The figure below shows a model of electrochemical flow through a synapse, and its equivalent circuit. The synaptic gap is modelled by a shunt resistance, Rs = 300 9. Other relevant values are RM1 = 18 KS2, RM2 = 280 KS2, RM3 = 2 K82, V = 1 V. Postsynaptic Membrane (RM2 ) Equivalent Circuit: RM2 RMS RS Presynaptic - Shunt RS cell Cell Firing Pathway - Active Region RM3 (a) Explain why electrical transmission is not possible across most synapses. (Tip: Rs is much smaller than RM2 and RM3). (1 mark) (b) In electrically transmitting synapses, the synaptic gap (shunt resistance Rs) is eliminated and the current flows directly from the presynaptic to the postsynaptic cell through RM1 and RM2, then across RM3. (i) Draw a circuit that represents this situation. (1 mark) (ii) Calculate the equivalent resistance of this circuit. (1 mark) (iii) Determine the current that flows from the presynaptic to the postsynaptic cell. (1 mark) (iv) Determine the voltage across the postsynaptic membrane (RM2). (1 mark) Page 15 of 24