Events -> action potential

• The surface of the tongue is covered in many small bumps known as papillae
• The surface of each papilla is covered in many taste buds
• Taste bud

  Contains many receptors known as chemoreceptors
• Chemoreceptors

  Sensitive to chemicals in food and drinks
• Chemoreceptor

  Covered in receptor proteins
• Receptor proteins

  Different receptor proteins detect different chemicals
• Sequence of events resulting in an action potential in a sensory neuron

  1. Chemoreceptors detect salt

  2. Sodium ions diffuse out

  3. Depolarization of chemoreceptor cell membrane

  4. Increase in positive charge (receptor potential)

  5. Stimulates voltage-gated calcium ion channels to open

  6. Calcium ions enter cytoplasm

  7. Stimulates exocytosis of neurotransmitter vesicles

  8. Neurotransmitter stimulates action potential in sensory neuron

  9. Sensory neuron transmits impulse to the brain
• If salt is present in the food

  Sodium ions diffuse out through highly selective channel proteins
• Increase in positive charge inside the cell

  Is known as receptor potential
• If sufficient stimulation by sodium ions and sufficient depolarization of the membrane

  The receptor potential becomes large enough to stimulate voltage-gated calcium ion channel proteins to open
• Calcium ions enter the cytoplasm of the chemoreceptor cell

  Stimulates exocytosis of vesicles containing neurotransmitters
• Neurotransmitter stimulates

  An action potential in the sensory neuron
• Sensory neuron transmits an impulse to the brain