Autonomic Nervous System I Flashcards
1
Q
Autonomic nervous system
A
- has 2 primary divisions
- the sympathetic nervous system (thoracolumbar division) and the parasympathetic nervous system (craniosacral division)
- a 3rd division, the enteric nervous system is sometimes included
- the SNS and PNS innervate smooth and cardiac muscle, secretory epithelial, and glands
- as such they contribute to regulation of arterial pressure, gastrointestinal motility and secretions, urinary bladder emptying, sweating, body temperature, and other processes
- SNS- fight or flight, PNS mediates vegetative responses involved in resting and digesting
- survival is possible without ANS, but physiological function is severely compromised
2
Q
Sympathetic nervous activation
A
- stimulation of heart rate at the SA node (positive chronotropic effect)
- stimulation of AV nodal conduction (positive dromotropic effect)
- stimulation of myocardial contractility (positive inotropic effects)
- via activation of B1-adrenergic receptors
- B1-adrenergic receptor antagonists such as propranolol are used to treat hypertension and tachycardias
3
Q
Parasympathetic nervous system activation
A
- inhibition of heart rate at the SA node (negative chronotropic effect)
- inhibition of AV nodal conduction (negative dromochronotropic effect)
- inhibition of artrial contractlity- mild
- the PNS does not significantly innervate other regions of the heart and thus does not exert major effects on the heart muscle itself
- strong vagal stimulation decreases contractility of the atria (negative inotropic effect)
4
Q
Pharmacological agonists and antagonists
A
- used as receptor specific activators or inhibitors
- agonist - activator; antagonist = inhibitor
- muscarine = exogenous agonist of muscarinic chlinergic receptors
- atropine is an exogenous antagonist of these receptors
5
Q
2 synapse pathway
A
- cell bodies of preganglionic neurons lie in CNS in columns in brain stem and spinal cord, their axons exit CNS and synapse with postganglionic neurons in peripherial ganglia
- sympathetic pre- short, post- long
- parasympathetic pre- long, post- short (lie within or close to target tissue)
- pre- axons- small diameter, slow, myelinated B fibers; post- axons- small diameter, slower, unmyelinated C- fibers
6
Q
Divergence
A
- average preganglionic axon in the SNS contacts and estimated 100 postganglionic neurons by collateral branching, thus contributing to a diffuse output pattern
- property of divergence enables the SNS to generate widespread responses of numerous effectors when physiologically necessary
- PNS: more discrete, one pre- synapses with 15-20 posts
7
Q
En passant synapses
A
- varicosites
- characteristic of the ANS and permit a single axon to have broad actions in target tissues
8
Q
Target transmitters of the ANS
A
- somatic neurons- the pathway between the CNS and effector cell is monosynapic
- neuron releases ACh binds to N1 nicotinic cholinergic receptos on the post synaptic membrane of the skeletal muscle cell (N1 receptor antagonist = d-tubocurarine; nicotinic receptor agonist= nicotine)
- for both Sym and Para pre release ACh- binds N2 nicotonic cholinergic receptors on postsynaptic membrane
- para post is ACh- muscarinic cholinergic receptor; sym post is norepinephrine adrenergic receptor either alpha or beta
9
Q
Chromaffin cells
A
- the SNS directly innervates the chromaffin cells of adrenal medulla which releases primarily epinephrine (~80%) and some norepinephrine
- hormones are carried by blood and broadly effect multiple tissues of the body
- the effects are similar to direct sympathetic stimulation, but last 5-10 times longer because the hormones are inactivated more slowly
- they reach tissues that do not receive sympathetic innervation (epi increases metabolic rate in almost all cell types
- the adrenal medulla secretes enough epi (+ norepi) to maintain a near normal blood pressure if sympathetic innervation to the heart is interrupted
- there can also be co-transmitters in their presynaptic terminals (ATP, neuropeptide Y)
10
Q
SNS target tissues
A
- express distinct adrenergic receptor subtypes with different affinities for epi and norepi
- sometimes use muscarinic cholinergic receptors (eccrine sweat glands), even though usually cholinergic receptors
- broadly activated by epi-norepi from the adrenal medulla
11
Q
PNS target tissues
A
-express various combinations of 5 muscarinic cholinergic receptors (M1-M5)
12
Q
Mechanism of action of alpha-1 adrenoreceptors
A
- in the inactive state, the alpha q subunit of the Gq protein is bound to GDP
- in the active state with norepinephine bound to the alpha 1 receptor, the alpha q subunit is bound to GTP
- phospholipase C work with the G protein mechanism
13
Q
Mechanism of action if Beta adrenoreceptors
A
- in the inactive sate, the alpha subunit of the Gs protein is bound to GDP
- in the active state, with norepinephrine bound to the B receptor, the alpha subunit is bound to GTP
- B1 and 2 have the same mechanisms
- the alpha part does in the adenylyl cyclase and ATP to cAMP to physiologic actions
14
Q
Mechnism of action of nicotinic cholinergic receptors
A
- exert their action through GPCRs
- PLC leading to generation of IP3 and DAG (M1, M3, M5; like alpha1-adrenergic receptors)
- inhibition of adenylate cyclase leading to decreased intracellular cAMP (M2, M4)
- nicotinic cholinoreceptors for acetylcholine
15
Q
Cholinergic and adrenergic receptors and properties
A
- N1 nicotinic ACh, ACh agonist, d-Tubocurarine antagonist
- N2 nicotinic ACh, ACh agnoist, Hexa-methonium antagonist
- M1, M3, M 5 muscarinic ACh, ACh agonist, Atropine antagonist, Galpha, PLC pinked enzyme, IP3 and DAG second messenger
- M2, M4 muscarinic ACh, Ach agnoist, Atropine antagonist, Galphai and Galpha0, adenylyl cyclase enzyme, decrease cAMP second messenger
- Beta 1 adrenergic, Epi (more than NE), propranolol/metoprolol antagonists, Galphas, adenylyl, increase cAMP
16
Q
effects of the ANS on organ system function
A
- in many cases the SNS and PNS exert opposing actions (HR is increased by SNS and decreased by the PNS, and GI motility is increased by PNS and decreased by SNS)
- in some cases they act in a complimentary manner- PNS activation causes penile erection and SNS activation causes ejaculation both aiding in male reproductive frunction
17
Q
Massive SNS discharge
A
- increase mydriasis and eyelid retraction (alpha 1)
- increase heart rate and force of contraction (beta 1)
- increase bronchial dilation (beta 2)
- increase vasoconstriction (alpha 1)
- increase sweating (muscarinic)
- increase cellular metabolism: epi from adrenal medulla (alpha and beta)
- increase blood flow to active muscles (vasodilation via B-adrenergic receptors of skeletal and coronary muscles contributes but local factors such as adenosine cause most of the vasodilation and decreased flow to GI system, kidney and skin
- activated primarily by centers in the hypothalamus, brain stem,and spinal cord and can respond rapidly-eg heat rate can double, and the urinary bladder can empty involuntarily in a matter of seconds
18
Q
Epinephrine has greater affinity for B adrenergic receptor
A
- epinephrine has a greater affinity than norepinephrine for B-adrenergic receptors, whereas norepi has somewhat greater affinity for alpha adrenergic receptors
- the adrenal meduallary contribution of the SNS reflects this difference in different target organs
- epi effects are more prominant in targets where B adrenergic receptors predominate, such as the heart, lungs, and liver, whereas norepi effects predominate in the vasculature where alpha adrenergic receptors are expressed
19
Q
Adrenal meduula
A
- releases epinephrine and norepinephrine into the bloodstream during activation of the sympathetic nervous system
- the effects of epinephrine and norepinephrine, including relative magnitude are illustrated for lots of places
20
Q
Pheochromocytoma
A
- tumor of the adrenal medulla
- secrete excessive amounts of norepinephrine (most common) epinephrine or both resulting in sustained hypertension and other effects (cold hands and feet, sweating and feeling hot)
- increased dopamine secretion rare
- less than 0.1% hypertension
- observed at all ages, male and female, especially in 40s and 50s
- tumors are well-circumscribed with weights ranging from 1 gram to several kilograms
- treatment- excise the tumor. To treat the symptoms, a combination of alpha1 and B1-adrenergic antagonists can be used
21
Q
Horner syndrome
A
- anhidrosis, (dryness of face)
- ptosis (dropping eye)
- miosis (constriction of eye)
1st order lesion- brainstem lesions interrupting descending tracts (stoke)
2nd order lesion- preganglionic sympathetic cell bodies or fibers supplying eye synapse in superior cervical ganglion
-3rd order lesion- postganglionic sympathetic cell bodies or fibers
22
Q
Anatomy of sympathetic division
A
Cell bodies of the sympathetic motor neurons lie in the intermediolateral cell column (lateral horn) between thoracic level T1 and lumbar level L3
- their axons enter the nearest paravertebral ganglion via a white ramus and synapse within that segment or travel to another para- or to a prevertebral ganglion
- the sympathetic chains extend from the upper part of the neck to the coccyx, and they are bilateral
23
Q
Anatomy of the sympathetic prevertebral plexus
A
- major prevertebral plexus are the celiac, superior mesenteric and inferior mesenteric
- the prevertebral plexus is bilateral and lies in front of the aorta and along its major arterial branches
- the ganglia and each associated plexus are named after the artery with which they are associated
- celiac- stomach, liver, pancreases, gallbladder, small intestine, spleen, kidneys
- superior mesenteric- innervating the small and large intestines
- inferior mesenteric- innervating the lower colon and rectum, urinary bladder, reproduction organ
