The Action Potential

• Neuron is at RMP (-70 mV)

• Initial depolarizing stimulus (EPSP) occurs

• Membrane potential reaches threshold (-55 mV) -> VG Na+ channels open and VG K+ channels are slow to open

• Na+ moves into the ell (depolarization)

• At AP peak, VG Na+ channels close, but VG K+ channels are fully open

• K+ leaves the cell (depolarization)

• VG K+ channels are slow to close, causing hyper polarization

• VG K+ channels close; neuron returns to RMP

Depolarization: the cell becomes more positive

Repolorization: the depolarized membrane returns to the resting membrane potential

Hyperpolarization: a membrane potential that is more negative than the resting membrane potential

Graded Potentials

What are they? Local potentials that diminish with time and distance

• Can be depolarization (EPSPs) or hyperpolarizations (IPSPs)

• Occur in the dendrites or soma (cell body) or neurone

• Caused by opening of ligand (chemical)-gated channels on the post-synaptic membrane

What happen if a single graded potential does not reach threshold?

Temporal summation = multiple graded potentials occur at once within a single neuron due to high frequency of APs from the presynaptic neuron

Spatial summation = multiple graded potentials occur at once from multiple presynaptic neurone