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Autonomic Nervous System (ANS)
• involuntary nervous system
• subconscious control
• consists of motor neurons that innervate smooth
muscle, cardiac muscle and glands
BIO L 105—lab 11-ANS------1
ANS pathway uses two-neuron chain
1. Preganglionic neuron in CNS
2. Postganglionic neuron in ganglion outside
CNS that extends to effector organ
Divisions of the ANS
• Sympathetic and Parasympathetic division
• Dual innervation- All visceral organs served by
both divisions, but cause opposite effects
• Dynamic antagonism between two divisions
maintains homeostasis
BIO L 105—lab 11-ANS------2
Role of the Sympathetic Division
• Mobilizes body during activity; "fight-orflight" system
– Increased heart rate; dry mouth; cold, sweaty
skin; dilated pupils
Role of the Parasympathetic Division
• Promotes maintenance activities and
conserves body energy
– Directs digestion, diuresis, defecation
– Blood pressure, heart rate, and respiratory
rates are low
BIO L 105—lab 11-ANS------3
Control of ANS Function
• Hypothalamus—main control center of ANS
activity
• Other controls from cerebral cortex, reticular
formation, and spinal cord
BIO L 105—lab 11-ANS------4
Neurotransmitters
• Somatic nervous system
– All somatic motor neurons release
acetylcholine (ACh); effects always
stimulatory
• ANS
– Preganglionic fibers release ACh
– Postganglionic fibers release norepinephrine
or ACh
– Effect is either stimulatory or inhibitory,
depending on type of receptors receiving
stimulus
BIO L 105—lab 11-ANS------5
Neurotransmitters
• Cholinergic fibers release neurotransmitter
ACh
– All ANS preganglionic axons
– All parasympathetic postganglionic axons at
effector synapse
• Adrenergic fibers release neurotransmitter NE
– Most sympathetic postganglionic axons
BIO L 105—lab 11-ANS------6