Lecture 2 - Neurons, neurotransmitters, drugs and mental function

Question 1

Synapses

Answer 1

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

Question 2

Electrical to chemical to electrical …

Answer 2

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

Question 3

Synaptic cleft

Answer 3

Space in between the presynaptic neuron and the post synaptic neuron or effector cell

Question 4

Axon terminal

Answer 4

holds the vesicles that contain neurotransmitters and these neurotransmitters are released from here

Question 5

Neurotransmitter

Answer 5

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

Question 6

Action potential process

Answer 6

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

Question 7

Neurotransmitter uptake? Yes or no?

Answer 7

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

Question 8

Drugs and neurotransmission

Answer 8

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

Question 9

Agonists

Answer 9

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)

Question 10

Indirect agonist

Answer 10

An indirect agonist enhances the release or action of an endogenous neurotransmitter

Question 11

Antagonists

Answer 11

Drugs that block or suppress agonist-mediated responses are known as antagonists - drugs that decrease the transmission of information across a synapse

Question 12

Neurotransmitter examples

Answer 12

Acetylcholine
Dopamine 
Noradrenaline 
Glutamate 
Serotonin

Question 13

Acetylcholine

Answer 13

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

Question 14

Parkinson’s disease

Answer 14

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

Question 15

Schizophrenia

Answer 15

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)

Question 16

Parkinsons and schizophrenia relationship

Answer 16

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

Question 17

Action of some psychoactive drugs at the synapse

Answer 17

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

Question 18

Agonist vs antagonist

Answer 18

Activates it vs decreases transmission

Question 19

Synaptic transmission series of events

Answer 19

Synthesis of neurotransmitter
Storage in synaptic vesicles 
Release into synaptic space 
Binding to receptor sites 
Deactivation through reuptake or breakdown

Question 20

Excitatory neurotransmitter

Answer 20

If the neurotransmitter has an excitatory effect on the neuron, the chemical reaction that occurs creates a graded or action potential

Question 21

Inhibitory neurotransmitter

Answer 21

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

Question 22

Agonist

Answer 22

is a drug that increases the activity of a neurotransmitter

Question 23

Agonists may

Answer 23

• 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

Question 24

Antagonist

Answer 24

A drug that inhibits or decreases the action of a neurotransmitte r

Question 25

Antagonists may …

Answer 25

• 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

Question 26

Alcohol can be

Answer 26

an aagonist and antagonist

Question 27

Nerve impulses are

Answer 27

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

Question 28

Schizophrenia involves

Answer 28

severe disturbances in thinking, speech, perception, emotion and behaviour

hallucinations are common (false perceptions that have a compelling sense of reality)

Question 29

Causal factors of schizophrenia

Answer 29

growing consensus that it results from a biologically based vulnerability factor that is set into motion by psychological and environmental events

Question 30

Dopamine hypothesis (schizophrenia)

Answer 30

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

Question 31

Dopamine receptors and people with schizophrenia

Answer 31

more dopamine rectors on neuron membranes than non-schizophrenics and these receptors seem to be overreactive to dopamine stimulation

Question 32

Reward system

Answer 32

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.