AQA · A-Level · Biology
Course version: 7402 · Version from Sept 2016
The Pacinian corpuscle should be used as an example of a receptor to…
Full specification wording
Receptors (A-level only): The Pacinian corpuscle should be used as an example of a receptor to illustrate that: receptors respond only to specific stimuli stimulation of a receptor leads to the establishment of a generator potential.
Receptors are transducers: they convert the energy of a stimulus into the electrical energy of a nerve impulse.
Checked against the AQA 7402 specification (opens in a new tab) on .
- Point 1 of 4
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
Receptors are transducers: they convert the energy of a stimulus into the electrical energy of a nerve impulse. Each type is specific, because only one form of energy can open its particular channel proteins. A Pacinian corpuscle, found deep in the skin and around joints and tendons, contains stretch-mediated sodium ion channels that open only when the membrane is physically deformed, so it responds to pressure and vibration and is completely insensitive to light, sound or chemicals. When pressure is applied, sodium ions enter and the membrane depolarises, and that local depolarisation is the generator potential. A generator potential is graded: a greater or faster pressure change deforms more channels, admits more sodium ions and produces a larger generator potential.
What earns the marks
- Receptors being specific because only one type of stimulus opens their channels.
- The Pacinian corpuscle responding to pressure or vibration through stretch-mediated sodium ion channels.
- Sodium ions entering and depolarising the membrane to give a generator potential.
- The generator potential being graded, so a larger stimulus gives a larger generator potential.
- An action potential being produced only when the threshold is reached.
Common mistakes and how to put them right
Calling the generator potential an action potential, when the generator potential is graded and local and the action potential is all-or-nothing.
Saying the receptor creates the impulse, rather than converting stimulus energy into a change in membrane potential.
Claiming a stronger stimulus gives a bigger action potential instead of a higher frequency of action potentials.
Writing sodium rather than sodium ions, which caps the marks available on these questions.
Forgetting that the time taken for the channels to open contributes to measured reaction time.
Exam tips
- Always write sodium ions or Na⁺, never just sodium, because mark schemes cap answers that omit the ion.
- Use the word transducer, or the phrase converts one form of energy into a nerve impulse, when defining a receptor.
- In reaction time questions, the delay at the receptor, at the synapses and in the muscle all count as separate reasons.
Try the lesson
The start of the Receptors (A-level only): The Pacinian corpuscle should be used as an example of a receptor to illustrate that: receptors respond only to specific stimuli stimulation of a receptor leads to the establishment of a generator potential. lesson, made from checked teaching notes for this specification point.
Have a go first
Which statement describes the specificity of a Pacinian corpuscle?
Listen
Receptors are transducers: they convert the energy of a stimulus into the electrical energy of a nerve impulse. Each type is specific, because only one form of energy can open its particular channel proteins. A Pacinian corpuscle, found deep in the skin and around joints and tendons, contains stretch-mediated sodium ion channels that open only when the membrane is physically deformed, so it responds to pressure and vibration and is completely insensitive to light, sound or chemicals. When pressure is applied, sodium ions enter and the membrane depolarises, and that local depolarisation is the generator potential. A generator potential is graded: a greater or faster pressure change deforms more channels, admits more sodium ions and produces a larger generator potential. A strong answer earns marks for these points. receptors being specific because only one type of stimulus opens their channels. the Pacinian corpuscle responding to pressure or vibration through stretch-mediated sodium ion channels. sodium ions entering and depolarising the membrane to give a generator potential. the generator potential being graded, so a larger stimulus gives a larger generator potential. Exam tip: Always write sodium ions or Na⁺, never just sodium, because mark schemes cap answers that omit the ion.
Key words
Say what each word means before you turn the card.
receptor specificity
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transduction
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stretch-mediated sodium ion channels
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generator potential
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See every definition
- receptor specificity
- Only one form of energy can open a receptor's particular channel proteins, so receptors respond only to specific stimuli.
- transduction
- Receptors convert the energy of a stimulus into the electrical energy of a nerve impulse.
- stretch-mediated sodium ion channels
- Channels in a Pacinian corpuscle that open only when the membrane is physically deformed, so it responds to pressure and vibration.
- generator potential
- The local depolarisation produced when sodium ions enter and the membrane depolarises, and it is graded.
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