Chapter 15 Autonomic Nervous System PDF

The Autonomic Nervous System Chapter 15 Chapter 15.1 – Divisions of the ANS Divisions are designed to maintain homeostasis Controls cardiac and smooth muscle, glands Sympathetic division – fight or flight Parasympathetic division – rest and digest Organs and systems receive input from each divisio...

The Autonomic Nervous System Chapter 15 Chapter 15.1 – Divisions of the ANS Divisions are designed to maintain homeostasis Controls cardiac and smooth muscle, glands Sympathetic division – fight or flight Parasympathetic division – rest and digest Organs and systems receive input from each division Chapter 15.1 – Sympathetic Division ● Thoracolumbar system – sympathetic signals come from thoracic and superior lumbar nerves ● A central neuron sends signals to the sympathetic chain ganglia (set of 23 ganglia on each side of the spinal cord) ● Each nerve leads to a ganglia at the same level as the target effector (organ to be innervated) ● Some axons travel past the chain ganglia and lead to a collateral ganglia (celiac, superior and inferior mesenteric) which are part of the enteric nervous system Chapter 15.1 ● Preganglionic fiber – from spinal cord to sympathetic ganglion, short, myelinated ● Postganglionic fiber – from ganglion to target effector, long, unmyelinated ● Adrenal medulla – gets direct connection from preganglionic fibers to release molecules ● A preganglionic fiber may have up to 20 targets Chapter 15.1 - Parasympathetic ● Preganglionic fibers lead to the terminal ganglia which is on or near the target effector, longer ● Intramural ganglia is in the wall of the target organ ● Postganglionic fibers are shorter ● Preganglionic fibers in the brain go straight to the ganglion through the cranial nerves to effect most organs Chapter 15.1 – Chemical Signaling ● 2 types of synapses – cholinergic and adrenergic ● Cholinergic – Ach released to nicotinic (ligand gated channel) or muscarinic (G protein receptor) receptors ● Adrenergic – norepinephrine is released to either an alpha receptor (3 types) or a beta receptor ( 2 types) ● Epinephrine (adrenaline) is the second signaling molecule in the adrenergic synapse ● Norepinephrine – is a neurotransmitter and hormone Chapter 15.1 - Varicosity Chapter 15.1 Sympathetic Parasympathetic Preganglionic ACH - nicotinic receptor ACh - nicotinic receptor Norepinephrine - alpha or beta adrenergic receptors ACh - muscarinic receptor of sweat glands and blood vessels of Postganglionic skeletal muscle ACh - muscarinic receptor Chapter 15.2 – Autonomic Reflexes and Homeostasis ● Afferent branch is the same as somatic reflex ● Efferent branch must relay to ganglia and then the target effector ● Autonomic system has baroreceptors to react to a stretch stimuli in the aorta and carotid arteries ● Referred Pain - conscious perception of autonomic sensation Chapter 15.2 ● Long reflex – afferent branch into spine or brain ● Short reflex – completely peripheral, local response, the synapse is in the ganglia ● Enteric nervous system – digestive organs have a short reflex based on distention of the stomach ● The heart rate would be 100 bpm without the parasympathetic signal to slow it down ● Autonomic tone – organs may have a sympathetic or parasympathetic tendency for homeostasis, Chapter 15.3 – Central Control ● A bright light in 1 eye makes both pupils constrict ● Somatic reflexes are never bilateral Chapter 15.3 - Hypothalamus ● Control center for many homeostatic mechanisms ● Regulates autonomic and endocrine function ● Role in pupillary reflexes ● 2 main pathways for communication – medial forebrain bundle and dorsal longitudinal fasciculus Chapter 15.3 – Queen Amygdala ● Part of limbic lobe responsible for emotion and memory function ● Strong connection to the hypothalamus Chapter 15.3 - Medulla ● Cardiovascular center ● Receives much input from hypothalamus ● Connects to cardiac accelerator nerves and vasomotor nerves Chapter 15.4 – Drugs that Affect the Autonomic Nervous System ● Endogenous chemical – substance produced by the body to interact with a receptor ● Exogenous chemical – substance introduced from outside the body ● Nicotine – large affect on ANS, can depolarize all nicotinic receptor synapses without ACh present, will cause vascular tone to be more sympathetic (increase BP), heart rhythm can be affected Chapter 15.4 – Sympathetic Effect ● Sympathomimetic drug – enhances adrenergic function by binding to receptors, increase norepinephrine production and release, and/or may block removal of norepinephrine (phenylephrine, cocaine, caffeine) ● Sympatholytic drug – interrupts adrenergic function by blocking receptors (beta blockers, clonidine) Chapter 15.4 – Parasympathetic Effects ● Parasympathomimetic drugs – enhance cholinergic effects (Pilocarpine – constrict pupils) ● Anticholinergic drugs – inhibit cholinergic effects (Atropine, scopolamine – dilate pupils and antiemetic)