Overview
This lecture explains the structure and functions of the autonomic nervous system, focusing on the differences between its two divisions: the sympathetic and parasympathetic systems.
The Autonomic Nervous System (ANS)
- The ANS is a branch of the peripheral nervous system that regulates involuntary functions like heart rate, digestion, and glandular activity.
- The ANS operates without conscious control, constantly adjusting body functions in response to signals from the central nervous system.
Sympathetic vs. Parasympathetic Divisions
- The ANS has two main divisions: the sympathetic and parasympathetic nervous systems.
- The sympathetic system prepares the body for "fight or flight," increasing alertness, heart rate, and energy use.
- The parasympathetic system promotes "rest and digest," conserving energy and facilitating maintenance activities like digestion.
Key Anatomical Differences
- Sympathetic nerve fibers originate in the thoracolumbar region (middle of the spinal cord).
- Parasympathetic nerve fibers originate in the craniosacral regions (base of the brain and lower spinal cord).
- Sympathetic ganglia are located close to the spinal cord, enabling quick, wide-reaching responses.
- Parasympathetic ganglia are near or inside target organs, allowing for targeted, specific responses.
- In the sympathetic system, preganglionic fibers are short and postganglionic fibers are long.
- In the parasympathetic system, preganglionic fibers are long and postganglionic fibers are short.
Structure Supports Function
- The sympathetic system's structure allows a single stress signal to trigger many organs quickly.
- The parasympathetic system's structure supports focused, individual organ regulation for bodily maintenance.
Key Terms & Definitions
- Autonomic Nervous System (ANS) — controls involuntary functions of internal organs, muscles, and glands.
- Sympathetic Nervous System — division of ANS for stress responses ("fight or flight").
- Parasympathetic Nervous System — division of ANS for calming and maintenance ("rest and digest").
- Ganglion — cluster of neuron cell bodies where synapses occur between ANS neurons.
- Preganglionic Fiber — axon leading from CNS to a ganglion.
- Postganglionic Fiber — axon leading from ganglion to effector organ.
Action Items / Next Steps
- Review the anatomical differences between sympathetic and parasympathetic systems.
- Prepare for next week ’s session on how the sympathetic nervous system communicates with organs.