The spark that travels the nerve

Science · The Human Body · ages 17-18

Name ______________________ Date ____________

What does one sodium potassium pump cycle move, using one ATP?
- Three sodium ions inward and two potassium ions outward
- Two sodium ions outward and three potassium ions inward
- Three sodium ions outward and two potassium ions inward
Which value is commonly used for a typical neurone's resting potential, measured inside relative to outside?
- About zero mV, with no voltage difference across the membrane
- About minus 70 mV, with the inside negative
- About plus 70 mV, with the inside positive
The sodium potassium pump is the main direct cause of a neurone's negative resting voltage.
Circle one: True False
Which voltage-gated channels mainly drive the rapid rise and then the fall of a typical neuronal action potential?
- Potassium channels drive the rise; sodium channels drive the fall
- Sodium channels drive the rise; sodium channels also drive the fall
- Sodium channels drive the rise; potassium channels drive the fall
Which sequence matches the rise, fall and dip below resting voltage in a typical neuronal action potential?
- Depolarisation, repolarisation, hyperpolarisation
- Repolarisation, depolarisation, hyperpolarisation
- Hyperpolarisation, depolarisation, repolarisation
Why can a typical neuronal action potential dip below resting voltage?
- Sodium channels reopen slowly and keep allowing sodium to enter
- Potassium channels close slowly and potassium keeps leaving
- The sodium potassium pump reverses and begins exporting potassium
An impulse has just passed an axon region. What limits immediate backward re-excitation of that region?
- Sodium channels there remain temporarily inactivated
- Sodium channels there remain open until the pump stops
- Potassium channels there permanently seal the membrane
The sodium potassium pump is blocked while a neurone still has ion gradients. What happens as continued ion movement weakens those gradients?
- The resting voltage tends to become less negative
- The resting voltage immediately becomes twice as negative
- The resting voltage remains unchanged despite gradient loss

Answer key

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The spark that travels the nerve W1-mt_0sh4w30ocz-s1

Three sodium ions outward and two potassium ions inward · Each cycle exports three sodium ions and imports two potassium ions using one ATP. This maintains the ion gradients.
About minus 70 mV, with the inside negative · Minus 70 mV is a common example, although resting values vary. The negative sign means inside is negative relative to outside.
False · Resting voltage depends mainly on ion gradients and greater potassium permeability. The pump maintains the gradients and makes a smaller direct contribution.
Sodium channels drive the rise; potassium channels drive the fall · Sodium entry through voltage-gated sodium channels drives the rise. Potassium exit through voltage-gated potassium channels drives the fall.
Depolarisation, repolarisation, hyperpolarisation · Depolarisation is the rise. Repolarisation is the fall toward rest. Hyperpolarisation is the brief dip below resting voltage.
Potassium channels close slowly and potassium keeps leaving · Delayed closure of voltage-gated potassium channels permits continued potassium outflow. Voltage can briefly become more negative than at rest.
Sodium channels there remain temporarily inactivated · The recently activated region is refractory because its voltage-gated sodium channels are temporarily inactivated. It cannot immediately generate another action potential.
The resting voltage tends to become less negative · The pump normally maintains the gradients. Without pumping, continued ion movement weakens them over time, and resting voltage tends to become less negative.