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Neural Communication. Action Potential Lesson 11. Action Potentials. Large and rapid change in membrane potential electrically-gated channels EPSPs threshold potential Occurs in axon triggered at axon hillock ~. axon hillock. AP Characteristics. Voltage-gated channels

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Neural communication

NeuralCommunication

Action Potential

Lesson 11


Action potentials
Action Potentials

  • Large and rapid change in membrane potential

  • electrically-gated channels

  • EPSPs

    • threshold potential

  • Occurs in axon

    • triggered at axon hillock ~



Ap characteristics
AP Characteristics

  • Voltage-gated channels

  • All or none

  • Slow

  • Non-decremental

  • Self Propagated

    • regenerated ~


+40

0

-55

-65

-75

Time

Vm


+40

0

-55

-65

-75

Time

Vm


+40

0

-55

-65

-75

Time

Vm


+40

0

-55

-65

75

Time

Vm


+40

C & E gradients

drive Na+ into cell

Depolarization

Na+ influx

0

Vm

-55

-65

-75

Time


+40

= 105 mV

Amplitude

Depolarization

Na+ influx

0

- 65 mV to +40 mV

Vm

-55

-65

-75

Time


+40

Repolarization

K+ efflux

0

Vm

-55

-65

-75

Time


After-

hyperpolarization

+40

0

Vm

-55

-65

-75

Time


Refractory period
Refractory Period

  • after AP

    • won’t fire again

    • relative & absolute

  • Relative

    • during after hyperpolarization

    • requires greater depolarization ~


Relative refractory period

+40

0

Time

Relative Refractory Period

Vm

-55

-65

-75


Absolute refractory period
Absolute refractory period

  • Na+ channels deactivate

    • will not trigger AP

    • must reset

  • Ball & Chain Model ~




Frequency code
Frequency Code

  • Pattern = Intensity of stimulus

    • frequency of APs

  • Place = type of stimulus

    • Visual, auditory, pain, etc.

    • Brain area that receives signal

    • Doctrine of Specific Nerve Energies ~


1.

2.

3.

FREQUENCY CODE

Weak stimulus

Moderate stimulus

Strong stimulus


Saltatory conduction
Saltatory Conduction

  • Myelinated neurons

    • oligodendroglia & Schwann cells

  • Transmit long distances

    • APs relatively slow, regenerates

    • EPSPs - fast, decremental

  • Saltatory: combines both types of current

    • speed without loss of signal ~


Saltatory conduction1
Saltatory Conduction

  • Nodes of Ranvier

    • action potentials

  • Myelinated

    • like electricity through wire

    • decremental but triggers AP at next node

  • Safety factor - trigger AP across 5 nodes

    • .2 - 2 mm apart

      • larger neurons  farther apart ~


Saltatory Conduction

Nodes of Ranvier


Psps vs aps

Graded

Summation

longer duration

*10-100 msec

chemical-gated

passive spread

instantaneous

decremental

All-or-none

short

1-2 msec

voltage-gated

propagated

slow

nondecremental

PSPs vs APs


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