lecture 19 - synaptic transmission Flashcards
How is information transferred between cells?
Chemically- via synaptic interactions
What are the features of a synapse? (7)
Pre-synaptic nerve terminal, synaptic cleft, post-synaptic cell, receptors, voltage gated Ca2+ channels, synaptic vesicles, neurotransmitter inactivation enzyme.
When an action potential arrives at an axon terminal, what are triggered?
Voltage gated calcium channels, allowing Ca2+ to enter the terminal
When calcium ions diffuse into the axon terminal during a synapse, what does this trigger?
Trigger synaptic vesicles to release neurotransmitters via exocytosis
What is the fundamental process in which synaptic vesicles release neurotransmitters?
Exocytosis
When neurotransmitters diffuse across the synaptic cleft, what occurs at the post-synaptic cell?
Neurotransmitters bind to chemically gated sodium ion channels, allowing them to open and release sodium into the cell, creating a graded depolarisation (local potential).
When chemically gated sodium channels close after depolarisation in the post-synaptic cell, what happens to the neurotransmitters that were bound to the channel?
They are released and broken down by enzymes.
When Acetylcholine is broken down after release from chemically gated sodium channels, what is formed?
AChE enzyme breaks it down into Acetate and Choline, which is reabsorbed by the axon terminal.
What is the enzyme used to break acetylcholine down into acetate and choline after it is release from the post-synaptic chemically gated sodium channels?
AChE
How does the axon terminal ‘recycle’ the neurotransmitter ACh?
The axon terminal reabsorbs choline from the synaptic cleft and combines it with Acetyl-CoA (from the mitochondria) to form acetylcholine which can then be released again via synaptic vesicles.
What is the name for a synapse that uses the neurotransmitter Acetylcholine?
Cholinergic synapse.
What is the overall process of synaptic transmission?
Action potential triggers Ca2+ channels, Ca2+ enters cells and triggers release of synaptic vesicles (containing neurotransmitters). neurotransmitters diffuse across synaptic cleft and bind to chemically gated Na+ channels creating a local potential. Neurotransmitters are release and broken down by enzymes before being reabsorbed by the terminal.
What kind of synaptic junction is involved in electrical synapses?
Gap junction
What are gap junctions?
Channels that connect the post- and pre- synaptic neuron that allow electrical signals to be passed on directly without chemical signals.
What is an electrical synapse?
An electrical event that allows a presynaptic cell to trigger an electrical signal in the postsynaptic cell directly, without chemical signals. (Ca2+ channels or neurotransmitters)
When pre- and post- synaptic cell membranes sit very close together, what will generally occur?
Cells will have gap junctions and will undergo electrical synapses.
In an electrical synapse, will a depolarisation in the pre-synaptic cell lead to a depolarisation or hyperpolarisation in the post-synaptic cell?
Depolarisation (always produce a like voltage change)
Why are electrical synapses rare?
They provide no opportunity for signal modulation - the sign of the potential cannot be changed to cause inhibition. i.e. depolarisation cannot lead to hyper-polarisation.
What does EPSP stand for?
Excitatory Post Synaptic Potential
What does IPSP stand for?
Inhibitory Post Synaptic Potential
What is an EPSP?
An electrical charge on the post-synaptic membrane that briefly depolarises it towards threshold, sometimes facilitating the firing of an action potential.
What is an IPSP?
An inhibitory electrical charge on the post-synaptic membrane that leads to a brief hyper-polarisation, moving the membrane away from the threshold, and inhibiting action potentials.
What are the excitatory neurotransmitters used to create EPSP?
Acetylcholine (ACh), norepinephrine, epinephrine and glutamate
What are inhibitory neurotransmitters used to generate IPSPs?
GABA
What are the two forms of postsynaptic potential summation?
Temporal and spatial summation
What is temporal postsynaptic potential summation?
When several stimulus arrive shortly after each other - i.e. secondary arrives before the first decays - the potentials sum allowing the threshold potential to be met, triggering an action potential.
What is spatial postsynaptic potential summation?
When two stimuli are received from 2 nerve terminals that sit close together, the local potentials will add together allowing the threshold to be reached, propagating an action potential.
What is a neuromuscular junction?
A junction, separated by a synaptic cleft, between an axon terminal and the sarcolemma of a muscle fibre.
Are synapses small or large at a neuromuscular junction?
Huge, Action potential likely to bring muscle fibre to threshold.
How many neurons are received by an individual muscle fibre?
1
