Lecture 23 Flashcards
What type of conduction is the action potential leaps between the nodes of ranvier?
a saltatory conduction.
What is a typical synapse?
A junction between nerve cells, where nerve impulses are transferred from one to the other.
What are the two types of synapse? What do they act through and what are their relative speed?
Electrical synapses and chemical synapses, an electrical synapse links neurons by the cytoplasm using gap junctions, the signal propagates very fast. A chemical synapse joins neurons at the synaptic cleft, a small physical gap between the neurons which is bridged by neurotransmitter, this is a slower, indirect propagation of the action potential.
What is the main special type of of chemical synapse?
The neuro-muscular junction, which joins nerves to muscle.
Which channel in the synaptic knob causes ions to rush in which will release the vesicles of neurotransmitter?
Voltage gated Ca2+ channels.
What are the 8 structures which make up a chemical synapse?
The presynaptic cell (output zone), the synaptic knob, the synaptic cleft, the postsynaptic cell, the voltage gated Ca2+ channels, vesicles, the cytoskeleton and mitochondria.
How are calcium ions able to flow into the cell despite their low (2-2.5mmolL-1) ECF value?
The ICF concentration of Ca2+ is even lower, in the micromol per litre range.
What steps lead up to the neurotransmitter being released?
- Action potential propagates down the axon to the pre-synaptic knob
- the knob becomes depolarised, opening Ca2+ channels and allowing Ca2+ in
- Ca2+ ions trigger the fusion of vesicles with the presynaptic membrane, expelling the neurotransmitter within.
How does the neurotransmitter transmit the signal to the post synaptic neuron?
- The neurotransmitter diffuses across the synaptic cleft, reaching the post synaptic membrane.
- here the neurotransmitter binds to specific receptors.
- If the neurotransmitter causes Na+ channels to open the post synaptic neuron will depolarise, if K+ channels open, repolarisation will occur. Cl- channels can also be opened, causing hyperpolarisation.
Which of the openable channels opening due to neurotransmitter will be an inhibitory signal? Which will be an excitatory?
K+ and Cl- channels will be inhibitory, Na+ channels will be excitatory.
What is net depolarisation and net hyperpolarisation of a post synaptic cell called?
net depolarisation is an excitatory post synaptic potential (EPSP) while net hyperpolarisation is an inhibitory post synaptic potential (IPSP).
When excess transmitter is released into the synaptic cleft, how is it switched off?
degradation by enzymes, reuptake into pre-synaptic knob, reuptake into glial cells. This removal process switches off signals and tends to require energy, one of the functions of the mitochondria found within the synaptic knob.
