Chapter 12 Part 5 Flashcards
what are 4 classes of opioids in the CNS
endorphins
enkephalins
endomorphins
dynorphins
what is the primary function of opioids and how do they accomplish this
to relieve pain
they inhibit the release of a neurotransmitter called substance P at synapses that relay pain sensations
______ have far more powerful pain-relieving effects than morphine or other opioids
dymorphins
do neuromodulators have short or long term effects?
long term effects that are relatively slow to appear
opioids are _____
neuromodulators
do responses triggered by neuromodulators have 1 step??
NO a number of steps and intermediary compounds
do neuromodulators affect the pre, post, (synaptic membrane) or both?
both
are neuromodulators released alone or with a neurotransmitter?
can be either
functionally, neurotransmitters and neuromodulators fall into 1 of 3 groups:
-compounds that have a DIRECT EFFECT on the membrane potential
-compounds that have an INDIRECT EFFECT on the membrane potential
-lipid-soluble gasses that exert their effects inside the cell
neuromodulators/neurotransmitters that have a direct effect on membrane potential function by….
opening or closing gated ion channels
give examples of neurotransmitters/neuromodulators that have a DIRECT EFFECT on membrane potential and thus function by opening/closing ion gated channels.
ACh
glycine
aspartate
what does ionotropic effects mean and what compounds exhibit this
ionotropic effects = altering ion movement across the membrane
ACh
glycine
aspartate
what are “first messengers”.
explain
first messengers=neurotransmitters
they deliver the message to receptors on the plasma membrane or within the cell
what are second messengers?
ions or molecules that are produced or released inside of the cell WHEN A FIRST MESSENGER BINDS TO ITS RECEPTOR
how do compounds that have an INDIRECT effect on membrane potential work?
they work through intermediaries – second messengers
a few neurotransmitters have both direct and indirect effects.
name them and state what the “direct effects” are called and what the “indirect effects” are called
glutamate
GABA
Norepinephrine
serotonin
direct effects = ionotropic
indirect effects = metabotropic
what exactly are indirect (metabotropic) effects?
involve changes in the metabolic activity of the postsynaptic cell
in compounds that bind to receptors on the plasma membrane, the link between the first messenger and the second messenger is…..
a G protein
when G protein binds Adenylate Cyclase, what secondary messenger is involved and what does it trigger?
CAMP (cyclic AMP)
can open membrane channels, inactivate intracellular enzymes, or both (depending on the nature of the postsynaptic cell)
what are 2 examples of neurotransmitters that have INDIRECT EFFECTS VIA INTRACELLULAR ENZYMES
NO and CO
they enter the cell and bind to enzymes that then promote the appearance of second messengers that can affect cellular activity
does a single neuron receive information across only 1 synapse?
no – a single neuron can receive information across thousands of synapses
the net effect on the transmembrane potential of the _______ determines how the neurons respond.
axon hillock
if the net effect is depolarization at the axon hillock, what will happen?
that depolarization affects the transmembrane potential at the initial segment. if threshold is reached at the initial segment, an action potential is generated and propagated along the axon
this integration process, which determines the rate of action potential generation at the initial segment, is the simplest level of __________ in the nervous system
information processing
what are postsynaptic potentials?
graded potentials that develop in the postsynaptic membrane in response to a neurotransmitter
what are the 2 major types of postsynaptic potentials that develop at neuron-neuron synapses?
excitatory postsynaptic potentials and inhibitory postsynaptic potentials
what does EPSP stand for
excitatory postsynaptic potential
explain what an excitatory post synaptic potential is (EPSP)
A graded depolarization caused by the arrival of a neurotransmitter at the postsynaptic membrane
an EPSP results from…
the opening of the chemically gated membrane channels that lead to depolarization of the plasma membrane
give a specific example of an excitatory postsynaptic potential (EPSP)
the graded depolarization that is produced by the binding of ACh is an EPSP
what is an IPSP (inhibitory postsynaptic potential)
a graded hyperpolarization of the postsynaptic membrane
for instance, an opening of chemically gated potassium channels may result in an IPSP
while hyperpolarization continues, (potassium continually leaves the cell), the neuron is said to be INHIBITED.
WHY?
because a larger than usual depolarizing stimulus is needed to bring the membrane potential to threshold
before an action potential will arise in an initial segment, local currents must depolarize that region by at least ___ mV
10
will a single EPSP result in an action potential?
NO
an individual EPSP only produces a depolarization of around 0.5mV
what is summation?
when individual EPSPs combine which integrates the effects of all the graded potentials that affect one portion of the plasma membrane.
“summation integrates the effects of all graded potentials that affect one portion of the plasma membrane”
the “graded potentials” are…..
EPSP’S, IPSP’S or both
what are the 2 forms of summation
temporal summation and spatial summation
differentiate between temporal summation and spatial summation
TEMPORAL SUMMATION = the addition of stimuli occurring in rapid succession at a SINGLE SYNAPSE
SPATIAL SUMMATION = simultaneous stimuli applied at DIFFERENT locations have a cumulative effect on the transmembrane potential
in temporal summation, are the stimuli coming at the same time?
NO. the stimuli are coming to the same location successively, and the first is being added to the next that comes in a chain
in spatial summation, are the stimuli coming at the same time?
YES. they’re coming at the same time but at different locations
which summation involves multiple synapses?
spatial
for both summations, an action potential results when…..
the transmembrane potential at the initial segment reaches threshold
in spatial summation, the degree of depolarization depends on….
how many synapses are active and their distance from the initial segment
the summation of EPSP’s is happening, but depolarization of initial segment has NOT reached threshold.
what happens?
the closer the initial segment gets to threshold, the easier it will be for the NEXT depolarizing stimulus to trigger an action potential
a neuron whose transmembrane potential shifts closer to threshold is said to be _____
facilitates
the larger the degree of facilitation, the ____ is the additional stimulus needed to trigger an action potential
smaller
what can change the postsynaptic membrane’s sensitivity to excitatory or inhibitory neurotransmitters?
neuromodulators, hormones, or both
by shifting the balance of EPSP’s and IPSP’s, neuromodulators promote…….
the facilitation or inhibition of CNS and PNS neurons
what is an axoaxonic synapse?
a synapse between the axons of 2 neurons
what is presynaptic inhibition?
the release of a neuromodulator (ie: GABA) inhibits the opening of voltage gated calcium channels in the synaptic terminal. this reduces the amount of neurotransmitter released when an action potential arrives there, and thus reduces the effects of synaptic activity on the postsynaptic membrane
presynaptic inhibition and facilitation are happening at what synapses?
axoaxonic
what is happening in presynaptic facilitation
activity at an axoaxonic synapse INCREASES the amount of neurotransmitter released when an action potential arrives at the synaptic terminal
which neurotransmitter is involved in presynaptic facilitation?
serotonin
in the presence of serotonin released at an axoaxonic synapse, voltage-gated calcium channels remain open ______
longer
in presynaptic facilitation, are the neurotransmitter’s effects suppressed or increased?
neurotransmitter’s effects are enhanced and prolonged
the degree of sensory stimulation or the strength of motor response is directly proportional to what?
THE FREQUENCY OF ACTION POTENTIALS
The frequency of action potentials depends on what?
the degree of depolarization above threshold
the greater the degree of polarization, the higher the frequency of action potentials
the membrane can respond to a SECOND stimulus only after…
the absolute refractory period ends
the maximum theoretical frequency of action potentials is established by…
the duration of the absolute refractory period
in which axons is the absolute refractory period the shortest?
in large diameter axons
