Autonomic Nervous System or ANS
Autonomic Nervous System or ANS described as visceral efferent system by Langley in 1898. All efferent axons leaving the CNS other than those of skeletal muscle belong to ANS.
ANS supplies efferent information to smooth muscle, glands & cardiac muscle. ANS modifies motor activities that have been initiated with in the involved effector organs. Neural activity of ANS may either be excitatory or inhibitory.
- It has two divisions
- Sympathetic (thorocolumular)
- Parasympathetic (craniosacral divisions)
ANS as the name implies is not under the control of structures of other nervous systems.
Unique difference from somatic nervous system is the presence of ganglia along their nerve trunks or in the wall of the effector organ. Ganglia are clusters of neurons of peripheral autonomic neurons which form swelling on the nerve trunk. It provides mechanism of synapsing for efferent fibre prior to innervating effector organs.
Peripheral distribution of nerve fibers
| Sympathetic | Parasympathetic | |
| Preganglionic | Short fibers and ganglia are close to spinal cord or brainstem with in the vertebral or collateral ganglia | CNS to collateral or terminal ganglia |
| Post ganglionic | Long fibers | Short fibers |