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

• Copious watery secretion

Sweat glands

Sympathetic stimulation

• Secretion of large quantities of sweat

Parasympathetic stimulation

• No effect

Apocrine glands

Sympathetic stimulation

• Thick odoured secretion

Parasympathetic stimulation

• No effect

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

• No effect

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

• Ejaculation

Parasympathetic stimulation

• Erection

Genitalia - female

Sympathetic stimulation

• Relaxation of uterus (beta-2)

Parasympathetic stimulation

• ?no effect

Adrenal medulla

Sympathetic stimulation causes secretion of:

• epinephrine (80%)
• norepinephrine (20%)

which last 5-10 times longer than when released by sympathetic neurons.

Kidney

?????