What is repolarisation on an oscilloscope trace?
A falling spike corresponds to repolarisation via potassium efflux (undershoots to approx. –80 mV)
Key Terms
What is repolarisation on an oscilloscope trace?
A falling spike corresponds to repolarisation via potassium efflux (undershoots to approx. –80 mV)
What is refractory period on an oscilloscope trace?
The oscilloscope trace returns to the level of the resting potential (due to the action of the Na+/K+ pump)
When will an action potential occur?
An action potential will only occur if the initial depolarization exceeds a threshold potential of approximately –55 mV
Are all neurones covered with myelin?
NO
In certain neurons, the axon may be covered by a fatty white substance called myelin which functions as an insulating layer
What is myelin and what produces it?
Myelin is a mixture of protein and phospholipids that is produced by glial cells (Schwann cells in PNS; oligodendrocytes in CNS)
What is the main purpose of myelin?
The main purpose of the myelin sheath is to increase the speed of electrical transmissions via saltatory conduction
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| Term | Definition |
|---|---|
What is repolarisation on an oscilloscope trace? | A falling spike corresponds to repolarisation via potassium efflux (undershoots to approx. –80 mV) |
What is refractory period on an oscilloscope trace? | The oscilloscope trace returns to the level of the resting potential (due to the action of the Na+/K+ pump) |
When will an action potential occur? | An action potential will only occur if the initial depolarization exceeds a threshold potential of approximately –55 mV |
Are all neurones covered with myelin? | NO In certain neurons, the axon may be covered by a fatty white substance called myelin which functions as an insulating layer |
What is myelin and what produces it? | Myelin is a mixture of protein and phospholipids that is produced by glial cells (Schwann cells in PNS; oligodendrocytes in CNS) |
What is the main purpose of myelin? | The main purpose of the myelin sheath is to increase the speed of electrical transmissions via saltatory conduction |
How is an action potential propagated along unmyelinated neurons? | Along unmyelinated neurons, action potentials propagate sequentially along the axon in a continuous wave of depolarisation |
How is an action potential propagated along myelinated neurons? | In myelinated neurons, the action potentials ‘hop' between the gaps in the myelin sheath called the nodes of Ranvier |
By what factor does myelination increase the speed of electrical conduction? | This results in an increase in the speed of electrical conduction by a factor of up to 100-fold |
What is the advantage of myelination? | The advantage of myelination is that it improves the speed of electrical transmission via saltatory conduction |
What is the disadvantage of myelination? | The disadvantage of myelination is that it takes up significant space within an enclosed environment |
What appears as white matter? | Regions of the nervous system composed of myelinated axon tracts appear as white matter, all other areas appear as grey matter |
What appears as grey matter? | Grey matter consists of neuronal cell bodies and dendrites, as well as support cells (glial cells) and synapses |
How do nerves transmit electrical impulses? | Nerves transmit electrical impulses by changing the ionic distribution across the neuronal membrane (membrane potential) |
When are electrical signals unable to be propagated? | Therefore, electrical signals are not able to be conducted when a semi-permeable membrane is absent |
What are synapses? | Synapses are the physical gaps that separate neurons from other cells (other neurons and receptor or effector cells) |
How do neurons transmit information across synapses? | Neurons transmit information across synapses by converting the electrical signal into a chemical signal |
What happens when an action potential reaches the axon terminal? synaptic transmission | When an action potential reaches the axon terminal, it triggers the opening of voltage-gated calcium channels |
What is there an influx of? synaptic transmission | Calcium ions (Ca2+) diffuse into the cell and promote the fusion of vesicles (containing neurotransmitter) with the cell membrane |
What is released into the synapse and by what process? synaptic transmission | The neurotransmitters are released from the axon terminal by exocytosis and cross the synaptic cleft |
What do neurotransmitters bind to? synaptic transmission | Neurotransmitters bind to specific receptors on the post-synaptic membrane and open ligand-gated ion channels |
What does the opening of ion channels cause? synaptic transmission | The opening of ion channels generates an electrical impulse in the post-synaptic neuron, propagating the pre-synaptic signal |
What happens to the neurotransmitters? synaptic transmission | The neurotransmitters released into the synapse are either recycled (by reuptake pumps) or degraded (by enzymatic activity) |
What are neurotransmitters? | Neurotransmitters are chemical messengers released from neurons and function to transmit signals across the synaptic cleft |
When are neurotransmitters released? | Neurotransmitters are released in response to the depolarisation of the axon terminal of a presynaptic neuron |