Synaptic transmission (15) Flashcards
What is the purpose/function of synapses?
electrical impulses cannot travel over the junction between neurons so neurotransmitters send impulses between neurons from neurons to effectors, the new impulses can be initiated in several different neurons for multiple simultaneous responses
Draw and label the structure of a synapse.
look at notes.
What are the 3 steps that happen in a presynaptic neurone when an action potential is transmitted from one neuron to another?
1) wave of depolarisation travels down presynaptic neuron, causing voltage-gated calcium ion channels to open
2) vesicles move towards and fuse with the presynaptic membrane
3) exocytosis of neurotransmitter into synaptic cleft
How do neurotransmitters cross the synaptic cleft?
via simple diffusion
Why is synaptic transmission unidirectional?
only the presynaptic contains vesicles of neurotransmitters and only the postsynaptic membrane has complementary receptors
What are the 3 steps that happen in a postsynaptic neuron when an action potential is transmitted?
1) neurotransmitter binds to specific receptor on postsynaptic membrane
2) sodium ion channels open
3) if influx of sodium ions raises the membrane to threshold potential an action potential is generated
What is summation?
when neurotransmitters from several sub-threshold impulses accumulate to generate an action potential
What are the 2 types of summation?
temporal
spatial
Where does summation not occur?
at neuromuscular junctions
What is temporal summation?
when 1 presynaptic neuron releases neurotransmitter several times in quick succession
What is spatial summation?
when multiple presynaptic neurons release neurotransmitter at the same time
What type of synapse uses acetylcholine as the primary neurotransmitter?
cholinergic synapse
What do cholinergic synapses use and as what?
use acetylcholine as the primary neurotransmitter
What 3 places are cholinergic synapses located at and for what?
1) motor end plate (muscle contraction)
2) preganglionic neurons (excitatory response)
3) parasympathetic postganglionic neurons (inhibitory response)
What are the 3 steps that happen to acetylcholine from the synaptic cleft?
1) hydrolysis into acetyl and choline by acetylcholinesterase (AChE)
2) acetyl and choline diffuse back into presynaptic membrane
3) ATP used to reform acetylcholine for storage in vesicles
What are the 2 importance’s of acetylcholinesterase (AChE)
- prevents overstimulation of skeletal muscle cells
- enables acetyl and choline to be recycled
What are the 3 steps that happen in an inhibitory synapse?
1) neurotransmitter binds to and opens chloride channels on postsynaptic membrane, and triggers potassium ion channels to open
2) chloride moves in and potassium ions move out via facilitated diffusion
3) potential difference becomes more negative (this is hyperpolarisation)
What is the structure of a neuromuscular junction?
synaptic cleft between a presynaptic neuron and a skeletal muscle cell
What are 3 ways drugs decrease synaptic transmission?
- inhibit release of neurotransmitter
- decrease permeability of postsynaptic membrane to ions
- hyperpolarise postsynaptic membrane
What are 2 ways drugs increase synaptic transmission?
- inhibit AChE
- mimic shape of neurotransmitter
What are the 5 differences between cholinergic synapses and neuromuscular junctions?
postsynaptic cell
AChE location
action potential
response
neurons involved
What is the difference between cholinergic synapses and neuromuscular junctions, in terms of postsynaptic cell?
CS - another neuron
NJ - skeletal muscle cell
What is the difference between cholinergic synapses and neuromuscular junctions, in terms of AChE location?
acetylcholinesterase
CS - synaptic cleft
NJ - postsynaptic membrane
What is the difference between cholinergic synapses and neuromuscular junctions, in terms of action potential?
CS - new action potential produced
NJ - end of neural pathway
What is the difference between cholinergic synapses and neuromuscular junctions, in terms of response?
CS - excitatory or inhibitory
NJ - always excitatory
What is the difference between cholinergic synapses and neuromuscular junctions, in terms of neurons involved?
CS - motor, sensory and relay
NJ - only motor
