Module 9 - synapses Flashcards
what are the 2 types of synapses
electrical and chemical
what is one way transmission called
rectifying
two way transmission?
non-rectifying
advantage of electrical synapses
fast and reliable
so used in escape reflexes
what are neurons connected by in electricla synapses
connexons in vertabrate
innexins in non-vertabrate
what do connexons/innexins form between neurons
gap junction
structure of connexons
6 subunits (connexins)
similar to ion channels but much bigger
why is a fly always able to fly away
uses electrical transmission whilst we use chemicaltransmission to capture it
what was missing in mutated drosophila who had no escape reflex
no innexins so no gap junctions
so the signal is transmitted down the giant fibres, but cant get past synapses
why are chemical synapses the more common and preffered synapse in animals
much more adaptable
what did otto loewi find when bathing fluid from one chamber with heart being stimulated was dripped into the next chamber without stimulation
the heart still slowed down
what did otto loewi discover as a consequence
‘vagus substance’ which ended up being ACh
so found out a water soluble chemical substance was stimulating the heart
why so many mitochondria in nerve terminals
vesciular release is very enrgy consuming
what are the 3 SNARE proteins
- synaptobrevin
- SNAP 25
- syntaxin
where is synaptobrevin located
on the vesicle
where is SNaP 25 and syntaxin located
on the membrane
what triggers the vesicles to release their contents
Ca2+
what is calcium sensed by in the vesicle
protein called synaptotagmin
in muscle, what is synaptic transmission called if it occurs with no AP or Ca2+ release
miniature end plate potential (since it is spontaneous release)
what is synaptic release with calcium called
evoked release/ End plate potential (in muscles)
what is one quantum
amount of trnsmitter per vesicle
what is quantal content
avg no. vesicles released in an evoked response
how do we calculate quantal content `
EPP current/1quantum current
what is key for vescle recycling
clathrin !!
what type of structure does clathrin form around vesicles
truncated icosohedral shape
with 20 hexagons and 12 pentagons
what 3 things are kept constant by clathrin
- vesicle size
- number of vesicles
- size of terminal
mechanism of action of botulinum toxin
a proteolytic enzyme
that cleaves SNARE proteins
stopping neurotransmitter release
how does ω-agatoxin work
blocks P/Q voltage gated Ca2+ channels
used by spider to subue its prey
how does ω-conotoxin work
blocks N-type voltage gated Ca2+ channels
used by cone snails to paralyse prey
how do α-neurotoxins work and what types are there
block nicotinic ACh receptors or to normal nicotinic receptors
- α-bungarotoxin
- α-cobratoxin
how can α-neurotoxins be used
not therapeutic
but have high affinity for nicotinc recpeotrs, so used as radioligands
how does physostigmine work
acts as AChesterase inhibitor
so = no breakdown of ACh
how can phygostigmine be used therapeutically
muscle weakness
boosts ACh conc,
how does tetanus toxin work
- toxin binds and enters in skeletal muscle junction but travels back up motor neurons into the CNS
- destroys SNARE proteins in inhibitory neurons that release GABA and glycine
- causes uncontrollable spasms
what bacteria causes tetanus
clostridium tetani
related to clostridium botulinum - botox
