MasteringA&P 06 Neurons

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What part of the nervous system performs information processing and integration?

central nervous system

Which of the following allows us to consciously control our skeletal muscles?

The somatic nervous system

Efferent nerve fibers may be described as motor nerve fibers.

True

Ions are unequally distributed across the plasma membrane of all cells. This ion distribution creates an electrical potential difference across the membrane. What is the name given to this potential difference?

Resting membrane potential (RMP)

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

Leak channels

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.

The plasma membrane is much more permeable to K+ than to Na+. Why?

There are many more K+ leak channels than Na+ leak channels in the plasma membrane.

The resting membrane potential depends on two factors that influence the magnitude and direction of Na+ and K+ diffusion across the plasma membrane. Identify these two factors.

The presence of concentration gradients and leak channels

What prevents the Na+ and K+ gradients from dissipating?

Na+-K+ ATPase

Where do most action potentials originate?

Initial segment

What opens first in response to a threshold stimulus?

Voltage-gated Na+ channels

What characterizes depolarization, the first phase of the action potential?

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

What characterizes repolarization, the second phase of the action potential?

Once the membrane depolarizes to a peak value of +30 mV, it repolarizes to its negative resting value of -70 mV.

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.

What is the first change to occur in response to a threshold stimulus?

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

What type of conduction takes place in unmyelinated axons?

Continuous conduction

An action potential is self-regenerating because __________.

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

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.

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.

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.

In which type of axon will velocity of action potential conduction be the fastest?

Myelinated axons with the largest diameter

Which neurotransmitter(s) is/are the body’s natural pain killer?

endorphins

What is the role of acetylcholinesterase?

destroy ACh a brief period after its release by the axon endings

The substance released at axon terminals to propagate a nervous impulse is called a(n) ________.

neurotransmitter

Enkephalins and endorphins are peptides that act like morphine.

True

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