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NROB60 FINAL NOTES STUDY
SET EXAM
properties of the action potential - Answer rising phaseovershoot falling phase undershootWhat happens when the current reaches threshold? - Answer generate APs at a low rate What happens when current increase? - Answer rate of AP generation increases increases the frequency of AP (all or none situation)What does the firing frequency of APs reflect? - Answer the magnitude of the DEPOLARIZING current (since hyperpolarizing would not allow threshold to be reached)What is one way stimulation intensity is encoded? - Answer firing frequency What causes ionic changes? - Answer depolarization causes increase in Napermeability by opening gates in pores or ion channels hyperpolarization - Answer more negative depolarization - Answer more positivewhat kind of current does the firing frequency reflect? - Answer depolarizing current (hyper polarization would not allow threshold to be reached) How can you flip the membrane potential? - Answer by changing the relative ionicpermeability of the membrane rising phase --> have inward Na+ current falling phase --> has outward K+ currentAP occurs during sudden shift in membrane properties How does the permeability of the membrane change for AP? - Answer membranechanges from K permeability to Na permeability to K permeability
how are interneurons depolarized? - Answer entry of Na+ through channels that aresensitive to NT released by other neurons What are the two types of channels? - Answer voltage gatedligand gated Voltage gated channels - Answer depends on a change in voltage in order to open andclose ligand gated channels - Answer ex. needs a neurotransmitter in order to open/close When is an AP generated? - Answer if the depolarizing stimulus passes the thresholResting potential - Answer only leak potassium channels are open (these are constantly in an open state) Rising Phase - Answer more and more sodium channels open (driving force of sodiumions rushing in) entry of Na+ (usually because Na+ channels are sensitive to membrane stretching) sodium influxOvershoot phase - Answer most positive state two processes occur simultaneously:
- sodium gates begin to close- K channels begin to open (these channels differ from leak potassium channels) because the relative permeability of the membrane favours Na --> membrane potentialapproached Ena which is GREATER than 0 mV Falling phase - Answer activation of voltage gated potassium channels are AT MAXIMUM Na channels are mostly al closedPotassium efflux Undershoot phase - Answer hyperpolarization occurs membrane potential returns to normalpotassium channels (not LEAK ONES) close little Na permeability and membrane approached Ek --> causes hyperpolarizationrelative to RMP until the VG K channels close again Which channel opens and closes faster? - Answer Na
-open at more negative potentials (therefore, can have AP occuring sooner) delayed rectifier - Answer Potassium conductance serves to rectify or reset membranepotential Structure of voltage gated potassium channels - Answer four separate polypeptidesubunits joint to form a pore absolute refractory period - Answer cannot fire an AP again Na channels are inactive since the membrane is strongly depolarized cannot be activated again and no further APs until the membrane potential goessufficiently negative to deinactivate the channels Relative refractory period - Answer We could get an AP again but we need more of adepolarizing current in order to bring it to threshold Membrane potential stays hyperpolarized until VG K channels close What is the propagation of action potentials influenced by? - Answer myelinationpropagation in unmyelinated axons vs myelinated axons - Answer Propagation in unmyelinated axon requires reproduction of the AP at each successive axonal segment
- slower
- Because we put in our stimulus and at each point along the axonshappening (from going from positive to negative) → we have change Propagation in myelinated axons requires reproduction of the action potential in thenodes of Ranvier (SALTATORY CONDUCTION)
- this increases the speed of conduction
- we are not having change occur at EVERY SINGLE POINT in the axon- AP regenerates at the nodes of ranvier Orthodromic - Answer AP travels in one direction
- does not go backwardsAntidromic - Answer Backward propagation What are the four factors that influence conduction velocity? - Answer spread of APalong membrane (dependent upon axon structure) path of positive charge (inside axon = faster, across the axonal membrane = slower)
- Down the inside of the axon: Axon is wide and very few membrane pores are open most current will flow inside the axon →
pores- Across the axonal membrane: If axon is narrow and there are many open membrane → most current will flow across membrane axonal excitability --> axonal diameter (bigger = faster) --> Smaller axons require greaterdepolarization to reach AP threshold → are more sensitive to being blocked by local anaestheticsnumber of vg Channels Myelin Schwann cells - Answer produce myelin in PNSOligodendrocytes - Answer Form myelin sheath in CNS Nodes of Ranvier - Answer VG Na channels are concentrated in these nodesWhy do membranes of dendrites and neuronal cell bodies NOT generate sodium dependent APs? - Answer they have very few VG Na channels Spike intiation zone - Answer the part of the neuron where an axon originates from thesoma (the axon hillock)
What are the two types of synapses? - Answer electrical and chemical Electrical synapses - Answer Widespread throughout the brain but RARE Very powerful Narrow cleft (gap junction) Cell are said to be "electrically coupled" Membranes have large channels (Connexon → formed by 6 connexins)
dendrodendritic synapse - Answer dendrite to dendrite Gray's type I synapse - Answer asymmetrical, usually excitatory Gray's type II synapse - Answer symmetrical, usually inhibitory What are the basic steps of chemical synaptic transmission? - Answer Neurotransmittersynthesis
Load NT into synaptic vesicles Vesicles fuse to presynaptic terminal Neurotransmitter spills into synaptic cleft Binds to postsynaptic receptors biochemical/electrical response elicited in postsynaptic cell Removal of NT from synaptic cleft (Have to remove the NT in order to stop the effect) What are the three major types of neurotransmitters - Answer amino acids aminespeptides
What are the three main NTs for fast synaptic transmission at most CNS synapses? -Answer glutamate
GABA glycine What NT is used for fast synaptic transmission at NMJ? - Answer ACh What are three things that Amines and AAs have in common? - Answer small organicmolecules
contain nitrogen stored and released from synaptic vesicles Two characteristics of peptides - Answer large molecules stored and released from secretory granules Three major amino acids - Answer GABA glutamate glycine 6 examples of amines - Answer ACh
What is different regarding neuropeptides (regarding how they are made)? - Answer -the long polypeptide is split in the Golgi Apparatus into smaller fragments
Active form of neuropeptides are the... - Answer smaller fragments How are neuropeptides transported t the axon terminal (which process)? - Answeraxoplasmic transport
anterograde transport - Answer cell body to axon terminal Primary difference between secretory granules and synaptic vesicles - Answer largerthan synaptic vesicles
not found close to the active zone NT release: difference between vesicles containing AA(+ amines) and vesiclescontaining neuropeptides - Answer Vesicles containing AA and amines are in active zone --> therefore, immediate response vesicles for neuropeptides are further away --> therefore, NOT ALWAYS TRIGGERED Steps for NT release (four steps) - Answer 1. NT are located in vesicles in axon terminal
- Influx of Ca 2+ due to action potential reaching the terminal and activating VG gatedcalcium channels
- Causes tethering, docking, and fusion of vesicles with membrane (exocytosis)
- docking must occur in order for the NT to be released
- NT are recycled using endocytosis what does docking require? - Answer calcium active zone - Answer the actual site of neurotransmitter release postsynaptic density - Answer the protein thickly accumulated in and just under thepostsynaptic membrane
(contains the NT receptors) glutamate and glycine are both.. - Answer amino acids (therefore they are abundant in all cells of the body) transporters - Answer concentrate the synthesized NT inside the vesicles (specialproteins embedded in the vesical membrane)
NT release of peptides - Answer Release of peptides generally requires high-frequencytrains of AP → so that the calcium ions throughout the terminal can build to the level required to trigger release away from the active zone This is a slow release What are the two classes of NT receptors? - Answer transmitter-gated ion channels(ionotropic)
G-coupled receptors (metabotropic) structure of transmitter-gated ion channels - Answer consists of 4-5 subunits
What are three basic steps for G-coupled receptor NT action? - Answer Bind to receptorproteins ( on the postsynaptic membrane)
Activate small proteins (receptor activates small G-protein that can move) Activate "effector" proteins (G-protein activates "effector proteins") What are possible "effector proteins"? - Answer Effector proteins can be G proteingated ion channels in the membrane
OR they can be enzymes that synthesize molecules called SECOND MESSANGERS thatdiffuse away in the cytosol
Difference between G-protein coupled receptors and transmitter gated receptors? -Answer - ALL three types of NT acting on this receptor can also have a SLOWER, LONGER LASTING AND MUCH MORE DIVERSE postsynaptic actions metabotropic receptors - Answer metabolic effects The same neurotransmitter can have _____________ postsynaptic actions - Answerdifferent
EXAMPLE: In the heart: -A metabotropic ACh receptor is coupled by a G protein to a potassium channel-Opening of potassium channel hyperpolarizes the cardiac muscle and reduces the rate of AP In the skeletal muscle: -The receptor is a transmitter gated ion channel → specifically a ACh gated ion channel
permeable to Na+ -Therefore, opening of this channelexcitable → depolrizes the muscle fibers → makes them more
autoreceptors - Answer Presynaptic receptors sensitive to NT released by presynapticterminal
Act as safety valve to reduce release when levels are high in synaptic cleft(autoregulation)
Allows for self regulation Common effect: inhibition of neurotransmitter release and sometimes NT synthesis what are the two ways NT can be recovered/degraded? - Answer - simple diffusion-destruction
Simple diffusion - Answer diffusion away from the synaptic cleft reuptake into the presynaptic axon terminal once inside, it is either destoryed or repackaged Common for most AA and amine NT when does simple diffusion usually occur (for what situation)? - Answer when a smallamount is released
Destruction - Answer -specifc enzyme is released into cleft
neurotransmission Why is there a huge difference between excitatory transmission at the NMJ and CNSsynapses? - Answer NMJ has evolved to be failsafe → IT NEEDS TO WORK EVERYTIME
Best way to ensure this is to generate an EPSP of a huge size What does EPSP summation allow the neuron to do? - Answer allows for neurons toperform sophisticated computations
integration = EPSPs added together to produce significant postsynaptic depolarization spatial summation - Answer EPSP generated simultaneously in different places alongthe dendrite (happens over an area)
temporal summation - Answer EPSP generated at same synapse in rapid succession,within 1-5 msec of one another (Happens very close together in time (they can add together)) What does the effectiveness of an excitatory synapse in triggering an AP depend on? -Answer on how far the synapse is from the spike-initiation zone
on the properties of the dendritic membrane what are the two differences between excitatory and inhibitory synapses? - Answer Binddifferent neurotransmitters
allow different ions to pass through channels What are the five steps for activating NE beta receptor? - Answer Binding of NE to the
receptor activates a G-protein in the membrane G-protein activates the enzyme adenylyl Adenylyl cyclase converts ATP into the second messenger cAMP cAMP activates a protein kinase The protein kinase causes a potassium channel to close by attaching a phosphate groupto it
modulation - Answer Can manipulate the channel without having a receptor on thechannel
What is the first identified NT? - Answer ACh Cholinergic - Answer a neuron that uses ACh Synthesized in all motor neurons noradrenergic - Answer Describing neurons or synapses that produce and releasenorepinephrine.
Dopaminergic - Answer a neuron that uses dopamine as a NT What are the three components of the criteria of a substance being an NT? - Answer -Synthesis and storage occurs in presynaptic neuron -Released by presynaptic axon terminal-Produces responses in postsynaptic cell
What can violate the dale's principle? - Answer peptides Co-transmitters - Answer Two or more transmitters released from one nerve terminal ex. An amino acid or amine plus a peptide How to make ACh - Answer acetyl CoA + Choline How is ACh broken down? - Answer acetic acid + choline choline is sent back to the nerve terminal (in order to resynthesizes the NT) chlorogenic system are important for? - Answer learning and memory NMJ what is the special enzyme that is required to synthesize ACh - Answer ChAT transfers an acetyl group from acetyl CoA to Choline Where does the synthesis of ACh occur? - Answer cytosol Where is ChAT synthesized? - Answer in the soma. It is transported to the axon viaaxoplasmic transport
What is the rate-limiting step in ACh synthesis? - Answer the availability of choline limitshow much ACh can be synthesized in the axon terminal
therefore, the transport of choline into the neuron is said to be the rate-limiting step How is ACh destroyed? - Answer Requires AchE degradation enzyme Secreted into cleft Can reuse the choline The acetic acid just diffuses away What are the three catecholamine NTs? - Answer dopamine, norepinephrine,epinephrine (aka adrenaline)
What amino acid are the three catecholamine NTs derived from? - Answer tyrosine Common things between the catecholamine NTs - Answer all contain catechol in neurons involved in movement, mod, attention, visceral function Process of catecholamine NTs synthesis - Answer tyrosine --> dopa --> dopamine --> NE--> epinephrine
enzymes involved in the process of catecholamine NTs synthesis (in order) - Answertyrosine hydroylase (TH), dopa decarboxylase, DBH, PNMT
What is the rate-limiting step in catecholamine synthesis? - Answer the activity of TH
