Neurons L29

A&P: Which of the following best describes the role of calcium in synaptic activity? Calcium diffuses across the synaptic cleft to bind with receptors on the postsynaptic cell. Calcium enters the postsynaptic cell and causes depolarization. Calcium enters the presynaptic cell and causes the release of ACh. Calcium breaks down acetylcholine.

Calcium enters the presynaptic cell and causes the release of ACh. As a presynaptic action potential reaches the synaptic terminal, voltage-gated calcium channels open. The open calcium channels allow calcium to diffuse into the synaptic terminal. This calcium influx causes synaptic vesicles to fuse with the presynaptic membrane. The content of these vesicles - acetylcholine - is then released into the synaptic cleft. Although this process consists of many steps, it happens quickly. It only takes 0.2-0.5 msec from when an action potential arrives at the synaptic terminal to when depolarization starts to occur in the postsynaptic cell.

A&P: Which of the following is defined as a graded hyperpolarization of the postsynaptic membrane? resting potential IPSP EPSP equilibrium potential

IPSP

A&P: ________ channels open or close in response to physical distortion of the membrane surface.

Mechanically gated

A&P: Which of the following definitions or descriptions is correct? Temporal summation occurs when a single synapse depolarizes once. Spatial summation involves multiple synapses that are active simultaneously. An inhibitory postsynaptic potential is a graded depolarization of the postsynaptic membrane. An excitatory postsynaptic potential is a graded hyperpolarization of the postsynaptic membrane.

Spatial summation involves multiple synapses that are active simultaneously

A&P: The small space between the sending neuron and the receiving neuron is the

Synaptic cleft

A&P: Curare is a drug that prevents ACh from binding to ACh receptors. How would you expect curare to affect events at a cholinergic synapse? Acetylcholinesterase (AChE) would not break down ACh. Vesicles would not release ACh. Calcium would not diffuse into the presynaptic neuron. The postsynaptic cell would not depolarize.

The postsynaptic cell would not depolarise Depolarization of the postsynaptic membrane is due to sodium ions entering the cell through open ACh receptors. These receptors only open when ACh is bound. Because curare prevents this binding, curare would also prevent the depolarization of the postsynaptic cell. Curare has similar effects at the neuromuscular junction, where curare blocks synaptic activity and prevents muscle contraction.

A&P: The acetylcholine receptor is an example of what type of channel?

a chemically gated channel Chemically gated channels open when they bind a specific molecule. This binding causes the channel to open, which allows ions to pass. The acetylcholine receptor is an example of this channel type because it opens when acetylcholine binds. As its name implies, the acetylcholine receptor "receives" acetylcholine before opening.

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

A&P: The effect that a neurotransmitter has on the postsynaptic membrane depends on the frequency of neurotransmitter release. the nature of the neurotransmitter. the characteristics of the receptors. the quantity of neurotransmitters released. all of the above

all of the above

A&P: IPSPs (inhibitory postsynaptic potentials) block the efflux of potassium ions. increase membrane permeability to sodium ions. are graded hyperpolarizations. block the efflux of calcium ions. are graded depolarizations.

are graded hyperpolarisations

A&P: The site in the neuron where EPSPs and IPSPs are integrated is the

axon hillock.

A&P: The ion that triggers the release of acetylcholine into the synaptic cleft is

calcium.

A&P: ________ open or close in response to binding specific molecules.

chemically gated

A&P: 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.

A&P: What causes calcium channels in the synaptic knob to open? the binding of calcium depolarization of the presynaptic membrane due to graded potentials depolarization of the presynaptic membrane due to an arriving action potential the binding of ACh

depolarization of the presynaptic membrane due to an arriving action potential When an action potential reaches the synaptic knob, voltage-gated calcium channels open. This allows Ca2+ to enter the neuron, causing ACh-containing vesicles to fuse with the plasma membrane. At rest, the concentration of calcium is very low inside the synaptic knob. This means that the small amount of calcium entering through channels can quickly change the calcium concentration several-fold.

A&P: In a(n) ________ synapse, current flows directly between cells.

electrical

A&P: Neurotransmitters exit the presynaptic cell via __________.

exocytosis Neurotransmitters, such as ACh, exit from vesicles that fuse with the plasma membrane of the presynaptic cell. In the case of ACh-containing vesicles, approximately 3000 neurotransmitter molecules are contained within each vesicle.

A&P: EPSPs (excitatory postsynaptic potentials) occur when

extra sodium ions enter a cell.

A&P: Which of the following is the most important excitatory neurotransmitter in the brain? noradrenaline serotonin glycine gamma aminobutyric acid glutamate

glutamate

A&P: Where is acetylcholinesterase (AChE) primarily located?

in the synaptic cleft AChE degrades acetylcholine to terminate synaptic activity. To degrade or hydrolyze ACh, AChE must also be located in the synaptic cleft. The speed at which this occurs (<20 msec) allows synaptic activity to be finely controlled.

A&P: When neurotransmitter molecules bind to receptors in the plasma membrane of the receiving neuron, the receiving neuron becomes more negative inside. ion channels in the plasma membrane of the receiving neuron open. ion channels in the plasma membrane of the sending neuron open. the receiving neuron becomes more positive inside. vesicles in the synaptic terminal fuse to the plasma membrane of the sending neuron.

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

A&P: A molecule that carries information across a synaptic cleft is a......

neurotransmitter

A&P: In a synapse, neurotransmitters are stored in vesicles located in the __________

presynaptic neuron

A&P: After acetylcholinesterase acts, the synaptic knob

reabsorbs the choline.

A&P: When ACh receptors open, what ion causes depolarization of the postsynaptic membrane?

sodium Positively charged sodium ions cross the postsynaptic membrane through open ACh receptors. This causes depolarization""the inside of the postsynaptic cell becomes less negative relative to the outside. If the depolarization is sufficient for the postsynaptic neuron to reach threshold, an action potential will be generated.

A&P: The buildup of depolarization when EPSPs arrive in rapid succession is called ________ summation.

temporal

A&P: When a second EPSP arrives at a single synapse before the effects of the first have disappeared, what occurs?

temporal summation

A&P: Binding of the neurotransmitter to its receptor causes the membrane to __________.

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

A&P If a signal from a sending neuron makes the receiving neuron more negative inside, the receiving neuron immediately generates an action potential. the sending neuron becomes more negative inside. the sending neuron becomes more positive inside. the receiving neuron is more likely to generate an action potential. the receiving neuron is less likely to generate an action potential.

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

A&P: When calcium ions enter the synaptic terminal, neurotransmitter molecules are quickly removed from the synaptic cleft. they cause vesicles containing neurotransmitter molecules to fuse to the plasma membrane of the sending neuron. the inside of the receiving neuron becomes more positive. the inside of the receiving neuron becomes more negative. they cause an action potential in the sending neuron.

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

A&P: An action potential releases neurotransmitter from a neuron by opening which of the following channels? voltage-gated K+ channels chemically gated Ca2+ channels voltage-gated Na+ channels voltage-gated Ca2+ 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.

A&P: Choose the correct sequence of events that occur at a cholinergic synapse. 1 - ACh binds to sodium channel receptors. 2 - The synaptic knob reabsorbs choline from the synaptic cleft. 3 - ACh is released through the exocytosis of synaptic vesicles. 4 - An arriving action potential depolarizes the synaptic knob. 5 - ACh is broken down by AChE.

4-3-1-5-2

A&P: Which of the following best describes how ACh causes depolarization of the postsynaptic membrane? ACh opens ACh receptors. ACh opens voltage-gated calcium channels. ACh causes vesicles to fuse, releasing neurotransmitter into the synaptic cleft. ACh activates acetylcholinesterase (AChE).

ACh opens ACh receptors. ACh receptors on the postsynaptic membrane are chemically gated ion channels. These channels open when they bind ACh. Once open, these channels allow sodium to enter, depolarizing the cell. Chemically gated channels are often called "receptors" because they must "receive" (or bind) a particular chemical before they can open.

A&P: What is the primary role of acetylcholinesterase (AChE) at a cholinergic synapse?

AChE degrades acetylcholine in the synaptic cleft. Degradation of ACh and removal of acetylcholine components, allows the postsynaptic cell to return to its resting potential after depolarization.

A&P: Which of the following would not have an effect on synaptic function? block neurotransmitter binding to receptors prevent neurotransmitter inactivation interfere with neurotransmitter reuptake interfere with neurotransmitter synthesis All of the above would affect synaptic function.

All of the above

A&P: Which of the following best describes the order of events in synaptic activity?

An action potential arrives and depolarizes the synaptic knob. Extracellular calcium enters the synaptic knob, triggering exocytosis of ACh. ACh binds to receptors and depolarizes postsynaptic membrane. ACh is removed by AChE.