Neural Communication Part 1

Question 1

Synapse

Answer 1

The site of neural communication.

Question 2

Charge, etc.

Resting membrane potential

Answer 2

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.

Question 3

The two key ions in neuronal communication

Answer 3

Sodium (Na+) and
potassium (K+)

Question 4

Chemical gradient

Answer 4

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.

Question 5

Electrical gradient

Answer 5

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.

Question 6

Cell membrane guardian

Phospholipid bilayer

Answer 6

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.

Question 7

Channels

Answer 7

Channels allow passive diffusion of molecules/ions into and out of a cell (along the chemical gradient).

Question 8

Pumps

Answer 8

Actively push ions against their chemical gradient. Require energy (ATP) to function.

Question 9

Na+/K+

Sodium/potassium pump

Answer 9

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.

Question 10

Potassium “leak” channels

Answer 10

Potassium can move freely via leak channels. Potassium will move with the chemical gradient of the cell.

Question 11

When a neurotransmitter molecule binds to a postsynaptic receptor, it can have one of two localized effects. Describe the two possible effects.

Answer 11

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).

Question 12

The transmission of postsynaptic potentials (PSPs) is:

Answer 12

Graded, rapid, and decremental.

Question 13

Graded E/IPSP Meaning

Answer 13

A stronger neurotransmitter signal creates stronger E/IPSPs (bumps).

Question 14

If two PSPs are both the same type, they will sum and produce a [answer] PSP.

Answer 14

Greater

Question 15

Two EPSPs in rapid succession synergize to:
Two IPSPs in rapid succession synergize to:

Answer 15

Two EPSPs in rapid succession synergize to produce a larger EPSP.
Two IPSPs in rapid succession synergize to produce a larger IPSP.

Question 16

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.

Answer 16

Action Potential

Question 17

Are action potentials graded?

Answer 17

No. Action potentials are all-or-nothing, not graded.

Question 18

Stages of An Action Potential (not in detail)

Answer 18

1. Resting potential
2. Rapid huge depolarization/Rising Stage
   (2.5. Overshoot)
3. Repolarization
4. Hyperpolarization
5. Back to resting potential

Question 19

Absolute Refractory Period (ARP)

Answer 19

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.

Question 20

Rapid huge depolarization (aka rising stage)

Answer 20

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.

Question 21

Repolarization

Answer 21

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.

Question 22

Hyperpolarization

Answer 22

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.

Question 23

Relative Refractory Period (RRP)

Answer 23

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.

Question 24

Effect of the subthreshold stimulation of an axon:

Answer 24

An excitatory potential is produced, but it is not sufficient to elicit an AP.

Question 25

Effects of the suprathreshold stimulation of an axon:

Answer 25

The threshold of excitation is exceeded, and the stimulation produces an action potential that continues undiminished down the axon.

Question 26

Conduction in an unmyelinated axon

Answer 26

Sodium channels are present all along an unmyelinated axon. Action potentials travel more slowly.

Question 27

Conduction in a myelinated axon

Answer 27

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.

Question 28

Terminal boutons (“buttons”) and how action potentials affect them

Answer 28

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.

Question 29

Dendrite membrane

Answer 29

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.