Action Potentials Flashcards
If an ion flows down a concentration gradient through a channel, what kind of transport is this?
Mediated diffusion
If you place a cell in a concentrated Mg solution, what will happen?
The cell volume will decrease (Mg is non pentrarint
Neuron
a single nerve cell
Can only send one type of signal in one direction
send electrical signals within the cell, and NT to signal between cells
Nerve
a collection of axons outside the brain/spinal cord
General overview of neuron communication
Dendrites ad the cell body receive information/stimuli.
They transmit an electrical signal along the axon
The electrical signal reachers the end of the axon
This triggers the release of a chemical neurotransmitter
The neurotransmitter then communicates with a neighboring cell
Afferent neuron
brings sensory information in
Efferent neuron
Tells muscles what to do
What compromises the CNS
spinal cord and brain
Microtubules
transport neurotransmitter to the axon terminal of the neuron
dynein
protein that moves NT from the axon terminal back to the cell body
kinesin
protein that moves NT to the synaptic terminal from the cell body
Resting membrane potential
Always more negative INSIDE than outside
In non-excitable cells=-5mV
in Excitable cells=-70mV
What kinds of cells are excitable?
only neurons and muscle cells
Why is the inside of a membrane negative?
Ion, but a large part is negatively charged proteins inside the cell
Na/K Pump
Active transport of ions 3Na out 2K in 1ATP used results in a build up of + ions outside the cell- the cell is polarized and at disequilibrium.
If a cell is at -70mV and the Na channels open, which way does Na go?
Into the cell
At rest, what where is there more Na? K? + charge?
There is more Na outside the cell
There is more K inside the cell
There is overall more + charge outside the cell
When is an ion said to be at equilibrium potential?
When the electrical gradient is equal and opposite the chemical gradient
What is the equiibrium potential for K?
-90mV
What is the equilibrium potential of Na?
+60mV
Will a cell ever be in equilibrium for both Na and K?
No, since EP for K is -90, and EP for Na is +60. Since it can never be both of these, ions are always in flux.
Action Potential
an impulse or signal transmitted along the membrane of an excitable cell by a transient change in the membrane potential. The cell will have an influx of + ions and become temporarily more + inside than outside.
All or None law
sn individual neuron either fires or doesnt. If the stimulus doesnt depolarize the membrane to threshold, no action potential will occur
What is threshold for an action potential?
-55mV
Mechanically gated ion channels
are found in sensory neurons, open in response to stretch of the membrane
chemically gated ion channels
open in response to ligand binding to a receptor. Channels open, +ions flow in, if enough flow in then they will trigger voltage gated ions to open
voltage gated ion channels
open in response to a change in voltage away from RMP. Specifically, they will open at -55mV. + ions will then rush into the cell, and it will rapidly depolarize to +30mC
Which types of channels start action potentials by creating small, local depolarizing events?
Mechanically gated and chemically cgated ion channels
Which type of channel causes a massive depolarization of the membrarne?
Voltage gated ion channels, will open when the membrane voltage reaches -55mV
What are some ways of making a graded potential into an action potential?
- Leave NT in the synapse for a long time, which will lead to repeated binding and opening of chemically gated channels
- Fire AP of the presynaptic neuron over and over again, continuing to release NT over and over again
- Have more than one presynaptic neuron release NT into the synapse
What gradients are present in a neuron?
There is more Na outside the cell, and more K inside the cell.
What Equilibrium potentials are relevent for action potentials?
Na will want to flow until the cell is at +60mV
K will want to flow until the cell is at -90mV
How do local anesthetics like lidocaine and novocaine work?
They block voltage gated ion channels
Pain receptors have numerous graded potentials i response to tissue damage, but no action potential will be reached, so the message of pain will not go to the brain.
Why do Na channels have inactivation gates?
because they have a positive feedback loop and can not resolve it on its own, while K has a negative feedback
refractory period
The period between action potentials where no action potential can be fired
Absolute refractory period
all voltage gated Na channels are either already open or inactivated. This means no more Na channels can open and the action potential can not occur.
relative refractory period
some voltage gated Na channels have returned to resting, but some are still inactivated. K channels may still be open, and the cell may be hyperpolarized. The AP could occur, it the stimulus was greater than normal
continual conduction
for unmylenated cells, the axon must be covered in Na/K pumps and voltage gated channels to maintain the signal (otherwise the leakage willl degrade the signal over distance)
What tyypes of cells are in the nervous system?
Neurons and Glial cells
Schwann cells
Glial cells that modify their plasma membranes to wrap axons, these insulate and prevent leakage.
Nodes of Ranvier
spaces between Schwann cells where pumps and channels still exist
Saltatory conduction
channels only exist at the nodes of ranvier, so the signal “jumps” from node-to node.
demyelination
removal of the myelin sheath/ the death of schwann cells
Multiple sclerosis
Immune attack of myelin sheath and killing of schwann cells
Is an autoimmune disease
sporadic/periodic attacks (flare ups)
