4. Autonomic Nervous System

Question 1

What is the autonomic nervous system?

Answer 1

Branch of the peripheral nervous system innervating smooth muscle tissue, glands, organs whose activity is not under conscious control

Parasympathetic and sympathetic neurones are classified based on their origin from the CNS

Slides 3-4 Autonomic Nervous System

Question 2

Where do parasympathetic and sympathetic nerves originate from?

Answer 2

Parasympathetic nerves originate from the medulla and sacral spinal cord
CRANIOSACRAL OUTFLOW

Sympathetic nerves originate from the thoracic and lumbar spinal cord
One fiber ends at ganglion and one fiber starts
THORACOLUMBAR OUTFLOW

Slide 5 autonomic nervous

Question 3

What are the synapses where acetylcholine (ACh) is released? (6 of them)

Answer 3

1. Preganglionic parasympathetic nerves at their ganglia
2. Preganglionic sympathetic nerves at their ganglia and at their synapses in adrenal medulla
3. Postganglionic parasympathetic nerves at their organ/tissue receptors
4. Preganglionic sympathetic nerves at their synapses in adrenal medulla
5. Somatic motor nerves at the neuromuscular junction in the skeletal muscles
6. The postganglionic fibres of the sympathetic system innervating all sweat glands (except in palms), and skeletal blood vessels release ACh

Slides 6-8 autonomic nervous

Question 4

What are the synapses where norepinephrine (NE) is released? (2 of them)

Answer 4

1. Postganglionic sympathetic nerves at their organ/tissue receptors
2. Sympathetic fibres innervating sweat glands in the palms (adrenergic sweating)

Slides 6-8 autonomic nervous

Question 5

What are the 2 neurotransmitters and their proportions released from the adrenal medulla?

Answer 5

The adrenal medulla releases epinephrine (adrenaline) (80%) and norepinephrine (20%) into circulation when stimulated by preganglionic sympathetic nerves

Phaeochromocytoma- a tumor of the adrenal medulla that releases large amounts of Epi and NE into circulation which raises heart rate and BP

Question 6

How is acetylcholine (ACh) synthesized?

What blocks ACh release?

Answer 6

Synthesized from choline and Acetyl coenzyme A

It is stored in neuronal vesicles, and released by nerve stimulation

Botulinum toxin blocks ACh release- causes skeletal muscle paralysis

Slide 10 autonomic nervous

Question 7

How are dopamine, norepinephrine, and epinephrine synthesized?

Answer 7

All synthesized from the amino acid tyrosine

Slide 11 autonomic nervous system

Question 8

How are cholinergic receptors broken down?

Answer 8

Slide 12 autonomic nervous system

Nicotinic and muscarinic

Question 9

What are adrenergic receptor types?

What are adrenergic receptors stimulated by?

Answer 9

Stimulated by norepinephrine

Split into α1, α2, and β

β breaks down into β1 β2 β3

Slide 14 autonomic nervous system

Question 10

What are the differences between parasympathetic functions and sympathetic functions?

Answer 10

Parasympathetic- rest and digest (relax)
Sympathetic- fight or flight (stressful)

Table on slide 16 autonomic nervous system

Question 11

What is dominant tone?

Answer 11

The dominant tone in an organ means that the branch of ANS (parasympathetic or sympathetic) innervating that organ is dominant or more active

Drugs (especially antagonists) affecting the system which is dominant will have a more noticeable effect in that organ

Question 12

How do ANS drugs and the heart work?

Dominant tone, parasympathetic sympathetic receptors, etc

Answer 12

Dominant tone- parasympathetic (except in ventricles)

Parasympathetic- Muscarinic M2
Agonists (ACh)- down heart rate and atrioventricular conduction
Antagonists (muscarinic blockers)- up heart rate and AC

Sympathetic- β1, β2
Agonists (NE, Epi, β1)- up heart rate, AC, contractility
Antagonists (β blockers)- down heart rate, AC, contractility

Slides 18-19 autonomic nervous system

Question 13

How do ANS drugs and the blood vessels work?

Dominant tone, parasympathetic sympathetic receptors, etc

Answer 13

Dominant tone- sympathetic
Most blood vessels do not have cholinergic innervation

Parasympathetic- muscarinic M3
Agonists (ACh, muscarinic agonists)- down blood pressure (vasodilation)
Antagonists (muscarinic blockers)- little or no effect (no cholinergic innervation)

Sympathetic- α1
Agonists (NE, Epi, α agonists)- up contraction, vascular resistance, blood pressure
Antagonists (α blockers)- down vasodilation, vascular resistance, blood pressure

Slides 20-21 autonomic nervous

Question 14

How do ANS drugs and the kidney work?

Dominant tone, parasympathetic sympathetic receptors, etc

Answer 14

Dominant tone- sympathetic
No cholinergic innervation

Sympathetic- β1
Agonists (NE, Epi, β1 agonists)- up renin secretion (which increases angiotensin and blood pressure)
Antagonists (β1 blockers)- down renin secretion (down angiotensin and blood pressure)

Slide 22 autonomic nervous

Question 15

How do ANS drugs and the urinary bladder work?

Dominant tone, parasympathetic sympathetic receptors, etc

Answer 15

Dominant tone- parasympathetic (detrusor muscle)
Parasymp & symp in sphincter

Parasympathetic- muscarinic M3, M2
Nerve stimulation and agonists (ACh)- detrusor contraction (sphincter relax)
Antagonists (muscarinic blockers)- detrusor relax (sphincter contract)

Sympathetic- α1, β3
Nerve stimulation & agonists- relax detrusor (parasymp dominates tho), contract sphincter
Antagonists (α1 blockers)- relax sphincter

Question 16

How do ANS drugs and the tracheal and bronchial smooth muscle work?
(Parasympathetic, sympathetic)

Answer 16

Parasympathetic- Muscarinic M2, M3
Nerve stimulation & muscarinic agonists (methacholine)- contract bronchial smooth muscle, up secretions
Antagonists (muscarinic blockers)- relax bronchial muscle, down secretions

Sympathetic- β2
Nerve stimulation & β2 agonists (albuterol, epinephrine)- relax bronchial muscle
Antagonists (β blockers)- β2 blockers contract bronchial muscle in asthmatics

Slides 25-26 autonomic nervous

Question 17

How do ANS drugs and the salivary and parotid glands work?

Dominant tone, parasympathetic sympathetic receptors, etc

Answer 17

Dominant tone: parasympathetic

Parasympathetic- Muscarinic M3, M2
Nerve stimulation & muscarinic agonists (pilocarpine, ChE inhibitors)- stimulate salivary and mucus secretions
Antagonists (muscarinic blockers)- inhibit saliva mucus secretions

Sympathetic- α1
Nerve stimulation & agonists- stimulate salivary secretions mildly

Slides 27-28 autonomic nervous

Question 18

How do ANS drugs and the gastrointestinal tract smooth muscle work?
(Dominant tone, parasympathetic sympathetic receptors, etc)

Answer 18

Dominant tone: parasympathetic

Parasympathetic- M3, M2
Nerve stim & muscarinic agonists- contract GI muscle, up GI secretions
Muscarinic antagonists (dicyclomine)- inhibit peristalsis, down gland secretions

Sympathetic- β2, β1, α1, α2
Nerve stim & agonists- relax GI muscle, inhibit secretions (α1 contracts sphincters)

Slides 29-30 autonomic nervous

Question 19

How do ANS drugs and the liver work?

parasympathetic sympathetic receptors, etc

Answer 19

Sympathetic innervation
Sympathetic stimulation, β2 receptor agonists

Epinephrine->β2->glycogenolysis, gluconeogenesis (up plasma glucose)

Sympathetic release of glucose from liver is useful during hypoglycemia

Question 20

Why are non-selective β blockers dangerous in diabetic patients taking insulin?

Answer 20

Non-selective β receptor blockers will prevent glycogenolysis and glyconeogenesis

Will not allow plasma glucose to increase in response to hypoglycemia)

Type 1 diabetic patients on insulin are prone to develop hypoglycemia and coma as side effect

Question 21

How do ANS drugs and the uterus work?

parasympathetic sympathetic receptors, etc

Answer 21

Sympathetic innervation
Sympathetic stimulation, β2 receptor agonists

Salbutamol, terbutaline (short acting beta 2 agonists - SABAs) -> β2 -> relaxation or uterine smooth muscle

SABAs can be used to prevent premature labour

Slide 32 autonomic nervous

Question 22

What are the 2 muscles in the eyes that have autonomic innervation?

Answer 22

1. Iris muscles (circular and radial)- control pupil size
2. Ciliary muscles (circular and longitudinal fibres)- control aqueous humor production and lens shape and image focus on retina

Question 23

How do ANS drugs and the eyes (pupillary muscles, ciliary muscles) work?
(Dominant tone, parasympathetic sympathetic receptors, etc)

Answer 23

Dominant tone: parasympathetic

Parasympathetic
Nerve stim & muscarinic agonists- miosis- sphincter contraction (iris circular muscle), contract longitudinal ciliary fibres, up lacrimation
Muscarinic antagonists (atropine)- mydriasis- sphincter relaxation

Sympathetic
Nerve stim & agonists- α1 agonists- mydrialysis (iris radial muscle contraction), α2 agonists- down aqueous production
Antagonists- β2 antagonists down blood flow, down aqueous humor secretion

Slide 35 autonomic nervous

Question 24

How do ANS drugs and the skeletal muscle work?

parasympathetic sympathetic receptors, etc

Answer 24

Motor nerves
Parasympathetic
Stimulation of motor neurones, nicotinic agonists
ACh->Nm->muscle contraction

Neuromuscular blockers (competitive and depolarizing types) will cause skeletal muscle relaxation (used during surgery)

Slides 36-37 autonomic nervous

Question 25

How do ANS drugs and the brain work?

parasympathetic sympathetic receptors, etc

Answer 25

Cholinergic and adrenergic receptors
Parasympathetic
ACh -> M1, M4 -> memory, coordination of muscle contraction

Muscarinic receptor stimulation:
Hippocampus- plays a role in memory (Alzheimer’s)
Striatum- ACh interacts with dopamine to control muscle contraction (Parkinson’s)