When a G protein activates the effector enzyme adenylate cyclase, the enzyme produces the second messenger cAMP.
Missing Word
cAMP
cAMP, cyclic adenosine monophosphate, is the second messenger made by adenylate cyclase. In metabotropic signaling it carries the message inside the postsynaptic cell, where it can open or close ion channels or activate enzymes.
Category: Neurotransmitters and Receptors
Question 2
Microglia are small glial cells that act as resident phagocytes, engulfing debris and pathogens in the central nervous system.
Missing Word
Microglia
Microglia are the immune cells of the central nervous system. They survey the tissue and engulf dead cells, debris and microbes, much like macrophages elsewhere in the body.
Category: Nervous Tissue
Question 3
Motor neurons and most other neurons of the central nervous system are multipolar, having a single axon and two or more receiving processes.
Missing Word
multipolar
Multipolar neurons have one axon and multiple dendrites. They are the most common structural type, including motor neurons and nearly all interneurons.
Category: Nervous Tissue
Question 4
Dendrites are the branched processes of a neuron that receive most incoming signals from other neurons at synapses.
Missing Word
Dendrites
Dendrites are the receptive processes of a neuron. Their branching provides a large surface for synapses, and they carry graded signals toward the cell body.
Category: Nervous Tissue
Question 5
White matter appears white because its axons are insulated by myelin, a lipid-rich covering formed by glial cells.
Missing Word
myelin
Myelin is the layered, lipid-rich wrapping made by oligodendrocytes in the central nervous system and Schwann cells in the peripheral nervous system. Its fat content makes regions full of myelinated axons look white.
Category: Organization of the Nervous System
Question 6
In the central nervous system, a localized cluster of neuron cell bodies is called a nucleus.
Missing Word
nucleus
A nucleus, in nervous system anatomy, is a group of neuron cell bodies inside the brain or spinal cord. The equivalent cluster in the peripheral nervous system is a ganglion.
Category: Organization of the Nervous System
Question 7
Depolarization is the change in membrane potential to a less negative value, as happens when sodium ions flow into a neuron.
Missing Word
Depolarization
Depolarization moves the membrane potential toward zero or positive values. Inward flow of positive sodium ions is the main cause of depolarization during an action potential.
Category: Action Potential
Question 8
The membrane voltage that must be reached to open enough voltage-gated sodium channels to start an action potential is called the threshold.
Missing Word
threshold
Threshold is the critical voltage, about -55 mV in a typical neuron, at which an action potential becomes self-sustaining. Graded potentials that do not reach it fade without producing an action potential.
Category: Action Potential
Question 9
The return of the membrane potential toward its negative resting value after the peak of an action potential, as potassium ions leave the neuron, is called repolarization.
Missing Word
repolarization
Repolarization is the falling phase of the action potential. Voltage-gated potassium channels open and positive potassium ions flow out, restoring the negative interior of the cell.
Category: Action Potential
Question 10
Neurotransmitter molecules are released from synaptic vesicles into the synaptic cleft by exocytosis.
Missing Word
exocytosis
Exocytosis is the fusion of a vesicle with the cell membrane to release its contents outside the cell. At the synapse it is triggered by calcium entering the axon terminal.
Category: Synaptic Transmission
Question 11
Amino acid neurotransmitters such as glutamate and glycine are cleared from the synaptic cleft mainly by reuptake into neurons or glial cells.
Missing Word
reuptake
Reuptake is the transport of a released neurotransmitter back into a presynaptic terminal or a nearby glial cell. It ends the signal for amino acid and biogenic amine neurotransmitters.
Category: Synaptic Transmission
Question 12
At the neuromuscular junction, a lower motor neuron releases the neurotransmitter acetylcholine, which produces an end plate potential in the skeletal muscle fiber.
Missing Word
acetylcholine
Acetylcholine is the neurotransmitter of the neuromuscular junction. It binds nicotinic receptors on the muscle fiber, producing the end plate potential that starts a muscle action potential.
Category: Synaptic Transmission
Question 13
A receptor that is itself a ligand-gated ion channel, opening directly when a neurotransmitter binds it, is called an ionotropic receptor.
Missing Word
ionotropic
An ionotropic receptor combines the neurotransmitter binding site and the ion channel in one protein, so it produces a fast postsynaptic response. Metabotropic receptors instead act through G proteins and second messengers.
Category: Neurotransmitters and Receptors
Question 14
GABA is an amino acid neurotransmitter whose receptors hyperpolarize the postsynaptic membrane, making it the major inhibitory neurotransmitter of the brain.
Missing Word
GABA
GABA, gamma-aminobutyric acid, is an amino acid neurotransmitter. Its receptors typically let chloride into the cell, hyperpolarizing it and making it less likely to fire.
Category: Neurotransmitters and Receptors
Question 15
Serotonin is a biogenic amine neurotransmitter synthesized from the amino acid tryptophan.
Missing Word
Serotonin
Serotonin is the biogenic amine made from tryptophan. The other major biogenic amines, dopamine, norepinephrine and epinephrine, are made from tyrosine instead.
Category: Neurotransmitters and Receptors