synaptic transmission and neurotransmitter release Flashcards
what is a synapse
neuroanatomical structure that permits communication between a neuron and its target cell
what is a synaptic cleft
physical gap between neuron and target cell
what are the 3 types of synapses
- axodendritic
- axosomatic
- axoaxonic
why are neurotrasnmitters stored in vesicles
- quantal release
- protection from degradation
- conservation (many NT are recycled)
what are the 4 steps in vesicular release
- action potential
- calcium entry
- membrane fusion
- endocytosis
how does calcium enter the synaptic terminal
- through voltage-gated calcium channels
- these are the N-type channels
- concentrated at active zones
what does the proton pump do
creates a proton gradient across the synaptic membrane
what do transmitter transporters do
uses energy of proton gradient to transport NTs into vesicles
what occurs when there is release from cytoskeleton
- action potential reaches the terminals
- causes voltage-sensitive calcium channels to open
- intracellular calcium concentrations increase
what is calcium-dependent phosphorylation of synapsin
causes the vesicles to detach from microfilaments (from cytoskeleton)
what are snares
vesicular (v-snare) vs terminal (t-snare)
what does snap-25 do
(t-snare) regulates the assembly of snares that tether the vesicle to the presynaptic membrane
what does synaptotagmin do
(v-snare) is a Ca2+ sensor and catalyzes membrane fusion
what are some effects of toxins on NT release
- tetanus toxin damages synaptobrevin
- botulinum toxins damage t-SNAREs and V-SNARES
what are 3 sources of botulism toxin
- toxicoinfectious botulism (grows in intestinal tract - often in foals)
- ingestion of preformed toxin (animal ingest contaminated feed, any age affected)
- infection in wounds (rare)
electrically-based cell communication
- allows ions to pass directly from the cytoplasm of one cell to the cytoplasm of another
- ion channels
- exist in only a few areas of mammalian CNS
- more common in invertebrates
what do electrical synapses permit
synchronous firing
what do gap junctions allow
rapid excitatory stimulation
- used to respond with high frequency in nerve cells
- stay open for seconds to minutes
what are ionotropic receptors
- ligand gated ion channel
- direct modulation of neuron excitability
what are metabotropic receptors
- G-protein coupled receptors
- indirect modulation of neuron excitability
- downstream regulation of ion channels
what are examples of ionotropic receptors
- Na+ and Ca2+ (depolarization/excitatory)
- Cl- (hyperpolarization/inhibitory)
autoreceptors
- on presynaptic terminals (ionotropic or metabotropic)
- regulates transmitter release (inhibits further NT release)
- can be a different subtype compared to postsynaptic receptors (potential for specific drugs to control NT release)
NT and the receptors that bind them
- many neurotransmitter systems have multiple receptor subtypes
- the different receptor subtypes can have differential distribution in the CNS and periphery
