ReceptorsAQA A-Level Biology: Flashcards
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Why are receptors described as specific?
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- Why are receptors described as specific?
- Each type of receptor responds to only one type of stimulus.
- What is a generator potential?
- A change in the potential difference across a receptor membrane in response to a stimulus.
- Describe the structure of a Pacinian corpuscle.
- The ending of a sensory neurone wrapped in layers of connective tissue (lamellae) separated by gel.
- What type of stimulus does a Pacinian corpuscle detect?
- Mechanical pressure.
- How does pressure produce a generator potential in a Pacinian corpuscle?
- Deformation opens stretch-mediated sodium ion channels, sodium ions diffuse in and the membrane depolarises.
- When does a generator potential produce an action potential?
- When it reaches the threshold, so voltage-gated sodium ion channels open.
- Which photoreceptors work in dim light and which pigment do they contain?
- Rods, containing rhodopsin.
- What do cones contain and when do they work?
- Iodopsin, in bright light.
- Why can rods work in dim light?
- Rhodopsin is broken down by low-intensity light and many rods share one bipolar neurone, so their generator potentials add up (spatial summation).
- Why do cones give high visual acuity?
- Each cone in the fovea has its own bipolar neurone, so adjacent points of light produce separate impulses.
- Why do rods give low visual acuity?
- Many rods share one bipolar neurone, so impulses from adjacent rods merge and two points of light are not distinguished.
- How do we see different colours?
- There are three types of cone sensitive to red, green and blue; the brain compares the proportions of stimulation.
- Why do we see only shades of grey in dim light?
- Only rods respond, and they have a single pigment, so wavelengths cannot be compared.
- Where are cones concentrated?
- In the fovea at the centre of the retina.
Exam questions on Receptors
- Pacinian corpuscles are receptors found in the skin of the fingertips. Each one is the ending of a sensory neurone wrapped in several layers of connective tissue, with a gel between the layers.Suggest how the structure of the corpuscle allows pressure on the skin to produce a response in the sensory neurone.2 marks
- A hiker walks at dusk. In the dim light she can make out the outline of the path and the trees but cannot tell what colour her jacket is. At midday she can read the fine print on her map and see colours clearly.Explain why she could not tell what colour her jacket was at dusk.2 marks
- A researcher records the potential difference across the membrane of the sensory neurone ending inside a Pacinian corpuscle while different stimuli are applied. Light pressure produced a small depolarisation but no action potentials. Moderate pressure produced a larger depolarisation and a short series of action potentials in the sensory neurone. Strong pressure produced an even larger depolarisation and a more rapid series of action potentials, each the same size as before. A bright light shone on the corpuscle produced no change at all.Explain why strong pressure produced a larger depolarisation than light pressure.3 marks
Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).