Bio 251 Study Guide Questions 13-20

Which of the following events initiates an action potential?

• Voltage-gated potassium channels open, causing the membrane to hyperpolarize.

• A graded potential reaches the axon hillock and triggers the opening of voltage-gated sodium channels.

• The inactivation of sodium channels leads to membrane depolarization.

• Ligand-gated ion channels open, allowing calcium ions to enter.

Which ion is primarily responsible for depolarization during an action potential?

• Potassium (K⁺)

• Calcium (Ca²⁺)

• Sodium (Na⁺)

• Chloride (Cl⁻)

What occurs during repolarization of the neuron’s membrane?

• Sodium channels open, causing the membrane to become more positive.

• Potassium ions leave the neuron, making the inside of the cell more negative.

• The neuron reaches a more positive potential, exceeding +30 mV.

• Both sodium and potassium channels close simultaneously.

During which phase of the action potential is the membrane most permeable to potassium?

• Depolarization

• Resting potential

• Repolarization

• Hyperpolarization

Which of the following best describes hyperpolarization?

• The inside of the neuron becomes more negative than its resting potential.

• The membrane potential becomes more positive than the resting potential.

• Sodium ions rush into the cell, making the membrane potential more positive.

• Potassium ions enter the cell, causing the membrane potential to exceed zero.

What is the function of voltage-gated sodium channels during an action potential?

• They allow potassium ions to enter the cell, initiating hyperpolarization.

• They open in response to membrane depolarization, allowing sodium to flow in.

• They close once the action potential reaches its peak, triggering repolarization.

• They regulate neurotransmitter release at the axon terminal.

What is the significance of the absolute refractory period?

• It prevents the action potential from reversing direction along the axon.

• It allows the neuron to generate another action potential immediately.

• It increases the strength of graded potentials, allowing summation.

• It ensures the action potential will travel faster along myelinated axons.

Which of the following statements best distinguishes graded potentials from action potentials?

• Graded potentials are all-or-nothing, while action potentials vary in size.

• Graded potentials diminish over time and space, while action potentials do not.

• Graded potentials occur at the axon hillock, while action potentials occur at dendrites.

• Graded potentials require voltage-gated ion channels, while action potentials do not.

How does myelin affect the conduction of action potentials?

• Myelin allows the action potential to travel continuously along the axon.

• Myelin slows down the action potential by preventing ion exchange along the axon.

• Myelin allows the action potential to jump between nodes of Ranvier, speeding conduction.

• Myelin eliminates the refractory period, enabling rapid action potential firing.

Which cells form myelin in the peripheral nervous system (PNS) and the central nervous system (CNS)?

• Oligodendrocytes in the PNS, Schwann cells in the CNS

• Astrocytes in the PNS, Schwann cells in the CNS

• Schwann cells in the PNS, oligodendrocytes in the CNS

• Schwann cells in both the PNS and CNS