TOPIC 8 Revision

Reflex arcs

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

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

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

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

How do you think habituation is achieved?

Plants

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

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.

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

Phytochromes can switch processes on and off:

Eyes

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

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

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.

Brain

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

Animal testing and diseases

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

The dopamine neurones in the basal ganglia die.

What are the treatments? Selegiline (an MAOI) L-Dopa Dopamine agonists Gene therapy Surgical approaches http://www.youtube.com/watch?v=sf1N0Zf5IqA L-3,4-dihydroxyphenylalanine ropinirole

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

So how can drugs help? SSRI’s!

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

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

GMOs

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

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

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

Environmental Concerns Health Concerns