Anatomy and Physiology Chapter 11

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) Action potential arrives at axon terminal (a) Voltage-gated calcium channels open (e) Neurotransmitter released into synaptic cleft (b) Neurotransmitter binds to receptors (f) Graded potential generated in postsynaptic cell (d) Neurotransmitter is removed from the synaptic cleft

Characteristics of Neurons

-They conduct impulses -They have an exceptionally high metabolic rate -They have extreme longevity

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

A neuron A neuron is the only type of presynaptic cell. Neurons release neurotransmitters, effectively changing an electrical signal or action potential into a chemical signal that can communicate across the synaptic cleft to the postsynaptic cell.

The concentration of ions in the chemical environment surrounding the neurons must be tightly regulated for neurons to function properly. Which of the following cells is most responsible for this?

Astrocytes

A change in membrane potential from -70mV to - 40 mV is:

Depolarization

The effect of acetylcholine can be stimulating or inhibiting. Which of the following gives the best explanation for why this is so?

Different postsynaptic cells will have different receptors.

Opening K+ or Cl- channels in a postsynaptic membrane would produce an inhibitory postsynaptic potential (IPSP).

True Opening K+ or Cl- channels in a postsynaptic membrane, resulting in K+ efflux or Cl- influx, respectively, would induce hyperpolarization. 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 depolarizing currents are required to induce an action potential (AP). Hyperpolarizing changes in potential are called inhibitory postsynaptic potentials (IPSPs).

Electrical coupling by gap junctions is present in:

Unitary smooth muscle

The central canal of the spinal cord is analogous to what part of the brain?

Ventricles

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

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

Which of the following peripheral nervous system (PNS) neuroglia form the myelin sheaths around larger nerve fibers in the PNS?

Which of the following peripheral nervous system (PNS) neuroglia form the myelin sheaths around larger nerve fibers in the PNS? Schwann cells (also called neurolemmocytes) surround all nerve fibers in the PNS and form myelin sheaths around the larger fibers. Myelin protects and electrically insulates nerve fibers, and it increases the transmission speed of nerve impulses.

What type of channel on the postsynaptic membrane binds neurotransmitter?

a chemically gated channel Chemically gated channels bind a specific chemical, which causes the channel to open. At chemical synapses, neurotransmitter molecules are released by the presynaptic neuron and bind to chemically gated channels on the postsynaptic cell membrane. The opening of these channels allows ions to diffuse across the membrane, causing a graded potential in the postsynaptic cell.

If a postsynaptic cell is stimulated to threshold by temporal summation this implies that ________.

a presynaptic neuron is sending frequent EPSP

What ion is entering the axon terminal at A, and what effect does it have?

Ca2+, which then causes release of neurotransmitter from the axon terminal Submit

what is the role of calcium in synaptic activity?

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

Which component has a role in the postsynaptic cell during synaptic activity?

Chemically gated channels 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.

What type of conduction takes place in unmyelinated axons?

Continuous

The presynaptic neuron releases neurotransmitters in response to an influx of _____ ions.

calcium

A major difference between smooth muscle fibers and skeletal muscle fibers in terms of calcium influx is that ________.

calcium ion influx occurs mostly from the extracellular fluid in smooth muscle

Calcium binds to this substance in smooth muscle contraction.

calmodulin

Neurotransmitters are important in functioning of _____ synapses.

chemical

Smooth muscle contains ________ that correspond to the Z discs of skeletal muscle.

dense bodies

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

What are the neuroglial cells that line the ventricles of the brain?

ependymal cells

by which method does the structure at B release neurotransmitter

exocytosis

What does the central nervous system use to determine the strength of a stimulus?

frequency of action potentials

Smooth muscle cells can contract as a unit because of the presence of __________.

gap junctions

Where do most action potentials originate?

initial Segement

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

integration center

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

Saltatory conduction is made possible by ________.

myelin sheath, schwann cells

The interior surface of a neuron's plasma membrane at resting membrane potential will have a ________.

negative charge and contains less sodium than outside of the cell

Destruction of which of the neuroglial cell types leads to the disease multiple scleroses (MS)?

oligodendrocytes

Myelin sheaths in the CNS are produced by the ________.

oligodendrocytes

All of the following are neuroglial cells except ________.

perikaryons

Inhibitory postsynaptic potentials cause the postsynaptic membrane to become more permeable to ________.

potassium

In addition to diffusion, what are two other mechanisms that terminate neurotransmitter activity?

reuptake and degradation To terminate neurotransmitter effects, neurotransmitter molecules must be removed from the synaptic cleft. Reuptake does this by moving neurotransmitter back into the presynaptic neuron. Diffusion causes neurotransmitter to drift away from the synaptic cleft. Degradation occurs when enzymes break down neurotransmitter. 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.

The box labeled D illustrates three mechanisms by which the effects of a neurotransmitter may be terminated. Which of the following mechanisms is NOT included in the figure?

reuptake of the neurotransmitter by transport into the postsynaptic cell

During membrane repolarization, there is a decrease in the membrane permeability to which ion?

sodium

If a postsynaptic neuron is stimulated to threshold by spatial summation this implies that ________.

the postsynaptic cell has many synapses with many presynaptic neurons

A membrane maintains its resting potential mainly because of _________.

the sodium-potassium pump

Reflexes are rapid, automatic responses to stimuli that will produce the same effect every time.

true

What opens first in response to a threshold stimulus?

voltage-gated Na+ channels

People with multiple sclerosis (MS) experience many challenging symptoms. Which statement best explains one cause of these difficulties?

Loss of oligodendrocytes in the central nervous system results in absence of the myelin sheath of neuronal axons, impairing rapid saltatory conduction. Submit

All of the following are found in the PNS EXCEPT ________.

Microglia

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 the postsynaptic cell membrane and allows ions to diffuse across the membrane. Neurotransmitter 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.

In multiple sclerosis, the cells that are the target of an autoimmune attack are the _________.

Oligodendrocytes

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. Submit

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

Nerve impulses are sent to slow the heart's rate of contraction. The nerve fibers sending these signals will most likely belong to which division of the nervous system?

Parasympathetic division

Neurotransmitters are removed from the synaptic cleft by all of the following except ______.

Presynapticinhibition

You are working on a new medication to selectively kill cancer cells. You test the drug on a culture of normal neurons to check for any side effects. Despite the presence of the drug, a normal resting membrane potential of −70 mV is maintained. Look at each of the figures below to analyze how the drug might be affecting the neuron. Figure A shows neuron activity under normal, or control, conditions (without the drug). Figure B shows neuron activity that has been altered due to exposure to the drug. Based on these results, the drug is most likely __________.

Preventing Na+ gated channels from opening

What type of neural processing involves the input traveling along one pathway, called a reflex arc?

Serial Processing

How does demyelination in the CNS due to multiple sclerosis typically affect nerve impulse transmission?

Slow sit down due to less myelin

While studying for an exam you reach for your coffee. To extend your arm your _______ nervous system is activated.

Somatic

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

Somatic Nervous system

__________ has occurred when a neuron is stimulated by more than one terminal.

Spatial Summation

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.

Which of the following best explains the convolutions and folds present in an adult brain?

The highly folded convolutions and flexures increase the brain's surface area and allows the brain to fit into the cranium

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 characterizes depolarization, the first 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. Submit

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.

Select the correct statement regarding chemical synapses. The release of neurotransmitter molecules gives cells the property of being electrically coupled. The synaptic cleft uses the action potential to transmit a chemical signal to the postsynaptic cell. Cells with gap junctions use chemical synapses. Neurotransmitter receptors are located on the axons terminals of cel

The synaptic cleft uses the action potential to transmit a chemical signal to the postsynaptic cell.

Suppose that both stimuli seen in these graphs happened equally at the same time on a postsynaptic membrane as a result of two different synapses. Which of the following best describes the result?

There would be little or no graded potential. In order for a graded potential to occur, there must be an overall change in membrane potential. Due to spatial summation, these stimuli would cancel each other.

Which of the following is NOT a characteristic of neurons?

They are mitotic

Which of the following statements is false in regard to action potentials?

They travel more slowly on myelinated fibers

A postsynaptic potential is a graded potential that is the result of a neurotransmitter released into the synapse between two neurons.

True

In myelinated axons the voltage-regulated sodium channels are concentrated at the nodes of Ranvier.

True

During the relative refractory period:

Exceptionally strong stimuli could trigger action potentials

Neurotransmitter is released from presynaptic neurons through what mechanism?

Exocytosis Neurotransmitter molecules are released from vesicles that fuse with the plasma membrane through exocytosis. Note that "exo-" means "outside" and "cytosis" means "cell." Once released, neurotransmitter diffuses across the synaptic cleft.

The hindbrain (rhombencephalon) divides into the metencephalon and the myelencephalon.

FALSE

What supplement should pregnant women take because it is important for development of the neural tube in a baby?

Folate

Collections of nerve cell bodies outside the central nervous system are called ________.

Ganglia

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.