Sympathetic Nervous System Lecture 2 PDF

C144/244 Lecture 2; 04/10/23 Fernando Gómez-Pinilla, Ph.D. Professor, Dept. Neurosurgery, Med. School Dept. Integrative Biology and Physiology UCLA Neural control of body functions Mostly voluntary control Mostly non-voluntary control Main action of ANS is to maintain Homeostasis • Homeostat...

C144/244 Lecture 2; 04/10/23 Fernando Gómez-Pinilla, Ph.D. Professor, Dept. Neurosurgery, Med. School Dept. Integrative Biology and Physiology UCLA Neural control of body functions Mostly voluntary control Mostly non-voluntary control Main action of ANS is to maintain Homeostasis • Homeostatic mechanisms have 3 essential elements: a sensor, an integrator and an effector. • Maintain a state through the dynamic modulation of tissue effectors (in this case pancreatic islet cells). • Stable oscillations with parameters remaining in functional range. Autonomic Nervous System • Control of homeostasis (housekeeping mechanisms). The maintenance of homeostasis is the act of keeping a system in a stable state by modulating physiological processes. • Works in concert with the endocrine system to continuously adjust blood chemistry, respiration, circulation, digestion, immune system, body temperature, sexual function, etc. • Plays a pivotal role controlling emotions. • Short latency response. Coordinates a fast physiological response during emergencies, but • Most of the time is doing housekeeping work Autonomic Nervous System (ANS) has 3 divisions: • Sympathetic nervous system (SNS): mobilization of energy particularly during emergency situations -- catabolic response. • Parasympathetic nervous system (PNS): digestion, nutrient assimilation, and energy conservation -- anabolic function. • Enteric nervous system, “little brain of the gut”. Sympathetic Nervous System (SNS) • Selective energy expenditure • Catabolic functions (energy usage) • Cardiopulmonary adjustment for intense activity (fight or flight) • In emergencies, it involves a coordinated and adaptive response which is immediate -- occurring without cognitive analysis Fight or Flight Reaction • • • • • • • Short latency, synergistic, and integrative response Heart acceleration Increase in blood pressure Dilation of blood vessels in skeletal muscle Constriction of blood vessels in GI tract and skin Pupil dilation Sweating Main Pathways of the Autonomic Nervous System Conversely to the somatic NS (one neuron), the SNS is a two-neuron circuit separated by one ganglion: Relative to ganglion location, travelling outgoing fibers (axons) are called A. Preganglionic (before ganglion): cell body located in the intermediolateral cell column in the spinal cord (T1-L3) arranged in a viscerotopic segmental organization B. Postganglionic (after ganglion): cell body located in ganglion outside spinal cord According to distance to spinal cord, ganglion can either be: A. Paravertebral along the sympathetic chain, or B. prevertebral (by the target) Also observe viscerotopic rostral to caudal segmental organization of the neuronal cell body in the spinal cord and corresponding innervated organ. Paravertebral Ganglia (sympathetic chain): close to spinal cord • • • • • • • Bilateral chain adjacent to the spinal cord. Rostral sympathetic chain forms cervical ganglia (superior, middle, inferior or stellate). Superior: head and neck. Middle and inferior (stellate): heart, lungs, bronchi. Each ganglion receives gray rami (myelinated) from the IML in spinal cord, and after synapsing postganglionic fibers (white rami (unmyelinated) supply the head, trunk, and limbs travelling alongside somatic peripheral nerves. In head region innervates glands and smooth muscle. In trunk and limbs, fibers innervates blood vessels in muscle (vasoconstrictor), skin (e.g. sweat glands), erector pili muscles. Prevertebral Ganglia (4): Close to target tissue • Preganglionic fibers (white rami, unmyelinated) with cell bodies in IML reach prevertebral ganglia via splanchnic nerves. • Adrenal medulla (specialized endrocrine gland) receives preganglionic fibers to stimulate release of norepinepherine). Prevertebral ganglia illustrated by SNS Innervation of Abdomen •Prevertebral ganglia (4) in abdomen are named according to associated arteries: •Celiac: stomach, foregut, liver, pancreas. •Superior mesenteric: midgut (small intestine). •Inferior mesenteric: hindgut (large intestine) •Pelvic-hypogastric plexus: urinary and genital Practice diagram: try to locate all components of the SNS pathways Viscerotopic organization in which the preganglionic neuron is located about the same antero-posterior level of the innervated target region in body ANS Signals at the Tissue Level Preganglionic neurons in SNS and PNS secrete acetylcholine, and postganglionc neurons in ganglia of both PNS and SNS have Nicotinic Cholinergic receptors. Postganglionic neurons: SNS secrete norepinephrine and target tissue has Adrenergic receptors (Catecholaminergic receptors; exceptions: sweat glands and adrenal medulla) PNS secrete acetylcholine and target tissue has Muscarinic cholinergic receptors. Note that these are G-protein coupled receptors (GPCRs). PNS or SNS activation triggers cascade of signals in target-tissue receptors Some toxins are deadly because they interfere with GPCR signals and thus disable the ANS. Two examples are cholera toxin and pertussis toxin which are secreted by bacteria. These toxins are often used in research to examine signal transduction. Most snake venom attack the ANS: Institute of Butantan in Brazil specialized