Lsn 21 Homework, VAP 11.8 - 11.13

What changes occur to voltage-gated Na+ and K+ channels at the peak of depolarization? - Activation gates of voltage-gated Na+‎ channels close, while inactivation gates of voltage-gated K+‎ channels open. - Inactivation gates of voltage-gated Na+‎ channels close, while activation gates of voltage-gated K+‎ channels open. - Inactivation gates of voltage-gated Na+‎ channels close, while inactivation gates of voltage-gated K+‎ channels open. - Activation gates of voltage-gated Na+‎ channels close, while activation gates of voltage-gated K+‎ channels open.

- Inactivation gates of voltage-gated Na+‎ channels close, while activation gates of voltage-gated K+‎ channels open.

After acetylcholinesterase acts, the synaptic knob reabsorbs the acetylcholine. reabsorbs the choline. reabsorbs the acetate. degrades the acetate. degrades the choline.

reabsorbs the choline.

In the formation of an action potential at the initial segment of an axon, what produces the brief hyperpolarization during the step in which the potassium channels begin closing? - Potassium ions enter the cell until all of the potassium channels have closed. - Potassium ions continue to leave the cell until all of the potassium channels have closed. - The stimulus that initiates the action potential causes voltage-gated sodium channels to open. - Sodium ions rush into the cell.

- Potassium ions continue to leave the cell until all of the potassium channels have closed.

Which of the following definitions or descriptions is correct? - Temporal summation occurs when a single synapse depolarizes once. - Spatial summation involves multiple synapses that are active simultaneously. - An inhibitory postsynaptic potential (IPSP) is a graded depolarization of the postsynaptic membrane. - An excitatory postsynaptic potential (EPSP) is a graded hyperpolarization of the postsynaptic membrane.

- Spatial summation involves multiple synapses that are active simultaneously.

Puffer fish poison blocks voltage-gated sodium channels like a cork. What effect would this neurotoxin have on the function of neurons? - Neurons would depolarize more rapidly. - The axon would be unable to generate action potentials. - The absolute refractory period would be shorter than normal. - Action potentials would lack a repolarization phase. - None, because the chemically gated sodium channels would still function.

- The axon would be unable to generate action potentials.

Why does regeneration of the action potential occur in one direction, rather than in two directions? - The inactivation gates of voltage-gated Na+‎ channels close in the node, or segment, that has just fired an action potential. - The inactivation gates of voltage-gated K+‎ channels close in the node, or segment, that has just fired an action potential. - The activation gates of voltage-gated K+‎ channels open in the node, or segment, that has just depolarized. - The activation gates of voltage-gated Na+‎ channels close in the node, or segment, that has just depolarized.

- The inactivation gates of voltage-gated Na+‎ channels close in the node, or segment, that has just fired an action potential.

What is the function of the myelin sheath? - The myelin sheath increases the speed of action potential conduction from the initial segment to the axon terminals. - The myelin sheath decreases the speed of action potential conduction from the initial segment to the axon terminals. - The myelin sheath increases the insulation along the entire length of the axon. - The myelin sheath decreases the resistance of the axonal membrane to the flow of charge.

- The myelin sheath increases the speed of action potential conduction from the initial segment to the axon terminals.

An action potential is self-regenerating because __________. - repolarizing currents established by the efflux of Na+‎ flow down the axon and trigger an action potential at the next segment - depolarizing currents established by the influx of Na+‎ flow down the axon and trigger an action potential at the next segment - repolarizing currents established by the efflux of K+‎ flow down the axon and trigger an action potential at the next segment - depolarizing currents established by the influx of K+‎ flow down the axon and trigger an action potential at the next segment

- depolarizing currents established by the influx of Na+‎ flow down the axon and trigger an action potential at the next segment

A characteristic of graded potentials is: - the effect spreads passively through local currents. - the nature of the graded change in membrane potential is determined by the properties of the Nissl bodies of the neuronal cell involved. - the effect of the transmembrane potential increases with distance from the site of stimulation. - the stronger the stimulus, the smaller and more concentrated is the area affected.

- the effect spreads passively through local currents.

What type of conduction takes place in unmyelinated axons? Electrical conduction Continuous conduction Saltatory conduction Synaptic transmission

Continuous conduction

Which of the following is defined as a graded hyperpolarization of the postsynaptic membrane? IPSP equilibrium potential EPSP resting potential

IPSP

In which type of axon will velocity of action potential conduction be the fastest? Unmyelinated axons with the largest diameter Myelinated axons with the largest diameter Myelinated axons with the smallest diameters Unmyelinated axons of the shortest length

Myelinated axons with the largest diameter

Which part of a neuron would probably be most affected by lead poisoning? Mitochondrion Throughout the entire membrane Axon hillock Synaptic knob

Synaptic knob

Which part of a neuron would probably be most affected by the application of Novocain? Axon hillock Throughout the entire membrane Synaptic knob Mitochondrion

Throughout the entire membrane

A shift of the resting transmembrane potential toward 0 mV is called non-polarization. hyperpolarization. depolarization. hypopolarization. repolarization.

depolarization.

EPSPs (excitatory postsynaptic potentials) occur when more calcium ions than usual leak out of a cell. chloride ions enter a cell. hyperpolarizations occur. more potassium ions than usual leak out of a cell. extra sodium ions enter a cell.

extra sodium ions enter a cell.

In saltatory propagation, a local current produces a(n): hyperpolarization. graded depolarization. resting potential. repolarization.

graded depolarization.

Voltage-gated sodium channels have both an activation gate and a(n) ________ gate. inactivation threshold swinging ion repolarization

inactivation

Graded potentials - may be either a depolarization or a hyperpolarization. - produce an effect that spreads actively across the membrane surface without diminishing. - produce an effect that increases with distance from the point of stimulation. - always cause repolarization. - are often all-or-none.

may be either a depolarization or a hyperpolarization.

The buildup of depolarization when EPSPs arrive in rapid succession is called ________ summation. spatial temporal electrical threshold chemical

temporal

Which type of membrane channels are found in axons? voltage-gated Ca2+ channels voltage-gated K+ channels voltage-gated Na+ channels chemically gated Na+ and K+ channels voltage-gated Na+ and K+ channels

voltage-gated Na+ and K+ channels

The generation of an action potential in a neuron requires the presence what type of membrane channels? chemically gated channels leakage channels voltage-gated channels membrane channels are not required

voltage-gated channels