Receptors

1. Forces stretching, compressing or moving the sensor chemicals Receptors light temperature

2. Forces stretching, compressing or moving the sensor chemicals Receptors light temperature

3. Module 1Communication and homeostasis 1.1.5 Sensory receptors

4. Starter • Different stimuli have different forms of energy, eg. light or chemical energy. Sensory receptors act as transducers and convert the energy of a stimulus into electrical energy. • Complete card sort on receptors and energy changes

5. Learning Objectives Success Criteria • To understand the roles of sensory and motor neurones, and explain how a resting potential is maintained • Outline the role of sensory receptors in mammals in converting different forms of energy onto nerve impulses (Grade E - D) • Describe the structure and explain the functions of sensory and motor neurones (Grade C –B) • Explain how the resting potential is established and maintained (Grade B – A)

6. Transducers Mechanoreceptor Pressure Sensor • Rings of connective tissue • Deformation on pressure • Deformation causes action potential • Transducers convert one sort of energy into another

7. Neurones • Write down 3 neurones and describe their structure and function. (you could do this as a table – or when you revisit your notes, you could re-write it as a table!) • Sensory neurones have long axons and transmit nerve impulses from receptors to an intermediate or motor neurone. The dendron carries impulse to the cell body and the axon that carries it away from the cell body. • Motor neurones have long axons and many short dendrites. They transmit nerve impulses to effectors (muscles and glands) all over the body. • Intermediate neurones (also called connector neurones or relay neurones) are usually much smaller cells. Transmit impulses between 2 neurones.

8. Neurone 1 Click button to reveal type of neurone and direction of impulse.

9. Sensory Neurone Impulse A B C E F G D Click any label to reveal name of structure.

10. Sensory Neurone Impulse Schwann Cell A B C E F G D Click button to reveal further information.

11. Sensory Neurone Impulse Schwann Cell A B C E F G D Found in mammals. Cell wraps itself around axon, enclosing it in many layers of plasma membrane. This creates a myelin sheath (largely lipids with some proteins) which speeds up conduction.

12. Sensory Neurone Impulse Cell Body A B C E F G D Click button to reveal further information.

13. Sensory Neurone Impulse Cell Body A B C E F G D Cell body contains neurone’s nucleus and cytoplasm with many mitochondria and ER. Groups of ribosomes are often visible as dark specs.

14. Sensory Neurone Impulse A B C Receptor E F G D Click button to reveal further information.

15. Sensory Neurone Impulse A B C Receptor E F G D Receptor cells are transducers – convert one form of energy e.g. light or heat into electrical energy. Often found in sense organs. Initiate the action potential in the sensory neurone in response to a stimuli.

16. Sensory Neurone Impulse A B C E F G D Synaptic knob Click button to reveal further information.

17. Sensory Neurone Impulse A B C E F G D Synaptic knob Axon terminates in a junction with next neurone. A gap of 20nm between them. The knob is packed with mitochondria and vesicles with neurotransmitter. This will diffuse across gap and excite/inhibit signal in next neurone.

18. Sensory Neurone Impulse A B C E F Axon G D Click button to reveal further information.

19. Sensory Neurone Impulse A B C E F Axon G D Extension of cytoplasm from the cell body. Carries electrical signal (action potential) from the cell body to the synaptic knobs in the central nervous system (CNS).

20. Sensory Neurone Impulse A B C E F G Node of Ranvier D Click button to reveal further information.

21. Sensory Neurone Impulse A B C E F G Node of Ranvier D 2-3μm gaps in the myelination of the axon. Occur between Schwann cells every 2-3mm.Help speed of transmission by enabling action potential to jump from one node to next.

22. A dendron carries impulses towards a cell body Axons carry nerve impulses away from a cell body Match the features… • Which of these are the correct structural and functional features of each of the neurones? Short dendrites Long dendron Short axon Long axon Impulse carried from receptor to CNS Impulse carried within CNS between neurones Impulse carried from CNS to effector

23. Task • Using pages 13 – complete worksheet with structure and functions of neurones • Include why relay (intermediate) neurones are important • In pairs using the ‘playdoh’ make a cell surface membrane

24. Neurone structure – answers on whiteboards

25. Key terms • Resting potential – the potential difference between the inside and the outside of the neurone (-70mV) when it is at rest (unstimulated). (Inside more –ve than outside). • Generator potential – the change in potential difference across the membrane when a stimulus is detected. Cell membrane becomes more permeable. • (The bigger the stimulus – the bigger the generator potential) • Action potential – a nerve impulse - caused by a rapid change in potential difference across the membrane – only triggered if the generator potential is large enough to reach the threshold level. (-55mV)

26. Neurones • Neurones, like all cells, have a plasma membrane which is impermeable to ions. • This allows maintenance of different ion concentrations inside and outside of the cell. • Proteins have a negative charge and are in high concentrations inside the cell • Sodium (Na+) and Potassium (K+) ions, are present in differing concentrations inside and outside of the neurone. • The lipid bilayer is impermeable to ions

27. Resting potential • All animal cell membranes contain a protein pump called the sodium-potassium pump. • This uses the energy from ATP splitting to simultaneously pump: • 3 sodium ions out of the cell • 2 potassium ions in. • More Na actively pumped out

28. 1 3 4 2 Resting potential 2 1 3 Action potential

29. Resting State • There is a potential (ie voltage) difference between the inside of an neurone and the outside. • This is due to the ions present.

30. Ion channels • Proteins in the membrane that can be in an open or closed state - When the neurone is at rest, most of the channels are closed • Some K+ channels are open and so K+ ions are free to diffuse through the channels in both directions. • The intracellular concentration of K+ remains higher, as K+ ions are acted upon by two forces: • Diffusion gradient: K+ ions move from a high concentration inside the cell to a low concentration outside the cell. • Electrical gradient: This makes the inside more negative and so attracts the K+ ions back into the cell.

31. Equilibrium • Eventually, an equilibrium is reached so there is no net movement of K+ ions • The diffusion and electrical gradients balance each other out. • The resting membrane potential is -60- -70 mV. This is the difference in charge between the inside and outside of the membrane. • At rest – the membrane is more permeable to K+ ions than Na+ or Cl- • Neural signals are the result of changes in the difference between the voltage of the inside vs the outside of the cell

32. Resting potential If this was to continue unchecked there would be no sodium or potassium ions left to pump, but there are also sodium and potassium ion channels in the membrane. These channels are normally closed, but even when closed, they "leak",allowing sodium ions to leak in and potassium ions to leak out, down their respective concentration gradients. However the membrane is more permeable to potassium than to sodium. • More K Diffuses out Na-K Exchange Pump

33. Resting potential – the potential difference or voltage across the neurone whilst at rest. Membrane of neurone – more + ve Axon of neurone – more –ve Extracellular fluid – more + ve The combination of the Na+K+ATPase pump and the leakage channels cause a stable imbalance of Na+ and K+ ions across the membrane. This imbalance causes a potential difference across all animal cell membranes, called the resting potential. The membrane is said to be polarised. The resting potential is always negative inside the cell, and varies in size from –20 to –200 mV in different cells and species. Normally about -65mV.

34. What happens during the resting state?

35. Task • Using your models describe and explain how the resting potential is established and maintained. • Complete exam question Jan 2013 – Qu 1 (a) and (b)

36. SOPI - sodium potassium pump sodium out; potassium in. So…what happens? • Sodium potassium pump uses ATP to actively transport 3 sodium ions out for every 2 potassium ions in to the neurone. • Potassium channels are open when neurone at rest and potassium ions diffuse back out of neurone through channels due to the concentration gradient. • Membrane is not permeable to sodium ions so they cannot diffuse back in. Thus a sodium ion electrochemical gradient is set up. • More positive ions outside of the cell, so positively charged outside

37. Identify the parts of the neurone labelled A to D. (4) • What is represented by the arrows on Fig 1.1? (1) (b) Describe and explain how the resting potential is established and how it is maintained in a sensory neurone. In your answer you should use appropriate technical terms, spelled correctly (4)

40. Plenary Create a table to compare sensory and motor neurones

41. Learning Objectives Success Criteria • To understand the roles of sensory and motor neurones, and explain how a resting potential is maintained • Outline the role of sensory receptors in mammals in converting different forms of energy onto nerve impulses (Grade E - D) • Describe the structure and explain the functions of sensory and motor neurones (Grade C –B) • Explain how the resting potential is established and maintained (Grade B – A)