Electrical Transport in Membranes

Question 1

What are the concentrations of k+ and na+

Answer 1

Na+ extracellular is greater than intracellular, K+ is opposite.

Question 2

Describe electrochemical gradient and membrane potential.

Answer 2

EC gradient combines concentration gradient and difference in charge (voltage) across the membrane. Membrane potential: difference in charge across the membrane.

Question 3

Describe cell membrane potential

Answer 3

it is negative inside relative to outside, determined by tendency of ions to move from high to low concentration.

Question 4

What occurs at equilibrium potential?

Answer 4

Movement of ions aren’t favorable.

electrical gradient for an ion is balanced by its concentration gradient, so there is no net flow across the membrane.

Question 5

Why doesn’t K+ move into cell and Na+ move in to cell at membrane potential?

Answer 5

Na+ channels are closed even though some K+ leaves through leak channels.

Question 6

What contributes to resting membrane potential?

Answer 6

Na+/K+ Atpase.

Question 7

Describe neuron structure

Answer 7

Dendrites receive info, causing action potential until terminal branches of axon are reached.

Question 8

Describe aspects of action potential

Answer 8

1. Resting State: Voltage-Gated (VG)
channels closed.
2. Stimulus: Few VG-Na+ channels open
causing depolarization.
3. Graded Potential: Subthreshold
stimulus, no action potential.
3. Threshold Potential: Membrane
potential that must be reached for an
action potential to occur.

Question 9

What are the steps of the action potential?

Answer 9

If Threshold reached, more depolarization due to VG-Na+ channels until potential is +40mV.

• VG-Na+ channels inactivate and delayed VG-K+ channels open, leading to repolarization.
• Undershoot/Hyperpolarization: Gated K+ channels stay open, potential dips below resting potential, then Gated K+ channels inactivate.

Question 10

Describe direction of action potential

Answer 10

Action potentials travel in only one direction down an axon because sodium channels in the neuron are refractory

Question 11

What is a refractory period?

Answer 11

Time it is difficult or impossible to stimulate another action potential

Question 12

What are absolute and relative refractory periods?

Answer 12

Absolute: Due to voltage-gated Na+ channels inactivation, Relative: Due to Undershoot

Question 13

Where does neurotransmission occur?

Answer 13

Electrical and chemical synapses.

Question 14

How do electrical synapses work?

Answer 14

Ions move between presynaptic and postsynaptic cells via gap junctions causing depolarization. Faster than chemical synapse

Question 15

Desrcibe chemical synapse:

Answer 15

Uses neurotransmitter generated from action potential. Released NT binds and opens transmitter-gated ion channels on the postsynaptic cell.
If enough NT is released over time, the membrane will depolarize enough to result in an action potential.

Question 16

What does acetylcholine do?

Answer 16

Neuron releases this to cause muscle contraction.

Question 17

What are the first steps of the neuromuscular junction?

Answer 17

1. Nerve impulse reaches terminal, depolarizes membrane, opens voltage-gated Ca2+ channels, triggers release of acetylcholine (Ach).
2. Ach binds receptors on postsynaptic cell, opening NTgated Na+ channel, depolarizing membrane

Question 18

What are the final steps of the neuromuscular junction?

Answer 18

3. Depolarization opens VG-Na+ channels, resulting in further depolarization and an action potential.
4. Depolarization activates VG-Ca2+ channels.
5. Stimulates Ca2+-gated Ca2+ release channel in sarcoplasmic reticulum to release Ca2+ into cytosol, leading to muscle contraction.