Exam 1 - Lecture 4

Graded potentials

small, temporary fluctuations in membrane potential restricted to the vicinity on the neuron where ion concentrations change; proportional to amount of neurotransmitter bound

Action potential

the electrical signal used for neuronal communication initiated by a really quick change in membrane voltage caused by ion currents flowing through voltage gated channels

Threshold

must be reached to trigger an action potential; reached due to opening of voltage gated Na⁺ channels

Upstroke

part of the action potential where the strong sodium influx and weak potassium efflux result in a large depolarization because voltage gated sodium channels are open while potassium channels are still closed

Downstroke

part of the action potential where strong potassium efflux and weak sodium influx result in repolarization of the membrane due to voltage gated sodium channels inactivating while potassium channels finally open

Afterhyperpolarization

brief period after the downstroke where slow-closing potassium channels continue to stay open after the action potential ends, hyperpolarizing the membrane below resting potential

Absolute refractory period

period of time after an action potential where it is impossible to generate new action potentials because voltage gated Na⁺ channels are inactivated

Relative refractory period

period of time after an action potential when enough voltage gated sodium channels have de-inactivated for another action potential to be produce, but only by a really strong stimulus to overcome afterhyperpolarization

Hodgkin-Huxley experiments

experiments that proved that Na⁺ and K⁺ were specifically leaving and entering the membrane using voltage gated channels, and that Na⁺ influx controls the early current while K⁺ efflux control the late current of the action potential

Action potentials are all-or-none because…

voltage gated sodium channels are self-regenerative because as sodium is let into the cell, the inside of the cell becomes more positive, which in turn opens more sodium channels creating a positive feedback loop

Inactivation

blocking process that closes the ion channel even while the stimulus continues

Deactivation

the normal closing of an ion channel that results from the removal of activating stimulus

Absolute refractory periods control…

one-way propagation of the action potential because action potentials can’t go backwards due to inactivated sodium channels that are left behind every action potential

Relative refractory periods control…

how the brain can use the frequency of action potentials as a way of measuring stimulus strength since during this period, only really strong stimuli can produce a back-to-back action potential

Properties of action potentials

initiated at the axon hillock, have to reach threshold potential, all or none, non-decremental, have refractory periods, and are very rapid

Saltatory conduction

occurs in myelinated axons and allows action potentials to “jump” down the axon via Nodes of Ranvier rather than traveling the entire axon, making transmission faster