which part of the neuron undergoes graded potentials
membrane
title: Graded potential text: Graded potential Graded potentials are changes in membrane potential that vary in size, as opposed to being all-or-none. They arise from the summation of the individual actions of ligand-gated ion channel proteins, and decrease over time and space. They do not typically involve voltage-gated sodium and potassium channels. These impulses are incremental and may be excitatory or inhibitory. They occur at the postsynaptic dendrite as a result of presynaptic neuron firing and release of neurotransmitter, or may occur in skeletal, smooth, or cardiac muscle in response to nerve input. The magnitude of a graded potential is determined by the strength title: Graded potential text: summated IPSPs, in an area of membrane reach the cell's threshold potential. Graded potential Graded potentials are changes in membrane potential that vary in size, as opposed to being all-or-none. They arise from the summation of the individual actions of ligand-gated ion channel proteins, and decrease over time and space. They do not typically involve voltage-gated sodium and potassium channels. These impulses are incremental and may be excitatory or inhibitory. They occur at the postsynaptic dendrite as a result of presynaptic neuron firing and release of neurotransmitter, or may occur in skeletal, smooth, or cardiac muscle in response to nerve title: Membrane potential text: +100 mV is the full operating range of membrane potential, the effect is that Na channels always pull the membrane potential up, K channels pull it down, and Cl channels pull it toward the resting potential. Graded membrane potentials are particularly important in neurons, where they are produced by synapses—a temporary change in membrane potential produced by activation of a synapse by a single graded or action potential is called a postsynaptic potential. Neurotransmitters that act to open Na channels typically cause the membrane potential to become more positive, while neurotransmitters that act on K channels typically cause it to title: Graded potential text: of the stimulus. Graded potentials that make the membrane potential less negative or more positive, thus making the postsynaptic cell more likely to have an action potential, are called excitatory postsynaptic potentials (EPSPs). Depolarizing local potentials sum together, and if the voltage reaches the threshold potential, an action potential occurs in that cell. EPSPs are caused by the influx of Na or Ca from the extracellular space into the neuron or muscle cell. When the presynaptic neuron has an action potential, Ca enters the axon terminal via voltage-dependent calcium channels and causes exocytosis of synaptic vesicles, causing neurotransmitter to be title: Graded potential text: of Cl or efflux of K. As with EPSPs, the amplitude of the IPSP is directly proportional to the number of synaptic vesicles that were released. The resting membrane potential is usually around –70 mV. The typical neuron has a threshold potential ranging from –40 mV to –55 mV. Temporal summation occurs when graded potentials within the postsynaptic cell occur so rapidly that they build on each other before the previous ones fade. Spatial summation occurs when postsynaptic potentials from adjacent synapses on the cell occur simultaneously and add together. An action potential occurs when the summated EPSPs, minus the