Nervous system & response

• What is a stimulus?

  A detectable change in the environment
• Why is the ability to respond to stimuli important for organisms?

  It increases their survival rate
• What are the two key sections of the nervous system?

  • Central nervous system (CNS): brain and spinal cord
  • Peripheral nervous system (PNS): receptor cells, sensory neurons, motor neurons
• What are receptors?

  Cells that detect stimuli
• What are the names of the two photoreceptors in the retina?

  Rods and cones
• What happens if the stimulus is large enough?

  It can establish a generated potential
• What is the threshold for sodium ions to generate an action potential?

  More than minus 55 millivolts
• What is the role of sodium ions in generating an action potential?

  They cause depolarization of the neuron
• What occurs if the stimulus is not strong enough?

  No action potential is generated
• What type of stimulus does the pacinian corpuscle respond to?

  Pressure
• Where are pacinian corpuscles primarily located?

  Deep in the skin
• What is the structure of the pacinian corpuscle?

  A sensory neuron wrapped in connective tissue
• What is found between the layers of connective tissue in the pacinian corpuscle?

  A viscous gel
• What type of channel proteins are present in the sensory neuron of the pacinian corpuscle?

  Stretch mediated sodium ion channels
• When do stretch mediated sodium ion channels open?

  When pressure is applied
• What happens to sodium ions when pressure is applied to the pacinian corpuscle?

  Sodium ions diffuse into the neuron
• What is the resting potential of a neuron?

  Approximately minus 70 millivolts
• What occurs when enough sodium ions diffuse into the neuron?

  An action potential is generated
• What is the process of generating an action potential in the pacinian corpuscle?

  1. Pressure applied to pacinian corpuscle
  2. Stretch mediated sodium channels open
  3. Sodium ions diffuse into neuron
  4. Inside of neuron becomes more positive
  5. If threshold of -55 mV is reached, action potential occurs
• What is the main function of the pacinian corpuscle?

  To detect pressure
• What happens to the plasma membrane of the sensory neuron when pressure is applied?

  It becomes deformed and stretched
• What is the result of the deformation of the plasma membrane?

  Stretch mediated sodium channels open
• What is the outcome if enough sodium ions enter the neuron?

  A response occurs due to action potential
• What is the overall role of the pacinian corpuscle in the nervous system?

  To enable response to pressure