Week 4 - ANS Physiology/Pharmacology Flashcards
What is the function of the ANS?
Controls visceral body functions and modulates BP, GI motility & secretion, bladder emptying, sweating & temperature maintenance
Where does activation of the ANS occur?
Hypothalamus: response to stress, BP control, Temp regulation
Brain stem (Medulla/Pons): hemodynamic and ventilatory control
Spinal cord
What are the divisions of the Autonomic Nervous System?
Sympathetic Nervous System
Parasympathetic Nervous System
Enteric Nervous System
What is the location of the SNS and its response?
Thoracolumbar – Fight, Flight, or Fright
-Increases responses
What is the location of the PNS and its response?
Craniosacral – Rest and Digest
- Relaxes and targets responses
- Salivation, Lacrimation, Urination, Digestion/Defecation, Sexual arousal
What is the Enteric Nervous System?
Third branch of ANS
A system of neurons and supporting cells within the walls of the GI tract including cells of the pancreas and gall bladder
Locally autonomous in contrast to sympathetic and parasympathetic but influenced by the SNS and PNS activity
What organs only have sympathetic innervation?
Spleen
Certain blood vessels
Piloerector muscles
What is response to SNS stimulation on the heart?
- Increased HR (SA node)
- Increased conduction velocity of AV node
- Increased automaticity, conduction velocity of His-Purkinje system
- Increased contractility, conduction velocity of the ventricles
What is response to PNS stimulation on the heart?
- Decreased HR (SA node)
- Decreased conduction velocity of AV node
- Minimal effect on His-Purkinje system
- Minimal effects with possible slight decrease in contractility of the ventricles
What is response to SNS and PNS stimulation on bronchial smooth muscle?
SNS = bronchial relaxation
PNS = bronchial contraction
What is response to SNS stimulation on the GI tract?
- Decrease motility
- Decrease secretion
- Sphincter contraction
What is response to PNS stimulation on the GI tract?
- Increase motility
- Increase secretion
- Sphincter relaxation
What is response to SNS stimulation on the urinary bladder?
- Smooth muscle relaxation
- Sphincter contraction
What is response to PNS stimulation on the urinary bladder?
- Smooth muscle contraction
- Sphincter relaxation
What is response to SNS stimulation on the eye?
- Mydriasis (pupil dilation)
- Relaxation of ciliary muscle for far vision
What is response to PNS stimulation on the eye?
- Miosis (pupil constriction)
- Contraction of ciliary muscle for near vision
What is response to SNS stimulation on the liver?
Glycogenolysis and Gluconeogenesis
What is response to PNS stimulation on the liver?
Glycogen synthesis
What is response to SNS and PNS stimulation on salivary gland secretion?
SNS = increase
PNS = marked increase
What receptors are SNS?
Adrenergic:
- Alpha-1/Alpha-2
- Beta-1/Beta-2
- Dopa-1/Dopa-2
What receptors are PNS?
Cholinergic:
- Muscarinic - M1,2,3,4
- Nicotinic - N1,2
What nerve conducts 75% of PNS signals?
Vagus nerve (CN X)
A local anesthetic blockade of the Stellate Ganglion causes what syndrome?
Horner’s Syndrome
What is Cushing’s Triad?
Increased ICP, Bradycardia, and Hypertension
- Intracranial HTN –> SNS mediated systemic HTN
- Activation of the PNS medullary centers via the baroreceptor slows the heart rate (baroreceptor response not enough to reduce HTN)
- Results in increased blood flow to the brain and further increased ICP
What is Autonomic Hyperreflexia?
- Disruption of efferent impulses down the spinal cord from T5 or higher
- Exaggerated SNS response to bowel, bladder, or surgical stimulation due to receptor sensitivity secondary to denervation
- Loss of inhibitory impulses results in pure SNS response (HTN)
What is the Thermogenesis Reflex?
- Sweating controlled by cholinergic fibers (blocked by atropine or nerve blocks)
- Shivering decreased in elderly, absent in newborns/infants, blocked by NDMR’s
- General anesthetics impair thermogenesis
What is the Baroreceptor Reflex?
- Stretch receptors in aorta and carotid arteries sense increased pressure which sends signals via Hering nerve and Vagus nerve to the medulla
- Causes decreased HR, BP, Contractility and PVR
- Phenylephrine (alpha1 agonist) increases BP and reflex decreases HR
What is the Chemoreceptor reflex?
- Central sense increased arterial CO2 and/or decreased arterial pH (hypercarbia increases minute ventilation
- Peripheral in carotid body respond to decreased pO2 (Hering/Vegus nerve increases RR and tidal volume –> increased minute ventilation) (may also see increased HR/CO)
What is the Bainbridge reflex?
- Increased CVP activates stretch receptors in the atria
- Afferent impulses through vagus inhibit PNS output resulting in tachycardia
- Seen during labor when contractions autotransfuse and increase CVP
What is the Bezold-Jarisch reflex?
Hypotension, Bradycardia, Coronary Dilation
- Noxious stimuli sensed in the cardiac ventricles
- Unmyelinated C-fibers of vagus send signal to enhance baroreceptor response, inhibit sympathetic output, and decrease PVR to make it easier for the heart to pump
- Increased blood flow to the myocardium to decreased work of the heart (cardioprotective)
What is the Valsalva reflex?
Increased intrathoracic pressure, Decreased venous return, Decreased cardiac filling, Decreased BP
- Baroreceptor increases HR, increases inotropy –> increased BP
- Baroreceptors cause PNS induced decrease HR
What is the Oculocardiac (Five & Dime) Reflex?
- Afferent impulses to pressure on the eye or pulling on eye muscle
- Efferent slowing of HR via the Vagus nerve
- Muscarinic response blocked by Atropine or Glycopyrrolate
What are some anesthetic interactions with the ANS?
- Alpha2 agonists (inhibitory) reduce anesthetic needs
- Fentanyl depresses SNS tone and promotes vagal activation
- Desflurane depresses the ANS, stimulates the SNS
- Depression of the SNS by anesthetics appears to dominate
- Regional anesthesia and SNS blockade
- Postoperative complications secondary to ANS dysfunction
How does aging affect the ANS?
- HTN and orthostasis
- Temperature regulation (increased or decreased)
- Increased circulating norepinephrine (receptor down-regulation/decreased responses to exogenous catecholamines)
- Beta agonists are going to have decreased effects on HR, CO, and vasodilation secondary to reduced receptor response
- Decreased renin, decreased aldosterone, increased atrial natriuretic factor leads to salt wasting and hypovolemia
What affect does DM have on the ANS?
20-40% insulin dependent DM have neuropathies (ANS)
Labile BP, gastroparesis, thermoregulation, vagal dysfunction
Increased aspiration risk, aggressive temp maintenance, increased c/o
How does dysautonomia affect the ANS?
Shy-Drager syndrome
Guillain-Barre
Lamber-Eaton
Familial
Orthostatic Hypotension, HR variability, BP lability
Where is norepinephrine and epinephrine synthesized?
From tyrosine in the adrenal medulla
80% epinephrine 20% norepinephrine
What is the release of Norepinephrine into the synaptic cleft dependent on?
Calcium
*Alpha2 receptors are pre-synaptic and provides a negative feedback loop that modulates the release of Norepi by inhibiting the Ca++ release mechanism
What terminates the action of Norepinephrine at the synapse?
Diffusion away from the synaptic cleft and metabolism by MAO & COMT
Reuptake = 80% Metabolism = 20%
How does reuptake of Norepinephrine occur and what is it dependent on?
Via two active transport mechanisms:
-One into varicosities & Second into cytoplasm synaptic vesicle for storage
Dependent on magnesium and ATP, cytoplasm may be blocked by drugs (cocaine & tricyclics)
How is Norepinephrine metabolized?
By MAO - although it is minimal (mostly reuptake)
Residual vulnerable to metabolism by COMT
COMT not affected by drugs – MAO inhibitors can increase levels of NE
Metabolized NE is excreted in urine as metabolite VMA (high levels of VMA indicate pheochromocytoma)
How is ACh synthesized, stored, and metabolized?
Synthesized in pre and post ganglionic parasympathetic nerves
-Choline acetyltransferase catalyzes acetyl coA in mitochondria to form ACh
Stored in synaptic vesicles, released via PNS
Metabolism: rapidly hydrolyzed by AChE, plasma cholinesterase is too slow to metabolize ACh unless succinylcholine or mivacuriumn is given