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Anatomy And Physiology 1 > Chpt. 10.6 - 10.8 > Flashcards

Chpt. 10.6 - 10.8 Flashcards

1
Q

Cell Membrane Potential

A
  • Cell membrane is usually polarized
  • inside is negative, outside is positive
  • polarization is due to an unequal distribution of positive & negative ions across the membrane
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2
Q

Membrane Permeability

A
  • Much more permeable to K+ than to Na+

- Determined by membrane channels

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3
Q

Distribution of Ions across membrane

A
  • K+ are major intracellular cations (wants to go out of cell)
  • Na+ are major extracellular positive ions (wants to go in cell)
  • This distribution is created by Na+/K+ Pump
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4
Q

Membrane Resting Potential

A
  • Resting nerve cell is not being stimulated to send an impulse, non-gated channels determine the membrane permeability to Na+ and K+ ions
  • -70mV, more negative inside cell, this negative potential helps Na+ enter the cell despite low permeability, but prevents K+ from leaving
  • 3 Na+ leak into the cell for every 2 K+ that leak out
  • Na+/K+ pump balances these leaks by pumping 3 Na+ out and 2 K+ in
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5
Q

Na+/K+ Pump

A
  • Maintains the concentration gradients for Na+ and K+ ions
  • Requires ATP in order to transport Na+ and K+ ions in opposite directions, maintaining the concentration gradients for those ions responsible for diffusion
  • Pumps 3 Na+ out and 2 K+ in
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6
Q

Hyperpolarization, Depolarization

A

Hyperpolarization:
-membrane potential becomes more negative
Depolarization:
-membrane potential becomes less negative

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7
Q

Threshold potential

A
  • approximately -55 mV
  • reaches this only when neurons are sufficiently depolarized
  • once reached, will trigger action potential
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8
Q

Action potential

A
  • Rapid change in membrane potential
  • When threshold is reached, voltage-gated Na+ channels near axon hillock open by trigger zone
  • Opening of voltage-gated Na+ channels trigger action potential
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9
Q

Trigger zone

A
  • First part of axon, cone-shaped axon hillock or initial segment
  • contains many voltage-gated Na+ channels
  • when threshold is reached, open for a brief moment, increasing sodium permeability
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10
Q

Ion Movement during Action Potential

A

1) Axon membrane @ rest (-70 mV)
2) When membrane threshold is reached, voltage-gated Na+ channels open, Na+ diffuses inward, membrane is depolarized
3) Voltage-gated K+ channels open, K+ diffuses outward, membrane is repolarized, brief period of hyperpolarization follows

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11
Q

Events leading to Impulse Conduction

A

1) Nerve cell membrane maintains resting potential by diffusing of Na+ and K+ down their concentration gradient as the Na+/K+ pump pumps them up the gradients
2) Pre-synaptic neuron releases vesicles w/ neurotransmitter after voltage-gated Ca2+ channels open and Ca2+ diffuses into pre-synaptic knob
3) Neurotransmitters bind to chemically-gated Na+ channels that allow Na+ in, depolarizing the membrane until threshold is reached
4) Once threshold is reached, voltage-gated Na+ channels in axon hillock open, increasing permeability of Na+ for a short while
5) Na+ ions diffuse inward, depolarizing the membrane
6) K+ channels open in axon, K+ ions diffuse outward, repolarizing the membrane
7) Action potential results that causes an electric current to stimulate adjacent portions of the membrane

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12
Q

Absolute refractory period

A

-axon’s voltage-gated Na+ channels temporarily not responsive and CANNOT be stimulated

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13
Q

Relative refractory period

A
  • repolarization is incomplete

- stimulus higher than usual intensity may trigger a new action potential

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14
Q

Saltatory conduction

A
  • conduction on myelinated axons, action potential appears to jump from node to node
  • myelin contains T H I C C lipids that prevents ions from flowing out of axon
  • nodes of Ranvier between Schwann cells allows axon membrane to have channels for Na+ and K+ ions that open during a threshold depolarization
  • action potential only occur at nodes of myelinated axons
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15
Q

Impulse Conduction Speed

A
  • Axon diameter affects conduction speed, T H I C C axons transmit faster than thin axons
  • Myelinated axons transmit impulses faster
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16
Q

Factors Affecting Impulse Conduction:

Increase in concentration of K+ in extracellular fluid

A
  • Reduces gradient for K+ to leave cell
  • Threshold potential reached w/ stimulus of lower intensity
  • Leads to more easier excitable neurons, perhaps convulsions (epilepsy)
17
Q

Factors Affecting Impulse Conduction: Decrease in concentration of K+ in extracellular fluid

A
  • Neurons can become hyperpolarized
  • Action potentials are not generated
  • Lack of impulses leads to muscle paralysis
18
Q

Factors Affecting Impulse Conduction: Decrease in permeability to Na+ ions

A
  • Stops impulses from passing through tissue fluid around axon
  • Impulses do not reach brain, no perception of touch and pain
19
Q

Synaptic potentials

A

-local potentials that result from changes in chemically-gated ions channels

20
Q

Excitatory neurotransmitters

A
  • Increase permeability to Na+ ions
  • Brings membrane closer to threshold
  • Increases likelihood of generating impulses
21
Q

Inhibitory neurotransmitters

A
  • Move membrane farther from threshold

- decrease likelihood of generating impulses

22
Q

EPSP

A
  • Excitatory postsynaptic potential
  • Membrane change in which neurotransmitter opens Na+ channels
  • Depolarizes membrane of postsynaptic neuron, as Na+ neuron enters axon
  • Action potential becomes more likely
23
Q

IPSP

A
  • Inhibitory postsynaptic potential
  • Membrane change in which neurotransmitter opens K+ channels (or Cl- channels)
  • Hyperpolarizes membrane of postsynaptic neuron, as K+ leaves axon
  • Action potential becomes less likely
24
Q

Summation of EPSPs and IPSPs

A
  • EPSPs and IPSPs are added together in summation
  • Net excitatory effect leads to greater probability of action potential
  • Net inhibitory effect does not generate action potentials
  • Summation occurs at AXON HILLOCK
25
Q

5 criteria of neurotransmitters

A

1) Synthesis of transmitter substance in the neuron
2) Storage of neurotransmitter or precursor in the presynaptic nerve terminal
3) Release of the neurotransmitter into the synaptic cleft to bind to target receptor on the postsynaptic membrane resulting in specific change in activity
4) Mechanism of removal of transmitter from the synaptic cleft
5) Exogenous application of neurotransmitter mimics the action of endogenously released transmitter

26
Q

Hebbian coincidence

A

-When the axon of cell A is near enough to excite cell B and persistently takes part in firing it, a connection is established between cell A and cell B that increases firing efficiency

27
Q

LTP

A
  • Long Term Potentiation
  • Persistent strengthening of synapses based on recent patterns of activity
  • Produce a long-lasting increase in signal transmission between two neurons
  • Can result in growth of new post-synaptic receptors and channels
28
Q

AMPA & NMDA receptors

A
  • Both respond to glutamate
  • Both are ionotropic (they allow ions to pass when open)
  • AMPA receptors typically do not allow Ca2+ to pass
  • AMPA receptors depolarize the dendrite which relieves the Mg2+ block of the NMDA receptor
  • NMDA allows Ca2+ to pass
29
Q

AMPA & NMDA ESSAY

A

“Coincidence is when two situations occur at the same time. In this case, only when two neurons fire together, they will be able to stimulate a separate neuron, making the two neurons depend on each other in order to invoke a response. When these two neurons are communicating with another, glutamate will bind to the NMDA channel and open. Yet no long-term potentiation, or LTP, occurs as a magnesium ion acts as blockage on the NMDA channel, preventing Ca2+ and Na2+ to flow in. In order to remove this Mg2+ ion, depolarization must occur to “unplug” the channel. This is where AMPA comes in play. AMPA receptors will bind to neurotransmitters released by high-frequency stimulation that allow Na2+ to enter the AMPA channel, depolarizing the membrane, and thereby opening the NMDA channel, as the increased positive charges dislodge the Mg2+ ion that was blocking the channel previously. Once opened, the NMDA channel will now allow the Ca2+ and Na+ to flow through and establish connection with the second neuron, activating protein kinases and establish the LTP. This establishes the basis of long term potentiation, and showcases that association of two channels that could not activate LTP by themselves can do it together by using two simultaneous inputs, creating a dependency on each other and allowing an adaptive response in order to create plasticity. “

30
Q

3 Factors that Alter Resting membrane potential

A

1) Na/K+ ATPase
2) Inherent negative charge
3) K+ leak

31
Q

Resting Permeability of pk : pNa : pCl

A

pK : pNa : pCl = 1 : 0.05 : 0.45

32
Q

Action Potential Permeability of pk : pNa : pCl`

A

pK : pNa : pCl = 1 : 12 : 0.45

33
Q

Neural Coding

A
  • Qualitative information (taste/hearing) depends upon which neurons fire; brain knows what type of sensory information travels on each fiber
  • Quantitative Information depend on 1) different neurons having different thresholds and 2) stronger stimuli that will cause a more rapid firing rate
34
Q

Memory

A
  • Physical basis of memory: a pathway (memory trace, engram) modified to make transmission easier
  • Synaptic potentiation: transmission mechanisms correlate w/ different forms of memory (immediate, short, and long-term)

Anatomy And Physiology 1 (12 decks)

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