Neurotransmitters Flashcards
Two main types of synapses are
1) Electrical
2) Chemical
What is a gap junction and what makes it up
a channel which forms a low resistance pore between cells
Connexins form a hemichannel in each cell called connexons. These Connexons join to form a gap junction.
Gap junctions make up what type of synapses
Electrical
How does a chemical synapse work
Action Potential invades and leads to release of a chemical transmitter which diffuses across a synaptic cleft to interact with ligand-gated ion channels in the postsynaptic membrane. Electrical signals are thus transduced into a chemical signal
Chemical transmission is unidirectional whereas electrical transmission is bi-directional
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Steps of chemical neurotr5ansmission
1) Transmitter is synthesized and stored in vesicles in the synaptic terminal
2) An action potential invades the terminal
3) Terminal depolarizes
4) Depolarization opens up the voltage gated calcium channels leading to influx of calcium
5) Calcium influx causes fusion of synaptic vesicles with presynaptic membrane (via SNARES) Release occurs in packets called quanta. Contents of 1 veisicle = 1 quanta
6) Transmitter is released into synaptic cleft and diffuses across
Postsynaptically
1) Transmitter binds to receptors
2) Opening or closing of ion channels occurs
3) Postsynaptic currents cause membrane potential change
What does the “high safety factor” of chemical synaptic transmission at the neuromuscular junction refer to?
Ensures that every time a motoneuron releases neurotransmitter, every muscle fiber it inntervates has a an AP and contracts
What are some of the anatomical specializations at the NMJ to ensure this high safety factor
many release sites for neurotransmitter, high number of receptors, high quantal content, and high probability of release for each quanta, high number of postsynaptic receptors
What is the neurotransmitter at the NMJ?
Acetylcholine
What type of receptors are present at the NMJ?
Nicotinic
Know that CNS synapses are much simpler anatomically than the NMJ synapses
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CNS synapses are also much more diverse than the NMJ, there are many different transmitters and responses can either be excitatory inhibitory or modulatory
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Two types of chemical transmission are
Ligand Gated and G- Protein Coupled
Fast transmission =
Ligand gated
What does it mean to say that Ligand gated channels are an integrated receptor?
The binding site for the ligand - neurotransmitter- is part of the same molecular complex as the channel. Binding of the ligand causes a conformational change in the channel resulting in gating activation.
G- Protein coupled Receptors mediate “neuromodulatory effects”, that is
Biochemical changes in the cell which alter function an/or excitability.
G- protein coupled receptors have 7 transmembrane spanning regions and when they bind a ligand, conformational change facilitates interaction with a G- Protein.
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At teh neuromuscular junction, chemical synaptic transmission is specialized for what?
High Safety factor to ensure that every time a motoneuron releases transmitter, every muscle fiber it innervates has an AP
- Many neurotransmitter release sites
- High number of receptors
- High quantal content
- High probability of release for each quanta
What is the Neurotransmitter at the NMJ and what type of receptor is present
Ach, Nicotinic
What is different about synapses in the CNS than synapses in the NMJ
CNS synapses are much simpler anatomically than the NMJ. Low Quantal content and low safety factor. Much more diverse as well… transmitter responses can be either excitatory, inhibitory, or modulatory
Ach
Excitatory
Glutamate
Excitatory
GABA
Inhibitory
Dopamine
Excitatory via D1, Inhibitory via D2
Norep
Excitatory
Substance P
Excitatory
Histamine Excitatory
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Calcium interacts with what proteins (directly) in the presynaptic terminals?
SNAREs
SNAREs do what
Facilitate docking of neurotransmitters at the postsynaptic terminal
Lmbert Eaton Myasthenic Syndrome is what
When small cell carcinomas release antibodies against presynaptic L- type calcium channels
Myasthenia Gravis
autoimmune disease that targets the nicotinic receptor at the NMJ
Botulinum toxin and SNARE proteins?
Yeah…SNARE proteins can be damaged by the clostridial bacterial toxins botulinum and tetanus.
Botox does what
Blocks Ach release at the NMJ
Myasthenia Gravis does what
Blocks Acetylcholine uptake by the NMJ
EPSP?
Excitatory Post-synaptic potential….increases the likelihood of an AP occurring.
What are the most common mediatorys of EPSP?
glutamate or aspartate
Remember that most synaptic inputs are far too small to elicit an AP on their own. How do neurons derive an AP from these types of inputs?
Summation
Neuronal somas and initial segments can integrate synaptic inputs and generate summation of inputs that would otherwise be too small to generate an AP alone
Two types of synaptic integration
Temporal Summation- occurs when two PSPs elicited in the same synapse occur close enough in time so that the first has not completely decayed before the second occurs
Spatial Summation: refers to addition of effects of two different synapses that are close enough in location
Know Brain energy metabolism resting and activated
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