Action Potentials in Squid Axons

Action Potentials in Squid Axons In 1952, Hodgkin and Huxley published a series of four papers in the Journal of Physiology (London) reporting their experiments to investigate the underlying events of the action potential. In their final paper, they derived a series of equations that describe the relationship between sodium conductance (gNa+), potassium conductance (gK+) and the membrane potential in a squid axon following electrical stimulation. Hodgkin and Huxley were awarded the Nobel Prize for this work. In this practical, you will use a computer program based on the Hodgkin and Huxley equations to show what is happening to the membrane potential, gNa+ and gK+ during and after electrical stimulation. An example of the output from the program is illustrated in figure 1. It can be seen that the electrical stimulation depolarises the membrane. Once a depolarisation of 30mV has occurred, the conductance to sodium ions increases rapidly and the membrane potential rises to +20mV. The rise in gK+ is slower in onset an d lasts for longer than the increase in gNa+. The fall in gNa+ and the associated rise in gK+ returns the membrane potential towards the resting value. Methods and Results    Q1 and 2. Investigate the effects of varying stimulus amplitude and duration by running all the simulations shown in the matrix below in Table 1: Enter a ‘X’ in the Table 1 matrix for experiments that produce an action potential, and record the peak height, amplitude, latency and threshold of any action potentials in Table 2 overleaf. For experiments that fail to elicit an action potential, enter a ‘O’ in the matrix below, and record a value of à ¯Ã¢â‚¬Å¡Ã‚ ¥ (infinity) for the latency and ‘-‘ for the other parameters in the table overleaf.    Q3. Plot two graphs to show the relationship between: (i) Stimulus strength and latency and (ii) Stimulus duration and latency. How these graphs should be plotted is not immediately obvious, and information on how to complete thi s task will not be explicitly given! The optimal solution to the problem is for you to find, but the following points are provided for guidance: It is not legitimate to plot infinity on graphs It is not appropriate to extrapolate beyond data points It is not legitimate to plot average latencies. The graphs must be plotted so that every value of latency (except à ¯Ã¢â‚¬Å¡Ã‚ ¥) is represented. Use the blank sheet on the proforma, there is no need to use graph paper. Graph 1 : Stimulus strength and latency Remember you need to distinguish different stim durations in this graph Stimulus Duration (ms) Graph 2: Stimulus Duration and Latency Make sure you distinguish different strengths as well Stimulus Strength (à ¯Ã‚ Ã‚ ­A/cm2) These can be plotted accurately using excel for your submitted report. Experiments with dual stimuli Q4. Run a simulation with the following parameters to demonstrate the absolute refractory period:    Briefly describe the responses obtained in simulations A and B in the space below: For simulation A and B in stimulus 1 they had peak heights of +17mv therefore producing an action potential. In stimulus 2, there is very little depolarisation in simulation A as peak height is -92mv. This is lower than the resting potential, therefore showing that the neuron did not fully recover from stimulus1.

ENaC and Hypertension Essay Example | Topics and Well Written Essays - 250 words

ENaC and Hypertension - Essay Example However, for individuals past the age of 45, the incidences of hypertension rise and affect more women than men [1]. In the U.S. 25% of Americans suffer from hypertension. High blood pressure varies amongst ethnic groups where African Americans have the highest risk for hypertension among Americans. Forty percent of African Americans have hypertension and it is more likely to be manifested at an earlier age than Caucasians. Hypertension is the primary cause of 25% of deaths in America today. Additionally, 47% of individuals with hypertension have blood pressure that is not under control. Most of hypertensives are resistant to common medications. They have to take more than one medication to render their blood pressure stable[3]. The pathogenesis of hypertension remains unknown. Blood pressure must be regulated to prevent damaging of vital organs. From this point, studying the molecular basis and human protein level of this disease is needed for early detection and for distinguish ing markers and designing targeting therapy. The kidneys play a major role in hypertension mainly in the maintenance of sodium balance within the body. They also maintain the balance of the volume of extracellular fluid that leads to the long term control of blood pressure. Therefore, any imbalance in sodium entry expands the blood volume leading to hormonal and vascular change in the kidneys and increasing blood pressure [2]. In relation to the various mechanisms involved in hypertension’s inheritance, two major categories exist. These are Mendelian hypertension and essential hypertension. The Mendelian form of hypertension occurs because of a single or small number of genes which are defective. These can also be either dominant or recessive [4]. In contrast, essential hypertension, which is a heterogeneous disorder of hypertension, is more complex and does not follow the kind of inheritance

Business Strategies of Marks and Spencer towards Their Business Essay

Business Strategies of Marks and Spencer towards Their Business Expansion into China - Essay Example This paper illustrates that Marks and Spencer were established in the year 1884 by Michael Marks and since then has grown rapidly to about 600 stores in the UK alone employing about 75000 individuals across the globe in diverse markets. However, the aspect of international expansion must be handled with caution as one of the most important mistakes made by multinational firms involves undermining the aspect of local sentiments and beliefs that can lead to disastrous consequences in terms of positioning of the brand in the new foreign markets. The company has a dedicated presence in about 40 nations across the globe. China holds considerable promise for Marks and Spencer for expanding its business as the nation holds a good position with regards to ease of doing business. According to a report published by the World Bank China ranks 79 among all the nations with regards to ease of doing business preceded only by India, Brazil, and Russia among the emerging markets. In addition, China is also the highest populated country in the world and its recent strides in economic growth have led to making it one of the major markets for retailers across the globe. Cities like Shanghai and Beijing score high on the list of international companies trying to expand internationally due to good market potential.A research study conducted to analyze the consumer behavior states certain key trends of the Chinese consumers that include a good growth in consumption patterns, greater sophistication of the consumers, a reduced trade up of products and brands, shift towards brand value and brand image and finally display of greater smarter purchasing trends among the consumers. In addition to this, the Chinese consumers have also become more inclined towards better service and are also influenced to some extent by Western brands.