Nerve Impulses and Body Systems

Introduction

In the human body, various sub-systems are present which interact between one another and with the main control system of the body that is nervous system to make the functioning of the system in an effective manner. In this assignment, the way nerve impulses are generated and propagated along with endocrine functioning is to be explained. Further, the negative and positive feedback system of the body that plays a role in the regulation physiological system is to be discussed. The way kidney functions and forms urine is also to be discussed.

Task 1

1.1 Describing the way nerve impulses are generated and propagated by neuron

The nerve impulse is generated as a result of a strong internal or external stimulus which triggers chemical and electrical charges in the neuron. The exterior side of the cell membrane of the neuron has large number of positively charged sodium ions which are more in number compared to the number of negatively charged potassium ions present in the inner side of the neuron cell membrane (Alfsen et al. 2018). The generation of the nerve impulse creates difference in the permeability of the neuron cell membrane which leads to depolarization and activation of the sodium-potassium pump. During this condition, three sodium ions bind with the transporter protein and then with a phosphate group which is transferred from the ATP to the protein so that shape of the protein changes to release the sodium ions outside the membrane (Nfor and Mokoli, 2016). As soon as the sodium ions come outside, two potassium ions bind with the transporter protein with the phosphate being removed leading the protein to return to original shape and release the potassium ions inside the cell. This depolarization leads to create action potential that makes the nerve impulses to more along the neuron to reach the axon endings. After the action potential, through a series of reactions the potassium ions return inside the cell with sodium ions being sent outside to reach polarisation. The nerve impulse when reaches the axon ending it is seen neurotransmitter is released which by binding with the dendrite of the other neuron creates pathway for the nerve impulse to be relayed from one neuron to another (Barz et al. 2019).

1.2 Analysing the way synapse receives and relays nerve impulses

The gap present between dendrite of one neuron and the axon of next neuron is known as synapse. The synapse relays the signal from pre-synaptic to post-synaptic neuron with the help of neurotransmitters. For instance, the cholinergic synapse releases Acetylcholine as the neurotransmitter to relay nerve impulses. In this process, at first, an action potential is raised at the pre-synaptic neuron which changes the voltage of the neuron leading the calcium channel to open causing calcium ions to diffuse inside the pre-synaptic neuron (Caon, 2018). The high concentration of the calcium ions leads the synaptic vesicles which contain the neurotransmitter to move towards the pre-synaptic neuronal membrane. It leads the vesicle to be fussed with the membrane and the neurotransmitter to be released within the synaptic cleft. The neurotransmitter then diffuses within the cleft towards the membrane of the postsynaptic membrane. At this position, the neurotransmitter binds with complementary receptors present in the post-synaptic neuron. The increased concentration of neurotransmitter makes the ligand-gated sodium channel present in postsynaptic neuron to be opened creating an action potential which causes the nerve impulse to be transferred from one neuron to the next (Fox et al. 2017; Preobrazhenskaya, 2017).

1.3 Locating endocrine glands and function of hormones

Task 2

2.1 Describing two instances of negative feedback system in the body

2.2 Describing two instances of positive feedback system in the body

The positive feedback is referred to the process in which the action produced at the end is caused more intensely to occur in the feedback loop (Liang et al. 2019). The two examples of positive feedback in the human body are lactation and childbirth. For instance, in childbirth, the uterine walls are to be starched to continue proper birth of the baby. During this phase, a hormone named oxytocin is released which acts to causes the uterine muscles to be contracted more extensively until the birth of the baby (Gefferie et al. 2018). For instance, in the case of lactation, the suckling action by the infant stimulated the body to produce prolactin leading production and secretion of milk. The more the infant suckles the more prolactin is released which leads to increased release of breast milk (Palaparthi, 2017).

2.3 Analysing mechanism of regulation for one positive and negative feedback

The negative feedback mechanism for thermoregulation informs that with the change in the internal body temperature the sensors present in the central nervous system relays messages to the hypothalamus to control different vital organs and system for normalising the body temperature. In case the body temperature rises and it is to be cooled down, then sweat glands are activated to release sweat which is then evaporated from the skin to draw in extra heat, in turn, providing a cooling impact on the body. In addition, vasodilatation occurs in which the blood vessels inside the skin is relaxed and increased flow of blood is maintained to the skin for leading the blood to be cooled by drawing it away from the warm inner body. Thus, in this way, the heat is radiated and the boy temperature is lowered (Morrison and Nakamura, 2019). However, in condition when the body temperature is low then vasoconstriction occurs in which the blood vessels of the body are constricted allowing the decreased flow of blood to the skin, in turn, trying to retain heat by making the blood flow through the warm inner body. In addition, the thyroid glands are stimulated to release hormone to increase the metabolism of the body where through increased generation of energy in the body the temperature is controlled to normal. Moreover, to increase the temperature the brain directs the body muscles to shiver in which through small movement warmth is created to raise the temperature of the body to normal (Haman and Blondin, 2017).

The positive feedback mechanism for labour and childbirth informs that with the pressing of the cervix by the head of the foetus during birth leads the nerves in the uterine region to send signals to the brain to inform the pituitary glands to be stimulated so that oxytocin can be released. The signals are sent with the help of an action potential in the axon of the neuron responsible for secreting oxytocin created due to the stretching of the uterus. The action potential is then conducted through sensory neurons through the spinal cord to the hypothalamus. This is followed by an action potential that is conducted by axon endings of the oxytocin-secreting neuron in the hypothalamohypophysial tract extending to the posterior pituitary where oxytocin secretion is increased. The release of the oxytocin impacts the smooth muscles of the uterus to be contracted through increased sodium permeability of the myofibrils present in the uterine region. Thus, further, the baby is pushed towards the cervix the more oxytocin release is stimulated in the brain and this goes on until the baby is delivered through the cervix (Uvnäs-Moberg et al. 2019).

Task 3

3.1 Examining the structure of the kidney

The kidneys are a pair of bean-shaped structures which are present posterior and below the liver. The kidneys are surrounded by three layers with the outermost layer made up of tough connective tissue known as renal fascia. The second layer following renal fascia is the perinatal fat capsule which assists to keep the kidneys in proper position. The third layer is known as renal capsule which is the innermost layer of the kidney. There are three regions of the kidney which are cortex, medulla and hilum. The renal cortex provides a granular look as a result of the presence of nephrons which are regarded as functional unit of the organ. The medulla is made up of many pyramidal tissues known as renal pyramids and in between the gaps of the pyramids, renal columns are present through which blood vessel of the kidneys passes through (Rizzo, 2015). The renal pyramids and the cortical region present in the adjoining areas are known as lobes of the kidney. The renal pelvis connects with ureter outside of the kidney and inside the kidney the renal pelvis braches to form major calyces which further bifurcates into minor calyces. The ureter which is connected with the kidney is urine collecting tubes that help the urine to be delivered out of the kidney to the urinary bladder (Glassock and Rule, 2016).

3.2 Explaining the structure of nephron and its associated blood vessels

The nephron is referred to the microscopic functional and structural unit of the kidney which is made up of renal tubule and renal corpuscle. The renal corpuscle is made up of bunch of blood capillaries forming the glomerulus and it encompasses the Bowman’s capsule. The capsule and the tubule are connected together and they are made up of epithelial cells with the presence of a lumen. There are adjacent peritubular capillaries present surrounding the tubule which runs in between ascending and descending areas of the tubule (Oxburgh, 2018).

3.3 Describing urine production

Mechanism of Ultrafiltration:

The process through which glomerular filtration happens is known as renal ultrafiltration. In this process, the blood which is to be filtered enters the glomerulus that is bunch of capillaries present in the kidney. The glomerulus is maintained inside a cup-shaped structure placed at the end of the nephron and the capillaries in the glomerulus have small pores representing fine mesh which are present between arterioles and venules. The flow of blood through the capillaries into the venules creates a fall in hydrostatic pressure. The glomerulus is found to be sandwiched between afferent and efferent arterioles. The efferent arterioles when constricted existing the glomerulus shows resistance towards blood flow which in turn creates a pressure drop that could not have been achieved if constriction did not occur (Dorn et al. 2018). The two arterioles change their sizes to decrease or increase the blood pressure in the glomerulus. The blood to be filtered enters through the afferent arterioles and is released through the efferent arterioles which are smaller in diameter compared to the afferent arterioles. This change in pressure leads the blood to be compressed and filtered out of impurities. The unique features of the glomerulus along with the heart providing blood to the kidneys assist to maintain proper glomerular pressure for ensuring effective ultrafiltration (Michel et al. 2015).

Mechanism of selective reabsorption:

The selective reabsorption is referred to the process in which selected molecules are filtered out through the capillaries along with the nitrogenous waste products. The mechanism includes at the first the co-transport of sodium outside and potassium inside the proximal convoluted tubule (PCT) in the form of active transport through the sodium-potassium pump by using ATP for maintaining a low amount of sodium ions inside the wall. The low concentration gradient indicates that sodium ions present in the glomerular filtrate are able to passively diffuse inside the wall of the PCT. However, the sodium ions are found to lack the ability to diffuse freely across the membrane and have the ability to only enter the membrane wall through special transporter proteins. There are many natures of transporter proteins present and each of them is responsible for transporting specific nature of molecules. The concentration gradient developed for sodium is seen to provide the energy which pulls all the molecules into the wall of the PCT. The sodium ions, glucose and amino acids enter inside the PCT and 65-70% of the water present in the glomerulus filtrates through osmosis. However, urea is smaller molecule which collects inside the PCT but all the water is reabsorbed in the blood through the loop of Henle and via the collecting duct system (Lee et al. 2018).

3.4 Explaining the role of the kidney in osmoregulation

The osmoregulation is the process through which the body maintain salt and water balance across the membranes. The Anti-diuretic Hormone (ADH) has a primary role in controlling the amount of urine to be formed during osmoregulation. The process of osmoregulation allows the body to maintain low amount of water and electrolytes at a constant level. In the process, when the blood becomes more concentrated in the body that is there is little amount of water being taken in and excessive water loss occurs from the body as a result of sweating it leads to rise of plasma solute concentration (Frenkel et al. 2015). This indicates that decrease in the blood volume is seen. The osmoreceptors present in the hypothalamus detect the increased level of plasma solute level in the body and provides signal to the pituitary gland to secrete ADH. After the release of ADH, it travels towards the kidney through the blood with the help of chemical messengers. The ADH regulates reabsorption of water by raising the permeability of the DCT (distal convoluted tubule) and collecting ducts to water through opening of water channel. The ADH binding on the specific cell surface in the DCT, as well as the collecting tubules, brings water channel towards the membrane surface. The water through this water channel enters the blood capillary from the glomerular filtrate to make the urine volume hypertonic and this phenomenon is called Anti-diuresis. However, when there is high amount of water the process is reversed where ADH release is inhibited so that the collecting ducts and DCT are impermeable to water resulting in large volume of hypotonic urine and this phenomenon is called Diuresis (Kanbay et al. 2019).

Conclusion

The above discussion informs that with the help of sodium-potassium pump active potential is created which leads the nerve impulses to be relayed through the neuron. The neurotransmitters help in relaying nerve impulse from axon of one neuron to dendrite of next neuron. The positive feedback mechanism of the body includes childbirth and lactation whereas example of negative feedback mechanism includes thermoregulation and blood pressure control. The ultrafiltration is the initial step in urine formation and it is followed by selective reabsorption. The ADH plays a primary role in osmoregulation where through Diuresis and Anti-diuresis the amount of urine is controlled.

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