Unit 9- Synapse Flashcards
What is the purpose of neurotransmitters and name 2
- as action potentials cannot cross the synapse so the nerve impulse are carried by neurotransmitters instead
- noradrenaline and acetyl choline
How do synapses work?
1- action potential arrives at presynaptic knob
2- calcium channels in in PreSK open so calcium ions diffuse into the cell down the conc gradient
3- this causes synaptic vesicles to fuse with the preSK cell membrane releasing the neurotransmitter by exocytosis
4- neurotransmitter diffuses across synaptic cleft
5- neurotransmitter binds to receptors on post synaptic membrane causing ion channels to open causing a local depolarisation in post synaptic membrane called the post synaptic potential which may set up an action potential
How are the neurotransmitters removed from the cleft and where do they end up?
- enzymes break down the neurotransmitters in the post synaptic membrane, the products the diffuse back across the cleft to be absorbed (endocytosis) and resynthesised in presynaptic neurone
- proteins in the presynaptic neurone membrane actively transport whole neurotransmitters back into presynaptic membrane
What is the enzyme that reads down acetyl choline called?
Acetylcholinesterase
What different types of ion channel synapses are there?
- excitatory ion channel synapses
- inhibitory ion channel synapses
What happens at an excitatory ion channel synapse?
- The neuroreceptors on the post synaptic cell membrane are Sodium channels
- when the channels open positive Na+ diffuse ions diffuse into, causing local depolarisation
- this is called excitatory postsynaptic potential (EPSP)
- so the PD is closer to the threshold potential
- action potential is more likely to happen
What happens at an inhibitory ion channel synapse?
- the neuroreceptor on post synaptic nicely membrane are chloride channels
- when the channels open ions diffuse in causing local hyperpolarisation
- called inhibitatory postsynaptic potential
- an action potential is less likely to happen as the PD is further away from the threshold
Give 2 typical neurotransmitters that cause an excitatory postsynaptic potential?
Ecetylcholine and glutamate
Give a neurotransmitter that causes an inhibitory postsynaptic potential:
Glycine or GABA
What nervous system is acetyl choline found?
-parasympathetic autonomic system
What pat of the nervous system is noradrenaline found?
- sympathetic autonomic nervous system
what is the spatial summation?
- this is the sum of all the post synaptic potentials from different synapses from all the dendrites
whats is the temporal summation?
- the sum of a sequence of post synaptic potentials at 1 single synapse in a time period
when will an action potential occur? and what is this process called?
when the grand post synaptic potential is above the threshold potential
- this is called summation or synaptic integration
-what is the grand post synaptic potential?
- the sum of all the excitatory and inhibitory post synaptic potentials across all the cells synapses
what is axon convergence?
when the post synaptic neurone has many inputs but only 1 output through its axon
how may chemical affect the synapse? 3
- affect the amount of neurotransmitter synthesises
- block or stimulate neurotransmitter release
- inhibit or mimc enzymes
- block calcium channels
- block neurotransmitter binding to receptors
- block neurotransmitter reuptake
how does nicotine affect the synapse?
- affects peripheral nervous system
- has similar structure to acetyl choline, so binds to acetyl choline receptors on post synaptic membrane
- this causes the release or adrenaline, dopamine and endorphins
- result: increased heart rate and blood pressure and feeling happy
what way does adrenaline affect the body?
- triggers fight or flight response in sympathetic nervous system
- increase heart rate and blood pressure
how do endorphins and dopamine affect the brain?
dopamine- leads to feeling of pleasure
endorphins- cause feeling of pleasure but leads to withdrawals and addiciction
how does cobra venom affect the synapse and body?
- binds irreversibly to acetyl choline receptors
- this prevents the binding of acetyl choline
- post synaptic membrane is not stimulated to depolarise
causing paralysis or death if nerves that stimulate breathing muscles are affected
how does lidocaine affect the synapse and body?
- blocks voltage gated dependent Na+ channels in post synaptic membrane
- Na+ cannot enter the cell when neurotransmitter binds
- action potential cannot form in the post synaptic cell
acts as an anaesthetic preventing impulses from being conducted
