BMB 1 - Neurophysiology Flashcards
What is Ohm’s law?
V = IR
Voltage = Current * Resistance
What is the Nernst equation?
E = (RT/ZF) x ln ([outside cell] / [inside cell])
What is the Goldman-Hodgkin-Katz equation?
True/False.
The Nernst equation gives the equilbrium potential for a single ion across a membrane.
True.
The Goldman-Hodgkin-Katz equation is like the Nernst equation but with multiple ions and with account taken for what other factor?
The relative permeability of the membrane to each ion species
True/False.
Passive electrical responses depend mainly on the strength of the membrane’s resistance.
True.
(I.e. cable properties)
Which is quicker, the conduction velocity of an action potential or that of the post-synaptic / electrotonic potential?
The post-synaptic / electrotonic potential
Post-synaptic / electrotonic potential cause a ________ (decreasing/increasing/non-decremental), _______ (graded/all-or-nothing) response.
Action potential cause a ________ (decreasing/increasing/non-decremental), _______ (graded/all-or-nothing) response.
Post-synaptic / electrotonic potential cause a decreasing, graded response.
Action potential cause a non-decremental, all-or-nothing response.
________ (small/large) diameter axons conduct action potentials more rapidly than ________ (small/large) diameter axons.
Large diameter axons conduct action potentials more rapidly than small diameter axons (smaller diameters have a higher resistance).
Which has a higher excitability (lower threshold) for action potential induction, small or large neurons?
Large
(larger area for voltage gate recruitment)
Myelinated axons conduct ________ (faster/slower) than non-myelinated axons of the same diameter.
Myelinated axons conduct faster than non-myelinated axons of the same diameter/
Name five forms of excitable cell.
- Neurons
- Skeletal muscle
- Cardiac muscle
- Smooth muscle
- Certain endocrine cells
True/False.
If the membrane permeability to a given ion is decreased, the transmembrane potential will move toward the Nernst potential for that particular ion.
False.
If the membrane permeability to a given ion is increased, the transmembrane potential will move toward the Nernst potential for that particular ion.
__________ refers to the ease with which ions can flow across a membrane.
Conductance refers to the ease with which ions can flow across a membrane.
In order to create a refractory period, depolarization leads to a temporary _________ of Na+ channels and a temporary _________ of K+ channels.
In order to create a refractory period, depolarization leads to a temporary inactivation of Na+ channels and a temporary activation of K+ channels.
Axons only have ion channels for which ion(s)?
Na+ and K+
(neuronal somata, dendrites, and excitable cells contain a wide variety of channels — most neurons also contain Ca2+-activated K+ channels and K+ channels activated by low [ATP])
What is effective in eliminating Na+ channel inactivation?
Only activated proteolytic enzymes on the inside
Which (or both) of the following have activation gates?
Which (or both) of the following have inactivation gates?
Na+ channels, K+ channels
Na+ channels, K+ channels
Na+ channels only
The absolute refractory period is most dependent on the number of what?
Voltage-gated Na+ channels
Name the toxin:
it selectively blocks Na+ current by fitting into the extracellular channel opening.
Tetrodotoxin
Name the toxin:
it selectively blocks K+ current from inside the membrane surface.
Tetraethylammonion
Describe the activation and inactivation of Na+ channels during the action potential cycle.
In an excitable cell, if the membrane permeability to K+ is increased, then the membrane potential approaches closest to the equilibrium potential value of which one of the following?
a. EK b. ENa c. ECl d. ECa
a. EK
In an excitable cell, if the membrane permeability to K+ is decreased, then the membrane potential approaches closest to the equilibrium potential value of which one of the following?
a. EK b. ENa c. ECl d. ECa
b. ENa
(think of membrane potential as a ratio between K+ and Na+ potentials)
A patient is given a drug that produces an adverse reaction, causing neuronal membrane permeability to increase to all ions. Which one of the following changes in the resting membrane potential, or action potentials, would most likely occur?
a. Resting membrane potential would approach EK
b. Resting membrane potential would not change much
c. Resting membrane potential would approach zero mV
d. action potentials would increase in amplitude
c. Resting membrane potential would approach zero mV
- If you increase the membrane permeability to more than one ion, then the equilibrium potential will approach the algebraic sum of all of these (all of them are going to depolarize towards 0) .*
- This happens in hypoxia or ischemia - blockade of synaptic transmission - then the membrane becomes leaky to all ions.*
This will be on the test
A 45-year-old woman is brought to the ER complaining of numbness and tingling sensations, difficulty walking in a coordinated fashion, and labored breathing. The symptoms appeared progressively after eating a meal at a local restaurant. The tingling began in the lips and mouth and spread to the face, neck, arms, and rest of the body. The meal included shrimp cocktail, salad, steak, a baked potato, and chocolate cake, and coffee for dessert. The patient has no history of neuromuscular disorders. Physical examination shows that superficial reflexes are absent and both deep tendon reflexes and responses to painful stimuli are hypoactive. The resident on duty suspects shellfish poisoning as the diagnosis (the toxic agent being saxitoxin) if one could place microelectrodes in the patient’s nerves and muscles, one would find normal resting membrane potentials. Action potentials would be smaller in amplitude, slower to rise to the peak, and somewhat increased in duration. Which one of the following choices best explains these effects of saxitoxin on action potentials?
a. Increased membrane permeability to K+
b. Decreased membrane permeability to K+
c. Blockade of voltage gated K+ channels
d. Activation of voltage-gated Na+ channels
e. Blockade of voltage-gated Na+ channels
e. Blockade of voltage-gated Na+ channels
- Saxitoxin is similar to tetrodotoxin. A 1:1 blockage - some voltage-gated sodium channels are not blocked and able to have action potentials.*
- AP amplitude reduced because fewer voltage-gated Na+ channels to recruit (explains why it is all now slower).*
- .Problem in CNS- brisk reflexes (release of control from upper neurons) o Distribution is more suggestive of peripheral neuropathy - reflexes are hypoactive - lower motor neuron problem.*
Which one of the following choices best represents the mechanism directly underlying overshoot of a typical neuronal or skeletal muscle action potential?
A. increased membrane permeability to Na+
B. increased membrane permeability to K+
C. increased activity of the Na-K pump
D. Decreased activity of the Na-K pump
A. increased membrane permeability to Na+
Which one of the following choices best describes the mechanisms responsible for repolarization of the action potential?
a. Activation of Na-K pump
b. Increased membrane PNa alone
c. Increased membrane PK alone
d. Na inactivation plus increased K+ activation
e. Inactivation of PNa alone
f. Inactivation of PK alone
d. Na inactivation plus increased K+ activation
Which one of the following mechanisms has the greatest influence in preventing a second action potential from summating with a previous action potential?
a. Hyperpolarizing afterpotential
b. Activation of the Na-K pump
c. Absolute refractory period
d. Relative refractory period
c. Absolute refractory period
Conduction velocity is proportional to the _________ of the nerve fiber, the _________ of the myelin sheath, and the _________ length
Conduction velocity is proportional to the diameter of the nerve fiber, the resistance of the myelin sheath, and the internodal length.
Myelinated axons use __________ (‘jumping’ or ‘leaping’) conduction.
Myelinated axons use saltatory conduction.
True/False.
The resistance of myelin sheaths is greater than that of axoplasm.
True.
True/False.
Excitability and action potential threshold are positively correlated.
False.
Excitability and action potential threshold are inversely correlated.
Give an example of a disease state that results in the following:
action potentials can be triggered spontaneously from zones of injury (i.e. there are ectopic foci at points of damage).
Multiple Sclerosis - paresthesias as a result of action potentials triggered in ectopic foci of demyelinated central axons
Which ion channel type is heavily concentrated in the nodal spaces of the axon?
Which is heavily concentrated in the internodal membrane?
Na+
K+
Describe the A nerve fibers (including relevant subtypes, if any).
Fairly large fibers
Aα - Efferent motor
Aβ - Afferent sensory
Aγ - Efferent motor
Aδ - Afferent sensory (pain)
Describe the B nerve fibers (including relevant subtypes, if any).
Preganglionic autonomic fibers
Describe the C nerve fibers (including relevant subtypes, if any).
Small, unmyelinated fibers that mediate pain
True/False.
Most axons are the wider ‘A’ fibers.
False.
Most axons are the smaller‘C’ fibers.
Describe each of the following for a large diameter axon:
Conduction velocity
Action potential threshold
Excitability
Amplitude
Fast
Low
High
High
Describe each of the following for a small diameter axon:
Conduction velocity
Action potential threshold
Excitability
Amplitude
Slow
High
Low
Low
Which two nerve fiber subtypes mediate pain?
Aδ and C
In large diameter axons, the internal resistance is _______ than in a small diameter axon.
In large diameter axons, the internal resistance is less than in a small diameter axon (more voltage-gated sodium channels).
Are compound action potentials all-or-nothing or graded?
Graded
(Remember, compound action potentials are the sum of all the APs of various axons within a single nerve fiber - so, some are active and some are inactive - leading to varying compound AP amplitudes.)
How can you increase the compound action potential of a particular nerve?
Increase the stimulus
(i.e. increase the recruitment of axons within the nerve fiber)
Why is it beneficial that Aδ and C fibers are relatively small (as compared to the other fiber types)?
Larger stimuli are needed to produce pain
(smaller nerves require more stimulation than larger nerves)
In cases of nerve damage, percutaneous measuring of conduction velocity will show ________ (normal, slower, quicker) speeds.
In cases of nerve damage, percutaneous measuring of conduction velocity will show slower speeds.
True/False.
In stimulating the median nerve to activate the thenar muscles, the more distal the stimulus is given, the longer it takes the action potential to reach the muscles.
True.
In cases of carpal tunnel syndrome, will conduction velocity be delayed for motor nerves or sensory nerves or both?
Both.
Although nearly all peripheral nerves are myelinated by Schwann cells, which two are myelinated by oligodendrocytes?
CN I, CN II
(hence why patients with MS are prone to optic neuritis)
If internodal areas of axon become demyelinated (like in MS), the uncovered _________ channels will open when they encounter the action potential, essentially forming a barrier.
If internodal areas of axon become demyelinated (like in MS), the uncovered potassium channels will open when they encounter the action potential, essentially forming a barrier.
What adaptation may restore conductive ability in demyelinated axons (e.g. in patients with MS)?
An increase in axonal sodium channel density
(to overcome the uncovered potassium channels)
Why is 4-amino pyridine a potential option for MS treatment?
It is a potassium channel blocker
(demyelinated neurons have uncovered potassium channels, thus inhibiting action potential conduction)
What effect does hypocalcemia have on (1) the amount of neurotransmitter released in a synapse and (2) the action potential threshold?
(1) Decreased
(2) Lowered
The amount of transmitter released is proportional to amount of ______ in the nerve terminal.
The amount of transmitter released is proportional to amount of Ca2+ in the nerve terminal.
The action potential threshold is largely decided by concentrations of what ion?
Calcium
(potassium is the resting state; sodium is the height of the action potential amplitude; calcium decides the threshold)
What effects do IPSPs have on the resting potential of a cell?
Hyperpolarization
(e.g. -65 mV to -70 mV)
Give the words coded in the following acronyms:
EPSP
EPP
MEPP
IPSP
EPSP — excitatory post-synaptic potential
EPP — end-plate potential
MEPP — spontaneous miniature endplate potential
IPSP — inhibitory post-synaptic potentials
Which of the following are depolarizing potentials?
Which are hyperpolarizing?
EPSP
EPP
MEPP
IPSP
EPSP, EPP, MEPP
IPSP
A. [Ca++] in terminal A must decrease
A. Lambert-Eaton syndrome
