Neuron Physiology Flashcards
0
Q
All - or - none response
A
There either is an impulse or there is not
1
Q
What is a nerve impulse?
A
A wave of electrical fluctuation that travels along the nerve cell’s plasma membrane
- neurons are excitable and conductive
2
Q
What causes ion gates to open?
A
Mechanical, chemical, or electrical stimuli
3
Q
What is an ion channel?
A
- Protein structure that spans the membrane
- Part of it forms a gate allowing the channel to open & close
- ion flow alters relative concentrations of charges, the membrane potential and the excitation of the neuron
4
Q
Restin neurons
A
- exhibits a resting membrane potential
- produced by relative concentrations of ions across the plasma membrane
- cell is polarized because on either side of the plasma membrane there is a very localized abundance of positive or negative ions.
5
Q
Locations for graded potential ion channels
A
- dendrites of sensory neurons (medically stimulated ion channels)
- dendrites and cell bodies of interneurons and motor neurons (chemically - stimulated channels)
- rarely in axons
6
Q
How to excite a neuron
Action Potentials
A
- full scale neural/nerve impulses
- generation of an A.P. follows the all - or - none principle
- always of the same size in a particular neuron
- can travel long distances before dying out
- there is a threshold level of stimulation that us characteristic for each neuron (usually constant)
7
Q
The resting membrane potential can be maintained by:
A
- Unequal distribution of ions across the plasma membrane
- Differences in the permeability of the plasma membrane to Na+ and K+
- more of K+ will move across than Na+
- Na+ has ion channels controlling its flow
8
Q
The Na+/K+ AtPase Pump
A
- maintains resting membrane potential by pumping Na+ out of the cell and K+ into the cell (against their respective concentration gradients)
- greater overall effect on Na+ (leaks into the cell very shortly)
9
Q
Graded potentials
A
- produced when a chemically - or mechanically - stimulated ion channel is opened
- not large enough to actually become a nerve impulse
- membrane more polarized = hyperpolarizing graded potential
- membrane less polarized = depolarizing graded potential
- potentials vary in size depending on strength or original stimulus
- useful for short - distance communication only
- affects small, local area of the neuron
10
Q
Phases in generating an action potential
- Depolarizing phase
A
- starts with graded potential
- Na+ channels open
- Na+ rushes into cell & causes it to become less negative with respect to outside the cell.
- causes even more channels to open
- even more Na+ rushes in
11
Q
Phases in generating an action potential
- Repolarizing phase
A
- previous threshold opens K+ electrically - stimulated channel
- opens slowly & coincides with closing of Na+ channel
- Na+ influx slows
- K+ flows out of the cell at an accelerating rate
- cell becomes negative (repolarizing)
- channel stays open until K+ starts coming back in
- channels now close
12
Q
Absolute Refractory Period
A
- a neuron cannot be stimulated again when it’s Already undergoing depolarization
- said to be refractory to further stimulation at this point
- called absolute refractory period
- large - diameter neurons have shorter refractory periods therefore conduct more impulses over a set period of time
13
Q
Relative refractory period
A
- a neuron can be re- stimulated, but only by a larger than normal stimulus
- occurs when K+ channels are till open but Na+ channels are still open but Na+ channels have returned to their resting state
14
Q
How a nerve impulse travels
A
- along length of a neuron in be direction
- because depolarization initiates depolarization of adjacent segment of neurons*
- self - propagating impulse travels away from each local depolarization, in one direction
- positive feedback
- impulse begins at axon hillock & travels down the axon
