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Neurology > Neurophysiology (2) > Flashcards

Neurophysiology (2) Flashcards

0
Q

Where does the AP originate in response to the monosynaptic or myostatic stretch reflex?

A

In the peripheral process of a sensory neuron ( the cell body of which lies in the dorsal root ganglion)

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1
Q

What causes the stimulus for the AP fired in response to testing a tendon reflex response?

A

Stretch of muscle spindle fibers is transduced into a graded electrical signal, called a receptor potential

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2
Q

What nerve is the signal transferred to from the sensory neuron in the stretch reflex? Where in the spinal cord is this located

A

Alpha-motoneuron, located in the spinal cord ventral horn

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3
Q

Other than the alpha motoneuron, what nerve does the afferent sensory nerve synapse on in the spinal cord?

A

Interneuron. May inhibit firing of the motoneuron

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4
Q

What provides the stimulus for activation of a voltage-charged gate?

A

Charged amino acids

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5
Q

What are two mechanisms that can contribute to the selectivity pore of ion channels?

A
  1. Narrow pore (only certain molecules can pass; steric hindrance)
  2. Charged region in pore
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6
Q

What is Ohm’s Law?

A

Voltage = current X resistance. V= IR

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7
Q

How do resistance and conductance (G) relate?

A

Resistance = 1/ conductance

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8
Q

Which biological structures act as resistors in a neuron? How then is resistance controlled?

A

Ion channels. Act like variable resistors and resistance is controlled by channel gating.

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9
Q

What biological structure serve as a capacitator in neurons? What are the consequences of having capacitators?

A

Lipid bilayer. Electrical signals are slowed by the storage of charge in the membrane (capacitative element)

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10
Q

What is the time constant? What does it determine?

A

Time for membrane potential to fall to 1/e of original potential charge. Determines time period over which electrical signals can be integrated in a cell. Voltage is maximal at the point of stimulation and decays exponentially with distance from that point.

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11
Q

At rest, what ion are neuronal cell membranes permeable to?

A

Primarily K+

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12
Q

What does the Nernst equation determine?

A

The membrane potential at equilibrium if the membrane were only permeable to one ion.

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13
Q

What is the equilibrium potential in neurons for K+? Na+? Cl-?

A 
K+ = -100 mV
Na+ = +50 mV
Cl- = -60 mV
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14
Q

What is the resting membrane potential for neurons typically?

A

-70 mV

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15
Q

What does the Goldman-Hodgkin-Katz equation predict?

A

The membrane potential at equilibrium when all permeant ions are taken into account

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16
Q

What two active pumps are responsible for maintaining the necessary ion concentration for the resting membrane potential?

A
  1. Na/K ATPase

2. Ca2+ ATPase

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17
Q

What does the complicated geometry of neurons mean for the membrane potential?

A

It is not the same at all points in the membrane (not isopotential) at a given time

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18
Q

Increasing what parameter will increase the time constant in electrotonic or passive signal propagation?

A

Increasing diameter of cable. Larger diameter means less contact with the membrane, so charge doesn’t leak as much

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19
Q

What causes the progressive decay in amplitude in passive (electrotonic) signal propagation?

A

Leakage of charge across membrane

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20
Q

There is also a slowing of response in passive signal propagation, what is responsible for this?

A

Charging of the membrane capacitance along the neuron

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21
Q

What type of signal is an active signal, that cannot be modeled by a simple RC circuit?

A

Firing of an AP

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22
Q

What is the undershoot, in which the membrane potential falls to less than the original called?

A

Afterhyperpolarization

23
Q

What indicates that selectivity is maintained but but that a different ion species dominates membrane permeability during depolarization, compared to K+ at rest?

A

The fact that membrane potential overshoots 0 mV. (Goes up to + 30)

24
Q

What are the two major types of neural electrical signals?

A
  1. Graded potentials

2. Action potentials

25
Q

Graded potentials are ________ responses. Action potentials are ______ responses.

A

Passive; active

26
Q

Why are action potentials/active responses voltage-dependent?

A

Because they rely on the opening of voltage-gated ion channels

27
Q

What is responsible for the upstroke in an AP?

A

Increase in membrane permeability to Na+

28
Q

What is responsible for the downstroke in an AP?

A

Inactivation of Na+ channels

29
Q

What is responsible for the undershoot or afterhyperpolarization in an AP?

A

Increased potassium conductance due to voltage-gated K channels remaining open for a bit after the Na channels have been inactivated

30
Q

For sodium channels, what is the difference between deactivated and inactivated?

A

Deactivation is the process of going from the open to the closed state, whereas inactivation means no ions can be conducted and no stimulus can activate them

31
Q

What is required to “reset” an inactivated Na channel?

A

A finite amount of time at a negative membrane potential ( resting or less)

32
Q

At resting membrane potential, what is the state of most Na channels?

A

Closed. As membrane becomes more depolarized, the probability of a Na channel being open increases, so by ~0 mV, almost all are activated

33
Q

What feature of K channels, in contrast to Na channels allows them to facilitate attainment of threshold and to cause afterhyperpolarization?

A

They open more slowly, compared to. Na channels and therefore remain open for longer. They also don’t have an inactivated state ( at least not on time scales relevant for discussion of AP firing)

34
Q

What is the relative refractory period? What channels are responsible?

A

Time after an AP during which a larger than normal stimulus would be required to fire a second AP. Is due to the K channels remaining open ( increased K permeability post-AP)

35
Q

What is the absolute refractory period? What is responsible for this.

A

The period of time after an AP in which no stimulus can produce an AP. This is due to a high number of Na channels being in the inactivated state. If Na permeability cannot be increased, then the voltage threshold required for an AP cannot be achieved

36
Q

Are Na channels considered positive are negative feedback? Why

A

Positive. The influx causes depolarization, which in turn opens more Na channels ( provided they aren’t inactivated, but only closed), cause more depolarization.

37
Q

Are K channels considered negative or positive feedback in terms of depolarization? Why

A

Negative feedback. They allow positive charge to leak out of the cell, which depolarized the cell (brings it back closer to resting potential)

38
Q

What is different about the amplitude of an AP signal over time compared to a graded potential? What accounts for the difference?

A

The amplitude remains the same in an AP, because the depolarization is regenerated in each patch of membrane ( the change membrane potential activates voltage-gated Na channels in each individual patch)

39
Q

How do active and passive signal propagation mechanisms work together to conduct an AP stimulus?

A

APs are generated at one point (usually axon initial segment or at a node of Ranvier) then travel electrotonically (passively) to the next patch (next node, etc. where another AP can be generated aka a new signal with the same amplitude of the original signal)

40
Q

T or F. Signals generated in the axon initial segment can propagate backwards into the soma and/or dendrites.

A

True. Signal propagation is only unidirectional in the axon itself

41
Q

What two factors prevent backwards propagation of the signal within the axon?

A
  1. Inactivation of Na channels

2. Refractory period ( which is due to Na channels, also K channels)

42
Q

Two ways to increase conduction velocity

A
  1. Increase axon diameter

2. Myelination

43
Q

What two ways does myelin increase conduction velocity?

A
  1. Increases the resistance (prevent ionic leak)
  2. Decreases the capacitance ( less charge gets stored, or “stuck” to the membrane walls, so more is available to propagate)

Basically : facilitates the electrotonic (passive) propagation by preventing loss of charge

44
Q

Other than myelination, etc why is decrement of the signal between nodes minimal?

A

Distance between nodes is short and AP current is usually very large

45
Q

What two groups of neurons have the most rapid conductiong speeds?

A
  1. Alpha motoneurons

2. Group 1 afferents

46
Q

In mammalian myelinated axons, what process is most important for repolarization?

A

Inactivation of Na channels ( more so than opening of K channels)

47
Q

Why do APs iniate in Nodes of Ranvier or in the axon initial segment?

A

These areas have a high density of Na channels ( also some geometric factors)

48
Q

Generalized epilepsy with febrile seizures is due to mutations in the Na channel subunit that alter their function how?

A

Mutations delay the inactivation of Na channels, leading to prolonged Na influx and thus hyperexcitability

49
Q

The alpha subunit of the Na channel has ___ domains, each consisting of ___ transmembrane spanning regions

A

4; 6

50
Q

Familial hemiplegic migraine is due to mutation in what type of channels?

A

P/Q-type Ca2+ channels ( CaV2.2 channels)

51
Q

What is the channels patchy in Episodic ataxia type 2?

A

Truncated mutants of CaV2.2 channels

52
Q

What is the pathology of Lambert-Eaton syndrome?

A

Antibodies to presynaptic voltage gated Ca channels are produced; often as part of a carcinoid syndrome in small cell carcinomas

53
Q

What is myotonia? Mutations in which channel may cause these?

A

Hyperexcitability of muscle. Mutation on Cl channels can cause

54
Q

Mutations in what channel underlie Episodic ataxia type 1? Where in the brain?

A

Kv1.1 type potassium channels, in Purkinje cells in the cerebellum

Neurology (23 decks)

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