NEUS 609 - Ramsey's Practice quiz

membrane potential (Vm)

The chord conductance equation sets the ___ equals to the conductance-weighted sum of equilibrium potenital

inward

A particular mammalian cell displays a chloride equilibrium potential of -60 mV. Due to a high resting potassium conductance and K+ Nernst quilibrium potential of -90 mV the cell’s resting potential is at -80 mV.  What is the direction of the chloride CURRENT at rest?

driving force = Vm-Eref = -80mv - (-60mv) = - 30 mV

properties essential to maintain stable negative Vm

• lipid bilayer impermeable to ions

• maintenance of asymmetric, constant ion concentrations across the bilayer

• a NET ionic current of 0 across the membrane

Main importance of ion channels

ion channels can achieve larger flux of ions than pumps and secondary transporters

larger surface area = larger capacitance, different lipid composition = different capacitance,

Capacitance is an intrinsic electrical property of biological membranes that describes the total amount of charge the membrane can store when exposed to a given potential. Charging (or discharging) of the membrane capacitor also influences the speed at which the membrane potential may be changed.

What properties of membrane determine their capacitance?

characteristics of voltage-gated Na+ channels

• activate and inactivate rapidly at depolarized potentials

• during AP upstroke, Na+ current decreases with the driving force for Na+ movement

• Na+ current decreases when Na+ channels inactivate

  • Most Na+ channels are inactivated during the first part of the repolarization phase

characteristics of K+ voltage-gated channels

• responsible for repolarizing phase of AP

• remain open as long as the axon is depolarized

characteristics of AP

• upstroke of AP is results of massive INCREASE in Na conductance

• at BOTH the most positive and the most negative potentials during AP, inward and outward currents are exactly equal

characteristics of refractory period

• threshold potential cannot be measured during the absolute ___

• during relative __ Na+ channels have begun to recover from inactivation

• K+ conductance contributes to the length of the relative refractory period

true statements about AP threshold and threshold potential

• threshold potential refers to where the Na+ channels start to open

• an increase in the K+ conductance will drive the threshold potential positively

• an increase in number of Na+ channels in the membrane shifts the threshold potential negatively

increased diameter

when the axon has an ___ then conduction velocity will increase, and more depolarizing current will be available in the adjacent membrane segment because internal resistance decreased

end plate potential

at NMJ, the ___ is created by a current with a reversal potential close to 0mV

decrease

removing Ca2+ from region surrounding the NMJ would ___ the release of ACh from motor neuron terminals

characteristics of mammalian electrical synapses

• small molecule including cAMP can pass through it

• depolarizing current will be transmitted to the postsynaptic membrane more rapidly than transmission at NMJ

Facilitation

___ at the NMJ refers to

• increased EPP amplitude when motor neuron is rapidly and repetitively stimulated

• is a presynaptic mechanism for increasing synaptic strength

• increased ACh release due to higher presynaptic Ca2+ levels at higher stimulation rates

reduce

Prolonged treatment with hemicholinium (a blocker of choline transporter) will ___ mEPP amplitude

0.4

A normal mEPP amplitude is ___ mV

increase

Exposure to neostigmine (an AChase inhibitor) will ___ mEPP amplitude

ACh

mEPP amplitude is determined by the amount of ___ in a synaptic vesicle

ACh action at the NMJ

• size of motor endplate potential (EPP) depends on magnitude of presynaptic depolarization

• When nAChRs in the motor endplate are initially activated by ACh, the driving force for Na⁺ entry is much larger than the driving force for K⁺ efflux

characteristics of EPSP

• EPSPs depolarize the cell towards the current reversal potential of the ligand-gated receptor

• Causes a depolarization lasting only a few milliseconds that subsequently decays back towards the cell's RMP

• Is excitatory because the cell is depolarized to its threshold potential

hyperpolarizing IPSP

In a neuron is found to selectively express GABA_A receptors, have a RMP = -80 mV, and a TP = -60 mV.  Assume the following equilibrium potentials for permeant ions:  E_Na = +60 mV, E_K = -90 mV, Ca = +130 mV, E_Cl = -85 mV.  Exposure of the cell to GABA is most likely to cause:

• GABA = chloride channel ligand

• RMP higher than chloride Eref so Cl comes in

LTP facts

• LPT may represent a cellular correlate of learning and memory

• Coincident stimulation of weak and strong synaptic inputs to the same neuron is can greatly improve synaptic function at the weak synapse

• Postsynaptic mechanisms for LPT may include augmented Ca²⁺ entry and activation on CaM kinase

• Presynaptic mechanisms of LPT may include generation of NO by neuronal nitric oxide synthase

• Increases in the number of synapses on each dendritic spine may follow LTP induction