Chapter 19 Flashcards
What is a membrane potential?
-the differences in electrical charges across the plasma membrane
How does the potential on the outside of a cell compare to he potential on the inside?
- outside: positive
- inside: negative
What does it mean to be polar?
-the membrane has a negative pole and a positive pole
What does depolarized and hyperpolarized mean?
- depolarized: moving more positive from the -70mV to the +30mV
- hyperpolarized: becoming more negative than -70mV
What is resting membrane potential?
- -70mV
- when the neuron is not conducting electrical signals
What are gated channels?
-allow specific molecules to diffuse across the membrane only when the gate channel is opened
In what direction does potassium and sodium move?
- potassium leaves the cell
- sodium enters the cell
What are stimulus gated channels?
-ion channels that open in response to a sensory or chemical stimulus
What are voltage gated channels?
-ion channels that open in response to voltage fluctuations
How does the sodium potassium pump contribute to the resting membrane potential?
- it pumps 3 sodium ions out of the cell
- it pumps 2 potassium ions into the cell
- ‘pumpkin” - pump k+ in
How do the leaky channels contribute to the resting membrane potential?
- they allow some potassium to leave the cell
- it causes the outside to stay more positive
What is a local potential?
-the slight shifts away from the resting membrane but not big enough for an action potential
What is excitation? This causes which channels to open? How does this affect membrane potential?
- depolarization
- stimulus triggers the opening of the Na+ channels
- the inside of the cell becomes way more positive
What is inhibition? This causes what channels to open? How does this affect membrane potential?
- hyperpolarization
- stimulus triggers the opening of the K+ channels
- the inside of the cell becomes more negative than the original resting potential
Local potentials are also called what?
-graded potentials
A local potential’s depolarization is related to the magnitude of the stimulus in what way?
-the amount of depolarization equals the amount of the stimulus
Where do local potentials travel?
- they are isolated to one region of the plasma membrane
- don’t travel to the end of the neurons
What is summation?
-the adding of local potentials in the attempt to reach the threshold potential thus creating an action potential
What is an action potential?
-membrane potential of an active neuron
What is the refractory period? Absolute? Relative?
- brief period which a local area of an axon’s membrane resists restimulation
- absolute: 0.5 ms after the threshold potential is surpassed it WILL NOT respond to any stimulus
- relative: the membrane is repolarizing but only responds to very strong stimuli
How does the magnitude of the stimulus relate to the action potential?
-the increase of magnitude of the stimulus causes a higher frequency NOT a higher response
How are action potentials conducted down the axon?
- as the reversal in polarity happens, the channels open and close
- this happens all along the membrane, one segment after another
Can action potentials move in either direction?
- no, only afferent or efferent
- the refractory period makes sure of this
What is the myelin sheath?
-insulated areas that resist ion movement
