Exam #3 Short Answer Practice Questions
Explain the regenerative property of the action potential.
During the action potential, an active inward current produced by depolarization spreads passively inside the axon and depolarizes an adjacent membrane region. This results in generation of another action potential in this adjacent region, and the cycle repeats; hence, the regeneration of the action potential.
You are working with a cell that is permeable to Cs+ and Mg2+ . The concentrations of Cs+ and Mg2+ in/out of the cell are as follows (in mM): ICF (mM) [Cs+] 100 [Mg2+ ] 15 & ECF (mM) [Cs+] 10 [Mg2+] 150. Calculate the equilibrium potential for each of the ions. You record from the cell and find that it has a resting membrane potential of -40 mV. Assume another cell releases a ligand that binds to an ion receptor channel on your cell that allows Mg2+ to pass through through the membrane. What would happen to the membrane potential?
ECs+ = -58mV EMg2+ = +29mV The membrane potential would depolarize because GHK predicts that Vm will move to the equilibrium potential (+29 mV) of the ion the cell is most permeable to.
Compare and contrast electrical and chemical synapses.
Electrical synapses allow for fast signal transmission and bidirectional communication between cells connected via an electrical synapse. Chemical synapses allow for a broad range of postsynaptic responses, but the transmission is slower in chemical synapses than electrical synapses.
What evidence indicates that EPPs are composed of MEPPs?
Experiments using Ca2+ and curare in the study of acetylcholine release at the neuromuscular junction led to the discovery of quantal fluctuations in the amplitude of EPPs. The amplitude of the smallest EPPs is similar in size to that of a single MEPP, and increments in the EPP response occur in units about the size of single MEPPs
What are the main structural and functional differences between ionotropic and metabotropic receptors?
Ionotropic receptors are ligand-gated channels that permit the flow of ions when stimulated. Metabotropic receptors are not directly associated with an ion channel; they bind to G-proteins and initiate an intracellular cascade of events leading to changes in membrane permeability
How does the voltage sensitivity of K+ conductance contribute to the action potential?
It enables the falling phase, allowing the action potential to finish running its course. Depolarization slowly activates the voltage-dependent K+ conductance, causing K+ to leave the cell and repolarizing the membrane potential toward EK. The hyperpolarization of the membrane potential causes the voltage-dependent K+ conductance to turn off, allowing the membrane potential to return to its resting level.
Describe the roles of NSF and SNAPs, SNAREs, synaptotagmin, and synapsin in neurotransmitter secretion. Which one is key in the initiation of transmitter release by Ca2+ ?
NSF and SNAPs: prime synaptic vesicles for fusion SNAREs (synaptobrevin, syntaxin, SNAP-25): link vesicle with the presynaptic membrane Synaptotagmin: binds calcium to trigger fusion of vesicles with the presynaptic membrane. Synapsin: keeps vesicles tethered within the reserve pool. Synaptotagmin is key in the initiation of transmitter release.
What is patch clamping? Explain how it can be used to show that properties of voltage-sensitive Na+ and K+ channels are responsible for the action potential.
Patch clamping is a technique in which a recording pipet is used to grip a cell membrane and record the electrical potential or flow of ions through one ion channel. The patch clamp method allows experimental control of the membrane potential, and it can be used to characterize the voltage dependence of membrane currents. It allows measuring minute electrical currents such as those originating from a single ion channel.
What is the magnitude of a typical neuron's resting membrane potential? Why do neurons and other cells have a negative resting membrane potential?
A typical neuron's resting membrane potential is approximately -65 mV. It is negative because resting membrane is permeable mainly to K+, and there is a concentration gradient for K+ across the plasma membrane with roughly a 13-fold excess of K+ inside the cell.
Give an example of a neurotransmitter in each category below. a) Purine b) Biogenic amine c) Amino acid d) Peptide
a) ATP b) Dopamine, norepinephrine, epinephrine, histamine, serotonin c) Glutamate, aspartate, GABA, glycine d) Substance P, methionine enkephalin, neurokinin A, neuropeptide K, neuropeptide, and any of the peptides listed in Figure 6.22
What are the three major types of ionotropic glutamate receptors, and why were they given their specific names? Why are two types of these receptors considered to be particularly important?
The three major types are NMDA, AMPA, and kainate receptors; they were named after their respective exogenous agonists. NMDA and AMPA receptors are particularly important because they are present in most central excitatory synapses.
