Lecture 30 - Neuronal Communication

Question 1

Structure and fundamental task of a neuron

Answer 1

structure: cell body (with nucleus), usually one long axon and several shorter, branching dendrites

function: to receive, integrate, conduct and transmit signals

Question 2

How did we figure out that neurons are discrete cells?

Answer 2

• a scientist injected ink into neurons and noticed that the ink diffused throughout the cell, but did not diffuse further

Question 3

Membrane potential

Answer 3

• the difference in the concentrations of ions on opposite sides of the membrane
• cell membranes: -70 to -40 MV
• depolarization: interior voltage becomes less negative
• hyperpolarization: interior voltage becomes more negative
• cells read change in voltage and use it as an intracellular signal

Question 4

When a neuron is not active, its membrane potential is called _______ ________

Answer 4

resting potential

Question 5

What channels do excitatory signals open? What about inhibitory signals?

Answer 5

excitatory: NA cation channels open, depolarize membrane

inhibitory: open either Cl- or K+ channels, suppresses firing -> hyperpolarize the membrane

Question 6

Membrane potentials _______ through the membrane

Answer 6

propagate; depolarization is spread to open channels down the axon => continues to spread depolarization

Question 7

What type of channel spreads the depolarization through the neuron/ nervous system/

Answer 7

Voltage-gated sodium channels?

Question 8

How is the membrane repolarized?

Answer 8

• requires delayed opening K+ channels
• these channels open in response to membrane depolarization (i.e., also voltage-gated), but have slower kinetics (i.e., open slower)
• ends the depolarization phase

Question 9

What 3 things give rise to a traveling action potential?

Answer 9

changes in
1. Na+ channels
2. K+ channels
3. current flows

Question 10

Explain the process of action potentials

Answer 10

1. resting state: all gated Na and K channels closed. resting potential is about -60mV
2. depolarizing phase: Na channels open, action potential starts when neuron is depolarized by about 20mV to its threshold potential. potential rapidly becomes positive, reaching a value of +40mV
3. repolarizing phase: Na channels inactivated and K channels open. once cell reaches its peak positive potential, it repolarizes, returning to a negative potential
4. hyperpolarizing phase: K channels remain open and Na channels close. often membrane potential becomes more negative than the resting potential

Question 11

At what specialized sites are neuronal signals transmitted?

Answer 11

synapses

Question 12

Chemical vs electrical synapses

Answer 12

chemical:
- neurotransmitters + receptors
- synaptic cleft
- common

electrical:
- gap junctions
- no neurotransmitters
- faster

Question 13

What is a neurotransmitter?

Answer 13

• a small signal molecule secreted by the presynaptic nerve cell at a chemical synapse to relay the signal to the postsynaptic cell
• diverse molecule types

Question 14

What happens when the action potential reaches the presynaptic site?

Answer 14

the depolarization of the membrane opens voltage-gated Ca channels that are clustered in the presynaptic membrane

Question 15

What happens after Ca channels open?

Answer 15

Ca influx triggers release of small molecules known as neurotransmitters into the cleft
- NTs are stored in membrane-enclosed synaptic vesicles and released by exocytosis

Question 16

What do the NTs do once they are released?

Answer 16

• they diffuse rapidly across the synaptic cleft and provoke an electrical change in the postsynaptic cell by binding to and opening ligand-gated ion channels

Question 17

What is commonly used to measure increases in intracellular Ca in neurons? What does this signify?

Answer 17

• fluorescent calcium sensors
• a way of measuring neuronal activity

Question 18

Neuromuscular junction

Answer 18

• specialized chemical synapse between a motor neuron and a muscle cell
• motor neurons release Ach onto AchR located on muscle cells

Question 19

AchR

Answer 19

• a ligand-gated ion channel
• opens transiently by acetylcholine released from the motorneuron

Question 20

Optogenics

Answer 20

• biological technique to control the activity of neurons or other cell types with light
• achieved by expression of light-sensitive ion channels in neurons
• channelrhodopsins are photosensitive ion channels that open in response to light