Principles of Nerve Conduction and Synaptic Transmission Flashcards
What is the movement of ions across a membrane determined by?
Ionic gradients
Charge of molecule
Membrane potential
Describe a neuron at resting state in terms of ions
Inside the cell there is a high concentration of potassium and a low concentration of sodium, chloride and calcium ions
Outside the cell there is a low concentration of potassium and a high concentration of sodium, chloride and calcium ions
What is the resting membrane potential and how is it maintained?
-70mV
Maintained by the permeability of the membrane to potassium and an energy dependent pump which moves the ions across the membrane
Describe the four main steps of an action potential
- Depolarisation to threshold
- Activation of sodium channels and rapid depolarisation
- Inactivation of sodium channels and activation of potassium channels
- The return to normal permeability and resting state
Describe the sodium and potassium channels involved
Both are voltage gated
Sodium channels are fast
Potassium channels are slow
Why can the action potential only move in one direction?
When an action potential occurs, sodium channels are opened, in turn causing more sodium channels to open due to the change in membrane potential
Behind the action potential, sodium channels close as they are time dependent, meaning the action potential can only move in one direction
Definition of a neurotransmitter
A substance that transmits nerve impulses across a synapse
Main characteristics of neurotransmitters
Synthesised endogenously
Available in sufficient quantity in the presynaptic neuron to exert an effect on the postsynaptic neuron
If externally administered, it mimics the endogenously- released substance
Describe the process of neurotransmission
Neurotransmitter contained in a vesicle
Membrane depolarisation opens voltage gated calcium channels, triggers vesicles to move to presynaptic membrane
Neurotransmitter moves across the synapse
Binds to a receptor on the post synaptic membrane
Acts on that receptor to increase or decrease activity of the post-synaptic neuron
Acting back on the presynaptic neuron to increase or decrease firing
Specific system for removing the transmitter or stopping its activity
What do the postsynaptic effects depend on?
The neurotransmitter
Which receptor it binds to
What does a fast excitatory neurotransmission cause?
An excitatory post-synaptic potential
What does a fast inhibitory neurotransmission cause?
An inhibitory post-synaptic potential
ACh synthesis and reuptake cycle
ACh formed in the synaptic terminal Packaged into vesicles Released into the synaptic cleft Broken down by ACh esterase Choline taken up, terminating the signal
Describe the main monoamine neurotransmitters and their characteristics
Noradrenaline, dopamine and serotonin
Only one receptor is an ion channel, the rest are G protein coupled receptors
Neurons originate in the brain stem projecting up into the cortex and other brain regions as well as down the spinal cord
Describe monoaminergic transmission
Monoamines are synthesised in the synaptic terminal
Packaged into synaptic vesicles and released
Action terminated by reuptake- energy dependent mechanism, ATPase creates concentration gradient which drives opening of channel, ions equilibrate as channel opens
Drugs can inhibit reuptake
Describe GABA and glutamate’s main characteristics and their synthesis and reuptake cycle
GABA is the major inhibitory neurotransmitter- all the receptors are inhibitory
Glutamate is the major excitatory neurotransmitter- all the receptors are inhibitory
Synthesised as part of the krebs cycle, rapidly taken up from the synapse after they have been released by transporters on glia, turned into glutamine and recycled back into the krebs cycle
Features of pre-synaptic receptors
Help to regulate neurotransmission
Often called autoreceptors because they control the release of their own neurotransmitter e.g. A2 adrenoceptor
In what ways can the signal end?
Stopping the signal from the presynaptic neuron (no more action potentials, closing Ca channels)
Stopping the release of the transmitter (pre-synaptic autoreceptors)
Stopping the activity of the transmitter by rapid enzymatic destruction, uptake into nerve terminals or neighbouring cells, diffusion away from the synapse followed by one or both of the above
How can you change activity at the synapse?
Agonists increase activity
Antagonists decrease activity
Reuptake inhibition- block reuptake/ recycling, increase activity at the synapse
Facilitate release- increase activity
Inhibit synthesis enzymes- decrease activity
Inhibit degradation enzymes- increase activity
Block release- decrease activity
