Chapter 15 - The Autonomic Nervous System And Visceral Reflexes

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Chapter 15 - The Auto

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A motor nervous system that controls glands, cardiac and smooth muscle to maintain homeostasis, actions are involuntary
ANS - Autonomic
Slower than somatic reflexes, include a visceral reflex arc, Example Elevated BP; baroreceptors stretch receptors (aorta & carotid), glossopharyngeal n., medulla, vagus n., heart pacemaker cells
Visceral Reflexes
(receptor, afferent neurons, interneurons, efferent neurons, effectors),
Visceral reflex arc
Mainly adapts body for activity, (“fight or flight”)
Mainly a calming effect, reduced energy expenditure, normal body maintenance (“rest & digest”)
Background rate of activity from both divisions
Autonomic Tone
Control nuclei in hypothalamus and other brain stem regions, motor neurons in SC, peripheral ganglia and fibers in cranial and spinal nerves, pathway involves 2 neurons
Neural Pathways
Soma in brainstem or SC, ends in ganglion
Begins in ganglion and extends to target cells
Post ganglionic
Short preganglionic and long postganglionic fibers, cell bodies in lateral horns and nearby gray matter of SC, fibers exit via spinal nerves T1 to L2 and go to nearby sympathetic chain ganglia, interconnected by nerve cords there are typically 3 cervical, 11 thoracic, 4 lumbar, 4 sacral, 1 coccygeal
Sympathetic Division; also called thoracolumbar,
Small myelinated, enter ganglia via white communicating rami
Unmyelinated, exit ganglia by gray communicating rami or other route
Enter ganglia, take one of 3 paths (end and synapse, go up or down the chain, pass through chain to another ganglia nearer target), fibers leave chain by: spinal n. (effectors in muscles and body wall), sympathetic n. (effectors in head and thoracic cavity), and splanchnic n. (effectors in abdominopelvic cavity), neural convergence and divergence are present
secretes steroid hormones
Adrenal Cortex
modified postganglionic sympathetic neurons, secretes hormones epinephrine (85%) and norepinephrine (15%) into blood stream
Adrenal Medulla
Also called craniosacral division, long preganglionic and short postganglionic fibers, cell bodies in brain stem and segments S2 to S4
Parasympathetic Division
preganglionic fibers end in terminal ganglia in or near target, little divergence more selective
exit via 4 cranial nerves, III Oculomotor, VII Facial, IX Glossopharyngeal, X Vagus
Preganglionic (brainstem)
 (lens and pupil of eye)
III Oculomotor
(tear, salivary, nasal glands)
VII Facial
(parotid salivary glands
IX Glossopharyngeal
contains 90% of all PS preganglionic fibers, (heart, bronchi, blood vessels to lungs, esophagus, liver, pancreas, stomach, small intestine, kidney & ureter, proximal half of colon)
X Vagus
form Pelvic Splanchnic ns.: (distal half colon, rectum, bladder, reproductive organs)
Preganglionic (sacral cord)
Within walls of digestive tract, innervates smooth muscle and glands, regulates motility of esophagus, stomach, intestines and secretion of digestive enzymes and acid, interacts with ANS
Enteric Nervous System
Secrete ACh, released by all Sym & Parasym PG fibers & Parasym POG fibers, a few Sym POG fibers
Cholinergic Fibers
all cardiac muscle, smooth muscle, and glands, two types, work via 2nd messenger systems
Muscarinic Receptors
all synapses in autonomic ganglia, cells in adrenal medulla, at neuromuscular junction, always excitatory, work via ligand-gated ion channels
Nicotinic Receptors
Secrete NE, released by almost all POG Sym fibers
Adrenergic Fibers
usually excitatory, two subclasses cause different effects, α1 (suppress synthesis of cAMP), α2 (use Ca+2 as 2nd messenger)
α-Adrenergic Receptors
usually inhibitory, two subclasses cause different effects, β1 & β2 (use cAMP as 2nd messenger), many drugs are designed to be receptor selective
β-Adrenergic Receptors
tend to last longer due to lingering effects of NE.
Sympathetic Effects
Most viscera receive dual innervation
Dual Innervation
cardiac, digestive, pupils,
Antagonistic Effects
salivary glands
Cooperative Effects
partial constriction of vessels due to baseline sympathetic innervation
Vasomotor Tone
Limbic system provides a pathway connecting sensory and mental experiences with the ANS
Cerebral Cortex
Major control center of the ANS, includes hunger, thirst, thermoregulation, emotions, and sexuality, output is mainly to more caudal areas of brainstem and then to cranial nerves and spinal cord.
House numerous ANS nuclei many in the reticular formation, for cardiac, vasomotor, salivation, swallowing, sweating, GI secretion, bladder control, pupil control, and others, output is via spinal cord and cranial nerves III, VII, IX, X
Midbrain, Pons and Medulla Oblongata:
Autonomic reflexes like micturation, defecation, erection, and ejaculation are integrated in the spinal cord
Spinal Cord