Autonomic Nervous System II Flashcards
Somatic neurons
- pathway from CNS and effector cell is monosynaptic
- neuron releases ACh which binds N1 nicotinic cholinergic receptors on the postsynaptic membrane of skeletal muscle cell
- N1 receptor antagoist= d-tubocurarine
- Nicotinic receptor agonist = nicotine
Pregangionic neuron
- in both the parasympathetic and sympathetic divisions, the preganglionic neuron releases ACh, which binds to N2 nicotinic cholinergic receptors on the post synaptic membrane of the post ganglionic neuron
- N2 receptor antagonist - hexamethonium
Post ganglionic neurons
- for para- ACh but postsynaptic receptor is muscarinic cholinergic (GPCR, M1-M5)
- M1, 3, 5- linked to activation of PLC, increases intracellular calcium and DAG
- M2,4 inhibit adenylyl cyclase and decreased cAMP
- atropine is muscarinic cholinergic receptor antagonist
Parasympathetic activation
- more discrete than sympathetic, produces effects through activation of cholinergic muscarinic receptors in tissues
- pupillary constriction/miosis (CN III)
- copious secretion of glands- nasal, lacrimal, submandibular (CN VII), Parotid (CN IX), gastric and pancreatic (CN X)
- GI peristalsis/ increased motility and sphincter relaxation, bronchial constriction; decreased heart rate (CN X)
- PNS fibers from S2-24 innervate pelvic structures- relaxation of the ureter and sphincter in conjuction with contraction of the detusor muscle during urination; rectal emptying; penile erection
Origination of PNS
-cranial PNS originates in nuclei in the midbrain, pons and medulla
and in sacral segments (S2-S4) in the spinal cord
-Medulla- dorsal motor nucelus of vagal nerve
Midbrain- Edinger-Westphal nucleus- ciliary ganglion- CN III
-Pons- Lacrimal nucleus- Pterygopalatine ganglion- lacrimal and nasal glands; Superior salivatory nucleus- submandibular ganglion
Medulla- Inferior salivatory nucleus- Otic ganglion- parotid gland; Dorsal motor nucelus of vagal nerve- CN X- heart, bronchial tree, stomach, sm intestine, lg intestine, urinary bladder, male genitalia
Nucleus ambiguus
- the nucleus ambiguus and dorsal motor nucleus of the vagus contain cell bodies of preganglionic fibers that travel with CN X to a host of terminal ganglia in the viscera of the thorax and abdomen
- tell Vagus what to do and what to do when
SNS and PNS influence on gut
- the myenteric and submucosal plexuses of the the gut are diffuse interconnected series of neuronal cell bodies, axons, and dendrites
- myenteric (Auerbach’s plexus)- highly interconnected meshwork of neuron cell bodies, axons, and dendrites on the surface spreading over the deep circular layer of muscle
The SNS and PNS influence on the function of the enteric
- distension of the gut by ingestion of food, and food itself activate mechanoreceptors and chemoreceptors in the epithelial lumen that innervate central control centers to activate the PNS (and inhibit the SNS) to promote digestion via enhanced motility and secretions
- cutting the parasympthatic fibers innervating the gut results in a decrease in GI wall muscle and sphincter tone, demonstrating that the PNS exerts a tonic effect on GI motility
SNS and PNS “talk” to sensory neurons and vice versa
- postgang neurons in PNS are in myenteric and submucosal plexus
- PNS innervation of GI system in oral gavity and anus- small of good initates signal from nose and mouth the cranial nerves in the brain stem which activats the PNS to cause salivation and secretion of digestive juices
- in myenteric plexus- PNS activation is depolarizing and generates APs lead to contractions of smooth muscle of gut
- norepi- sympathetic- relaxing smooth muscle of gut and sphincter contriction
SNS and PNS for micturition
- filling of bladder sympathetic control dominations causing relaxation of detrusor muscle (Beta 2), and contract internal sphincter (alpha 1)
- during micturition, parasympathetic control predominates, causing contraction of the detrusor muscle and relaxation of internal sphincter
Autonomic functions in higher brain areas
-hypothalamus (head ganglion of the ANS) and by nuclei in the midbrain, pons and medulla, and brain stem( cardiovascular function, respiration, temp regulation, micturition, thirst, GI motility, and hunger
Descending cortical control of autonomic output
- fear: initiates fight or flight
- panic attacks: initate spontaneous fight or flight response
- emotional stress or painful stimuli- lead to massive vasodilation and hypotension (vasovagal syncope)
- seizures- can induce sudden cardiac death from massive sympathetic output and arrhymias
- chronic stress- can lead to peptic ulcers from increased gastric acid secretino
- sleep deprivation- in rates leads to death from loss of thermoregulation and cardiovascular control
- congnitive activity- can inititate sexual arousal
- nervousness- can lead to diarrhea
Visceral afferents overwhelm cortical function
nothing else sems to matter
- hunger
- nausea
- dyspnea
- visceral pain
- bladder and bowel distention
- hypothermia and hyperthermia
