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S1B5: Physiology > Ionic Basis of Excitation 2 > Flashcards

Ionic Basis of Excitation 2 Flashcards

1
Q

What are the 2 possible types of graded potentials? What membrane change accomplished each of them? What is the final result?

A
  1. EPSP (excitatory postsynaptic potential)
    1. depolarizing from rest
      1. opening up non-selective cation channels
      2. Na+ goes in first b/c drivign force is higher
    2. incrased excitability
  2. IPSP (inhibitory postysynaptic potential)
    1. hyperpolarizign from rest
      1. open chloride channels, (Cl- enters cell)
      2. open potassium channels (leaves cell, inside more negative)
    2. decreased excitability
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2
Q

What type of change results from graded potentials?

A

local change of membrane potential

generally does not affect equilibrium potential

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3
Q

What are the 3 major ways membrane permeability is changed via receptors?

A
  1. Receptor directly coupled with channel
    1. ligand-gated
  2. Receptor activates G-protein coupled
    1. second messenger
    2. slow response
  3. Receptor opens channel for one ion and this ion affects permeability to another ion (ICaK)
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4
Q

What the two types of selectivity associated with ion channels? Provide examples.

A
  • non-selective
    • ion w/ biggest driving force determine direction & size potential change
      • channels that allow any cation
      • at rest, Na+ moves most (furthes from equilibrium); leads to depolarization
  • selective
    • permeability change determines potential change
      • decreased permeability to K+; leads to depolarization
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5
Q

What is the major postsynaptic receptor?

A
  • Glutamate
    • Types: AMPA/Kainate and NMDA
      • ionotropic = fast
      • increased conductances Na+. Ca++, K+
    • Type: metabotropic
      • G-protein coupled
      • Effectors = phospholipase C, adenylyl cyclase, ion channels
      • Closing K+ or openign Ca++ = increased neuronal firing
      • Presynaptically: autoreceptors to limit glutamate release
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6
Q

What is a major inhibitory receptor? What is the difference between the two types?

A
  • GABA
    • hyperpolarizes post synaptic membrane (IPSP)
    • GABA A- Receptors
      • Cl- channel–> hyperpolarizaion
      • “fast” response
      • Potentiate GABA response
        • benzodiasepines (Diasepam), barbiturates
      • block GABA channel
        • picrotoxin, penicillin
    • GABA B- Receptors
      • G-protein coupled receptor
      • K+ conductance –> hyperpolarization
      • “slow” response
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7
Q

How does depolarization spread through a membrane? What happens to its amplitude as it spreads?

A
  • Passive spread- no regeneration
  • decremental in amplitude
    • b/c leak across membrane
  • travels short distances?
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8
Q

Opening of ionotropic glutamate receptors at postsynaptic membrane will:

A: excite the cell (depolarize)

B: Inhibit the cell (hyperpolarize)

C: increase permeabilty for sodium only

D: increase permeability for chloride only

A

A: excite cell (depolarize)

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9
Q

What are the 3 possible outcome from an graded potential?

A
  1. Fails to meet threshold
    1. no action potential
  2. Reach spike threhold
    1. Action potential is generated
  3. Surpass spike threshold
    1. More action potentials are generated
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10
Q

How is information coded by action potentials?

A

number and frequency of action poentials

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11
Q

Are action potentials the same in all types of cells?

A

No, they vary in amplitude, duration and shape

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12
Q

What are the imporant voltage-gated ion channels involved in regulating action potentials?

A
  1. Sodium gated channels
    1. Rapid opening– (activation-gate)
      1. Na+ rushes in (selective)
      2. depolarization
    2. Slow inactivation (inactivation-gate)
      1. Na+ movement stops
  2. Potasium gated channels
    1. voltage sensor
    2. delayed opening (sequential to Nav)
      1. K+ rushes out (selective; durign AP far away from Ek)
      2. Repolarizaion
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13
Q

Describe the sequential opening of Nav and Kv

A

Both channels are closed

Once the graded potential reaches the threshold, Na+ channels open

This further deopolarizes the membrane & opens more Na + channels

Na+ channels close and K+ channels open

Na+ channels reset to original position while K+ channels remain open

Both channels are closed

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14
Q

During what period is it impossible to generate an additional action potential becasue the threshold is infinately high?

During what period is a higher than normal stimulus required to initiate an action potential?

A
  • absolute refractory
    • due to increase in gNa+ and subsequent inactivation
      • not possible to open Na+, b/c all are already open, so it is impossible to generate an AP
  • Relative refractory
    • some inactivated Na+ channels and high gK+ make depolarization difficult
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15
Q

What are the 2 major impacts of the refractory period? What is the typical length of the refractory persiod for skeletal muscles & neurons and cardiac muscles?

A

Skeletal muscles & neurons ~2ms; Cardiac muscles ~250ms

  1. Unidirectional transmission
  2. limits frequency
    1. preseves informaiton to be coded
    2. precents tetanus of cardiac muscle
    3. short refractory in skeletal muscle to allow fusign of single muscle twitches to contorl overall muscle contraction
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16
Q

In the relative refractory period the stimulus to evoke action potentials needs to be

A: just above the resting spike threshold

B: Sub-threshold

C: Not applicable, no stimulus no matter how high can elicity an AP in this period

D: Much higher than at rest to get to AP threshold

A

D: Much higher than at rest to get to AP threshold

17
Q

What type of conduction occurs at the node of Ranvier? What type of voltage gated channels are numerous here?

A

Active, regenerative conduction

lots of voltage gated sodium channels

18
Q

How does an axon accomplish unidirection movement of action potentials?

A
  • Na+ channels are closed, open or inactivated
    • inward Na+ current depolarizeds in the active region
    • depolarizaton spreads both ways
    • AP travels only one way, because in only one direction are there sodium channels that are no longer in refractory period
      • due to inactivated Na+ channelsa dn activated K+ channels
19
Q

What are the 2 major factors affectign Action Potential conductio velocity?

A
  1. Axion Diameter
    1. larger diameter = greater cross sectional area = larger number mobile ions = faster conduction
    2. lowers axial resistance
    3. faster conduction velocity
  2. Saltatory Conduction (Myelination)
    1. increased membrane insulation adn resistance (less leaky)
    2. action potential “jumps” from node to node
    3. faster conduction velocity
20
Q

Which cells are responsible for myelination int eh central nervious system? Peripheral nervous system?

A

Central: Oligodendrocyte

Peripheral: Schwann

21
Q

Where can you find a high concentratin of voltage gated potassium channels along a myelinated axond? Voltage gated sodium channels?

A
  • High density voltage-gated K+ channels at myelin internodes
    • ensure nice negative resting membrane potential, ready to be activated
  • High density of voltage-gated sodium channels at nodes of ranvier
22
Q

Which type of fibers are myelinated? A-type or C-type?

A

A-type: myelinated

C-type: non-myelinated

23
Q

What is the name of the disease the results in an immune-mediated inflammatory disease in which myelinated axons in the CNS are attacked and destroyed.

What is the physical result of demyelinating these axons?

A

Multiple Sclerosis

  • Decreasing conduction velocity
  • frequency related block
  • total conduction block
  • ectopic impulse generation
  • increase in mechanosensitivity
  • crosstalk

B/C unequal distribution of channels

  • Nav at nodes, K channels at internodes
  • exposed K+ channels can block conduction
  • electronic condubtion
24
Q

Why is it unlikely that as a physician it will be unlikely to see one action potential?

A
  • Conduction in a Nerve Trunk
    • Compound Action Potentials
      • may be heterogeneous fiber types
        • A-type
        • C-type
      • many sizes
      • conduction velocies vary

S1B5: Physiology (5 decks)

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