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Most of the cells in the body are ______ charged. state an example
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_____ & _____ can drastically change their voltage
Neurons & muscles
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____ cells are not excitable and their job is to support neurons/ maintain extracellular environment
Glial cells
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If the cell is not symmetrical, we call it _____
polarized
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Cells communicate with dendrites and axon terminals. Dendrites _____ neurotransmitters while axons terminals ______ neurotransmitters
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We name our neurons by what they ______.
Name the type of neuron if its neurotransmitter is:
glutamate
dopamine
serotonin
norepinephrine
Ach
- release
- glutamatergic
- dopaminergic
- seratonergic
- noradrenergic
- cholinergic
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Neurons can _____ a lot a of different types of neurotransmitters but can only _____ one type.
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Nerves:
Tracts:
- bundle of axons from diff. neurons in PNS
- bundle of axons from diff. neurons in CNS
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Clusters of cell bodies in the brain are called _____. Clusters of cell bodies in the PNS are called _____.
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Two types of synapses are ______ & _____.
chemical & electrical synapses
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Chemical synapses do not touch each other due to the presence of a _____ ______
synaptic cleft
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electrical synapses connect to each other via ____ ____
gap junctions
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Electrical synapses spread _______ and are found in places that require ____ _____
- action potentials
- quick reflexes
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Purkinje cell (3)
- takes input from 1000s of neurons
- integrates info
- makes a decision
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Bipolar cell is the only neuron in the body that can't?
fire an action potential
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_____ ____ is the site where we receive transmitter
dendritic spine
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Excitatory transmission tends to be near the ______. Inhibitory transmission tends to be near the _____
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Postsynaptic densities are _____ rich
electron
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Presynaptic/ axon terminal side always the side with _____ filled with one type of _____
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Axon terminal will bind to receptors, _____ _____ ion channels, and the info from transmitter will be transmitted to the _____ ____
- ligand gated ion channels
- postsynaptic spine
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The three expected members of the chemical synapse
- presynaptic terminal
- postsynaptic terminal
- glial cell
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If we want cell, like heart muscles cells, to fire uniformly, we have to connect them via ____ _____
gap junctions
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Neurons in the brain want to fire action potentials which start at the _____ ____
axon hillock
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Blood brain barrier
continuous capillaries, even the glial cells are wrapped in capillaries for extra reinforcement. Only O2 in and CO2 out
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Oligodendrocytes myelinate axons in the ____ and schwann cells myelinate axons in the ____
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The electrical flow that myelin insulates is basically formed by ____ _____.
ion movement
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Ligand gated ion channel's proteins will be expressed at _______ at chemical synapse. When the neurotransmitter binds, the ligand gated ion channel open up and ions diffuse across their _______ ______
- dendrites
- electrochemical gradient
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After positive volgate gated ion channels open, what two things determine ion movement?
- permeability
- electrochemical gradient
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Where are voltage gated channels expressed
from the axon hillock all the way to the axon terminal
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We measure voltage by comparing
charge inside the cell to outside
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Resting membrane
when the neuron is not experiencing any info, nothing is communicating with it.
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Membrane potential
The momentary potential
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EPSPs & IPSPs are due to ____ ____ ion channels and occur at the _____
- ligand gated ion channels
- dendrites
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Glutamate is likely to release ___ and glycine and GABA are likely to release ___
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Three reasons why neurons are negative
- The Na+/K+ pumps are electronegative (net negative of -1)
- Inside the cell we have a lot of negatively charged particles like DNA, most proteins etc, they contribute to net negativity
- We have more K+ leak channels than we have Na++
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Nerst potentials for K+, Na+, Ca++, Cl-
around -90V for K+, +56 for Na+, +40 for Ca++ & -60 for Cl-
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We are much more permeable at rest to ___ than we are to ___. Because we express more ___ leak channels than ___ leak channels
- K+
- Na+
- K+ leak channels
- Na+ leak channels
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calculating driving force
Voltage of the cell minus the equilibrium potential for the ion (Vm is membrane potential & Eion is equilibrium potential)
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If we have a massive driving and zero permeability, _____ _____ ____ occurs. If there is no driving force but massive permeability, current will be ______. We must know both to determine _____ ____. With a huge driving force however, we will be able to determine that there is a ______ for a current flow.
- minimal current flow
- minimal
- current flow
- potential
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Action potential resting state (REVIEW):
Resting state (9)
- All voltage gated ion channels are closed, along with the ligand gated ion channels. Only thing open are leak channels
- There is an activation gate and an inactivation gate on Na+ and K+ only has an activation gate
- Activation gates are closed and the inactivation gate is open (when either of the gates are closed, ionic motion is halted
- IF the cell is negative, the Na+ & K+ activation gates are closed. IF the cell is positive they Na+ & K+ are open.
- Na+ activation gates open/close quickly
- K+ activation gates open/close slowly
- If the cell is negative, both the Na+ & K+ inactivation gates will open and if it is positive, it will close
- Both inactivation gates are very slow
- Changes will occur in the gates when we become more (+) than threshold (-55) not more (-)
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Action potential story:
Threshold (6)
- We get to threshold with EPSPs at the dendrites and it'll lead to action potentials at the axon hillock
- At -50 Na+ activation gates open up fast and first
- Na+'s driving force would be around -120
- Na+ ions will want to enter, the permeability will also increase drastically (near equilibrium potential for Na+)
- Na+ is trying to make the neuron hit its equilibrium potential
- K+ can't do much about it, its only source of influence at the moment are the leak channels
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Action potential story:
action potential (8)
- At the peak of the action potential, inactivation gates close
- Permeability for Na+ goes down to zero
- Activation gate is still open because the cell is still positive
- Activation gate for K+ finally opens. The membrane potential (+30) minus the equilibrium potential (-90). This gives us a membrane potential of +120 inside the cell
- So Na+ will be forced out to make the inside more (-)
- K+ is trying to make the cell its own equilibrium potential
- At this point, the only channels open (repolarization/hyperpolarization) Leak K+ channels & Voltage gated K+ channels
- This will make the cell really (-) so eventually the activation gate for K+ channels will have to close and the inactivation gate will reopen, leaving the only other open channel being the K+ leak channel
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Action potential story
Resting potential
- We get back to resting potential with the K+ leak channel, NOT the Na+/K+ pump
- Rest will be perturbed by ligand gated ion channels at the dendrites
- Dendrites will have ionic flow called EPSPs and IPSPs
- The only thing that influences opening and closing is voltage, unless it’s a leak channel
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3 reasons we can't fire action potentials during refractory period
- Reason 1: K+ channel is still open, so we have a K+ leaving for every Na+ that enters
- Reason 2: Na+ Inactivation gate is closed, so the orientation will not allow it. (absolute refractory period)
- Reason 3: At relative refractory period, we can fire another action potential but it'll be very hard. It is possible because some of our Na+ inactivation gates have opened
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Axons communicate by _______ of different regions at different times sending _____ moving. The purpose of all of this is to get the ______ ______ to +20mV, allowing ____ to come in and binds to the synaptic vesicle causing _____ _____
- depolarization
- voltages
- axon terminal
- Ca++
- vesicular exocytosis
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Thought experiment: What if we blocked the voltage gated K+ channels, what will the equilibrium potentials and action potentials look like? (6)
- At rest the only channels open are leak channels
- The voltage gated Na+ channels will open and head towards the Na+ equilibrium potential
- Action potential's peak will not be any different
- Inactivation gate will close
- Repolarization will stall or take a very long time without K+ voltage gated channels. The only repolarization will be through the very few K+ leak channels.
- There will also be no hyperpolarization, keep in mind it is due to the extra permeability of K+ from the K+ voltage gated channels
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Thought experiment: What if we modified the amino acid sequence of the Na+ inactivation gate so it closes 200ms more swiftly (4)
- At rest the only channels open are leak channels
- The voltage gated Na+ channels will open and head toward the Na+ equilibrium potential
- Action potential's peak will be shorter because we are stopping the permeability of Na+ more quickly than usual
- Everything else would be normal
- *if we cut it off faster and faster we may get to a point that all we get are EPSPs without action potential
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Nicotinic receptors are found in ____ muscle and the _____. They are _______
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Ligand gated ion channels is found at _____. Neural transmission occurs at the ____, Voltage gated Na+ & K+ channels at the ____ _____
- dendrites
- soma
- axon hillock -axon terminal
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_____ ____ is the region we are attempting to get to threshold -45mV to eventually get to action potential.
axon terminal
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