Chapter 5: How Neurons Communicate and Adapt Flashcards
1
Q
who was the first to isolate a chemical messenger in their successful heartbeat experiment?
A
Otto Loewi
2
Q
first neurotransmitter discovered in the PNS and CNS; activates skeletal muscles in the SNS; either excites or inhibits internal organs in the ANS
A
acetylcholine (ACh)
3
Q
ACh can ___ skeletal muscles in the somatic nervous system and may ___ various internal organs in the autonomic system
A
excite; excite or inhibit
4
Q
Loewi stimulated ___ to the heart, resulting in the heart rate increasing, and identified the chemical that carries the message to speed up heart rate in frogs as ___
A
the accelerator nerve; epinephrine
5
Q
chemical messenger that acts as a neurotransmitter in the CNS and as a hormone to mobilize the body for fight or flight during times of stress (aka adrenaline)
A
epinephrine
6
Q
___ and ___ are the same substance, produced by the adrenal glands located ___
A
adrenaline + epinephrine; atop the kidneys
7
Q
in mammals, the chemical that accelerates heart rate is ___
A
norepinephrine
8
Q
Loewi’s experiments show that acetylcholine from the vagus nerve ___ heartbeat, and epinephrine from the accelerator nerve ___ it
A
inhibits; excites
9
Q
neurotransmitter that accelerates heart rate in mammals; found in the brain and in the sympathetic division of the ANS; aka noradrenaline
A
norepinephrine
10
Q
chemical messengers released by a neuron onto a target to cause an excitatory or inhibitory effect
A
neurotransmitters
11
Q
outside the CNS, many of the neurotransmitters circulate the bloodstream as ___
A
hormones
12
Q
under the control of the hypothalamus, the ___ releases hormones into the bloodstream to excite/inhibit targets
A
pituitary gland
13
Q
why are hormones slower than CNS neurotransmitters?
A
they have to travel larger distances to get to their receptors
14
Q
the confirmed # of transmitters is ___, with most of the work being done by ___
A
60; 10
15
Q
disorder of the motor system correlated w/ a loss of dopamine from the substantial nigra and characterized by tremors, muscular rigidity, and a reduction in voluntary movement
A
Parkinson disease
16
Q
who found that, in Parkinson disease, the substantial nigra had degenerated?
A
Constantin Treatikoff
17
Q
chemical examination of the brains of Parkinson patients showed that disease symptoms appear when the level of ___ was reduced to ___ of normal in the basal ganglia
A
dopamine; less than 10%
18
Q
Urban Ungerstedt found that injecting a neurotoxin called ___ selectively destroyed the dopamine-containing neurons and produced symptoms of Parkinson disease
A
6-hydroxydopamine
19
Q
loss of dopamine-containing substantia nigra neurons has been linked to environmental factors such as ___
A
insecticides, herbicides, fungicides, flu virus, toxic drugs
20
Q
some Parkinson patients who receive dopaminergic drugs as therapy have become ___, despite showing no such tendencies before treatment
A
shopaholics or compulsive gamblers
21
Q
membranous compartment that encloses a fixed number (quantum) of neurotransmitter molecules
A
synaptic vesicles
22
Q
A
a. microtubule
b. mitochondrion
c. synaptic vesicle
d. storage granule
e. postsynaptic receptor
f. presynaptic membrane
g. synaptic cleft
h. postsynaptic membrane
i. neurotransmitter
j. channel
23
Q
transport structure that carries substances to the axon terminal
A
microtubule
24
Q
organelle that provides the cell with energy
A
mitochondrion
25
round granule that contains neurotransmitter
synaptic vesicle
26
large compartment that holds synaptic vesicles
storage granule
27
site to which a neurotransmitter molecule binds
postsynaptic receptor
28
encloses molecules that transmit chemical messages
presynaptic membrane
29
small space separating presynaptic terminal and postsynaptic dendritic spine
synaptic cleft
30
contains receptor molecules that receive chemical messages
postsynaptic membrane
31
how does the astrocyte surrounding the synapse contribute to chemical neurotransmission?
- supplying the building blocks for neurotransmitter synthesis
- confining the movement of neurotransmitters to the synapse
- mopping up excess neurotransmitter molecules
32
functional integration and physical proximity of the presynaptic membrane, postsynaptic membrane, and their intimate association w/ surrounding astrocytes
tripartite synapse
33
5 step process of neurotransmission
1. the neurotransmitter is synthesized inside the neuron
2. it's packaged + stored within vesicles at the axon terminal
3. it's transported to the presynaptic membrane + released into the cleft in response to an action potential
4. it binds to + activates receptors on the postsynaptic membrane
5. it's degraded or removed so it will not continue to interact w/ a receptor and work indefinitely
34
process that occurs when a neurotransmitter is released from a presynaptic neuron and binds to a receptor on the postsynaptic neuron
anterograde synaptic transmission
35
protein molecule that pumps substances across a membrane
transporter
36
___ transmitters are synthesized in the cell body, packed in membranes on the Golgi bodies, and transported on microtubules to the axon terminal
peptide
37
___ transmitters cannot be packaged/stored in vesicles, which are composed of lipids, but are rather synthesized "on demand" when an action potential reaches the axon terminal
lipid
38
___ transmitters are generated within the cells by enzymes, but they are able to permeate cell membranes and thus are not stored within the cell
gaseous
39
___ are not biochemically synthesized but are made in the hearts of dying stars, can be packed/stored in vesicles, and released into synaptic cleft
ion
40
neurotransmitters that are packaged into vesicles can be found at 3 locations at the axon terminal
1. granules
2. microfilaments
3. presynaptic membrane
41
the presynaptic membrane is rich in ___ channels
voltage-activated Ca+ channels
42
3 steps of neurotransmitter release
1. when an action potential reaches the voltage-sensitive terminal, it opens calcium channels
2. incoming calcium ions bind to proteins, forming a complex
3. this complex binds to vesicles, releasing some from filaments + inducing others to bind to the presynaptic membrane and to empty their contents by exocytosis
43
protein that has a binding site for a specific neurotransmitter and is embedded in the membrane of a cell
transmitter-activated receptors
44
embedded membrane protein; acts as
1. a binding site for a neurotransmitter
2. a pore that regulates ion flow to directly/rapidly change membrane voltage
ionotropic receptors
45
embedded membrane protein with a binding site for a neurotransmitter linked to a G protein; can affect other receptors or act with second messengers to affect other cellular processes, including opening a pore
metabotropic receptor
46
self-receptor in a neuronal membrane; that is, it responds to the same transmitter released by the neuron; part of a negative feedback loop allowing the neuron to adjust its output
autoreceptors
47
who concluded that the smallest postsynaptic potential is produced by the release of the contents of just 1 synaptic vesicle?
Bernard Katz
48
of neurotransmitter molecules, equivalent to the content of a single synaptic vesicle, that produces a just-observable change in postsynaptic electric potential
quantum
49
the # of quanta released from the presynaptic membrane in response to a single action potential depends on:
1. the amt of Ca+ that enters the axon terminal in response to the action potential
2. the # of vesicles docked at the membrane, waiting to be released
50
neurotransmitter inactivation can happen in 4 ways:
1. diffusion
2. degradation
3. reuptake
4. astrocyte uptake
51
7 types of synapses
1. dendrodendritic
2. axodendritic
3. axoectracellular
4. axosomatic
5. axosynaptic
6. axoaxonic
7. axosecretory
52
dendrites send messages to other dendrites
dendrodendritic
53
axon terminal of one neuron synapses on dendritic spine of another
axodendritic
54
terminal with no specific target - secretes transmitter into extracellular fluid
axoextracellular
55
axon terminal ends on cell body
axosomatic
56
axon terminal ends on another terminal
axosynaptic
57
axon terminal ends on another axon
axoaxonic
58
axon terminal ends on tiny blood vessel and secretes transmitter directly into blood
axosecretory
59
which type of synapse is the most common in mammalian nervous systems?
chemical
60
area of contact between adjacent cells in which connexin proteins in each cell form connecting hemichannels, which, when open, allow ions to pass between the two cells (aka electrical synapse)
gap junction
61
gap junction
62
electrical synapses are ___ than chemical
faster
63
gap junctions allow ___ to exchange substances
glial cells + neurons
64
large biomolecules such as ___ cannot fit thru gap junctions
nucleic acids + proteins
65
gap junctions at axon terminal synapsing on dendrites and cell bodies allow for ___ transmission
dual chemical + electrical
66
why do mammals rely on chemical synapses more than gap junctions?
chemical synapses = plasticity, they can amplify/diminish a signal, and change with experience, mediating learning
gap junctions = speed + efficiency
67
neurotransmitters themselves do not determine excitation/inhibition, but ___ make the call
the ion channel associated w/ the receptor
68
- large active zone
- wide cleft
- dense material on membranes
- round vesicles
excitatory synapse
69
- small active zones
- narrow cleft
- sparse material on membranes
- flat vesicles
inhibitory synapse
70
the differing locations of excitatory and inhibitory synapses:
excitatory = dendritic tree
inhibitory = cell body/soma
71
the exocytosis mechanism for digestion in a single-celled organism is parallel to the ___ for communication in more complex creatures
release of a neurotransmitter
72
ionotropic receptor
73
metabotropic receptor
74
4 criteria for identifying neurotransmitters
1. the transmitter must be synthesized in the neuron or otherwise be present in it
2. when the neuron is active, the transmitter must be released and produce a response in some target
3. the same response must be obtained when the transmitter is experimentally placed on the target
4. a mechanism must exist for removing the transmitter from its site of action after its work is done
75
a suspect chemical that has not yet been shown to meet all the neurotransmitter criteria
putative transmitter
76
why is identifying chemical transmitters in the CNS hard?
there are thousands of synapses packed around every neuron, preventing easy access to a single synapse + its activities
77
all motor neuron axons leaving the spinal cord use ___ as a transmitter
acetylcholine
78
explain the Renshaw loop
- each axon has an axon collateral within the spinal cord synapses on a nearby CNS interneuron
- this interneuron synapses on the motor neuron's cell body
79
what enables a motor neuron to inhibit itself from overexcitation?
the Renshaw loop
80
today, the term neurotransmitter applies to chemicals that:
1. carry a message from the presynaptic membrane of one neuron to another by influencing postsynaptic membrane voltage
2. change the structure of a synapse
3. communicate by sending messages in the opposite direction
81
5 classes of neurotransmitters:
1. small-molecule
2. peptide
3. lipid
4. gaseous
5. ion
82
quick-acting neurotransmitter synthesized in the axon terminal from products derived from the diet
small-molecule transmitters
83
how do small-molecule transmitters work?
- synthesized from dietary nutrients + packaged ready for use in axon terminals
- after released from a terminal button, it is quickly replaced at the presynaptic membrane
84
many neuroactive drugs are designed to reach the brain by the same route that ___ transmitters follow - the digestive tract
small-molecule
85
ACh molecules are synthesized from ___ by 2 enzymes, then broken down
choline + acetate
86
acetylcholine synthesis
1. acetyl CoA carries acetate to the transmitter synthesis site
2. ChAT transfers acetate to choline to form ACh
87
any chemical in limited supply that restricts the pace at which another chemical can be synthesized
rate-limiting factor
88
amine synthesis
tyrosine -> L-Dopa -> dopamine -> norepinephrine -> epinephrine
89
what enzyme is the rate-limiting factor in the production of dopamine, norepinephrine, and epinephrine?
the 2nd enzyme tyrosine hydroxylase
90
which neurologist administered L-dopa to a patient with Parkinson disease?
Oliver Sacks
91
by increasing the amount of dopamine in remaining synapses, L-dopa relieved the symptoms of ____
Parkinson disease
92
serotonin is synthesized from the amino acid ___
L-tryptophan
93
amine neurotransmitter; helps to regulate mood + aggression, appetite + arousal, perception of pain, and respiration
serotonin
94
amino acid neurotransmitter; typically excites neurons
glutamate (Glu)
95
amino acid neurotransmitter; typically inhibits neurons
gamma-aminobutyric acid (GABA)
96
structural difference between glutamate and GABA
they are the same except GABA does not have a carboxyl group on the bottom
97
glutamate is widely distributed in CNS neurons, but it becomes a neurotransmitter only if it is ___
appropriately packaged in vesicles at the axon terminal
98
___ is a much more common inhibitory transmitter in the brainstem and spinal cord, where it acts within the Renshaw loop
glycine (amino acid transmitter)
99
neurotransmitter that controls arousal + waking; can cause the constriction of smooth muscles; when activated in allergic reactions, constricts airway + contributes to asthma
histamine
100
histidine is converted by the enzyme ___ into histamine
histidine decarboxylase
101
the purine ___ consists of a molecule of adenine attached to a ribose sugar molecule and 3 phosphate groups
adenosine triphosphate (ATP)
102
a molecule that plays a central role in promoting sleep, suppressing arousal, + regulating blood flow to various organs thru vasodilation
adenosine
103
short, multifunctional amino acid chain (fewer than 100); acts as a neurotransmitter + can act as a hormone; may contribute to learning
neuropeptides/peptide transmitters
104
the process of neuropeptide synthesis/transport is relatively ___ compared to small-molecule neurotransmitters
slow
105
neuropeptides perform an enormous range of functions in the nervous system, acting as hormones that:
- respond to stress
- enable a mother to bond with her infant
- regulate eating + drinking, pleasure + pain
- contribute to learning
106
opium, morphine + related synthetic chemicals like heroin mimic the actions of endogenous brain opioid neuropeptides:
enkephalins, dynorphins, endorphins
107
___, released in response to exercise (runner's high), has many times the analgesic potency of morphine
beta-endorphin
108
unlike many transmitters that bind to receptors associated w/ ion channel, neuropeptides are ___ and have no direct effects on ___
metabotropic; postsynaptic membrane voltage
109
peptide transmitters activate ___ that indirectly influence ___
synaptic receptors; cell structure + function
110
why can't neuropeptides be taken orally as drugs like small-molecule transmitters?
digestive processes degrade neuropeptide amino acid chains
111
class of lipid neurotransmitters, including anandamide + 2-AG, synthesized at the postsynaptic membrane to act on receptors at the presynaptic membrane; affects appetite, pain, sleep, mood, memory, anxiety, and stress response
endocannabinoids
112
___ is the target of all cannabinoids, and are found at ___
CB1 receptors; both the glutamate and GABA synapses
113
___ act as neuromodulator to inhibit release of glutamate and GABA, thus dampening ___
cannabinoids; neuronal excitation/inhibition
114
3 gaseous neurotransmitters
1. nitric oxide (NO)
2. carbon monoxide (CO)
3. hydrogen sulfide (H2S)
115
how do gaseous transmitters work?
- cells synthesize them on demand
- gas diffuses away, easily crossing cell membrane, immediately becoming active
116
gaseous neurotransmitter; acts to dilate blood vessels, aid digestion, & activate cellular metabolism
nitric oxide (NO)
117
gaseous neurotransmitter; activates cellular metabolism
carbon monoxide (CO)
118
gaseous neurotransmitter; slows cellular metabolism by preventing oxygen from binding in the mitochondria
hydrogen sulfide (H2S)
119
2 parts of an ionotropic receptor
1. a binding site for a neurotransmitter
2. a pore/channel
120
how does an ionotropic receptor work?
- neurotransmitter attaches to binding site
- receptor quickly changes shape, either opening the pore or closing it
121
ionotropic receptors are usually ___ because ___
excitatory; they bring about rapid changes in membrane voltage
122
ionotropic receptor
123
how does a metabotropic receptor work?
- transmitter binds to receptor
- triggers activation of a G protein
- affects ion channels or cells metabolic activity
124
metabotropic receptor
125
guanyl nucleotide-binding protein couples to a metabotropic receptor; binds to other proteins when activated
G protein
126
3 subunits of G protein
alpha, beta, gamma
127
what does the alpha subunit do on a G protein?
- detaches when a neurotransmitter binds to G protein's receptor
- detached subunit can bind to other proteins within cell membrane or intracellular fluid
128
what happens when an alpha subunit binds to a nearby ion channel?
the channel structure changes, modifying the flow of ions (open/close) - this influences membrane's electric potential
129
what happens when an alpha subunit binds to an enzyme?
second messenger is activated
130
metabotropic receptors allow for the possibility that a single neurotransmitter's binding to a receptor can activate an escalating sequence of events called ___
an amplification cascade
131
the amplification cascade effect results in ___
many downstream proteins (second messengers, channels or both) being either activated or deactivated
132
ACh has an excitatory effect on skeletal muscles, where it activates an ___ receptor, and an inhibitory effect on heart rate, where it activates a ___ receptor
ionotropic; metabotropic
133
how is there variety of small-molecule neurotransmitter receptor subtypes?
alternative forms of each subunit can assemble in unique combinations to make a functional receptor
134
why does the brain contain so many receptor types for each neurotransmitter?
each subtype has slightly different properties which confer different activities
135
can different transmitters coexist in the same terminal or synapse?
yes
136
neurons that use acetylcholine as its main neurotransmitter
cholinergic neurons
137
at a skeletal muscle, cholinergic neurons are ___
excitatory, producing muscle contractions
138
the main transmitter-activated ionotropic channel receptor
nicotinic acetylcholine receptor (nAChr)
139
what happens when ACh or nicotine binds to the nAChr?
the pore opens, allowing simultaneous efflux of K+ and influx of Na+, depolarizing the muscle fibre
140
cholinergic neurons in the CNS synapse with ___ to prepare the body's organs for fight or flight
sympathetic norepinephrine (NE) neurons
141
cholinergic neurons in the CNS synapse with ___ to prepare the body's organs for rest and digest
parasympathetic acetylcholine (ACh) neurons
142
norepinephrine (NE) receptors on the ___ are excitatory, while NE receptors on the ___ are inhibitory
heart; gut
143
acetylcholine (ACh) receptors on the ___ are excitatory, while ACh receptors on the ___ are inhibitory
gut; heart
144
the ENS uses over __ neurotransmitters that are identical to those in the CNS
30
145
the 2 main small-molecule transmitters used by the ENS are:
serotonin + dopamine
146
neural pathways that coordinate brain activity thru a single neurotransmitter; its cell bodies lie in a brainstem nucleus; axons are distributed thru a wide CNS region
activating systems
147
the 4 activating systems
1. cholinergic
2. dopaminergic
3. noradrenergic
4. serotonergic
148
- active in maintaining attention + waking EEG pattern
- plays a role in memory by maintaining neuron excitability
- death of these neurons and decrease in this neurotransmitter in the neocortex are related to Alzheimer disease
cholinergic system (acetylcholine)
149
- this transmitter release causes repetition of behaviours
- the neurotransmitter system most affected by addictive drugs + behaviours
- increases in this transmitter activity may be related to schizophrenia
- decreases in this transmitter activity may be related to deficits of attention
mesolimbic pathways of the dopaminergic system
150
- active in maintaining normal motor behaviour
- loss of this neurotransmitter is related to muscle rigidity + dyskinesia in Parkinson disease
nigrostriatal pathways of the dopaminergic system
151
- active in maintaining emotional tone
- decreases in its neurotransmitter activity are related to depression
- increases in its neurotransmitter are related to mania
- decreased neurotransmitter activity is associated with hyperactivity and ADHD
noradrenergic system (norepinephrine)
152
- active in maintaining waking EEG pattern
- changes in its neurotransmitter activity are related to OCD, tics and schizophrenia
- decreases in its neurotransmitter activity are related to depression
- abnormalities in brainstem 5-HT neurons are linked to disorders like sleep apnea and SIDS (sudden infant death syndrome)
serotonergic system (serotonin)
153
in a rat brain, AChE permeates the cortex and is especially dense in the ___
basal ganglia
154
2 treatment strategies for Alzheimer disease
drugs that either
- inhibit enzyme acetylcholinesterase (raises levels of ACh)
- raise the # of nicotinic receptors
155
how can Parkinson disease be triggered by the ingestion of certain toxic drugs?
the drugs may act as selective neurotoxins that specifically kill dopamine neurons in the substantia nigra
156
how many people does Parkinson disease affect?
20 per 100,000
157
behavioural disorder characterized by delusions, hallucinations, disorganized speech, blunted emotion, agitation or immobility, + a host of associated symptoms
schizophrenia
158
how many people does schizophrenia affect?
1 in 100
159
mood disorder characterized by prolonged feelings of worthlessness and guilt, disruption of normal eating habits, insomnia, a general slowing of behaviour, frequent thoughts of suicide
major depression
160
disordered mental state of extreme excitement
mania
161
behaviour characterized by compulsively repeated acts and repetitive, often unpleasant, thoughts
obsessive-compulsive disorder (OCD)
162
___ brains with more ___ are more plastic, thus likely to show more alterations in neural organization
large; synapses
163
relatively persistent/permanent change in behaviour that results from experience
learning
164
when an axon of cell A is near enough to excite a cell B and repeatedly or persistently takes part in firing it, some growth process or metabolic change takes place in one or both cells such that A's efficiency, as one of the cells firing B, is increased
Hebb synapse
165
who described the synaptic basis of learning as: learning in which the conjoint activity of nerve cells serves to link them?
Eric Kandel
166
what happens when the marine slug, Aplysia californica, is threatened?
it withdraws its vulnerable body parts: the gill & siphon
167
habituation + sensitization are both ___ behaviours for humans
unconscious
168
learned behaviour in which the response to a stimulus weakens with repeated presentations
habituation
169
small, fast, random eye movements designed to keep photoreceptors exposed to ever-changing visual stimuli to prevent habitation
saccades
170
the marine slug, Aplysia californica, ___ to waves in the tidal zone where it lives
habituates
171
results of habituation
1. influx of calcium ions in response to an action potential decreases
2. less neurotransmitter released at presynaptic membrane
3. less depolarization of postsynaptic membrane
172
conclusion of Eric Kandel's experiment on the marine slug Aplysia californica
withdrawal response weakens with repeated presentation of water jet (habituation) due to decreased Ca2+ influx & subsequently less neurotransmitter release from the presynaptic axon terminal
173
can sensory/motor neurons generate action potentials after habituation?
yes
174
as habituation develops , the EPSP's in the motor neuron become ___
smaller
175
how do the EPSPs in the motor neuron decrease in size as habituation develops?
the motor neuron is receiving less neurotransmitter from the sensory neuron across the synapse, indicating habituation is also taking place in the presynaptic axon terminal of sensory neurons
176
as habituation happens, the Ca2+ influx ___ in response to the voltage changes associated w/ an action potential
decreases
177
voltage-activated calcium channels during habituation become ___ responsive to voltage changes + more ___ to the passage of calcium ions
less; resistant
178
learned behaviour in which the response to a stimulus strengthens with repeated presentations
sensitization
179
neural results from sensitization
1. serotonin reduces K+ efflux thru potassium channels, prolonging an action potential on the siphon sensory neuron
2. the prolonged action potential results in more Ca2+ influx & increased transmitter release
3. causes greater depolarization of the postsynaptic membrane after sensitization
180
sensitization vs. habituation
sensitization: influx of Ca2+, more neurotransmitter release, potassium channels
habituation: efflux of Ca2+, less neurotransmitter release, calcium channels
181
the # and size of synapses ___ in habituation, and ___ in sensitization
decreases; increases
182
what plays an important role in carrying instructions about structural changes during learning to nuclear DNA?
the second messenger cAMP
183
in the fruit fly Drosophila, the genetic mutation ___ lacks the enzymes necessary to degrade cAMP, resulting in abnormally high levels, while the other mutation ___ reduces levels of cAMP below the normal range
dunce; rutabaga
184
fruit flies with both mutations dunce or rutabaga are impaired in acquiring habituation/sensitized responses (learning) bc their levels of ___ cannot be regulated
cAMP
