Neurochemistry Flashcards
action potential reaches the pre-synaptic terminal
voltage-gated Ca2+ channels open
Ca2+ enters terminal
Ca2+ causes synaptic vesicles to fuse with the presynaptic membrane
release neurotransmitter into the synaptic cleft=exocytosis
steps of exocytosis
vesicles
SNARE proteins
voltage-gated Ca2+ channels open
Ca2+ sensor
vesicles
packets of neurotransmitters
SNARE proteins
v-SNARES and t-SNARES
docked at presynaptic membrane, waiting to fuse
Ca2+ sensor
synaptotagmin
fusion and neurotransmitter release
If someone is exposed to a toxin that changes neurotransmitter release at muscles, they may experience ______
A. Muscle weakness or paralysis
B. Muscle tightening or spasms
C. Death
D. All of the above
neurotransmitters
basis of communication between neurons
many different chemicals act as neurotransmitters in brain: glutamate, GABA, dopamine, serotonin, norepinephrine, acetylcholine
each neuron uses one (or maybe two or three!) neurotransmitters; different neurons use different neurotransmitters
each neurotransmitter can trigger a different effect on the post-synaptic cell
neurotransmitter production
neurons must synthesize their neurotransmitter and move it to vesicles
a specific enzyme (protein) is involved in producing each neurotransmitter
often, that enzyme converts an amino acid we derive from our diet into a neurotransmitter
neurotransmitters cross the synaptic cleft
neurotransmitters diffuse across until they reach the post-synaptic membrane
extra neurotransmitter is degraded by enzymes, or taken up by presynaptic terminals or astrocytes
post-synaptic density
dendrites/spines have post-synaptic densities with receptors
neurotransmitters bind to receptors on post-synaptic membrane
ionotropic receptors
ligand-gated ion channels
chemically activated by neurotransmitter binding
coupled to G-proteins, which in turn couple to other enzymes/channels (GPCR)
slower biochemical changes within the cell (second messenger systems)
metabotropic receptors
receptor activates G-protein (so also called G-protein coupled receptor)
agonist
an naturally occurring molecule (ligand) or drug can bind to the receptor and open in
unbound receptor
receptors are normally closed
antagonists
some substances bind to receptors but do not activate them. instead, they simply block agonists from binding to the receptors
Ligand-gated ion channels are activated by ____
A. Ions
B. Neurotransmitters
C. Voltage
D. Temperature
B. neurotransmitters
neurotransmitters/receptors open post-synaptic ion channels
cation (Na+, K+, Ca2+) or anion (Cl-) channels
post-synaptic potential (PSP)
electrically charged ions cross membrane
excitatory or inhibitory PSP
PSP can spread through dendrite to cell body and axon hillock
excitatory post-synaptic potential (EPSP)
cations flow in-> depolarize the neuron
inhibitory post-synaptic potential (IPSP)
anions flow in-> hyperpolarize the neuron
Whether a PSP is excitatory or inhibitory depends on the
____
A. Type of neurotransmitter released
B. Size and shape of the action potential
C. Type of voltage-gated channel that opens
A. type of neurotransmitter released
C. type of voltage-gated channel that opens
cations enter cell
membrane potential becomes less negative
depolarizes (less polarized)
excitatory post-synaptic potential
anions enter cell (or cations exit)
membrane potential becomes more negative
hyperpolarizes (more polarized)
inhibitory post-synaptic potential
summation and integration
dendrites receive contacts from many neurons
individual EPSP/IPSP is very small and graded
summation
combining signals
integration
translating signals into a decision on whether to send an output to the next neurons
many excitatory and inhibitory inputs are summed
if the sum reaches threshold potential, an action potential is triggered
action potentials begin at the axon hillock (initial segment of the axon)
spatial summation
occurs if potentials come from different parts of cell
temporal summation
occurs if potentials arrive at axon hillock at slightly different times
True of False: Temporal summation is more important than
spatial summation in action potential generation
A. True
B. False
B. False
what are neurotransmitters?
synthesized and stored in presynaptic neuron
released from presynaptic axon terminal by an action potential
has specific receptors that recognize it on postsynaptic membrane
applying the substance changes the postsynaptic cell
blocking release of substance prevents these changes in the postsynaptic cell
types of neurotransmitters
amino acids or derivative of amino acids-glutamate, GABA, dopamine, serotonin, norepinephrine, acetylcholine
small proteins- neuropeptides
steroids
gases- nitric oxide, carbon monoxide
lipids- endocannabinoids
co-release
cell can contain several neurotransmitters
likely each vesicle only contains one type of neurotransmitter
glutamate and GABA
most abundant neurotransmitters in the brain
glutamate
main excitatory neurotransmitter
excitation
allows one neuron to activate another
GABA
main inhibitory neurotransmitter
inhibition
stops/blocks the activation of a neuron
seizures and loss of consciousness/coma
result from glutamate/GABA imbalances
glutamate receptors
released by terminals
3 ionotropic receptors: AMPA, NMDA, and Kainate receptors
1 class of metabotropic receptors: mGluR
ionotropic: AMPA receptor and Kainate receptor
cation: Na+ enters cell, K+ leaves cell
overall main effect is Na+ enters cell
EPSP
ionotropic: NMDA receptor
both ligand-gated and voltage-gated
glutamate
Mg2+ block released by depolarization
cation: Na+ & Ca2+ enter the cell, K+ leaves cell
Overall effect is Na+ & Ca2+ enter cell
EPSP
activation of AMPA receptors
release Mg2+ block and open NMDA receptors
important in learning and memory
GABA receptors
2 ionotropic receptors: GABAa and GABAc
1 class of metabotropic receptors: GABAb
ionotropic: GABAa receptor
Cl- enters cell
IPSP
binding sites for drugs that increased receptor function ex. sedatives, anesthetics, alcohol
ionotropic: glycine receptor
Cl- enters cell
IPSP
spinal cord, brainstem
A seizure can be caused by too much _______, and a coma can be caused by too much _______
A. GABA, glutamate
B. glutamate, GABA
C. GABA, glycine
B. glutamate, GABA
norepinephrine/noradrenaline
originates in locus coeruleus and projects throughout brain
arousal and sleep/wake
mood
cognitive function
sympathetic nervous system
norepinephrine/noradrenaline receptors
metabotropic a1, a2, b1, b2
overproduction of norepinephrine
anxiety, stress, hyperarousal, PTSD (prazosin & propranolol)
serotonin (5-HT)
originates in dorsal raphe and projects throughout brain
sleep/wake cycle
feeding (hunger and satiety)
mood
serotonin receptors
matabotropic 5-HT receptors (15 receptors)
dopamine (DA) origins
1) ventral tegmental area and projects to limbic and cortical. areas- reward and reinforcement
2) substantia nigra and projects to striatum/caudate- motor control
dopamine receptors
metabotropic D1-D5 receptors
dopamine receptors starting to die
schizophrenia, drug addiction, Parkinson’s disease (L-dopa)
acetylcholine (ACh) in CNS
originates from the basal forebrain
cholinergic cell bodies and projections contain acetylcholine
acetylcholine lost
Alzheimer’s disease
ionotropic acetylcholine receptor in CNS
nicotinic acetylcholine receptor
metabotropic acetylcholine receptor in CNS
muscarinic acetylcholine receptor
acetylcholine in PNS
neuromuscular junction
ionotropic acetylcholine receptor in PNS
nicotinic acetylcholine receptor
Neuromodulatory transmitter receptors tend to be ______
A. Ionotropic
B. Metabotropic
B. metabotropic
most modulatory transmitter receptors are metabotropic
autoreceptors
on presynaptic axon terminal membrane
negative feedback loop
important to turn off the receptor to stop the over-release of the neurotransmitter
autoreceptors include
metabotropic receptors
NE a2 receptors
GABAb receptors
