Biol 176 - For Exam 4 - Chap 48

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Most of the neurons in the human brain are

interneurons.

Most of the organelles in a neuron are located in the

cell body

In certain large animals, this type of neuron can extend beyond one meter in length

a sensory neuron.

For a neuron with an initial membrane potential at -70 mV, an increase in the movement of potassium ions out of that neuron's cytoplasm would result in

hyperpolarization of the neuron.

Though the membrane of a "resting" neuron is highly permeable to potassium ions, its membrane potential does not exactly match the equilibrium potential for potassium because the neuronal membrane is

slightly permeable to sodium ions.

The operation of the sodium-potassium "pump" moves

sodium ions out of the cell and potassium ions into the cell.

A "resting" motor neuron is expected to

exhibit a resting potential that is more negative than the "threshold" potential.

The "threshold" potential of a membrane

is the minimum depolarization needed to operate the voltage-gated sodium and potassium channels.

Action potentials move along axons

more rapidly in myelinated than in non-myelinated axons.

A toxin that binds specifically to voltage-gated sodium channels in axons would be expected to

prevent the depolarization phase of the action potential.

After the depolarization phase of an action potential, the resting potential is restored by

the opening of voltage-gated potassium channels and the closing of sodium activation gates.

In the sequence of permeability changes for a complete action potential, the first of these events that occurs is

the opening of voltage-gated sodium channels.

Saltatory conduction is a term applied to conduction of impulses

jumping from one node of Ranvier to the next in a myelinated neuron.

The surface on a neuron that discharges synaptic vesicles is the

presynaptic membrane.

Neurotransmitters are released from axon terminals via

exocytosis

Neural transmission across a mammalian synaptic gap is accomplished by

impulses causing the release of a chemical signal and its diffusion across the gap.

The observation that the acetylcholine released into the junction between a motor neuron and

a ligand-gated sodium channel.

An inhibitory postsynaptic potential (IPSP) occurs in a membrane made more permeable to

potassium ions.

The activity of acetylcholine in a synapse is terminated by

its degradation by a hydrolytic enzyme on the postsynaptic membrane.

Neurotransmitters categorized as inhibitory would are expected to

hyperpolarize the membrane.

When several EPSPs arrive at the axon hillock from different dendritic locations,

spatial summation.

When several IPSPs arrive at the axon hillock rapidly in sequence from a single dendritic location, hyperpolarizing the postsynaptic cell more and more and thus preventing an action potential, this is an example of

temporal summation.

Assume that a single IPSP has a negative magnitude of - 0.5 mV at the axon hillock, and that a single EPSP has a positive magnitude of + 0.5 mV. For a neuron with initial membrane
Copyright © 2008 Pearson Education, Inc. 8
potential is -70 mV, the net effect of the simultaneous arrival of 6 IPSPs and 2 EPSPs would be to move the membrane potential to

-72 mV.

The primary neurotransmitter from the parasympathetic system that influences its autonomic

acetylcholine.

The heart naturally slows when responding to

acetylcholine.

What happens when a neuron's membrane depolarizes?

The neuron's membrane voltage becomes more positive.

Why are action potentials usually conducted in only one direction along an axon?

The brief refractory period prevents reopening of voltage-gated Na+ channels.

A common feature of action potentials is that they

are triggered by a depolarization that reaches the threshold.

Which of the following is a direct result of depolarizing the presynaptic membrane of an axon terminal?

Voltage-gated calcium channels in the membrane open.

Where are neurotransmitter receptors located?

on the postsynaptic membrane

Temporal summation always involves

myelinated axons.

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