5. Neurophysiology II Flashcards
Synaptic transmission
How to convert an electrical signal into a chemical signal and back again.
- Presynaptic region
- ____ to ____
- ____ triggered transmitter
release - Synaptic cleft
- diffusion of ____ - Postsynaptic region
- ____ to ____
- ____-linked potential changes
electrical
chemical
voltage
neurotransmitters
chemical
electrical
receptor
Presynaptic region in axon terminal
Chemical storage of neurotransmitter in synaptic vesicles.
Presynaptic potential and thus ion channels regulate neurotransmitter release
Voltage-gated channels conduct AP’s down the axon to the terminal (1).
Depolarization gates open voltage- gated ____ channels to permit entry of Ca+2 into presynaptic terminal during an AP (2).
This influx of Ca+2 is the trigger for synaptic vesicles already ____ (3) to fuse with the membrane (4) and release ____ into the synaptic cleft (5).
Ca++
docked
NT
Presynaptic region: vesicles docked and ready to go
First line of synaptic vesicles in position to release when signal of Ca2+ elevation received
Voltage gated Ca2+ channels ____ close by to make process more accurate and rapid - 200 μs
Ca2+ rises from 100 nM to 100 μM – ____x
physically
1000
Presynaptic region: vesicles in terminal bouton
* \_\_\_\_ provides energy to load NT into vesicles * \_\_\_\_-demanding region of the cell
mitochondria
energy
Presynaptic region: synaptic vesicle
____ helps dock, and binds increasing ____ to initiate release
• Load vesicles with NT ○ \_\_\_\_: proton pump to pump + charge protons (acts as counter ion to negative charges of glutamate) • Proteins necessary for targeting vesicles at release ○ \_\_\_\_ ○ \_\_\_\_ - key protein needed to move vessels into right position • Proteins involved with docking of vessels ○ \_\_\_\_ ○ \_\_\_\_ • Synaptotagmin: where \_\_\_\_ binds ○ Reason why we have rapid entry of Ca++
synaptotagmin
Ca++
glutamate
calmodulin-dependent kinase II
synapsin
synaptophysin
synaptobrevin
calcium
Presynaptic region: targeting, docking and fusion of synaptic vesicle
Also “____” release
• \_\_\_\_: anchor vesicle • \_\_\_\_: calcium binding unit C2A and C2B • When vesicles are waiting for AP in absence of Ca++ ○ Loosely \_\_\_\_ and primed • When Ca++ enters via channels ○ \_\_\_\_ twisting of docking proteins ○ \_\_\_\_ of synaptoatotegmin start to move - putting their elbows through double membrane ○ Takes a lot of \_\_\_\_ to break vesicular and PM at synapse • Fusion of vesicular and PM takes a lot of energy ○ Mediated through \_\_\_\_ changes of protein • Expansion of pore ○ NT released • Kiss and run ○ A little semi-opening for a little \_\_\_\_ to release and it closes up again ○ \_\_\_\_ emptying of synaptic vesicle on plasma membrane • Membrane turnover on synaptic membrane
kiss and run
synaptobrevin synaptotegmin tethered tighter C2 energy allosteric NT incomplete
Transport of synaptic vesicle
Is ____ until after docking with SNARE complex, my boy!
____ leads synaptotagmin to insert in the membrane causing a mechanical
trigger that opens the pore.
____ isoforms cleave SNAP 25, syntaxin or synaptobrevin, thus preventing neurotransmitter release
t-SNAREs are the target snares on the ____.
v-SNAREs are on the ____.
[points to tethering complex] You can see it is tethered and the tethering complex brings it close and holds it in position. The SNARE complex begins to loosely form and is ____ until fusion. This happens so neurotransmitter can be released immediately
when calcium arrives.
Once calcium comes in, that fusion occurs really quickly, and the neurotransmitter is released.
[points to bottom diagram] This is the best picture showing how ____ is
primed and interacts with the v and t-SNARES. Once that calcium comes in, you can really see the Synaptotagmin starting to fuse.
reversible
Ca++
botox
plasma membrane
vesicle
reversible
synaptotagmin
Botox soldiers with chainsaws
____ used for injection, exhibits an LD50 of 40-56 ng when injected iv, one of most powerful toxins known
• Cleave \_\_\_\_ machinery ○ B, D, F, and G cleave \_\_\_\_ ○ A and E cleave \_\_\_\_ and \_\_\_\_ • Impede with botox - prevent synaptic release, prevents vesicular fusion • Injecting botox into regions with \_\_\_\_ interactions - preventing the movement of those muscles ○ No laughter lines, wrinkles because you prevent the NM transmission
snare synaptobrevin snap-25 syntaxin neuromuscular
Synaptic cleft: the gap between two neurons or between a neuron and its effector organ
- Neurotransmitters diffuse across the synaptic cleft to the postsynaptic membrane
- Neurotransmitter is either taken up into the ____ terminal or inactivated by ____ located in the cleft.
____ volume: 200-300 angstroms small enough for fast diffusion
Filled with matrix, enzymes, receptors, other proteins
• \_\_\_\_ - feedback mechanisms, can stop or induce interactions
presynaptic
enzymes
small
autoreceptors
How does the neurotransmitter signal stop?
- ____ degradation. (e.g. acetylcholinesterase)
- Messages can be transported back into the ____ terminal for recycling.
- ____ of the message away from the site of the post-synaptic receptors.
Important to limit concentration of transmitter both ____ and ____ to ensure specific signaling
enzyme
presynaptic
diffusion
spatially
temporally
Increasing 5-HT (serotonin) in synaptic cleft by blocking uptake
• Inhibit \_\_\_\_ uptake, thereby resulting in a build up of serotonin in the cleft
presynaptic
Postsynaptic region
• Receptors for the neurotransmitter
– ionotropic vs metabatropic:
type dictates ____
• Neurotransmitter binding causes change in the membrane potential
– the particular ion flowing through the channel will determine whether the effect is ____ or ____ depending upon its Nernst potential
• Ionotropic channels ○ Ligand gated ion channels • Metabotropic channels ○ GPCR • Choice between is going to affect the speed of the response • \_\_\_\_ can activated both in same synapse, but lead to different outcomes • NT targets and opens ionotropic: ○ If Na-selective: lets more Na+, thereby depolarize - \_\_\_\_ ○ If K-selective (flows out), or Cl- (flows in): hyperpolarize - \_\_\_\_ • NT targets metabotropic: ○ Essentially an enzyme, and acts as a GPCR ○ Activates \_\_\_\_ pathway § Alters state of \_\_\_\_ channels - can open them § However, they can also \_\_\_\_ the channels (opposite scenario) ○ Change \_\_\_\_ transcription, learning signals
timing
excitatory
inhibitory
glutamate
EPSP
IPSP
second messenger
ion (ionotropic)
close
gene
Postsynaptic region: Ionotropic receptors
- Ionotropic receptors are ____ gated channels
- Distinct agonist binding and pore regions of receptor – contain all ____ aspects of normal ion channels
- Very ____ – low msec
•Examples:
NMDA – binds ____,
____ permeable depolarization- excitatory
GABA A – binds ____, Cl- permeable, ____ entry hyperpolarization- inhibitory
____ – dental pain
• Need NT binding site ○ Acetylcholine has two binding sites • Binding leads to allosteric changes, opening the pore and allows ions to travel in direction of electrochemical gradient • P2X for \_\_\_\_ important in dental pain
ligand
exciting
fast
glutamate
Na+/Ca+
GABA
Cl-
P2X
ATP
Ionotropic P2X receptors: key mediators of dental pain
- Identify dental pulp nerves by injecting with fluorescent dye, allowing transport to soma in ____ before removing
- Extracellular ____ applied to cell initiates action potentials, adapting. Pharmacologically and immunohistochemically identified as P2X2/P2X3 hybrid channel
- Think ATP released from ____ dental tissue
- Recorded from patch clamp - you add ATP - you see AP coming from the neuron
- Occur in a ____, two ____
trigeminal ganglion ATP inflamed trimer domains
Postsynaptic region: Metabotropic receptors
Receptor initiates multiple steps before changing membrane potential
Links to depolarization or hyperpolarization more ____ because more steps
Much ____ than ionotropic receptors but can have longer ____ effects
Important for ____ signal
G-protein coupled, tyrosine kinases etc
• G-proteins ○ Requires hydrolysis of \_\_\_\_ to GDP following allosteric changes in receptor • Usually span \_\_\_\_ membranes • Alpha, beta and gamma subunits ○ \_\_\_\_: PLC, release of Ca+ from ER, and can activate phospho on membrane ○ \_\_\_\_: stimulatory - increases activity of adenylate cyclase and increase cAMP ○ \_\_\_\_: inhibitory - reduce cxn of cAMP
variable slower modulating amplifying GTP 7 Aq Gs Gi
Postsynaptic region: Metabotropic receptors
- Binding of neurotransmitter initiates allosteric changes in receptor
- G protein activated – GDP replaced by GTP, ____ dissociates from Gβγ
- Much more GTP than GDP so initially supply no problem but can be after continued stimulation
- Gα and/or Gβγ activate additional enzymes – in this case Gα stimulates ____ to produce cAMP• GTP to GDP, release of P, transferred to GDP, activating ____
• Binds adenylate cyclase, turning ATP to cAMP
• More GTP to GDP usually within cell
○ Not the ____ step
• Beta, gamma, are very ____ on their own
Galpha
adenylate cyclase
Galpha
rate-limiting
active
Postsynaptic region: Metabotropic receptors and the release of intracellular Ca2+
- Stimulated receptor activates ____
- Gqα activates ____
- PLC activates ____
- IP3 binds to membrane on ____
- ____ released from ER
- Mediates many actions• ____ are the second biggest source of Ca++ in cell
○ ____ leading to release of signal
Gqalpha PLC IP3 ER Ca++
lysosome
TLR3
Adrenaline (epinephrine) has multiple responses depending upon what GPCR it stimulates
* Different receptors depending on g-proteins coupled to * Alpha1 - Gq - PLC - IP3 - release of \_\_\_\_ from ER - contraction of \_\_\_\_ muscle * Alph2 - Gi - \_\_\_\_ adnylyl cyclase - reduction o of Camp * Beta - Gs - increase \_\_\_\_ - increased by cAMP (blocked by \_\_\_\_)
Ca++ smooth inhibits adenylate cyclase beta blockers
Proposed purinergic signaling pathways underlying the cellular responses associated with P2 receptor activation in various areas of the tooth
Be aware that a single neurotransmitter (ATP)
Can initiate ____ in a single organ.
Many of these linked to ____
• P2Y6 (metabotropic channel (leads to transcriptional regulation of cytokine \_\_\_\_) • P2X7 - cytokine \_\_\_\_ • Mechanical stress - P2Y - \_\_\_\_ - second messengers - influence inflammation • Nerve cells - \_\_\_\_ stimulation P2X2A3 - pain • Stimulate ATP mediating via \_\_\_\_, leads to activation of inflammasome \_\_\_\_ - used to trigger maturation and release of \_\_\_\_ (major inflammatory cytokine around) • Occurs in both \_\_\_\_ and \_\_\_\_ cells • Drugs based on \_\_\_\_ to stop pain ○ Opioid crisis will force development of more analgesic pathways
multiple responses
inflammation
IL6 IL8 PKA ATP connexin NLRP3 IL1beta neural non-neural purines
Postsynaptic density: molecular scaffolding to keep receptors in place, mediate effects of stimulation
- PSD across from docked synaptic vessicles
- ____ and ____ elements
- Clusters ____ and receptors
- Important in ____ potentiation - ____ – ____- transcription• When PS receptors stimulated they’re support in PS density
• NMDA important in learning
• Organization in PSM is critical in consequences of NT activation
○ ____
○ Very tightly regulated underneath the ____
cytoskeletal regulatory ion channels long-term NMDAR CAMKII
rafts
membrane
PSD-95 marks synapse location on dendrites
____ –
gets synaptic vesicles to pre- synaptic release site
PSD-95
SYNAPSE
* Protein that indicates where PSD are located * Neuron in culture and stain in green (PSD-95) * Synapsin in yellow * Many sites where \_\_\_\_ and \_\_\_\_ are together (\_\_\_\_and \_\_\_\_)
synapsin synapsin PSD presynaptically postsynaptically
Key steps in synaptic transmission
- An AP travels down axon and depolarizes presynaptic terminal.
- ____ channels open in response to the depolarization.
- Ca+2 enters the synaptic terminal through Ca+2 channels.
- Increased [Ca+2] activates neurotransmitter release from ____.
Ca++
vesicles
Key steps in synaptic transmission
5. Neurotransmitter in the synaptic cleft either:
a) binds to ____ on the postsynaptic membrane
b) is ____ or ____ away or is recycled before it binds to a receptor
6. The post-synaptic membrane potential changes:
a) Depolarizes if excitatory
b) Hyperpolarizes if
inhibitory
receptors
degraded
diffused
Many drugs of interest interfere with synaptic transmission
Drugs can be used to enhance or impede many steps in synaptic process
• Drugs that have been developed target neurotransmission - multiple ways to increase or decrease the transmission by manipulating the process • Agonistic: ○ Increase synthesis of \_\_\_\_ (precursor) ○ Destroy degrading \_\_\_\_ ○ Inhibit the negative feedback of autoreceptors ○ Stop the \_\_\_\_, increasing cxn in cleft • Antagonistic ○ Increase molecules that break down NT ○ Break down molecules that synthesize ○ Block \_\_\_\_ receptors
NT
enzymes
reuptake
postsynaptic
