Lecture 4 synapses neurotransmitters and hormones Flashcards
Explain electrical synapses
- Formed up of gap junctions which is a small gap made of connexons (channel proteins)
- Connexons allow fast transmission of ions between neurons.
-Generates change in the membrane potential of post- synaptic neuron
-Prioritises speed (reflex and motor impulses)
Explain chemical synapses
- Transmit chemical signals.
- Pre-synaptic neuron contains Vesicles filled with neurotransmitters- which are released in the synaptic cleft.
- Post synaptic neuron receptors bind to neurotransmitters.
- Slower
How does a chemical synapse work?
1- Action potential reaches axon terminal
2- This signals for voltage-gated calcium channels to open and ca enters cell
3- Calcium entering signals for vesicles to be released and the neurotransmitters to bind to the receptors
4- Neurotransmitters are either positive or negative
5- If excitatory: NA channels open (depolarisation) Action potential will pass
inhibitory Chloride (hyperpolarization)
What is the difference between spatial and temporal summation
Spatial summation is where multiple presynaptic neurons send simultaneous signals
Temporal is where one rapidly fires signals
Explain Ionotropic receptors
- Ion channels.
- When a neurotransmitter binds to it, the receptor opens allowing ions to pass through and rapidly change the membrane potential of post-synaptic.
- Fast, brief and precise.
Explain metabotropic receptors
-Activate intracellular signalling cascades when neurotransmitters bind to them.
- The binding activates a G protein
- Which binds to an ion channel to influence opening/closing OR to activate other intracellular signalling which can start biochemical changes in the cell.
- For slower and complex processes.
What happens to the signal after it is transmitted?
- Recycles to the pre-synaptic cleft by cells (Reuptake)
OR - Degraded/ neutralised by enzymes
If neither of these occurred there would be continuous action potential which would over stimulate the neuron.
Examples of neurotransmitters and if they are excitatory or inhibitory
Excitatory:
- Acetylcholine: muscle control
- Glutamate: learning and memory
- Norepinephrine/ noradrenaline: arousal and flight or fight
- Serotonin: mood appetite and sensory perception
Inhibitory:
- Dopamine: reward and motivation
- GABA: relaxation and calming
Explain serotonin
Low levels can relate to depression. So serotonin reuptake inhibitors are common treatment. Meaning after carrying a signal serotonin is reabsorbed by nerve sells and SSRIs block reuptake so more serotonin is available.
What are the neuromodulatory systems
The are sets of systems in the brain which use different neuro transmitters.
They regulate different behaviours
Explain the Norepinephrine system
- Mainly flight or fight.
Also arousal, alertness and attention
And regulation.
Explain the serotonin system
Serotonin is produced in 2 places.
1- Rostral: for regulation of sleep
2- Caudal nuclei: for pain related sensation.
And impacts mood particularly depression- which effects sleep and pain sensation
Explain Acetylcholine system
Muscle contraction (and sleep wake cycle, learning, arousal and memory)
Dopamine system
Either
1- Produced in the Substantia nigra and projected to striatum to control voluntary movement
OR
2- Produced in the ventral tegmental area, projected to frontal cortex for control of reward system.
Dopamine and its effects (Parkinson’s and drugs)
- Dopamine causes euphoria and pleasure.
- Surges are released when doing beneficial behaviours to reinforce brain to do these behaviours
- Drugs produce 10x amount of dopamine and highjack the reward system
-Brain therefore adapts its sensitivity to dopamine as it cannot handle all of it. And so it diminished dopamine receptors. - Dopamine is also in control of Voluntary movement
- In Parkinson’s disease, movement is impaired caused by the loss of dopamine.
