarded by the vertebral column. On the contrary, the basic structure of the peripheral nervous system consists of sensory neurons, motor neurons, and sensory receptors ("Nervous System," 2001). The system is responsible for sending messages from the brain to other parts of the body. PNS is divided into the afferent and efferent divisions with the afferent division consists of distinctively structured sensory receptor for transmitting information to the CNS about the body's internal environment ("Peripheral Nervous System," 2010). The efferent division is made up of sensory and motor neurons for sending information from CNS to body organs for appropriate responses.
Efferent division is divided into somatic nervous system with peripheral nerve fibers that transmit sensory information to the CNS and motor nerves connected to skeletal muscle ("Divisions of the Nervous System," n.d.). The other part is autonomic nervous system with splanchnic or visceral nerves connected to the CNS for mediating visceral functions and innervating glands, viscera, and blood vessels ("Parts of Nervous System," n.d.). The autonomic division is divided into the sympathetic division made up of a series of interconnected neurons for speeding up heart rate, widen pupils, flight response, and relax bladder. It also contains parasympathetic division contains interconnected neurons enhances intestinal and gland activity, slows the heart rate, constricts pupils, and contracts the bladder (Bailey, n.d.).
Major Endocrine Organs:
The endocrine system is basically made up of glands and organs that produce and secrete hormones and chemical substances from the body, which regulate cells or organs activity. These hormones are responsible for regulating the growth of the body, body metabolism, and sexual development and function. Some of the major organs or glands of the endocrine system include hypothalamus, pituitary, pancreas, thyroid, parathyroid, adrenals, thymus, ovaries, testes, pineal, and stomach ("The Endocrine System," n.d.).
Hypothalamus is an organ located in the lower central section of the brain and releases hormones that are secreted into an artery that transports them to the pituitary gland. The pituitary gland contains a glandular anterior section and a neural posterior section and secrets hormones that control growth making the most important endocrine organ ("Endocrine System," 2012). The endocrine system consists of two adrenal glands i.e. The inner and outer parts whose main function is to produce various hormones. While the outer part regulate salt and water balance in the body, the inner part increases blood pressure and heart rate during bodily stress. Pancreas secrets two vital hormones that sustain a constant level of sugar or glucose in the blood for the body to have fuel that produces and maintains energy stores ("Endocrine System," n.d.).
The pineal gland in the middle of the brain releases a hormone known as melatonin that helps in regulating the wake-sleep cycle. The thyroid gland is at the lower part of the neck to regulate the metabolism of the body and parathyroid gland secret hormone that regulate calcium levels in the bone and blood metabolism (Kemp & Stoppler, n.d.). Ovaries are female gonads that produce estrogens and progesterone for maturation of reproductive organs whereas testes are male gonads that stimulate maturation of male reproductive organs. Thymus is a gland that produces vital hormones for developing cells of the immune system ("Endocrine," n.d.).
Homeostatic Control of Blood Glucose Levels:
Homeostasis can be described as the process that enables living organisms to sustain relatively constant levels of temperature, water, pH, and ions balance. This process is critical for the effective functioning of an individual because cells require a stable environment for their survival. Homeostasis mechanisms are governed by processes known as negative feedback as they respond to environmental changes through releasing molecules like hormones to restore the levels with the normal range ("Describe the Homeostatic Regulation," n.d.).
Since cells obtain energy from glucose, homeostasis control of blood glucose levels is vital because too much glucose is toxic whereas little glucose contributes to starvation. At point 1, the glucose level in the blood is within its normal range and continues to fluctuate with time due to digestion after eating and the release of insulin. The digestion process after a meal results in increased glucose levels while lower blood levels are experienced due to loss of glucose in the urine (James, 2004). Points 2 and 3 are the two pancreatic receptors for the increase and decrease of glucose respectively due to homeostasis. These receptors have the responsibility of monitoring blood glucose levels because of its significance in each cell for respiration ("Sugar Homeostasis," n.d.).
Points 4 and 5 are the liver, which acts as the storehouse for glycogen through insulin and glucagon hormones that control concentration of blood glucose. While the increase of blood sugar levels results in secretion of insulin, the decrease of these levels secrets glucagon (Paul, n.d.). As these levels are regulated through the homeostasis process, they come back to normal range as reflected by point 6. Points 7 and 8 represent type I and type II of diabetes mellitus respectively since type I diabetes mellitus is insulin dependent while type II of this disease is insulin independent ("Homeostatic Mechanisms," n.d.).
Sensory Receptors in the Human Skin:
The human skin consists of several sensory receptors that obtain information from the external environment. While the sensory receptors are located in different parts in the skin, they are mainly concerned with five distinct senses i.e. cold, pain, touch, heat, and pressure. These five categories are usually grouped together as the single sense of touch in the categorization of the five sense of the entire human body. Notably, the sensory receptors in the human skin also vary greatly based on their structure ("Sensory Receptors," n.d.).
Ruffini's end organs are highly branched nerve endings which are small swellings at the end of every branch of the nerve ending within a fluid filled capsule in the linking tissue. This sensory receptor in the human skin responds to stress or distension in the deeper dermis ("Human Skin Sensory Receptors," n.d.). While they contain a spiral of nerve endings in a swirling mass of special Schwann cells, Meissner's corpuscles are situated in the dermal papillae of hairless sections of the skin surface and respond to touch. Pacinian corpuscles are located in deep dermis or hypodermis in the skin and respond to vibration and pressure. Free nerve endings are simple receptors located at the end of sensory neurons and respond to a combination of sensations such as heat, touch, cold, and pain ("Sensory Receptors in the Human Skin," n.d.).
Merkel's disc is closely linked to the Merkel's cells that are located in the epidermis though they are located in the dermis and respond to light touch. Similarly, noiceptors are found in the dermis and respond to pain, cold, and heat since they are pain receptors ("Chapter 49," n.d.). Chemoreceptors and thermoreceptors are sensory receptors that respond to chemical sensations and respond to cold or hot temperature respectively ("Sensory Systems," n.d.). Bulboid corpulses is regarded as a thermoreceptor that responds to the sensation of cold temperatures.
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