13:16
Chapter 16
Janet Carlino
Overview
This video explains the autonomic nervous system (ANS), a part of the motor division of the peripheral nervous system that controls involuntary bodily functions. It contrasts the ANS with the somatic nervous system, highlighting the ANS's role in regulating organs, muscles, and glands. The video details the two main divisions of the ANS: the sympathetic (fight or flight) and parasympathetic (rest and digest), explaining their structural and functional differences, including neuronal pathways, neurotransmitters, and their opposing effects on various body systems like the heart, lungs, eyes, and digestive tract. The importance of dual innervation and the balance maintained by these systems is emphasized.
How was this?
Save this permanently with flashcards, quizzes, and AI chat
Chapters
- The autonomic nervous system (ANS) is part of the motor division, carrying signals from the CNS to effectors.
- Unlike the somatic system's voluntary control of skeletal muscle via a single neuron, the ANS controls involuntary functions (heart rate, digestion) using smooth muscle, cardiac muscle, and glands.
- The ANS employs a two-neuron pathway: a preganglionic neuron from the CNS to a ganglion, and a postganglionic neuron from the ganglion to the target organ.
Understanding the ANS is crucial because it governs essential bodily functions that operate without conscious thought, maintaining homeostasis and responding to internal and external changes.
Deciding to move your arm (somatic) versus your heart beating automatically (autonomic).
- The ANS has two primary divisions: sympathetic (fight or flight) and parasympathetic (rest and digest).
- The sympathetic division prepares the body for action by increasing alertness, heart rate, and metabolism.
- The parasympathetic division conserves energy by slowing down bodily processes like heart rate and promoting digestion.
- Most organs receive input from both divisions (dual innervation), allowing for a balance of opposing effects.
Knowing the distinct roles of the sympathetic and parasympathetic systems helps explain how the body mobilizes for action and recovers for maintenance, demonstrating the principle of physiological balance.
The sympathetic system increasing heart rate during a stressful event, while the parasympathetic system slows it down during relaxation.
- The sympathetic division is also called the thoracolumbar division because its preganglionic neurons originate in the thoracic and lumbar spinal cord.
- In the sympathetic system, preganglionic neurons are short and synapse in ganglia close to the spinal cord (sympathetic chain ganglia), with long postganglionic neurons extending to targets.
- The parasympathetic division is the craniosacral division, with preganglionic neurons originating in the brainstem and sacral spinal cord.
- In the parasympathetic system, preganglionic neurons are long, traveling near the target organ, where they synapse in terminal ganglia, resulting in very short postganglionic neurons.
The anatomical differences in neuron length and ganglion location explain the speed and reach of each division's influence on target organs.
Sympathetic: short preganglionic neuron, long postganglionic neuron; Parasympathetic: long preganglionic neuron, short postganglionic neuron.
- All preganglionic neurons (sympathetic and parasympathetic) are lightly myelinated and release acetylcholine (ACh).
- All postganglionic neurons are unmyelinated.
- Most sympathetic postganglionic neurons release norepinephrine (NE).
- Parasympathetic postganglionic neurons release acetylcholine (ACh).
The specific neurotransmitters used by each neuron type are critical for signal transmission and determine the effect on the target organ, forming the basis of drug targets for various conditions.
ACh is released by both preganglionic neurons, but NE is released by sympathetic postganglionic neurons, while ACh is released by parasympathetic postganglionic neurons.
- The sympathetic division mobilizes energy and prepares the body for action ('fight or flight').
- It increases respiration rate, dilates pupils for better vision, and stimulates breakdown of stored energy (like lipids and glycogen).
- Blood flow is redirected from non-essential areas (digestion, skin) to muscles and the heart.
- It increases blood clotting ability and causes goosebumps as part of a heightened alert state.
Understanding sympathetic functions explains the body's immediate responses to stress, danger, or intense physical activity, highlighting its role in survival.
During a stressful event, pupils dilate to let in more light, and blood is shunted to muscles for potential escape or confrontation.
- The parasympathetic division conserves energy and promotes maintenance and recovery ('rest and digest').
- It decreases heart rate and respiration rate, constricts pupils for near vision, and enhances digestion by increasing secretions and motility.
- It promotes relaxation and returns the body to a baseline state.
- It relaxes the internal urethral sphincter to allow urination.
The parasympathetic system's functions are essential for long-term health, allowing the body to repair, digest, and conserve resources when not under immediate threat.
After a meal, the parasympathetic system increases digestive secretions and gut movement to efficiently process food.
Key takeaways
- The autonomic nervous system controls involuntary bodily functions essential for survival and homeostasis.
- The sympathetic and parasympathetic divisions have opposing but complementary roles, enabling the body to respond dynamically to different situations.
- Structural differences in neuron length and ganglion location distinguish the sympathetic (short pre, long post) from the parasympathetic (long pre, short post) systems.
- Neurotransmitter release (ACh vs. NE) at the postganglionic synapse is a key differentiator between the sympathetic and parasympathetic divisions.
- The sympathetic system prioritizes energy mobilization and defense during stress, while the parasympathetic system focuses on energy conservation and restoration during rest.
- Dual innervation allows for precise regulation of organ function by balancing the influences of both ANS divisions.
Key terms
Autonomic Nervous System (ANS)Somatic Nervous SystemMotor/Efferent DivisionPreganglionic NeuronPostganglionic NeuronGanglionSympathetic DivisionParasympathetic DivisionFight or FlightRest and DigestDual InnervationThoracolumbar DivisionCraniosacral DivisionSympathetic Chain GangliaTerminal GangliaAcetylcholine (ACh)Norepinephrine (NE)
Test your understanding
- How does the autonomic nervous system differ from the somatic nervous system in terms of control and target organs?
- What are the primary functions of the sympathetic and parasympathetic divisions, and why is dual innervation important for organ regulation?
- Describe the structural differences in the neuronal pathways of the sympathetic and parasympathetic nervous systems, including the origin and length of pre- and postganglionic neurons.
- What neurotransmitters are released by preganglionic neurons and by postganglionic neurons in both the sympathetic and parasympathetic divisions?
- Explain how the sympathetic and parasympathetic systems functionally influence specific organs like the heart, lungs, and digestive tract.