Study Guide for Ch. 11b

What is the correct order for the events of neurotransmitter release from the synaptic terminal? 1) Extracellular Ca2+ enters terminal and binds to sensor protein in the cytoplasm 2) Exocytosis of neurotransmitter into synaptic cleft 3) Action potential reaches axon terminal 4) Ca2+-protein complex stimulates fusion of the docked synaptic vesicle with the plasma membrane 5) Voltage-gated Ca2+ channels open

3, 5, 1, 4, 2

What is produced when depolarization of a cell membrane reaches threshold?

A new action potential is produced.

Most synapses are thought to employ more than one neurotransmitter, and synapses may be located in close proximity to each other. What receptor property prevents one neurotransmitter (e.g., norepinephrine) from activating a nearby receptor for another neurotransmitter (e.g., acetylcholine)?

Differences in receptor structure

Which of the following statements best describes the movement of ions across the plasma membrane?

Each ion species follows its own diffusion gradient, regardless of differences in the concentration of other ion species.

______________ ion channels are closed until opened by specific signals.

Gated

_______________ ion channels are always open and are responsible for the permeability of the plasma membrane to ions when the plasma membrane is unstimulated.

Leak

What effect does acetylcholine have on the postsynaptic neuron?

Ligand-gated sodium ion channels open and sodium diffuses in.

Identify the correct sequence of structures involved in the passage of information across a chemical synapse.

Presynaptic terminal; synaptic cleft; postsynaptic membrane

_______________ cannot cross the plasma membrane because they are too large to fit through the leak ion channels.

Proteins

__________ summation occurs when multiple action potentials arrive simultaneously at two different presynaptic terminals that synapse with the same postsynaptic neuron cell body.

Spatial

For a typical neuron, what limits the maximal frequency attainable of action potentials moving down an axon?

The refractory period

Neuron A stimulates Neuron B to produce action potentials at a maximum frequency. Which of the following describes the strength of the stimulus produced by Neuron A?

The stimulus could be maximal or supramaximal.

The _______ is a period of time when a membrane cannot respond to another stimulus (no matter how strong).

absolute refractory period

A recently depolarized area of a cell membrane cannot generate an action potential because of the

absolute refractory period.

Exercise: For the following three sentences, determine if the condition would best be treated with a drug that is a cholinergic agonist or an antagonist. 1. In Alzheimer's disease, there is a loss of cholinergic signal transmission in the brain, and patients are given a cholinergic _____________. 2. In myasthenia gravis, antibodies may reduce the ability of acetylcholine to bind its receptors in skeletal muscle. These patients may benefit from therapy with drugs that are cholinergic ________________. 3. A farm worker severely poisoned by an insecticide that prevents acetylcholine function will benefit from receiving a cholinergic __________. The correct answers should be, in order:

agonist; agonist; agonist

The equilibrium centers of the brain receive information from inner ear structures as well as the retina of the eyes. This arrangement is an example of a ______ circuit.

converging

Ralph is someone who tends to make counterproductive decisions in dealing with his life. He was secretly taking cocaine, a "recreational" drug that inhibits dopamine neurotransmitter reuptake. While this increase of dopamine stimulated his pleasure center, he soon found that the same dose of cocaine failed to have the intensity of effect that it gave him when he first took it. Ralph increased the dosage, and soon the same problem caused him to increase his cocaine dose again. If he stopped taking the drug, he experienced horrible withdrawal symptoms. Ralph was addicted. Homeostatic regulation of receptor levels often forms the basis of addiction. In Ralph's case the increased release of dopamine caused a progressive

decrease in dopamine receptor numbers in dopaminergic postsynaptic membranes.

As these ions enter the cell, the cell membrane undergoes _________________, with the membrane potential increasing to a peak of approximately +30mV.

depolarization

The membrane potential becoming more positive in value is called _________ whereas, _________ refers to the membrane potential becoming more negative than the resting membrane potential.

depolarization; hyperpolarization

When traveling along an axon, the cell membrane immediately ahead of an action potential depolarizes because of _________

diffusion of sodium current

Synapses in which gap junctions allow ions to diffuse quickly from cell to cell are called ______ synapses.

electrical

Structures called _________blank are involved in electrical synapses.

gap junctions

The membrane potential actually dips lower than -70mV because the potassium channels do not close quickly enough. This phase is called ________________

hyperpolarization

When a neuron releases a neuromodulator that _____ the release of neurotransmitters from another neuron, this is called presynaptic facilitation.

increases

Depolarization occurs because

more sodium ions diffuse into the cell than potassium ions diffuse out of it.

Compounds classified as ______ alter synaptic transmission by changing neurotransmitter receptor numbers or affecting the breakdown and/or removal of neurotransmitter.

neuromodulators

Imagine a motor neuron with a resting potential of -80 mV and a threshold potential of -50mV. Two graded postsynaptic potentials arrive at the trigger zone at the same time. The first is an EPSP that, by itself, would flood the trigger zone with enough Na+ ions to change the membrane potential by +45 mV. The second is an IPSP that would, by itself, cause enough K+ ions to leave to change the membrane potential of the trigger zone by -10 mV. The simultaneous arrival of these two graded potentials can be predicted to

open voltage-gated Na+ channels and result in an action potential.

A __________________ neuronal circuit is associated with complex neuronal processes, such as solving mathematical equations.

parallel after-discharge

A higher concentration of ______________ ions can be found on the inside of the plasma membrane.

potassium

As cations leave the cell, the membrane potential at that part of the membrane once again becomes negative. This phase of the action potential is called ________________________ , because the resting membrane potential is being reestablished.

repolarization

The plasma membrane is ____________ permeable and allows some, but not all, substances to pass through it.

selectively

A higher concentration of _______________ ions can be found on the outside of the plasma membrane.

sodium

The concentration of _________ ions is much greater outside the cell as compared to inside the cell, whereas the concentration of _________ ions is much greater inside the cell as compared to outside the cell.

sodium; potassium

As a result of calcium ions diffusing into the presynaptic cell,

synaptic vessels migrate to the plasma membrane and release acetylcholine.

When threshold is reached, depolarization of the same magnitude occurs for all action potentials. If threshold is not reached, an action potential does not begin at all. This describes

the all-or-none law.

Hyperpolarization, or afterpotential, occurs because

the increased potassium ion permeability lasts slightly longer than the time required to bring the membrane potential back to its resting level.

An action potential will not occur unless the membrane potential at the ___________ (the initial segment of the axon) reaches a level called ____________.

trigger zone; threshold

For each ATP molecule used, the sodium-potassium pump transports

two K+ into the cell and three Na+ out of the cell.

An action potential arriving at the presynaptic terminal causes

voltage-gated calcium ion channels to open, and calcium ions to diffuse into the cell.

As the peak of the action potential is reached, the sodium channels close and the __________________ open, allowing these ions to diffuse out of the cell.

voltage-gated potassium channels

When threshold is reached, ___________ of the initial segment open briefly, allowing ______________ to diffuse into the cell.

voltage-gated sodium channels; sodium