Receptors are specfic- they only detect on particular stimulus. 

Receptors in the nervous system convert the energy of the stimulus into the electrical energy used by neurones. Here's how they work...

Resting potential (-70mv):

  • When a nervous system receptor is in its resting state there is a difference in charge between the inside and outside of the cell. 
  • This inside of the cell is more negatively charged. 
  • This creates a voltage(potential difference) across the membrane. 
  • The potential difference when the cell is at rest is called its resting potential and it is generated by ion pumps and ion channels. 

Generator potential:

  • When there is a stimulus, the cell membrane is excited and becomes more permeable, causing the sodium ion channel proteins to open.
  • Sodium ions travel back into the cell because there is now a concentration gradient.
  • This alters the potential difference - this is known as the generator potential. 
  • Depolarisation occurs.
  • A bigger stimulus excites the membrane more, causing a bigger movement of ions and a bigger change in potential difference, so a bigger generator potential is produced. 

Action potential(+40mv):

  • A generator potential can trigger an action potential if it is big enough and reaches the threshold level. 
  • An action potential is an electrical impulse down a neurone.
  • All action potentials are the same size
  • A stronger stimuli causes more action potential because there's a higher frequency 
  • Weak stimuli causes less action potential because there's a lower frequency
  • If a stimulus is too weak it will not reach the threshold level and an action potental will not be formed. 

Pacinian corpuscles:

These are mechanoreceptors- they detect mechanical…


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