1. Friday, 21 September 2018
3.6 Organisms respond to changes in their internal and external environments Receptors
• explain the features of sensory reception which are common to all receptors • describe the structure of a Pacinian corpuscle • explain the stimulus which Pacinian corpuscles respond to • explain how a Pacinian corpsule produces a generator potential in response to a specific stimulus.

2. Sensors and effectors What is a stimuli?
What are sensory cells (sensors)?
What are effector cells (effectors)?
Make & complete a table to show as many as you can remember!
Stimuli
Receptor
Effector
Light
Retina (eye)
Iris muscle
Pressure
Touch receptor
Skeletal muscle

3. Sensory receptors
These are specialised cells that detect a change in the surroundings to trigger a nerve impulse
They are energy transducers, as they convert a change in energy (a stimulus) into an electrical impulse

4. Generating nerve impulses
How does a neurone actually generate an impulse?
Firstly – which receptors detect which energy changes?
What does this energy type convert to?
Electrical energy (From -70mV to +40mV)

5. Receptors and energy Receptors Energy changes detected
Rods & cones in retina
Light intensity and range of wavelengths
Olfactory cells (nose)
Presence of volatile chemicals
Taste buds, hard palate & epiglottis & oesophagus
Presence of soluble chemicals
Pacinian corpuscles (skin)
Pressure on skin
Cochlea (Ear)
Vibrations in air
Proprioceptors (muscle spindles)
Length of muscle fibre

6. An Named example:
Pacinian corpuscle
What is it?
How does it work?

7. Pacinian Corpuscle’s
Abundant deep in skin – Fingers, soles of the feet, external genitalia. Occur in joints, ligaments and tendons to show a change of direction
When pressure is applied the membrane becomes distorted and stretched
Sodium channels are then open and sodium ions diffuse into the neurone
The sodium ions change the potential of the membrane and it becomes depolarised producing a generator potential
The generator potential
creates a nerve impulse
(action potential) along
the sensory nerve to the
CNS