1. 6.5 Neurons and Synapses Understanding:
Neurons transmit electrical impulses
The myelination of nerve fibers allows for salutatory conduction
Neurons pump sodium and potassium ions across their membranes to generate a resting potential
An action potential consists of depolarization and repolarization of the neurons
Propagation of nerve impulses is the result of local currents that cause each successive part of the axon to reach the threshold potential
Synapses are junctions between neurons and between neurons and receptor on effector cells
When pre-synaptic neurons are depolarized they release a neurotransmitter into the synapse
A nerve impulse is only initiated if the threshold potential is reached
Applications:
Secretion and reabsorption of acetylcholine by neurons at synapses
Blocking of synaptic transmission at cholinergic synapses in insects by binding of neonicotinoid pesticides to acetylcholine receptors
Nature of science:
Cooperation and collaboration between groups of scientists: biologists are contributing to research into memory and learning.
Skills:
Analysis of oscilloscope traces showing resting potentials and action potentials.

2. Communication in the body
Two systems:
Endocrine system
Nervous system
Role of system
Organs involved
What does each organ do?

3. Endocrine
Nervous

5. Endocrine Consists of glands, pancreas and reproductive organs Releases hormones

6. Nervous Consists of nerve cells called neurons Central and peripheral 85 billion neurons in humans

7. Neuron
Label the following: Cell body Axon Dendrite Axon terminal Nucleus Myelin sheath
Understanding:
Neurons transmit electrical impulses

8. Neuron

9. No myelin sheath Nerve impulse 1 metre/second
Non- Myelinated
No myelin sheath Nerve impulse 1 metre/second
Understanding:
The myelination of nerve fibers allows for salutatory conduction

10. Myelination
Many layers of phospholipids bilayers Schwann cells deposit myelin when they grows round the axon Node of Ranvier = gap between myelin deposited by adjacent Schwann cells.
Understanding:
The myelination of nerve fibers allows for salutatory conduction

11. Myelination
Nerve impulse jumps from one node of Ranvier to the next. Saltatory conduction 100 metres/second
Understanding:
The myelination of nerve fibers allows for salutatory conduction

12. Non Myelinated
Myelinated

13. Non Myelinated No myelin layers Impulse is 1m/s
Schwann Cells make myelin that wraps round axon
Impulse jumps between Nodes of Ranvier 100m/s

14. Resting Potential (–70mV)
Overall there is a charge imbalance Negative charge on the inside Positive charge on the outside
Understanding:
Neurons pump sodium and potassium ions across their membranes to generate a resting potential

15. Resting Potential (–70mV)
No transmission = resting potential There IS a potential difference across the membrane Due to an imbalance of positive and negative charges across the membrane
Understanding:
Neurons pump sodium and potassium ions across their membranes to generate a resting potential

16. Resting Potential (–70mV)
Sodium potassium pump pumps 3 sodium ions out for every 2 potassium ions in Membrane is also 50 times more permeable to potassium ions Potassium ions leak back across the membrane faster than sodium ions Build up of positive ions on outside of membrane creates difference in charge Sodium concentration gradient very steep
Understanding:
Neurons pump sodium and potassium ions across their membranes to generate a resting potential

17. Action potential Rapid change in membrane potential
Depolarisation – negative to positive
Repolarisation – positive to negative
(inside membrane of axon)
Understanding:
An action potential consists of depolarization and repolarization of the neurons

18. Depolarisation (+30mV)
Due to opening of sodium channels Allows sodium ions to diffuse into neuron down concentration gradient Reverses the charge imbalance Inside becomes positive
Understanding:
An action potential consists of depolarization and repolarization of the neurons

19. Repolarisation (–70mV)
Rapidly after depolarisation Sodium channels close Potassium channels open Potassium ions diffuse out of ion down their concentration gradient Inside of cell becomes negative again
Understanding:
An action potential consists of depolarization and repolarization of the neurons

20. Resting Potential (–70mV)
Returns to resting potential before another impulse can be sent Sodium potassium pump moving sodium ions out, and potassium ions in
Understanding:
An action potential consists of depolarization and repolarization of the neurons

21. Label the diagrams Summarise what happens during each stage
Include the following on the diagrams:
Label pumps/proteins
What are pumps/proteins doing at each point
K+ and Na+ movement
Overall charges inside and outside
The potential inside the neuron (+30/-70mV)
Understanding:
An action potential consists of depolarization and repolarization of the neurons

22. Action Potential Depolarisation Repolarisation Sodium channels
Sodium ions
Potassium channels
Potassium ions
Charge change inside neuron
Overall charge in neuron after

23. Charge change inside neuron Overall charge in neuron after
Action Potential
Depolarisation
Repolarisation
Sodium channels
Open
Close
Sodium ions
Diffuse into neuron
Stay inside neuron
Potassium channels
Closed
Potassium ions
Diffuse out of neuron
Charge change inside neuron
Negative to positive
Positive to negative
Overall charge in neuron after
Positive (+30mV)
Negative (-70mV)

24. Nerve impulses
Start at one end of a neuron Propagated along axon to other end of neuron Ion movements that depolarise one part of the neuron trigger depolarisation of the neighboring part
Only move in one direction as they are only initiated at one end of the neuron
Understanding:
Propagation of nerve impulses is the result of local currents that cause each successive part of the axon to reach the threshold potential

25. Local Currents
The propagation of an action potential along the axon is due to sodium ion movements Sodium ion concentration increases inside the axon during depolarisation Some sodium ions then diffuse inside the axon to the area that has not yet been depolarised The same happens outside of the axon, however sodium ions move from the area that has not been depolarised to the area that has
Understanding:
Propagation of nerve impulses is the result of local currents that cause each successive part of the axon to reach the threshold potential

26. Local Currents
This causes the membrane potential in the unpolarised area to rise from -70mV to -50mV The Sodium channels are voltage-gated and open when a membrane potential of -50mV has been reached This is known as the threshold potential
Understanding:
Propagation of nerve impulses is the result of local currents that cause each successive part of the axon to reach the threshold potential

28. Oscilloscope Traces
Membrane potentials can be measured Displayed in an oscilloscope Time on x-axis Membrane potential on y-axis Resting potential = -70mV Local currents = rise to -50mV Action potential = narrow spike to +30mV Returns to resting potential = -70mV
Skills:
Analysis of oscilloscope traces showing resting potentials and action potentials.

30. Synapses
Junctions between cells in the nervous system Chemicals (neurotransmitters) send signals across synapses
Understanding:
Synapses are junctions between neurons and between neurons and receptor on effector cells

32. Synaptic Transmission
Nerve impulse propagated along pre- synaptic neuron until it reaches the end of the neuron and the pre-synaptic membrane
Understanding:
Synapses are junctions between neurons and between neurons and receptor on effector cells

33. Synaptic Transmission
2. Depolarisation of pre- synaptic membrane causes calcium ions (Ca2+) to diffuse through channels in the membrane into the neuron
Understanding:
Synapses are junctions between neurons and between neurons and receptor on effector cells

34. Synaptic Transmission
3. Influx of Ca2+ causes vesicles containing neurotransmitter to move to the pre-synaptic membrane and fuse with it
Understanding:
Synapses are junctions between neurons and between neurons and receptor on effector cells

35. Synaptic Transmission
4. Neurotransmitter is released into the synaptic cleft by exocytosis
Understanding:
When pre-synaptic neurons are depolarized they release a neurotransmitter into the synapse

36. Synaptic Transmission
5. Neurotransmitter diffuses across the synaptic cleft and binds to receptors on the post synaptic membrane
Understanding:
When pre-synaptic neurons are depolarized they release a neurotransmitter into the synapse

37. Synaptic Transmission
6. The binding of the neurotransmitter to the receptors causes adjacent sodium channels to open
Understanding:
When pre-synaptic neurons are depolarized they release a neurotransmitter into the synapse

38. Synaptic Transmission
7. Sodium ions diffuse down their concentration gradient into the post-synaptic neuron, causing it to reach its threshold potential
Understanding:
A nerve impulse is only initiated if the threshold potential is reached

39. Synaptic Transmission
8. An action potential is triggered in the post- synaptic membrane and is propagated along the neuron
Understanding:
Synapses are junctions between neurons and between neurons and receptor on effector cells

40. Synaptic Transmission
9. The neurotransmitter is rapidly broken down and removed from the synaptic cleft
Understanding:
Synapses are junctions between neurons and between neurons and receptor on effector cells

42. Acetylcholine
Used as a neurotransmitter at many synapses Produced from choline (diet) and acetyl (aerobic respiration) Loaded into vesicles and released into synaptic cleft Binding sites are specific
Applications:
Secretion and reabsorption of acetylcholine by neurons at synapses

43. Acetylcholinesterase
Breaks acetylcholine into chlorine and acetate Reabsorbed back into pre-synaptic neuron where it is converted back into a neurotransmitter
Applications:
Secretion and reabsorption of acetylcholine by neurons at synapses

44. Neonicotinoids What are they? What do they do? Advantages?
Arguments against?
Applications:
Blocking of synaptic transmission at cholinergic synapses in insects by binding of neonicotinoid pesticides to acetylcholine receptors