IB Biology HL Option A.5

Explain how diazepam (valium) affects the nervous system. Include the role of GABA. What are some uses of diazepam?

- binds to allosteric site on GABA receptors in post-synaptic membranes - GABA is inhibitory neurotransmitter which binds to receptor causing chloride channels to open and hyper-polarisation of post-synaptic neuron by entry of chloride ions - binding of diazepam causes chloride ions to enter at greater rate which inhibits nerve impulses in post-synaptic neuron - diazepam is sedative used to reduce anxiety, panic attacks, insomnia and sometimes as muscle relaxant

Explain how tetrahydrocannabinol (THC) affects the nervous system.

- binds to cannabinoid receptors in pre-synaptic membranes which inhibits release of neurotransmitters causing excitation of post-synaptic neurons - inhibitory psychoactive drug and sedative - causes disruption of psychomotor skills, short-term memory impairment, intoxication and stimulation of appeptite

Explain how cocaine affects the nervous system.

- binds to dopamine re-uptake transporters (membrane proteins that pump dopamine back into pre-synaptic neuron) - binding blocks transporters causing build up of dopamine in synaptic cleft and continual excitement of post-synaptic neuron - excitatory psychoactive drug

What are the two types of psychoactive drugs? How does each affect post-synaptic transmission? Provide examples of each.

- excitatory drugs increase post-synaptic transmission e.g. nicotine, cocaine, amphetamines - inhibitory drugs decrease post-synaptic transmission e.g. alcohol, benzodiazepines (Valium), tetrahydrocannabinol (THC)

Describe the effect of excitatory neurotransmitters on the nervous system.

- excitatory neurotransmitters excite post synaptic neuron for few milliseconds to many seconds - produces depolarisation which may trigger action potential

Describe how fast-acting neurotransmitters work.

- fast-acting neurotransmitters cross synapse and bind to receptors <1 millisecond after action potential arrives at pre-synaptic neuron - receptors are gated ion channels and open/close in response to neurotransmitter binding which causes brief and immediate change in post-synaptic membrane potential

Describe the effect of inhibitory neurotransmitters on the nervous system.

- inhibitory neurotransmitters inhibit formation of action potential in post-synaptic neuron - due to membrane potential becoming more negative when neurotransmitter binds to post-synaptic membrane - hyperpolarisation makes threshold harder to reach which inhibits nerve impulse

What are the effects of stimulants?

- make person more alert, energetic and self-confident - increase heart rate, blood pressure and body temperature

Explain how pramipexole affects the nervous system. What are some uses of pramipexole?

- mimics dopamine by binding to dopamine receptors in post-synaptic membrane at dopaminergic synapses - acts as agonist by having same effects as dopamine when it binds - used to treat early stages of Parkinson's disease and sometimes as anti-depressant

What are pain receptors? Where are they located? How do they allow us to feel pain?

- pain receptors are endings of sensory neurons that detect stimuli and convey impulses to CNS - impulses reach sensory areas of cerebral cortex which causes us to experience pain - receptors located in skin and other parts of body

Explain the effect of different anaesthetics on awareness.

- patient under general anaesthetics has no awareness of surgical - some procedures are unnecessary or undesirable to have unconscious patient e.g. removing brain tumour from partially conscious patient to monitor effect on brain - some patients retain awareness when they have not been given a high enough dose of anaesthetics and may or may not feel pain - during emergency c-section minimised dose of anaesthetics is best for mother and child however, spinal block now used to keep patient awake and remove pain sensation from beyond spinal cord

Describe how pre-synaptic neurons can successfully trigger an action potential in post-synaptic neuron using excitatory neurotransmitters.

- release of one excitatory neurotransmitter from one pre-synaptic neuron is not enough to trigger action potential - one pre-synaptic neuron must repeatedly release neurotransmitter or several adjacent neurons must release neurotransmitter simultaneously

Explain how slow-acting neurotransmitters work. Provide an example.

- slow-acting neurotransmitters (neuromodulators) take hundreds of milliseconds to effect post-synaptic neurons e.g. serotonin - diffuse through surrounding fluid and affect groups of neurons - cause release of secondary messengers inside post-synaptic neurons which sets off sequence of intracellular processes that regulate fast synaptic transmission - can modulate fast synaptic transmission for long periods of time

NOS: What cases may cause new drugs to be quickly introduced for use? When is this acceptable and what are the risks?

- some trials have great differences between placebo and drug patients so trials are abandoned as drug is introduced immediately - some cases have groups of patients who campaign for new drug to be introduced before it has been fully tested - may be acceptable for terminal diseases e.g. AIDS - risk of harmful side-effects which may only be discovered when large number of patients are given drug

Identify and describe 3 factors which affect drug addiction.

1. genetic predisposition: some people more vulnerable to addiction due to genes 2. social environment greatly affects likelihood of taking drugs and becoming addicted e.g. peer pressure, poverty, mental health 3. dopamine secretion: prolonged at high levels with addictive drugs causing feelings of well-being and pleasure e.g. cocaine and alcohol affect dopamine secreting synapses

How do stimulants work?

act by mechanisms to make body respond as though it has been naturally stimulated by sympathetic nervous system

What is the effect local anaesthetics?

causes area of body to become numb

What is the effect of anaesthetics in general?

causes reversible loss of sensation in part or all of body

What is the effect of general anaesthetics?

causes unconsciousness and total lack of sensation

Define summation.

combined effect from multiple releases of excitatory and inhibitory neurotransmitters by pre-synaptic neurons in post-synaptic neuron

Define stimulant.

drugs that promote activity of nervous system

What are endorphins? Describe how they act as pain killers.

endorphins are oligopeptides secreted by pituitary gland and act as natural painkillers by blocking feelings of pain - bind to receptors in pathways used in perception of pain which inhibits synaptic transmission and prevents pain from being felt

How does learning arise?

learning of new skills is connected to formation of new synapses in hippocampus and other parts of brain

How does longer-term memory arise?

longer-term memory may be due to remodelling of synaptic connections between neurons

How do anaesthetics work?

many anaesthetics affect more than one sense organ and can also inhibit signals to motor neurons and other parts of nervous system

State some examples of stimulants.

mild stimulants of caffeine in coffee, strong stimulants used to treat depression, cocaine

How many synapses can form pre-synaptic neurons form with post-synaptic neurons?

more than one pre-synaptic neuron can form synapse with same post-synaptic neuron

How do psychoactive drugs affect the brain?

psychoactive drugs affect brain and personality by altering functioning of some synapses in brain

How does long-term potentiation arise? Why is it important?

secondary messengers persist for days and cause long-term potentiation which is central to synaptic plasticity necessary for memory and learning

Explain the role of slow-acting neurotransmitters in memory and learning.

slow-acting neurotransmitters cause release of secondary messengers inside post-synaptic neurons that promote synaptic transmission by: - increasing number of receptors in post-synaptic membrane - chemical modification of receptors to increase rate of ion movement when neurotransmitter binds

What are inhibitory neurotransmitters?

small molecules that are inactivated by specific enzymes in membrane of post-synaptic neuron

What determines whether an action potential is reached via summation?

whether or not action potential is reached depends on balance of effects of excitatory and inhibitory neurotransmitters i.e. whether threshold potential is reached