Intro to ANS

Question 1

what are the 3 branches to the CNS?

Answer 1

• ANS
• somatic NS
• neuroendocrine system

Question 2

what does the ANS act on?

Answer 2

• exocrine glands
• smooth muscle
• cardiac muscle
• metabolism
• in host defence

Question 3

what are some targets of the ANS?

Answer 3

• pupillary constriction: constriction mediated by PNS via oculomotor nerve
• cephalic and gastric phases of digestion: vagal nerve PNS mediation
• basal HR: PNS dominant at rest

Question 4

what targets only receive one branch of the ANS?

Answer 4

blood vessels

only SNS innervation

Question 5

what NT do all pre-ganglionic fibres release?

Answer 5

ACh

Question 6

describe the features of the PNS

Answer 6

• long pre-ganglionic
• short post-ganglionic
• all transmitters ACh
• discrete (1:1)

Question 7

describe the features of the SNS

Answer 7

• short pre-ganglionic
• long post
• releases mainly A and NA
• mass discharge

Question 8

describe the sensory neurones in the enteric nervous system

Answer 8

• sensory neurons are connected to mucosal chemoreceptors and stretch receptors
• they detect chemical substances in gut lumen or tension in gut wall caused by food
• info relayed to submucosal and myenteric plexus by interneurones

Question 9

describe the motor neurones of the enteric NS

Answer 9

• motor neurones release ACh or Substance P

- contract SM, vasoactive intestinal peptide or NO to relax SM

Question 10

describe the somatic NS

Answer 10

long neurones with eventual ACh release

Question 11

what are nicotonic receptors?

Answer 11

• found at ALL autonomic ganglia
• stimulated by nicotine/ ACh
• type 1 - ionotropic

Question 12

what are muscarinic receptors?

Answer 12

• found at effector organs innervated by PNS post-ganglionic fibres
• stimulated by muscarine/ACh
• type 2: G-protein coupled

Question 13

what effect would blockade of nicotinic ACh receptors have on HR at rest and then in exercise?

Answer 13

Rest: PNS dominant so inc. in HR if PNS blocked
Exercise: SNS dominant so dec. in HR if SNS blocked

Question 14

what are the subtypes of muscarinic receptors?

Answer 14

M1: neural e.g. forebrain (learning and memory) - Gq
M2: cardiac e.g. inhibitory autoreceptors - Gi
M3: exocrine and smooth muscle e.g. hypothalamus - Gq
M4: periphery e.g. prejunctional nerve endings
M5: striatal dopamine release

Question 15

where are adrenoreceptors found?

Answer 15

• found at all effector organs innervated by post-ganglionic SNS fibres
• not sweat gland
• stimulated by NA/A
• type 2

Question 16

describe how acetylcholine produced

Answer 16

Acetyl CoA + Choline –> ACh + CoA

enzyme: choline acetyl transferase

Question 17

how is it degraded?

Answer 17

acetylcholine esterase

Question 18

how is NA/A produced?

Answer 18

tyrosine --> DOPA --> Dopamine --> NA (--> via PNMT into A)
enzymes:
tyrosine hydroxylase
DOPA decarboxylase
dopamine beta hydroxylase

Question 19

what are the 2 uptake mechanisms?

Answer 19

1. Monaminde oxidase A (MAO-A)

2. Cathecol-O-Methyl Transferase (COMT)