Unit A - Describing the Nerve Impulse and Synapse Flashcards
What is the charge outside of the axon during resting membrane potential?
Positive relative to the inside
What is the charge inside of the axon during resting membrane potential?
Negative relative to outside
What are the three things that the cell membrane of the axon contains? What is needed for them to work?
- Non-Voltage Gated Ion Channels - do not require a charge to work (some require chemicals instead)
- Voltage-Gated Ion Channels - Require a specific charge to work
- Na+/K+ Pump - Require STP to work
At what potential difference is an axon’s resting membrane potential?
-70mV
What is the polarization of the axon?
Process of generating a resting membrane potential (the potential to do work).
What are the two things that are negatively charged that help achieve polarization? Why do they not go through the cell membrane?
Negatively charged proteins - too large to go through the membrane
Chloride ions - cannot go through the selectively permeable membrane
What does the sodium-potassium exchange pump do in the axon?
Uses ATP to pump 3 sodium ions out of the axon and 2 potassium ions into the axon.
uses a single ATP
Some ion channels in the axon membrane are ____ ____.
Why?
Always open
To ensure the inside of the axon is negative relative to the outside of the membrane.
What is another word for nerve impulses?
Action Potentials
When is the nerve impulse/action potential established?
When the axon is depolarizing. (passes the threshold)
When a stimulus is applied to an axon, what initially happens to the axon?
It triggers the opening of a few non-voltage gated Na+ gates
When no voltage passes through voltage-gated Na+ and K+ gates they remain ____
Closed
What is the threshold needed to trigger the action potential?
-55mV
What happens when a stimulus occurs but does not reach threshold potential?
Returns to normal without triggering.
What happens when the threshold is reached and the action potential is triggered?
What happens to the polarity?
What is the voltage peak?
Voltage-gated NA+ channels open allowing even more NA+ to diffuse into the cell.
Polarity is reversed abruptly (becoming depolarized)
+35mV
What happens when peak voltage is reached in a neuron?
- Causes the closing and inactivation of voltage-gated NA+ channels
- Voltage-gated K+ channels open (allowing for K+ to diffuse out)
*The NA+/K+ pump helps assist the repolarization process.
What is the process called of decreasing action potential?
is it fast?
Repolarization - very fast (ms - s)
What is the period where repolarization happens? What cannot be done in this interval?
The period is called the refractory period. An impulse cannot be activated during this time.
What happens after repolarization has reached the resting potential? Why?
It causes hyperpolarization (lower voltage than resting potential) because the K+ channels close slowly.
What happens after hyperpolarization?
The membrane then returns to its resting potential.
How does the action potential travel down the axon?
Why doesn’t it go backwards?
As the sodium moves into the axon, it diffuses into other parts of the axon, activating the threshold.
because of the refractory period. (that’s all the detail necessary to know)
Where are Action potentials generated?
Where the axon membrane is exposed.
what is continuous conduction?
Where does it occur?
Action potentials occur at every location along the membrane.
Unmyelinated neurons.
What is faster continuous conduction or saltatory conduction?
Why?
Saltatory conduction
fewer channels open, shorter recovery, and less ion flow
What is Saltatory conduction?
Action potentials that “jump” from one node of Ranvier to the next.
What is the threshold level?
The size of the stimulus necessary to make a response.
What is the all or none response?
Increasing the intensity of stimuli above threshold will not produce an increased nerve impulse, speed, or force of contraction.
What are two ways intensity detection is interpreted?
- Amount of neurons stimulated
- Increased frequency of action potentials.
What is a Synapse?
Small spaces between neurons or between neurons and effectors.
What is a Neuromuscular Junction?
They are the specific synapses between a motor neuron and a muscle.
What are the seven Steps to fire a synapse.
- Nerve impulse (action potential) moves along the axon to the end plate (axon terminal/presynaptic) Which has small vesicles containing chemicals called neurotransmitters.
- The neurotransimitters (ex: acetylcholine) are released from the presynaptic neuron and travel to the post-synaptic neurons via diffusion.
- Neurotransmitters bind to receptors on the postsynaptic dendrite.
- An excitatory neurotransmitter, OPENS cheically gated sodium channels → causing depolarization
- Action potential!
- The neurotransmitter is eventually deactivated by an enzyme (ex. Cholinesterase), resulting in the closure of cheically gated sodium channels.
- Post-synaptic neuron begins repolarization. Componenets of neurotransmitter get reabsorbed by presynaptic knob and repackaged in vesicles.
What is acetylcholine?
A common excitatory neurotransmitter.
What is Cholinesterase?
An enzyme that breaks down acetylcholine (neurotransmitter)
What is the difference between excitatory vs. inhibitory Neurotransmitters?
Excitatory - Stimulates an action potential
Inhibitory - prevents an action potential
What is summation?
Many different neurons may influence a single neuron. Summation is the outcome of the simultaneous release of two or more excitatory and inhibitory neurotransmitters in a synapse.
