Chapter 11 A&P

Which glial cells have the most diversity of function? What are some examples of their many functions?

Astrocytes-- most abundant and diversely functioning glial cells. Examples of their many functions include: anchoring neurons to capillaries, aiding in the exchanges between neurons and blood, guiding the migration of young neurons, and helping control the chemical environment around neurons.

Sodium Potassium pump

Constantly transports Na+ and K+ ions in opposite directions. K+ is transported into the cell, which increases the K+ concentration inside the cell. At the same time, Na+ is transported out of the cell, which increases the Na+ concentration outside the cell. Although it's easy to remember that the pump moves ions in opposite directions, remembering which ion goes which way may be more difficult. To help you remember, think PUMPKIN ("PUMP K INto the cell).

T or F: Diffusion efficiency depends on the number of postsynaptic receptors.

False. Diffusion efficiency does not depend on the number of postsynaptic receptors.

The diffusion of what ion, across the neuronal membrane, is responsible for local currents that depolarize regions of the axon to threshold?

Na+ (sodium) >>> sodium enters cell during beginning of action potential. Further depolarizes membrane

The concentrations of which two ions are highest outside the cell?

Na+ and Cl-

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

Na+-K+ ATPase Pump moves 3 Na+ out of cell and 2 K+ into cell for every ATP it hydrolyzes. Pump action prevents Na+ and K+ gradients from running down as these ions passively move through leak channels.

Prozac belongs to a class of drugs known as selective serotonin reuptake inhibitors (SSRIs), which block the removal of serotonin from its receptor, thereby enhancing a patient's mood. What mechanism allows serotonin to remain on its receptors longer?

SSRIs inhibit the reuptake of serotonin back into the presynaptic neuron, which increases the level of serotonin in the synaptic cleft.

What does 0 mV on the Y-axis of an action potential tracing represent?

The cell's membrane is at equilibrium.

Many neurons have many short, branching extensions called dendrites. What is the benefit of these structures for a neuron?

The dendrites provide a large surface area for connections from other neurons. The branching and extensive membrane surface area creates a large amount of membrane dedicated to synapses with other neurons.

The doctor is concerned about Mr. M's weakness. She orders an EKG. Why might an EKG be an appropriate test for this patient?

The heart is a muscle too, so whatever is making his skeletal muscles weak might be affecting it. >> The heart, like any other muscle, depolarizes and repolarizes. So if abnormal extracellular K+ levels have been interfering with his skeletal muscle function, as indicated by his weak reflexes, they might be interfering with his heart function too - a much more serious problem!

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

The membrane potential changes from a negative value to a positive value. >> The plasma membrane, which was polarized to a negative value at the RMP, depolarizes 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. >>> This is the minimum value required to open enough voltage-gated Na+ channels so that depolarization is irreversible.

How does achieving threshold at the axon hillock trigger an action potential? (The axon hillock already has closed voltage-gated channels in its resting state. It is where voltage-gated channels begin and chemically gated channels stop. Graded potentials do not occur on the axon)

Threshold causes the opening of the first Na+ voltage-gated channels at the axon hillock. Submit

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?

Voltage-gated Na+ channels change shape, and their activation gates open. >>> Yes! The activation gates of voltage-gated Na+ channels open very rapidly in response to threshold stimuli. The activation gates of voltage-gated K+ channels are comparatively slow to open.

Where are action potentials regenerated as they propagate along a myelinated axon?

at the nodes of Ranvier

Voltage-gated channels are typically found on _______, not ______.

axons, not dendrites

If the membrane of a postsynaptic dendrite is setting up a graded potential, what must have happened after neurotransmitter was released by the presynaptic terminal? The neurotransmitter __________.

bound at postsynaptic receptors to open postsynaptic ion channels >>> Diffusion carries the transmitter from higher to lower concentration. The transmitter binds to a receptor on the postsynaptic membrane and effects a cascade of events, resulting in the opening of ion channels. These lead to graded potentials, which may set up an action potential.

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

chemically gated; postsynaptic >>> the neurotransmitter is a chemical released from the presynaptic membrane, so it would open chemically gated channels on the postsynaptic membrane.

EPSPs result in a local __________, which brings the membrane potential closer to zero.

depolarization

Incoming messages to the dendrites or cell body pass through neuroplasm to the axon hillock. If a threshold stimulus value is reached at the axon hillock, ________ passes down the axon to the ___________ containing synaptic vesicles.

depolarization; presynaptic terminal

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

either depolarize or hyperpolarize >>> the neurotransmitter can cause the postsynaptic membrane to either depolarize or hyperpolarize, depending on which ion channels are opened.

Neurons release neurotransmitters, effectively changing an ________ or _______ into a chemical signal that can communicate across the synaptic cleft to the postsynaptic cell.

electrical signal or action potential

Which membrane potential occurs because of the influx of Na+ through chemically gated channels in the receptive region of a neuron?

excitatory postsynaptic potential >>a type of graded potential, occurs because of the influx of Na+ through chemically gated channels in receptive region (postsynaptic membrane) of a neuron.

Neurotransmitter is released from presynaptic neurons through what mechanism? Once released, neurotransmitter diffuses across ____________.

exocytosis; synaptic cleft. >> "exo-" means "outside" and "cytosis" means "cell"

At the postsynaptic membrane: following diffusion across the synapse, the neurotransmitter binds at receptors on the postsynaptic membrane and sets up a _________.

graded potential

In chemical synapse, when neurotransmitter binds, the channel opens. Once open, these channels allow the movement of ions across the postsynaptic membrane, which generates a ___________ in the postsynaptic cell

graded potential

If the receiving neuron is more negative inside, it is _____ likely to generate an action potential.

less

What is the major role of the Na+-K+ pump in maintaining the resting membrane potential?

maintaining the concentration gradients for Na+ and K+ across the cell membrane. Pump actively transports Na+ and K+ ions against their concentration gradients. Without pump, diffusion of Na+ and K+ through leakage channels would eventually eliminate concentration gradients.

Different classes of neurotransmitters are grouped according to their ______ and each class is affected by different drugs.

molecular structure

Complete the following sentence. The operation of the Na+−K+Na+−K+ ATPase pump __________.

moves 3 Na+Na+ to the ECF and 2 K+K+ to the cytoplasm

What is the body's master control system?

the nervous system

A resting neuron has a greater negative charge on the inside surface of the plasma membrane, and a greater positive charge on the outside surface. This partitioning of charge creates a voltage difference across the membrane known as _______________, which can be measured using a ________.

the resting membrane potential; voltmeter

What is the electrochemical gradient of an ion?

the sum of the electrical and concentration gradients for that ion

As you start working out, you notice that your heart rate and breathing rate start to increase. Which division of your nervous system is generating this response? Be as specific as possible.

the sympathetic division of the autonomic nervous system;

How do calcium ions enter the synaptic terminal? What do they then bind to? What does this cause?

through calcium channels; bind to vesicles containing neurotransmitters; causes the vesicles to fuse with plasma membrane of the sending neuron, releasing neurotransmitters into the synaptic cleft

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

voltage-gated Ca2+ channels >> opening of these channels causes calcium to move into the axon terminal. Calcium inside the neuron causes the vesicles to merge with the membrane and release the neurotransmitter via exocytosis into the synaptic cleft.

If potassium was the only ion moving, the potential would stabilize at minus ______. However, the + charged sodium ions leak into the neuron, which slightly offsets the negative charge and raises voltmeter reading to -70 milivolts.

90 milivolts

Differences between voltage-gated K+ channels and voltage-gated Na+ channels (3)

>> The direction of ion movement through the channel >> The inactivation mechanism

Cl− is a common, negatively charged extracellular ion. Predict the effect on the RMP if many Cl−Cl− gated channels are suddenly opened.

A more negative RMP would result... Cl− is negatively charged and has a higher concentration in the ECF. The opening of Cl−Cl− channels would allow more negative charge to attempt to enter the cytoplasm. If the cell's normal RMP were -70mV, it would now become more negative. The farther away the RMP is from zero, either in the positive or in the negative direction, the greater the separation of charges is. This is called hyperpolarization. When the RMP moves closer to 0 mV, depolarization occurs.Congratulations! You've successfully examined the construction of the resting membrane potential, an important concept in any human cell.

During the action potential of a neuron, which ion is primarily crossing the membrane during the depolarization phase, and in which direction is the ion moving?

Na+ is entering the cell.

If a signal from a sending neuron makes the receiving neuron more negative inside,

the receiving neuron is less likely to generate an action potential.

What must occur for threshold to be reached?

Enough excitatory potentials add up to open voltage-gated channels at the axon hillock.

Similarities between voltage-gated K+ channels and voltage-gated Na+ channels (3)

-- The stimulus that triggers opening -- The polarity of the substances they transport across the membrane -- The placement of the channel protein relative to the membrane

Assume you have a membrane with only potassium leakage channels. The RMP is -90mV. Predict the RMP if we add Na+Na+ leakage channels.The most likely RMP value of Na+Na+ is __________. Imagine that the cell membrane from the previous problem becomes more permeable to Na+Na+. Predict how this will affect the RMP.

-70 mV; The RMP will be more positive.

While the neurotransmitter is in the synaptic cleft, what are the 3 factors that affect its ability to bind at the postsynaptic cell. Each will decrease the effect of the neurotransmitter to initiate or to maintain an action potential.

1. Can be taken up into the presynaptic membrane via a receptor protein 2. Can be broken down by an enzyme 3. Can simply diffuse away to an area of lesser concentration. Each will decrease the effect of the neurotransmitter to initiate or to maintain an action potential.

The resting membrane potential depends on what 2 factors?

1. Presence of sodium and potassium gradients across the plasma membrane. there are more sodium ions outside and more potassium ions inside the neuron. 2. Differential permeability of the plasma membrane to sodium and potassium ions. Leak channels in plasma membrane allow Na and K ions to diffuse, or leak, down concentration gradient. The membrane contains many more potasssium leak channels than sodium ones so membrane is much more permeable to potassium ions.

Myelin sheath increases the velocity of conduction by two mechanisms...

1. myelin insulates the axon, reducing the loss of depolarizing current across the plasma membrane 2. the myelin insulation allows the voltage across the membrane to change much faster >>> because of these two mechanisms, regeneration only needs to happen at the widely spaced nodes of Ranvier, so the action potential appears to jump.

Tetraethylammonium (TEA) blocks voltage-gated K+ channels so K+ cant pass even when channels are open. However, TEA leaves K+ leakage channels largely unaffected. How would you expect action potential to change if you treated a neuron with TEA?

Action potential would depolarize as usual, but repolarization phase would take longer, causing the action potential to be more broad in time. >> once voltage Na+ channels open during depolarization phase, those same NA+ channels quickly inactivate. In other words, open Na+ channels inevitably inactivate regardless of whether K+ channels open or not. Means that depolarization phase of action potential stops on its own. Once Na+ channels inactivate, membrane potential is set by other open channels. If voltage-gated K+ channels are blocked by TEA, then the membrane will be (slowly) set, by leakage channels, to the resting membrane potential.

Which component has a role in the postsynaptic cell during synaptic activity: a) Vesicles filled with neurotransmitter b) chemically gated channels c) axon terminal d) calcium channels

B >> Neurotransmitter binds to receptors on the postsynaptic cell. These chemically gated channels open, allowing the transfer of the "signal" from a presynaptic neuron to the postsynaptic cell.

Which of the following choices best represents synaptic transmission? a) presynaptic cell body to dendrite to synapse b) presynaptic axon to synapse to postsynaptic axon c) presynaptic axon to synapse to dendrite or postsynaptic cell body

C

What is the role of calcium in synaptic activity?

Calcium influx into the synaptic terminal causes vesicle fusion. >>> When action potential reaches synaptic terminal, voltage-gated channels open and Ca enters cell. Ca causes vesicles to fuse with presynaptic membrane and release neurotransmitter into synaptic cleft.

_________ gated channels must be located on the receptive surfaces of neurons, where neurotransmitters can activate them.

Chemically

What type of channel on the postsynaptic membrane binds neurotransmitter?

Chemically gated channels bind a specific chemical, which causes the channel to open

What kinds of gated channels are typically found in high concentrations at the dendrites?

Chemically gated... concentrated on the receptive region of a neuron, where they open in response to neurotransmitter binding.

Predict the possible effect of a drug that totally blocks the neurotransmitter receptor on the postsynaptic membrane. For example, curare is a neurotoxin used by several South American cultures. The primary effect of curare is that acetylcholine, a major neuromuscular neurotransmitter, cannot bind at its receptor because curare is blocking it. Predict the possible effects of curare on the postsynaptic membrane and muscle.

Local graded potential and action potential transmission is blocked, and there is no response by the postsynaptic cell, the muscle. >>> Local graded potential and action potential transmission is blocked, and there is no response by the postsynaptic cell, the muscle.

What type of conduction takes place in unmyelinated axons?

Continuous conduction >>> An action potential is conducted continuously along an unmyelinated axon from its initial segment to the axon terminals. The term continuous refers to the fact that the action potential is regenerated when voltage-gated Na+‎ channels open in every consecutive segment of the axon, not at nodes of Ranvier.

How would an increase in extracellular K+ affect repolarization? Remember there is a lot more K+ inside the cell than there is outside it, even if extracellular K+ increases.

Decrease the concentration gradient, so during repolarization less K+ will diffuse out of the cell.

What is the main receptive portion of the neuron?

Dentrite; provide an enormous surface area for receiving signals from other neurons.

_______ move the membrane potential closer to threshold. Ones that cumulate a relative 15 to 20 mVmV change at the axon hillock region result in threshold being reached and the subsequent opening of the voltage-gated channels in this region.

EPSPs

A group of natural chemicals that reduce the perception of pain?

Endorphins

What does the nervous system affect?

Every one of our thoughts, actions, and emotions. Uses neurotransmitters, which are chemicals used by nervous system to send signals between neurons. different classes of neurotransmitters are grouped according to their molecular structure and each class is affected by different drugs. controls and coordinates functions throughout the body and responds to internal and external stimuli

______ synapses allow the movement of Na+ into the neuron, depolarizing the membrane.

Excitatory

T or F: Calcium ions play a role in hyperpolarization during an action potential.

False

T or F: Direct signaling involves the activation of G proteins.

False... Indirect signaling involves intracellular second messenger molecules, typically via G protein pathways.

T or F: One of the basic functions of the nervous system is to release hormones into the bloodstream that travel around the systemic blood circulation to communicate with cells in multiple locations within the body.

False; Hormones are released by endocrine organs. The nervous system does have some control over endocrine function, but the endocrine system is considered a separate signaling system.

Indirect signaling involves intracellular second messenger molecules, typically via _______ pathways. Direct signaling involves neurotransmitters that bind to ligand-gated ion channels and leads directly to changes to the polarization of the membrane.

G protein

Describe graded potentials...

Graded potentials can result in either depolarization or hyperpolarization of the membrane and vary in strength. Both EPSPs and IPSPs are graded potentials. The signal strength of each varies depending on both temporal and spatial summation.

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. >> Closing of voltage-gated channels is time dependent. Typically, the inactivation gates of voltage-gated Na+‎ channels close about a millisecond after the activation gates open. At the same time, the activation gates of voltage-gated K+‎ channels open.

During the hyperpolarization phase of the action potential, when the membrane potential is more negative than the resting membrane potential, what happens to voltage-gated ion channels?

K+ channels close. Na+ channels go from an inactivated state to a closed state. >>> K+ channels opened by depolarization. Means that as membrane potential repolarizes and then hyperpolarizes, these k+ channels close. This causes it to return to resting membrane potential via leakage channel activity. Resetting Na+ gated channels to closed (but not inactivated) state preps them for next action potential

During an action potential, hyperpolarization beyond (more negative to) the resting membrane potential is primarily due to __________.

K+ ions diffusing through voltage-gated channels. >>> Large number of voltage-gated K+ channels opening during repolarization quickly make membrane potential more - as + charged K leave cell. K+ continue to leave through open chanels as membrane potential passes (becomes more - than) the resting potential. This hyperpolarization phase of action potential is due to K+ ions diffusing through voltage-gated K+ channels. Membrane potential remains more - than resulting potential until gated K+ channels close. This period of hyperpolariation important in relieving voltage-gated Na+ channels from inactivation, readying them for another action potential.

The repolarization phase of the action potential, where voltage becomes more negative after the +30mV peak, is caused primarily by __________.

K+ ions leaving the cell through voltage-gated channels >>> The opening of voltage-gated K+ channels allows K+ ions to exit the cell, repolarizing the membrane

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

Leak channels; Na+ and K+ are ubiquitous, and they allow for the diffusion of these ions across plasma membranes.

What statement describes exocytosis?

Membrane organelles fuse with the membrane and release contents out of the cell. >>> The rise in intracellular Ca+2 binding with receptor proteins triggers the synaptic vesicles to fuse with the membrane and release contents out of the cell.

_________ cells are small and ovoid with relatively long "thorny" processes. Their processes touch nearby neurons, monitoring their health, and when they sense that certain neurons are injured or are in other trouble, the microglial cells migrate toward them. Where invading microorganisms or dead neurons are present, the microglial cells transform into a special type of macrophage that phagocytizes the microorganisms or neuronal debris.

Microglial

Which type of glial cells monitors the health of neurons, and can transform into a special type of macrophage to protect endangered neurons?

Microglial cells

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

Myelinated axons with the largest diameter

What is the direct role of neurotransmitter at a chemical synapse?

Neurotransmitter binds to receptors on postsynaptic cell membrane and allows ions to diffuse across the membrane. >>Leaves the presynaptic neuron by exocytosis and binds receptors on the postsynaptic cell membrane, opening the channels. When ions enter the postsynaptic cell, a graded potential takes place.

Are biogenic amine neurotransmitters such as dopamine considered to be proteins?

No, it simply means that dopamine has at least one amine functional group in its molecular structure.

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. >> The plasma membrane was depolarized to a positive value at the peak of the first phase of the action potential. Thus, it must repolarize back to a negative value.

_____________ myelinate axons in peripheral nervous system neurons, which allow faster propagation of action potentials down an axon. They serve an important role in neuronal function but are not directly involved in synaptic activity.

Schwann cells

Which ions are most responsible for hyperpolarization?

Potassium; excess efflux of potassium causes the hyperpolarization phase of the action potential.

Which step of nerve or muscle firing would be directly affected by a change in extracellular K+ ? The only part of nerve firing that depends directly on K+ is ________, so a change in extracellular K+ is going to affect this.

Repolarization

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)-- the baseline potential that can be recorded across the plasma membrane of an excitable cell prior to excitation.

________ is a mechanism that occurs when the presynaptic cell repackages neurotransmitter molecules from the synaptic cleft. (moving neurotransmitter back into the presynaptic neuron).

Reuptake

_______ circuits are involved in the control of rhythmic activities such as breathing, the sleep-wake cycle, and repetitive motor activities like walking. A signal travels through a chain of neurons, each feeding back to previous neurons in the pathway. The oscillation of the signal can create cyclical activity in the pathway.

Reverberating

Which statement is correct regarding the polarization of a neuronal membrane and the formation of a resting membrane potential?

Sodium/Potassium pumps maintain concentration gradients; sodium and potassium move down their concentration gradients through leakage channels. As Na+ leaks into the cell, the Na+/K+ pump actively transports Na+ back out of the neuron to maintain a gradient for Na+.

What division of the nervous system is most specifically responsible for voluntary motor control?

Somatic- composed of somatic motor nerve fibers that conduct impulses from the central nervous system to skeletal muscles. It is often referred to as the voluntary nervous system because it allows us to consciously control our skeletal muscles.

What best describes the Na+ and K+ concentrations across a neuron's plasma membrane?

The Na+ concentration is higher outside the cell compared to inside. The K+ concentration is higher inside the cell compared to outside.

You are going to record RMP from a cell using an electrode. You place your electrode and record a resting membrane potential every millisecond. You record an initial value of -70mV; however, over time you notice that your recordings become more and more positive until the RMP reaches 0mV. Assuming that Na+Na+ and K+K+ are the major determinants of RMP in this cell, which of the following could best explain your results?

The cell's Na+Na+-K+K+ ATPase pumps have stopped functioning... Since the RMP eventually becomes zero, the concentration of ions on either side of the membrane would be roughly equal. Without active processes to maintain concentration gradients, we would expect the concentration of ions on either side of the membrane to equilibrate.

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. >>> At the peak of the depolarization phase of the action potential, the inactivation gates close. Thus, the voltage-gated Na+‎ channels become absolutely refractory to another depolarizing stimulus.

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 inside surface of the plasma membrane accumulates more negative charge because of the presence of Na+ and K+ gradients and the selective permeability of the membrane to Na+ and K+.

You discover that a new chemical compound interacts with K+ voltage-dependent channels. What would be the effect on a neuron if the chemical came into contact with the axonal membrane?

The neuron would be unable to repolarize. >> K+ is used to repolarize the membrane after Na+ rushes into the membrane.

In a myelinated axon, how do the nodes of Ranvier differ from other segments of the same axon?

The nodes are more permeable to ions. >>> In myelinated axons, voltage-gated channels are largely confined to the nodes of Ranvier. This means the nodes are much more permeable to ions than the myelinated segments where voltage-gated channels are absent.

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; high number of K+ leak channels ensures membrane is highly permeable to K+. Concentration gradient for K+ means that K+ diffuses out of the cell, leaving the inside of the cell negatively charged. In contrast, the few Na+ leak channels means membrane is almost impermeable to Na+. The concentration gradient for Na+ means that Na+ will diffuse into the cell through the few leak channels that are open for it.

During action potential propagation in an unmyelinated axon, why doesn't the action potential suddenly "double back" and start propagating in the opposite direction?

The previous axonal segment is in the refractory period.

Hypothetically, what would be the most immediate effect of doubling the number of Na+ leakage channels in the plasma membrane?

The resting membrane potential would become less negative (more positive).

Suppose a drug is developed that blocks K+ leakage channels. The drug prevents ions from passing through those channels. If this drug was applied to a neuron, what would be the most immediate effect on that neuron?

The resting membrane potential would become less negative (more positive). Drug that blocks K+ leakage channels would prevent this loss of K+ ions. With fewer positive ions leaving the cell, the membrane potential wouldn't be as negative. That is, the membrane potential would immediately become less negative (more positive).

The myelin on myelinated neurons can be degraded or destroyed in diseases such as multiple sclerosis-a process called demyelination. If a myelinated neuron was affected by demyelination, how would this affect action potentials in that neuron?

The speed of action potential propagation would be slower.

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

There are many more K+ leak channels than Na+ leak channels. More leak channels means more leakiness. Permeability to K+ is greater than the permeability to Na+, so K+ contributes the most to determining the resting membrane potential.

What is the basic condition when a neuron is described as polarized?

There is a separation of positive and negative charges across a membrane. Polarization describes a condition where there is some sorting into poles. In a neuron, the inside of the cell is slightly negative compared to the positive charge (provided primarily by Na+) outside of the cell.

T or F: A neuron can have only one axon, but the axon may have occasional branches along its length.

True

T or F: As long as neurotransmitter molecules remain in the synaptic cleft, the chemically gated channels on the postsynaptic cell will continue to bind them and cause graded potentials.

True

T or F: Calcium ions in the synaptic terminal of the sending neuron have no effect on neurotransmitter molecules in the synaptic cleft.

True

T or F: The central nervous system does play a role in voluntary motor control, but it also has other functions.

True

T or F: If the neuron membrane becomes more permeable to Na+, Na+ will transport across the membrane, causing the cell to depolarize.

True; In either a graded or action potential, Na+ is transported into the cell faster than during resting potentials. As Na+ enters the cell, the inside of the cell becomes more positive, or depolarized.

_______ neurons function as sensory neurons in the peripheral nervous system.

Unipolar

What kinds of gated channels are typically found on axons?

Voltage-gated channels on the axons open in response to a change in membrane voltage.

When an action potential arrives at the end of the axon terminal, a series of events take place that result in the release of neurotransmitter from the presynaptic axon. What correctly describes the primary stimulus for vesicles to move toward the cell membrane and eventually release their contents.

Voltage-gated membrane channels open, and Ca+2 enters the cytoplasm, increasing intracellular calcium. >>> Calcium enters the cytoplasm as a result of changes in the gated channel protein, increasing cytoplasmic content of Ca+2.

What is meant by an EPSP?

a localized change in the membrane potential resulting in a less negative membrane voltage. >> EPSPs result in a local depolarization, which brings the membrane potential closer to zero.

A postsynaptic cell can be a neuron, a muscle cell, or a secretory cell. What is an example of a presynaptic cell?

a neuron is only type of presynaptic cell

Signals are passed from sending neuron to receiving neuron at a junction called a...?

a synapse

What type of event is required for an action potential to be generated?

a threshold level depolarization... The axolemma must be depolarized to threshold in order to generate an action potential.

Differences between graded potentials and action potentials

a. Graded potentials can result from the opening of chemically gated channels; action potentials require the opening of voltage-gated channels. b. Greater stimulus intensity results in larger graded potentials, but not larger action potentials. c. Graded potentials occur along dendrites, whereas action potentials occur along axons. Submit

___a___ cells, or neurolemmocytes, very specifically form myelin sheaths around the larger nerve fibers in the PNS __b__ cells very specifically line the central cavities of the brain and spinal cord and circulate cerebrospinal fluid. __c__ glial cells monitors the health of neurons, and can transform into a special type of macrophage to protect endangered neurons?

a. Schwann b. Ependymal c. Microglial

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

acetylcholine; acetylcholine is broken down by acetylcholinesterase before being returned to the presynaptic neuron's axon terminal.

Transmission at the chemical synapse (i.e., release of neurotransmitters from the presynaptic axon and binding at the postsynaptic) occurs in response to an ________.

action potential

Do muscle cells occur before or after a synapse?

after >> A muscle cell is a type of postsynaptic cell that responds to stimulation by contracting

In serial processing....

all of the neurons are activated in succession, one after the other like in a spinal reflex.

What condition will increase the diffusion of molecules, such as neurotransmitters?

an increase in the amount of neurotransmitter exocytized by the presynaptic axon.

During what part of the action potential do voltage-gated Na+ channels begin to inactivate (their inactivation gates close)?

at the end of the depolarization phase, as the membrane potential approaches its peak value >>> Voltage-gated Na+ channels are opened by depolarization and then quickly inactivated. Once inactivated, these channels cannot pass Na+ ions. At the peak of the action potential, a large number of Na+ channels are open, but they are rapidly inactivating. As the action potential enters the repolarization phase, the number of open Na+ channels continues to decrease because more and more inactivation gates close. The number of inactivated Na+ channels is greatest towards the end of the repolarization phase.

The sympathetic nervous system is a division of the _______ nervous system, which consists of visceral (_______) motor nerve fibers that regulate the activity of smooth muscle, cardiac muscle, and glands.

autonomic; involuntary

Functions of the brain stem

breathing, heart rate, blood pressure, swallowing

Events that occur during synaptic activity are listed here, but they are arranged in an incorrect order. Choose the correct order of these events below. (a) Voltage-gated calcium channels open (b) Neurotransmitter binds to receptors (c) Action potential arrives at axon terminal (d) Neurotransmitter is removed from the synaptic cleft (e) Neurotransmitter released into synaptic cleft (f) Graded potential generated in postsynaptic cell

c, a, e, b, f, d 1. Action potential arrives at axon terminal 2. Voltage-gated calcium channels open 3. Neurotransmitter released into synaptic cleft 4. Neurotransmitter binds to receptors 5. Graded potential generated in postsynaptic cell 6. Neurotransmitter is removed from the synaptic cleft

When an action potential arrives at the synaptic terminal, it causes the opening of ___________.

calcium channels

Amines lack the required ______ group needed for an amino acid.

carboxylic acid

Graded potentials are generated by ________ gated channels, whereas action potentials are produced by _________ gated channels.

chemically; voltage

Which is a factor that determines the rate of impulse propagation, or conduction velocity, along an axon?

degree of myelination of the axon

K+ exits to the extracellular fluid following _________ and Na+ influx.

depolarization

Which event would be directly affected if a neuron had a mutation that prevented the production of voltage-gated Na+ channels?

depolarization leading to action potentials.. The voltage-gated Na+ channels cause the rapid depolarization phase of the action potential.

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 >>> The Na+‎ diffusing into the axon during the first phase of the action potential creates a depolarizing current that brings the next segment, or node, of the axon to threshold.

Opening K+ or Cl- channels in a postsynaptic membrane, resulting in K+ efflux or Cl- influx, respectively, would induce __________. As the membrane potential increases and is driven farther from the axon's threshold, the postsynaptic neuron becomes less and less likely to "fire," and larger _________ currents are required to induce an action potential (AP). ___________ changes in potential are called inhibitory postsynaptic potentials (IPSPs).

hyperpolarization; depolarizing; Hyperpolarizing

When potassium channels have been open long enough to go below resting membrane potential, ________ has occurred. When a neuron is stimulated and sodium channels open, the process of ________ has begun.

hyperpolarization; depolarization

What is the function of the myelin sheath?

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

Where do most action potentials originate?

initial segment >>adjacent to the tapered end of the cell body, known as the axon hillock.initial segment

A converging circuit has many ______, but only one ______. This circuit allows different sensory stimuli to elicit a single memory.

inputs; output

There is a lot more K+ ________ the cell than there is _____ it, even if extracellular K+ increases.

inside; outside

The nervous system processes and interprets sensory input and then decides what should be done at each moment during a process called _____________?

integration

What component of the reflex arc determines the response to a stimulus?

integration center

When neurotransmitter molecules bind to receptors in the plasma membrane of the receiving neuron,

ion channels in the plasma membrane of the receiving neuron open.

A secretory cell is a type of _________ cell. A common type of secretory cell is found in a sweat gland or salivary gland. Secretory cells occur _______ a synapse.

postsynaptic; after

In a chemical synapse, the graded potential can be either excitatory or inhibitory. If its excitatory, the postsynaptic neuron will be _______ likely to generate an action potential. If the graded potential is inhibitory a postsynaptic action potential is ______ likely

more; less

Ependymal cells line many open cavities in the central nervous system (CNS). Ependymal cells have cilia on the side of the cell that face these openings. What is the most likely function of these ciliated cells?

movement and circulation of cerebrospinal fluid... cilia are an indication that the cells they appear on are moving fluids past the surface of the cells.

Saltatory propagation occurs in _________ axons, in which action potentials _________.

myelinated; move from one node of Ranvier to another Saltatory propagation is much faster than continuous propagation. The speed of propagation along an axon varies in two ways: 1) myelin sheaths limit the movement of ions across the axon membrane, thereby requiring the action potentials to "leap" from node to node during propagation, thus traveling at a greater speed; and 2) the diameter of the axon directly relates to the speed of propagation (i.e., the larger the diameter of the axon, the faster the speed of propagation).

A resting neuron has a greater ______ charge on the inside surface of the plasma membrane, and a greater ______ charge on the outside surface.

negative; positive

As positively charged potassium ions leak out of the neuron, the inside surface of membrane becomes _______ charged compared to outside surface.

negatively

Supporting cells of the nervous system are collectively called

neuroglia

The synaptic terminal of a sending neuron contains numerous vesicles filled with ______, chemicals that carry info across the synaptic cleft.

neuron transmitters

A molecule that carries information across a synaptic cleft is a

neurotransmitter

Let's consider a scenario in which the resting membrane potential changes from −−70 mVmV to +70 mVmV, but the concentrations of all ions in the intracellular and extracellular fluids are unchanged. Predict how this change in membrane potential affects the movement of Na+Na+. The electrical gradient for Na+Na+ would tend to move Na+Na+ __________ while the chemical gradient for Na+Na+ would tend to move Na+Na+ __________.

out; in

Sodium ions tend to diffuse ______ of the cell.

outside

In the brain, vision originates in the rods and cones in the retina. Separate regions of the brain decode basic information, like color, shapes, intensity of light, and there are other regions that decode information like position in space, and awareness of patterns. As you use your visual system, all of these regions are working simultaneously. This simultaneous awareness of all regions working at the same time is due to which processing pattern listed below?

parallel processing

The __________ nervous system is a division of the autonomic nervous system, which consists of visceral (involuntary) motor nerve fibers that regulate the activity of smooth muscle, cardiac muscle, and glands.

parasympathetic

Structures of the nervous system surrounding, but not part of the central nervous system are part of the

peripheral nervous system

A neuron, like any other cell, has _____ and ____ ions inside and outside.

positively and negatively charged ions

When the vesicles fuse; they dump their contents into the environment outside the presynaptic axon terminal. Some of this neurotransmitter will simply drift away; however, the majority of it will diffuse across the synapse to receptors on the __________. When the neurotransmitters bind to these receptors, the ____________ has received the "message" that the presynaptic cell has sent and can then pass it on to others.

postsynaptic cell

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

presynaptic neuron >> neurotransmitters are stored in the axon terminals of the presynaptic neuron.

Role of myelin in Schwann cells?

protects and electrically insulates nerve fibers, and it increases the transmission speed of nerve impulses.

What does the integration center do?

receives sensory information (input), determines the proper response, and then signals the appropriate effector(s) to produce the response.

The neurotransmitters affect the __________, changing the distribution of charge across its membrane.

receiving neuron

To terminate neurotransmitter effects, neurotransmitter molecules must be removed from the synaptic cleft. In addition to diffusion, what are two other mechanisms that terminate neurotransmitter activity?

reuptake and degradation

Which neuron circuit pattern is involved in the control of rhythmic activities such as breathing?

reverberating circuit

The node-to-node "jumping" regeneration of an action potential along a myelinated axon is called __________.

saltatory conduction.... Saltatory conduction is derived from the Latin word saltare, which means leaping.

In parallel processing, inputs are...

segregated into many pathways, and different parts of the neural circuitry deal simultaneously with the information delivered by each pathway.

The nervous system uses its millions of sensory receptors to monitor changes occurring both inside and outside the body. The gathered information is called what?

sensory input

A person with depression will be prescribed drug that inhibits or slows the body's uptake of the neurotransmitter ______?

serotonin plays role in bodys regulation of sleep, appetite adn mood. Drugs that block uptake of seratonin function to relieve depression and anxiety

Diffusion works better over ___________ distances, so an increased distance between the neurons would __________ affect diffusion.

shorter; negatively (slow)

What characterizes depolarization? (...penetration info the...)

small, consecutive steps of Na+ penetration into the axon along its length. >> The direction of flow for the Na+ ion is from the extracellular fluid into the cytoplasm (ICF). This occurs in small, consecutive steps.

An action potential is propagated down an axon by the opening and closing of ____________. When an action potential arrives at the synaptic terminal, it causes the opening of ___________.

sodium and potassium channels; calcium channels

Sodium potassium pump actively transports ____ ions out of the neuron and _____ ions back in, compensating for the sdoium and potassium leaks. Thus, the pump helps maintain the resting membrane potential

sodium; potassium

Ingoing messages on the postsynaptic neuron are most commonly _________ or _________.

somatic or dendritic

Two EPSPs are generated at the same time by two separate synapses, bringing the cell to threshold is example of ______ summation. Two EPSPs occur close enough in time to bring the cell to threshold is example of ______ summation.

spatial; temporal

Two consecutive neurons communicate at a _______, where they physically come together.

synapse

The small space/narrow gap between the sending neuron and the receiving neuron is the

synaptic cleft

When an action potential reaches the synaptic terminal, the vesicles fuse with the plasma membrane of the sending neuron, releasing neurotransmitters into the ____________.

synaptic cleft

An action potential in the sending neuron travels down the axon until it reaches a what?

synaptic terminal

What criterion is used to functionally classify neurons?

the direction in which the nerve impulse travels relative to the central nervous system. >>Functional classification groups neurons according to direction the nerve impulse travels relative to the central nervous system. Based on this, there are sensory neurons, motor neurons, and interneurons.

Imagine you changed the concentration of K+ outside a neuron such that the resting membrane potential changed to -80 mV (from the normal resting value of -70 mV). What have you changed?

the electrical gradient for K+ and the concentration gradient for K+. The electrical gradient for K+ is directly related to the membrane potential. Bc membrane potential has changed,

An action potential in one segment of axon causes adjacent sections of axon membrane to reach threshold through what mechanism?

the generation of local currents

What happens after neurotransmitters are released into the synaptic cleft?

they diffuse across synaptic cleft to bind to receptors in the plasma membrane of the receiving neuron. Here, the receptors

Bundles of neurons (or axons) are called ______ in the central nervous system. In the peripheral nervous systems, bundles of axons are called ______.

tracts; nerves

Characteristics of K+ leakage channels

transmembrane protein channels that are always open to allow K+K+ to cross the membrane without the additional input of energy

When calcium ions enter the synaptic terminal, they cause...

vesicles containing neurotransmitter molecules to fuse to the plasma membrane of the sending neuron.

Resting potentials are generated by the actions of leakage channels and the Na+/K+ pump and do not directly involve ____________ channels.

voltage-gated

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

voltage-gated channels