Exam I | Membrane Potentials & Nerve Conduction Flashcards
(76 cards)
1
Q
What is action potential?
A
conduction within neurons
2
Q
what are synapses?
A
conduction between nuerons
3
Q
what is another name for membrane potential?
A
membrane voltage
4
Q
what is “potential”
A
voltage
5
Q
what is neurotransmission?
A
mechanisms by which cells of the nervous system communicate
6
Q
how fast is neurotransmission?
A
150 m/s
7
Q
What is voltage?
A
potential difference in charge between two points (in space)
8
Q
what is current?
A
movement of charged ions, usually with their concentration gradient
9
Q
what is gradient?
A
gradual change from one point to another
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)
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
12
Q
What are the ligands in neurotransmission?
A
hormones or neurotransmitters
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
14
Q
what is a perturbation?
A
“change”
15
Q
what is depolarization?
A
moving from a more negative voltage to a less negative voltage (a positive change)
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
17
Q
What is the Nernst potential (or equilibrium potential) for Na+?
A
+60.6 mV
18
Q
What is the Nernst potential (or equilibrium potential) for K+?
A
-96.82 mV
19
Q
How does the extracellular concentration of Na+ compare to intracellular concentration?
A
extracellular concentration is greater
20
Q
How does the extracellular concentration of K+ compare to intracellular concentration?
A
extracellular concentration is less
21
Q
What is the resting potential of skeletal muscle?
A
-95 mV
22
Q
What is the resting potential of neurons?
A
-60 to -70 mV
23
Q
What is the resting potential of smooth muscle cells??
A
-60 mV
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
25
The leakage of K+ renders the cell more ____, while the leakage of Na+ renders the cell more _____.
negative (hyperpolarization); positive (depolarization)
26
How do ions pass through the membrane?
- ion channels
| - ion pumps
27
How is membrane potential physiologically useful?
- intracellular communication (neuronal transmission)
| - source of energy
28
Chord conductance equation
- 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
29
what 3 things determine membrane potential?
- ion concentration gradients across membrane
- charge gradient across the membrane
- membrane permeability of ions
30
Disregarding the NaK pump, what 3 things determine how efficiently K+ leaves the cell?
- concentration gradient of K+
- rate of ion leakage
- membrane charge gradient
31
what will eventually stop K+ from leaking out of the cell by diffusion?
electrical driving force caused by excess Na+ outside the cell
32
What is the major determinant of resting membrane potential?
leakage of K+
33
The summation of graded potentials influences what?
membrane potential
34
How do neuronal graded potentials become action potentials?
when the graded potential is sufficiently large enough to depolarize the neuronal membrane beyond its threshold potential at the axon hillock
35
What is the axon hillock?
junction of axon with cell body
36
How are action potentials propagated along the axon towards the synaptic terminal?
- 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
Where does action potential occur? What conditions must be met for it to occur? Does it change over time?
- 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
What is attenuation?
decrease
39
What 3 factors determine whether or not the summation of graded potentials generates an action potential?
- number
- strength
- type
40
What is EPSP?
excitatory post-synaptic potential (depolarizing)
41
What is IPSP?
inhibitory post-synaptic potential (hyperpolarizing)
42
What is the most abundant type of excitatory neurotransmitter in the human brain?
Glutamate
43
What is the most abundant type of inhibitory neurotransmitter in the human brain?
GABA
44
Describe what the voltage-gated Na+ channels do in action potential sequence.
- 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
Describe what voltage-gated K+ channels do during the action potential sequence.
- 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
What is repolarization?
hyperpolarization
47
Which open faster, K+ or Na+ channels?
Na+ channels
48
why do action potentials not occur in the soma or dendrites?
they do not have the appropriate channels
49
Distinguish absolute refractory period from relative refractory period.
- 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
List the action potential sequence (5 steps).
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
How long does depolarization/hyperpolarization take (the absolute refractory period)?
2 milliseconds
52
How long is the relative refractory period?
3 milliseconds
53
Where are the only 2 locations where voltage-gated channels are present?
- proximal axon (hillock)
| - nodes of Ranvier (regions where there is no myelination)
54
What are Nodes of Ranvier? How does signal conduction occur at these points?
gaps between myelination on the axon; slow but strong compared to saltatory conduction
55
What myelinates neurons in the PNS? In the CNS?
Schwann cells; oligodendrocytes
56
saltatory conduction
- 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
What is the relationship between axon diameter and speed of conduction, and what explains that relationship?
- inversely proportional; the greater the diameter, the faster the conduction (smaller velocity)
- smaller axons tend to be unmyelinated
58
What are larger axons usually responsible for? Smaller axons?
- larger axons involved in proprioception
| - smaller axons responsible for thermal sensation, pain, and touch
59
what 2 things determine speed of conduction along axons or nerves?
- degree of myelination
| - size of axon
60
Which is faster, motor or sensory nerves?
motor. nerve conduction velocity is smaller.
61
what is the conduction velocity for the median sensory nerve? Median motor nerve?
45-70 m/s; 49-64 m/s
62
what is the conduction velocity for the ulnar sensory nerve? Ulnar motor nerve?
48-74 m/s; 49+ m/s
63
What is the conduction velocity for the peroneal motor nerve?
44+ m/s
64
What is the conduction velocity for the tibial motor nerve?
41+ m/s
65
What is the conduction velocity for the sural sensory nerve?
46-64 m/s
66
central motor fibers are usually what type of fibers?
Aa fibers
67
what is the difference between a nerve and a neuron?
- a nerve is a bundle of axons without the soma
| - nerve is a connective tissue, neuron is a cell
68
What is a fasicle?
bundle of axons
69
What are the connective tissue layers of nerves, from superficial to deep? Say something about each of the layers.
- epineurium: vascular and enervated
- perineurium: encapsulates fascicles
- endoneurium: encapsulates myelin sheath
70
What is MS?
demyelinating disease of the CNS
71
What are 5 symptoms of MS?
- muscle weakness
- fatigue
- memory deficits
- pain
- impaired speech
72
How is MS diagnosed?
- clinical presentation
- MRI evidence
- elevated gamma globulins (due to T-cell proliferation)
73
Hyponatremia is clinically defined as what?
serum sodium less than 135 mEq/L
74
What is hypocalcemia tetany?
muscle spasms resulting from hypocalcemia causing hyperexcitability in muscle and nervous tissue
75
What is the normal range for potassium in the blood?
3.5- 5.5 mEq/L
76
What are the consequences of severe hyperkalemia?
- cardiac arrhythmias
- respiratory distress
- neurological consequences
