Lecture 7: Membrane Potential

Question 1

Neurons

Answer 1

Specialized for communication with other cells in the form of electrical impulses (ion gradiant)

Question 2

In vertebrates, most neurons are part of the —-

Answer 2

CNS

Question 3

Dendrites

Answer 3

Receive information

Question 4

Axons

Answer 4

Conducts outgoing information

Question 5

Terminal knobs

Answer 5

where impulses are transmitted to the target cell

Question 6

Myelin Sheath

Answer 6

wraps most vertebrate axons (lipid rich)

Question 7

Membrane potential/membrane voltage

Answer 7

Difference in charge across a membrane

Question 8

Resting potential

Answer 8

The membrane potential when a nerve cell is in an unexcited state.
-70mV

Question 9

Negative voltage

Answer 9

Inside of the cell is negative compared to the outside

Question 11

What contributes to the difference in charge across the membrane?

Answer 11

1. Na+/K+ ATPase pump pumps 3 Na+ ions out per 2K+ ions pumped in
2. K+ ions are the charged substance with the most permeability in a resting nerve cell. (Flow out through potassium leak channels, following their concentration gradient)

Question 12

Equilibrium with K+ in the cell

Answer 12

Balance is reached between the concentration gradient favouring K+ leaving the cell and the electrical gradient favouring K+ staying in the cell. (-70mv)

Question 13

Action Potential (2)

What it is x2+ includes

Answer 13

• Changes in membrane potential after a stimulus and is the basis for neural communication
• include depolarization and repolarization phases

Question 14

During resting membrane, ion permeability for Na+ and K+ is

Answer 14

low

Question 15

During depolarization (4):

Answer 15

• a decrease in the electrical potential difference across a membrane
• A stimulus causes sodium channels to open, sodium diffuses in
• If the stimulus results in depolarization above a threshold value of -50mv, then voltage gated sodium channels open (and sodium goes in inside reverse and be +)
• The increased permeability to Na+ ions results in a membrane potential of about +40mV

Question 16

During repolarization (4):

Answer 16

• The depolarization (increasing voltage) triggers the opening of voltage-gated potassium channels
• Sodium gated channels close
• Membrane potential goes back to negative (-80mV) Too much K+ leaves
• Large negative membrane potential causes the voltage-gated potassium channels to close

Question 17

Why is it -80mV not -70mV

Answer 17

Because K+ channels are slow to close

Question 18

Although the membrane voltage changes during the action potential, the

Answer 18

Na+ and K+ concentration gradients are barely affected. Overall number of ions on either side are barely affected

Question 19

An action potential is propagated along a neuron by

Answer 19

triggering action potentials in adjacent portions of the membrane

Question 20

Continous conduction (4)

Answer 20

• occurs in unmeylinated axons
• The flow of current causes the membrane in the region just ahead to become depolarized
• The action potential is propagated without any loss of intensity
• Portion of the membrane that juist experienced the action potential will be in a bried refractory period (Na+ channels cant reopen for a few ms)

Question 21

Saltatory conduction (5)

Answer 21

• occurs in myelinated axons
• Impulses in myelinated axons are 20X faster than in an unmyelinated axon
• Myelin prevents the passage of ions across the membrane
• Most Na+ and K+ channels are found in or near unmyelinated regions called: Nodes of Ranvier
• Action Potential at node of Ranvier triggers an action potential at the next node

Question 22

Synapse

Answer 22

The specialized junction of a neuron with its target cell

Question 23

Presynaptic cell

Answer 23

Conducts the impulse towards a synpase (eg. neuron)

Question 24

Synaptic vesicles

Answer 24

Storage for neurotransmitters in the terminal knobs of axons

Question 25

Neurotransmitters

Answer 25

Chemical that binds to the postsynpatic cell

Question 26

Synaptic cleft

Answer 26

Space that seperates the two cells

Question 27

Postsynpatic cell

Answer 27

• receives the impulse (eg: another neuron or muscle)

Question 28

In synaptic transmission, depolarization causes (2)

Answer 28

• voltage gated calcium channels to open in the presynaptic cell
• calcium diffuses into the cell

Question 29

In synpatic transmission, increased Ca2+ in the cell triggers (4)…

Explain the entire process

Answer 29

• synaptic vessicles to fuse with the plasma membrane
• The neurotransmitters are released and bind selectively to receptors (ligant-gated ion channels)
• The binding of receptors causes influx of Na+ (Na+ gates open) which excites the cell and causes depolrization
• On the other hand, the binding of receptors can cause an inhibitory reaction, less likely to generate AP: influx of Cl- ions makes the membrane potential move - instead of +

Question 30

After being released, how are neurotransmitters processed? (2)….

Answer 30

• enzymes destroy the neurotransmitters in the synaptic cleft (eg: acetylcholinesterase hydrolzes acetylcholine)
• Reuptake of neurotransmitter into the presynaptic cell