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An Action Potential in a Neuron Essay - 2501 Words

Action potential An action potential is a rapid electrical impulse where the resting membrane potential is increased by roughly 100mv. This is due to the rapid changes in membrane permeability to sodium and potassium ions. An action potential is only formed if the threshold value is exceeded which is why it is known as an all or none response. Action potentials only occur in electrically excitable cells as these cells possess voltage activate channels which open in response to the depolarisation of cells. These cells are neurons which use electrical signals for nervous conduction and myocytes which use electrical signals for muscle contraction. The formation of an action potential depends on the following things 1) gating (opening and closing) of potassium and sodium channels which changes the permeability properties. The gating of these channels depends on the membrane potential and time 2) intracellular concentrations and extracellular concentrations of sodium, potassium,calcium ions 3) membrane properties which include, resistance During an action potential, membrane potential rapidly rises and becomes more positive and creates spikes which propagate long distances along nerve/muscle. Conduction allows info from sensory organs to brain. How action potential rises?
The events of an action potential were studied on a giant axon of the squid. This is because the axons of squid are unmyelinated, have large diameters (500 to 1000 micrometers) and the potentials are easily measured from the inside. It is also possible to measure the intracellular and extracellular concentration of sodium ions. When electrodes were placed in the inside fibre to excite it, there was a rapid increase in concentration of sodium ions inside the cell. To confirm that the sodium ions were causing the action potential, the concentration of sodium ions in the extracellular solution were decreased by replacing some sodium ions with sucrose; this consequently reduced the amplitude of the action potential. The first stage of the action potential is the 'initial depolarisation' in which the membrane potential becomes more positive. This occurs due to a stimulus such as electrical stimulation, mechanical compression or application of chemicals. In chemical stimulation substances like acetylcholine stimulates uptake of sodium ions into nerve cells. The depolarisation of the cell is detected by voltage gated sodium channels which open in response to the membrane becoming more positive. However an action potential is only triggered when sufficient sodium ion channels are opened and the threshold value of the cell is exceeded.

The paper is one of the two recipents of the “Innovation and Potential Impact Award” of NIER track.

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Action Potential Essay - 665 Words - Free Essay …

5. Explain how a non-mylenated neuron can maintain a resting potential and undergo an action potential. 9 marks

We propose to carefully document collaboration strategies employed in the context of a specifically designed virtual world environment that supports distributed usability evaluations. The system called INspect‐World has been successfully employed for teaching the cognitive walkthrough usability inspection method in an undergraduate HCI class with 79 student participants. An initial analysis of 36 hours of screen recording reveals interesting team learning and collaboration behaviors at different stages of the usability inspection session. We see our findings encompassed in the dimensions of collaboration technology, human‐centeredness, and learning in particular. This paper describes the twofold motivation behind the project. Our ambition is to provide design insights in the form of carefully documented collaboration strategies for novel teaching tools in software engineering education. We also aim to support the development of virtual world based tools for distributed software engineering processes in the industry sector.

First an initiating injury transforms an elderly brain into an elderly brain on a trajectory towards expressing . The injury could be anything from a serious bump on the head to a highly traumatic event such as the loss of a spouse. The initiating injury leads to the second step which is chronic nervous tissue inflammation. This is where the Age-Based Hypothesis encompasses deposition since inflammation of brain tissue activates the deposition cycle. In the third step, the chronically inflamed brain tissue moves into a new state (change-of-state) that may kick off any of several intracellular molecular cascades that lead to synaptic dysfunction and neuronal death. It’s synaptic dysfunction and neuronal death that result in dementia.

An Action Potential in a Neuron

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Bavidra kulendrarajah Describe the generation of an action potential in smooth and cardiac muscle The cardiac muscle is myogenic as it can generate its own action potential at a constant rate which leads to the heart pumping in a regular rhythm. The cardiac action potential originates in a specialised knot of myocytes known as the sinoatrial node which is found in the right atrium at the upper end of the crista terminalis. In these myocytes the membrane potential depolarises spontaneously and once threshold is reached an action potential is generated which propagates to other myocytes within the heart which are connected by gap junctions. As the SAN is responsible for generating the action potential at a regular rate of about 60-100 beats per minute it is often referred to as the pacemaker, however its activity can be modulated by inputs of the autonomic nervous sytem; the vagus nerve decreases the heart rate whereas sympathetic nerves increase the heart rate. Once the action potential is generated in the SAN it is then propagated to the right and then the left atrium within about 40ms. The impulse is then propagated to the atrio-ventricular node which is found in the base of the right atrium. The impulse is prevented from spreading to the ventricles due to the atrioventricular ring made of non conduction fibrous tissue. In order for the impulses to reach the ventricles the impulses are propagated through the atrioventricular bundle of HIS which originates from AV node and divides into a left and right branch either side of the interventricular septum. This bundle then terminates as purkinje fibres which conduct action potential to the ventricular myocytes and causes simulataneous contraction in both ventricles from the apex upwards. The action potentials generated in different regions of the heart vary in their initiation time, shape and duration. This occurs because the heart is a heterogenous organ where the myocytes in different regions are specialised for specific functions and this results in the cells having a differing permeability to different ions due to them having a distinct set of ion channels. Another factor affecting action potential is that different regions of the heart have differing membrane capacitance. Myocytes that are found in the SAN, AVN are specialised in generating action potentials, whereas atrial and ventricular myocytes are specialised in conduction and the myocytes that make up the bundle of his and purkinje fibres are specialised in conducting the impulses. Sino-atrial node The heart has three intrinsic pacemaking tissues which are the SA, AV nodes and the purkinje fibres. The key function of these tissues is to spontaneously depolarise the membrane to threshold and generate action potentials at a regular rhythm. The primary pacemaker is the SAN node as it generates the highest frequency of action potentials and it is these that are propagated around the heart. However if the myocytes in the SAN are damaged, the role of setting the heart rate is taken over by the AVN node. The maximum diastolic potential that occurs during phase 4 (occurs after repolarisation) is roughly between -60mv and -70mv. In comparison to the atrial and ventricular myocytes the resting membrane potential is less negative and this is due to the large influx of sodium ions through the sodium ion channels. However the resting membrane potential is not stable and it gradually depolarises to a threshold of about -55mv. The main reason why the

Essay On Action Potential - Oxbridge Notes
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