1. Some Most All Role of receptors WAL:
An overview of the nervous system receive sensory information
WAL:
All
Most
What are the main features of sensory reception?
Some
What is a Pacinian corpuscle and how does it work??
What are the main features of sensory reception?
Starter – Use the following words to explain how heart rate is controlled: chemoreceptors, parasympathetic, SA node, pH

2. Today we are covering from the specification:
Pages of your textbook

3. Role of receptors
Sensory reception is the function of sense organs, whereas sensory perception involves making sense of the information from the receptors. This is largely the function of the brain.

4. Receptors - Pressure
A Pacinian corpuscle
Yteach resource

5. Pacinian corpuscle
Respond to change in mechanical pressure. As with all sensory receptors, a Pacinian corpuscle:
Is specific to a single type of stimulus (e.g. pressure)
Produces a generator potential by acting as a transducer – converts stimuli into a response that can be understood by the body, namely nerve impulses.

6. Pacinian corpuscle
The stimulus is always some form of energy, e.g. heat, light, sound or mechanical energy. The nerve impulse is a form of energy
All receptors convert the energy of the stimulus into a nerve impulse known as a generator potential.

7. Pacinian corpuscle Layers of connective tissue separated by a gel
Blood capillary

8. Stretch-mediated sodium channels (Permeability change when shape changes)
Resting Potential:
Positive outside – negative inside
Pressure:
Distorts & opens Na+ channels
Action potential:
Inflow of Na+ depolarises membrane

9. Pacinian corpuscle
In it’s normal (resting) state, the stretch-mediated sodium channels of the membrane around the neurone of a pacinian corpuscle are too narrow to allow sodium ions to pass along them. In this state, the neurone of the pacinian corpuscle has a resting state.
When pressure is applied to the corpuscle, it changes shape and its neurone becomes stretched

10. Pacinian corpuscle
This stretching widens the sodium channels in the membrane and sodium ions diffuse into the neurone.
The influx of sodium ions changes the potential of the membrane (depolarised), thereby producing a generator potential
The generator potential in turn creates an action potential (nerve impulse) that passes along the neurone and then, via other neurones to the CNS.

11. Receptors working together in the eye
Receptors respond to only one type of stimulus.
It also only responds to a certain intensity of stimulus.
This means the body must have a range of receptors, each responding to a different intensity of stimulus.

12. Photoreceptors
These are found in the retina. There are two types Rods and Cones and they are arranged as shown:
Outer !
Inner
Light
Pigmented Layer
Ganglion Cells
Rod
To Optic Nerve
Bipolar Neurones
Cone

13. Light receptors
Both rod and cone cells act as transducers by converting light energy into the electrical energy of a nerve impulse.

14. Rod cells
Cannot distinguish different wavelengths of light and therefore produce images only in black and white.
Rod cells are more numerous than cones.

15. Rod cells
Many rod cells share a single sensory neurone. Rod cells can therefore respond to light of very low intensity.
This is because a certain threshold value has to be exceeded before a generator potential is created in the bipolar cells to which they are attached.

16. Rod cells
A number of rod cells are attached to a single bipolar cell (= retinal convergence), there is a much greater chance that the threshold value will be exceeded than if only a single rod cell were attached to each bipolar cell.
As a result, rod cells allow us to see in low light intensity (i.e. at night), although only in black and white.

17. Changes in the electrical potential of a receptor when stimulated by three separate stimuli. Only the third stimulus produces a generator potential high enough to trigger a nerve impulse.

18. A rod cell opsin Rhodopsin (pigment in rod cells broken down) LIGHT
Signal from
Bipolar cell

19. A rod cell
As many rod cells are joined to the same bipolar cells, only a single impulse will be stimulated.
This means that they cannot distinguish between the separate sources of light that stimulated them.
2 dots close together will appear as a single blob. Rod cells therefore have low visual acuity.

20. Cone cells
Cone cells are of three different types, each responding to a different wavelength of light. Depending on the proportion of each type that is stimulated, we can perceive images in full colour.
Each cone cell usually has its own bipolar cell connected to a sensory neurone. This means that often the generator potential is not exceeded. As a result, cone cells only respond to high light intensity and not to low light intensity.

21. Cone cells
Cone cells contain a different pigment to rod cells (iodopsin). This requires a higher light intensity to be broken down and create a generator potential.
As cone cells are attached to their own bipolar cell, if 2 adjacent cells are stimulated, the brain receives 2 separate impulses.
Cone cells give very accurate vision, they have good visual acuity.

22. Greater numbers than cones Fewer numbers than rods
Rod cells
Cone Cells
Rod-shaped
Cone-shaped
One type
Red, green & blue types
Greater numbers than cones
Fewer numbers than rods
Distributed more in the periphery
Fewer at periphery, concentrated in fovea
Poor acuity
Good acuity
High sensitivity
Low sensitivity
Rhodopsin pigment
Iodopsin pigment
Iodopsin pigment

23. Cone cells
Light is focussed by the lens on a point known as the fovea. The fovea therefore receives the highest intensity of light.
Therefore cone cells, but not rod cells, are found at the fovea. The concentration of cone cells diminishes further away from the fovea. At the peripheries of the retina, where light intensity is at its lowest, only the rod cells are found.

24. Wavelengths of light absorbed by different cones

25. Colour Blindness
If you have normal vision you will see a figure seven in reddish brown dots.
People with red-green colour blindness will not see the 7, why?
These people lack red sensitive cones, but the green stimulated cones are stimulated by the red light, so all dots appear green

26. Plenary– Reflections: What did you learn?
Role of receptors
An overview of the nervous system receive sensory information
WAL:
All
Most
What are the main features of sensory reception?
Some
What is a Pacinian corpuscle and how does it work??
What are the main features of sensory reception?
Plenary– Reflections: What did you learn?
What do you want to find out? How might you find this out? What skills did you use? How did your group function? What worked and what didn’t? What connections did you make? How was your thinking pushed? Why did you choose the approach you did? What did you enjoy and why? How could you have done it differently?