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caps 301 > Neurophysiology and CNS > Flashcards

Neurophysiology and CNS Flashcards

1
Q

diffusion

A

Movement of solute (ion) from area of high conc to low conc. Occurs through random thermal movement

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2
Q

facilitated diffusion

A

Required for ions - charged, not lipid soluble, cannot directly diffuse.
Ion channels (integral membrane proteins) create passage for molecules that cannot diffuse across membrane.

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3
Q

Resting membrane potential

A

-70mV

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4
Q

Function of Na+/K+ ATPase in RMP generation + maintenance

A

2 K+ in, 3 Na+ out
- RMP infl by both Na and K
- Large diffusion of K+ outwards (-90)
- Small diffusion of Na+ inwards (+60)
- No anion diffusion
- -70mV resting membrane potential

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5
Q

Depolarisation

A

Incr permeability to Na+ -> shifts membrane potential to E(Na)=60 -> Vm becomes more pos
Can be done by decr K permeability or change chemical gradient
* induces neuron firing

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6
Q

Hyperpolarisation

A

Incr permeability to K+ -> shifts membrane potential to E(K)=-90 -> Vm becomes more neg
Can be done by decr Na permeability or change chemical gradient
* inhibits neuron firing

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7
Q

Neuron

A
  • Input from dendrites
  • Soma or cell body
  • Axon
  • Output at axon terminal
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8
Q

Excitable cells

A

Harness diff in charge b/w outside and inside
- Have diff in ion concentration across a selectively permeable membrane
- More neg on inside
- Charge difference located at cell membrane
- Ex: neurons, cardiac+skeletal muscle

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9
Q

Electrical activity requires…

A
  • Selectively permeable membrane
  • Differential distr/charge gradient across membrane
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10
Q

Differential distribution

A

of ions greater on one side than other.
Neurons concentrate higher K+ inside, higher Na+ outside

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11
Q

K+ equilibrium potential

A

-90mV (potential from inside cell)

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12
Q

Na+ equilibrium potential

A

+60mV (potential from inside cell)

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13
Q

Relative ionic permeability

A

Greater an ion’s permeability, more influence on membrane voltage
Most cells: K+:Na+ = 50:1
K+ has much more influence; resting membrane potential (-70) is closer to -90 than +60
(Due to more open K+ channels at rest)

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14
Q

Action potential, regenerative event?

A

Electrical event triggered when Vm reaches threshold: rapid membrane depolarisation (goes toward ENa) -> rapid return toward RMP (-70)
Results from increased Na+ permeability, followed by incr K+ permeability
Regenerative event: AP in one part of membr initiates AP in further part of membr

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15
Q

Threshold

A

-50.

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16
Q

All-or-none

A

Stimuli below threshold: no AP.
Stimuli above threshold: AP of same size

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17
Q

Resting state

A

-70mV
- Na+ channel: activation closed, inactivation open. Na+ stays out
- K+ channel: activation closed. K+ stays in

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18
Q

Rising phase

A

-50 to ENa (+60). At peak, greater Na+ permeability from open Na+ channels
- Na+ channel: activation and inactivation open. Na+ flows in
- K+ channel: activation closed. K+ stays in

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19
Q

Overshoot

A

When Vm is above 0 during AP

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20
Q

Falling phase

A
  • ENa to EK (-90)
  • Na+ channel: activation open, inactivation closed. Na+ stays out
  • K+ channel: activation open, K+ flows out
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21
Q

After-hyperpolarisation

A
  • Vm is close to EK because K+ channels are open
  • Rise back to RMP
  • Na+ channel: activation and inactivation closed. Na+ stays out
  • K+ channel: activation open. K+ flows out
22
Q

voltage-gated ion channels

A
  • Have voltage sensor which moves in response to d(Vm) -> coupled to activation gate (opens channel)
  • Depolarisation -> opening of activation gate
  • Most also have inactivation gate: depolarisation -> closes inactivation gate
  • Na+ channel has both, K+ channel only activation
  • At MRP: activation gate closed, inactivation gate open
23
Q

Ionic conductance changes during AP

A

Na+ conductance (gNa) peaks in rising phase
K+ conductance (gK) peaks in falling phase
During afterhyperpolarization, gNa resting value, gK still elevated (K channels still open)
gK>gNa at rest (leaky K channels)

24
Q

Absolute refractoriness

A

After AP, stimulus fails to evoke AP
- Some Na+ channels inactivated
- gK not at resting yet (voltage gated channels still open)

25
Q

Relative refractory period

A

After AP, greater stimulus intensity is needed to generate AP

26
Q

Generator potential

A

membrane depolarization occurring as a response to stimulus (initial depolarization sub threshold not considered part of AP).
Produced at sensory endings in periphery.
Stronger stimulus; larger depolarisation.
AP prod if GP->threshold
No refractory

27
Q

Positive feedback depolarization

A
  • Generator pot opens some Na+ channels
  • Na+ conductance results in further depolarisation
  • More depolarized -> activation gates open
  • Keeps looping
28
Q

Electrotonus

A

How electrical signals propagate
1. Current enters thru ion channel (Na+), depolarizing that region. (ATP needed)
2. + charge is adjacent to - charged membr regions; + charge propagates along. Depolarization spreads (passive process)
3. As current travels, charge leaks outward (electrotonic decay) - doesn’t propagate indefinitely
- Initial site was -40, adjacent keep decreasing until -70
4. Distance electrotonus can travel is length constant

Axons generally longer than length constant

29
Q

Axial resistance

A

Depends on diameter. Ra incr when diameter decr

30
Q

Length constant

A

lambda = sqrt(Rm/Ra)
propagation distance incr when:
- membrane resistance incr
- axial resistance decr/diameter incr

31
Q

Active propagation

A

AP activates voltage-gated channels that regenerate depolarisation (let in Na+)

32
Q

Resistance

A

Affects rate of AP propagation. diameter incr, resistance decr, AP faster

33
Q

Capacitance

A

Affects rate of AP propagation
- +’s outside and -‘s inside are attracted to e/o. If there were a - outside, it would be repelled. Membrane is storing charge
- Changing charge takes time
- Proportional to surf area
- inversely proportional to membrane thickness
- myelin incr thickness: decr cepacitance
- Less capacitance -> charge changing faster -> faster AP propagation

34
Q

myelin

A
  • Incr AP propagation rate by decr capacitance
  • Schwann cells in PNS
  • Oligodendrocytes in CNS
  • Allows voltage gated channels to be conc at nodes of ranvier
35
Q

saltatory conduction

A

Between nodes of Ranvier:
- AP travels electrotonically
- myelin
- capacitance low, charge time short
- membrane thicker, Rm incr, longer length constant

At node of Ranvier:
- Active propagation
- Capacitance greater, charge time longer
- Slower AP
- Voltage gated channels

36
Q

excitatory synaptic transmission

A
  • Excitatory neurotransmitters (eg glutamate) bind to receptors that generate depolarizing PSPs
  • brings Vm close to threshold
  • Excitatory postsynaptic potential (EPSP)
  • Receptor types: AMPA and NMDA receptor gated channels
37
Q

AMPA-gated channel

A

On post-synaptic membrane, interacts w glutamate
- Allow both Na+ in and K+ ions out through pore
- Gen EPSP w potential around 0mV
- Brings postsynaptic neurons closer to threshold
- NMDA channels blocked by Mg2+
- Fast EPSP

38
Q

Dendritic summation of EPSPs

A
  • EPSPs decrease in amplitude while travelling to soma
  • Single EPSP doesn’t reach threshold: summate to cause AP firing post-synaptically
39
Q
  1. Temporal summation
A

Repetitive activation of single synapse, one right after the other. Reaches threshold at soma (insert pic)

40
Q
  1. Spatial summation
A

Simultaneous activation of multiple synapses on same dendrite. Reaches threshold at soma (insert pic)

41
Q

inhibitory synaptic transmission

A

Inh neurotransmitters (eg. GABA) bind to receptors which generate PSPs, Lowers Vm (away from threshold)
- Inhibitory postsynaptic potential (IPSP, below -70)
- GABAa receptor allows Cl- to enter; generates IPSP Ecl=-70

42
Q

Synaptic transmission

A
  1. AP propagates in presynaptic neuron
  2. Ca2+ enters axon terminal (voltage gated Ca2+ channel)
  3. Neurotransmitter released thru exocytosis
  4. Neurotransmitter binds to postsynaptic receptor
  5. Specific ion channels open in postsynaptic membrane (chemical messenger gated ion channels)
43
Q

Postsynaptic membrane effects

A

Binding of neurotransmitter induces conformational change of channel (opens)
- Ion movement generates synaptic current (Isyn)
- Isyn generates change in Vm (postsynaptic potential)

44
Q

Motor unit

A

alpha motor neuron and all muscle fibers it innervates
- alpha motor neuron can branch many time; APs travel down all branches
- Simultaneously initiate excitation of each muscle fiber
- All motor units innervating skeletal muscle = motor unit pool

45
Q

Anatomy of NMJs

A
  1. presynaptic terminal
  2. synaptic cleft
  3. postsynaptic membrane
    - contacts muscle at midpoint
46
Q

NMJ presynaptic terminal

A
  • ACh synth and stored in vesicles
  • Machinery for release of ACh: SNARE proteins and Ca2+ sensor associated w each vesicle and membrane
  • Soma creates empty vesicles, transported on MTs
  • Ach synth in terminal from acetyl CoA and choline
  • Vesicles organized into active zones
47
Q

NMJ synaptic cleft

A
  • 50nm space
  • basal lamina (ECM)
  • Adhesion and alignment of active zones (pre) and muscle junctional folds (post)
  • Acetylcholinesterase anchored in matrix, close to AChRs
48
Q

NMJ postsynaptic membrane, perijunctional zone

A
  • Longitudinal junction folds - SA for AChR
  • AChRs at peaks of each fold - positioned opposite active zones
  • Perijunctional zone: next to motor endplate, has many voltage-gated Na+ channels (site of AP initiation)
  • second type of AChR in other areas of muscle membrane - fetal development, inflammation, denervation
49
Q

Steps involved in neuromuscular transmission

A
  1. Each terminal end of a-MN simult activated by axonal AP
  2. AP activates voltage-gated Ca2+ channels, lets Ca2+ in
  3. ACh vesicles dock w synaptic membrane, exocytose ACh
  4. ACh diffuses across cleft, binds to AChRs at postjunctional folds
  5. AChRs open and allow Na+ in and K+ ions out = depolarization
  6. AChE in basal lamina hydrolyzes ACh into acetate and choline: terminates NM transmission
50
Q

Postsynaptic junction physiology

A
  • EPPs (end-plate potential) only propagates short distance
  • Perijunctional region has many voltage-gated Na+ channels - ensures AP threshold reached
  • EPP always large enough to reach AP threshold at perijunctional membrane (~40mV) (high safety factor - transmission and contraction always occur)

caps 301 (12 decks)

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