Hyperpolarised membranes, neurons

An inhibitory input increases the influx of Cl to make the inside of the neuron more negative. This hyperpolarisation, the inhibitory postsynaptic potential (IPSP), takes the membrane potential further away from threshold and firing. It is the mirror-image of the EPSP and will reduce the chance of an EPSP reaching threshold voltage. 

Figure 2.9 Hyperpolarisation-activated cation current 4 and its role in pacemaking in a guinea-pig thalamic relay neuron. (Adapted from Figs 2 and 14 in McCormick, DA and Pape, H-C (1990) J. Physiol. 431 291-318. Reproduced by permission of the Physiological Society.) (a) Records showing the time-dependent activation of the h-current by hyperpolarisation and its deactivation on repolarising, (b) Interpretation of rhythmic activity in a thalamic relay neuron. (1) The inter-spike hyperpolarisation activates 7h to produce a slowly rising pacemaker depolarisation. (2) This opens T-type Ca " channels to give a more rapid depolarisation, leading to (3) a burst of Na" spikes (see Fig. 2.8). At (4) the depolarisation has closed (deactivated) the h-channels and has inactivated the T-channels. The membrane now hyperpolarises, assisted by outward K+ current (5). This hyperpolarisation now removes T-channel in-activation and activates 7h (6), to produce another pacemaker potential...

The Na" channel has a receptor site for cyclic GMP when cyclic GMP is bound, the channel is closed. This leads to a decrease in the intracellular Na ion concentration, resulting in hyperpolarisation of the cell membrane. This decreases the release of the neurotransmitter glutamate into the synapse that connects the photoreceptor cell to the bipolar neurones. In this specific case, a decrease in the neurotransmitter concentration in the synapse is a signal that results in depolarisation of the bipolar cell. The action potential in the bipolar cells communicate with ganglion cells, the axons of which form the optic nerve. Thus action potentials are generated in the axons which are... 

The GABAA receptor is now believed to be the major target site for anaesthetic action. The GABAA receptors exist as a family of subtypes with their pharmacology determined by their composition. GABAA receptors are pentameric and comprise of two a, two 3 (or 0), and one y (or s) subunits, which assemble to form a chloride-sensitive pore. When the receptor is activated, transmembrane chloride conductance increases, resulting in hyperpolarisation of the postsynaptic cell membrane and functional inhibition of the postsynaptic neurone. 

HTi ia,ib, id,ie,if Gfc type Inhibition of adenylyl cyclase decreased production of cAMP membrane hyperpolarisation inhibition of neuronal firing. 

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