Excitable cells 9: Synaptic Transmission Flashcards
3 Types of neuron
Sensory - touch, smell, taste, temperature
Motor - control muscle action (directly or indirectly)
Inter-neurone - connect neurons
Describe in detail an electrical synapse
Symmetrical morphology
Bidirectional transfer of information
Pre and post synaptic membranes very close (3.5nm) and connected via gap junctions
- allow electronic and metabolic continuity between cells
Ions can flow through gap junctions
Instantaneous transfer between cells - unlike chemical synapses
What is a gap junction formed from?
Connexon pour
- formed by 6 connexins
Gap junction formed from 1 pre and 1 post synaptic connexon
Contrast the main characteristics of each synapse type
Electrical
- often symmetrical, bidirectional
- gap junctions (connexins)
- Very fast (no synaptic delay)
- Ca2+ independent
- Temperature insensitive
- Large synapse
- limited function (usually excitatory)
- Synchronised activity
Chemical
- Highly developed structure
- Polarised (structure and function)
- Slow (synaotic delay)
- Ca2+ dependent
- Temperature sensitive
- Thousands of small synapse
- Versatile (excitatory and inhibitory)
- Specific point-to-point activity
3 types of chemical synapse
Axo-dendritic
Axo-somatic
Axo-axonic (including pre-synaptic terminal to other pre-synaptic terminal)
Main anatomical difference between excitatory and inhibitory synapses?
Excitatory have Asymmetrical membrane differentiations
Inhibitory have symmetrical membrane differentiations
Main excitatory and inhibitory Neurotransmitters?
Inhib -> (GABA) gamma aminobutyric acid
Excite -> Glutamate
Describe catecholamine (e.g. DA, NA) pathway of synthesis
Synthesised in the nerve terminal
- Uptake of Tyrosine by L-amino acid transporter
- Tyrosine converted by tyrosine hydroxylasae to DOPA
- DOPA converted by decarboxylation to DA
- DA taken up by vesicles by VMAT (transporter)
If vesicles contain DA Beta-hydroxylase, DA converted to NA
Where does peptide NT synthesis take place? Give brief overview
Synthesised in the cell body from newly transcribed pre-pro-peptides (much larger precursor)
- packaged into vesicles and transported to axon terminal
Where are each type of NT stored?
Most transmitters stored in 40-50nM synaptic vesicles
e.g. GABA, glutamate, DA, ACh
Neuropeptides are stored in larger >100nm Dense core vesicles
e.g. Somatostatin, Enkephalin
Why are NTs stored in vesicles?
Achieve very high concentrations (100mM)
Protection from cytoplasmic enzymes
Allows for regulation (of synaptic release)
