Nervous System Flashcards
communication within the PNS
nerve fibres
sensory reflex arc
synapses
release of NT
2 types of nerve fibres in PNS
afferent - sensory info to CNS
efferent - signals from CNS to periphery
sensory reflex arc pathway
sensory receptors to afferent nerve fibres to dorsal root ganglion with cells bodies of neurones to spinal cord to interneurones (relay) to efferent to effector cell
spinal cord structure
dorsal horn - sensory
lateral horn - spinal preganglionic neurones of ANS
ventral horn - somatic motor neurones
active zone
where vesicles released in synapse
release of NT process
synthesis
storage to protect from enzymes and package at high conc
release - dock, Ca, fusion, exocytosis, endocytosis recycling
activation of ionotropic/G-coupled
inactivation by enzymes by breakdown
somatic NS
voluntary muscle contraction
efferent pathway (motor neurone to skeletal muscle) - single neurone with cell body in ventral horn of spinal cord or nuclei within higher brain centres
1 neurone from spinal cord so can be very long (over 1m)
motor neurone synapses at NMJ/endplate
NT is ACh and choline reabsorbed to presynaptic terminal
autonomic NS
efferent pathway - 2 neurones in series of preganglionic N in brain stem/lateral horn of spinal cord synapses in ganglion (cell bodies) then postganglionic N with cell body in autonomic ganglion outside CNS synpase with effector cells
what NT is released from the preganglionic neurone in both sympathetic and parasympathetic nervous systems?
acetylcholine, ACh
where is NT released from? (structure in NS)
varicosities - swellings on axons which contain vesicles with NT
what NT is used as well as ACh in sympathetic NS?
noradrenaline, NA
released from most postganglionic neurones except sweat glands which use ACh
cholinergic synapses
ACh
2 classes: nAChR (nicotinic), mAChR (muscarinic)
nAChR cholinergic synapses
nicotinic, ligand-gated ion channels, ionotropic
ACh/nicotine activates
5 protein subunits (2a, b, y, d) form channel
bind to alpha to open, M2 transmembrane domain creates channel
like colander not pore
mAChR cholinergic synapses
muscarinic, G-protein coupled, metabotropic
ACh/muscarine/noradrenaline/adrenaline activates
7 transmembrane domains
G protein with aby resting bound to GDP
receptor binds G alpha when activated and GDP replace by GTP so target protein activated
noradrenergic synapses
noradrenaline NT
adrenoceptors (a/b) are G-protein coupled
GPCRs after split
yb of G protein splits with alpha and activates GIRKs (G-protein-gated-inward-rectifier K channel) so open K channel
somatic motor neurones synapses
parasympathetic motor neurone synapses
sympathetic motor neurone synapses
nAChR
nAChR in ganglia and mAChR at effectors
nAChR in ganglia, NA activate and a/b adrenoceptors (nAChR in adrenal medulla causes adrenaline release, nAChR in ganglia causes mAChR in sweat glands)
what receptors are at an NMJ
nAChR - nicotinic acetylcholine receptors
breakdown of ACh
acetate and choline
cholinergic transmission in NMJ
1) SYNTHESIS: choline reuptake Na dependent
precursor choline + acetyl CoA from mitochondria makes choline
acetyltransferase (ChAT) makes ACh
2) STORAGE: active pump H into vesicle by vAChT w/ energy, 2 H out + ACh in
3) RELEASE: blocked by various toxins by blocking Na and Ca channels
4) ACTIVATION: quanta of NT activates nAChR so causes mEPP (miniature end plate potential) which summate and AP so contraction
5) INACTIVATION: AChE acetylcholinesterase breaks ACh
hemicholinium 3
blocks choline reuptake
not used clinically
vesamicol
uptake and storage of ACh in vesicles inhibited
not used clinically
TTX in cholinergic transmission
blocks voltage-gated Na channels so no AP and no release of NT from pufferfish (they get it from sea)
Conatoxins
snails
block P/Q and N-type voltage-gated Ca channels so no NT release