What is saltatory conduction
Depolarization spread through the skipping of Nodes of Ranvier
What is the composition of myelin?
Phospholipids 70%(cholesterol) and Proteins 30% and water obvs
What cells produces myelin? Where are they found?
Schwann cells in PSN
Oligodendrocytes in CNS
Does a thicker nerve fibre have a larger or smaller conduction velocity?
Thick fibre = Larger conduction velocity
What 4 things effect axon conduction velocity?
1) Increase Fibre Diameter
2) Myelination. Decrease membrane Capacitance
3) Increase membrane resistance, close more channels
4) Increasing inward current. Change ions
How do you decrease membrane Capacitance?
by increasing myelination (the thicker the myelin the farther the cations and anions are from each other). increases nerve conduction velocity
How do you increase membrane resistance?
By increasing myelination (the thicker the myelin the less cations leak outward) increases nerve conduction velocity. See
How long is an axonal AP?
0.5 ms
How long is a cardiac AP?
100ms
What happens to Na+ channels at the peak of AP?
Inactivate
What happens to Na+ channels in hyperpolarisation?
Change from inactive to closed
What order to local anesthetics block conduction in nerve fibres?
Small Myelinated axons
Non-myelinated axons
Large Myelinated axons
How do local anesthetics work?
Block Na channels preventing APs
What is capacitance? how does it related to resistance
Ability to store charge. High capacitance = more current to charge, decrease spread in local current.
inversly related to resistance
What is resistance? How is thisi related in to a human axon?
Resisitance depends on the number of channels open. Lower the resistance = more channels open = more loss of local current across membrane = reduced spread
For a quick conduction velocity you want a ______ capacitance and a ________ resistance
Low capacitance
High resistance
What happens if EC Na+ is reduced
The AP amplitude is reduced and if it gets lower than the threshold amount then no AP will be triggered
What is conductance abbreviated as?
G
Explain the threshold in terms of channels.
Voltage opens a number of VGNaC which lets in Na into the cell and depolarises the membrane a bit. If enough channels open then lots of Na+ rushes in and causes a bigger depolarisation which opens more VGNC. This is a positive feedback loop
How many transmembrane domains does a Na channel have? Which one is responsible for the Voltage gate
6
TM4
How many subunits in a voltage gated channel?
4 subunits made up of 6 TM domains
Why are myelinated axons more effective and transporting charge? C and R?
high membrane resistance
low membrane
capacitance
What appears in high conc at the nodes of ranvier?
Na channels
How does disease such as MS disrupt conduction velocity?
Stops saltatory conduction
Explain how an AP passes a signal on to the next neuron. STeps
1) Normal AP. Na and K VGCs
2) VGCC open, calcium influx
3) Calcium induces vesicles to exocytose
4) Ligand gated Na channels on opposite neuron open
5) depolarization continues
Explain neurotransmitter release from post synnatic neuron..
) Normal AP. Na and K VGCs
2) VGCC open, calcium influx
3) Ca2+ binds to synaptotagmin
4) Vesicle brought close ot membrane
5) Snare complex makes a fusion pore
What does Nifedipine do?
Calcium channel blocker
How does the Calcium channel activation and inactivation compare to Na?
Much more slowly
How many ACh binding sites are there on a Nicotinic Acetlyscholine channel?
2
In skeletal muscle, what is the transmitter and receptor on the post-ganglionic neuron?
Trick Q. There is only one axon in skeletal muscle straight to Skel muscle (motorneuron). ACh and Nicotinic ACh Receptor (the only one to do this apart from the symp branch to the adrenal gland that has a direct axon)
Name a drug that blocks nAChR?
d-Tubocurarine. Competitive blocker
How does succinylcholine work?
Inhibits adjacent Voltage gated Na+ channels
What type of channel is mAChR? Where is it found?
GPCR. Produces a slower response
Found in Para and sometimes Symp (sweat glands)
What type of channel is nAChR? Where is it found?
LGNaC. Faster reaction
Post-ganglionic neurons in Autonomic NS (Symp and Para) and also Motorneurons (skeltal muslce)