Nervous system:
• ANS regulates everyday
requirements of vital
body functions without
conscious participation
of mind (involuntary)
Sympathetic and parasympathetic divisions 
typically function in opposition to each 
other. But this opposition is better termed 
complementary in nature rather than 
antagonistic. The sympathetic division 
typically functions in actions 
requiring quick responses. 
• The parasympathetic division 
functions with actions that do 
not require immediate reaction. 
• Consider sympathetic as "fight 
or flight" and parasympathetic 
as "rest and digest
Prepares body for physical action (Fight or 
Flight):
– Increased heart rate
– Increased blood pressure
– Redistribution of blood flow - ↑ flow to skeletal 
muscle, ↓ flow to skin and organs
– ↓ GI activity
– Dilation of pupils and bronchioles
– ↑ blood glucose
Opposite effects to SNS
• Prepares the body for feeding and digestion
– Slows heart rate
– Lowers blood pressure
– Promotes GI secretions
– Stimulates GI movement
– Constricts the pupil
– Empties bladder and rectum
Acetylcholine is the neurotransmitter for 
parasympathetic division, act on muscarinic 
and nicotinic receptors. 
• Noradrenaline is the neurotransmitter for 
sympathetic division, act on adrenoceptors