Lab #7: Neurophysioogy of Nerve Impulse Flashcards
Which neuroglial cells are responsible for producing a myelin sheath?
What division of the NS are they in?
- Schwann Cells: PNS
- Oligodendrocytes: CNS
What part of the neuron receives the information/stimulus
dendrites
Where part of the neuron does a true AP start?
axon hillock
What part of the neuron are NT released?
axon terminals
What device is use to measure membrane potential?
voltmeter (mV)
Define membrane potential
the charge difference between the inside and outside of the cell
What is membrane potential when a neuron is at rest/RMP?
-70mV
Define depolarization
occurs when MP becomes more positive (influx of Na+)
Define repolarization
occurs when MP becomes more negative (efflux of K+)
Define hyperpolarization
occurs when repolarization overshoots and MP becomes more negative than RMP
How do MP changes occur?
when ions flow through membrane channel (LG and VG ion channels)
When do VG ion channel open?
open at a certain charge/by depolarization
What type of channel is chemically regulated?
LG ion channels; open when bound to ligand/neurotransmitter
What type of channel is voltage regulated?
VG ion channels; respond to charge/voltage
T/F: ions can flow across myelinated parts of the axon
F, myelin inhibits VG Na+ channels, therefore ions can only flow around unmyelinated parts of axon (Nodes of Ranvier)
What are the Nodes of Ranvier?
unmyelinated areas of axon
Will an AP be conduced faster through a myelinated or unmyelinated axon?
myelinated because AP will travel from node to node, thus increasing speed
Define threshold
the minimum MP required for an AP (the “rapid” depolarization part)
What is the voltage value for threshold? What happens at this point?
-55mV; VG Na+ channel open -> influx Na+ -> rapid depolarization
Is the amplitude of the AP in activitiy 3 generated the same as you would expect in an intact neuron inside the human body?
No, because human neuronal AP peaks at +30-40mV, but the exercise peaked at 100mV
In activity 3, you increased the voltage of the stimulus beyond the minimum voltage needed to trigger an AP. Did the amplitude of the AP change? Why/why didn’t it change?
- increasing stimulus did NOT increase amplitude of AP -> AP are “all or none” (either happens or doesnt)
- a change in size/strength of stimulus only increases frequency of AP
Compare the effects of tetrodotoxin (TTX) and Lidocaine. What do they do the same, and what do they do differently?
BOTH: block/inhibit VG Na+ channels; inhibit AP (but not equal)
TTX: irreversible and faster inhibition of VG Na+ channels
Lidocaine: slow inhibition of VG-Na channls
Define inactivation
a channel is open but is blocked, so NO ions can travel through -> act as if it were closed
Why is it harder to generate a second action potential during the relative refractory period?
in RRP, it is difficult to generate a 2nd AP because you are further away from threshold because VG-K+ are slow to close (must be at threshold; -55mV to have AP)
Why is it important that a neuron has a refractory period?
limits how many AP + signals can be sent; controls release of NT
What two main factors determine AP conduction velocity?
presence of myelin and diameter of axon
-> large diameter means increased AP conduction velocity
Which well-known disease is caused by the deteroration of myelin?
multiple sclerosis
In what ways would breakdown of myelin affect functions of the nervous system?
if no myelin along axon -> slower AP because no saltatory conduction
What was the effect of lowering/removing Ca++ ions from the extracellular fluid?
if no Ca++ -> no fusion of vesicles with pre-synaptic membrane -> no NT released into synaptic cleft -> no AP
What was the effect of adding Mg++ ions to the extracellular fluid?
- Mg++ prolongs duration of AP -> decrease freq of AP
- suppresses activity of neuron (excitability)
T/F “When a neuron is stimulated with a high-intensity stimulus, a large action potential is produced, and more neurotransmitters are released at the axon terminal.”
Explain your answer
False
large stimulus = increase freq of AP (does not generate a “large AP”)
however, increase in freq of AP = increase release of NT
How does the increase in frequency of an AP affect NT release?
more NT will be released
