Autonomic Physiology 1-2

Question 1

Describe the anatomy of the sympathetic and parasympathetic branches of the ANS.

Answer 1

• Summary of Parasympathetic Anatomy:
• Origin: Craniosacral (brainstem and S2-S4 of the spinal cord).
• Preganglionic Neuron: Long, releases ACh, synapses in ganglia near or within the target organs.
• Postganglionic Neuron: Short, releases ACh, acts on muscarinic receptors.
• Localized, specific effects (rest and digest).
• Summary of Sympathetic Anatomy:
• Origin: Thoracolumbar (T1-L2)
• Preganglionic Neuron: Short, releases ACh, synapses in sympathetic chain or collateral ganglia.
• Postganglionic Neuron: Long, releases norepinephrine (except in sweat glands, where it uses ACh), acts on adrenergic receptors (α and β).
• Widespread effects on organs (fight or flight).

Question 2

Describe the neurotransmitters, receptors and functional aspects of the ANS.

Answer 2

Neurotransmitters: ACh (Acetylcholine), NE (Norepinephrine), Epi (Epinephrine), and dopamine.

Receptors: Cholinergic (nicotinic and muscarinic) and adrenergic (α and β).

Sympathetic System: “Fight or flight” response; increases heart rate, bronchodilation, vasoconstriction, and inhibits digestion.

Parasympathetic System: “Rest and digest” response; decreases heart rate, bronchoconstriction, increases digestion and urination, and promotes rest.

Question 3

Describe the effect of autonomic innervation on major internal organs.

Answer 3

• Heart:
• Sympathetic = Increases heart rate, contractility
• Parasympathetic = Decreases heart rate, mild reduction in contractility
• Blood Vessels:
• Sympathetic = Vasoconstriction (except skeletal muscles)
• Parasympathetic = Minimal effect (localized vasodilation in some areas)
• Lungs:
• Sympathetic = Bronchodilation, decreased mucus production
• Parasympathetic = Bronchoconstriction, increased mucus production
• GI Tract
• Sympathetic = Decreases motility, inhibits secretion
• Parasympathetic = Increases motility, stimulates secretion
• Bladder:
• Sympathetic = Relaxes detrusor, contracts sphincter
• Parasympathetic = Contracts detrusor, relaxes sphincter
• Eyes:
• Sympathetic = Pupillary dilation, reduced tear production
• Parasympathetic = Pupillary constriction, increased tear production
• Liver/Pancreas:
• Sympathetic = Increases glucose release, inhibits insulin
• Parasymathetic = Promotes insulin secretion, glucose storage
• Sweat Glands:
• Sympathetic = Stimulates sweat production (cholinergic)

Question 4

Describe simple autonomic reflexes.

Answer 4

All have a simlar pathway of Stimulus, sensory input, integration and motor output. Some also have voluntary control. Allow for the maintenance of Homeostasis.

Examples below: reflex, stimulus, response, effect

Baroreceptor, Reflex Change in blood pressure, Adjusts heart rate and vessel tone, Maintains blood pressure

Pupillary Light Reflex, Bright light entering the eye, Pupillary constriction (miosis), Protects retina and improves vision

Micturition Reflex, Bladder stretching due to urine accumulation, Bladder contraction and sphincter relaxation, Promotes urination

Defecation Reflex, Rectal wall stretching due to fecal accumulation, Rectal contraction and sphincter relaxation, Promotes defecation

Sweating Reflex, Body overheating detected by thermoreceptors, Sweating to cool the body, Reduces body temperature

Hering-Breuer Reflex, Excessive lung inflation detected by stretch receptors, Inhibition of inspiration, promoting expiration, Prevents lung over-inflation