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15.1.514-15 · Homeostasis and Control

Sequence of Events Resulting in an Action Potential — Cambridge AS & A Level Biology 9700 Revision Notes & Topical Questions

5 min read 5 parts Lesson 20 of 31 1 quiz

📚 Cambridge AS & A Level Biology 9700 Hub / Topical Revision
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Lesson summary

15.1.5 Sequence of Events Resulting in an Action Potential — CAMBRIDGE AS & A LEVEL BIOLOGY 9700 — REVISION NOTES notes: Describe how a taste chemoreceptor generates an action potential in a sensory neurone.Papillae — the tongue surface is covered with small bumps.Taste buds — ea…

  • Chemoreceptors
  • Receptor proteins
  • Below threshold
  • Above threshold
  • Receptor potential
  • Voltage-gated channel

Part 1 of 3Taste receptors

Papillae
  • Papillae the tongue surface is covered with small bumps.
Taste buds
  • Taste buds each papilla's surface is covered with taste buds.
Chemoreceptors
  • Chemoreceptors each taste bud contains receptor cells sensitive to chemicals in food and drink.
Receptor proteins
  • Receptor proteins each chemoreceptor is covered in receptor proteins, and different proteins detect different chemicals.

Part 2 of 3Sequence for detecting salt

1
Salt dissolved in saliva provides sodium ions.
2
Na+ diffuse through selective channel proteins in the microvilli of the chemoreceptor.
3
The cell membrane depolarises; the increase in positive charge is the receptor potential.
4
If depolarisation is sufficient, voltage-gated Ca2+ channels open.
5
Ca2+ enter the cytoplasm and stimulate exocytosis of vesicles containing neurotransmitter from the basal membrane.
6
The neurotransmitter stimulates an action potential in the sensory neurone.
7
The sensory neurone sends the impulse to the brain.

Part 3 of 3Threshold

Below threshold
  • Below threshold the receptor cell is not sufficiently depolarised and no impulse is sent.
Above threshold
  • Above threshold the receptor stimulates the sensory neurone.
Strength
  • Strength the frequency of impulses increases with stimulus strength.

Key terms

TermMeaning
PapillaSmall bump on the tongue surface.
Taste budGroup of chemoreceptors on a papilla.
Receptor potentialPositive charge increase inside the receptor cell.
Voltage-gated channelChannel opened by a change in membrane potential.
ExocytosisRelease of vesicle contents from a cell.
NeurotransmitterChemical released to stimulate a neurone.

Avoid these mistakes

1
Saying Na+ directly cause the action potential in the neurone — Ca2+ triggers neurotransmitter release.
2
Saying the chemoreceptor is the sensory neurone — it is a separate specialised cell.
3
Saying every stimulus produces an impulse — the receptor potential must reach threshold.
4
Saying amplitude rises with stimulus strength — frequency rises.

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