Neurobiology IIII ( Lecture 24-28) Flashcards
What is equilibrium potential.
membrane potential that exactly opposes the concentration gradient.
– charge of the plasma membrane that is equal but opposite to the concentration gradient.
In a cell permeable to only one ion, the _____ equation can be used to calculate the equilibrium potential.
Nernst Equation
The constant 61 in the _____ equation represents what three things
1) Faraday’s constant for electrical forces
2) physiological temperature for 37 degrees
3) universal gas content
The resting potential of a neuron is _____ mV
-70
The greater the ________ to an ion species, the greater the ion species will make to the membrane potential
permeability
Membrane potential for Na+, K+ and Cl- can be calculated through the _________ equation.
GHK
Goldman-Hodgkin-Katz
The resting membrane potential is largely due to the movement of ______ out of the cell.
K+
(T/F) the resting membrane potential is equal to the K+ equilibrium potential
False, there are still small channels of Na+ open in the resting state that may cancel out the effect of some K+ moving out
The Na+ / K+ ATPase pumps pumps ______ out of each cell for every ______ pumped in. This unequal transport results in the inside of the cell to be more ______.
3 Na+
2 K+
negative
The contribution of the Na+/ K+ pump is …
create a small electrical gradient in order for concentration gradients to remain down allowing ions to diffuse to produce charge separation
Transient changes in membrane potential from the resting level produce electrical signals and can occur in the form of ______ and ________
graded potentials
action potentials
Talk about the steps from being polarized to hyperpolarization
- Polarization — Resting membrane potentials starts at -70mV, which means that is is polarized.
- Depolarization– The membrane is depolarized, meaning charges go towards 0.
- Overshoot – This refers to the reversal of the membrane potential. The inside is not more positive compared to the outside
- Repolarizing– When depolarized membrane returns to its resting value
- Hyperpolarized – when potential is more negative than the resting potential
Graded potentials in neurons are depolarizations or hyperpolarizations that generally occur in _____ and ______
cell bodies / dendrites
What are graded potentials?
Graded potentials refer to changes in the membrane potential that are limited to a small area of the plasma membrane. Charges flow from the origin to adjacent regions of the plasma membrane, which are still at resting potential.
Define the steps of graded potential ( 3 steps)
- A region of the membrane has been depolarized by a small chemical signal. The opening of cation channels result in the potential to be less negative than adjacent areas.
- Positive charges ( K+) flow away from the depolarized area toward regions that are more negative
- Outside the cell, positive charge will from more positive membrane regions to less positive regions.
Graded potentials are called “graded” because _____________
magnitude change in potential can vary
In addition to the movement of ions on the inside and outside of cell, charge is ________ because _______
lost across membranes
the membrane is permeable to ions through open membrane channels
Local current is ________, ______ as the distance from the site of the origin of the graded potential increases.
This is also unique to graded potentials
decremental, decreasing
What is Summation ? (unique to graded potentials)
If additional stimuli occurs before the graded potential dies away, they can be added to the depolarization of the first stimulus
________ allow excitable membranes to conduct large, rapid changes in membrane potential called ______.
Voltage-gated ion channels
Action Potentials
When the membrane is at resting potential ( negative) , both K+ and Na+ channels tend to be _____. _______ tends to open them.
Closed.
Depolarization
2 key differences between Na+ and K+ channels.
- K+ channels tend to be slower / more sluggish than Na+ channels. Na+ channels respond rapidly to depolariziation. During repolarization, K+ channels are also slower to close.
- Na+ channels have a state of being inactive that limits the Na+ flux by blocking the channels shortly after depolarization. When the membrane repolorizes, Na+ channels go back to being in a closed state
The resting membrane potential is close to the _____ equilibrium potential because there are more open ____ channels than _____ channels. (these are leak channels)
K+
K+/ Na+
What are the 6 steps of Action potential
- There is a stimulation from ligand-gated ion channels that summate and depolarize the membrane to the the threshold of membrane potential.
- Voltage-gated Na+ channels open in respond to the threshold, activating a positive feedback of Na+ entry causes more depolarization which opens more Na+ channels.
- The positive feedback causes the membrane to overshoot
- When the potential reaches the peak of a the value, Na+ positive feedback declines abruptly since inactivation breaks the cycle.
- The K+ channels then start to slowly open, causing K+ ions to flow out of the cell, which is the process of repolarization
- Repolorization causes the Na+ channels to go back to its closed state while Ka+ channels also close. Before the K+ channels close, K+ hyperpolarizes towards the K+ equilibrium .
Na+ channels open and depolarizing is a _____ feedback loop.
positive
What is the threshold potential
-55mV
What is the all-or-none manner ?
When an action potential fires, they fire at maximal point of do not fire at all.
What is the absolute refractory period
It is the state where voltage gated Na+ channels are readily open and have proceed to its inactive state. The block channels must be removed by repolarization in order to reopen to another stimulus.
What is the relative refractory period ?
The relative refractory period follows right after the absolute refractory period. At this point, some K+ channels are still open and some Na+ channels have returned to its resting state. At this point, it is possible to for a new stimulus to depolarize the membrane above threshold but the stimulus must be greater than the previous absolute refractory period.
What must happen in order for a new action potential to be stimulated.
In order for a new action potential to be stimulated, a stimulus must be greater than the previous absolute refractory period.
Action potentials are propagated from ______, which _______
trigger zones , which have an abundance of Na+ / K+ channels
What is one distinguishing characteristic about amplitudes and actions potentials
They do not lose amplitude as they travel along the axon
Positive charge from depolarized trigger zone spreads by ________ to ______, repelling by the ______ that entered the cytoplasm and _____ by the negative charge of the resting membrane potential
local current flow to adjacent section of the membrane
Na+ // attracting
Explain the positive feedback loop in Na+ channels
when the action potential travels to point B. it depolarizes it causing Na+ channels to open up and more Na+ to flow into the cell
When signals reach to point B, Point A voltage-gated Na+ channels are _____. It is now in the _______ period.
inactive.
Absolute refractory period
(T/F) Action potentials can move backward
False. Action potentials can only move in one direction
(T/F) Action potential propagation is faster in myelinated axons
true
How does myelination help ?
Myelination prevents leakage of current to cytoplasm
Describe what happens in a myelinated axon.
Myelinated axons are wrapped with myelinated sheaths with nodes of Ranvier in between.
The nodes of Ranvier has high concentration of Na+ voltage-gated ion channels that allow depolarization. When sodium ions enter the channel, they reinforce the amplitude of action potential. Which leads to saltatory conduction
What is Saltatory conduction
The jump of action potential as it travels from node to node
A synapse can pass ____ or _____ signals to another cell
electrical or chemical
Electrical synapse pass signals _____ through _____
Directly / gap junctions
Chemical synapses use _____ to pass information
neurotransmitters
Gap junctions consists a pair of ________, one in the ______ and the other in ______ cell
hemichannels
presynaptic / postsynaptic
These hemichannels form a ______ between the _____ of the two cells
bridge / cytoplasm
How does small intracellular metabolites pass through cytoplasms of the cell
They travel through pores
Each pair of hemichannels are called _____, and they consists of _______
connexons
6 identical protein subunits
Electrical synapses occurs mainly in neurons of the ___ nervous system
CNS
(T/F) information in gap junctions can only flow in one direction
False.
Gap junctions can flow in both direction
Examples of where electrical synapses are found include ___, ____. ___, _____.
Glial cells
smooth muscle cells
Cardiac cells
non-excitable cells, like pancreatic B cels
The primary benefit of electrical synapses are ____
rapid conduction
What is the synaptic cleft.
Gap between the pre and post synaptic neuron
(T/F) information passing through chemical synapses can only flow in one way
True, this is due to the synaptic cleft
What is axon terminal ?
The end of the presynaptic cell where there is slight swelling
Synaptic vesicles contain _____
neurotransmitters at the presynaptic active zone
What is the post-synaptic density region
Region at the post-synaptic cell that ensures close proximity to the presynaptic release sight
Describe the mechanism of neurotransmitter release
- An action potential reaches the terminal of the presynaptic cleft.
- Terminals process voltage-gated Ca+ channels, which is opened due to depolarization , causing Ca+ ions to flow in
- Ca+ leads to the fusion of docked vesicles in the synaptic terminal membrane
- Ca+ binds to synaptotagmin proteins which are associated with SNARE proteins. SNARE proteins anchor vesicles on the plasma membrane and undergo Ca+ dependent confrontational changes to stimulate vesicle fusion with the plasma membrane
- after fusion, vesicles either completely dissolve with the membrane or fuse briefly and then withdraw into terminals
3 ways neurotransmitters are removed from the synaptic cleft
- Diffuse way from the receptor site
- Enzymatically transformed into inactive substances
- Reuptake ( back to presynaptic axon terminal)
