Lecture 17 - Nervous Systems 2

Question 1

Resting potential (3)

Answer 1

Membrane potential when neuron is not firing, inside of membrane is more electronegative, outside of membrane is defined as 0 mV

Question 2

The resting potential is determined by several transmembrane proteins: (4)

Answer 2

1. Potassium (K+) leak channels
2. Sodium ion (Na+) voltage-gated channels
3. Potassium (K+) voltage-gated channels
4. Proton pumps

Question 3

Potassium (K+) leak channel

Answer 3

Allows K+ to leak across cell membrane

Question 4

Sodium ion voltage-gated channel (3)

Answer 4

Open or closed depending on difference in electric charge across cell membrane (membrane potential), when closed Na+ cannot cross neuron’s membrane, when open Na+ can cross the neuron’s membrane

Question 5

Potassium (K+) voltage-gated channels

Answer 5

Open or closed depending on difference in electric charge across cell membrane (membrane potential)

Question 6

Proton pump

Answer 6

Causes inside of neuron to become more electronegative

Question 7

Why is the inside more electronegative? (5)

Answer 7

Na+ voltage-gated channels are closed or K+ voltage-gated channels are closed, proton pump trades 3 Na+ positively charged ions for 2 K+, leading to fewer positive charges on the inside of the neuron, therefore causing the inside to be more electronegative, K+ can cross leaky channels and the concentration gradient favors a net export of K+

Question 8

Equilibrium gradient of K

Answer 8

When the electrochemical gradient favors a net import of K+ but at the resting potential there is no net movement of K+

Question 9

Action potential

Answer 9

A rapid change in electrical potential across a cell membrane

Question 10

Threshold potential (2)

Answer 10

Membrane potenital that will trigger an action potential, at this threshold the Na+ voltage gated channels open and phase I (depolarization) begins

Question 11

Depolarization phase

Answer 11

After reaching the threshold potential, phase 1 (aka depolarization phase) begins, in which Na+ ions rush in causing a decrease in electronegativity

Question 12

Repolarization phase (3)

Answer 12

Phase 2 (aka repolarization phase) in which Na+ voltage-gated channels close, K+ voltage gated channels open, and K+ moves out of cell via K+ voltage-gated channels and K+ leaking ion channels

Question 13

Hyperpolarization phase (3)

Answer 13

After phase II ends and the membrane potential drops to resting potential, the hyperpolarization phase begins. Due to loss of K+, the membrane potential becomes slightly more negative than the resting potential. K+ voltage gated ion channels flip between open and closed before finally closing.

Question 14

Propagation of action potentials along a neuron (3)

Answer 14

1. Na+ enters axon, where it attracts negative charges and repels positive charges
2. Neighboring membranes depolarize, causing the inside to become more electropositive. The threshold potential is reached.
3. This causes an action potential in the neighboring membrane, causing the Na+ voltage gated ion channels to open. Na+ depolarizes the membrane

Question 15

Propagation of action potentials along a neuron pt 2 (3)

Answer 15

“upstream” action potentials cause “downstream” membranes to depolarize, the action potential is propagated along the axon from “upstream” to “downstream”, “upstream” Na+ voltage gated channels need to reset before they can fire again

Question 16

Triggering an action potential

Answer 16

The trigger comes from another neuron

Question 17

Synapse

Answer 17

The interface between the two neurons

Question 18

Synaptic cleft

Answer 18

The space between the two communicating nerve cells

Question 19

Neurotransmitter

Answer 19

A molecule that transmits a signal between two neurons or a neuron and an effector cell

Question 20

Presynaptic neuron

Answer 20

The neuron that releases neurostransmitters

Question 21

Postsynaptic neuron

Answer 21

The neuron that receives neurotransmitters

Question 22

Excitatory neurotransmitter (3)

Answer 22

Makes the postsynaptic neuron more likely to produce an action potential, excitatory neuropeptides bind to receptors in the postsynaptic neuron causing the opening of + ion channels, + ions then rush into postsynaptic neuron

Question 23

Inhibitory neurotransmitter

Answer 23

Makes the postsynaptic neuron less likely to produce an action potential, ethanol mimics the inhibitory neurotransmitter GABA