13.5 Synapses Flashcards
Why are synapses important?
• prevent impulses travelling in wrong direction
• allow different neurones to communicate
• convergence
• divergence
What is convergence (in neurones)?
Impulses from multiple neurones passed onto one neurone.
What is divergence (in neurones)?
Impulse from one neurone is passed on to more than one neurone.
What synapse specifically do you need to know about?
Cholinergic synapse
Describe the structure of a presynaptic neurone.
Smooth endoplasmic recticulum
Synaptic vesicles
Ca+ ion channels
Mitochondria
Describe the structure of the post synaptic neurone.
Na+ ion channels
What do synaptic vesicles contain?
Neurotransmitters
What two categories of synapse are there?
Excitatory
Inhibitory
What is the gap between the presynaptic and post synaptic neurone called?
Synaptic cleft
What does the smooth endoplasmic reticulum do in the presynaptic neurone?
Produces vesicles (containing neurotransmitters)
When do the Na+ ion channels open?
In the presence of neurotransmitters
What is an excitatory neurone?
Results in the depolarisation of post synaptic neurone.
What is an inhibitory neurone?
Synapses which stop an action potential being set up in post synaptic neurone by causing hyper polarisation.
How is an impulse transmitted across a synapse? (8 marks)
Action potential arrives at synaptic knob
Ca2+ ions channels open & Ca2+ ions diffuse into synaptic knob
Exocytosis
Neurotransmitters diffuse across the synaptic cleft to the post synaptic membrane
Neurotransmitters bind with specific receptors on post synaptic membrane
Sodium channels open and sodium ions diffuse into post synaptic neurone
Post synaptic membrane is depolarised
Action potential generated in post synaptic membrane
Synaptic knob repolarised
Neurotransmitters broken down in post synaptic neurone
Why is the impulse only transmitted one way?
Only the presynaptic neurone produces neurotransmitters
Only the post synaptic neurone has receptors for neurotransmitters
Only the post synaptic neurone has calcium ion channels
In some synapses , the amount of neurotransmitters from a subtle impulse is not enough to trigger an action potential, so the impulse can be transmitted due to summation. What is summation?
Build up of neurotransmitters, until the threshold is reached for an action potential to be generated.
What is spatial summation?
Multiple presynaptic neurones release neurotransmitters to one post synaptic neurone, to reach the threshold.
What is temporal summation?
Several action potentials over a short period of time, release lots of neurotransmitters , these build up, and reach the threshold.
How can a drug/chemical stimulate synapses to create more action potentials?
Inhibit enzyme that breaks down neurotransmitters
Drug binds in place of neurotransmitters (drug isn’t broken down)
Stops neurotransmitters from being absorbed
How do painkillers work?
Block channels from opening in post synaptic neurone,
this inhibits the production of action potentials
