Neural Communication I (EXAM 2) Flashcards
what happens when a neurotransmitter binds to a receptor?
there is either an EPSP or a IPSP
what is an EPSP? what does it do to the neuron?
excitatory post-synaptic potential
- depolarizes the membrane from -70mv to 67mv
- increases the likelihood of an action potential
- brings the charge closer to 0, gets more positive
what is an IPSP? what does it do to the neuron?
inhibitory post-synaptic potential
- hyperpolarizes the membrane from -70mv to -72 mv
- decreases the likelihood of an action potential
- brings the charger further from 0, gets more negative
what are the characteristics of post synaptic potentials?
- they are graded - can vary in size
- they are rapid
- they are decremental - the further you get, the weaker it is
what is spacial summation?
- when two EPSPs happen at the same time, they make a bigger EPSP
- same for IPSPs
- if IPSP and EPSP happen at the same time, they cancel out
- they sum over multiple synapses
what is temporal summation?
- a single EPSP followed by another EPSP creates a larger EPSP
- same for IPSPs
what is required in order to have an action potential?
- we need to have summation of EPSPs and IPSPs over time (temporal) and space (spacial)
- sum of EPSPs and IPSPs that reaches the axon terminal segment has to depolarize membrane above threshold of excitement (-55mV)
what is an action potential?
a massive, brief reversal of the membrane potential that is the main method of brain communication
- from -70mv to +55mv
- all-or-none
- not graded - same shape and size every time
- not decremental
- starts at the initial segment and travels to the terminal
what are the proteins responsible for depolarization of the membrane?
voltage-gated sodium channels
what are the proteins responsible for repolarization of the membrane?
voltage-gated potassium channels
how do voltage-gated sodium channels work?
- they are closed when membrane is resting, open at threshold of excitation
- electrical and chemical gradient both want sodium to move inside
- sodium flows in and is responsible for rise of action potential from negative to positive
- 1ms after the gate opens, a ball plugs the gate and inactivates the protein until the cell is back at resting
what is the absolute refractory period?
- when the ball in the voltage gated sodium channel plugs and inactivates the protein, we can’t have another action potential
- so between the peak of the AP and the resting membrane potential, we can’t have another AP
- if we cannot return to resting potential, we are unable to ever have a AP again
how do voltage-gated potassium channels work?
- start to open during the rising phase of the AP
- at the peak of the AP, the inside of the cell becomes positive
- this causes the electrical and chemical gradients to want potassium to move outside
- potassium moves out, which causes repolarization
- is also responsible for hyperpolarization because the gate closes too slow
- sodium potassium pump restores ion balance over time
what is the relative refractory period?
- during hyperpolarization, it is harder to get to threshold because the cell is further from threshold
- cell is more negative than at resting
give a summary of the process of an action potential
- depolarization (action potential) - reach threshold, sodium comes into the cell (makes cell positive)
- repolarization - potassium leaves the cell (makes cell more negative)
- hyperpolarization - briefly becomes too negative because too much potassium leaves
how does conduction work in an unmyelinated axon?
- Na+ channels present all along the axon
- AP is regenerated at the Na+ channels as it moves down the axon
- every time the AP is regenerated, it is slightly slowed down
- conduction speed is limited by number of Na, and AP decays if there are too few Na
how does conduction work in a myelinated axon?
- myelin causes the action potential to decay less quickly as it spreads
- Na+ channels in gaps between myelin (Nodes of Ranvier)
- Na+ channels can be more spread apart = faster action potential
what’s the difference in the location of sodium channels in unmyelinated vs. myelinated axons?
unmyelinated axons - Na+ channels everywhere
myelinated axons - Na+ channels only at the Nodes of Ranvier
how does the speed and direction of signals differ in unmyelinated and myelinated axons?
- action potential is faster down myelinated axons than myelinated axons
- myelinated axons have fewer sodium channels
- myelinated axons spend more time travelling (linked to less Na+ channels)
- action potential only travels in one directions because of Na+ channels
- because voltage gated sodium channels in earlier parts of the axon are in an inactivated state
what is the axon terminal?
- axon ends in terminal boutons (“buttons”)
- bouton has vesicles filled with neurotransmitters
- vesicles also have phospholipid bilayer
what happens at the axon terminal during an action potential?
- action potential depolarizes the bouton
- causes the voltage-gated Ca++ channels to open
- Ca++ causes SNARE complex to activate
- calcium is a very potent signalling molecule
- SNARE complex fuses the vesicles with membrane
- neurotransmitters released into the synapse
what does the synapse consist of?
- axon terminal has and releases neurotransmitters
- dendrite membrane has special receptors that fit with neurotransmitters
- receptors are often just (closed) channels that open when they bind to neurotransmitters
- ligand-gated ion channels
what are the differences between post-synaptic potentials and action potentials?
- PSPs are graded, APs are not
- PSPs are amplitude modulated (am), APs are frequency modulated (fm)
- am - stronger signal are represented by a bigger change in voltage
- fm - number of action potentials per second
- PSPs are rapid, and APs are a little slower
- PSPs are decremental, APs are not
