Neurotransmitters 1 Flashcards
Fast, reliable, and bidirectional mode of communication throughout the CNS
Electrical synapses/gap junctions
Electrical synapses/gap junctions allow what type of molecules to pass from one cell into another? What type of passage?
Ions and small molecules (<1000 Da); Diffusion
What proteins form the electrical synapse/gap junction? Be specific in the makeup.
- Connexins, ~20 of them
- 6 connexins form 1 connexon
- 2 connexons align to form a channel
What are electrical synapses important in? List 4.
- Embryonic stem cells
- Retina
- Auditory system
- Cortex
What regulates an electrical synapse? List 4.
- Cytosolic pH
- Cytosolic calcium
- Phosphorylation
- Voltage
This is caused by mutations in one connexin
The most common form of inherited deafness in Caucasian populations (DFNB1)
What do electrical synapses allow?
Allow groups of similar neurons to be synchronized e.g. hormone-secreting neurons in hypothalamus - get burst of hormone secretion; neocortical interneurons; cells of adrenal medulla
Explain the membrane potentials in pre and post-synaptic neurons
- Potential in downstream neuron won’t go as high
- Signal will be degraded
- Signal is less intense, more spread out
- Not faithfully transmitter. Quick, but can’t keep doing this forever
Do electrical synapses have a synaptic delay?
Yes, ~0,1 msec
What is the predominant mode of signaling?
Chemical synapses
Which type of synapse (electrical or chemical) is faster?
Electrical synapses. (Chemical are not quite as fast)
2 key features of a chemical synapse
- Synaptic vesicles
2. Receptors on post-synaptic ending
What is the major different in contact of pre and post synaptic membranes in chemical and electrical synapses?
Electrical synapse-connected by desmosomes, no synaptic cleft, touching each other
Chemical synapse-no direct contact with each other, 2-4x bigger membrane space, contain synaptic cleft ~20 nm
In vesicular release for major neurotransmitters, an action potential propagates down an axon and does what to the presynaptic terminal?
Depolarizes it
What is the consequence of depolarization of the presynaptic terminal in vesicular release?
Opens voltage gated Ca2+ channels
What is the difference in intracellular and extracellular concentration of Ca2+ ?
[Ca2+] outside = mM (10^-3)
[Ca2+] inside = uM (10^-6)
much smaller inside
What initiates fusion of synaptic vesicles with plasm membrane in vesicular release?
Influx of Ca2+. After depolarization, calcium voltage gated channels open and calcium ions enter down their electrochemical gradient. (Equilibrium potential for Ca = ~100 mV)
After fusion of synaptic vesicles with plasma membrane, vesicle content is released into this very small region
Synaptic cleft
What type of receptors on post-synaptic cells do released transmitters act on?
Ligand gated ion channels or receptors that use G proteins (GPCRs)
True or false: Transmitters can only act on receptors on the post-synaptic cell
FALSE. They can also act on receptors on the pre-synaptic terminal
What inactivates transmitter? List 4.
Na+ dependent reuptake, degradation and/or diffusion, or glial metabolism
Vesicular membrane must be retrieved. What two events facilitate this?
Exocytosis followed by endocytosis
Pre-synaptic vesicles contain more than one kind of vesicle. Release from these types has a different Ca2+ dependence and occurs at a different place
Large dense core vesicles (LDCVs)
Calcium is a crucial player of vesicle release. What are two of its sources?
- Usually comes across the synaptic plasma membrane to start release
- Can also be liberated from intracellular space