Chapter 4 - Neural Conduction and Synaptic Transmission Flashcards
Membrane potential
The diffrence in electrical charge between the inside and the outside of a cell
Microelectrodes
Extremely fine recording electrodes, which are used for intracellular recording
Resting potential
The steady membrane potential of a neuron at
rest, usually about −70 mV
Polarized
In the context of membrane potentials, it is a membrane potential that is not zero
Ions
Positively or negatively charged particles
Ion channels
Pores in neural membranes through which specific ions pass
Sodium-potassium pumps
An ion transporter that actively exchanges three Na+ ions inside the neuron for two K+ ions outside
Transporters
Mechanisms in the membrane of a cell that actively transport ions or molecules across the membrane
Postsynaptic potentials (PSPs)
Potentials that move the postsynaptic cell’s
membrane potential away from the resting state
Depolarize
To decrease the resting membrane potential
Hyperpolarize
To increase the resting membrane potential
Excitatory postsynaptic potentials (EPSPs)
Graded postsynaptic depolarizations, which increase the likelihood that an action potential will be generated
Inhibitory postsynaptic potentials (IPSPs)
Graded postsynaptic hyperpolarizations, which decrease the likelihood that an action potential will be generated
Graded potentials
All postsynaptic potentials (i.e., both excitatory
postsynaptic potentials and inhibitory postsynaptic potentials), are graded potentials, which means that the amplitudes of postsynaptic potentials are proportional to the intensity of the signals that
elicit them: Weak signals elicit small PSPs, and strong signals elicit large ones
Axon hillock
The conical structure at the junction between the axon and cell body
Axon initial segment
The segment of the axon where action potentials are generated— located immediately adjacent to the axon hillock
Threshold of excitation
The level of depolarization necessary to generate an action potential; usually about −65 mV
Action potential (AP)
A massive momentary reversal of a neuron’s
membrane potential from about −70 mV to about +50 mV
All-or-none responses
Responses that are not graded; they either
occur to their full extent or do not occur at all
Spatial summation
The integration of signals that originate at different sites on the neuron’s membrane
Temporal summation
The integration of neural signals that occur at
different times at the same synapse
Voltage-gated (or voltage-activated) ion channels
Ion channels that open and close in response to changes in the level of the membrane potential
Absolute refractory period
A brief period (typically 1 to 2 milliseconds) after the initiation of an action potential during which it is impossible to elicit another action potential in the same neuron
Relative refractory period
A period after the absolute refractory period during which a higher-than-normal amount of stimulation is necessary to make a neuron fire
Antidromic conduction
Axonal conduction opposite to the normal direction; conduction from axon terminals back toward the cell body
Orthodromic conduction
Axonal conduction in the normal direction—from the cell body toward the terminal buttons
Nodes of Ranvier
The gaps between adjacent myelin sheaths on an
axon
Saltatory conduction
Conduction of an action potential from one node of Ranvier to the next along a myelinated axon
Dendritic spines
Tiny protrusions of various shapes that are located on the surfaces of many dendrites
Tripartite synapse
A synapse that involves two neurons and an astroglia
Directed synapses
Synapses at which the site of neurotransmitter release and the site of neurotransmitter reception are in close proximity
Nondirected synapses
Synapses at which the site of neurotransmitter release and the site of neurotransmitter reception are not close together
Synaptic vesicles
Small spherical membranes that store neurotransmitter molecules and release them into the synaptic cleft
Golgi complex
Structures in the cell bodies and terminal buttons of neurons that package neurotransmitters and other molecules in vesicles
Coexistence
The presence of more than one neurotransmitter in the same neuron
Exocytosis
The process of releasing a neurotransmitter
Receptors
Cells that are specialized to receive chemical, mechanical, or radiant signals from the environment; also proteins that contain binding sites for particular neurotransmitters
Ligand
A molecule that binds to another molecule; neurotransmitters are ligands of their receptors
Receptor subtypes
The different types of receptors to which a particular neurotransmitter can bind
Ionotrpoic receptors
Receptors that are associated with ligand-activated ion channels
Metabotropic receptors
Receptors that are associated with signal proteins and G proteins
G proteins
Proteins that are located inside neurons (and some other cells) and are attached to metabotropic receptors in the cell membrane
Second messenger
A chemical synthesized in a neuron in response to the binding of a neurotransmitter to a metabotropic receptor in its cell membrane
Autoreceptors
A type of metabotropic receptor located on the presynaptic membrane that bind to their neuron’s own neurotransmitters
Reuptake
The drawing back into the terminal button of neurotransmitter molecules after their release into the synapse; the most common mechanism for deactivating a released neurotransmitter
Enzymatic degradation
The breakdown of chemicals by enzymes—one of the two mechanisms for deactivating released neurotransmitters
Enzymes
Proteins that stimulate or inhibit biochemical reactions without being affected by them
Acetylcholinesterase
The enzyme that breaks down the neurotransmitter acetylcholine
Gap junctions
Narrow spaces between adjacent neurons that are
bridged by fine tubular channels containing cytoplasm, through which electrical signals and small molecules can pass readily
Amino acid neurotransmitters
A class of small-molecule neurotransmitters, which includes the amino acids glutamate, aspartate, glycine, and GABA
Glutamate
The most prevalent excitatory neurotransmitter in
the central nervous system
Aspartate
An amino acid neurotransmitter
Glycine
An amino acid neurotransmitter
Gamma-aminobutyric acid (GABA)
The amino acid neurotransmitter that is synthesized from glutamate; the most prevalent inhibitory neurotransmitter in the mammalian central nervous system
Monoamine neurotransmitters
Small-molecule neurotransmitters that are synthesized from monoamines and comprise two classes: catecholamines and indolamines
Dopamine
One of the three catecholamine neurotransmitters
Epinephrine
One of the three catecholamine neurotransmitters
Norepinephrine
One of the three catecholamine neurotransmitters
Serotonin
An indolamine neurotransmitter; the only member of this class of monoamine neurotransmitters found in the mammalian nervous system
Catecholamines
The three monoamine neurotransmitters that are
synthesized from the amino acid tyrosine: dopamine, epinephrine, and norepinephrine
Indolamines
The class of monoamine neurotransmitters that are synthesized from tryptophan; serotonin is the only member of this class found in the mammalian nervous system
Acetylcholine
A neurotransmitter that is created by the addition of an acetyl group to a choline molecule
Soluble-gas neurotransmitters
A class of unconventional neurotransmitters that includes nitric oxide and carbon monoxide
Nitric oxide
A soluble-gas neurotransmitter
Carbon monoxide
A soluble-gas neurotransmitter
Endocannabinoids
A class of unconventional neurotransmitters that are chemically similar to the active components of marijuana
Anandamide
The first endogenous endocannabinoid to be
discovered and characterized
Neuropeptide transmitters
Peptides that function as neurotransmitters, of which about 100 have been identified; also called
neuropeptides
Pituitary peptides
One of the five categories of neuropeptide transmitters; it contains neuropeptides that were first identified as hormones released by the pituitary
Hypothalamic peptides
One of the five classes of neuropeptide transmitters; it consists of those first identified as hormones released by the hypothalamus
Brain-gut peptides
Neuropeptides that were first discovedred in the gut
Opioid peptides
One of the five classes of neuropeptide transmitters; it consists of those with a structure similar to the active ingredients of opium
Miscellaneous peptides
One of the five categories of neuropeptide transmitters; it include those neuropeptide transmitters that don’t fit into one of the other four categories
Agonists
Drugs that facilitate the effects of a particular
neurotransmitter
Antagonists
Drugs that inhibit the effects of a particular
neurotransmitter
Receptor blockers
Antagonistic drugs that bind to postsynaptic receptors without activating them and block the access of the usual neurotransmitter
Atropine
A receptor blocker that exerts its antagonistic effect by binding to muscarinic receptors
Botox
Botulinium toxin; a neurotoxin released by bacterium often found in spoiled food. It blocks the release of acetylcholine at neuromuscular junctions and has applications in medicine and cosmetics
Periaqueductal gray (PAG)
The gray matter around the cerebral aqueduct, which contains opiate receptors and activates a descending analgesia circuit
Endogenous
Naturally occurring in the body (e.g., endogenous
opioids)
Enkephalins
The first class of endogenous opioids to be discovered
Endorphins
A class of endogenous opioids
