synapse structure Flashcards
What is a synapse
a synapse is the specialized zone of contact at which one neuron communicates with another neuron or effector cell
There are 2 major tymes of synaptic transmission
Electrical and chemical
Electric: single step, fast, bidirectional
Chemical: multiple steps, synaptic delay, unidirectional, plasticity
electric synapse
size: 3.5 nm wide, each apposing cell contributes a connexon, a hemi channel thats composed of 6 connexins
Pore: 1.5 nm permeable to ions, ATP second messengers (for glia, neocortex, development)
Distribution: invertebrate, early embryonic stages, brainstem and many interneurons and astrocytes
Chemical synapse
Tripartite (pre and post synapse, with a synaptic cleft), glial cells also hold together these synapses
Major steps in synaptic transmission:
1. NT synthesis at presyn sites or soma if its a peptide and packed into synap vesicles
AP opens Ca channels allowing for CA influx
3. Vesicle fusion and NT release
4. NT diffusion across cleft and binding with post synaptic receptors
5. post synap response IE PSPs or GPCRs
6. Termination of NT action by reuptake, diffusion, enzymatic hydrolysis
Quantal NT release
miniature endplate potential (mEPP) is the building block of evoked EPPs
molecular control of NT Release
Docking, priming the fusion
SV fusion machinery
SNARE and accessory proteins attach to the CA and they are able to bind with CA channels and sensors
Post synaptic responses
Post synaptic potential (PSP)
receptor mediated responses
Synaptic plasticity and retrograde modulation
EPSPs: depolarization with a Cation influx (via Glutamate or Ach NTs)
IPSPs: hyperpolarize with CL- influx, GABA, Dopamine, 5HT, Glycine
Slow effects: metabolic receptor mediate it is indirects can be 5HT or neuropeptides
ionotropic vs metabotropic
ionotropic: receptor is ion channel, FAST
Metabotropic: inderectly linked to in channels, can be GPCR, or RTK, its SLOE, with a 2nd messengert cascade
receptor type determines NT effect, ie effect of Ach depends upon receptor (nicotinic- excitatory, with NA inflow) (muscarinic- excitatory or inhibitory subtypes)
synaptic plasticity and modulation
short term plasticity: sub seconds to minutes
LTP: hours or longer: can be potentiaion or depression, often includes structural changes, critical for memory or learning
Retrograde synaptic signaling
Brain- derived neurotrophic factor (BDNF)
CBD
NO: postsynaptic CA-> activate NO enzyme and NO production-> No gas diffuses back to presynapse-> guanylate cyclase-> cGMP
Myasthenia Gravis
Description: autoantibodies against nicotinic ACH receptors in skeletal muscle
Features: muscle weakness( especially ocular)
Treatment: ACE inhibitors, immunosuppressive Abs
Lambert-Easton Myasthenic syndrome
Description: Autoantibodies against presynaptic voltage gates ion channels
Feature: muscle weakness (hips and shoulders)
treatment: immunosuppression
Parkinsons Disease
Description: degeneration of dopaminergic neurons in the brainstem
Features: tremor, rigidity, akinesia, postural stability
Treat with ldopa, dopamine agonists, amhetamine, coke
