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Physiology > Exam I | Membrane Potentials & Nerve Conduction > Flashcards

Exam I | Membrane Potentials & Nerve Conduction Flashcards

1
Q

What is action potential?

A

conduction within neurons

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2
Q

what are synapses?

A

conduction between nuerons

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3
Q

what is another name for membrane potential?

A

membrane voltage

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4
Q

what is “potential”

A

voltage

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5
Q

what is neurotransmission?

A

mechanisms by which cells of the nervous system communicate

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6
Q

how fast is neurotransmission?

A

150 m/s

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7
Q

What is voltage?

A

potential difference in charge between two points (in space)

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8
Q

what is current?

A

movement of charged ions, usually with their concentration gradient

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9
Q

what is gradient?

A

gradual change from one point to another

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10
Q

what are the 3 types of stimulus that might cause membrane channels to open?

A
  • change in membrane potential (voltage-gated channel)
  • binding of specific molecules (ligand-gated)
  • mechanical deformation of the membrane (mechanical or stretch-gating)
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11
Q

What is membrane potential, and what is responsible for it?

A
  • difference in charge across membrane (of myocyte membrane or synaptic membrane)
  • always refers to inside of a cell
  • due to the imbalance of ions, activity of NaK pump, and ion channels
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12
Q

What are the ligands in neurotransmission?

A

hormones or neurotransmitters

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13
Q

What are graded potentials? (5 points)

A
  • a localized change in membrane voltage that varies in amplitude with stimulus intensity.
  • Amplitude is proportional to intensity of stimulus.
  • may be depolarization (excitatory) or hyperpolarization (inhibitory).
  • occur in the dendrites and soma of cell body due to abundant channels
  • change in membrane potential weakens with distance from point of origin
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14
Q

what is a perturbation?

A

“change”

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15
Q

what is depolarization?

A

moving from a more negative voltage to a less negative voltage (a positive change)

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16
Q

Nernst potential: what is another name for it, what does it solve for, and what do you need to know to solve?

A
  • aka equilibrium potential
  • solves for voltage (membrane potential) for a single ion
  • need to know concentration gradient to solve
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17
Q

What is the Nernst potential (or equilibrium potential) for Na+?

A

+60.6 mV

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18
Q

What is the Nernst potential (or equilibrium potential) for K+?

A

-96.82 mV

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19
Q

How does the extracellular concentration of Na+ compare to intracellular concentration?

A

extracellular concentration is greater

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20
Q

How does the extracellular concentration of K+ compare to intracellular concentration?

A

extracellular concentration is less

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21
Q

What is the resting potential of skeletal muscle?

A

-95 mV

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22
Q

What is the resting potential of neurons?

A

-60 to -70 mV

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23
Q

What is the resting potential of smooth muscle cells??

A

-60 mV

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24
Q

What is the charge of cells relative to the outside, and why?

A

(-)70, because

  • of the NaK pump
  • in general the concentration of fixed anionic proteins inside the cell is greater relative to the outside
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25
Q

The leakage of K+ renders the cell more ____, while the leakage of Na+ renders the cell more _____.

A

negative (hyperpolarization); positive (depolarization)

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26
Q

How do ions pass through the membrane?

A
  • ion channels

- ion pumps

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27
Q

How is membrane potential physiologically useful?

A
  • intracellular communication (neuronal transmission)

- source of energy

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28
Q

Chord conductance equation

A
  • sums up concentration gradients of all the various ions across the membrane and multiple membrane channels based on their permeability
  • differs from Nernst equation because it applies to multiple ions
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29
Q

what 3 things determine membrane potential?

A
  • ion concentration gradients across membrane
  • charge gradient across the membrane
  • membrane permeability of ions
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30
Q

Disregarding the NaK pump, what 3 things determine how efficiently K+ leaves the cell?

A
  • concentration gradient of K+
  • rate of ion leakage
  • membrane charge gradient
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31
Q

what will eventually stop K+ from leaking out of the cell by diffusion?

A

electrical driving force caused by excess Na+ outside the cell

32
Q

What is the major determinant of resting membrane potential?

A

leakage of K+

33
Q

The summation of graded potentials influences what?

A

membrane potential

34
Q

How do neuronal graded potentials become action potentials?

A

when the graded potential is sufficiently large enough to depolarize the neuronal membrane beyond its threshold potential at the axon hillock

35
Q

What is the axon hillock?

A

junction of axon with cell body

36
Q

How are action potentials propagated along the axon towards the synaptic terminal?

A
  • as a “wave” (of depolarization) of sodium channels that open along the axon from the cell body to axon terminals
  • at a constant amplitude (requiring abundant ATP)
37
Q

Where does action potential occur? What conditions must be met for it to occur? Does it change over time?

A
  • only occur at axon (hillock and Nodes of Ranvier)
  • occurs when graded potential at the axon hillock exceeds threshold potential
  • require large amounts of ATP
  • does not change in voltage/amplitude over time
38
Q

What is attenuation?

39
Q

What 3 factors determine whether or not the summation of graded potentials generates an action potential?

A
  • number
  • strength
  • type
40
Q

What is EPSP?

A

excitatory post-synaptic potential (depolarizing)

41
Q

What is IPSP?

A

inhibitory post-synaptic potential (hyperpolarizing)

42
Q

What is the most abundant type of excitatory neurotransmitter in the human brain?

43
Q

What is the most abundant type of inhibitory neurotransmitter in the human brain?

44
Q

Describe what the voltage-gated Na+ channels do in action potential sequence.

A
  • Open up at the threshold potential (about -55 mV) and let Na+ rush into the cell. Result is depolarization (cell interior more positive)
  • As membrane potential “reverses” (exceeds 0), sodium channels close, preventing further depolarization
45
Q

Describe what voltage-gated K+ channels do during the action potential sequence.

A
  • Let K+ rush out of the cell after Na+ channels close during the action potential sequence
  • result is hyperpolarization (cell interior is more negative)
  • channels close as the membrane potential returns to resting value
46
Q

What is repolarization?

A

hyperpolarization

47
Q

Which open faster, K+ or Na+ channels?

A

Na+ channels

48
Q

why do action potentials not occur in the soma or dendrites?

A

they do not have the appropriate channels

49
Q

Distinguish absolute refractory period from relative refractory period.

A
  • during absolute refractory period, neuron is incapable of generating another AP. ARP corresponds to time when depolarization/repolarization is occuring.
  • neuron may regenerate another AP in relative refractory period, but only if the stimulus is very strong.
50
Q

List the action potential sequence (5 steps).

A

1) a stimulus initiates a graded potential that depolarizes membrane towards the threshold potential (-55 mV)
2) Voltage gated Na+ channels open, Na+ rushes into cell, further depolarizing membrane
3) as membrane potential ‘reverses’ (exceeds 0) Na+ channels close, preventing further depolarization
4) K+ channels open, K+ rushes into cell causing hyperpolarization. They will close as resting membrane potential is reached
5) a brief afterpotential takes membrane below RMP

51
Q

How long does depolarization/hyperpolarization take (the absolute refractory period)?

A

2 milliseconds

52
Q

How long is the relative refractory period?

A

3 milliseconds

53
Q

Where are the only 2 locations where voltage-gated channels are present?

A
  • proximal axon (hillock)

- nodes of Ranvier (regions where there is no myelination)

54
Q

What are Nodes of Ranvier? How does signal conduction occur at these points?

A

gaps between myelination on the axon; slow but strong compared to saltatory conduction

55
Q

What myelinates neurons in the PNS? In the CNS?

A

Schwann cells; oligodendrocytes

56
Q

saltatory conduction

A
  • signal conduction within the myelinated axon
  • conducted much more rapidly than at the nodes
  • but rapidly loses strength and dissipates, but then restored at each node of Ranvier
57
Q

What is the relationship between axon diameter and speed of conduction, and what explains that relationship?

A
  • inversely proportional; the greater the diameter, the faster the conduction (smaller velocity)
  • smaller axons tend to be unmyelinated
58
Q

What are larger axons usually responsible for? Smaller axons?

A
  • larger axons involved in proprioception

- smaller axons responsible for thermal sensation, pain, and touch

59
Q

what 2 things determine speed of conduction along axons or nerves?

A
  • degree of myelination

- size of axon

60
Q

Which is faster, motor or sensory nerves?

A

motor. nerve conduction velocity is smaller.

61
Q

what is the conduction velocity for the median sensory nerve? Median motor nerve?

A

45-70 m/s; 49-64 m/s

62
Q

what is the conduction velocity for the ulnar sensory nerve? Ulnar motor nerve?

A

48-74 m/s; 49+ m/s

63
Q

What is the conduction velocity for the peroneal motor nerve?

64
Q

What is the conduction velocity for the tibial motor nerve?

65
Q

What is the conduction velocity for the sural sensory nerve?

66
Q

central motor fibers are usually what type of fibers?

67
Q

what is the difference between a nerve and a neuron?

A
  • a nerve is a bundle of axons without the soma

- nerve is a connective tissue, neuron is a cell

68
Q

What is a fasicle?

A

bundle of axons

69
Q

What are the connective tissue layers of nerves, from superficial to deep? Say something about each of the layers.

A
  • epineurium: vascular and enervated
  • perineurium: encapsulates fascicles
  • endoneurium: encapsulates myelin sheath
70
Q

What is MS?

A

demyelinating disease of the CNS

71
Q

What are 5 symptoms of MS?

A
  • muscle weakness
  • fatigue
  • memory deficits
  • pain
  • impaired speech
72
Q

How is MS diagnosed?

A
  • clinical presentation
  • MRI evidence
  • elevated gamma globulins (due to T-cell proliferation)
73
Q

Hyponatremia is clinically defined as what?

A

serum sodium less than 135 mEq/L

74
Q

What is hypocalcemia tetany?

A

muscle spasms resulting from hypocalcemia causing hyperexcitability in muscle and nervous tissue

75
Q

What is the normal range for potassium in the blood?

A

3.5- 5.5 mEq/L

76
Q

What are the consequences of severe hyperkalemia?

A
  • cardiac arrhythmias
  • respiratory distress
  • neurological consequences

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