PHYSIOLOGY

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

Myelinated axons with the largest diameter

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

Na+-K+ ATPase

Which brain area is considered to be the headquarters of the ANS?

hypothalamus

The myelin sheath that covers many CNS axons is formed by

oligodendrocytes

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.

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.

Parasympathetic functions include all of the following except

dilation of the airways.

Most vital organs receive ________ innervation. That is, they receive input from both sympathetic and parasympathetic divisions.

dual

Binding of the neurotransmitter to its receptor causes the membrane to __________.

either depolarize or hyperpolarize

EPSPs (excitatory postsynaptic potentials) occur when

extra sodium ions enter a cell.

Binding of a neurotransmitter to its receptors opens __________ channels on the __________ membrane.

chemically gated; postsynaptic

Functions of astrocytes include all of the following except

conducting action potentials.

Which of the following is an effect of parasympathetic activation?

constriction of the pupils

A visceral motor neuron whose cell body is within the CNS is called a(n) ________ neuron.

preganglionic

In a synapse, neurotransmitters are stored in vesicles located in the __________.

presynaptic neuron

The ________ nervous system controls the skeletal muscles.

somatic

The Na-K ion exchange pump actively transports

3 intracellular sodium ions for 2 extracellular potassium ions.

Hyperpolarize

: The membrane potential is more negative than the resting membrane potential.

________ channels open or close in response to binding specific molecules.

Chemically gated

What type of conduction takes place in unmyelinated axons?

Continuous conduction

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.

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

Leak channels

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.

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)

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

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

depolarize

The membrane potential is becoming more positive than the resting membrane potential.

repolarize

The membrane potential is moving from a more positive value toward resting membrane potential.

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 function of the myelin sheath?

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

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 effect would decreasing the concentration of extracellular potassium ions have on the resting membrane potential of a neuron? (Module 11.7C)

The resting membrane potential would become more negative because more potassium ions would leave the cell through potassium leak channels.

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

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

The mechanism by which the neurotransmitter is returned to a presynaptic neuron's axon terminal is specific for each neurotransmitter. Which of the following neurotransmitters is broken down by an enzyme before being returned?

acetylcholine

What neurotransmitter is released by all parasympathetic neurons? (Module 14.5B)

acetylcholine

The all-or-none principle states that

all stimuli great enough to bring the membrane to threshold will produce identical action potentials.

Define spinal reflex.

an automatic response to a stimulus that is controlled in the spinal cord and can function without input from the brain.

All of the following are true of muscle spindles except that they

are found in tendons.

Ganglionic neurons usually synapse with preganglionic neurons in the_______

autonomic ganglia

The anterior root of a spinal nerve contains

axons of motor neurons.

A decrease in the autonomic tone of the smooth muscle in a blood vessel would result in

both an increase in vessel diameter and an increase in blood flow through the vessel.

Which of the following would lead to increased heart rate?

both increased sympathetic input and decreased parasympathetic input

Control of the diameter of the respiratory passages depends upon

both parasympathetic and sympathetic levels of stimulation.

The posterior root ganglia mainly contain

cell bodies of sensory neurons.

Clusters of ganglionic sympathetic neurons lying along either side of the spinal cord are called sympathetic ________ ganglia.

chain

Spinal nerves

contain both sensory and motor.

Which of the following describes the posterior root ganglion?

contains cell bodies of sensory neurons

Opening of sodium channels in the axon membrane causes

depolarization and increased positive charge inside the membrane.

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

Regions of the CNS where neuron cell bodies dominate constitute the ________ matter.

grey

Alzheimer's disease is characterized by all of the following except that it

has a clear genetic basis.

In a typical undisturbed cell, the extracellular fluid (ECF) contains high concentrations of sodium ions and chloride ions, whereas the cytosol contains __________.

high concentrations of potassium ions and negatively charged proteins

Parkinson's disease is the result of

inadequate production of dopamine by substantia nigra neurons.

Activation of the parasympathetic division of the ANS results in __________.

increased motility and blood flow in the digestive tract

Where do most action potentials originate?

initial segment

All of the following are a part of a monosynaptic reflex arc except

interneuron

The descending spinal tract that crosses to the opposite side of the body within the pyramids of the medulla oblongata is the ________ tract.

lateral corticospinal

A viral disease that destroys the neuronal cell bodies of the anterior gray horn will

lead to muscle weakness or paralysis.

Bill contracts a viral disease that destroys cells in the posterior gray horns in his spinal cord. As a result, which of the following would you expect?

loss of sensation in his torso

Motor neurons whose cell bodies are within the spinal cord are called ________ neurons.

lower motor

Define dual innervation

means that a given body system receives instructions from both the sympathetic and parasympathetic divisions of the ANS.

In a(n) ________ reflex, a sensory neuron synapses directly on a motor neuron.

monosynaptic

Neurons that have several dendrites and a single axon are called

multipolar

The ________ division of the autonomic nervous system is known as the "rest and digest" division.

parasympathetic

A posterior and anterior root of each spinal segment unite to form a

spinal nerve

If the chemically gated sodium channels in the postsynaptic membrane were completely blocked,

synaptic transmission would fail.

The minimum stimulus required to trigger an action potential is known as the

threshold.

The statement "Its ganglia are usually near or within the end organ" is

true only for the parasympathetic nervous system.

Regions of the CNS with an abundance of myelinated axons constitute the ________ matter.

white

Descending (motor) pathways always involve at least ________ motor neuron(s).

two

Sensory neurons of the PNS are

unipolar

Ganglionic neurons have axons that innervate ________.

visceral effectors

A gated channel that responds to changes in transmembrane potential is called a(n) ________ channel.

voltage gated

What opens first in response to a threshold stimulus?

voltage gated Na+ channels

An action potential releases neurotransmitter from a neuron by opening which of the following channels?

voltage-gated Ca2+ channels

The generation of an action potential in a neuron requires the presence what type of membrane channels?

voltage-gated channels