chapter 4 Flashcards
membrane potential
the difference in electrical charge between the inside and the outside of a cell
resting potential
the steady membrane potential of about -70 mV is called the neuron’s resting potential
ions
the salts in neural tissue separate into positively and negatively charged particles called ions
ion channels
These unequal distributions of Na + and K+ ions are maintained even though there are specialized pores
natrium
sodium jions
kalium
potassium ions
electrostatic pressure
from the resting membrane potential
because opposite charges attract, the -70 mV charge attracts the positively charged Na+ ions into resting neurons
concentration gradient
they are more likely to move from areas of high concentration to areas of low concentration than vice versa
sodium-potassium pump
ion transport is performed by mechanisms in the cell membrane that continually exchange three Na+ ions inside the neuron for two K+ ions outside
transporters
mechanisms in membrane of a cell that actively transport ions or molecules across the membrane
neurotransmitters
chemicals that diffuse across the synaptic clefts and interact with specialized receptor molecules on the receptive membranes of the next neurons in the circuit
depolarize
decrease the resting membrane potential, from -70 to -67 mV, for example
hyperpolarize
increase the resting membrane potential from -70 to -72 mV
EPSP’s
excitatory postsynaptic potentials
increase the likelihood that the neuron will fire
IPSPs
inhibitory postsynaptic potentials
decrease the likelihood that the neuron will fire
axon hillock
the conical structure at the junction between the cell body and the axon
threshold of excitation
-65 mV
when an action potential is generated
action potential
massive but momentary - lasting for 1 millisecond - reversal of the membrane potential from about -70 to about +50
all or none response
the action potential either occurs to their full extent or do not occur at all
integration
adding or combining a number of individual signals into one overall signal
done through spatial summation and temporal summation
voltage-activated ion channels
ion channels that open or close in response to changes in the level of the membrane potential
absolute refractory period
a brief period of about 1 to 2 milliseconds after the initiation of an action potential during which it is impossible to elicit a second one
relative refractory period
the period in which it is possible to fire the neuron again but only by applying higher-than normal levels of stimulation
the end of the relative refractory period is the point at which the amount of stimulation necessary to fire a neuron returns to baseline
myelin
insulated from the extracellular fluid by segments of fatty tissue
nodes of ranvier
the gaps between adjacent myelin segments
saltatory conduction
the transmission of action potentials in myelinated axons
dendritic spines
nodules of various shapes that are located on the surfaces of many dendrites
synaptic vesicles
packages small- molecule neurotransmitters and are typically synthesized in the cytoplasm of the terminal button
microtubules
transport the vesicles to the terminal buttons
at a rate of about 40 centimeters per day
exocytosis
the process of neurotransmitter release
Ca2+
when stimulated by action potentials these channels open and Ca2+ enter the button
the entry causes synaptic vesicles to fuse with the presynaptic membrane and empty their contents into the synaptic cleft
receptors
a protein that contains binding sites for only particular neurotransmitters
neurotransmitter can influence only those cells that have receptors for it
ligand
any molecule that binds to another
ionotropic receptors
associated with ligand-activated ion channels
metabotropic receptors
G proteins - Guanosine-triphosphate-sensitive proteins
receptor activates G protein
Does not directly open ion channels
Requires metabolism
Effects are slower,longer-lasting, more diffuse and more varied than ionictropic receptors
autoreceptors
metabotropic receptors that have two unconventional characteristics
they bind to their neurons own neurotransmitter molecules
they are located on the presynaptic, rather than the postsynaptic, membrane
reuptake
the majority of neurotransmitters, once released, are almost immediately drawn back into the presynaptic buttons by transporter mechanisms
enzymatic degradation
neurotransmitters are degraded in the synapse by the action of enzymes
amino acid neurotransmitters: glutamate, GABA, glycine
common in the proteins we consume, whereas GABA is synthesized by a simple modification of the structure of glutamate
Glutamate is the most prevalent excitatory neurotransmitter in the mammalian central nervous system
GABA is the most prevalent inhibitory neurotransmitter
Monoamines: dopamine,serotonin, epi/norepipephrine
catecholamines
each is synthesized from the amino acid tyrosine
Tyrosine is converted to L-dopa which in turn is converted to dopamine
Catecholamines
Catecholamines
synthesized from the amino acid tyrosine
indoamines
different structure than catecholamines
adrenergic
release epinephrine
noradrenergic
release norepinephrine
acetylcholine
small molecule neurotransmitter
broken down in the synapse by the enzyme acetylcholinesterase
cholinergic
neurons that release acetylcholine
unconventional neurotransmitters
act in ways that are different from those that neuroscientists have come to think of as typical for such substances
nitric oxide
soluble-gas neurotransmitters
produced in the natural cytoplasm and immediately diffuse through the cell membrane into extra-cellular fluid and then into nearby cells
endocannabinoids
are neurotransmitters that are similar to delta-9-tetrahydrocannabinol
the main psychoactive constituent of marijuana
synthesized from fatty compounds in the cell membrane; they tend to be released from the dendrites and cell body
tend to have most of their effects on presynaptic neurons inhibiting subsequent synaptic transmission
THC
main psychoactive constituent of marijuana
anandamide
produced immediately before they are released
like soluble gases
agonists
drugs that facilitate the effects of a particular neurotransmitter
antagonists
drugs that inhibit the effects of a particular neurotransmitter
atropine
receptor blocker that exerts its antagonist effect by binding to muscarinic receptors, thereby blocking the effects of acetylcholine on them
curare
an extract of a certain class of woody vines
South American natives have long used curare on the tips of darts they used to kill their game
receptor blocker at cholinergic synapses, but it acts at nicotinic receptors
by binding to nicotinic receptors, blocks transmission at neuromuscular junctions
thus paralyzing them
botox
neurotoxin released by a bacterium often found in spoiled food
blocks the release of acetylcholine at neuromuscular junctions and is thus a deadly poison
endogenous opioids
occurring naturally within the body
all endogenous opioid neurotransmitters are neuropeptides and their receptors are metabotropic
morphine
addictive
effective analgesic (painkiller)
Periaqueductal gray (PAG)
area of the brain stem around the cerebral aqueduct, which connects the third and fourth ventricles; this part of the brain stem is PAG
