Autonomic Nervous System Flashcards
what are the two primary divisions of the autonomic nervous system?
the sympathetic nervous system (thoracolumbar division) and the parasympathetic nervous systems (craniosacral division)
sometimes the enteric nervous system is included
what does the autonomic system innervate?
smooth and cardiac muscle, secretory epithelia and glands
what responses do the SNS and PNS mediate?
SNS- fight or flight
PNS- resting and digesting
both are capable of more discrete actions in context
T or F: Survival without the ANS is possible and physiologically normal.
F. Survival is possible but physiological function is severely compromised
what effects does the sympathetic nervous system have on the heart?
it stimulates the heart rate at the SA node (positive chronotropic effect), stimulates AV nodal conduction (positive dromotropic effect) and stimulates myocardial contractility (positive inotropic effect)
what effect does the parasympathetic nervous system have on the heart?
it inhibits the SA node, inhibits AV node conduction and mildly inhibits atrial contractility
(negative chronotropic, dromotropic and inotropic effects)
how does the parasympathetic nervous system decrease heart rate? What other regions of the heart does the PNS significantly innervate?
via activation of muscarinic cholinergic receptors
only significantly innervates the SA nodal region
what receptors do the sympathetic nervous system activate in the heart?
beta 1-andrenergic receptors
what are beta 1-andrenergic receptor agonists used to treat and what are the improvements being made to help?
tachycardia and hypertension (propranolol)
now been replaced by newer cardioselective beta blockers
where do preganglionic and postganglionic cell bodies of the ANS lie?
pre-within the CNS
post-in peripheral ganglia that project to target tissues
what are the relative lengths of pre and post ganglionic neurons in the SNS? the PNS?
SNS- short preganglionic and long postganglionic
PNS- long preganglionic and short postganglionic
what are the difference between motor neurons, preganglionic and postganglionic axonx?
motor: large diameter, fast myelinated alpha neuron
pre: small diameter, slow conducting myelenated B fibers
post: small, slow, unmelinated C fibers
how do the SNS and PNS differe in divergence?
SNS neuron contacts ~100 postganglionic neurons and has high divergence (wide spread effect)
PNS neuron contacts 15-20 postganglionic neurons and is not divergent (more discrete innervation)
what is an “en passant” synapse?
it is synapses in passing that allows a single axon to have broad actions in target tissues.
what is the pathway of a somatic neuron?
monosynaptic, neuron releases ACh and activates N1 nicotinic cholinergic receptors on the postsynaptic membrane
what is an agonist and an antagonist of a N1 nicotinic cholinergic receptor?
antagonist- d tubocurarine
agonist- nicotine
what is the preganglionic transmitter in both the SNS and PNS? What is its receptor and what is an antagonist of that receptor?
acetylcholine that binds to N2 nicotinic cholinergic receptors
hexamethonium
what are the neurotransmitter and postsynaptic receptor in the PNS?
ACh
muscarinic cholinergic receptor (subtypes M1-M5)
what are the neurotransmitter and postsynaptic receptor in the SNS?
norepinephrine andrenergic receptor (alpha and beta subtypes)
what is one pathway that the SNS without a postganglionic neuron?
the SNS directly innervates chromaffin cells of the adrenal medulla that releases epinephrine (mostly) and norepinephrine into the blood
what is the implication of the direct innervation of chromaffin cells by a preganglionic neuron from the SNS?
hormones are carried all over the body and effect multiple organs. They have similar effects to neuronal processes but last much longer because they are inactivated more slowly
what is the function of other transmitters besides ACh and norepi?
they are co transmitters
What SNS receptors do tissues have and what is the exception?
they have different andrenergic receptors with different affinities for epi and norepi (alpha and beta)
exception: eccrine sweat glands use muscarinic cholinergic receptors and ACh
what PNS receptors do tissues have?
muscarinic cholinergic receptors M1-M5
what transmitter and receptor does the SNS use to activate the adrenal medulla directly?
ACh and N2 nicotinic receptors
what activates an alpha1 adrenoreceptor and what are the subsequent events?
norepinephrine binds and activates alpha one which phosphorylates the GDP of a G protein. The cellular effects that this causes is mediated by phospholipase C
what activates a beta adrenoreceptor and what are the subsequent events?
norepinephrine binds and activates beta, phosphorylating the GDP of a G protein. The cellular effects are mediated by adenylyl cyclase and an increase in cAMP
describe the nicotinic cholinergic receptor
ACh opens a fice subunic ion channel for Na and K
how do muscarinic cholinergic receptors exert their action?
they are g protein coupled receptors that change the intracellular environment
what are the agonists and antagonists for N1 nicotinic ACh receptors?
agonists: ACh and nicotine
antagonists: d-tubocurarine
what are the agonists and antagonists for N2 nicotinic ACh receptors?
agonists: ACh and nicotine
antagonist: hexamethonium
which receptors are ionotropic and which are metabotropic?
ionotropic: nicotinic ACh receptors (N1 and N2)
metabotropic: muscarinic and adrenergic receptors
what are the agonists and antagonists for muscarinic receptors? are they the same for all subtypes?
agonists: ACh and muscarine
antagonist: atropine
yes, they are all the same.
how do the subtypes of muscarinic receptors produce their effects?
M1, M3 and M5 activate lipase C generating IP3 and DAG
M2 and M4 inhibit adeylate cyclase leading to decreased cAMP
which adrenergic receptors have a higher affinity for epinephrine and which have a higher affinity for norepinephrine?
alpha receptors prefer norepinephrine and beta receptors prefer epinephrine although both can be activated by either transmitter
how do the alpha subtypes of adrenergic receptors differ?
alpha one receptors activate phospholipase C and alpha two receptors inhibit adenylyl cyclase
how do the beta subtypes of adrenergic receptors differ?
they differ in their agonists and antagonists although they all receive epinephrine and norepinephrine.
what alteration in blood flow does the SNS elicit and which receptors are typically involved?
increase blood flow to active muscles (beta receptors) and a decreased flow to the GI system, kidney and skin (alpha receptors)
where is the ANS activated?
hypothalamus, brain stem and spinal cord
what axis is activated in the acute stress response?
the hypothalamic-pituitary-adrenocortical axis
what contributes to the difference in different target organs within the SNS?
the adrenal medullary contribution- only time when epinephrine is secreted in the SNS activation and it preferentially activates beta adrenergic receptors
which parts of the body are alpha and beta receptors predominant?
alpha-vasculature
beta- heart lungs and liver
what is a pheochromocytoma and what does it secrete?
neoplasm of the adrenal medulla that secretes excessive amounts of norepinephrine (most common), epinephrine or both
causes hypertension and other effects
what percentage of hypersensitive patients have pheochromocytomas? when are they most common?
less than 0.1%
most common during 30s and 40s
describe a pheochromocytoma and its treatment.
well circumscribed tumor 1g-several kg
excise tumor and treat the symptoms with alpha1 and beta1 adrenergic antagonists
what is horner’s syndrome and what does it cause?
injuries to the SNS causing partial constriction of the pupil (miosis), drooping eyelid (ptosis) and dryness of the face (anhydrosis)
what are the orders of lesions that cause horner’s syndrome?
1st order: brain stem lesion (ie stroke)
2nd order: preganglionic cell bodies or fiber lesion
3rd order: postganglionic cell bodies or fiber lesions
describe the anatomy of innervation to the pupil that is interrupted in horner’s syndrome.
1) hypothalmus to intermediolateral column in the spine 2) preganglionic sympathetic neuron with cell body in intermediolateral colum synapses with 1 and sends axon to superior cervical ganglion 3) postganglionic sympathetic neuron with cell body in SCG sends axons to pupillary dilator muscles
where do the cell bodies of presynaptic sympathetic nerves lie? where do their axons go?
in the lateral horn of the spinal column between T1 and L3.
axons go through white ramus to paravertebral ganglion, down the chain to another paravertebral ganglion or to a prevertebral ganglion
where does the prevertebral plexus lie and what are its components?
lies in front of the aorta and along its branches.
celiac-innervates stomach, liver, pancreas, gallbladder, SI, spleen and kidney
superior mesenteric- SI and colon
inferior mesenteric- lower colon, rectum, bladder and reproductive organs
how can the broadness of the PNS be compared to the SNS?
PNS is more discrete than SNS
what effect does the PNS have on the eye and through what nerve?
pupillary constriction (miosis) cranial nerve III
what effect does the PNS have on glandular secretions? what nerves are involved?
causes copious secretion of nasal, lacrimal and submandibular( Cr VII), parotid (Cr IX), gastric and pancreatic (Cr X)
what effects does the PNS have on peristalsis, bronchi and heart rate? what nerve is this mediated by?
increased motility and sphincter relaxation, bronchial constriction and decreased heart rate
(Cr X)
where do the PNS nerves that innervate the pelvis originate? what do they do?
S2-4
relax ureter and sphincter and contract detrusor muscle to urinate, empty rectum and facilitate erection
where is the origin of the preganglionic fibers of the PNS?
cranial nerves originatte in brain stem and travel through Cr III (oculomotor), VII (facial),IX (glossopharyngial) and X (vagus)
S2-4
how much of the PNS is controlled by the vagus?
75%
what is the path of Cr III?
Edinger-Westphal nucleus- Cr III->cilliary ganglia
what is the path of Cr VII?
superior salvatory nucleus- CrVII->pterygopalatine and submandibular ganglia
what is the path of Cr IX?
inferior salivatory nucleus- Cr IX-> otic ganglion
what is the path of CrX?
dorsal motor nucleus and the nucleus ambiguus- Cr X->terminal ganglia in the viscera of the thorax and abdomen
how do the SNS and PNS interact?
sometimes they exert opposing actions but other times they act in a complimentary manner (sex)
what body system has more neurons than the spinal cord?
GI system
what are the two main plexuses of the gut and what do they control?
myenteric (controls motility) and submucosal (controls secretions) plexuses
how is the gut activated to digest food?
mechanoreceptors and chemoreceptors are activated by food and activate the PNS and inhibit the SNS
what happens if you cut the PNS fibers that innervate the gut?
decrease in GI muscle and sphincter tone
where do postganglionic parasympathetic neurons primarily reside? where is innervation particularly extensive?
the myenteric and submucosal plexuses
in the mouth and anus
what is released from parasympathetic nerve terminals and what effect does it have in the myenteric plexus?
ACh is released and depolarizes post synaptic cells to initiate action potential and contract the smooth muscle of the gut
what effect does norepinephine have on the myenteric plexus?
hyperpolarizes and relaxse muscle while ausing sphincter contraction
can cause blockage of food movement
what effect does the SNS have on the bladder? what receptors does it use?
relaxes the detrusor muscle (beta2 adrenergic receptor) and contracts the internal sphincter (alpha 1 adrenergic receptor)
what effect does the PNS have on the bladder?
constricts the detrusor muscle and releases the internal sphincter (muscarinic receptors)
what other areas of the nervous system control autonomic functions?
hypothalamus, midbrain, pons, medulla and brain stem
what is the function of the brain stem autonomic centers?
to relay control initiated at higher levels in the brain
is regulation of respiration an ANS function?
no it is not but it is involuntary
what do descending cortical pathways regulate? where do they connect?
fear, panic stress ect.
connect to the spinal cord or indirectly through the hypothalamus
what are the three pathways of vasovagal syncope and what is it?
emotional fainting- thoughts in the cortex lead to activation of vasodilation in the hypothalamus, through SNS vasodilator nerves of the muscles and to the heart through the vagus. this rapidly slows the heart
what is the primary cause of vasovagal syncope?
rapid increase of blood flow to the muscles and resultant fall in arterial pressure reduces blood flow to the brain
how does nervousness cause diarrhea?
upsetting the balance between SNS and PNS activation with an insufficient transit time for the gut to reabsorb water
in what 8 situations do visceral afferents overwhelm cortical function?
huger, nausea, dyspnea, visceral pain, bladder and bowel distention, hypothermia and hyperthermia
