Synapse Flashcards
What is the difference between chemical and electrical synapses?
electrical is when the current flows directly through gap junctions whereas in chemical, a chemical travels through the cleft
Chemical synapses occur between neurons and?
other neurones, muscle cells, gland cells
Describe the events at a chemical synapse
- An arriving action potential depolarises the axon terminal membrane of a presynaptic neurone.
- Depolarisation of the axon terminal membrane opens voltage-gated calcium ion channels, and calcium ions (Ca2+ ) enter the cytosol of the axon terminal. This results in ACh release from the synaptic vesicles by exocytosis.
- ACh diffuses across the synaptic cleft and binds to receptors on the postynaptic membrane. Cation (Na+, K+) channels open, producing a graded depolarisation due to Na+ inflow.
What are a few transmitters?
Acetylcholine. (ACh), GABA, dopamine, serotonin, endorphins, substance P, glutamate
What are 3 methods of neurotransmitter removal?
re -uptake by pre synaptic neuron, often recycled and used again
diffusion - passive process, can’t be used in situations with high frequency AP
enzymatic destruction - enzymes breakdown neurotransmitters
What are excitatory neurotransmitters?
Transmitter causes depolarisation increasing cell activity
What are inhibitory neurotransmitters?
Transmitter causes hyperpolarisation which decreases cell activity
What is a EPSP?
An excitatory postsynaptic potential, is a graded depolarization caused by a neurotransmitter at the postsynaptic membrane.
An EPSP results from the opening of chemically gated ion channels in the plasma membrane that lead to membrane depolarization.
What is summation?
A post-synaptic cell will ‘fire’ only if it receives sufficient excitation to drive the MP beyond threshold
This occurs when it receives many excitatory inputs (and few inhibitory inputs) within a short time period
What is convergence?
each neuron receives many inputs from other cells
What is divergence?
each neuron then synapses with many other cells
What is a motor end plate?
synapse between a motor nerve and a muscle fibre
What does the action potential create at a motor end plate?
muscle contraction
What neurotransmitter is used at neuromuscular junctions?
acetylcholine
What enzyme breaks down acetylcholine?
acetyl cholinesterase
How can drugs affect synapses?
they can block the synapses by affecting the synthesis, release, action, second message system, and inactivation of the transmitter
What does botox (botulinum toxin) do?
prevents the release of transmitter from motor nerves
How do beta-blockers affect synaptic activity?
they prevent receptors being stimulated by neurotransmitters by binding to receptors
