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29: neuronal communication
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- 1what is a membrane potential?the voltage across a plasma membrane
- 2what is the resting potentialthe voltage at rest, not sending signals
-60 to -80 mV - 3How can the resting potential be modelled?by two chambers separated by an artificial membrane that is permeable only to K+
- 4how can the equilibrium potential for given K+ concentrations be calculated?using the Nernst Equation
- 5Modelling the resting potential- High conc of KCl in inner chamber and low conc in outer. voltage across: 0 mV
- K+ will start to diffuse across the membrane down its concentration gradient from inner --> outer
- Cl- cant follow, negative charge builds up on inner side
- K+ will keep diffusing until the membrane of inner becomes so negative it stops K+ from leaving
- the chemical gradient pulling K+ into the outer chamber is balanced by the electrical gradient pulling K+ back to inner chamber: equilibrium potential - 6What is the Equilibrium Potential?the chemical gradient pulling K+ into the outer chamber is balanced by the electrical gradient pulling K+ back to inner chamber
- 7Resting potential in cells- Na+/K+ pump uses ATP to pup
3 Na+ out
2 K+ in
- This maintains a difference in concentrations across the membrane - 8How resting potential works- Na+ can only move through channels that are closed at rest
- K+ moves out the cell down its concentration gradient through K+ selective channels that are open at rest
- Cl- and other negatively charged ions cannot cross the membrane w/ K+ so leads to an excess of negative charge on the inside of the membrane
- K+ will continue until the chemical gradient is balanced by the electrical gradient - 9why isnt the resting potential -90mVbecause the membrane is slightly permeable to other ions so it is between -60 and -80mV
- 10action potentials are due to ______changes in membrane permeability to sodium (Na+)
- 11what respond to changes in membrane potentialvoltage gated Na+ and K+ channels in neurones
- 12action potentials1. Resting potential: voltage gated channels are closed
2. Stimulus depolarises membrane above a threshold value --> opens voltage gated Na+ channels --> Na+ flows into the cell moving the membrane potential towards the sodium equilibrium potential
3. never reaches +64mV, as voltage gated Na+ channels inactivate (close) and voltage gated K+ channels open
4. Outflow of K+ moves membrane potential back to equilibrium potential for K+. potential usually undershoots the resting potential as the permeability to K+ is at first higher than at rest. voltage gated K+ channels close --> resting potential restored - 13What is the equilibrium potential for sodium?~+64 mV
- 14What are the 3 types of channels1. Potassium leak (always open)
2. Voltage gated sodium channels (opens quick in response to depolarisation)
3. Voltage gated potassium channels (slower) - 15action potentials travel ___in one direction
towards the synaptic terminals - 16how direction of propagation worksinactivated Na+ channels behind the zone of depolarisation prevent the action potential from travelling backwards (due to a delay)
- 17conduction speed1. Speed increases with axons diameter
2. Myelin sheath increases speed (and allows diameter to be smaller)
3. Action potentials only form at the Nodes of Ranvier (gaps in myelin sheath where voltage gated Na+ channels are found)
--> called Saltatory Conduction - quick - 18Synaptic transmission- Neurones synthesise and package neurotransmitters into synaptic vesicles
1. Synaptic terminal (presynaptic) contains lots of voltage-gated Ca2+ channels whihc open when an action potential depolarised the membrane
2. increase in cytosolic Ca2+ triggers fusion of synaptic vesicles with the membrane and releases them into the synaptic cleft
3. neurotransmitter diffuses and binds to receptors on the postsynaptic cell - 19what happens to the neurotransmitter after release?1. Diffuse out of the synaptic cleft
2. Be taken up by surrounding cells
3. Be degraded by enzymes - 20What are the two categories of post synaptic potential1. Excitatory postsynaptic potentials (EPSPs)
2. Inhibitory postsynaptic potentials
(IPSPs) - 21Excitatory postsynaptic potentials (EPSPs)They are depolarisations which bring the membrane potential toward threshold for firing an action potential
- 22Inhibitory postsynaptic potentials (IPSPs)They are hyperpolarizations that move the membrane potential farther from the threshold
- 23What happens to postsynaptic potentialsthey are graded and do not regenerate
- A single EPSP is usually too small to trigger an AP
- TEMPORAL SUMMATION: two EPSPs are produced in rapid succession
- SPATIAL SUMMATION: EPSPS produced nearly simultaneously by different synapses on the same postsynaptic neurone add together - 24what other receptors can neurotransmitters bind toG-protein coupled receptors (metabotropic receptors)
- activates a signal transduction pathway involving second messengers -> slower onset but last longer
e.g. lead to phosphorylation of ligand-gated ion channels to make them more/less responsive to neurotransmitter or to inc/dec the number of these receptors in the post synaptic membrane = changing the way a synapse behaves
-> increasing/decreasing connectivity
basis for complex higher functions - learning and memory - 257 different types of neurotransmitter1. Acetylcholine
2. Glutamate
3. Gamma-aminobutyric acid (GABA)
4. Glycine
5. Dopamine
6. Serotonin
7. Enkephalin - 26Acetylcholine (ACh)Ligand-Gated Ion Channel: acts on Nicotinic ACh receptors
Metabotropic Receptor: muscarinic ACh receptors - 27GlutamateAmino acid
Ligand-Gated Ion Channel: acts on several types, NMDA receptors, AMPA receptors, kainate receptors
Metabotropic Receptor: Metabotropic glutamate receptors - 28Gamma-aminobutyric acid (GABA)Amino Acid
Ligand-Gated Ion Channel: GABA↓A receptor
Metabotropic Receptor: GABA↓B receptor - 29GlycineAmino Acid
Ligand-Gated Ion Channel: Glycine receptor - 30DopamineAmine
Metabotropic Receptor: Dopamine receptor - 31SerotoninAmine
Metabotropic Receptor: Serotonin receptor - 32EnkephalinPeptide
Metabotropic Receptor: Enkephalin (Opioid) receptor
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- (101) Biology Fichas sobre 29: neuronal communication , creado por max brain el 22/12/2017.
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- max brain
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