3. Chapter 6: ANS

4 are the 4 main physiological functions regulated by the ANS

- Regulation of heart rate and cardiac contractility

- Visceral and cutaneous blood flow distribution

- GI motility and digestion

- Urogenital processes

describe the preganglionic fibers of both the SNS and PSNS

cholinergic fibers that release ACh to activate nicotinic receptors

describe the postganglionic fibers of the SNS

adrenergic fibers that release NE to activate either alpha or beta adrenergic receptors

describe the postganglionic fibers of the PSNS

cholinergic fibers that release ACh to activate M2 or M3 muscarinic receptors

what are the physiologic responses seen with activation of the sympathetic nervous system

- Increased heart rate and cardiac contractility

- Vascular vasoconstriction in skin and viscera with shunting of blood flow to skeletal muscle

- Hepatic glycogenolysis

- Bronchiolar and pupillary dilation

- Contraction of spleen

physiologic responses seen due to activation of the SNS is mediated by what

combined activation of peripheral sympathetic nerves innervating specific target organs and the adrenal medulla

what are the physiologic responses seen with activation of the parasympathetic nervous system

- Reduced heart rate

- Stimulation of GI secretions and peristalsis

- Contracts body of urinary bladder

- Modulates immune function

what is the action and receptor used with sympathetic activation of the radial muscle of the iris

pupillary dilation → alpha 1 receptor

what is the action and receptor used with sympathetic activation of the ciliary muscle of the eye

slight relaxation via beta 2 receptors

what is the action and receptor used with parasympathetic activation of the sphincter muscle of the iris

pupillary constriction via M3 and M2 receptors

what is the action and receptor used with sympathetic activation of the bronchiolar smooth muscle of the lungs

bronchiole dilation via beta 2 receptors

what is the action and receptor used with parasympathetic activation of the bronchiolar smooth muscle of the lungs

brochiole contraction via M2 and M3 receptors

what is your prototypical anti-cholinergic/muscarinic antagonist drug

atropine

how will atropine affect the lungs

allows for bronchodilation by blocking muscarinic receptors during respiratory distress

what is the action and receptor used with sympathetic activation of the SA node, atria, AV node, and ventricles of the heart

increased HR, contractility, automaticity, and conduction via the activation of beta 2 receptors

what is the action and receptor used with parasympathetic activation of the SA node, atria, AV node, and ventricles of the heart

decreased HR, contractility, automaticity, and conduction via the activation of M2 receptors

describe SNS activation of the coronary and pulmonary blood vessels

causes constriction via alpha 1 receptors and dilation via beta 2 receptors

describe SNS activation of blood vessels in skeletal muscle

causes constriction via alpha 1 receptors and dilation via beta 2 receptors

which receptors predominate the skeletal muscle

beta receptors

describe SNS activation of blood vessels in the skin and mucosa

constriction via alpha 1 receptors

describe SNS activation of blood vessels in the abdominal viscera

causes constriction via alpha 1 receptors and dilation via beta 2 receptors

describe ANS activity in the GIT in terms of motility

- SNS: low motility → a1, a2, b1, b2

- PNS: high motility → M2 and M3

what kind of drug is used to treat diarrhea

anti-cholinergic drugs because they slow down the motility of the GIT

describe ANS activity in the GIT in terms of its sphincters

- SNS: high tone → alpha 1

- PNS: low tone → M3, M2

describe ANS activity in the GIT in terms of its secretions

- SNS: inhibition → alpha 2

- PNS: stimulation → M3, M2

describe ANS activity in the urinary bladder in terms of its sphincters

- SNS: contraction → alpha 1

- PNS: relaxation → M3

describe ANS activity in the urinary bladder in terms of its detrusor muscle in the bladder wall

SNS: relaxation → B2

PNS: contraction → M3

describe the sympathetic activity of the kidneys in terms of both renin release and the renal vessels

- renin: increase secretion → B1

- renal vessels: constrict → alpha 1

describe the sympathetic activity of the liver

glycogenolysis via alpha 1 receptors and gluconeogenesis via beta 2 receptors

what happens in the uterus in terms of receptors depending on if the animal is pregnant or not

- Non-gravid: nothing going on with receptors

- Gravid (pregnant): up-regulate beta receptors for relaxation

what kind of drugs are used to treat pre-term labor

beta agonists because they help activate beta receptors that cause relaxation of the uterus

the sweat glands in horses are mediated by what type of response

adrenergic: sedatives cause profuse sweating

what receptor type is responsible for erection of the pilomotor muscles in hair shafts during SNS activation

alpha 1

what are Nonadrenergic-noncholinergic neurons

fibers that do not exhibit the histochemical characteristics of cholinergic or adrenergic fibers

what is one of the primary vasoactive NT's of NANC fibers

nitric oxide: important contributor to penile erection

what is viagra used for in vet med

pulmonary hypertension in small animals and navicular disease in horses: inhibits phosphodiesterase V so that nitric oxide can hang around longer and convert GTP to cGMP

what is a possible side effect of a phosphodiesterase V inhibitor such as viagra being given in conjunction with nitrates for chest pain

too much vasodilation that can cause BP to tank

what is the mechanism of action of atropine as an adjunct to anesthesia

blocks muscarinic receptors thus blocking the activation of PSNS so that heart rate/lung function will increase

The amount of ACh available at synaptic sites can be enhanced by drugs that block what enzyme

acetylcholine esterase

what is the mechanism of action of organophosphates

irreversible AChE inhibitors that result in way too much ACh which causes SLUD

what does SLUD stand for

salivation, lacrimation, urination, defecation: symptoms of organophosphate poisoning

what is the antidote for organophosphate poisoning

atropine

what are the 3 endogenous catecholamines secreted by most spp

epinephrine, norepinephrine, and dopamine

the 3 endogenous catecholamines are also present as _______ FDA-approved drugs

exogenous

where are muscarinic M2 receptors predominantly found

heart

where are muscarinic M3 receptors predominantly found

in the heart, but to a lesser extent than M2

where are alpha-1A adrenoreceptors predominantly found

vascular smooth muscle, CNS, and kidneys

where are alpha-1B adrenoreceptors predominantly found

vascular smooth muscle and CNS

where are alpha-1D adrenoreceptors predominantly found

CNS of ruminants more than any other spp

where are alpha-2A adrenoreceptors predominantly found

CNS, brainstem, and spinal cord: they are agonists used for sedation

where are alpha-2B adrenoreceptors predominantly found

vascular smooth muscle

where are beta-1 adrenoreceptors predominantly found

heart

where are beta-2 adrenoreceptors predominantly found

bronchiolar smooth muscle and skeletal muscle

where are beta-3 adrenoreceptors predominantly found

adipose tissue and skeletal muscle

what is the purpose behind the feeding of beta agonists to food animals 30 days before slaughter

beta receptors are present in skeletal muscle and fat -> builds weight on the carcass

where are dopamine 1/2 receptors predominantly found

CNS and kidneys

dopamine receptors are deficient in patients with what disease

parkinson's

how many muscarinic subtypes are there

5 but we focus on 2 and 3

what are the alpha receptor subtypes

- a1: A, B, and D

- a2: A, B, and C

how many beta receptor types are there

3

how many dopamine receptor types are there

2

beta-adrenergic receptors are expressed mainly where

- heart: b1

- bladder: b2/b3

- liver: b2

- kidney: b1

- bronchial, uterine, and vascular smooth muscle: b2

alpha-1 adrenergic receptors are expressed mainly where

- vascular smooth muscle

- radial eye muscle

- smooth muscle of urogenital tract

what is the role of methylxanthines and what is there significance in vet med

- drugs such as caffeine, theobromine, and theophylline that elicit changes similar to activation of beta receptors in the heart except beta blockers do not work against them -> CNS stimulants

- theobromine: chocolate poisoning

- theophylline: used to treat asthma in cats

how can acepromazine reduce

BP

blocks interaction of NE with adrenergic receptor sites in blood vessels

which drug is known as a mixed alpha-beta receptor agonist

epinephrine

given that epinephrine is a mixed alpha-beta agonist, what condition is it best known for treating

anaphylaxis: beta receptor agonist counteract bronchoconstriction and alpha receptor agonist counteracts vasodilation

an alpha blocker would have what effect on BP

decrease

a beta agonist would have what effect on lung function

increase

an alpha agonist would have what effect on the receptors of the CNS

depress them: sedatives

a beta blocker would have what effect on heart rate

decrease it

an anti-cholinergic would have what effect on GIT motility

slow it down

a beta agonist would have what effect on the uterus

relaxation to prevent pre-term labor

a cholinergic drug would do what to heart rate

decrease it

an anti-cholinergic drug would do what to salivary secretions

decrease them

what are the two branches of sympathomimetic drugs

- adrenergic: resembles effects of stimulation of adrenergic neurons as direct acting alpha/beta agonists

- adrenomimetic: stimulates effects of EPI and NE -> indirect release of endogenous stores of catecholamines

what are the 2 branches of sympatholytic drugs

- receptor/adrenergic blocking drugs: inhibit effects of sympathomimetic drugs and inhibit responses caused by stimulation of adrenergic receptors -> alpha or beta blockers

- adrenolytic/neuronal blocking effects: inhibit responses caused by adrenergic neurons and deplete catecholamines such as NE

what are the 2 branches of parasympathomimetic drugs

- cholinergic: resembles effects caused by stimulation of postganglionic parasympathetic neurons -> direct acting cholinergic agonists such as ACh

- cholinomimetic: stimulates effects of ACh -> indirect acting such as organophosphate poisonings

what are the 2 branches of parasympatholytic drugs

- cholinergic blockers: inhibits effects of ACh by blocking N or M receptors -> atropine and anti-diarrheal drugs

- anticholinergic: neuronal blocking effects inhibit responses caused by stimulation of postganglionic parasympathetic neurons and inhibit release of ACh from its terminal -> botulinum toxin and paralytic drugs