Synaptic Transmission Flashcards
1
Q
What is a synapse?
A
- junction between two neurones
2
Q
Structure of synapse
A
- myelin sheath
- axon terminal
- vesicles of neurotransmitter
- synaptic cleft (gap)
- post synaptic membrane
- pre synaptic membrane
- mitochondrion
3
Q
Feature of synapse (1)
A
- one single impulse can be transmitted to multiple neurones, creating number of simultaneous responses
4
Q
Feature of synapse (2)
A
- summation (build up of the neurotransmitter in the synapse)
- as a result of low frequency action potentials producing insufficient amounts of neurotransmitter for an action potentials to be generated in the post synaptic neurone
5
Q
What are the two types of summation?
A
- Temporal summation
- Spatial summation
6
Q
Temporal summation
A
- single pre synaptic neurone releases neurotransmitter many times over a short period of time, eventually surpassing threshold
7
Q
Spatial summation
A
- multiple pre synaptic neurones release enough neurotransmitter to exceed threshold in post synaptic neurone to trigger action potential
8
Q
First step of synaptic transmission
A
- action potential arrives at axon terminal, leading to depolarisation of the pre synaptic membrane
9
Q
Second step of the synaptic transmission
A
- voltage gated calcium channels open and calcium ions enter the axon terminal
10
Q
Third step of the synapse transmission
A
- Calcium ions cause synaptic vesicles to fuse with the pre-synaptic membrane and release neurotransmitter by exocytosis
11
Q
Forth step of the synaptic transmission
A
- Neurotransmitter (acetylcholine) diffuses across synaptic cleft, and binds to receptors on the post-synaptic membrane
12
Q
Fifth step of the synapse transmission
A
- Depolarisation of the post-synaptic neurone
Receptors on the post-synaptic membrane are located on sodium ion channels, which are normally closed. - When neurotransmitter binds to receptors, the channels change shape and open, allowing sodium ions to enter the post-synaptic neurone, leading to depolarisation.
- This must be above threshold to generate an action potential.
- Synapses able to produce new action potentials are called excitatory synapses.
13
Q
Sixth step of synaptic transmission
A
- Reuptake of neurotransmitter
- Acetylcholinesterase enzyme breaks down acetylcholine into acetyl and choline, which move back across the cleft into the presynaptic neurone (called ‘recycling’).
- This helps prevent continued actions potentials in the postsynaptic neurone.
- ATP released by mitochondria helps recombine choline and acetyl, which gets stored in vesicles for future use.
- Sodium ion channels close in the absence of acetylcholine in receptor sites.
14
Q
In a reflex arc, impulses only travel in one direction (unidirectionality) How are synapses adapted to make this happen?
A
- Neurotransmitter can only be released from the presynaptic neurone but the receptors are only found on the postsynaptic membrane - this sets up a concentration gradient, making sure impulses travel in one direction only.
15
Q
Why do you think so many mitochondria and endoplasmic reticulum need to be in the pre-synaptic neurone?
A
- Lots of mitochondria allows for production of large quantities of ATP in aerobic respiration.
- ATP is needed to: actively transport calcium ions back out of the synaptic knob after an impulse has passed through; repackage acetylcholine into its synaptic vesicles via active transport, providing ATP for the sodium ion-potassium ion pump to restore resting potential.
- Endoplasmic reticulum are involved in production, storage and transport of protein, and as neurotransmitters are made of protein, this is why there are large amounts.
