peripheral nervous system Flashcards

1
Q

in the autonomic nervous system what type of fibres are used

A

preganglionic fibres: myelinated B fibres

postganglionic fibres: unmyelinated C fibres

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2
Q

what is basic structure of parasympathetic system

A

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

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3
Q

what is basic structure of sympathetic system?

A

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

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4
Q

where is enteric nervous system innervated

A

myenteric plexus and submucosal plexus

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5
Q

what does activation of myenteric plexus cause?

A

increase in tonic contraction

increase rate and intensity of rhythmic contractions

increases velocity of conduction

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6
Q

what does activation of submucosal plexus cause

A

increases secretory activity and modulates intestinal absorption

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7
Q

what types of muscarinic receptors are there, are they excitatory or inhibitory?

A

M1-3
M1 and 3 are excitatory
M2 is inhibitory

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8
Q

what types of adrenoceptors are there, are they excitatory or inhibitory?

A

alpha1-2, beta1-2
alpha and beta 1 is excitatory
beta and alpha 2 are inhibitory

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9
Q

how do presynaptic parasympathetic fibres relate to postsynaptic ones

A

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

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10
Q

how is release of neurotransmitter of postganglionic neurones to effector regulated

A

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

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11
Q

what neurotransmitters are used in the intrinsic neurones of the enteric system

A

5HT, purines and peptides (including enkaphalins and substance P)

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12
Q

how does co-transmission effect autonomic ganglia

A

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

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13
Q

what is NANC transmission?

A

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

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14
Q

what are known NANC transmitters

A

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

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15
Q

what is action on NO in NANC transmission

A

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

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