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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
Q

T/F: AP don’t have an all or nothing response

A

F, threshold has to be reached to send signal

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26
Q

RMP can be altered by ________ resulting in AP

A

stimulus

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27
Q

Stimulus examples of how RMP can be altered:

A
  • electrical (lightning/electrocution)
  • chemical (neurotransmitters/hormones)
  • mechanical (pressure/stretch)
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28
Q

What happens if there’s not enough reduction in AP?

A
  • subthreshold/local response occurs: membrane becomes depolarized over small distance (nonpropagated potential)
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29
Q

Nonpropagated potential:

A
  • aka synaptic/generator/electrogenic potentials
  • size of potential change decreases exponentially w/ distance from initiation site
  • potential will die out and not conducted
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30
Q

Threshold point:

A
  • 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
Q

T/F: positive mV causes change in membrane conductance of ions and continues depolarization

A

F, it would stop depolarization

32
Q

Steps for AP at membrane:

A
  1. threshold point
  2. membrane then repolarizes
  3. AP depolarizes adjacent membrane
33
Q

How does membrane repolarize?

A
  • membrane returns to RMP

- neurons go through hyperpolarization

34
Q

T/F: AP is self propagating through electrical impulse.

A

T

35
Q

Suprathreshold stimulus:

A
  • bigger than one needed for threshold

- doesn’t increase size of AP

36
Q

VG Na+ channel:

A
  • “fast” acting
  • rapid activation time
  • has double gating system
37
Q

VG K+ channel:

A
  • slower activation time

- has single gate that can be opened / closed

38
Q

Step one of mechanism w/ Na+ and K+ (at rest):

A
  • VG Na+ and K+ are closed
  • Na+ not moving
  • K+ leak channels open: K+ moves
39
Q

Step two of mechanism w/ Na+ and K+ (depolarization stimulus applied):

A
  • many VG Na+ open: Na+ moves into cell w/ gradient

- mem slowly depolarizes to threshold point

40
Q

Step three of mechanism w/ Na+ and K+ (threshold point):

A
  • AP initiated, so no going back

- positive feedback mechanism: Na+ entry causes more Na+ to open until all are open

41
Q

Step four of mechanism w/ Na+ and K+ (depolarization phase):

A
  • Na+ entry moves membrane potential towards Na+ equilibrium potential
  • membrane rapidly depolarizes and overshoots to isoelectric point
  • inside becomes positive
42
Q

Step five of mechanism w/ Na+ and K+ (VG K+ channels open):

A
  • K+ moves out of cell w/ electrochemical gradient

- slows depolarization, which counteracts impact of Na+ entry

43
Q

Step six of mechanism w/ Na+ and K+ (repolarization phase):

A
  • begins when membrane potential reaches 30 to 50 mV
  • Na+ conductance decreases: less Na+ into cell
  • K+ conductance increases: more K+ leaves cell
44
Q

Step seven of mechanism w/ Na+ and K+ (hyperpolarization phase):

A
  • 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
Q

Refractory period:

A
  • minimum time required after AP is generated before membrane can respond to another stimulus
  • short refractory period = can conduct impulses more frequently
46
Q

Absolute refractory period:

A
  • 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
Q

Relative refractory peroid:

A
  • 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
Q

T/F: AP is a widespread response that occurs at multiple areas on membrane

A

F, it’s a local response that occurs at one specific area on membrane

49
Q

Propagation:

A
  • AP initiated at one part of membrane triggers APs in neighboring areas
50
Q

Self propagation:

A
  • domino effect

- AP can’t travel back to previous activated areas because of refractory period

51
Q

Nerve impulse:

A
  • wave of depolarization followed by wave of repolarization along axon
  • basically wave of AP
52
Q

T/F: increase in diameter of axons leads to decrease in velocity of AP

A

F, should lead to increase in velocity b/c of lower resistance to conduction

53
Q

Insulation around core conductors prevents…

A
  • loss of current to surrounding media
  • plasma membrane: acts as insulator
  • cytoplasm: core conductor
54
Q

Myelin:

A
  • type of insulator
  • is a lipid (poor conductor of ion current)
  • covers plasmalemma of axon in most neurons
55
Q

Myelin prevents the loss of…

A

current and flow of ion between ECF and ICF

56
Q

Myelin sheath:

A
  • produced by myelin producing cells around axon
  • covers axon
  • Schwann cells: covers nerves in PNS
  • oligodendrocytes: covers nerves in CNS
57
Q

Nodes of Ranvier:

A
  • 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
Q

Nodes of Ranvier conserves E because…

A
  • uses less ATP

- Na+/K+ ATPase needed to return to RMP b/c ions only cross membrane at nodes

59
Q

T/F: Axon fiber type affects speed transmission

A

T

60
Q

Order of largest to smallest axon types:

A
  • larger axon = faster transmission
  • alpha
  • beta
  • gamma
  • delta
61
Q

A alpha neuron for sensory / afferent is…

A
  • myelinated
  • largest axon
  • fastest conduction velocity out of the other types
62
Q

A alpha fiber for sensory / afferent carries info from…

A
  • proprioceptors
63
Q

A alpha fiber for sensory / afferent subtypes:

A
  • indicate area of origin
  • type 1a: from muscle spindle
  • type 1b: from Golgi tendon organ
64
Q

A beta fiber for sensory / afferent:

A
  • type 2

- from muscle spindles, rapid touch, pressure receptors

65
Q

A gamma fiber for sensory / afferent:

A
  • type 3

- relays info about fast pain, cold temp, non-specific touch

66
Q

C fibers for sensory / afferent:

A
  • unmyelinated
  • type 4
  • relays info about slow pain and warm temp
67
Q

A alpha fiber for motor / efferent:

A
  • somatic motor neurons
  • myelinated
  • for skeletal muscle
68
Q

A beta fiber motor / efferent:

A
  • preganglionic fibers

- for autonomic motor output

69
Q

C fiber motor / efferent:

A
  • postganglionic fibers

- for autonomic motor output

70
Q

VGC in plasma membrane is responsible for…

A

AP

71
Q

Resting state of VG Na+ channel:

A

gates closed

- cell not permeable to Na+

72
Q

Activation state of VG Na+ channel:

A

gates opened

- cell permeable to Na+

73
Q

Inactivation state of VG Na+ channel:

A

one closed and the other opened

- cell not permeable to Na+

Physiology (33 decks)

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