Receptors Energy transducers They detect a change in a particular form of energy ( eg . light)

3. Receptors • Energy transducers • They detect a change in a particular form of energy (eg. light) • This change is called the stimulus • The receptors then convert this energy into a form of electrical energy call a • nervous impulse

11. How are nervous impulses generated? (1) • Neurones have channels in their membranes • There are two types or channels, which are specific to either sodium or potassium ions. Normally these are closed • There are also sodium potassium pumps which pump sodium out of the cell and potassium in • More sodium is pumped out than potassium is pumped in, so overall the inside of the cell is negativerelative to the outside. We say it is polarised • The difference in charge across the membrane is called a membrane potential

12. How are nervous impulses generated? (2) • Nervous impulses are generated by changing the permeability of the membrane by opening the sodium channels • Na+ moves into the cell, making it less negative, relative to the outside – we say it is depolarised. • In receptor cells the stimulus causes sodium channels to open allowing Na+ into the cell. • If a few channels open there will be only a small change in the membrane potential – we call this a generator potential • If the stimulus is large a lot of channels open more Na+ will enter the cell causing a large enough change in the potential difference to stimulate a nervous impulse or an action potential

16. Resting potential • The inside of the neurone is negative relative to the outside • The potential difference is about -70mV

18. http://highered.mcgraw-hill.com/sites/0072507470/student_view0/chapter11/animation__the_nerve_impulse.htmlhttp://highered.mcgraw-hill.com/sites/0072507470/student_view0/chapter11/animation__the_nerve_impulse.html

19. How is the impulse transmitted along the neurone? • An action potential in a region of the neurone creates “local currents” around it • These “local currents” stimulate the sodium channels ahead of the action potential to open.

20. Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+

21. Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+

22. Myelinated and non myelinated neurones • Myelinated neurones • Have a myelin sheath made of individual neurones • About 1/3 of neurones in the peripheral nervous system

24. Myelinated and non myelinated neurones • Myelinated neurones • Have a myelin sheath made of individual neurones • About 1/3 of neurones in the peripheral nervous system • Impulse is transmitted much faster than in non myelinated neurones

26. Myelinated and non myelinated neurones • Myelinated neurones • Have a myelin sheath made of individual schwann cells • About 1/3 of neurones in the peripheral nervous system • Impulse is transmitted much faster than in non myelinated neurones • Carry impluses over longer distances, between receptors and the CNS and between the CNS and the effectors

27. Myelinated and non myelinated neurones • Non Myelinated neurones • Still associated with schwann cells, but one schwann cell can be loosely wrapped over several neurones • No saltatory conduction, action potential moves continuously along the neurone • Slower transmission • Usually shorter and so carry impulses over shorted distances • Often use in co-ordination of functions like the action of the digestive system and breathing