Signalling Flashcards
What is the neurone?
The principal unit of signal transduction?
What is a synapse?
The small spaces between neuronal cells.
What are the two types of synapse?
Electrical (less common, simple) and chemical (common, more complex).
What happens at a synapse?
Electrical conduction is converted to chemical conduction, in most cases.
What is a graded potential?
Changes in charge of the dendrite/cell body region that are variable in amount.
What is an action potential?
Changes in charge of the axon are always identical.
How do graded potentials and action potentials differ?
Changes in the charge of the dendrite/cell body are variable in amount, whereas changes in the charge of the axon are always identical.
What are the types of electrical responses?
Intrinsic (silent, beating and bursting) and response to external - sustained response, accommodation and delay.
How is neuronal activity measured?
Activity is measured by treating the membrane as part of a circuit, and charge separation is caused by the membrane’s ability to selectively prevent movement of ions.
What is impalement?
Measuring charge movement and change in electron i fine electrodes
What is patch clamping?
Looking at an isolated piece of membrane and looking at channel activity - large electrodes.
What can clamping be used to measure?
Voltage or amplitude.
What is the most widely used electrical technique for measuring ion channels?
The patch clamp technique.
How do electrical and chemical synapses differ in terms of path length?
electrical - 2nm, chemical - 20-40nm.
What is the transmission agent of electrical and chemical synapses?
Ionic for electrical, chemical transmitter for chemical.
How does the direction of electrical and chemical synapses differ?
Electrical synapses are bidirectional whereas chemical synapses are unidirectional.
What is the method of action potential generation at chemical synapses?
Action potential invades, there is Ca2+ influx, depolarisation and release of neurotransmitter and diffusion, ligand binding, depolarisation, transmitter recycling and vesicular membrane recycling.
What are the features of fast chemical transmission?
Transmitter is released directly into the cleft and ligand binding directly stimulates the opening of Na+ channels.
What are the features of slow chemical transmission?
Large vesicles release transmitter, which is not necessarily directed towards post synapitic channels. Ligand binding functions through G protein and G protein causes ion channels to open.
What is the threshold?
The membrane potential that results in the neurone generating the action potential.
What is the equation for potential?
Current x resistance.
What does resistance come from?
Closed channels - prevents ion movement.
What are ion channels?
Protein tubes that span the membrane.
What is facilitated diffusion?
Diffusion of ions through channels where no ATP is needed.
What are the two types of channel in a typical neuron?
Electrically gated (voltage gated) and chemically gated (ligand gated).
What are the different voltage gated ion channels involved in in neurons?
Na+ - depolarisation, K+ - repolarisation, Ca2+ - neurotransmitter release.
What does charge separation result from?
The different permeability of the membrane to positive and negative ions.
What is the Nernst equation important for?
Understanding ion channel behaviour.
What does the Nernst equation assume?
There is a difference in the concentration of an ion across a membrane, the membrane is selectively permeable to one type of ion only.
What is the reversal potential?
The membrane potential at which there is no ionic current.
What does the value of the reversal potential tell you?
A clue as to the ion that stimulates action potential for the cell.
What does the reversal potential depend on?
The concentrations and relative permeability of all the ions involved in generating a current - use the Goldman equation.
What is the Goldman equation?
It takes into account permeability for three main ions and gives the membrane potential.
