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Northeastern University
BIOL 3405
Neuro Bio

STUDY GUIDE: EXAM 2, NEUROBIOLOGY, SPRING 13 ION CHANNEL STRUCTURE / FUNCTION 1. General principles a. ion selectivity and gating i. how does ion selectivity and driving force determine the direction of ion flow? ii. how are stretch-activated receptors similar to voltage-gated receptors? iii. optogenetics employs light-activated receptors 1. differentiate channelrhodopsin versus halorhodopsin a. what light activates each? b. does activation result in depolarization or hyperpolarization? (optogenetics videos shown in lecture are available on Blackboard with lecture 8) b. ionotropic versus metabotropic receptors i. compare and contrast their: 1. mechanism of action 2. time course (onset and offset) 3. signal strength (amplification of signal?) 2. Ion channels underlying action potentials a. review channels listed on your color slide i. compare and contrast A-type potassium channels with transient sodium channels (including mechanism of inactivation- see figure 5 from Armstrong and Hille review) ii. what is meant by spike frequency adaptation? (calcium-activated potassium channels plays a big role) b. patch clamp methods (make sure you know how to interpret voltage-clamp traces) i. compare and contrast cell-attached versus whole-cell recording 1. which measures microscopic versus macroscopic currents? 2. single channel conductances are in what range? 3. how do single channel recordings support Hodgkin & Huxley’s findings? a. sodium channel inactivation as well as time course of potassium channel function b. blockers you should know: TTX (voltage-gated sodium), AP5 (NMDA-R), 4-AP (assume voltage-gated K channels only) 3. Ion channel structure a. what is a hydropathy plot and which direction shows regions of hydrophobicity? b. which voltage-gated ion channels are structurally similar? i. how does the S4 voltage sensor work? ii. how does the pore loop selectivity filter work? c. which ion channel gene family is the most diverse? i. if a neuron was hyperpolarized, what would be the effect of the inward- rectifying potassium channel? ii. how does more calcium affect the calcium-activated potassium channel’s outward current (increase or decrease)? iii. you are expected to understand the other specific potassium channels listed on slides (delayed rectifier, two-pore channel, hERG) d. channelopathies i. anti-seizure drugs affect which ligand-gated ion channel? (see lecture 10 slides) ii. understand the technique of expressing mutant receptor genes in Xenopus oocytes in order to analyze their altered function iii. understand how mutation in hERG leads to changes in heartbeat QT interval iv. from Waxman review article: 1. what are the 3 types of channelopathies and how do they differ? (fig. 1) 2. understand the 2 examples of transcriptional channelopathies (peripheral nerve injury and multiple sclerosis) discussed in lecture ie. figures 2, 3 right side only, 4, 6 3. how might changes in nociceptors or dorsal horn neurons lead to chronic pain? v. hypothesize how different channel mutations might lead to channelopathies (example we discussed in lecture was on Benign familial neonatal seizures) SYNAPTIC TRANSMISSION 4. Types of synapses a. Compare/contrast electrical and chemical synapses i. how do they differ in: 1. speed of transmission (what mediates their response?) 2. amplitude of postsynaptic response (concept of coupling coefficient) 3. other parameters? ii. what are gap junction proteins called? 1. where might we find them in vertebrates? a. understand Mauthner cell circuit for c-bend escape reflex in goldfish 2. understand the benefits/limitations of electrical synapses a. benefits- low synaptic delay, high coupling coefficient, bidirectional (synchronizing networks, escape behaviors) b. limitations- no temporal summation, requires large amount of membrane contact iii. understand spatial versus temporal summation 1. how does a dendrites’ passive properties affect PSPs (see lecture 10)? b. Chemical signaling machinery i. in a pre- and post-synaptic pair of neurons, where would you expect to find: 1. voltage-gated sodium versus calcium channels? 2. excitatory versus inhibitory synapses? 3. synaptic vesicles versus neurotransmitter-gated receptors? 4. how do boutons en passant differ from the axonal terminal? ii. mitochondria are abundant in soma as well as pre- and post-synaptic elements 1. what are various neuronal signaling functions that require energy? c. Synthesis and storage of neurotransmitters i. compare/contrast small molecule versus peptide neurotransmitters 1. speed of axonal transport 2. type of synaptic vesicles (large dense core or small, clear?) 3. are the neurotransmitters themselves, or their synthetic enzymes made in the soma? 5. Excitation-secretion release of neurotransmitter (go over answer key for NT release hypotheses) a. measuring neurotransmitter release at frog neuromuscular junction i. differentiate nerve-evoked EPPs and spontaneous MEPPs 1. what is the effect of: a. lowering calcium? b. increasing 4-AP? ii. differentiate number of quanta released versus size of individual quanta 1. what vesicle recycling disorders affect these parameters? 2. what did freeze-fracture electron microscopy tell us? iii. understand Llinas (82) voltage-clamp experiments to demonstrate calcium- dependent neurotransmitter release 1. what is the effect of adding a calcium buffer (BAPTA)? 2. what did capacitance measurements tell us? a. how do we measure neurotransmitter release? b. what are the normal steps for vesicle recycling? i. how does a “kiss and run” exocytosis differ? ii. how does dynamin differ from dynein? 3. understand steps involving SNARE proteins a. why does Botox cause flaccid muscle paralysis? 6. Nicotinic acetylcholine receptors a. properties (where are they located, how is it synthesized, broken down, what poison blocks the channel, etc) i. differentiate agonist versus antagonist effects (in general) 1. does the body produce any endogenous antagonists? b. current underlying EPPs
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