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Autonomic Nervous System

Part of nervous system that controls visceral functions including:

  • Cardiac muscle,
  • smooth muscle (blood vessels, GIT, urinary bladder etc)
  • glands (secretions)

This system is not under voluntary control

Sympathetic division

►Thoracolumbar (T1to L2)

Parasympathetic division

►Craniosacral (III, VII, IX, X cranial nerves & S1to S4)

Dual supply

►All the viscera supplied by both the divisions of ANS

►Sympathovagal balance determines the ultimate function of the viscera

In autonomic nervous system:

►Two neuron chain from CNS to effector organ

►Pre and postganglionic neurons

Somatic nervous system

►Single neuron connects CNS with effector organ


►Cluster of neurons outside CNS

Autonomic ganglion

►Site of synapse between autonomic pre & post ganglionic fibers

►Paravertebral ganglionic chain

►Prevertebral (collateral) ganglia

Cell body of preganlionic neuron

►Lies in CNS

►Spinal cord (sympathetic division)

►Brain and spinal cord (parasympathetic division)

Cell body of postganglionic neuron

►Lies in autonomic ganglia

Sympathetic nervous system

►Short preganlionic fibers

►Long postganglionic fibers

Parasympathetic nervous system

►Long preganlionic fibers

►Short postganglionic fibers

Neurotransmitter released:

Cholinergic fibers

►Fibers releasing acetylcholine

Adrenergic fibers

►Fibers releasing noradrenalin

►All preganlionic fibers are cholinergic

►All postganglionic parasympathetic fibers are cholinergic

►Almost all postganglionic sympathetic fibers are adrenergic

►postganglionic sympathetic fibers to sweat glands and piloerector muscles are cholinergic


►Nicotinic receptors -in autonomic ganglia

►Muscarinic receptors -in effector organs stimulated by postganglionic cholinergic fibers

►Adrenergic receptors -in effector organs stimulated by postganglionic adrenergic fibers

►α adrenergic receptors (α1 and α2)

►βadrenergic receptors (β1 and β2)

Functions of Autonomic Nervous System

Sympathetic and parasympathetic components of ANS function to maintain homeostasis at subconscious level -maintain stable internal environment

Sympathetic nervous system

►Prepares and mobilizes the body in emergency (fright, fear, pain, rage etc)

►Fight or flight reaction

Parasympathetic nervous system

►Conserves and stores energy -puts the body in cool and calm state

In Autonomic nervous system (ANS)

Mass discharge of sympathetic system

►Simultaneous discharge of all portions of sympathetic nervous system as a unit

►Due to activation of hypothalamus as a result of fright, fear or pain

►Also called alarm or stress response of the body

►Prepares the body for ‘emergency’

►Mass discharge of sympathetic system

►Increased BP

►Increased blood flow to active muscles

►Less blood flow to skin and GIT

►Increased rate of cellular metabolism

►Increased glycogenolysis and lipolysis

►Increased muscle strength

►Increased mental activity

►Papillary dilation

►Increased respiratory rate

functions of autonomic nervous system cont.

Sympathetic and parasympathetic tone

►Basal rate of discharge

►Allows single division to adjust stimulation level of an organ

►Sympathetic tone to blood vessels

Browse articles on Drugs Acting on Autonomic Nervous System

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