Neuroscience Quiz 2/08/18

What give the axon their shape?
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What determines ion selectivity?Pore diameter, local environment, amino acids and interactions between ions and water.When do voltage-gated K+ channels open?They begin to open slowly upon depolarization but they are responsible for repolarization.When are sodium channels inactivated?After the peak voltage of the cellWhat does scorpion toxin do?It inhibits delayed rectifier K+ channels.What do potassium leak channels do for the neuron?Shape the duration and frequencies of action potential. It is always open.Are there more sodium leak channels or potassium leak channels?Potassium leak channelsWhy does Action potential propagate in one direction?The membrane behind the action potential is in refractory period.What does the speed of the action potential depend on?It depends on how far the depolarization goes. Also diameter of an axon and how much myelination is there.What are the two types of synapses?Chemical and Electrical. Chemical is more common.What are gap junctions?They have large pores so substances can diffuse easily between the cytoplasm of pre and post synaptic neurons. Made of hemi channels which is made of connexins. Can let in most ions and small organic molecules. Cause synchronization between neurons.When do connexins close?When there is a high concentration of calcium inside the cell.What is the importance of calcium?It is a messenger as well as an ion. With high calcium levels there is less synchronization.What do receptors do?If there is chemical signal it is converted back into electrical.What are secretory granules?Large diameter vesicles that contain solubble protein. In neurons they store neurotransmitters.What are the 2 categories of CNS synaptic membrane differences?Symmetrical: Gray's Type II -> Inhibitory Assymetrical: Gray's Type I -> ExcitatoryWhat are the synaptic arrangements?Axo-dendritic, Axo-somatic- Axo-Axonic, Dendro-dendritic. Most common is axo-dendritic.What are oscillations of Vm?Fluctuations in membrane voltageWhat is the neuromuscular junction?The synapse between a motor neuron and a skeletal muscle cell. Junction folds ensure that NT is focally released and folds increase surface area so there is a large number of receptors to activate.What does neurotransmission require?Synthesis of NT in the presynaptic nerve terminal. Storage of nT in secretory vesicles or synaptic vesicle Release of NT into the synaptic cleft or space. This release is Ca 2+ dependent Receptors on postsynaptic membrane A means for terminationWhat are the types of NT?Amino acid: glutamate, GABA, glycine. Fast at CNS Amine NT: Acetylcholine and norepinephrine. Ach is fast at NMG.Describe the process of excocytosis?Vesicles are firstly docked, Protein in vesicle interacts PM Voltage gated Ca 2+ channels sense depolarization and open which causes inward flux of calcium Increase in calcium causes vesicles to fuse and release contents into the synaptic cleftWhat are the active zones?Synaptic machinery: Ca 2+ channels, Ca 2+ snesors, SNAREs and vesicles. More AZ stronger synapse. Mediates synaptic releaseWhat do SNARES do?They dock synaptic vesiclesWhat are synaptogamins?Calcium sensors. They trigger vesicle fusion by inducing a conformational change.How do NT act on postsynaptic cell?They bind to receptors which causes a conformational change.What are transmitter-gated ion channels?Membrane-spanning proteins that consist of 4 to 5 sub units to form a pore. They are permeable to more than one ionWhat is synaptic integration?Neurons in the brain receive inputs from other neurons. This process describes how neurons add these inputs before generation of nerve inputs or action potential.Describe Ach process:AP reaches axon terminal of motor neuron. Ca2+ channels open, enters the axon terminal moving down its electrochemical gradient Ca 2+ entry causes Ach to be released by exocytosis Ach diffuses diffuses across the synaptic cleft and bind to its receptor on the sarcolema Ach binding opens ion channels in the receptors that allow passage of Na into the muscle fiber and K out of the muscle fiber. More Na ions than K ions exit which induces a local change in the end plate potential Ach effects terminated by its breakdown by acetylcholinesterase and diffusion away from the junctionHow does one study NT release?Show that molecule is localized and synthesized in a neuron Immunohistochemistry to distinguish between different types of neurons Synthesize enzyme or neurotransmitter Neuropharmacological analysis Molecular analysis of receptorsWhat do g protein receptors do?Amplify a signalWhat is the rate limiting step of the NMJ?The amount of choline in the extracellular spaceHow can one distinguish between different types of ligand-gasted ion channels?Pharmacology, Kinetics, PermeabilityDifference between glutamate and GABA gated receptors:Glutamate gated receptors let in cations GAB gated receptors let in Cl-, are inhibitory when the membrane is hyperpolarized