14.4 - Receptors Flashcards
What is the difference between sensory reception and sensory perception?
- Sensory reception: The function of receptors that detect stimuli from the environment.
- Sensory perception: The interpretation of sensory information, primarily by the brain
What are the two main features of sensory receptors?
1) Specificity:
- Each receptor responds to one specific type of stimulus.
- Example: Pacinian corpuscles respond to mechanical pressure, not heat or light.
2) Acts as a transducer:
- Converts stimulus energy (e.g., mechanical, light) into nerve impulses (electrical energy).
- Example: Pacinian corpuscles convert mechanical pressure into a generator potential.
Describe the structure and location of Pacinian corpuscles.
- Found deep in the skin, especially on the fingers, soles of the feet, and external genitalia.
- Also found in joints, ligaments, and tendons to help detect changes in joint direction.
Structure: - Central sensory neuron surrounded by layers of tissue separated by gel (resembles an onion in cross-section).
Where are Pacinian corpuscles found, and what is their function?
Found in the skin and joints; they detect mechanical pressure and convert it into a generator potential.
How do Pacinian corpuscles generate an action potential?
1) In the resting state, stretch-mediated sodium channels are too narrow for sodium ions to pass.
2) Mechanical pressure deforms the Pacinian corpuscle.
3) The membrane around the neuron stretches, opening sodium channels.
4) Sodium ions diffuse into the neuron, causing depolarization and generating a generator potential.
5) If the generator potential reaches the threshold, it creates an action potential.
What are the main differences between rod and cone cells in the retina? Include:
- shape
- number
- distribution
- visual acuity
- sensitivity to light
- pigment
- colour sensitivity
Why do rod cells have high sensitivity to light?
- Many rod cells are connected to a single bipolar cell (retinal convergence).
- Summation: Signals from multiple rod cells combine to exceed the threshold for a generator potential.
- Rhodopsin: Pigment in rod cells breaks down with low light energy, enabling response to dim light.
- MISCONCEPTION: Students often think rod cells provide detailed vision. However, their convergence reduces resolution, lowering visual acuity.
Why do cone cells have high visual acuity?
- Each cone cell is connected to its own bipolar cell and sensory neuron.
- This allows the brain to distinguish between light sources that stimulate adjacent cone cells.
- High light intensity is required to break down iodopsin, allowing precise color and sharp vision
Explain why cone cells provide better visual acuity than rod cells.
Each cone cell has a separate bipolar connection, so light from different sources generates distinct impulses, improving resolution.
How does the distribution of rod and cone cells support vision?
- Fovea (high light intensity): High concentration of cone cells for color and detailed vision.
- Periphery (low light intensity): Rod cells dominate for dim light detection.
Compare the pigments in rod and cone cells.
- Rhodopsin (Rod cells): Breaks down in low light intensity, enabling night vision.
- Iodopsin (Cone cells): Requires higher light intensity for breakdown, supporting color vision.
- Three types of iodopsin in cone cells respond to red, green, or blue light, enabling full-color vision.
—> MISCONCEPTION: Students sometimes think rod cells detect color. Rod cells detect only black and white due to a single pigment type
how does summation differ in rod and cone cells?
Rod cells:
- Many rod cells converge onto one bipolar cell.
- Summation of signals increases sensitivity to low light but reduces visual acuity.
Cone cells:
- Each cone cell connects to a single bipolar cell.
- No summation, so high visual acuity but less sensitivity to dim light.
Explain how the Pacinian corpuscle acts as a transducer.
- A transducer converts one form of energy (stimulus energy) into another (electrical energy).
- In the Pacinian corpuscle:
1) It converts mechanical pressure into a generator potential.
2) Pressure deforms the layers of tissue, stretching the membrane of the sensory neuron.
3) Stretch-mediated sodium channels open, allowing sodium ions to diffuse in.
4) This depolarizes the membrane, creating a generator potential.
5) If the generator potential reaches the threshold, an action potential is generated.
Describe how rod cells enable vision in low light conditions.
- Rod cells are sensitive to low light intensity because:
1) Many rod cells connect to a single bipolar cell (retinal convergence), allowing summation of signals.
2) This increases the likelihood of exceeding the threshold for a generator potential.
3) The pigment in rod cells, rhodopsin, breaks down in low light, initiating the signal. - However, rod cells provide poor visual acuity because the brain cannot distinguish between individual light sources stimulating the same neuron.
Explain why cone cells are concentrated in the fovea but rod cells dominate the retinal periphery.
- The fovea receives the highest intensity of light, ideal for cone cells, which require bright light to function.
- Cone cells provide high visual acuity for detailed and color vision, which is essential in bright light.
- The retinal periphery has lower light intensity, where rod cells dominate.
- Rod cells are sensitive to dim light and allow night vision, compensating for reduced brightness at the periphery.
Why do rod cells give poor visual acuity compared to cone cells?
1) Many rod cells are connected to a single bipolar cell (retinal convergence).
- This means multiple signals are combined, and the brain perceives them as one.
- The result is reduced ability to distinguish between light sources, leading to poor resolution.
2) In contrast, each cone cell connects to its own bipolar cell.
- This direct connection allows the brain to distinguish between individual light sources, giving cone cells high visual acuity.
What are rod and cone cells examples of
Photoreceptors
