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Baroreceptor reflex
- the most important feedback loop of the autonomic system
- regulates the blood pressure
- found in carotid and aortic arch
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autonomic tone
- day to day influence exerted by the autonomic nervous system
- provides basal level contol over which reflex regulation is superimposed
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basal level
- the division of the nervous system that takes predominance in an organ when the organ is innervated by both the sympathetic and parasympathetic system
- most organs have the parasympathetic system as basal level/tone (EXCEPT the vascular system which is only innervated by sympathetic nervous system)
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2 sites that drugs work on in parasympathetic nervous system
- synapses between preganglionic and postganglionic neurons
- junctions between postganglionic and their effector organs
- ex:
- CNS-------->ganglion--------->organ
CNS--------->ganglion---------- >organ
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adrenal medulla
influences the body by releasing epinephrine into the bloodstream
similar in function to a postganglionic neuron; ex: CNS~~~~~>A. medulla=====>organs
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2 sites where drugs affect sympathetic nervous system
- synapses between preganclionic and postgonglianic nerons, including the adrenal medulla
- junctions between postganglionic neurons and their effector organs
see fig. 13-3 on pg 109
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3 neurotransmitters of the parasympathetic nervous system
- acetylcholine, epinephrine, norepinephrine
- any given junction in pns uses ONLY ONE neurotransmitter
note: dopamine can be put in this group although its role is not consistent
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acetylcholine
neurotransmitter used in most junctions of the pns
-
acetylcholine is neurotransmitter released by:
- preganglionic neurons of para.nerv. sx. and symp. nerv. sx.
- all postganglionic neurons
- all motor neurons to skeletal muscles
- most postganglionic neurons of symp. nerv. sx. that go to sweat glands
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norepinephrine
neurotransmitter released by most all postganglionic neurons of symp. nerv. sx.
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epinephrine
major neurotransmitter released by adrenal medulla
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2 receptor types of peripheral nerv. sx.:
cholinergic and adrenergic recepters
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cholinergic receptors respond to what?
mediate responses to acetylcholine
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adrenergic receptors respond to what?
epinephrine and norepinephrine
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what are the 3 receptor subtypes for cholinergic receptors?
nicotinic N, nicotinic M, muscarinic
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what are the 4 major subtypes of adrenergic receptors?
alpha 1, alpha 2, beta 1, beta 2
*dopamine is also classified adrenergic but dopamine receptors do NOT respond to epi or norepi- ONLY to dopamine
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where is dopamine found primarily?
CNS
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what does receptor subtypes mean?
it means that even though there could be receptors that respond to the same transmitter doesn't mean that they will indeed react to that transmitter.
ex: peripheral receptors that respond to acetylcholine can be found in differnt places but even though they belong to the cholinergic family they are slightly different and require a subtype. pg. 110
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muscarinic agonists
cholinergic receptor subtype
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bethanecol is used to treat:
urinary retention
-
mechanism of action for bethanicol (urinary retention trx)
binds reversibly to muscarinic cholinergic receptors causes activation
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bethanicol adverse effects
cardiovascular system hypotension----> smooth muscle relaxation, decrease heart rate
alimentary system----> diarrhea, abdominal cramps
urinary tract----->contraction may cause bladder rupture
exacerbation of asthma-----> bronchoconstriciton
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muscarinic distribution are in:
heart, bladder, lungs
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atropine mechanism of action
blocks muscarinic receptors
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atropine pharmacologic effects
- heart increases rate
- exocrine glands-decreases secretions
- smooth muscle bronchial relaxation
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atropine therapeutic use:
- ocular surgery
- bradycardia- stimulates rate
- muscarinic agonist poisoning
- prevention of secretions
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atropine adverse effects:
- xerostomia (dry mouth)
- blurred vision and photophobia
- elevation of intraocular pressure
- urinary retention
- constipation
- anhidrosis--->absence of sweat
- tachycardia
- asthma
-
atropine drug interactions:
avoid comining atropine with other drugs capable of causing muscarinic blockade
-
atropine preparations/administration:
- atropine for cholinesterase inhibitor poisoning (insecticides)
- reversal of bradychardia (IV administration)
- opthalmology (eye drops to open pupil)
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cholinergic effects:
- increase secretions
- increase urine output
- diahrrea
-
muscarinic antagonists (anticholinergic drugs)
- ipatropium bromide- decrease asthma secretions
- antisecretory anticholinergics- Hyoscyamine---> death rattle "lots of mucus secretions"
- Dicyclomine- GI antidiahrreal
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receptor substype Nicotinic N:
- located in autonomic system
- stimulation of parasympathetic and sympathetic nerves and release of epi from adrenal medulla
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Nicotinic N:
- located in neuromuscular junction
- response to activation is contraction of skeletal muscle
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Muscarinic receptors: (feed/breed actions)
- parasympathetic target organs:
- eye-contract ciliary muscle focuses lens for near vision, contraction of iris
- heart- decrease heart rate
- lung- constriction of bronchi
- bladder- increase bladder pressure and decrease bladder sphincter= voiding/peeing
- GI tract- salivation, increase gastric secretions, increase intestinal tone, defecation
- sweat glands- generalized sweating
- sex organs- erection
- clood vessels- vasodilation
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alpha 1:
- eye- increase pupil size
- arterioles- constriction
- veins-constriction
- sex organs (male)-ejaculation
- prostate capsule- contraction
- bladder- contraction of sphincter (to pee)
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beta 1:
- heart- increased rate, increase force of contraction, increase AV conduction
- kidney- renin release (blood pressure)
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beta 2:
- arterioles, lung, heart, skeletal muscle- dilation
- bronchi- dilation
- uterus- relaxation
- liver- glycogenolysis
- skeletal muscle- enahnced contraction, glycogenolysis
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dopamine:
kidney- dilation of kidney vascular
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neurotransmission at cholinergic junctions is terminated by:
breakdown of acetylcholine by acetylcholinesterase
-
neurotransmission at adrenergic junctions is terminated by:
reuptake of intact norepi into nerve terminals
-
following reuptake norepi can be:
stored in vesicles for reuse or destroyed by monoamine oxidase (MAOI)
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