Excitatory postsynaptic potentials

The AMPA receptors for glutamate, the nicotinic acetylcholine receptor and the 5-HT3-receptor for serotonin are cation channels (Table 1). When they open, the major consequence is a sudden entry of Na+, depolarization and an excitatory postsynaptic potential (EPSP Fig. 1). 

Figure 1.4 Ionic basis for excitatory postsynaptic potentials (EPSPs) and inhibitory postsynaptic potentials (IPSPs). Resting membrane potential ( — 70 mV) is maintained by Na+ influx and K+ efflux. Varying degrees of depolarisation, shown by different sized EPSPs (a and b), are caused by increasing influx of Na. When the membrane potential moves towards threshold potential (60-65 mV) an action potential is initiated (c). The IPSPs (a b ) are produced by an influx of Cl. Coincidence of an EPSP (b) and IPSP (a ) reduces the size of the EPSP (d)...

Figure 5.2 Temporal summation. Multiple excitatory postsynaptic potentials (EPSPs) produced by a single presynaptic neuron in close sequence may add together to depolarize the postsynaptic neuron to threshold and generate an action potential.

Figure 5.3 Spatial summation. Multiple excitatory postsynaptic potentials (EPSPs) or inhibitory postsynaptic potentials (IPSPs) produced by many presynaptic neurons simultaneously may add together to alter the membrane potential of the postsynaptic neuron. Sufficient excitatory input (A and B) will depolarize the membrane to threshold and generate an action potential. The simultaneous arrival of excitatory and inhibitory inputs (A and C) may cancel each other out so that the membrane potential does not change.

Imon, H., Ito, K., Dauphin, L. McCarley, R. W. (1996). Electrical stimulation of the cholinergic laterodorsal tegmental nucleus elicits scopolamine-sensitive excitatory postsynaptic potentials in medial pontine reticular formation neurons. Neuroscience 74, 393-401. 

FIGURE 6-1 Path of excitation in a simplified spinal reflex that mediates withdrawal of the leg from a painful stimulus. In each of the three neurons and in the muscle cell, excitation starts with a localized slow potential and is propagated via an action potential (a.p.). Slow potentials are generator potential (g.p.) at the skin receptor the excitatory postsynaptic potentials (e.p.s.p.) in the interneuron and the motoneuron and end-plate potential (e.p.p.) at the neuromuscular junction. Each neuron makes additional connections to other pathways that are not shown. 

Both NMDA and AMPA receptor components of excitatory postsynaptic potentials (EPSPs) are produced by the brief (1 ms) appearance of free transmitter in the synaptic cleft (Fig 15-10A). Synaptically released glutamate thus... 

EPSP excitatory postsynaptic potential HIF hypoxia-inducible factor... 

Excitatory postsynaptic potentials (EPSPs), spikes from, 172... 

Activation of ionotropic mechanisms creates postsynaptic potentials. An influx of cations or efflux of anions depolarizes the neuron, creating an excitatory-postsynaptic potential (EPSP). Conversely, an influx of anions or efflux of cations hyperpolarizes the neuron, creating an inhibitory-postsynaptic potential (IPSP). Postsynaptic potentials are summated both... 

When receptors are directly linked to ion channels, fast excitatory postsynaptic potentials (EPSPs) or inhibitory postsynaptic potentials (IPSPs) occur. However, it is well established that slow potential changes also occur and that such changes are due to the receptor being linked to the ion channel indirectly via a second messenger system. 

B. Long-term potentiation in the dentate gyrus recorded in vivo. The graph plots the early rising slope of the field excitatory postsynaptic potential (EPSP) in response to low frequency stimulation (700 pA, 100 ms, 0.05 Hz). Four trains of high frequency stimulation (700 pA, 82.5 ms, 400 Hz) were dehvered at time 0. This produced an immediate increase in the EPSP slope (post-tetanic potentiation) and a sustained relatively constant enhancement that lasted for at least 60 minutes. Representative traces are included below the graph. Note the obvious increase in size of the superimposed population spike (downward deflection). 

Whittington MA, Traub RD, Jeffreys JG (1995) Synchronized oscillations in interneuron network driven by metabotropic glutamate receptor activation. Natime 373 612-615 Whittington MA, Traub RD, Faulkner HJ, Stanford IM, Jeffreys JG (1997) Recurrent excitatory postsynaptic potentials induced by synchronized fast cortical oscillations. Proc Natl Acad Sci U S A 94 12 198-12 203... 

Each of their receptors transmits its signal across the plasma membrane by increasing transmembrane conductance of the relevant ion and thereby altering the electrical potential across the membrane. For example, acetylcholine causes the opening of the ion channel in the nicotinic acetylcholine receptor (AChR), which allows Na+ to flow down its concentration gradient into cells, producing a localized excitatory postsynaptic potential—a depolarization. 

When an excitatory pathway is stimulated, a small depolarization or excitatory postsynaptic potential (EPSP) is recorded. This potential is due to the excitatory transmitter acting on an ionotropic receptor, causing an increase in cation permeability. Changing the stimulus intensity to the pathway, and therefore the number of presynaptic fibers activated, results in a graded change in the size of the depolarization. When a sufficient number of excitatory fibers are activated, the excitatory postsynaptic potential depolarizes the postsynaptic cell to threshold, and an all-or-none action potential is generated. 

Acetylcholine and agents acting at the autonomic ganglia or the neuromuscular junctions interact with nicotinic cholinergic receptors to initiate the end plate potential in muscle or an excitatory postsynaptical potential in nerve. The nicotinic receptor in skeletal muscle is a pentamer composed of four distinct subunits. 

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