SysPhy- Synaptic Transmissions

SysPhy- Synaptic Transmissions

1. Synapses are the junctions between neurons and other cells, acting as functional contacts

   • Found between Neurons, neurons+muscle cells, and neuron+Tissue

2. 2 types of Synapses, Electrical and Chemical

   • ELECTRICAL
     • Pre+Post synaptic mem held together at gap junctions
       • Held together by integeral mem pro's called connexanons
     • Opposing mem are held 2nm apart
     • Proteins between pores allow movement between 2 cells, 2 neurons share a mem
     • Present in both PNS and CNS but rare, seen in vesticular nuclei, eyes, cilery ganglia
   • CHEMICAL
     • Discovered by Otto Loewi
       • Noticed release of Chem (Acetylcholine)
     • Pre-Post synaptic cells not directly coupled
     • Mostly studied in the NMJ, but can also be seen in the adrenal Medulla, synaptosomes, and brain slices
     • Big diff between CNS and PNS: NMJ=arrival of single AP results in fast release of NT, Much slower in CNS, numerous AP needed for release of single vesicle

3. NT Release is Ca dependant as:

   • Removal of Ca from Extracellular fluid tissue fluid results in no nerve impulse
   • Ca Chelators
   • Non-Specific blockade of Ca channels
   • Fluroesense imaging, e.g. injection of aequorin into synapses

4. Sequence of Events

   • 1) Ca channel opens, Ca2+ increase causes fusion of synaptic vesicles with presynaptic mem's, release of neurotransmitter into synaptic cleft
     • 2) Transmitter diffuses across cleft+Binds with postsynaptic receptors, Recep-operated ion channels open, creating ion current, which (depending on trans+recep) excites or inhibits the postsynaptic neuron
       • 3) Signal is terminated when trans is released from recep. Recep is then broken down+taken up by neurons, these transmitters could be biogenic amines, peptides, V. large range
         • Trans can be metabolised by either extracellular tissue/Intracellular neuron or glial
           • EXTRACELLULAR: Metabo within synapse turns ACH into acetate (Sorted out in liver)+Cheline (Which re-enters synapse ''Re-cycled'')
           • INTRACELLULAR: Metabo active transport into cell, Metabolises nor-adrenaline into Monoamine+Oxidase (both can be seen in urine)