Action Potentials & Permeability Flashcards
The best way to observe neuron electrical signals is to use
intracellular microelectrode
electrical signals produced by neurons are caused by
responses to stimuli
Two types of electrical potentials
Receptor potentials and Synaptic Potentials
Receptor potentials are due to the activation of
sensory neurons by external stimuli, such as light, sound, or heat
synaptic potentials allow…
transmission of information from one neuron to another
A fundamental problem for neurons is that their axons are not good electrical conductors.
1) How do they compensate for this?
2) What does this compensation allow them to do?
1) neurons have evolved a “booster system”
2) allows them to conduct electrical signals over great distances despite their intrinsically poor electrical characteristics.
The electrical signals produced by the neurons “booster system” are called
action potentials
What is an action potential?
a) an active response generated by the neuron
b) is a brief (about 1 ms) change from negative to positive in the transmembrane potential
the amplitude of the action potential is
independent of the magnitude of the current used to evoke it
larger currents do not elicit larger action potentials
the intensity of a stimulus is encoded in the ______ of action potentials rather than in their _________
Frequency
amplitude
If the membrane potential is made more negative than the resting potential this leads to______; if more positive, ________
What happens as a result?
Hyperpolarization: nothing very dramatic happens
Depolarization: if it passes the threshold potential, an action potential occurs
Differences in the intensity of a stimulus between action potentials, receptor potentials, and synaptic potentials
action potentials: intensity is encoded by frequency; not amplitude
receptor potentials: amplitudes are graded in proportion to the magnitude of the sensory stimulus
synaptic potentials: amplitude varies according to the number of synapses activated and the previous amount of synaptic activity.
Electrical potentials are generated across the membranes of neurons because
(1) there are differences in the concentrations of specific ions across nerve cell membranes, and
(2) the membranes are selectively permeable to some of these ions.
ion concentration gradients are established by proteins known
active transporters
What are active transporters?
Proteins that actively move ions into or out of cells against their concentration gradients.
The selective permeability of membranes is due largely to
Ion channels
What are ion channels?
proteins that allow only certain kinds of ions to cross the membrane in the direction of their concentration gradients
generate the resting membrane potential, action potentials, and the synaptic potentials and receptor potentials that trigger action potentials
Ion Transports and Ion Channels
Electrical Gradient
Difference in + and – charges across a membrane
Concentration Gradient
Difference in distribution of ions across a membrane
responsible for the resting membrane potential
A continual resting efflux of K+
the equilibrium potential, can be predicted by a simple formula called….
What is that formula?
Nernst equation
To measure the Electrochemical Equilibrium in an Environment with More Than One Permeant Ion use
the Goldman equation
Hodgkin and Katz showed that the inside-negative resting potential arises because
(1) the membrane of the resting neuron is more permeable to K+ than to any of the other ions present, and
(2) there is more K+ inside the neuron than outside.
while the resting neuronal membrane is only slightly permeable to Na+, the membrane becomes extraordinarily permeable to Na+ during the ______ and ______ phase
rising phase and overshoot phase
