Module 8 - Transmission within neurons Flashcards
How is an action potential propagated?
The Na⁺ ions that have entered in the cell can move forwards in the cell and cause next parts tp reach threshold potential, triggering another AP (this process continues throughout the neuron)
The Na⁺ ions won’t cause APs the wrong way because previous parts will be in a refractory period and unable to have an AP triggered
Why is attenuation in dendrites not a big problem?
Short distances are involved with there being many inputs
Dendrites and action potentials
Dendrites can generate action potentials but transmission is passive - no AP wave (would be able to have waves with more Na⁺ channels; however, there are only a couple at the start of the dendrite so not possible)
Saltatory conduction: the key features allowing for conduction within axons
50-100x more sodium channels than in dendrites, reducing the likelihood of attenuation
Better insulation - preventing unintended leaks
Increasing diameter
Decreasing conductivity (??????????????????????????)
Giant squid axons
Axonal diameter increased instead of using myelination to speed up transmission
Normal axon - 20μm, giant squid axon - 1mm
(This axon is the one used in the water jet response to escape predators)
Why is myelination a preferred method of speeding up APs instead of enlarging axons?
Enlarging axons limits the size of the nervous system
Myelination: what does it do and how does it speed up transmission?
Myelins are a protective layer made of fatty acids and proteins that surround the parts of the axon between the nodes of Ranvier (internodes)
Myelination allows for greater Na⁺ channel concentrations (~10x, 1200/µm²) at nodes of Ranvier and prevents leakage of Na⁺ ions throughout the axons
Multiple sclerosis: what is it, who is most at risk, what is it caused by, and how is it diagnosed?
A common autoimmune disease in northern Europe
The most common age range is 15-50 years old at diagnosis and women are two-three times more likely to develop MS than men (true of all autoimmune diseases)
Involves an immune attack on the oligodendrocytes that make the myelin sheathes on the internodes within the CNS
The Visual Evoked Potential Test, MRI
Multiple sclerosis: what are the risk factors and how do the VEP and MRI tests diagnose MS?
Genetic basis suggested but also there is a strong correlation between vitamin D deficiency during development and MS
The Visual Evoked Potential Test - the visual neurones are the first neurones affected and so a possible delay (due to slow neuron conduction) can be detected by electrodes attached to the scalp
MRIs are the best way to diagnose (but they require more equipment and are more expensive) as they can see plaques in the brain which signal the stage of MS that the individual is in
Why is unmyelination such an issue?
Since there are no Na⁺ channels in the internodes, neurones struggle to generate waves of APs
Guillain-Barré syndrome: what is it, what risk factors may cause it and what are the symptoms?
An autoimmune disorder in which Schwann cells are attacked and peripheral nervous system neurons become demyelinated
About 40% of people develop it after they have had either Campylobacter food poisoning or infection with cytomegalovirus. It has also been reported that GBS can occur after infection with CV-19
About 20% of people with GBS are unable to walk 6 months after the onset of the disease and many will suffer from impaired respiratory function
What are the sudden increases in disability and the returns to a lower level of disability called?
Relapses and remissions
