Receptors extended

• When receptors (such as chemoreceptors) are stimulated they are depolarized
• If the stimulus is very weak or below a certain threshold

  The receptor cells won’t be sufficiently depolarized and the sensory neuron will not be activated to send impulses
• All-or-nothing principle

  An impulse is only transmitted if the initial stimulus is sufficient to increase the membrane potential above a threshold potential
• Threshold levels in receptors often increase with continued stimulation
• Greater stimulation is required

  Before impulses are sent along sensory neurons
• Chemoreceptors

  Specialized cells that detect a specific type of stimulus and affect the sensory neuron's electrical activity
• Other receptors

  Just the ends of the sensory neurons