Synapse and Action Potential Flashcards
How are called synapses including the axon of a presynaptic neuron and the dendrite of another?
Axodendritic
How are called synapses including the axon of a presynaptic neuron and the axon of another?
Axoaxonic
How are called synapses including the axon of a presynaptic neuron and the cell body of another?
Axosomatic
How are called synapses including the dendrite of a presynaptic neuron and the dendrite of a postsynaptic neuron?
Dendrodendritic
What are the structures that contain neurotransmitters which will be released into the synapse?
Synaptic vesicle (will fuse with the membrane through exocytosis)
How are called the larger synaptic vesicles?
Neurosecretory granules
What are the presynaptic events?
- Production of neurotransmitters in the soma - transport through the axon
- Generation of action potential
- Fusing of the synaptic vesicles with the membrane and releasing of the contents (exocytosis)
What are ionotronic receptors?
receives ions within the extracellular space
Ionotronic receptors are often paired with what?
neurotransmitter-gated-ion channels
What do neurotransmitter-gated-ion channels do with ionotronic receptors?
In order to let the ions pass, the channel needs to be bound to a neurotransmitter
What are metabotropic receptors?
activate a protein when bound to a neurotransmitter, which will influence the functioning of the neuron
How are neurotransmitters disposed of after a communication with another neuron? (3 ways)
Diffusion: into the extracellular fluid
Degradation: by enzymes (ex: acetylcholine is broken down by acetylcholinesterase)
Reuptake: by transporters of the neuron that secreted the neurotransmitters at first
What are ions?
Electrically charged particles present in the intracellular and extracellular fluids
What are cations?
Ions that have a net positive charge
What are anions?
Ions that have a net negative electrical charge
What is diffusion?
process by which molecules move from an area of high concentration to an area of low concentration
What are the concentrations of Na+ and K+ ions in and out of the neuron when it is NOT conducting an action potential?
Na+ is 10 times more concentrated in the extracellular fluid than in the intracellular fluid, and K+ is 20 times more concentrated in the intracellular fluid than in the extracellular fluid
What is electrostatic pressure?
phenomenon by which ions are of the same charge repel each other and ions that are of opposite charge attract each other
Anions attracted to positively charged electrode become?
Anodes
Cations attracted to negatively charged electrode become?
Cathodes
What is the resting membrane potential? What value does it have?
the difference in charge (voltage) between the inside and the outside of the neuron when not conducting action potentials
Vm = -70mV
What is Vm?
Voltage across the membrane
What is mV?
Millivolts
What is the equilibrium potential?
the voltage across the membrane (Vm) at which the forces of electrostatic pressure and diffusion counteract each other
• Every ion has its own equilibrium potential (K+ = -90mV, Na+ = +60mV)
How are action potentials initiated?
when stimulus to the neuron triggers the opening of Na+ channels
What are stretch activated channels?
Na+ channels that can be activated by stretching of the membrane or the displacement of cytoskeletal elements
What are voltage-gated Na+ channels?
Have voltage sensors and sensitivity filters (to only certain ions, aka Na+)
Depolarization of the membrane is detected by the voltage sensors causing the channels to open
What is depolarization?
to reduce polarity (to make less negative), the inside of the neuron becomes less electrically negative relative to the outside due to Na+ influx
Cause the Na+ channels to open
What is the activation treshold?
the minimum amount of depolarization that must occur for an action potential to be initiated, which is about -55 mV
What is overshoot?
when the depolarization of the membrane continues well past Vm = 0mV
What happens when Vm reaches +30mV?
K+ channels open and K+ ions flow outside of the neuron, causing the voltage of the neuron to repolarize.
Na+ channels close and Na+ cannot enter the neuron anymore
What is the absolute refractory period?
the voltage at which further depolarization of the neuron is impossible and another action potential cannot be initiated in that neuron because Na+ channels are still closed
What is repolarization?
Potassium exiting the cell, voltage across the neuron membrane drops drastically, even below the resting potential
What is the relative refractory period?
period (after-hyperpolarization) where the voltage is below the resting potential and therefore another action potential is possible but more difficult to induce
How do we reverse the concentration that we are left with after an action potential so we can start again?
• Sodium-Potassium pumps use an ACTIVE process to restore the original ratios (uses ATP)
Switch Na+ with K+ inside the cell
What is the all or none law?
The fact that more stimulation than necessary for the neuron to be depolarized to threshold will not result in a stronger action potential (a punch on the arm vs a stroke on the arm will result in the SAME action potential)
How is an action potential communicated through the axon?
During depolarization, Na+ enter the membrane and moves down the axon, which triggers the activation of voltage-gated Na+ channels (causing the depolarization of those other sections)
What is orthodromic conduction?
action potentials only move from the soma to the axon terminals
What is antidromic conduction?
when an action potential moves in the inverse way (to the cell body)
Can only be achieved in labs
What is salvatory conduction?
At the nodes of Ranvier (breaks in the myelin); there is a concentration of Na+ channels which regenerate the action potential
