[BME 235] Autonomic Nervous System
What neurotransmitter is secreted by ANS preganglionic fibers?
Acetylcholine is secreted by preganglionic neurons in both divisions.
What mechanism enables each system to have different effects (inhibition or excitation) on different target tissues, even though the same neurotransmitter is used?
Different types of receptors. Target cells respond to the same neurotransmitter differently depending on the type of receptor they have for it. There are two different classes of receptors for acetylcholine and two classes or receptors for norepinephrine.
What mechanism enable the sympathetic and parasympathetic systems to have differing effects on the same target tissue?
Dual innervation. Sympathetic and parasympathetic fibers secrete different neurotransmitters (norepinephrine and acetylcholine). The receptors on target cells vary
What is an example of "antagonistic" effects arising from dual innervation?
Ex: heart rate decreases (parasympathetic) vs heart rate increases (sympathetic)
What other CNS structures play a role in autonomic function?
Hypothalamus, cerebral cortex, midbrain, => pons, medulla oblongata, spinal cord reflexes
Where do sympathetic preganglionic neurons originate?
In the lateral horns and nearby regions of spinal cord grey matter. Thoracic and lumbar regions of the spinal cord.
How do the effector pathways of the ANS differ from those in the somatic nervous system?
In the somatic pathway, a motor neuron from brainstem or spinal cord issues a myelinated axon that reaches all the way to skeletal muscles. In the autonomic pathway, a signal must travel across two neurons to get to the target organ.
What organs or structures does the autonomic nervous system act upon?
It controls glands, cardiac muscle, and smooth muscle. Primarily the viscera of thoracic and abdominal cavities.
In a nutshell, what is the autonomic nervous system?
It is the self-governed nervous system (independent of our will). It controls HR, BP, and temp. It is a motor nervous system.
What is meant by the term "dual innervation"?
Meaning that the viscera receive nerve fibers from both parasympathetic and sympathetic divisions.
What neurotransmitter is secreted by ANS postganglionic fibers?
Norepinephrine is secreted by nearly all sympathetic postganglionic neurons. Acetylcholine is secreted by postganglionic parasympathetic neurons.
Which branch of the ANS (sympathetic or parasympathetic) has preganglionic neurons that form cranial nerves III, VII, IX and X?
Parasympathetic branch of the autonomic nervous system
Where do sympathetic preganglionic neurons synapse with postganglionic neurons?
Paravertebral ganglia on sympathetic chain of ganglia
What is an example of an autonomic function that does not depend on dual innervation?
Regulation of blood pressure and routes of blood flow. The effectors responsible for this effect receive only sympathetic fibers.
What are the two main divisions of the ANS and how do they differ?
Sympathetic (fight or flight) and parasympathetic (rest and digest)
Where do parasympathetic preganglionic neurons originate?
The brain and sacral regions of the spinal cord. Midbrain, pons, and medulla. Sacral spinal cord segments S2 to S4
What is the Enteric Nervous System?
The nervous system of the digestive tract.
What is the sympathetic chain?
The sympathetic chain is a chain composed of afferent and efferent axons for involuntary control of bodily functions. Series of longitudinal ganglia adjacent to both sides of the vertebral column from cervical to coccygeal levels
Where do parasympathetic preganglionic neurons synapse with postganglionic neurons?
They synapse in terminal ganglia nearby to the target organs
What are visceral reflexes? Provide one example.
Visceral reflexes are unconscious, automatic, stereotyped responses to stimulation involving visceral receptors and effectors. Example: baroreceptors controlling blood pressure.