Intro To ANS

Question 1

What is an observed effect of blocking nicotinic acetylcholine receptors at rest?

Answer 1

Constipation due to blockage of PNS and therefore gut motility

Question 2

What is the effect of blocking nicotinic ACh receptors on heart rate during rest and exercise?

Answer 2

During rest- the PNS is dominant so heart rate increases when PNS is blocked

During exercise- the SNS is dominant so heart rate increases when PNS is blocked

Question 3

what are the principle targets of the autonomic nervous system?

Answer 3

• exocrine glands e.g. salivary glands
• smooth muscle e.g. lungs, vessels, bladder
• cardiac muscle
• metabolism e.g. liver, GI
• host defence e.g. skin

Question 4

name targets dominated by the PNS

Answer 4

• eye–>pupillary constriction: mediated by PNS via CNIII
• GI–>cephalic and gastric phases of digestion via CNX
• cardiac tissue–>basal heart rate: dominated by PNS at rest
• bladder–> micturition
• lung–> bronchoconstriction
• salivary glands

Question 5

what do all pre-ganglionic fibres in the ANS release?

Answer 5

Acetylcholine

Question 6

what length pre- and postganglionic fibres does the sympathetic nervous system have?

Answer 6

short preganglionic

long postganglionic

Question 7

what length pre- and postganglionic fibres does the parasympathetic nervous system have?

Answer 7

long preganglionic

short postganglionic

Question 8

describe the discharge of sympathetic and parasympathetic NTs?

Answer 8

para: discrete
symp: divergent (mass discharge) - multiple actions will take place at once to accompany an event

Question 9

why is enteric nervous system special?

Answer 9

doesn’t need concious input all the time

myenteric and submucosal plexuses do the coordination

Question 10

what do the sensory neurones of the ENS do?

Answer 10

they are linked to mucosal chemoreceptors and stretch receptors to detect chemical substances in the gut lumen or tension in gut wall caused by food

information is then relayed to submucosal and myenteric plexuses by interneurones

Question 11

what do the motor neurones of the ENS release to carry out motor function?

Answer 11

release ACh or substance P to contract smooth muscle

release vasoactive intestinal peptide or NO to relax smooth muscle

Question 12

where are nicotinic receptors found?

Answer 12

in all autonomic ganglia (mid region)

Question 13

what are the properties of nicotinic receptors?

Answer 13

stimulated by nicotine/ACh
type 1- ionotropic therefore fast acting
found in ganglia and muscle

Question 14

where are muscarinic receptors found?

Answer 14

at the effector organ (end region) innervated by the parasympathetic NS - rarely is SNS but there are exceptions

Question 15

properties of muscarinic receptors?

Answer 15

stimulated by muscarine/ ACh

type 2- G protein coupled

slower receptor

Question 16

what are the important subtypes of muscarinic receptors?

Answer 16

M1- neural e.g. in the forebrain (Gq)

M2- cardiac e.g. inhibitory autoreceptors (Gi)

M3- exocrine & smooth muscles e.g. hypothalamus (Gq)

Question 17

where are adrenoreceptors found?

Answer 17

at all effector organs (end region) innervated by the SNS e.g. cardiac tissue,
and sweat glands

these are type 2 G protein coupled receptors

Question 18

how is acetylcholine produced?

Answer 18

acetyl CoA+ choline–> ACh + CoA

via choline acetyl transferase

Question 19

how is ACh degraded?

Answer 19

by acetylcholine esterase to produce choline and acetate

Question 20

how is Adrenaline/ Noradrenaline produced?

Answer 20

tyrosine–>DOPA–>dopamine–>NA(—>A via PNMT)

tyrosine hydroxylase
DOPA decarboxylase
Dopamine beta hydroxylase

Question 21

how is NA/A degraded?

Answer 21

uptake 1 protein into presynaptic terminal to be broken down by Monoamine Oxidase A (MAO-A)

uptake 2- cathecol-O-methyl transferase (COMT)