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Physiology > Neuronal Cell Excitability > Flashcards

Neuronal Cell Excitability Flashcards

1
Q

Two major components of nervous system:

A
  • CNS: brain and spinal cord

- PNS: nerves that enter and leave from CNS

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2
Q

How many pairs of nerves are in the PNS?

A
  • 12 pairs cranial

- 31 pairs spinal

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3
Q

Sensory nerves in PNS:

A
  • afferent

- from skin and skeletal muscle

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4
Q

Motor nerves in PNS:

A
  • efferent
  • somatic: to skin and skeletal muscle
  • autonomic: to endocrine glands and visceral organs
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5
Q

Autonomic motor nerves have two parts:

A
  • parasympathetic (PNS): lower heart rate and contraction

- sympathetic (SNS): higher heart rate and contraction

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6
Q

Enteric nervous system:

A
  • gastrointestinal

- has local sensory and motor of its own

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7
Q

Neuron:

A
  • nerve cell
  • functional unit of NS
  • excitable
  • cell membrane: plasmalemma/neurilemma
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8
Q

4 basic components of neuron:

A
  • soma / cell body (1)
  • dendrites (many)
  • axon: has a hillock and terminal (many and many)
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9
Q

Function of soma/cell body:

A

directs synthesis of neurotransmitter

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10
Q

T/F: Dendrites have areas w/ receptors for neurotransmitters

A

T

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11
Q

Function of axon:

A

carries action potential (AP) to other nerve cells / effectors

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12
Q

T/F: axon hillock is where axon enters the cell body

A

F, it’s where axon leaves the cell body

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13
Q

Axon hillock:

A
  • site where AP are generated

- has increased [ ] of VG Na+ channels

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14
Q

T/F: axon terminal contains neurotransmitter vesicles that transmit into other nerve cells at synapses

A

T

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15
Q

Glial cells:

A
  • nonexcitable
  • myelin forming glial cells: increase rate of signal movement
  • Schwann cells in PNS
  • oligodendrocytes in CNS
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16
Q

Types of glial cells:

A
  • satellite cells
  • astrocytes
  • microglia
  • ependymal
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17
Q

Satellite cells:

A
  • nonmyelin-forming

- supportive

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18
Q

Astrocytes:

A
  • at synapses in blood brain barrier
  • secretes ions/chem
  • helps w/ ECF homeostasis by maintaining chem environment
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19
Q

Microglia:

A
  • helps w/ immune system
  • may contribute to neurodegenerative diseases
  • scavengers in CNS
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20
Q

Ependymal:

A
  • in epithelial
  • stem cells
  • contribute to CSF: part of ECF
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21
Q

Graded potential (GP):

A
  • involves gates ion channels
  • amp is directly proportionate to strength of stimulus
  • decreases in strength as it spreads from origin b/c of current leak / cytoplasmic resistance
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22
Q

Hyperpolarization:

A
  • caused by efflux of K+
  • makes cell more neg/polar than RMP
  • makes it less likely to generate AP than at RMP
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23
Q

Depolarization:

A
  • caused by influx of Na+
  • reverses RMP from negative to positive
  • causes local reduction in membrane potential b/c of movement of positive ions into cell
  • enough reduction = AP
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24
Q

Action potential (AP):

A
  • rapid and large change in membrane potential followed by return to RMP
  • occurs in excitable cells
  • VGC in plasma membrane responsible for AP
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25
T/F: AP don't have an all or nothing response
F, threshold has to be reached to send signal
26
RMP can be altered by ________ resulting in AP
stimulus
27
Stimulus examples of how RMP can be altered:
- electrical (lightning/electrocution) - chemical (neurotransmitters/hormones) - mechanical (pressure/stretch)
28
What happens if there's not enough reduction in AP?
- subthreshold/local response occurs: membrane becomes depolarized over small distance (nonpropagated potential)
29
Nonpropagated potential:
- aka synaptic/generator/electrogenic potentials - size of potential change decreases exponentially w/ distance from initiation site - potential will die out and not conducted
30
Threshold point:
- minimal amount of depolarization needed to convert MP into AP - positive feedback occurs - needs 15-30 mV depolarization of RMP to initiate AP - causes rapid increase in rate of depolarization - spike potential: decreases potential from 0 mV and then to 30 mV
31
T/F: positive mV causes change in membrane conductance of ions and continues depolarization
F, it would stop depolarization
32
Steps for AP at membrane:
1. threshold point 2. membrane then repolarizes 3. AP depolarizes adjacent membrane
33
How does membrane repolarize?
- membrane returns to RMP | - neurons go through hyperpolarization
34
T/F: AP is self propagating through electrical impulse.
T
35
Suprathreshold stimulus:
- bigger than one needed for threshold | - doesn't increase size of AP
36
VG Na+ channel:
- "fast" acting - rapid activation time - has double gating system
37
VG K+ channel:
- slower activation time | - has single gate that can be opened / closed
38
Step one of mechanism w/ Na+ and K+ (at rest):
- VG Na+ and K+ are closed - Na+ not moving - K+ leak channels open: K+ moves
39
Step two of mechanism w/ Na+ and K+ (depolarization stimulus applied):
- many VG Na+ open: Na+ moves into cell w/ gradient | - mem slowly depolarizes to threshold point
40
Step three of mechanism w/ Na+ and K+ (threshold point):
- AP initiated, so no going back | - positive feedback mechanism: Na+ entry causes more Na+ to open until all are open
41
Step four of mechanism w/ Na+ and K+ (depolarization phase):
- Na+ entry moves membrane potential towards Na+ equilibrium potential - membrane rapidly depolarizes and overshoots to isoelectric point - inside becomes positive
42
Step five of mechanism w/ Na+ and K+ (VG K+ channels open):
- K+ moves out of cell w/ electrochemical gradient | - slows depolarization, which counteracts impact of Na+ entry
43
Step six of mechanism w/ Na+ and K+ (repolarization phase):
- begins when membrane potential reaches 30 to 50 mV - Na+ conductance decreases: less Na+ into cell - K+ conductance increases: more K+ leaves cell
44
Step seven of mechanism w/ Na+ and K+ (hyperpolarization phase):
- membrane potential moves toward K+ equilibrium potential - more negative than resting level - VG K+ channels are slow to close, so K+ still open while Na+ closed - K+ will eventually close but K+ has leak channels still open - Na+/K+ ATPase pump restores ion balance and RMP
45
Refractory period:
- minimum time required after AP is generated before membrane can respond to another stimulus - short refractory period = can conduct impulses more frequently
46
Absolute refractory period:
- most Na+ gates haven't reset yet, so can't reopen - Na+ conductance is too slow to generate enough flow to trigger AP - no stimulus here can initiate another AP - occurs about 1 ms after AP initiated (from beginning of AP to 2/3 of repolarization)
47
Relative refractory peroid:
- after absolute refractory period - lasts until RMP is established - needs stronger stimulus than normal to reach threshold b/c has to overcome hyperpolarization effect of VG K+ channel - amplitude of second AP is lower than normal
48
T/F: AP is a widespread response that occurs at multiple areas on membrane
F, it's a local response that occurs at one specific area on membrane
49
Propagation:
- AP initiated at one part of membrane triggers APs in neighboring areas
50
Self propagation:
- domino effect | - AP can't travel back to previous activated areas because of refractory period
51
Nerve impulse:
- wave of depolarization followed by wave of repolarization along axon - basically wave of AP
52
T/F: increase in diameter of axons leads to decrease in velocity of AP
F, should lead to increase in velocity b/c of lower resistance to conduction
53
Insulation around core conductors prevents...
- loss of current to surrounding media - plasma membrane: acts as insulator - cytoplasm: core conductor
54
Myelin:
- type of insulator - is a lipid (poor conductor of ion current) - covers plasmalemma of axon in most neurons
55
Myelin prevents the loss of...
current and flow of ion between ECF and ICF
56
Myelin sheath:
- produced by myelin producing cells around axon - covers axon - Schwann cells: covers nerves in PNS - oligodendrocytes: covers nerves in CNS
57
Nodes of Ranvier:
- gaps that are between myelin producing cells - place where ion exchange can occur - has saltatory conduction: AP "jumps" from node to node - increases velocity of AP by reducing the resistance to conduction - 50x faster than unmyelinated neurons
58
Nodes of Ranvier conserves E because...
- uses less ATP | - Na+/K+ ATPase needed to return to RMP b/c ions only cross membrane at nodes
59
T/F: Axon fiber type affects speed transmission
T
60
Order of largest to smallest axon types:
- larger axon = faster transmission - alpha - beta - gamma - delta
61
A alpha neuron for sensory / afferent is...
- myelinated - largest axon - fastest conduction velocity out of the other types
62
A alpha fiber for sensory / afferent carries info from...
- proprioceptors
63
A alpha fiber for sensory / afferent subtypes:
- indicate area of origin - type 1a: from muscle spindle - type 1b: from Golgi tendon organ
64
A beta fiber for sensory / afferent:
- type 2 | - from muscle spindles, rapid touch, pressure receptors
65
A gamma fiber for sensory / afferent:
- type 3 | - relays info about fast pain, cold temp, non-specific touch
66
C fibers for sensory / afferent:
- unmyelinated - type 4 - relays info about slow pain and warm temp
67
A alpha fiber for motor / efferent:
- somatic motor neurons - myelinated - for skeletal muscle
68
A beta fiber motor / efferent:
- preganglionic fibers | - for autonomic motor output
69
C fiber motor / efferent:
- postganglionic fibers | - for autonomic motor output
70
VGC in plasma membrane is responsible for...
AP
71
Resting state of VG Na+ channel:
gates closed | - cell not permeable to Na+
72
Activation state of VG Na+ channel:
gates opened | - cell permeable to Na+
73
Inactivation state of VG Na+ channel:
one closed and the other opened | - cell not permeable to Na+

Physiology (33 decks)

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