Lecture 2 - Neurons, neurotransmitters, drugs and mental function Flashcards
Synapses
Neurons communicate with each other across special junctions called synapses.When an action potential arrives at an axon terminal a special chemical called a neurotransmitter is released at the synoptic cleft. Receptors at the postsynaptic neuron respond to the neurotransmitter and generate a graded potential
Electrical to chemical to electrical …
Electrical signal down the presynaptic neuron and then changed to a chemical signal at the synapse and then changed back into an electrical signal at the postsynaptic neuron so you have action potential to chemical/neurotransmitter release to production of graded potential which then travels down the dendrite
Synaptic cleft
Space in between the presynaptic neuron and the post synaptic neuron or effector cell
Axon terminal
holds the vesicles that contain neurotransmitters and these neurotransmitters are released from here
Neurotransmitter
Neurotransmitters are chemical messengers that transmit a signal from a neuron across the synapse to a target cell
Neurotransmitter is synthesised and then stored in vesicles
Action potential process
Action potential propagates down the axon and reaches the axon terminal and causes the vesicles to move out towards the synaptic cleft and they merge with the membrane of the cell (exocytosis) and release the neurotransmitter into the synaptic cleft and the neurotransmitter binds to receptors on the post synaptic cell which then produces a graded potential in its dendrites
Neurotransmitter uptake? Yes or no?
There is also neurotransmitter uptake, it doesn’t just sit in the synaptic cleft forever as after a period of time it gets taken up again into the axon terminal and then remanufactured into neurotransmitters
Drugs and neurotransmission
Drugs can have an effect by altering neurotransmitter synthesis, storage, release, binding or reuptake
Many drugs are psychoactive meaning that they have an effect on behaviour or cognition and they have this effect by changing the way information is transmitted from one neuron to another
Agonists
Drugs that bind to a receptor of a cell and trigger a response by the cell are called agonists. Agonists often mimic the action of a naturally occurring substance (has an effect at the synapse as if neurons were actually releasing the compound I.e. neurotransmitters)
Indirect agonist
An indirect agonist enhances the release or action of an endogenous neurotransmitter
Antagonists
Drugs that block or suppress agonist-mediated responses are known as antagonists - drugs that decrease the transmission of information across a synapse
Neurotransmitter examples
Acetylcholine Dopamine Noradrenaline Glutamate Serotonin
Acetylcholine
Acetylcholine - affects muscles (neurons to muscles i.e. neuromuscular junctions) therefore disrupting these synapses causes problems with movement as well as memory)
At cholinergic synapses …
Agonists (activates it) = nicotine, black widow spider venom
Antagonists (decreases transmission) = scopolamine (suppresses motion sickness), botulinum toxin
Parkinson’s disease
Affects ~1% of the population
Tremour, muscle rigidity, slowness of movement (bradykinesia), postural instability, involuntary shifts of posture (dystonia and dyskinesia), shuffling, wide-based gait with forward leaning posture, leading to festination
Deep brain stimulation (treatment) - involves putting electrode deep into some brain structures affected by Parkinson’s and having the electrode connected to a pacemaker which is continually generating electrical pulses which are continually applied to the neurons that are at the top of the electrode and you can artificially activate these neurons by applying electrical stimulations and causes them to creat action potentials and this can be effective in depressing some symptoms
Schizophrenia
Affects ~1% of the population
Positive (meaning aspect of new rather than goods) symptoms
Delusions, hallucinations, disorganised thinking
Negative symptoms (loss of normal function) Blunted affect, poverty of speech and thought, apathy
Cognitive symptoms
Poor working memory, disruption in executive function and attention (changes in cognitive function)
Parkinsons and schizophrenia relationship
PD is treated by boosting dopamine whereas S is treated by drugs that suppress dopamine
Dopamine antagonists have antischizophrenic effects. These drugs produce Parkinsonian symptoms
PD is associated with degeneration of the substantia nigra , a midbrain nucleus with output neurons that release dopamine (so in PD you are getting a loss of dopamine release)
PD can be treated with dopamine agonists e.g. L-Dopa and Bromocriptine
Dopamine agonists (amphetamine, cocaine and L-Dopa) trigger schizophrenic episodes in normal individuals
Too little dopamine areas that affect motility = causes Parkinson’s
Too much dopamine in cognitive areas = causes schizophrenia
Action of some psychoactive drugs at the synapse
Coffee - adenosine antagonist
Marijuana - THC receptor agonist
LSD - suppresses serotonergic neurons (affects serotonin)
Prozac- serotonin reuptake inhibitor (SSRI) ( boosts moods as it inhibits the reuptake of serotonin at the synapse which means that it sits in the synapse for longer)
Ecstacy/MDMA - serotonin agonist
Cocaine - dopamine agonist
Amphetamine - dopamine agonist
Agonist vs antagonist
Activates it vs decreases transmission
Synaptic transmission series of events
Synthesis of neurotransmitter Storage in synaptic vesicles Release into synaptic space Binding to receptor sites Deactivation through reuptake or breakdown
Excitatory neurotransmitter
If the neurotransmitter has an excitatory effect on the neuron, the chemical reaction that occurs creates a graded or action potential
Inhibitory neurotransmitter
If the transmitter is inhibitory, it increases the negative potential inside the neuron and makes it more difficult for an action potential to be initiated by that cel
Agonist
is a drug that increases the activity of a neurotransmitter
Agonists may
- enhances a neuron’s ability to synthesise, store or release neurotransmitters OR
- mimic the action of a neurotransmitter by binding with and stimulating postsynaptic receptor sites
- bind with and stimulate postsynaptic receptor sites
- make it more difficult for neurotransmitters to be deactivated, such as inhibiting reuptake
Antagonist
A drug that inhibits or decreases the action of a neurotransmitte r
Antagonists may …
- reduce a neuron’s ability to synthesis, store or release neurotransmitters
- prevent a neurotransmitter from binding with the post synaptic neuron by fitting into and blocking the receptor sites on the postsynaptic neuron
Alcohol can be
an aagonist and antagonist
Nerve impulses are
communicated between neurons by chemical neurotransmitters travelling across a synapse from the axon terminals of one cell to specialised receptors on post synaptic neurons which are subsequently excited or inhibited
Schizophrenia involves
severe disturbances in thinking, speech, perception, emotion and behaviour
hallucinations are common (false perceptions that have a compelling sense of reality)
Causal factors of schizophrenia
growing consensus that it results from a biologically based vulnerability factor that is set into motion by psychological and environmental events
Dopamine hypothesis (schizophrenia)
The symptoms of schizophrenia particularly positive symptoms are produced by overactivity of the dopamine system in areas of the brain that regulate emotional expression, motivated behaviour and cognitive functioning
Dopamine receptors and people with schizophrenia
more dopamine rectors on neuron membranes than non-schizophrenics and these receptors seem to be overreactive to dopamine stimulation
Reward system
The regions of the brain comprising the “reward system” use the neurotransmitter dopamine to communicate. Dopamine-producing neurons in the ventral tegmental area (VTA) communicate with neurons in the nucleus accumbens in order to evaluate rewards and motivate us to obtain them.
