Sympathetic Nervous System Functions

The simultaneous activation of the entire sympathetic division, leading to a coordinated response in all target organs.

The release of different neurotransmitters by different postganglionic sympathetic neurons, leading to specific effects on target organs.

A series of physiological changes that prepare the body for a stressful situation, including increased heart rate, blood pressure, and breathing.

The original idea that the sympathetic division always produces a uniform effect on all target organs.

The use of the sympathetic division to respond to specific stimuli, by targeting only certain organs.

The ability of postganglionic sympathetic neurons to fire different types of action potentials and release different neurotransmitters.

A sudden onset of intense fear or discomfort, often accompanied by physical symptoms like rapid heartbeat and dizziness.

A neurotransmitter released by postganglionic sympathetic neurons, responsible for various physiological responses.

Sympathetic neurons control a variety of organs and functions, and their responses can vary based on the target organ. For example, they can induce vasoconstriction in arteries and regulate gut motility and secretion.

Parasympathetic neurons work in a specific and reflexive manner to control organ function. They are involved in simple involuntary reflexes that are often triggered by sensory input.

The baroreceptor reflex, which helps regulate blood pressure, is mediated by preganglionic parasympathetic neurons in the dorsal motor nucleus of the vagus.

Urination in response to a full bladder is an example of a parasympathetic reflex.

Salivation, triggered by the sight or smell of food, is a parasympathetic reflex.

Vagovagal reflexes are parasympathetic reflexes occurring within the gastrointestinal tract. An example is the contraction of the colon in response to food in the stomach.

Bronchoconstriction, the narrowing of the airways, can be triggered by parasympathetic reflexes in response to stimuli in the lungs.

The pupillary light reflex, which controls the size of the pupil in response to light, is a parasympathetic reflex that can be tested clinically.

The hypothalamus coordinates autonomic responses affecting functions like feeding, temperature control, sleep-wake cycles, fluid balance, emotions, sexual drive, reproduction, motivation, and other brain functions, aligning these brain activities with autonomic control.

The hypothalamus can trigger the "fight or flight" response, preparing the body for immediate action in response to perceived threats.

The hypothalamus, a key region in the forebrain, sends signals to various brainstem areas, including the parabrachial nucleus, medullary raphé, NTS, central gray matter, locus coeruleus, dorsal motor nucleus of the vagus, nucleus ambiguus, and the intermediolateral cell column of the spinal cord, to coordinate autonomic outputs.

The hypothalamus has a significant role in regulating autonomic functions, integrating them with other brain activities and coordinating responses to the body's needs.

While the hypothalamus is the primary mediator, other forebrain regions, particularly those involved in the limbic system, directly project to brainstem nuclei involved in autonomic control.

The limbic system, a network of brain structures involved in emotions, motivation, and memory, plays a significant role in influencing autonomic responses. Many of its structures have direct connections to brainstem nuclei involved in autonomic control.

Visceral sensory information integrated in the brainstem can influence or even override the forebrain's control over autonomic output.

Although the brainstem can function independently to maintain homeostasis, forebrain regions play a crucial role in coordinating and modulating autonomic activity.

The process by which the ANS monitors internal conditions, compares them to a set-point, and adjusts organ function to maintain balance.

The ANS's ability to anticipate future needs and adjust organ function proactively.

The internal target value that the ANS strives to maintain for a specific physiological parameter (e.g., blood pressure).

Sensory receptors located in visceral organs that provide information to the CNS about internal conditions.

Nerves that transmit information from the visceral receptors to the CNS.

The central nervous system's control centers for the ANS, responsible for processing information and sending out commands to organs.

The ability of the ANS to adjust organ function in anticipation of exercise, preventing a metabolic imbalance.

Sensory input from internal organs, like the heart or stomach, can influence the activity of brain regions responsible for thinking and awareness.

The vagus nerve, a crucial part of the autonomic nervous system (ANS), carries sensory information from internal organs to the brain.

Electrical stimulation of the vagus nerve, delivered through an implanted device, can reduce seizures in some individuals.

The effectiveness of vagus nerve stimulation suggests that visceral input plays a crucial role in regulating brain function, potentially impacting seizures.

The vagus nerve carries sensory information from internal organs, including the lungs, heart, and digestive system.

Stimulating different parts of the vagus nerve might have a targeted effect on brain activity, potentially leading to fewer side effects.

Investigating specific pathways within the vagus nerve might reveal more effective and targeted treatments for conditions like epilepsy.

Research into the effect of vagus nerve stimulation on brain activity may lead to the development of new medications that target specific pathways, reducing the need for invasive stimulation.

The spinal cord is the central nervous system in some primitive chordates, and it plays a crucial role in coordinating activity among different root levels in vertebrates.

The medulla is the most vital part of the brain, responsible for coordinating all visceral control and optimizing it for survival.

Autonomic ganglia are not just simple relays, they integrate autonomic activity at peripheral sites. This integration is enhanced by the variety of neurotransmitters released by interneurons.

Transection of the low cervical spinal cord can disrupt complex responses but does not affect basic homeostasis.

Autonomic hyper-reflexia is a maladaptive reflex that can occur with spinal cord injuries, leading to hypertension and sweating in response to stimuli like a full bladder.

The brain's evolution involved the development of a three-part structure, with the more rostral (forward) parts taking on a dominant role over time.

Destruction of the medulla leads to instant death, highlighting its crucial role in maintaining life support.

Humans can continue to live indefinitely with only a medulla, spinal cord, and peripheral ANS, demonstrating the importance of these structures for basic homeostasis.