Autonomic nervous system
Key notes Autonomic: an independent system that runs on its own The ANS is a visceral and involuntary sensory and motor system The visceral motor fibers in the autonomic nerves are accompanied by visceral afferent fibers. Most of afferent fibers supply information that originates from sensory receptors in the viscera. Activity of these receptors may not reaches the level of consciousness. Visceral afferent fibers that mediate sensation include nociceptors that travel in sympathetic nerves, such as the splanchnic nerves.
Housekeeping and vegetative function of ANS are slow, last longing & less focused. The ANS has central integrative components in the hypothalamus and brainstem autonomic nuclei that receive input from visceral and somatic afferents as well as from more rostral brain regions. Example of ANS function: Response of circulation to change in body position
Functions of the ANS Maintenance of homeostasis in response to the normal fluctuations of controlled variables (e.g., the negative feedback regulation of blood pressure). Integration of the stress response, including the response to exercise and the classic fight or flight response. Integration of visceral function (e.g., coordination of organs in the digestive system after the ingestion of food).
Disorders of ANS Asthma Constipation Diarrhea Ulcers Hypertention Heart desease Stroke..
Three subdivision of ANS Sympathetic Parasympathetic Enteric nervous system
The efferent path of the ANS as contrasted with the somatic motor system
Anatomical organization of sympathetic nervous system
Sympathetic nervous system Typically activated under condition of fight, fright, & flight and during extensive exercise Each preganglionic sympathetic fiber synapses with many postganglionic neurons across several ganglia, producing widespread generalized effects.
Sympathetic innervation of the adrenal medulla Preganglionic sympathetic axons terminate on the chromaffin cells. When stimulated, the chromaffin cells release epinephrine into the circulation
Anatomical organization Parasympathetic nervous system
Parasympathetic nervous system Parasympathetic N.S. is more focused in its activity Cranial and sacral division Dorsal motor nucleus (DMV) is largely secretomotor, Nucleus ambiguus is visceromotor. The DMV supplies visceral organs: -Neck (pharynx, larynx), -Thoracic cavity (trachea, bronchi, lungs, heart, esophagus) -Abdominal cavity (including much of the GI tract, liver, pancreas) The nucleus ambigus contains two groups of neurons: (1) Dorsal group (branchiomotor) that activates striated muscle in the soft palate, pharynx, larynx, and esophagus. (2) Ventrolateral group that innervates and slows the heart.
Chemical Transmission Acetyl-CoA + Choline transferase Acetylcholine Tyrosine hydroxylase DOPA Decarboxylase Dopamine hydroxylation Norepinephrine methylation Epinephrine Cholinergic and adrenergic fibers : Ach & Norepinephrine
Chemical Transmission Co-release of multiple neurotransmitter from nerve endings Modulatory action of autonomic transmitter VIP, NO: nonadrenergic, noncholinergic (NANC) e.g. in salivary gland Sympathetic axons innervating sweat glands and blood vessels in skeletal muscle secret Ach
Mechanism of transmitter removal at postganglionic ending 1- Reuptake (50-80%) 2- Diffusion 3- Destruction (MAO & COMT)
Receptors on the effector organ Cholinergic receptors: Nicotinic: Ion conductance, Ganglion, Skeletal muscle Muscarinic (M 1,M 2,M 3 ): IP3/DAG, camp, g k, NO(EDRF)
Adrenergic receptors: Alpha (α1, α2): IP3/DAG, camp Beta (β1, β2, β3): camp
Responses of effector organs to ANS impulses
Table Continued
Sympathetic and parasympathetic tone Tone caused by basal secretion of adrenal medullae Effect of sympathetic and parasympathetic denervation Denervation supersensitivity
Stimuli that enhance the secretion of catecholamines
Brain stem control of ANS Modularly, pontine and mesencephalic control of ANS Hypothalamus: Head ganglion of the ANS Couple emotion to autonomic response Control integrative autonomic function: Body temperature Appetite Water intake Heart rate Arterial pressure Sexual activity Lactation Growth
Higher brain areas control brain stem autonomic center Medial prefrontal areas Insular Amygdala Psychosomatic disease