Module 4- Midterm-Nerves Flashcards
1
Q
what are excitable cells?
A
-use resting membrane potential to generate an electrochemical impulse called action potential
2
Q
what is an action potential?
A
- language of the nervous system
- the way the nerve cells communicate with it
- necessary for muscle contractions
3
Q
what are the components of a nerve?
A
- dendrites
- cell body
- axon
- myelin sheath
- nodes of ranvier
- collaterals
- terminal bouton or axon terminal
4
Q
voltage gated channel
A
- found in muscle and nerve cells
- voltage K and voltage Na
- found on axon
- essential for the generation of AP
- open when the cell becomes more positive
5
Q
voltage gated Na channel
A
- depolarization of membrane occurs when membrane potential becomes more positive
- activation gates open
- Na+ flows in
- inactivation gate closes, channel cannot open
- channel returns to resting state and the inactivation gates open again
5
Q
voltage gated Na channel
A
- depolarization of membrane occurs when membrane potential becomes more positive
- activation gates open
- Na+ flows in
- inactivation gate closes, channel cannot open
- channel returns to resting state and the inactivation gates open again
6
Q
Absolute refractory period
A
- during the period where the inactivation gate is closed, the gate will not open regardless of the strength of stimuli
- no AP can take place
7
Q
voltage gated K channels
A
- only contains one gate
- opens when membrane depolarizes
- start opening when inactivation gates close on sodium
- depolarization of membrane
- brief pause, then K+ channels open
- K flows in
- gate closes and returns to resting config.
- channel ready again
8
Q
What are the steps of an action potential?
A
- strong depolarization at the axon hillock
- Na+ channels open, Na+ rushes in
- cell depolarizes to 35+mv
- Na+ channels become inactivated, K begin to open
- K+ rushes out of the cell
- membrane begins to repolarize
- K continues to flow out and membrane hyperpolarizes to -90
- K channels close and no more K leaks
- membrane returns to resting potential
9
Q
What is the relative refractory period?
A
- period during action potential where the membrane is hyperpolarized
- period is caused by the K+ channel, as they are slow to open and close (allows K to leave the cell after -70mv)
- during this period in time, it is possible to fire another AP, however a larger stimulus is required to reach the threshold
10
Q
what is the threshold for generating an AP
A
- the value is -55mv
- this is the period during an AP where almost ALL Na gates are opened
- if you reach this value, you will have an AP
- the movement of other ions will not be sufficient enough to counteract the potential
11
Q
Axon propagation
A
-movement of AP down an axon to the terminal
12
Q
axon propagation down an unmyelinated nerve
A
- inside the membrane is positive (due to influx of Na)
- positive charge is attracted to and moves toward resting part of membrane, creating current
- adjacent area of membrane now depolarizes, triggering Na+ to move in, creating a new AP
- repetition of this procedure causes propagation of the AP along the membrane
13
Q
Unidirectional Nature of the AP
A
- the reason that the AP cannot go backward in direction when the previous membrane returns to resting state is because the inactivation gates
- you cannot open these gates again no matter the amount of stimulus, therefore an AP cannot occur
- by the time that these gates open again, the AP will be too far down the axon to affect the area
14
Q
Saltatory Conduction
A
- voltage-gated channels only exist at the nodes of Ranvier, gaps in the myelin
- positive charge from the existing is attracted to and moves toward next node of Ranvier which is negative
- node of Ranvier depolarizes, Na+ rushes in and another AP is generated
- repetition of the process, causes AP to be propagated along the axon
- quicker than unmyelinated
