Neurotransmission

Question 1

What is the resting membrane potential?

Answer 1

• -70mV*
• Inside of neuron has net negative change relative to outside
• More potassium leak channels than sodium: membrane more permeable to K+ than Na+

Question 2

What is the potential difference?

Answer 2

When positive and negative electrical changes are held apart.

Question 3

What is the potential difference across plasma membrane called?

Answer 3

Membrane potential.

Question 4

How is the resting membrane potential maintained?

Answer 4

Through sodium potassium exchange pump.

Question 5

Describe the function of the Sodium Potassium Exchange Pump

Answer 5

Grabs 3 sodium ions and forces it outside of neutron against concentration gradient.
Grabs 2 potassium ions to inside of neutron.
Requires ATP (energy)

Question 6

What types of ion channels are in plasma membrane of neuron?

Answer 6

• Passive (leak) channels

- Active (gated) channels

Question 7

How do the passive (leak) channels work?

Answer 7

“Doors” in plasma membrane that is always open (i.e. passive sodium and potassium channels which maintain resting membrane potential).

Question 8

How do the active (gated) channels work?

Answer 8

• Shut at rest
• Requires a key/stimulus to unlock the channel.
• Ions to move in and out of neuron.
• Change membrane potential making it more or less negative

Question 9

What are the 3 types of active gated channels?

Answer 9

• Chemically gated channel
• Voltage gated channel
• Mechanically gated channel

Question 10

What stimulus is required to open chemically gated channels?

Answer 10

Specific chemical.

Question 11

What stimulus is required to open voltage gated channels?

Answer 11

Change in voltage.

Question 12

What stimulus is required to open mechanically gated channels

Answer 12

-Mechanical Stimulus (plasma membrane physically distorted- pull, push, stretch).

Question 13

What is a graded potential?

Answer 13

Local and temporary change in the membrane potential.

Question 14

What happens if several stimuli arrive on neuron at same time?

Answer 14

Net effect on membrane potential is sum of all graded potentials.

Question 15

What happens when the membrane potential is less than -55mV or -60mV at axon hillock.

Answer 15

Neuron will discharge an action potential.

This travels from axon hillock –> axon terminal.

Question 16

What is an action potential?

Answer 16

• Brief reversal of the membrane potential
• Starts at axon hillock, the propagates down axon to axon terminal in 1 direction
• All or none event

Question 17

What are the four key steps involved in generating an action potential?

Answer 17

1) Stimulus that initiates action potential is a graded depolarization- large enough to open voltage-gated sodium channels.
Opening of channels occur at the threshold (-60mV).
2) Voltage-gated sodium channels open and sodium ions move into the cell. Membrane potential rises to +30mV. Inside contains more positive ions than negative ones.
3) Sodium channels close, voltage-gated potassium channels open. Potassium ions move out of cell.
4) Potassium channels close, both sodium and potassium channels return to their normal states. Voltage-gated potassium channels close as membrane reaches resting potential (-70mV) via sodium-potassium exchange pump.

Question 18

How does the brief reversal of the membrane potential move

Answer 18

• A fuse: myelin increases speed of propagation of action potentials as it wraps around axon.
• AP jumps segments without myelin (nodes of Ranvier)
• Faster with larger diameter

Question 19

What is an important key point to remember for neurotransmission?

Answer 19

Sodium rushes in at beginning of action potential

Question 20

What are the two kinds of neurotransmitters present in chemical synapse?

Answer 20

• Peptide neurotransmitters

- Amine and Amino Acid Neurotransmitters

Question 21

How are peptide neurotransmitters stored in the axon terminal?

Answer 21

In the secretory granules.

Question 22

How are amine and amino acid neurotransmitters stored in axon terminal.

Answer 22

In the synaptic vesicles.

Question 23

What are the four key steps involved in the release of an amine or amino acid neurotransmitter from the axon terminal?

Answer 23

1. Arrival of action potential at axon terminal.
2. Voltage-gated calcium (Ca2+) channels open and Ca2+ enters presynaptic neuron.
3. Synaptic vesicle fuses to plasma membrane.
4. Neurotransmitter released into synaptic cleft via exocytosis.

Question 24

What effect does neurotransmitter have on the postsynaptic neuron?

Answer 24

• Binds to receptor on membrane of post-synaptic neuron.
• Positively charged sodium ions flow into postsynaptic neuron, changes membrane potential to less negative
• Binds to receptor then activates G protein to open ion channels and activates enzymes in postsynaptic neuron.

Question 25

What processes decrease the amount of neurotransmitter that is present in the synaptic cleft?

Answer 25

1) Re-uptake: recycling neurotransmitter back inside presynaptic neuron.
2) Enzymatic Degradation: enzyme breaks neurotransmitter into smaller parts.
3) Drifts away from synapse, no longer exerts effect.