nervous coordination

• Two factors contribute to establishing and maintaining the resting potential

  • The active transport of sodium ions and potassium ions
  • Differential membrane permeability
• What is the voltage across the membrane at resting potential?

  -70mV
• How is resting potential maintained?

  Sodium potassium pumps transports 3 sodium ions out of the neurone for every 2 potassium ions that are transported in. The membrane is impermeable to sodium and permeable to potassium.
• What happen in response to the stimulus to make the inside of the neurone less negative?

  Sodium channels open. Sodium diffuses into the neurone down the electrochemical gradient.
• Sodium and potassium ions can only cross the axon membrane through proteins.

  Explain why.

  can not pass through the phospholipid bilayer;because water soluble / not lipid soluble / charged / hydrophilic /hydrated;
• What happens if the threshold (around -55mV) is reached?

  Depolarisation occurs. More sodium channels open, sodium diffuses rapidly into the neurone.
• hyperpolarisation is...


  when the potential difference across this section of axon membrane briefly becomes more negative than the normal resting potential
• factors affecting the speed of conduction...

  • myelinated neurons
  • diameter of axon
  • temperature
• how does the diameter of the axon affect the speed of conduction

  Impulses are conducted at a higher speed when the axon is thicker due to the greater surface area. This increases the rate of diffusion of sodium and potassium ions through protein channels.
• How does the temperature affect the speed of conduction

  The colder the temperature the slower the speed of conduction.

  There is less kinetic energy available for the facilitated diffusion of sodium and potassium ions
• Exercise increases HR, describe the role of receptors in controlling heart rate

  
  

  Chemoreceptors detect a change in CO2

  impulses sent to the medulla

  more impulses to SAN

  by sympathetic nerve
• When a wave of electrical activity reaches the AVN, there is a short delay before a new wave leaves the AVN. Explain the importance of this short delay.

  
  

  Allow atria to empty / contract/ventricles to fill;

  Before ventricles contract;
• When the heart beats, both ventricles contract at the same time.Explain how this is coordinated in the heart after initiation of the heartbeat by the SAN.

  • Electrical activity only through Bundle of His / AVN
  • Wave of electrical activity passes through both ventricles at the same time