BIO 392 Quiz Questions

What type of ion channel opens directly in response binding of acetylcholine on receptors in the motor end plate (in other words: acetylcholine binds to what type of ion channel)?

Ligand-gated cation

Temporal summation is

Membrane potential produced as two or more inputs, occurring at different times but from the same neuron are added together.

The myelin sheath increases the velocity of conduction by the following mechanism(s).

Myelin insulates the axon, reducing the loss of depolarizing current across the plasma membrane. & The myelin insulation allows the voltage across the membrane to change (travel) much faster.

The Na+/K+ pump transports ________.

Na+ out of and K+ into the cell

Image a world without electrical gradients (this is a hypothetical situation that does not exist). What would happen to the Na+ concentration gradient? (assume there are leak channels to Na+ so Na+ can move)

Na+ would leak into the cell until the Na+ concentration inside the cell equaled the Na+ concentration outside

The ____ can be used to calculate the equilibrium potential of a specific ion for a given concentration gradient

Nernst equation

Which of the following statements best describes the drop in voltage below the resting state, as shown at point 4?

Some voltage-gated potassium channels are still open.

When the neuron is at rest, which statement is true? (note that the activation gate is also known as the voltage-sensitive gate)

The activation gate is closed and the inactivation gate is open.

The resting membrane potential (RMP) depends on two factors that influence the magnitude and direction of Na+ and K+ diffusion across the plasma membrane. Identify these two factors. (hint: there is one factor that sets up the concentration gradients of K+ and Na+: this factor is NOT directly responsible for the magnitude and sign of the RMP.

The presence of concentration gradients and leak channels

Which of the following occurs when a myofibril contracts?

Thin and thick filaments slide past each other, but do not change in length.

What opens first in response to a threshold stimulus?

Voltage-gated Na+ channels

What is the first change to occur in response to a threshold stimulus? (Note: the activation gate is also known as the voltage-sensitive gate)

Voltage-gated Na+ channels change shape, and their activation gates open.

The afterhyperpolarization of the action potential is due primarily to

Voltage-gated Na+ channels inactivated; Voltage-gated K+ channels open.

The falling phase of the action potential is due primarily to

Voltage-gated Na+ channels inactivated; Voltage-gated K+ channels open.

The rising phase of the action potential is due primarily to

Voltage-gated Na+ channels open; Voltage-gated K+ channels closed.

What type of ion channel opens in response to an action potential arriving at the axon terminal (in the presynaptic cell)?

Voltage-gated calcium

Which of the following statements best describes the decline in voltage, as shown at point 3?

Voltage-gated potassium channels are open.

Action potential in the muscle fiber are initiated by local depolarization at the motor end plate. Action potential that travel down the sarcolemma are propagated by the following channels:

Voltage-gated sodium

Maintaining a polarized membrane potential at rest requires energy

Y

A neuron has a resting potential of -70 mV and a threshold voltage of -50 mV. There are currently three active synapses on the neuron's dendrites, each located the same distance from the axon. The potential changes are + 40 mV at synapse 1, + 20 mV at synapse 2, and -10 mV at synapse 3. These synaptic potentials diminish by 50% by the time they reach the trigger zone. Will this neuron produce an action potential at this time? Explain. (Hint: Draw a graph of the voltage changes.)

Yes. At the trigger zone, all potentials have halved and will sum as follows: +20mV (originated at synapse 1), + 10mV (originated at synapse 2), -5mV (originated at synapse 3) sum to produce a total potential change of +25mV. The neuron required a minimum change of +20 mV (-70 mV + 20 mV = -50 mV), so it will produce an action potential.

The electrical gradient is defined as

a difference in the net charge between two regions

The neurotransmitter released at the neuromuscular junction:

acetylcholine

The preganglionic neuron releases ____ in the parasympathetic division, and _____ in the sympathetic division

acetylcholine; acetylcholine

ATP _______ the myosin head

allosterically modulates

Sodium levels are increased in a patient in the ECF. Assuming that all else remains unchanged (this means that intracellular sodium levels are the same as in a normal person), how will this affect the membrane potential?

it will become less negative than -70 mV (e.g. -60 mV) because the concentration gradient of sodium is steeper, so there will be more movement of sodium down its electrochemical gradient.

During an action potential, when does membrane permeability to sodium INCREASE most rapidly?

during the steepest portion of the depolarization phase

The membrane potential is defined as

electrical disequilibrium between the ICF and the ECF (ions are not distributed evenly between the ECF and the ICF, especially across the membrane)

Identify the transport process by which acetylcholine is released into the synaptic cleft.

exocytosis

Which muscle fiber type has few mitochondria and low capillary density?

fast-twitch glycolytic; white muscle

Reducing the amount of acetylcholine released at the neuromuscular junction will cause _______

fewer nicotinic receptors to be open

Fast-twitch white muscle fibers rely on ________ for energy.

glycolytic metabolism

Potassium levels are ____ inside the cell than outside the cell

higher

Muscle tension develops faster in a fast-twitch muscle fibers because of

higher myosin ATPase activity

If a small amount of chlorine is leaked into the cell, the cell would

hyperpolarize

Choose which items that are correctly matched. Note that some textbooks refer to the voltage gate as the 'activation gate'.

inactivation gate - closed during repolarization

Epinephrine will have the following physiological effect

increased heart rate

Autonomic neurons are mostly involved in

involuntary actions

The concentration gradient of sodium across the plasma membrane favors the ___ movement of sodium when sodium channels open

inward (sodium is moving into the cell)

The following factor increase the duration of a single muscle twitch

less rapid removal of Ca2+ ions from the sarcoplasm

Myasthenia gravis is a disorder that is characterized by

loss of ACh receptors

Sodium levels are ____ inside the cell than outside the cell

lower

dual innervation of the heart is beneficial because it gives you

more control of heart rate because you can both increase and decrease it

Increasing the amount of acetylcholine released at the neuromuscular junction will cause _______

more nicotinic receptors to be open

The following factor decrease the duration of a single muscle twitch

more rapid removal of Ca2+ ions from the sarcoplasm

The equilibrium potential of potassium is the membrane potential of a hypothetical cell that is very permeable to potassium at a given concentration gradient. For potassium, the equilibrium potential is ____

negative (approximately -90 mV)

Autonomic (motor) neurons are subdivided into the

sympathetic and parasympathetic divisions

Which autonomic division elicit a body-wide response (as opposed to a more localized regulation of individual organs)

sympathetic pathway

A substance produced by Clostridium botulinum, blocks the release of acetylcholine from the motor neuron. Application of this substance will have the following effect on the skeletal muscle fiber (think of the effect of botox):

It will cause muscle relaxation

Drug X inhibits acetylcholinesterase action within the neuromuscular junction resulting in the buildup of acetylcholine at the neuromuscular junction. What would drug X do to the membrane potential of the muscle fiber?

It would remain depolarized.

At rest (in a resting neuron, so we're talking about the resting membrane potential), there is a little bit more ___ than ______

K+ efflux; Na+ influx

The major determinant (because there are more leak channels for this ion) of the resting potential of all cells is

K+ electrochemical gradient

When voltage - gated K+ channels of a resting neuron open,

K+ leaves the neuron.

Image a world without electrical gradients (this is a hypothetical situation that does not exist). What would happen to the K+ concentration gradient? (assume there are leak channels to K+ so K+ can move)

K+ would leak out of the cell until the K+ concentration inside the cell equaled the K+ concentration outside

The following is important for maintaining a negative resting membrane potential: Leak channels specific to ____ in a membrane causes this ion to leave the cell, while ___ cannot follow this ion. (A-: negatively charged ions)

K+; A-

Sodium and potassium ions can diffuse across the plasma membranes of all cells because of the presence of what type of channel?

Leak channels

Put these myofibers in the order they would be recruited as the body moves from a weak to a strong stimulus: 1. glycolytic fast-twitch fibers; 2. fatigue-resistant oxidative fast-twitch fibers; 3. fatigue-resistant slow-twitch fibers.

3, 2, 1

The value of the resting membrane potential in a typical neuron is ________.

-70 mV

Put these events in the correct chronological sequence: 1. Acetylcholine binds to receptors on the motor end plate. 2. End-plate potentials trigger action potentials. 3. Ca2+ is released from the sarcoplasmic reticulum. 4. Transverse tubules convey potentials into the interior of the cell.

1, 2, 4, 3

The following opens the voltage-gated sodium channel

A local depolarization

What is the name of the enzyme that degrades acetylcholine?

Acetylcholinesterase

Which of the following statements best describes the steep rise in voltage, as shown at point 2?

All voltage-gated sodium channels open.

Curare, a deadly arrowhead poison, can cause death by asphyxiation (deprivation of oxygen) because it prevents the use of skeletal muscle used for breathing. When curare affects the muscle, acetylcholine is still released but it does not cause an action potential in the muscle fiber. Curare is the following

Antagonist on the nicotinic receptors

Extracellular [Cl-] is far greater than intracellular [Cl-]. In the membrane of a resting nerve cell, when chemically gated Cl- channels open,

Cl- ions enter the cell and the cell becomes hyperpolarized.

The first thing that occurs when the axon terminal releases ACh is _________.

Diffusion across the synaptic cleft

During a contraction, which band(s)/zones becomes more narrow?

I band and H zone

What changes occur to voltage-gated Na+ and K+ channels at the peak of depolarization?

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

Where do most action potentials originate?

Initial segment or axon hillock (a.k.a. the trigger zone)

What creates the membrane potential?

Ion concentration gradients between the ECF and the ICF; the selective permeability of the membrane

A neuron has a resting potential of -70 mV and a threshold voltage of -50 mV. There are currently three active synapses on the neuron's dendrites, each located the same distance from the axon. The potential changes are + 20 mV at synapse 1, + 20 mV at synapse 2, and -10 mV at synapse 3. These synaptic potentials diminish by 50% by the time they reach the trigger zone. Will this neuron produce an action potential at this time? Explain. (Hint: Draw a graph of the voltage changes.)

No. At the trigger zone, all potentials have halved and will sum as follows: +10mV (originated at synapse 1), + 10mV (originated at synapse 2), -5mV (originated at synapse 3) sum to produce a total potential change of +15mV. The neuron required a minimum change of +20 mV (-70 mV + 15 mV = -55 mV), so it will not produce an action potential.

________ is the backup energy molecule that can be rapidly converted to ATP in active skeletal muscle.

Phosphocreatine

Identify the states of the voltage-gated Na+ channel. State during repolarization

Repolarization

Which phase of the action potential is depicted in the image below? The three to the left are voltage-gated sodium channels, the three to the right are voltage-gated potassium channels.

Repolarization

Ions are unequally distributed across the plasma membrane of all cells. This ion distribution creates an electrical potential difference across the membrane in a cell at rest. What is the name given to this potential difference? (Hint: All cells exhibit an electrical potential difference across their plasma membranes. Only excitable cells can alter this difference by generating action potentials. Thus, an excitable cell, like a neuron, exhibits both a resting and an excited state).

Resting membrane potential (RMP)

On average, the resting membrane potential is -70 mV. What does the sign and magnitude of this value tell you?

The inside surface of the plasma membrane is much more negatively charged than the outside surface.

What characterizes depolarization, the first phase (also known as the 'rising phase) of the action potential?

The membrane potential changes from a negative value to a positive value.

What event triggers the generation of an action potential?

The membrane potential must depolarize from the resting voltage of -70 mV to a threshold value of -55 mV.

In order for high-force crossbridges to form in contracting skeletal muscle, calcium must

bind to troponin which moves the tropomyosin

An agonist on muscarinic receptors will have the following effect

decreased heart rate

Atropine (an antagonistic on muscarinic receptors) will have the following effect

decreased peristaltic movements in the gut

When sodium channels open, sodium rushes into the cell. This will cause

depolarization (inner side of the membrane becomes more positively charged)

As ATP binds to the myosin head at the beginning of a muscle contraction cycle, the myosin head immediately

detaches from actin.

The concentration gradient of potassium across the plasma membrane favors the ___ movement of potassium when more potassium channels open

outward (potassium is moving into the ECF)

Skeletal muscle fibers with the greatest endurance rely on ________ for energy.

oxidative phosphorylation

The vagus nerve is part of the _____

parasympathetic pathway

Consider the following movement of ions across the membrane due to an increase in membrane permeability to these ions (e.g. movement of chloride results from opening of chloride channels). Which of the following would NOT cause the membrane potential to change from -70 mV to +30 mV? (there are actually two correct answers, just pick one)

potassium ions leaving the cell

The falling phase of the action potential is similar to

repolarization

After death, when metabolism stops, in which step of the contractile cycle must skeletal muscles remain?

rigor state

Just after a neuron fired an action potential, it cannot fire another one. This period is called

the absolute refractory period

Detachment of myosin from actin requires

the binding of ATP to change the conformation of myosin's actin-binding site

The resting membrane potential depends on each item below, EXCEPT:

the greater permeability of the membrane to anions rather than cations.

The equilibrium potential is defined as

the membrane potential that exactly opposes the concentration gradient of a certain ion at a given concentration gradient; at this point there is no net movement of that ion across the membrane

Which of the following statements best describes the neuromuscular junction?

the point of synapse between a motor neuron and the muscle fiber that it innervates

Which statement is correct regarding the effect of somatic motor neurons on the target tissue

they can only be excitatory

The A zone contains

thick and thin filaments

The binding of calcium to which molecule causes the myosin binding sites to be exposed in skeletal muscle?

troponin

The site of calcium regulation in the skeletal muscle cell is ___ (hint: we're looking for something to which calcium can bind)

troponin and tropomyosin complex

True or false? The equilibrium potential of Na+ is the membrane potential of a hypothetical cell that is very permeable to Na+ at a given concentration gradient. For Na+, the equilibrium potential is positive

true

The resting membrane potential results from

uneven distribution of ions across the cell membrane and differences in membrane permeability to Na+ and K+.