8.1.3 Action Potentials

• What is the threshold membrane potential for an action potential to occur?

  $- 55 mV$
• Stages of the action potential in the correct order

  1️⃣ Depolarization

  2️⃣ Repolarization

  3️⃣ Hyperpolarization
• During depolarization, voltage-gated sodium channels open, allowing $Na^{ + }$ ions to rush into the cell.
• During hyperpolarization, the membrane potential dips below the resting potential.
• What happens to the membrane potential during repolarization?

  Decreases to -70 mV
• The resting membrane potential is typically around $- 70 mV$.
• Leak channels allow $K^{ + }$ ions to flow out of the cell, contributing to the negative resting membrane potential.
• What ratio of $Na^{ + }$ to $K^{ + }$ ions does the sodium-potassium pump maintain?


  $3 Na^{ + }$ out to $2 K^{ + }$ in
• Match the ion with its approximate concentration inside and outside the neuron:

  $Na^{ + }$ ↔️ 15 mM inside, 150 mM outside

  $K^{ + }$ ↔️ 150 mM inside, 5 mM outside
• What causes the membrane potential to dip below the resting potential during hyperpolarization?

  $K^{ + }$ channels stay open
• During repolarization, $K^{ + }$ ions flow out of the cell.
• Arrange the stages of the action potential based on ion movement

  1️⃣ $Na^{ + }$ rushes in

  2️⃣ $K^{ + }$ flows out

  3️⃣ $K^{ + }$ continues to flow out
• The membrane potential during an action potential typically starts from a resting potential of -70 mV
• Order the stages of an action potential:

  1️⃣ Depolarization

  2️⃣ Repolarization

  3️⃣ Hyperpolarization
• During depolarization, voltage-gated sodium channels open, allowing $Na^{ + }$ ions to flow into the cell.
• During repolarization, voltage-gated potassium channels open, allowing $K^{ + }$ ions to flow out
• Hyperpolarization occurs because potassium channels remain open, causing the membrane potential to dip below -70 mV
• Match the stage of action potential with its corresponding ion movement and membrane potential:

  Depolarization ↔️ $Na^{ + }$ in, $+$$30 mV$

  Repolarization ↔️ $K^{ + }$ out, $- 70 mV$

  Hyperpolarization ↔️ $K^{ + }$ continues out, below $- 70 mV$
• The resting membrane potential of a neuron is typically around -70 mV
• The uneven distribution of ions inside and outside the neuron contributes to the resting membrane potential.
• Leak channels allow $K^{ + }$ ions to flow out of the cell, contributing to the negative potential
• The sodium-potassium pump transports 3 Na^{ + }</latex> ions out and $2 K^{ + }$ ions in.
• The concentration of $K^{ + }$ ions inside the neuron is significantly higher than outside, approximately 150 mM
• The concentration of $Na^{ + }$ ions is higher outside the neuron than inside.
• The action potential consists of three main stages: depolarization, repolarization, and hyperpolarization
• Match the stage of action potential with its corresponding ion movement and membrane potential:

  Depolarization ↔️ $Na^{ + }$ in, $+$$30 mV$

  Repolarization ↔️ $K^{ + }$ out, $- 70 mV$

  Hyperpolarization ↔️ $K^{ + }$ continues out, below $- 70 mV$
• Ion channels are essential for establishing and maintaining the resting membrane potential.
• Leak channels, such as those for K^{ + }</latex>, contribute to the stable resting membrane potential around -70 mV
• Order the types of action potential conduction from slowest to fastest:

  1️⃣ Continuous conduction

  2️⃣ Saltatory conduction
• Saltatory conduction occurs in myelinated axons and is faster than continuous conduction.
• During the absolute refractory period, no new action potential can be generated because sodium channels are open or inactivated
• Refractory periods ensure unidirectional propagation of action potentials.
• When the membrane potential reaches the resting level again, the potassium channels remain open
• What are the two types of refractory periods?

  Absolute and relative
• The refractory periods ensure that action potentials travel in one direction along the axon.
• An action potential occurs when the membrane potential reaches a threshold of $- 55 mV$
• Stages of an action potential

  1️⃣ Depolarization

  2️⃣ Repolarization

  3️⃣ Hyperpolarization
• During depolarization, what ion rushes into the cell?

  $Na^{ + }$
• During repolarization, voltage-gated potassium channels open, allowing $K^{ + }$
• During hyperpolarization, the membrane potential briefly dips below the resting potential.