01 May INSTRUCTIONSThis assignment is worth 17% of your final mark. Print out this PDF, preferably in colour. If you don’t
INSTRUCTIONS
This assignment is worth 17% of your final mark. Print out this PDF, preferably in colour. If you don’t have a
colour printer, then use the screen version alongside a black and white printout so that you can see the pink
traces in figures 2,3&4. This is important. Fill in all answers on the back sheets of your printout. Then, when
you are happy with your answers, copy them onto the FLO answer form. PLEASE NOTE: ONCE YOU
OPEN THE ONLINE ANSWER FORM, YOU WILL HAVE ONLY ONE HOUR IN WHICH TO
ENTER ALL OF YOUR ANSWERS. AFTER 60 MINUTES, IT WILL CLOSE, WHETHER OR NOT
YOU HAVE FINISHED. We will not re-open the site!!! All answers must be filled on the online form.
Attempt every question. Late submission results in 5% deduction per day or part day unless an extension is
granted in advance. The assignment closes at 5pm on Monday 29th April 2019.
____________________
BACKGROUND
Figure 1 shows a fictitious neural circuit, which includes parts of 6 neurons: A, B,C,D and the axons of cells E
and F. A-D are simple cells with a soma and axon but no dendrites. Cell A makes nicotinic, cholinergic
excitatory synaptic connection onto Cell C; cell B makes a glutamatergic (AMPA receptor) synapse onto cell C,
which in turn makes an inhibitory synaptic connection, via GABA acting on GABAA receptors with Cell D.
Cell D uses ATP as its fast transmitter.
Recording microelectrodes in the cell
bodies of A,B,C&D measure the membrane
potential (Vm) of each cell, over 190ms. We
We do not record cells E and F, but we can
stimulate their axons together (at the jagged
arrow) with a stimulating electrode. Note that
axons of A,B and C are thick; axons of
D&F are of intermediate diameter and axon of
cell E is very thin. Cell F uses 5-HT (acting on 5-HT3 receptors) as its transmitter and cells D and E are both
purinergic, releasing ATP onto P2x receptors.
• Figure 2 shows Vm of neurons A-D, in millivolts over a period of about 190ms.
• All four cells are initially at their resting membrane potentials (shown by black dashed lines).
• We apply a small shock, via a stimulating electrode (a small stimulus artefact appears simultaneously on
all 4 traces), which initiates 1 action potential in axon E and 1 in axon F at exactly the same moment.
• Action potentials in E&F then travel down to their terminals and evoke excitatory post-synaptic
potentials in both cell A and cell B, triggering one action potential in A and two in B.
• Action potentials in A and B then propagate down their respective axons, leading to summating
excitatory synaptic potentials in Cell C, which also fires an action potential
• Cell C’s action potential then propagates down its axon, eventually releasing gamma amino butyric acid
which acts on GABAA receptors on cell D, causing an inhibitory synaptic potential.
PART 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 and
ion substitutions on the activity of the same circuit. All the
information you need is provided in this assignment text.
An example is given in Figure 3. Note that the original
control traces (no drugs – exactly as shown in Figure 2) are
included (as faint pink lines) and the traces in the presence
of the drug is the thicker black line. Original resting
membrane potentials are shown as dotted lines – this should
help you work out what has changed.
Attachments:
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