graded potential and action potential

Question 1

graded potential: define

Answer 1

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.

Question 2

where does graded potential occur?

Answer 2

it tends to occur in dendrites of neuron and in the soma (cell body) of neuron. it mostly does not pass into axons..

Question 3

relationship between graded potential and trigger zone

Answer 3

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.

Question 4

most neurotransmitters are _____ gated ion channels.

Answer 4

ligand

Question 5

graded potential decays because:

Answer 5

1. neurotransmitters leave receptors and ion channels close

2. ions disperse inside the cell

Question 6

what is the most common cause of an inhibitory potential in neurons? why is it inhibitory?

Answer 6

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.

Question 7

depolarisation

Answer 7

the cell interior becomes less negative

Question 8

hyperpolarisation

Answer 8

the cell interior becomes more negative

Question 9

action potential: define

Answer 9

a property of excitable cells (i.e., nerve, muscle) that consists of a rapid depolarization, or upstroke, followed by repolarization of the membrane potential.

Question 10

features of action potential

Answer 10

1. stereotypical size and shape
2. propagating
3. all-or-none

Question 11

threshold: define

Answer 11

the membrane potential at which the action potential is inevitable.

Question 12

at threshold, what is the relationship between inward and outward current? what happens as a result?

Answer 12

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).

Question 13

what causes the rapid depolarisation during action potential?

Answer 13

an inward Na+ current.

Question 14

what is an overshoot in action potential?

Answer 14

The overshoot is the brief portion at the peak of the action potential when the membrane potential is positive.

Question 15

what neurotransmitters abolish action potentials?

Answer 15

Tetrodotoxin (TTX) and lidocaine. they block voltage-sensitive Na+ channels.

Question 16

what blocks voltage-gated K+ channels?

Answer 16

Tetraethylammonium (TEA)

Question 17

what causes repolarisation during action potential?

Answer 17

an outward K+ current

Question 18

how is an action potential produced?

Answer 18

see notion notes: Class notes A/Resting, Graded and Action Potential

Question 19

absolute refractory period: define

Answer 19

is the period during which another action potential cannot be elicited, no matter how large the stimulus.

Question 20

absolute refractory period: explain

Answer 20

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.

Question 21

relative refractory period: define

Answer 21

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.

Question 22

relative refractory period: explain

Answer 22

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.

Question 23

how is action potential propagated?

Answer 23

the spread of local currents to adjacent areas of membrane, which are then depolarized to threshold and generate action potentials.

Question 24

what increase action potential conductance velocity, and why?

Answer 24

1. increased fiber size: Increasing the diameter of a nerve fiber results in decreased internal resistance; thus, conduction velocity down the nerve is faster.
2. 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).

Question 25

postsynaptic action potential: define

Answer 25

a graded potential change produced in the postsynaptic neuron in response to the release of a neurotransmitter by a presynaptic terminal. may be depolarising (EPSP) or hyperpolarising (IPSP).