Effects of ANS stimulation
Some organs the two system act against each other.
Most organs are dominately controlled by one of the systems (not both).
Sympathetic vs parasympathetic
Sympathetic
- Fight or flight response
- Tend to fire as a complete system
Parasympathetic
- Rest and digest response
- Never discharges as a complete system
Tone
Sympathetic tone constricts systemic arterioles to about 1/2 of maximum diameter.
Parasympathetic tone maintains normal GIT motility.
Dual innervation
Most organs are innervated by both, but in most, one system dominate.
- GIT - parasympathetic system dominate
- Heart rate - parasympathetic system dominate
Some organs only have sympathetic innervation
- Adrenal medulla
- Kidney
- Pilomotor muscles
- Sweat glands
Sympathetic and parasympathetic stimulation
Eyes
Sympathetic stimulation
- Pupillary dilation (alpha-1)
- via contraction of radial dilator muscle of iris
Parasympathetic stimulation
- Pupillary constriction
- via contraction of sphincter muscle of the iris
- Focusing of the lens
- via contraction of ciliary muscle
Nasal, lacrimal, salivary, and GIT glands
Sympathetic stimulation
- Vasoconstriction
- Reduce rate of secretion
- Secretions more concentrated with enzymes and mucus
Parasympathetic stimulation
Sweat glands
Sympathetic stimulation
- Secretion of large quantities of sweat
Parasympathetic stimulation
Apocrine glands
Sympathetic stimulation
Parasympathetic stimulation
GIT
Sympathetic stimulation
- When strongly stimulated, inhibits peristalisis and increased tone of sphincters (alpha-1)
Parasympathetic stimulation
- (dominant) Increases overall activity
Lung
Sympathetic stimulation
- Dilation of trachea and bronchioles (beta-2)
Parasympathetic stimulation
- Constriction of trachea and bronchioles
- Increase in airway secretions
Heart
Sympathetic stimulation
- Increases rate and contractility (beta-1)
Parasympathetic stimulation
- (dominant) Decrease rate and contractility
Systemic blood vessels
Sympathetic stimulation
- Vasoconstriction in GIT and skin (alpha-1)
- Vasodilation in skeletal muscles (beta-2)
Parasympathetic
Arterial blood pressure
Sympathetic stimulation
- Increase blood pressure (alpha-1, beta-1)
(by both increasing in cardiac output and peripheral resistance)
Parasympathetic
- Decrease blood pressure
(smaller amount, by only decreasing cardiac output without changing peripheral resistance)
Urinary bladder
Sympathetic stimulation
- Relaxation of detrusor muscle
- Contraction of trigone and sphincter (alpha-1)
Parasympathetic stimulation
- Contraction of detrusor muscle
- Relaxation of trigone and sphincter
Genitalia - male
Sympathetic stimulation
Parasympathetic stimulation
Genitalia - female
Sympathetic stimulation
- Relaxation of uterus (beta-2)
Parasympathetic stimulation
Adrenal medulla
Sympathetic stimulation causes secretion of:
- epinephrine (80%)
- norepinephrine (20%)
which last 5-10 times longer than when released by sympathetic neurons.
Kidney
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