Neurons Part 2 Flashcards
Understand the sequence of events at a chemical synapse
- Neuron synthesizes neurotransmitters (smaller ones in axon terminals and larger ones=neuropeptides, in cell body).
- Action Potential reaches presynaptic terminal, enabling Calcium to enter via calcium channels and this sometimes causes release of neurotransmitter from the terminals, into the synaptic cleft.
- Neurotransmitters diffuse across the synapse and attach to receptors on the post-synaptic neuron. This results in an effect on the post synaptic neuron.
4.Neurotransmitters then separate from receptors. They may be recycled by the pre synaptic neuron, be diffused, or decay. - Sometimes post synaptic neurons release neurotransmitters to exert an effect on the presynaptic neuron. eg feedback loop.
Explain what a neurotransmitter is, noting that there are different classes of neurotransmitter (You don’t need to memorize the different classes yet. You will be encountering many of them in later topics in far more detail).
A neurotransmitter is a substance released by a neuron at a synapse, which has an effect upon another cell post-synapse. Often the other cell is a neuron, might might also be eg a muscle fibre etc.. There are many different types, including amino acids, modified amino acids, neuropeptides, monoamines , purines and gas.
Explain what is meant by the term vesicle and what vesicles do.
A vesicle is a tiny parcel of something wrapped in a membrane.
Distinguish between ionotropic and metabotropic effects.
Note, you do not need to study the various hormones in this section.
Ionotropic effect is where a neurotransmitter binds to a receptor and in so doing, alters the shape of the receptor, such that a specific ion experiences an effect. An example is the neurotransmitter Acetylcholine binding to a receptor, causing the receptor to “unwind” a bit and thus allowing sodium ions to pass through.
A Metabotropic effect is where a neurotransmitter binds to a receptor, resulting in the receptor “bending” such that a small particle is released into the cell which then has flow on effects.
This type pf effect tends to be fractionally slower to occur, but lasts a bit longer, and is able to exert an influence over a little wider area cf ionotropic.
Discuss the different things that can happen to a neurotransmitter after it has been released.
After it has been released, a neurotransmitter may diffuse away, may be specifically broken down within the synapse (and components may then be recycled in the pre-synaptic neuron) (or may be metabolised)or may be actively taken up by transporters in the pre-synaptic neuron (re-uptake) and re-used.
Discuss the effects of drugs at the synapse, distinguishing between agonists and antagonists
Drugs may bind to neurotransmitter’s receptor sites. An agonist substance mimics or increases the usual effect of a neurotramsmitter binding to its receptor, whereas an antagonist effect blocks the usual action.
Distinguish between drug affinity and efficacy.
Drug affinity refers to how strongly a drug binds to a receptor.
Drug efficacy refers to how well a drug can activate the receptor.They are separate concepts.
Define the term addiction / substance abuse.
Repeated use of a substance despite it having a deleterious effect on health/relationships. Why occurs is a complex mix of experiences, genetics, opportunities, personality. Thought release of dopamine to be what underlies any addiction.
Distinguish between the actions of the following types of drugs and cite examples of a drug of each type:
Stimulants, Nicotine, Opiates, Marijuana, Hallucinogens, Alcohol.
Stimulant eg cocaine, increases or prolongs the release of dopamine in Nucleus Accumbens.
Nicotine stimulates Acetylcholine receptors on neurons to release dopamine.
Opioids attach to endorphin receptors in the brain which inhibit Gaba, which in turn, increases dopamine. (gaba is inhibitory).
Marijuana stimulates Norepinephrine post synaptic receptors and inhibits gaba. (If inhibit Gaba, results in increased dopamine).
LSD decreases serotonin, which results in increased dopamine.
Valium increases Gaba, which reduces anxiety/arousal.
Alcohol has a biphasic effect; initially stimulatory (increasing dopamine) and later is depressive.
Whilst dopamine does seem increased in pleasant experiences and is released by addictive substances, the increase is small and blocking the release of dopamine is not entirely successful at reducing addiction, so dopamine is not the entire story of why addiction occurs.
Discuss the significance of self-stimulation studies in rats.
The self-stimulation studies in rats, found that rats would deliberately seek to repeat the stimulation, as it was enjoyable. It was found that the rats would react this way because they were stimulating the release of dopamine, which gave them pleasure, and especially associated with stimulation of the area known as the Nucleus Accumbens.
Discuss the genetics of alcoholism (only very briefly).
It seems that those with alcoholic parents, have greater risk genetically of becoming alcoholics. It also seems that those with parents of “poorer parenting ability”are more likely to become alcoholic, if coupled with.susceptible genes. also, greater risk of alcoholism if mothers imbibed whilst offspring in utero.
Most significant study found sons of alcoholics far more likely to seem behaviourally to “be able to hold their liquor” but long term this means they probably don’t “call it an evening” until have consume many more drinks than peers, and this then may be what sets them on the path to alcoholism.
Those with a gene to produce less alcohol dehydrogenase (which metabolises alcohol) are far less likely to be alcoholic as even small amounts of alcohol can cause flushing and feeling ill. This genetic condition is far more common in asians.
