How the neuron works

How the neuron works

1. The resting potential: normally the outside of the cell is positively charged and the inside is negatively charged.

   • outside cell: high sodium (Na)
     • chlorine (Cl) is the dominate negative
   • inside cell: high potassium (K)
     • other negative ions are found inside too: phosphates and sulfates
   • The cell membrane has special gateways for only Na, K, and Cl and the larger ions are trapped inside the cell
   • The movement of Na and K is what causes a wave of deploization
     • At rest the cell membrane is much more permeable to K and Na (about 50x)
   • When Na is moving into the cell there is more K moving out of the cell.
     • All those big negatively charged ions are trapped inside
   • Active transport keeps more positive ions on the outside by the Na/K pumps
     • This pump pulls 3 Na outside and only 2 K inside
   • The nerve impulse: A neuron will only trigger an impulse along its axon when it has been stimulated. The stimulus has to be strong enough to send a wave of depolarization along the axon, beyond the neuron's threshold. It cannot send a mild or strong response, either it responds or it doesn't
     • Depolarization
       • Occurs when the gates of the K close and the gates of the Na open
       • The Na moves to the inside of the cell, causing the inside to become positive and the outside to become negative
         • This change In the charge is called action potential
       • Depolarization of any one part of the axon causes the gates of the Na to open, so the depolarization ripples along the entire length of the neuron
       • Repolarization
         • Depolarization only occurs for a small fraction of a second
         • Right after the sodium channels open to cause depolarization:
           • The K gates re-open
             • The potassium ions move out
           • The Na gates close
           • There is a rapid active transport of the Na out of the axon by the Na/K pump
           • Polarity is re-established
         • Refractory period: the time between an impulse and the next time the axon may be available for another impulse