Autonomic Nervous System

Question 1

Two Subdivisions of ANS

Answer 1

1. Sympathetic Nervous System (SNS)
2. Parasympathetic NS (PNS)

Question 2

Fiber Types and Receptors

Answer 2

• Fibers from CNS to ganglion = preganglionic fibers
  Cholinergic (ACh)
  Myelinated
• All postganglionic Para fibers & few pg sympathetic fibers are also cholinergic
• Majority of pg sympathetic fibers are adgrenergic (noradrenaline)

Question 3

Cholinergic Neurons

Answer 3

• Acetylcholine: Synthesis and Degradation
• All SNS and PNS PREganglionic neurons
• All PNS POSTganglionic neurons
• SNS POSTganglionic for sweat glands and some blood vessels

Question 4

Cholinergic Receptors

Answer 4

Muscarinic (m1, m2, m3): g-coupled receptors in PNS
m1 = CNS neurons, sweat glands: IC Ca up
m2 = Myocardium, smooth muscle: open K channels, cAMP down
m3 = glands, smooth muscle, endothelium: IC Ca up

Nicotinic (n2, n1=skeletal muscles): ion gated
n2 = postganglionic neurons: open Na/K channels, depolarization

Question 5

Noradrenergic Neurons

Answer 5

• Norepinephrine: Synthesis and Degradation
• Most SNS postganglionic neurons
• Adrenal medulla releases some NE into blood stream

Question 6

General Functions of ANS

Answer 6

Tonic Activity:
Active under “normal” conditions
Ability to increase or decrease activity (trying to balance)
Ratio of PNS/ANS determines net effect on organ

Reflex Activity:
“response” to a change in environmental (may not require cortical processing)
many basic autonomic reflexes can be modulated by other inputs to CNS or by higher brain centers

Question 7

Dual Innervation by SNS vs PNS

Answer 7

• Cooperative Effects: both PNS & SNS promote same physiological goal
  Ex: Salivary glandsSNS - viscous secretion vs PNS - water secretion
  Lacrimal glands: both cause secretion
  Reciprocal: One system inhibits while other stimulates activity of the target organ which allows fine control of organ function
  Ex: Fight or Flight (SNS) vs Rest and Digest (PNS)

Question 8

Responses to Sympathetic Activation

Answer 8

CNS: alertness up
Eyes: pupillary dilation, mydriasis
Bronchi: dilation
Skin: perspiration
Liver: glycogenesis
GI tract: peristalsis down; sphincter tone up; blood flow down
Heart: rate and force and BP up
Fat Tissue: lipolysis; fatty acid mobilization
Bladder: sphincter tone up
Skeletal muscle: blood flow up; glycogenesis up

Question 9

Responses to Parasympathetic activation

Answer 9

Eyes: accommodation for near vision; miosis
Bronchi: constriction; secretion up
Heart: rate and BP down
GI tract: secretion up, peristalsis up; sphincter tone down
Bladder: sphincter tone down

Question 10

Autonomic Agonists and Antagonists

Answer 10

a1: Norepinephrine (agonist)
b1: Norepinephrine (agonist)
b2: epinephrine (agonist)
nicotinergic cholinoreceptors: Ach & nicotine (agonists)
Muscarinergic cholinoreceptors: Ach (agonist); Atropine (antag)