peripheral nervous system Flashcards
in the autonomic nervous system what type of fibres are used
preganglionic fibres: myelinated B fibres
postganglionic fibres: unmyelinated C fibres
what is basic structure of parasympathetic system
originates in S2-4 and cranial nerves 3,7,9 and 10
long preganglionic neurones and short post ganglionic neurones
nictonic receptors at ganglion, muscarinic receptors between postganglionic fibre and effector
what is basic structure of sympathetic system?
originates in T1-L2
short preganglionic neurones, long post ganglionic neurones
preganglionic neurones also synapse directly onto adrenal medulla in kidney
nicotinic receptors at ganglion and adrenal medulla, adrenoreceptors between postganglionic neurones and effectors,
exception is sympathetic innervation of sweat glands in skin, uses Ach
where is enteric nervous system innervated
myenteric plexus and submucosal plexus
what does activation of myenteric plexus cause?
increase in tonic contraction
increase rate and intensity of rhythmic contractions
increases velocity of conduction
what does activation of submucosal plexus cause
increases secretory activity and modulates intestinal absorption
what types of muscarinic receptors are there, are they excitatory or inhibitory?
M1-3
M1 and 3 are excitatory
M2 is inhibitory
what types of adrenoceptors are there, are they excitatory or inhibitory?
alpha1-2, beta1-2
alpha and beta 1 is excitatory
beta and alpha 2 are inhibitory
how do presynaptic parasympathetic fibres relate to postsynaptic ones
parasympathetic presynaptic/ganglionc fibres synapse onto 20 postsynaptic ones each
more than 1 presynaptic fibre can synapse onto a postsynaptic fibre, so the ratio in most organs is 1 to 1 pre to post
exception is the gut which has lots of postsynaptic fibres, causing a ratio of 1:8000
how is release of neurotransmitter of postganglionic neurones to effector regulated
sympathetic:
modulated by alpha 2 autoreceptors of presynaptic, postganglionic neurone
activation of alpha 2 receptors cause auto-inhibitory feedback via inhibition of adenylate cyclase and reduction of calcium entry to presynaptic neurone
NA is also modulated to lesser extent via Ach on M2 receptors, opiates on delta receptors, histamine on H2 receptors, dopamine on D2 receptors, adenosine on P1 receptors and prostaglandin E
parasympathetic:
also autoinhibitory feedback but to lesser extent of Ach using M2 receptors
what neurotransmitters are used in the intrinsic neurones of the enteric system
5HT, purines and peptides (including enkaphalins and substance P)
how does co-transmission effect autonomic ganglia
co transmission of other neurotransmitters can either cause a :
slow excitatory effect (such as LHRH, which causes reduction is potassium permeability)
inhibitory effect (opiates and muscarinic receptors, causean increase in potassium permeability)
these effects are postsynaptic
what is NANC transmission?
no adrenergic non cholinergic transmission, this happens at effector-postganglion synapse
there is often residual action due to one or more other effectors (NANC transmission)
NANC can be excitatory via ATP and substance P
NANC can be inhibitory via neurotensin or opioids
action of NANC is tissue dependent; it is excitatory in vas deferent and blood vessels, inhibitory in the gut
what are known NANC transmitters
dopamine: sympathetic neurones including kidney
GABA: enteric neurones
5HT: enteric neurones
ATP: post ganglionic sympathetic e.g in blood vessels and vas deferens, is responsible for fast excitatory post synaptic potentials and rapid phase contraction of sympathetic innervation of many smooth muscle tissues, works on P1 and P2 receptors
peptide transmitters: such neuropeptide Y
prostaglandins, substance P, histamine, nitric oxide
what is action on NO in NANC transmission
nitric oxide is short lived gas which acts as transmitter
nitric oxide mediates relaxation of stomach induced by vagal (parasympathetic) stimulation and other muscle from intrinsic NANC nerves
vasodilator effects of Ach and bradykinin also use NO
mechanism of NO: causes increase in cGMP
