Autonomic Nervous System Flashcards
What are the two sequential neurons that compose the ANS?
- preganglionic neuron
- postganglionic neuron
Describe the preganglionic neuron.
- cell bodies are located within CNS
- axons are myelinated
- neurotransmitter is ACh
Describe the postganglionic neuron.
- cell bodies are located in peripheral ganglia
- axons are not myelinated
-neurotransmitter is
+ACh is parasympathetic
+NE in sympathetic
What some generalizations regarding the ANS?
- most parasympathetic and almost all sympathetic postganglionic fibers merely touch or pass near to the effector cells of the organs they innervate
- terminal ends of these fibers usually have enlarged varicosities where neurotransmitter and large numbers of mitochondria are stored
Cell body of each sympathetic preganglionic neuron lies where?
-intermediolateral horn of the spinal cord (T1-L2)
Describe how the sympathetic preganglionic fibers travel.
- can synapse with postganglionic neurons upward or downward in the paravertebral chain
- preganglionic fiber can pass for variable distances through the chain and then through one of the sympathetic nerves to synapse in a peripheral sympathetic ganglion
What are some characteristics of postganglionic sympathetic fibers?
- pass through the gray rami
- are type C fibers
- make up about 8% of the fibers in the average nerve
- control blood vessels, sweat glands, piloerection muscles
Where is the thoracic sympathetic chain?
Lies against neck of ribs and costovertebral junctions
-12 thoracic ganglia pairs
+first one often fused with inferior cervical ganglion
+referred to as stellate ganglion collectively
-cervical ganglion
+superior, middle, inferior
The preganglionic sympathetic supply to the thoracic viscera are from _________.
T1-5
The postganglionics are from the thoracic sympathetic chain are from where? How do they exit?
- superior, middle, and inferior cervical ganglia
- T1-T5 paravertebral ganglia
- they exit the chain as direct fibers and travel downwards to enter the thorax -> as cardiopulmonary splanchnic nerves
The cardiopulmonary splanchnic nerves travel on their own and do not accompany other nerves or vessels.
:)
What is the function of the thoracic sympathetic chain?
- coronary artery dilation
- increase HR
- bronchodilation
What are splanchnic nerves??
- composed of preganglionic fibers and visceral sensory fibers
- supply abdominal viscera
- synapse in prevertebral ganglia
Location and synapses of greater splanchnic nerves?
- T5-T9
- synapses in celiac ganglion
Location and synapses of lesser splanchnic nerves
- T10-T11
- synapses in the superior mesenteric ganglion
Location and synapses of the least splanchnic ganglion
- T12
- synapses in the aorticorenal ganglion
When the adrenal medulla is stimulated by the sympathetic system what does it secrete?
- secrete about 80% epi and 20% NE
- hormones last 5-10x longer than neurotransmitter versions
What does circulating NE do?
-constricts most blood vessels of the body
+greater effect on blood vessels in skeletal muscles so greater effect on raising arterial pressure
- increases heart activity
- inhibits GI tract
- dilates pupil
Secretory cells of the adrenal medulla are what?
- postganglionic neurons
- have rudimentary fibers that secrete epi and NE
What does circulation epinephrine do?
- raises arterial pressure to a lesser extent than NE
- increases cardiac output more than NE
- has 5-10x as great effect on metabolism as NE
- can increase metabolic rate of whole body as much as 100% above normal
What is the alarm or stress response?
-occurs when there is a mass discharge of the entire sympathetic system
What does the alarm response induce physiologically?
- increased arterial pressure
- reroute get of blood flow to active muscles
- increased rates in cellular metabolism
- increased blood glucose conc
- increased glycolysis in liver and muscle
- increased muscle strength
- increased mental activity
- increased blood coagulation
About 75% of all parasympathetic fiber are in what?
Vagus nerve
Most preganglionic fibers pass all the way to the organ that is to be innervated.
;)
Where are postganglionic parasympathetic fibers found? What do they use as their neurotransmitter?
- are located in the wall of the organ
- use ACh as their neurotransmitter
What cranial nerves carry parasympathetic signals?
- oculomotor (III)
- facial (VII)
- glossopharyngeal (IX)
- vagus (X)
What are the functions of the oculomotor nerve?
- supplies fourth of the six extrinsic muscles of the eye and the levator palpebrae superioris
- preganglionic: from Edinger-Westphalia nucleus to the ciliary ganglion
- postganglionic: from the ciliary ganglion to the sphincter pupillae muscle
What are the functions of the facial nerve?
- primary motor nerve to muscles of facial expression
- carries sensation of taste from anterior 2/3 of tongue
Preganglionics: from superior saliva tort and lacrimal nuclei to submandibular/sublingual ganglia
-postganglionics: to lacrimal glans, submandibular gland, sublingual gland, adn mucus glands of mouth and nose
What is the function of the glossopharyngeal nerve?
- carries general sensation and sensation of taste from posterior 1/3 of the tongue
- preganglionics: from inferior saltatory nucleus to otic ganglion
- postganglionics: to parotid gland
What is the function of the vagus nerve?
-motor supply to muscles of the 4th and 5th pharyngeal arches and is important in swallowing and speaking
Outline the parasympathetics of the vagus nerve.
-major parasympathetic supply to thoracic and abdominal organs
Preganglionics: from dorsal motor nucleus
Postganglionics: myenteric plexus of wall of gut tube all the way to the left colic fissure
What is the course if the vagus nerve?
- runs parallel to esophagus (innervates esophagus)
- passes posterior to root of lung on each side
- pierces diaphragm with esophagus
- becomes gastric nerve
- supplies viscera in thoracic cavity
What are the vagus nerve branches?
- cardiac branches to cardiac plexus
- pulmonary branches to pulmonary plexus
- esophageal branches to esophageal plexus
- left recurrent laryngeal nerve from left vagus (hooks around arc of aorta to left of ligamentum arteriosus)
- right recurrent laryngeal nerve from right vagus (raisers in neck, not thorax)
How is ACh produced? Broken down?
- acetyl CoA + choline -> ACh (choline acetyl transferase)
- ACh -> choline + acetate ion (acetylcholinesterase)
Describe how NE is produced?
- hydroxylation of tyrosine to dopa
- decarboxylation of dopa to dopamine
- transport of dopamine into the vesicles
- hydroxylation of dopamine to NE
- in the adrenal medulla, 80% of NE is methylated to form epi
How is NE removed?
- reuptaken
- diffusion
- destruction by monoamine oxidase -> found in nerve endings
- destruction by catechol-O-methyl transferase (COMT) -> present in all tissue
- NE/epi is active for only a few seconds when secreted directly into the tissues, but is active in blood until destroyed by COMT
What are muscarinic ACh receptors?
- muscadine is a poison from toadstools
- receptors are found on all effector cells stimulated by postganglionic cholinergic neurons
What are nicotinic ACh receptors?
- found in autonomic ganglia at synapses between preganglionic and postganglionic neurons
- present in neuromuscular junctions in skeletal muscle
What are alpha adrenergic receptors?
- NE excited mainly alpha receptors but also beta receptors to a lesser extent
- epi excited both alpha and beta almost equally
- certain alpha receptors are excitatory; others are inhibitory
What are alpha receptors associated with?
- vasoconstriction
- iris dilation
- intestinal relaxation
- intestinal sphincter contraction
- pilomotor contraction
- bladder sphincter contraction
- inhibition of neurotransmitter release
What do beta1 adrenergic receptors do?
- cardio acceleration
- increased myocardial strength
- lipolysis
What do beta2 adrenergic receptors do?
- vasodilation
- intestinal relaxation
- uterus relaxation
- bronchodilation
- calorigenesis
- glycogenolysis
- bladder wall relaxation
What do beta3 adrenergic receptors do?
-thermogenesis
What are the sympathomimetic drugs?
- NE
- epi
- methoxamine
- phenylephrine (alpha receptors)
- isoproterenol (beta receptors)
- albuterol (beta2 receptors)
What drugs cause release of NE?
- ephedrine
- tyramine
- amphetamine
What does reserpine do?
-blocks synthesis and storage of NE
What does guanethidine do?
-blocks release of NE
What does phenotype amine/phentolamine do?
-block sympathetic alpha receptors
What does propranolol do?
-blocks sympathetic beta1 and beta2 receptors
What does metoprolol do?
-blocks mostly sympathetic beta1 receptors
What does hexamethonium do?
-blocks transmission through autonomic ganglia
What do parasympathetic drugs that act of cholinergic effector organs do?
- not rapidly destroyed by cholinersterase
- include pilocarpine and methacholine
- act directly on muscarinic receptors
What drugs inhibit acetylcholineesterase?
- neostigmine
- pyridostigmine
- ambenonium
What are drugs that block cholinergic activity?
- atropine
- homatropine
- scopolamine
What are the effects the ANS on the eye?
Sym: pupil dilation
Para: pupil constriction, lens focusing
Sympathetic stimulation of glands
-causes secretion of large amounts of sweat
+cholinergic to most sweat glands (few adrenergic fibers in palms and soles)
+actually a parasympathetic function distributed via sympathetic fibers
Parasympathetic stimulation of glands
- strongly stimulates lacrimal, nasal, salivary, and many GI glands
- strongly stimulates GI glands of upper tract
- lower tract mostly stim,halted via the enteric system
ANS stimulation on GI tract
Sym: strong stimulation inhibits peristalsis, normally not dependent on sympathetic stimulation
Para: promotes peristalsis, relaxes sphincters
ANS on heart
Sym: increases HR and strength of contraction
Para: decreases HR and strength of contraction
ANS of systemic blood vessels
Sym: constricts most blood vessels
Para: has almost no effect
ANS on arterial pressure
Sym: results in acute increase in arterial pressure but little effect long term
Para: decreases pumping of heart but little effect on blood pressure
General effects of ANS
Sym: inhibits most endodermal structures
Para: excited most endodermal structures
What are some characteristics of the ANS?
-can change visceral function rapidly and intensely
+HR can be increased to twice normal within 3-5 secs
+arterial pressure can be doubled within 10-15 secs
\+sweating can begin within seconds
