Neurophysiology Revision Flashcards
Summarise how an electrical impulse is processed in a neuron
Impulse arrives at cell body through dendritic branches. It then gets passed along the axon in the form of APs at the node of Ranvier by saltatory conduction (myelinated) before being passed to the target at the boutons.
What are the cells responsible for myelination in the NS?
Glial cells:
- PNS = Schwann cells (1 internode)
- CNS = oligodendrocytes (many internodes)
Describe the process of saltatory conduction
Conduction down the neuronal axon flows rapidly to the node. Here, it slows down and an ionic depolarisation occurs (controlled by Na+ channels). Then fast conduction inside the axon resumes
What are the pre-synaptic events for chemical secretion?
Synaptic Docking and Fusion
- V-SNARE on vesicle (containing NT) recognises and forms a complex with T-SNARE at the pre-synaptic membrane
- the complex forms a strong bond that pulls the membranes close
- complexin binds to the protein complex inhibiting exocytosis
- an AP triggers a Ca2+ influx which causes synaptotagmin to displace complexin allowing exocytosis to proceed
Summarise the synaptic events associated with NT release
NT are released by exocytosis, diffuse to the post-synaptic membrane and bind to either ionotropic receptor (receptor is ion channel) or metabotropic receptors (receptor is activator of G-protein which modulates ion channel)
Describe the post-synaptic responses that can take place
The flow of ions through the channel trigger PSPs (post-synaptic potentials)
- excitatory PSP = net flow of ‘+ve’ ions into cell = depolarisation
- inhibitory PSP = net flow of ‘-ve’ ions into cell = hyperpolarisation
Describe how nerve conduction is investigated in patients
Sum of all APs in a nerve/stimulus in a target is measured
- reduced amplitude = less axons
- reduced conduction velocity = less myelin
