True or false

1. True or false • The pacinian corpuscle is a receptor • The pacinian corpuscle is found in the skin • The pacinian corpuscle is stimulated by heat • The pacinian corpuscle is a mechano-receptor • The pacinian corpuscle creates an action potential using calcium ions • The pacinian corpuscle contains stretch-mediated ion channels • The pacinian corpuscle will fire no matter how much pressure is puton it • A potential difference in the corpuscle is called a generator potential • The generator potential is not related to the strength of the stimulus • The more the corpuscle is stimulated the more impulses you get in the axon

2. SENSORY RECEPTORS.

3. SENSORY RECEPTORS. Objectives: E - Describe the structure of a pacinian corpuscle using diagrams and pictures D – Explain how the receptor works C – Analyse data to interpret the function of the receptor

4. An organism is subjected to many different types of stimuli. Each type of receptor is specialised to respond to only one type of stimulus – there is no such thing as a “generalised receptor”. Since every receptor generates action potentials on stimulation, if each receptor responded to several different types of stimuli, they would all generate action potentials so there would be no way of discriminating between the different stimuli.

5. Sensory homunculus: This model shows what a man's body would look like if each part grew in proportion to the area of the cortex of the brain concerned with its sensory perception.

6. Example of a simple receptor The Pacinian corpuscle. Located in the dermis of the skin, especially in the palm of the hands, fingers and the underside of the feet; also found in joints and tendons and the external genitalia. Called a mechanoreceptor responding to mechanical stimuli; sensitive to pressure i.e. something pushing hard on the skin.

7. p587 Soper • Label the diagrams

9. Structure of a Pacinian corpuscle Concentric layers of connective tissue separated by a viscous gel surround the un-myelinated end of the dendron of a sensory neurone enclosed in a capsule (in section it looks like a section through an onion bulb). Normally round in section when at rest. Read the article. Summarise how the Pacinian corpsucle functions as a sensory receptor.

10. How it works • An applied pressure on the skin (e.g. pushing on a key on a computer keyboard, or sitting on a hard surface) distorts the concentric layers • This results in deformation of the cell membrane of the sensory neurone. • Deformation opens the ion channels in the membrane (changes the shape of the protein slightly) so Na+ ions pass into the neurone. • This produces a depolarisation called a generator potential of about 1mV across the membrane.

11. DESCRIBE!!!!!!! 2 marks 2 marks

12. DESCRIBE!!!!!!! 3 marks

13. If the generator potential exceeds the threshold it triggers the generation of action potentials at the first node of Ranvier • nerve impulses are then transmitted along the length of the sensory neurone to the CNS. • When the pressure stimulus is removed the corpuscle resumes its normal shape producing another transitory deformation of the receptor membrane in the process and another brief generator potential, which will also generate action potentials to indicate the pressure, has been removed.

14. The size of the generator potential is • proportional to theamount of opening of the ion channels, • which is proportional to the amount of deformation, • which is proportional to the intensity of the stimulus, • so the size of the generator potential is proportional to the intensity of the stimulus (called a graded response). • The number of action potentials generated is proportional to the size of the generator potential • the stronger the stimulus the bigger the generator potential the more action potentials are generated (a frequency coded response) In summary, theapplied pressuredepolarisation  generator potential action potentials