Lecture 16; The Chemical Brain 2 Flashcards
What is the function of electrical synapses?
Physically connects cytoplasm of two cells
if one cell depolarises, so does the other
Reduction of signal strength as it passes
Faster
Used in some Reflexes • Escape Responses
Bidirectional
What are the advantages of chemical synapses?
Synaptic delay’ but • GAIN (Amplification) Unidirectional (one-way) The post synaptic neurones can either depolarise of hyper polarise reater complexity of processing • Produce long-lasting changes... • Synaptic plasticity • LTP, LTD
Where are gap junctions present between?
neurons
glial cells, including astrocytes, oligodendrocytes, and microglia;
ependymal cells
eptomeningeal cells.
What does each neurone have?
many incoming synapses, and may have multiple outgoing synapses
What are necessary for action potentials?
Simultaneous signals
What is involved in a tripartite synapse?
Astrocytes
What do astrocytes do?
They recycle NTs
If glutamate is left over, it will use the G-G cycle in order to return back to neurone and create more NTs
Have own receptors which respond to NTs
How are microglia now involved in the Tripartite Synapse?
Microglia now also known to regulate synapses
Resident macrophage in the CNS
Without microglia, what do you not get properly?
Synaptic plasticity, microglia is very involved in the development of synapses being known as a synaptic modellers
What is a method to define a NT?
- Must be present within the presynaptic neuron
- Must be released in response to presynaptic depolarization, and must be Ca2+-dependent
- Specific receptors for the substance must be present on the postsynaptic cell
How to tell apart NT and Neuromodulator apart?
A NT has a;
Anatomically-specialised junction (release site)
Across narrow cleft (distance of effect)
What can delivering new dopamine producing cells to Parkinsons patients do?
can restore function, without recreating synapses
How are Neuromodulators different to NTs?
released at axon terminals, but can act outside synaptic clefts
How do NTs get to the synapse?
along the tracks microtubules provide, they travel down the soma
the directional movement of these membrane bound vesicles is due to the family of motor proteins linking the vesicles to the microtubule
Kinesin travels down soma
Dyenin travels up to the soma
What are NT receptors either?
Ionotropic or Metabotropic
What do Ionotropic receptors consist of?
Combined Binding site + Ion channel
• Short latency (10-50 ms)
• Postsynaptic (usually…)
What do Metabotropic receptors consist of?
Binding site not associated with Ion channel
• G-protein / 2nd Messenger
• Longer latency
• Pre- and post-synaptic
What NTs are involved in both Metabotropic and Ionotropic receptors?
ACh
GABA
Glutamate
5-HT
What two entrances does metabotropic receptors use?
Using G protein to activate Ion channel
Using G protein to create a signalling cascade
Which receptors associated with glutamate is Ionotropic?
NMDA, AMPA, Kainate
Excitatory response
Which receptors associated with glutamate is Metabotropic?
Group I, II, III
I - slow and excitatory response
II & III - slow and inhibitory response
What can glutamate receptors be?
pre-, post- and extra-synaptic
Why do NT Receptors have different locations and actions?
- Some Depolarise or Hyperpolarise the post-synaptic neuron
- Some physically alter the synapse to change future responses
- Increase strength of future de- or hyper-polarisation
- Achieved by adding / removing different receptors
- Synaptic plasticity • LTP, LTD
What is GABA A receptor?
consists of five subunits that span the membrane
they bind together creating a chloride channel
When chloride travels through it changes the membrane potential
Does GABA have inotropic and metabotropic receptors?
yes
What is conditioning?
This is where the function of synapses can be altered and modulated so that it can increase productivity.
An example could be instead of one receptor being activate, 3 are instead leading to many intracellular reactions and eventually altered gene expression.
