Lecture 4. Autonomic Nervous System(1).pdf

Autonomic Nervous System Assos. Prof. Dr. Dilek Özbeyli • The autonomic nervous system is an involuntary system that controls and modulates the functions primarily of visceral organs. • Each pathway in it consists of two neurons; a preganglionic neuron and a postganglionic neuron. Heart muscle H...

Autonomic Nervous System Assos. Prof. Dr. Dilek Özbeyli • The autonomic nervous system is an involuntary system that controls and modulates the functions primarily of visceral organs. • Each pathway in it consists of two neurons; a preganglionic neuron and a postganglionic neuron. Heart muscle Heart muscle Organization of the autonomic nervous system. The somatic nervous system is included for comparison. ACh, Acetylcholine; M, muscarinic receptor; N, nicotinic receptor; NE, norepinephrine. *Sweat glands have sympathetic cholinergic innervation. Terminology • Adrenergic neurons release norepinephrine; receptors for norepinephrine on the effector organs are called adrenoreceptors. • Cholinergic neurons release acetylcholine (ACh); receptors for ACh are called cholinoreceptors or muscarinic receptors. Heart muscle Heart muscle Nonadrenergic, noncholinergic neurons: • Some postganglionic parasympathetic neurons of the gastrointestinal tract that release peptides • e.g., substance P or • e.g., nitric oxide (NO) as their neurotransmitter rather than ACh. Neuroeffector Junctions of the Autonomic Nervous System • The junctions between postganglionic autonomic neurons and their effectors • They are analogous to the neuromuscular junctions of the somatic nervous system but not the same. Figure 16.1.4 – Autonomic Varicosities. Instead of a synaptic end bulb, neurotransmitters release from swellings along the length of a fiber to the target effector. Inhibit https://link.springer.com/chapter/10.1007/978-3-030-87266-3_41/figures/1 Stimulate peristalsis Sympathetic Nervous System • One category of preganglionic neuron synapses on postganglionic neurons in paravertebral ganglia (e.g., superior cervical ganglion). • Other category of preganglionic neuron synapses on postganglionic neurons in prevertebral ganglia (e.g., celiac ganglion). Adrenal medulla • The adrenal medulla is a specialized ganglion • The cell bodies of its are located in the thoracic spinal cord. • Their axons synapse (Ach) on chromaffin cells • Chromaffin cell release epinephrine and norepinephrine • PNMT catalyzes the conversion of norepinephrine to epinephrine, a step that, requires cortisol Thoracic spinal cord • Sympathetic postganglionic adrenergic nerves release both the classic neurotransmitter (norepinephrine) and nonclassic neurotransmitters adenosine triphosphate [ATP] and neuropeptide Y. Target tissue(e.g. Vessel wall) contraction Sympathetic Adrenergic Varicosities ATP Norepinephrine Neuropeptite Y Functions • The overall function is to mobilize the body for activity. • Fight or flight response is rarely employed It operates continuously to modulate the functions • Heart, • Blood vessels, • Gastrointestinal tract, • Bronchi, • Sweat glands. Fight or Flight Response • The body responds to fear, extreme stress, and intense exercise with a massive, coordinated activation of the sympathetic nervous system including the adrenal medulla. • + redistribution of blood flow away from skin, kidneys, and splanchnic regions toward skeletal muscle • + decreased gastrointestinal motility and secretions Arterial pressure, Hearth rate Cardiac output, Metabolic rate, Blood glucose concentration, Mental activity Alertness Take a difficult exam, run away from a burning house, fight an attacker) Preganglionic neurons of the parasympathetic division arise from • Nuclei of cranial nerves (CNs) III, VII, IX, X and • Sacral spinal cord segments S2–S4; Therefore the parasympathetic division is called craniosacral. Parasympathetic Cholinergic Varicosities • Release both the classic neurotransmitter (ACh) and • Nonclassic neurotransmitters (e.g., vasoactive intestinal peptide [VIP], NO). Parasympathetic Nervous System • The overall function of the parasympathetic nervous system is restorative, to conserve energy. Autonomic Innervation of the Organ Systems • Most organs have both sympathetic and parasympathetic innervation. • These innervations operate reciprocally or synergistically to produce coordinated responses. • For example, the heart has both sympathetic and parasympathetic innervations. Ciliary muscle contract Lens becomes curved Hypothalamic and Brain Stem Centers • Centers in the hypothalamus and brain stem coordinate the autonomic regulation of organ system functions. • Thanks for your attention….