Reflexes and Receptors Flashcards
What is a reflex?
Responses to the environment that are not processed by the brain?
Why are reflexes rapid?
Nervous responses, usually to increase chances of survival- avoid damage
What neurons are involved in the reflex?
- Sensory neuron
- Relay neuron
- Motor neuron
What receptors detect light?
Rods and cones in the retina
What receptors detect temperature?
Thermoreceptors in the skin and the hypothalamus
What receptors detect a change in pressure?
Pacinian corpuscle
How is the pacinian corpuscle adapted to its function?
It has concentric rings of connective tissue
How does the Pacinian corpuscle work?
It responds to a CHANGE in pressure as the tissue distorts and triggers an impulse in the nerve fibre
What are rods?
- Photoreceptors
- Can only see in black and white (cannot distinguish different wavelengths)
- Used in the dark (low light intesity)
- May converge into one bipolar cell
What is retinal convergence?
When lots of rods converge into one bipolar cell
What happens in retinal convergence?
- When light hits rod cells there is the hydrolysis of rhodopsin
- this generates a generator potential
- Which travels down the rod cell
- This goes to bipolar cell via a synapse
- If bipolar cell receives a signal above the threshold value- the cell can pass
What is the important of the generator potential threshold?
- If bipolar cell receives a signal above the threshold value- the cell can pass the signal to the next cell in the optic nerve
- Eventually goes to brain
Why are lots of rods needed?
- Lots of rods in the bipolar cell increases the chance of more than one being stimulated
- More than one generator potential
What is the disadvantage of pooling signals?
- Low visual acuity
- If lights hits receptors, the brain won’t be able to distinguish between two points
How many types of cone cells are there
Three
What are the advantage of cone cell over rod cells?
They are red, blue and green
They can differentiate between different wavelengths of light
One cone cell to one bipolar cell
Better visual acuity
What is the pigment in cone cells?
Iodopsin- one for each type of cone cell
Where are most cone cells in the retina?
There is a higher density of cone cells in the fovea
Where are most rod cells in the retina?
In the periphery
Which type of cells have better visual acuity and why?
Cone cells because each type of cone cell has its own connection to a single bipolar cell. High resolution. There is no retinal convergence
What part of the eye receives the highest light intensity?
The fovea
What is a stretch mediated sodium channel? (Pacinian corpuscle)
A special type of Na+ channel that changes its permeability to sodium ions when it is distorted
What is the sequence of events by which the Pacinian corpuscle creates a generator potential?
- pressure on Pacinian corpuscle
- distorts shape
- stretches neuronal membrane
- widens stretch mediated sodium channels
- allows sodium ions to enter the neurone
- changes potential of membrane (depolarises)
- produces generator potential
What are the advantages of simple reflexes?
- They prevent damage to the body
- They are quick
Explain how applying pressure to the Pacinian corpuscle produces the changes in membrane potential.
- The concentric layers of connective tissue distort
- This causes the stretch-mediated sodium ion channels to open
- The greater the pressure the greater the number of sodium ions
