Neural Communication Part 1 Flashcards
Synapse
The site of neural communication.
Charge, etc.
Resting membrane potential
The resting membrane potential is between -60 and -80 mV, meaning the voltage inside the neuron is 60-60 mV less than the outside of the neuron.
The two key ions in neuronal communication
Sodium (Na+) and
potassium (K+)
Chemical gradient
Determines the direction ions will flow in an open channel. Ions will naturally flow from high-concentration to low concentration areas.
Sometimes electrical and chemical
gradients are at odds, causing an
equilibrium that =/= 0mV.
Electrical gradient
Determines the direction ions will flow in an open channel. Ions will naturally flow from high-concentration to low concentration areas.
Sometimes electrical and chemical
gradients are at odds, causing an
equilibrium that =/= 0mV.
Cell membrane guardian
Phospholipid bilayer
Tightly packed with hydrophilic phosphate heads (facing outwards) and hydrophobic lipid tails (facing inwards). A cell barrier that works to block dangerous entities from entering the cell.
Channels
Channels allow passive diffusion of molecules/ions into and out of a cell (along the chemical gradient).
Pumps
Actively push ions against their chemical gradient. Require energy (ATP) to function.
Na+/K+
Sodium/potassium pump
Embedded within the cell membrane, uses ATP to move 3 Na+ ions out of the cell for every 2 K+ ions it moves into the cell.
Potassium “leak” channels
Potassium can move freely via leak channels. Potassium will move with the chemical gradient of the cell.
When a neurotransmitter molecule binds to a postsynaptic receptor, it can have one of two localized effects. Describe the two possible effects.
When a neurotransmitter molecule binds to a postsynaptic receptor, it can:
1. Depolarize the membrane (e.g., decrease membrane potential from -70 to -67mV). This triggers an excitatory postsynaptic potential (EPSP).
2. Hyperpolarize the membrane (e.g., increase the membrane potential from -70 to -72mV). This triggers an inhibitory postsynaptic potential (IPSP).
The transmission of postsynaptic potentials (PSPs) is:
Graded, rapid, and decremental.
Graded E/IPSP Meaning
A stronger neurotransmitter signal creates stronger E/IPSPs (bumps).
If two PSPs are both the same type, they will sum and produce a [answer] PSP.
Greater
Two EPSPs in rapid succession synergize to:
Two IPSPs in rapid succession synergize to:
Two EPSPs in rapid succession synergize to produce a larger EPSP.
Two IPSPs in rapid succession synergize to produce a larger IPSP.
If the sum of the EPSPs and IPSPs that reach the axon initial segment is sufficient to depolarize the cell membrane above its threshold of excitation, then an [answer] is generated.
Action Potential
Are action potentials graded?
No. Action potentials are all-or-nothing, not graded.
Stages of An Action Potential (not in detail)
- Resting potential
- Rapid huge depolarization/Rising Stage
(2.5. Overshoot) - Repolarization
- Hyperpolarization
- Back to resting potential
Absolute Refractory Period (ARP)
1–2 milliseconds during which a neuron is incapable of producing another action potential.
(During the ARP, voltage-gated K+ channels open and K+ ions rapidly exit the neuron.)
Potassium leak channels are always open, and not to be confused with the voltage-gated potassium channels.
Rapid huge depolarization (aka rising stage)
Na+ channels open during this stage, and sodium flows into the cell, flipping the charge of the inside of the cell membrane from negative to positive. K+ voltage-gated channels are still closed.
Na+ channels have built-in inactivation and will shut off/close after ~1ms. Potassium leak channels are always open, and not to be confused with the voltage-gated potassium channels.
Repolarization
Sodium/Na+ channels close, and voltage-gated potassium/K+ channels open. K+ ions rush out of the cell, rapidly returning the cell to a negative charge.
Potassium leak channels are always open, and not to be confused with the voltage-gated potassium channels.
Hyperpolarization
Slow closing of voltage-gated K+ channels leads to the hyperpolarization stage, which is when the inside of the cell’s membrane potential is more negative than the default membrane potential. Shortly after that, the membrane will return to its resting potential. This hyperpolarization stage is the cell’s relative refractory period.
Potassium leak channels are always open, and not to be confused with the voltage-gated potassium channels.
Relative Refractory Period (RRP)
Follows/is after the absolute refractory period. 2-4 miliseconds during which a neuron is resistant to, but not incapable of, producing an action potential. During the RRP, Na+ channels can be opened, and the cell membrane potential is hyperpolarized.
Effect of the subthreshold stimulation of an axon:
An excitatory potential is produced, but it is not sufficient to elicit an AP.
Effects of the suprathreshold stimulation of an axon:
The threshold of excitation is exceeded, and the stimulation produces an action potential that continues undiminished down the axon.
Conduction in an unmyelinated axon
Sodium channels are present all along an unmyelinated axon. Action potentials travel more slowly.
Conduction in a myelinated axon
Sodium channels only need to be present at nodes of ranvier (gaps between myelin sheath), and conduction is much more efficient/action potentials travel down a myelinated axon much more quickly.
Terminal boutons (“buttons”) and how action potentials affect them
At the end of an axon, terminal boutons have vesicles filled with neurotransmitters. Action potentials depolarize boutons and cause voltage gated Ca++ channels to open. Ca++ causes vesicles to fuse with the cell membrane and release their neurotransmitters into the synaptic cleft.
Dendrite membrane
This membrane has synaptic receptors that fit like a lock and key with the neurotransmitters. When a specific neurotransmitter reaches a dendrite membranes’s receptors, it evokes a PSP.
