The autonomic nervous system (ANS) is a functional division of the nervous system, unlike the central and peripheral nervous systems which are structural.
It consists of efferent neurons that control:
Smooth muscle cells (e.g., around blood vessels)
Cardiac muscle cells (heart tissue)
Gland cells
The control by ANS is mostly autonomous, not requiring conscious involvement.
Subsystems of Autonomic Nervous System
Sympathetic Nervous System (SNS)
Originates in the middle of the spinal cord.
Neurons have short axons synapsing near the spine, followed by long axons to target cells.
Known as "fight or flight" system.
Parasympathetic Nervous System (PNS)
Originates in the brain stem and lower spinal cord.
Neurons have long axons to ganglia distant from the soma, followed by short axons to target cells.
Known as "rest and digest" system.
Structural Similarities and Differences
Both SNS and PNS typically consist of two-neuron chains connecting the CNS to target cells.
Differences:
SNS: Short first axon, long second axon.
PNS: Long first axon, short second axon.
Functional Differences
Sympathetic Nervous System:
Prepares body for fight or flight.
Decreases blood flow to intestines, increases to skeletal muscles.
ANS has more roles, affecting pupil size, sexual responses, and other gland secretions.
Recommended to study ANS functions in the context of individual organ systems.
Conclusion
Understanding the autonomic nervous system's roles and functions is crucial for comprehending how the body manages various autonomic processes without conscious input. The SNS and PNS work together to balance the body's responses to different situations. Further study should be integrated with the study of specific organ systems.