16. Changing Membrance Potential

Neurons electrically excitable cause

• Due to the resting potential

Types of Gated Ion Channels (GI_C’s)

1. Voltage gated

   • direct changes in memebrane portential (MP’s)

   • found in axon plasma membrances only or in presynaptic terminals

2. Mechincally gates

   • respond to mechincal virtation or pressure stiumli

   • Connected to special dentrite regions that are developed for gathering sensory info

3. LIgand gated

   • Chemicals

   • speicfic to a ligand

   • mostly on cell body regions/ dendrite regions

Electtrial signals in Neurons

2 types

1. Graded potentials (local)

   • short communication only

   • LIgand + mechanical channels

   • dependant on how much stimulus you have (chemicals)

2. Action Potentials

   • short + long distance communicaiton

   • voltage gated channels

Graded potentials in depth

• present in cells body/ dendrite regions

• Deloprizaiton or hyperpolaization

• small dervations from -70mv

GP’s :stimulus stregnth + summation

1. amplitude of GP’s depends on stimulus strength

   • ammount of pressure on a mechanical gate

   • ammount of ligands released

2. summation

   • how close signals are in time

   • can be added togetehr to become larger

Action potencials in depthh

• Large enough GP can cause AP

  • reaching threashold

    • ACTION POTENTIAL !!

• We need large enough charge in MP from GP’s to reach trigger zone

  • greater tahn normal number of VGIC’s here

• ALL OR NONE PRINCIPLE

• max 35mv

VG K+ C’s have one gate

VG Na+ C’s have 2 gates

1. Extracellular gate

   • AKA activation gate

2. Cytosol side gate

   • AKA inactivation gate

Process of action potencial

1. Resting potential (-70mv)

   • all VGIC’s closed

• Na+ inactivation gate is open

  • activaiton gate is closed

2. GP cuases threshold in trgger zone

   • opens activation gate (Na+)

   • VG Na+ C’s open

   • Na+ rushed into cell

     • depolarization

3. approaching +35mv

   • Inactivation gate closes

   • Na+ cant go through

   • VG K+ C’s opening

     • K+ moves out of cell

     • Inside of cell becomes more negative

       • repolarization

   • Na/K+ pump always working

4. Back to RP (SIKE!!!)

   • Activation gate closes

   • inactivation gate opens

     • able to be reactivated

5. Hyperpolarization/afterpotential

   • VGK+C’s stay open too long

     • causes MP to drop to approx. -90 mV

       • eventually the VGK+C’s close and RP is maintained

Refreactory period

• Absolute

  • cannot fire

  • Na+ inactivation gate must return to restign state

• Relative

  • Harder to stimulate

  • needs suprethreshold stimulus

  • K+ still not closed BTW

Strong vs Weak stimulus

• Determined by frequency of AP’s

  • until max rate