MMED2933: Fundamental Neuroscience- Fictitious Neural Circuit- Neuroscience Assignment Help

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Neuroscience Assignment Help:

Task: Here is a fictitious neural circuit, consisting of 4 nerve cells, A,B,C,D. Cell A makes excitatory synapses onto both cells B and C through the release of acetylcholine, acting on nicotinic receptors. Cell C makes an inhibitory synaptic contact, via releasing GABA onto GABAA receptors on cell D, giving rise to an inhibitory synaptic potential. Cell B releases glutamate which acts on NMDA receptors on Cell D. Cell D is also cholinergic (like cell A). A microelectrode has been inserted into each of these cells so that we can record membrane potential, including synaptic potentials and action potentials. A second microelectrode (in grey) has been inserted into cell A; this can be used for passing controlled amounts of current (measured in nA) into cell A to artificially shift its membrane potential. Overleaf is a diagram (Figure 2) showing the electrical activity in each of the four cells in millivolts, as recordings of membrane potential (A-mV, B-mV, C-mV and D-mV), together with a fifth trace which shows the current injected into cell A's cell body in units of nanoAmps, via the grey microelectrode (AnA). The recordings last a total of about 120 milliseconds. The sequence of events All three cells are initially at their resting membrane potential (represented by dotted lines). Then about - 0.4 nA of hyperpolarizing current is injected into Cell A for about 8ms, via the grey electrode, causing a hyperpolarisation which is visible in A-mV. Then, about 5ms later, a depolarising current pulse is injected via the same grey microelectrode, into cell A, with an amplitude of +0.4nA and a duration of 8ms. This causes a depolarisation of Cell A which triggers an action potential in the axon hillock of cell A which is followed by a short after-hyperpolarisation lasting about 15ms. The action potential in cell A then propagates down its axon including both branches and triggers the release of acetylcholine from its synaptic terminals (shown as small solid black triangles in Figure 1). This transmitter acts on nicotinic receptors on Cells B and C, causing excitatory post-synaptic potentials (“EPSPs”) lasting for a period of about 45ms. These depolarising synaptic potentials are large enough to evoke 2 action potentials in cell B, but only evoke one action potential in cell C. These then propagate down their respective axons to their terminals. Cell C releases GABA, which acts on GABAA receptors on cell D to evoke an inhibitory postsynaptic potential (“IPSP”), while cell B releases glutamate onto NMDA receptors on cell D causing summating EPSPs, which then evoke an action potential in cell D. PART A. (5 MARKS/18) In the diagram below, twenty features are numbered (1-20 in brackets on the diagram). The dashed arrows or dashed lines either point to a feature or define the start and finish of a feature). There is also a list of 26 neural characteristics overleaf (A-Z). Match each feature (1-20) with the characteristic (A-Z) that best describes it (not all the characteristics correspond to features) – (Note: no answer/characteristic is used twice): ART B In this part of the assignment, you are required to use your understanding of the basis of electrophysiological activity to predict the effects of a range of drugs, toxins, ion substitutions and current pulses on the activity in the same circuit as Part A. Overleaf we have printed 8 copies of the same figure, with the original traces shown in pale pink with their original resting potentials shown as dotted lines. If you can’t see the pink (original) traces, then use a screen copy– you will definitely need to see exactly how each trace has changed! I will put a JPEG file copy of part B online orientated in landscape to make this easier. Superimposed on each pink original is a solid thicker black trace, showing how a particular drug has modified each cell’s activity. For Cell A, the modified traces are designated #1 AmV, #2 A-mV, #3 A-mV etc to #8 A-mV in the 8 copies. For cell B they’re named: #1 B-mV, #2 B-mV, #3 B-mV etc to #8 B-mV. For cell C....I'm sure you get the picture. The tricky bit is that I have shuffled the CellA's traces between figures 1-8. For example, #1 A-mV may have been swapped with #4 A-mV. Perhaps #3 A-mV may have been shifted to #8 A-mV. This means that in each of the 8 panels, all the Cell A traces are jumbled up as are all the cell B traces, and Cell C traces and Cell D traces. However, I have not mixed up Cell A traces with Cell B etc (I am not that mean). Please note: the two parts of cell A's traces (A-mV and A-nA) have been kept together. The aim of this exercise is for you to use your knowledge of neuronal function to determine which traces belong to which drug/toxin/ion substitution or current pulse regime. Please bear in mind that each drug/toxin or ion substitution (but not current pulses) is added to the fluid bathing the entire circuit (ie: it is not being applied to a single cell; it is being applied to all four cells at the same time). It is important to remember that some drugs or ion substitutions can affect several cells or synaptic mechanisms, whereas others are highly specific for one cell. Some drugs will have absolutely no effect on some cells if they don't express the target receptor! In addition, a drug can modify the activity of one cell, which then leads to subsequent, modified responses in the next cell in the chain. So to work this out, you need to understand how the circuit in Figure 2 really works and how each change would affect Cell A, then Cell B and Cell C and, in turn, Cell D. PART C – multiple choice questions 53. The four major components of the cell membrane are: a. cholesterol, phospholipids, glycolipids and proteins b. triglycerides, proteins, phospholipids and glycolipids c. phospholipids, cholesterol, triglycerides and proteins d. phospholipids, cholesterol, triglycerides and saccharides e. cholesterol, glycolipids, proteins and saccharides 54. Ion channels always have one of the following features – which? a. a charged region that detects transmembrane voltage (membrane potential) b. sugar groups coupled to the region that faces the inside of the cell c. a transmembrane pore that allows ions to pass through under some conditions d. binding sites for transmitter substances e. intracellular binding sites for cell metabolites 55. The equilibrium potential for an ion is defined as the potential at which: a. the number of positively charged ions leaving the cell exactly equals the number of negatively charged ions entering the cell b. Na+, K+ and Cl- ions are in equilibrium across the membrane c. the tendency for the ion to move down its concentration gradient is exactly counterbalanced by its tendency to move down its electrical gradient d. there are equal numbers of ions inside and outside the membrane e. the Na+/K+ co-transporter exactly counterbalances the movement of ions through ion channels in the membrane 56. Calcium ions contribute little to the resting membrane potential in most cells despite the fact that they have a large transmembrane concentration gradient and hence a very positive equilibrium potential. Why? a. because Ca++ ions are too insoluble to contribute to resting potential b. because Ca++ ions are too large to pass through proteinaceous ion channels c. because there are no Ca ion channels in normal cells d. because Ca++ ions are so toxic to the cell e. because Ca ion channels are rarely open at resting membrane potential 57. Three important elements involved in nerve cell electrical signaling are potassium, sodium and calcium. Which of the following shows these 3 ions, in descending order of concentration, as they occur in the cytoplasm of a healthy neuron? a. K+, Na+, Ca++ b. K+, Ca++,Na+ c. Na+, Ca++, K+ d. Na+, K+, Ca++ e. Ca++, K+, Na++