1. TOPIC 8 Revision

2. Reflex arcs

3. Reflex arcs are simple nerve pathways responsible for our reflexes (rapid, involuntary responses to stimuli)

4. Potential difference (mV)
Repolarisation ~
Depolarisation ~
+40
Potential difference (mV)
-70
Hyperpolarisation ~

7. Another action potential cannot be generated in the same section of membrane for ~5msec. This is the REFRACTORY PERIOD.
Why is it important?

9. Synaptic transmission
Excitatory presynaptic cells:
E.g. Cholinergic synapses using acetylcholine.
Neurotransmitter decreases the membrane potential making it more excitable (as makes the membrane more permeable to Na+ ions)
Inhibitory presynaptic cells:
Neurotransmitter increases the membrane potential (hyperpolarized) usually by opening Cl- channels and thus harder to depolarize sufficiently

10. How do you think habituation is achieved?

11. Plants

12. The Cholodny-Went model explains growth curvature as a result of unequal auxin distribution due to transport of auxin.
Criticisms include:
Small sample size
V small conc. involved

13. The 2 isomers are photoreversible:
Is there more Pr or Pfr in the light then?
In sunlight both reactions occur but Pr Pfr is dominant as more red light is absorbed.

14. Germination experiments with lettuce seeds – what does it show?
Red light
Red
Far red

15. Phytochromes can switch processes on and off:

16. Eyes

17. Vesicles – membranes containing rhodopsin Neurone of the ganglion cell
Axons of the ganglion cell form the optic nerve
Bipolar neurone
Vesicles – membranes containing rhodopsin
Neurone of the ganglion cell

19. Rhodopsin broken down
Non-specific cation channels
Na+ diffuse in through open cation channels
Na+ channels closed
Na+ move down conc. gradient
Na+ actively pumped out
Na+ actively pumped out
Membrane slightly depolarised -40mV
Membrane hyperpolarised
Glutamate
No NT released. Cation channels in bipolar cell open, depolarising membrane, generating AP in neurone of optic nerve
NT released, binds to bipolar cells preventing it depolarising

20. Critical period
Light deprivation leads to narrower columns in the visual cortex.
Visual stimulation is required for the refinement of columns
Axons compete for target cells in the visual cortex. If some axons are not firing, they’re cut back and lost.

21. Brain

22. Outline the various functions of the brain’s structures
Include the thalamus, hypothalamus, hippocampus and medulla oblongata

23. Animal testing and diseases

24. There are 4 ethical frameworks that we can discuss for the role of animals in medical research:
Importance of consent (animals have rights)
Animal welfare
Animal suffering and experience of pleasure
Utilitarianism

25. The dopamine neurones in the basal ganglia die.

26. What are the treatments? Selegiline (an MAOI) L-Dopa Dopamine agonists
Gene therapy
Surgical approaches
L-3,4-dihydroxyphenylalanine
ropinirole

27. Serotonin is a neurotransmitter that helps determine mood.
It is produced by neurones in the brain stem

28. So how can drugs help?
SSRI’s!

29. The effect of drugs…
Serotonin is a chemical released from a synapse in your brain – it gives you feelings of pleasure 
Sensory neuron
= Prozac
What does Prozac do to the synapse? Explain how Prozac helps to treat someone with depression
Motor neuron

30. We have around 3.2 billion bases that make up our DNA.
Why did we want to sequence the 20,000-25,000 genes?
Understand how our genotype affects our phenotype
Improve treatment of diseases (identify drug targets)
Avoid risk factors specific to our own genotype

31. GMOs

32. Cut with SAME restriction endonuclease
Produces sticky ends
Ligase attaches DNA sections
Don’t forget the two types of bonding!!

33. Genetically modifying plants
Plasmid carrying the desired gene and an antibiotic resistance gene (marker gene)
Genes incorporated in the plant DNA of some cells

34. Herbicide resistant gene
How do we know the gene has been successfully incorporated?
Promoter
Herbicide resistant gene
Chl R
We use marker genes:
Genes incorporated in the plant DNA of some cells
Incubation in growth medium with antibiotic
Only cells with the new genes survive
Micropropagation
Plant growth substances stimulate shoot and root growth

35. Environmental Concerns
Health Concerns