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psl201: physiology > week 3 > Flashcards

week 3 Flashcards

1
Q

diff bw GPs and APs in terms of…
a) location
b) channel types involved
c) ions involved
d) duration

A

GPs vs APs:
a) dendrites/soma/sensory receptors vs axon
b) ligand and mechanically-gated vs voltage-gated
c) Na+, Cl-, or K+ vs Na+ and K+
d) few msec to seconds vs 1-2 msec

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2
Q

phases of an AP (3)

A
  1. depolarization
  2. repolarization
  3. after-hyperpolarization
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3
Q

when do Na+ channels open?

A

once threshold is reached (~-55mV)

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4
Q

do VGSCs operate in a positive or negative feedback system?

A

positive

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5
Q

why does the peak depolarization of an AP only reach +30mV? why not reach the EP of Na+ (+60mV)?

A

because soon after the VGSCs open, they inactivate

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6
Q

what causes repolarization? (2)

A
  1. at rest, K+ leaks out of cell, so cell becomes more negative.
  2. VGPCs open (recall: EC of K+ = out).
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7
Q

which are faster: VGSC or VGPC?

A
  • VGSCs are faster.
  • this is why the repolarization phase (which depends on VGPCs) takes longer and overshoots (after-hyperpolarization).
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8
Q

do VGPCs operate in a positive or negative feedback system?

A

negative

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9
Q

review: at rest, is Na+ or K+ more permeable?

A

K+

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10
Q

what brings the membrane to threshold?

A

sum of the graded potentials

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11
Q

what restores resting membrane potential?

A

Na+/K+ pump

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12
Q

are the activation and inactivation gates open or closed at…
a) rest
b) depolarization
c) repolarization

A

a) rest: activation = closed, inactivation = open
b) depolarization: activation = open, inactivation = open
c) repolarization: activation = open, inactivation = closed

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13
Q

why are threshold and suprathreshold stimuli equal in size?

A

bc all-or-none principle

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14
Q

what is a refractory period? whats the diff bw absolute and relative refractory periods?

A

refractory period: decreased excitability following an AP because VGSCs are inactive until membrane potential is at rest.

absolute: ALL VGSCs are inactive. spans all of de and most of repolarization. second AP cannot occur.

relative: SOME VGSCs are inactive. last part of re and after-hyperpolarization. second AP may occur with stronger stimulus.

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15
Q

what is most common local anesthetic dentists use to “freeze” you and how does it work?

A
  • lidocaine
  • works as VGSC blocker, preventing APs (pain)
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16
Q

can you completely block membrane from generating AP?

A
  • yes
  • keep membrane depolarized above threshold to stop influx of sodium.
  • inject KCl to destroy concentration gradient for K+ (will keep inside of cell positive, keeping VGSC inactive).
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17
Q

if APs are all-or-none, how do we differentiate strong vs weak stimuli?

A
  • frequency coding
  • strong stimuli encoded in higher frequency of APs
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18
Q

what are the cons of an unmyelinated axon? (2)

A
  • leakage of ions
  • decreased conduction velocity
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19
Q

how does the propagation of APs work in unmyelinated axons?

A
  • A = depolarized
  • positive charge of A attracted to negative charge of B
  • B = depolarized
  • cycle continues
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20
Q

what makes the propagation of APs unidirectional?

A

absolute refractory period

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21
Q

what are the factors affecting propagation? (3)

A
  1. refractory period (makes it unidirectional)
  2. axon diameter (larger = faster)
  3. myelination (saltatory conduction = faster)
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22
Q

how does the propagation of APs work in myelinated axons?

A
  • high density of VGSC at nodes of ranvier
  • AP jumps from node-to-node
23
Q

in electrical synapses, neurons are linked together by ___. what do these contain?

A
  • gap junctions
  • contain connexins that allow ions to cross
24
Q

functions of electrical synapses in the nervous system? (5)

A
  1. rapid communication
  2. ions or second messengers
  3. usually bidirectional communication
  4. excitation and inhibition at same synapse
  5. identified in retina, cortex, brainstem (breathing), and hypothalamus (neuroendocrine neurons).
25
Q

describe functional anatomy of chemical synapses (5)

A
  1. presynaptic neuron releasing neurotransmitter
  2. postsynaptic neuron accepting neurotransmitter
  3. synaptic cleft
  4. unidirectional communication
  5. usually axodendritic, some axosomatic or axoaxonic
26
Q

describe the anatomy of a synapse (7)

A
  1. presynaptic axon terminal (AP arrives here)
  2. neurotransmitter-containing vesicles
  3. depolarization opens VG Ca2+ channels
  4. neurotransmitter dropped into synaptic cleft
  5. receptors
  6. enzymes
  7. reuptake molecules
27
Q

how can leftover neurotransmitter be removed? (3)

A
  1. enzymatic breakdown
  2. diffusion
  3. reuptake
28
Q

what is synaptic delay? what is it caused by?

A
  • 0.5–5 msec between arrival of AP and change in postsynaptic cell.
  • caused by changes in Ca2+ entry, vesicle docking, and release of neurotransmitter
29
Q

what are the 2 types of receptors that allow signal transduction at chemical synapses?

A
  1. channel-linked (ionotropic): ligand-gated, fast acting, close as soon as neurotransmitter leaves.
  2. g-protein coupled (metabotropic): slow acting
30
Q

describe the steps of…
a) direct coupling
b) second messenger systems

A

[discussing g-protein coupled receptors]

a) neurotransmitter binds, activates g-protein, opens/closes ion channels.

b) neurotransmitter binds, activates g-protein, activates/inhibits enzyme, produces second messenger, opens/closes ion channels or produces other cell responses.

31
Q

whats a PSP?

A

change in membrane potential in response to receptor-neurotransmitter binding.

32
Q

most common EPSP neurotransmitter? IPSP?

A

EPSP: glutamate

IPSP: GABA

33
Q

what makes an EPSP fast or slow?

A

whether channel-linked or g-protein coupled receptors are used

34
Q

in inhibitory synapses, what happens if K+ channels open? Cl- channels?

A

K+: moves out = IPSP

Cl-: moves in = IPSP (or stabilizes MP)

35
Q

why are IPSPs more important than EPSPs? (3)

A
  • more specific
  • more accurate
  • shape info
36
Q

diff bw divergence and convergence?

A

divergence: axon of one neuron has several collaterals that communicate to several other neurons.

convergence: many PREsynaptic terminals converge onto one postsynaptic neuron.

37
Q

recall: temporal vs spatial summation

A

temporal = one stimulus, close times.

spatial = multiple stimuli, same times.

38
Q

more APs = more neurotransmitter released + ___ IPSP or EPSP in the next neuron.

A

greater

39
Q

what is presynaptic modulation?

A

regulation of communication across a synapse on presynaptic neuron (axoaxonic)

40
Q

what is presynaptic facilitation vs inhibition?

A

facilitation: modulating neuron results in modulated neuron releasing more neurotransmitter

inhibition: modulating neuron results in modulated neuron releasing less neurotransmitter

41
Q

diff between axoaxonic vs axodendritic/axosomatic ???

A

axoaxonic excites/inhibits one synapse and is selective

others excite/inhibit postsynaptic neuron and is nonselective (“overall”)

42
Q

what is Ach used for and where is it found?

A
  • muscular contractions
  • PNS and CNS (most abundant neurotransmitter in PNS)
43
Q

how is Ach synthesized? broken down?

A

synthesis: Acetyl CoA + choline = acetylcholine + CoA (CAT = enzyme for synthesis)

breakdown: Acetylcholine = acetate + choline (AChE = enzyme for degredation)

44
Q

what is the Ach competitive agonist? what does it do?

A
  • curare
  • blocks Ach, prevents voluntary movements
45
Q

cholinergic receptors can be of what types? (2)

A
  • nicotinic (ionotropic, EPSP)
  • muscarinic (metabotropic, EPSP or IPSP)
46
Q

which type of cholinergic receptor is abundant in CNS?

A

metabotropic (muscarinic)

47
Q

name the 5 biogenic amines

A
  1. dopamine
  2. epinephrine
  3. norepinephrine

tyrosine ^

  1. serotonin (tryptophan)
  2. histamine (histidine)
48
Q

serotonin (3)

A
  • CNS (mainly brainstem)
  • regulates sleep + emotions
  • related directly to plasma concentration of tryptophan
49
Q

histamine (3)

A
  • CNS (mainly hypothalamus)
  • regulates wakefulness
  • commonly known for paracrine actions (allergies)
50
Q

which amino acid neurotransmitters are at excitatory vs inhibitory synapses?

A

excitatory: glutamate, aspartate

inhibitory: GABA, glycine

51
Q

name the 6 neuropeptides

A
  1. endogenous opioids
  2. TRH
  3. ADH
  4. oxytocin
  5. substance P
  6. orexin
52
Q

name one unique neurotransmitter. why is it uniqe?

A
  • NO (gas)
  • unique bc cannot be stored; created on spot as needed.
53
Q

is the effect determined by the receptors or the ligand for Ach?

A

receptor

psl201: physiology (21 decks)

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