graded potential and action potential Flashcards
graded potential: define
small membrane potential change that decays with both time and distance. its effect is brief and local.
a potential change of variable amplitude and duration that is conducted decrementally. it has no threshold or refractory period.
where does graded potential occur?
it tends to occur in dendrites of neuron and in the soma (cell body) of neuron. it mostly does not pass into axons..
relationship between graded potential and trigger zone
the closer an input is to the trigger zone, the greater effect it will have on the likelihood of an action potential being fired down an axon.
most neurotransmitters are _____ gated ion channels.
ligand
graded potential decays because:
- neurotransmitters leave receptors and ion channels close
2. ions disperse inside the cell
what is the most common cause of an inhibitory potential in neurons? why is it inhibitory?
the entry of Cl-. since the ions are negatively charged, a hyperpolarisation occurs.
an inhibitory potential can also be caused by K+ exiting the neuron.
depolarisation
the cell interior becomes less negative
hyperpolarisation
the cell interior becomes more negative
action potential: define
a property of excitable cells (i.e., nerve, muscle) that consists of a rapid depolarization, or upstroke, followed by repolarization of the membrane potential.
features of action potential
- stereotypical size and shape
- propagating
- all-or-none
threshold: define
the membrane potential at which the action potential is inevitable.
at threshold, what is the relationship between inward and outward current? what happens as a result?
At threshold potential, net inward current becomes larger than net outward current.
The resulting depolarization becomes self-sustaining and gives rise to the upstroke of the action potential.
If net inward current is less than net outward current, no action potential will occur (i.e., all-or-none response).
what causes the rapid depolarisation during action potential?
an inward Na+ current.
what is an overshoot in action potential?
The overshoot is the brief portion at the peak of the action potential when the membrane potential is positive.
what neurotransmitters abolish action potentials?
Tetrodotoxin (TTX) and lidocaine. they block voltage-sensitive Na+ channels.
what blocks voltage-gated K+ channels?
Tetraethylammonium (TEA)
what causes repolarisation during action potential?
an outward K+ current
how is an action potential produced?
see notion notes: Class notes A/Resting, Graded and Action Potential
absolute refractory period: define
is the period during which another action potential cannot be elicited, no matter how large the stimulus.
absolute refractory period: explain
the inactivation gates of the Na+ channels are closed when the membrane potential is depolarized. They remain closed until repolarization occurs. No action potential can occur until the inactivation gates open.
relative refractory period: define
An action potential can be elicited during this period only if a larger than usual inward current is provided.
It begins at the end of the absolute refractory period and continues until the membrane potential returns to the resting level.
relative refractory period: explain
The K+ conductance is higher than at rest during this period, and the membrane potential is closer to the K+ equilibrium potential and, therefore, farther from threshold. more inward current is required to bring the membrane to threshold.
how is action potential propagated?
the spread of local currents to adjacent areas of membrane, which are then depolarized to threshold and generate action potentials.
what increase action potential conductance velocity, and why?
- increased fiber size: Increasing the diameter of a nerve fiber results in decreased internal resistance; thus, conduction velocity down the nerve is faster.
- myelination: Myelin acts as an insulator around nerve axons and increases conduction velocity. Myelinated nerves exhibit saltatory conduction because action potentials can be generated only at the nodes of Ranvier (gaps in the myelin sheath).
