Exam review questions 2 Flashcards
Which parts of a neuron are shown by a Golgi stain that are not shown by a Nissl stain?
The axons and the dendrites.
The Nissl stain distinguishes between neurons and glia, but it does not show the axons or dendrites.
What are the three physical characteristics that distinguish axons from dendrites?
1) Length: Axons can be more than 1m, dendrites rarely over 2mm.
2) Thickness:
3) Structure: Dendrites appear as trees, whereas an axon is usually singular that branches at the end.
Of the following structures, state which ones are unique to neurons and which are not: nucleus, mitochondria, rough ER, synaptic vesicle, Golgi apparatus.
Unique: Synaptic vesicle.
Non-unique: Nucleus, mitochondria, rough ER, Golgi apparatus.
What is myelin? What does it do? Which cells provide it in the central nervous system?
A white fatty substance that is generated by glial cells (Schwann cells and oligodendrocytes). It provides electrical insulation for some axons, and increases the conduction velocity of action potentials by allowing saltatory conduction.
What two functions do proteins in the neuronal membrane perform to establish and maintain the resting membrane potential?
1) They form Sodium-Potassium pumps that exchange extracellular K+ for intracellular Na+
2) They form permeable potassium channels in the membrane that allow the movement of K+ ions across the membrane, down their concentration gradient.
On which side of the neuronal membrane are Na+ ions more abundant?
Outside the cell.
When the membrane is at the potassium equilibrium potential, in which direction (in or out) is there a net movement of potassium ions?
There is no net movement of potassium ions at the equilibrium potential, since equilbrium signifies balance.
There is a much greater K concentration inside the cell than outside. Why, then, is the resting membrane potential negative?
There is an large concentration of Na+ outside the cell, and the sodium-potassium pumps exchange 2 K+ (to inside) for 3 Na+ (to outside).
When the brain is deprived of oxygen, the mitochondria within neurons cease producing ATP. What effect would this have on the membrane potential? Why?
The Sodium-Potassium pump requires ATP to function, so it would no longer be able to keep the resting membrane potential negative and pump out the Na+ as it flows in from the ion channels.
The membrane potential would depolarize.
How is the Nernst equation caclulated?
Define membrane potential (V m) and sodium equilibrium potential (E Na). Which of these, if either, changes during the course of an action potential?
V m: The membrane potential is the voltage across the neuronal membrane at any moment.
E Na: A state in which the diffusional and electrical forces of Na+ are equal and opposite, and there is no net movement of Na+ across the membrane.
The membrane potential changes during the action potential, as the membrane depolarizes. An equilibrium potential is constant.
What ions carry the early inward and late outward currents during the action potential?
Early inward current is caused by Na+ flowing inside the cell. There is a large driving force on Na+ towards the negative side of the membrane (inside the cell).
Late outward current is caused by K+ flowing out of the cell. This is because now that the membrane potential is positive, there is a large force driving K+ out of the cell, towards the negative side of the membrane (outside the cell).
Why is the action potential referred to as “all-or-none”?
What is meant by quantal release of neurotransmitter?
Neurotransmitters are released into a synapse in packaged vesicles called quanta. Quantal release is the mechanism by which most traditional endogenous neurotransmitters are transmitted throughout the body. Electrical synapses do not use quantal neurotransmitter release. The goal of any synapse is to produce either an excitatory postsynaptic potential (EPSP) or an inhibitory postsynaptic potential (IPSP), which generate or repress the expression, respectively, of an action potential in the postsynaptic neuron.
You apply ACh and activate nicotinic receptors on a muscle cell. Which way will current flow through the receptor channels when Vm = -60 mV? When Vm = 0 mV? When Vm = 60 mV? Why?
-Nicotinic ACh receptors are permeable to Na and K
*Vm= -60mV, net current inward toward Ena (causes depolarization)
*Vm= 0mV, would be the reversal potential because these is the point at which the current flow would reverse; right between Ena and Ek; NO CURRENT FLOWS
*Vm= 60mV, outward net current toward Ek (causes hyperpolarization)
This chapter discussed a GABA-gated ion channel that is permeable to Cl. GABA also activates a G-protein-coupled receptor, called the GABAB receptor, which causes potassium-selective channels to open. What effect would GABAB receptor activation have on the membrane potential?
-GABA-gated Cl ion channels would bring the membrane toward Ecl (-65mV)
*if Vm was less, activation would cause hyperpolarization
-activation of GABAb receptors would cause K-selective channels to open and bring the Vm toward Ek (-80mV)
-if Vm was less, activation would cause hyperpolarization
You think you have discovered a new neurotransmitter, and you are studying its effect on a neuron. The reversal potential for the response caused by the new chemical is -60 mV. Is this substance excitatory or inhibitory? Why?
Reversal potential is the critical value of membrane potential at which the direction of current flow reverses.
-inhibitory
- if neurotransmitter causes Vm to move toward a value more positive than the action potential threshold, neurotransmitter action would be excitatory, otherwise inhibitory
- reversal potential of -60mV suggests that the neurotransmitter activates ion channels that make the membrane more negative
- movement toward this value is likely to be more negative than the action potential threshold, making it less likely for firing (inhibition)
A drug called strychnine, isolated from the seeds of a tree native to India and commonly used as rat poison, blocks the effects of glycine. Is strychnine an agonist or an antagonist of the glycine receptor?
- blocks the effects of glycine
- antagonist
- high doses eliminate glycine-mediated inhibition in circuits of the spinal cord and brain stem
- leads to paralysis of the respiratory muscles
Why is an excitatory synapse on the soma more effective in evoking action potentials in the postsynaptic neuron than an excitatory synapse on the tip of a dendrite?
- current entering through synapse must spread spike-initiation zone; zone must be depolarized beyond threshold
- depolarization decreases as a function of distance along a dendrite
- soma is closer so it will be more effective
What are the steps that lead to increased excitability in a neuron when NE is released presynaptically?
- The NE receptor bound to a b receptor activates G-protein in the membrane.
- G-protein activates the adenylyl cyclase enzyme.
- Adenylyl cyclase converts ATP into the second messenger cAMP.
- cAMP activates a protein, kinase.
- Kinase causes a potassium channel to close by attaching a phosphate group to it. This produces little change in membrane potential but increases the membrane resistance and increases the length constant of dendrites. This enhances the response that a weak or a distant excitatory synapse produces. This effect can last longer than that of the presence of the transmitter.
List the criteria that are used to determine whether a chemical serves as a neurotransmitter. What are the various experimental strategies you could use to show that ACh fulfills the criteria of a neurotransmitter at the neuromuscular junction?
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What are three methods that could be used to show that a neurotransmitter receptor is synthesized or localized in a particular neuron?
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Compare and contrast the properties of (a) AMPA and NMDA receptors and (b) GABAA and GABAB receptors.
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Are the dorsal root ganglia in the central or peripheral nervous system?
Peripheral nervous system.
Define:
1) Anterior
2) Rostral
3) Posterior
4) Caudal
1) Pointing toward the nose / back (Latin: beak)
2) Pointing toward the nose / back (Latin: beak)
3) Pointing toward the tail / back (Latin: tail)
4) Pointing toward the tail / back (Latin: tail)
Define:
1) Dorsal
2) Ventral
3) Midline
4) Medial
1) Pointing up in mammals (Latin: “back”)
2) Pointing down in mammals (Latin: “belly”)
3) Invisible line running down the middle of the nervous system
4) Structures closer to midline