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94 Cards in this Set
- Front
- Back
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retrograde transmission
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signal from postsynaptic cell to presynaptic neuron terminal
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sympathetic preganglionic fibers leave the CNS through
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thoracic and lumbar spinal nerves
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parasympathetic preganglionic fibers leave the CNS through
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cranial nerves (3, 7, 9, 10) and 3rd and 4th sacral spinal roots
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where do preganglionic sympathetic fibers terminate
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most short and terminate in paravertebral chains on either side of vertebral column; remaining linger and terminate in prevertebral ganglia in front of vertebrae
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where do postganglionic sympathetic fibers go from ganglia
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to tissues innervated
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ganglia associated with parasympathetic fibers
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ciliary, pterygopalatine, submandibular, otic, and several pelvic ganglion
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where do the majority of parasympathetic preganglionic fibers go
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ganglion cells distributed diffusely or in networks in walls of innervated organs
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what is meant by the terms synpathetic and parasympathetic
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anatomical designations-do not depend on type of transmitter chemical released nor on kind of effect evoked by nerve activity
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where do many sensory pathways that end in CNS terminate
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integrating centers of hypothalamus and medulla
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enteric nervous system (ENS)
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large, highly organized collection of neurons located in the walls of the GI system (from esophagus to distal colon)
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plexuses in ENS
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myenteric (Auerbach) and submucous (meissner)
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where do plexuses of ENS receive preganglionic fibers from
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parasympathetic system and postganglionic sympathetic axons; sensory fibers from gut
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what role do sympathetic and parasympathetic fibers play in the ENS
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modulatory role; deprivation does not abolish GI activity
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neuron-neuron and neuromeuscular jxns can be described as
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relatively tight; effects rapid and localized
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jxns btwn autonomic neuron terminals and effector cells
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transmitter released fromchain of varicosities in postganglionic nerve fiber in regionof smooth muscle cells; effects slower and often involve many effector cells
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jxn clefts in somatic vs autonomic
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autonomic wider, somatic has boutons
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cholinergic fibers release
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acetylcholine
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what fibers are cholinergic
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all preganglionic efferent autonomic fibers and somatic motor fibers to skeletal muscle (almost all efferent fibers leaving CNS); parasympathtic preganglionic and a few postganglionic
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noradrenergic
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release norepinephrine; aka adrenergic fibers; used by most postganglionic sympathetic fibers
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what are adrenal medullary cells embryologically analogous to
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postganglionic sympathetic neurons
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cotransmitter substance
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released by most autonomic nerves in addition to their primary transmitter
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what are potential targets in neurotransmitter fxn for drugs
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synthesis, storage, release, termination of action, receptor effects
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what do the small number of large dense-cored vesicles located farther from the synaptic membrane contain
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high concentration of peptide cotransmitters
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what do the large number of smaller clear vesicles contain
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primary neurotransmitter (like acetylcholine)
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where are vesicles synthesized
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in soma and transported to terminal by axonal transport
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vesicle-associated membrane proteins
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serve to align vesicles to release sites on inner neuronal cell membrane and paticipate in triggering release of transmitter
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syaptosomal nerve-associated proteins (SNAPs)
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contained in corresponding release site on inner surface of nerve terminal membrane
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what is acetylcholine synthesized from
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acetyl-CoA and choline
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what enzyme catalyzes formation of acetylcholine
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choline acetyltransferase (ChAT)
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where is acetylcholine synthesized
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in mitochondria
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choline transported (CHT)
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transports choline from ECF into neuron terminal; sodium-dependent membrane
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what drugs can block the symporter CHT
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hemicholiniums
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how is acetylcholine transported from cytoplasm into vesicles
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vesicle-associated transporter (VAT); driven by proton efflux
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what drug can block the antiporter VAT
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vesamicol
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how many molecules of acetylcholine per vesicle
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1000 to 50000
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how are vesciles concentrated on inner surface of nerve terminal
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interaction of SNARE proteins on the vesicle and inside of terminal cell membrane (SNAPs)
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what is release of transmitter dependant on
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extracellular calcium
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how does Ca2+ trigger release
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interacts with VAMP synaptotagmin on vesicle membrane and triggers fusion
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One depolarization can release how many quanta onto the synaptic cleft
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several hundred
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what is acetylcholine vesicle release process blocked by
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botulinum toxin through enzymatic removal of 2 aas from one or more of the fusion proteins
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acetylcholinesterase (AChE)
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efficiently splits acetylcholine into choline and acetate
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adrenergic neuron neurotransporter synthesis
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transport precursor tyrosine into nerve ending which is then synthesized into the catecholamine transmitter and then stored in vesicles
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rate limiting step in catecholamine transmitter synthesis
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conversion of tyrosine to dopa
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what can the rate limiting step be inhibited by
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tyrosine analog metyrosine
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vesicular monoamine transported (VMAT)
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high-affinity antiporter for catecholamines located in the wall of storage vesicles
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what can inhibit VMAT
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reserpine alkaloids; causes depletion of transmitter stores
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norepinephrine transporter (NET)
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carrier norepinephrine and similar molecules back into cell cytoplasm from synaptic cleft
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what is NET commonly called
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uptake 1 or reuptake 1
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what can NET be inhibited by
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cocaine and tricyclic antidepressants; result in increased transmitter activity in synaptic cleft
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cotransmitter substances released with norepinephrine
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ATP, dopamine-B-hydroxylase, peptide cotransmitters
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what indirectly acting and mixed sympathomumetics are capable of releasing stored transmitter from noradrenergic nerve endings by a calcium-independent process
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tyramine, amphetamines, ephedrine
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How do tyramine, amphetamines, ephedrine cause their effect Step 1
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excellent substrates for monoamine transporters and avidly taken up into noradrenergic nerve endings by NET
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How do tyramine, amphetamines, ephedrine cause their effect Step 2
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in the nerve ending they are transported by VMAT into vesicles displacing norepinephrine
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How do tyramine, amphetamines, ephedrine cause their effect Step 3
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norepinephrine is expelled into synaptic space by reverse transport via NET
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how can catecholamine turnover be estimated
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metabolic products excreted in urine
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primary mechanisms for termination of action of norepinephrine released from noradrenergic nerves
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1) simple diffusion with eventual metabolism in plasma or liver 2) reuptake into nerve terminal by NET (most common) or into perisynaptic glia or other cells
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SLC protein general transport mechanism
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use movement of Na+ down gradient as energy source
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what family is NET a member of
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SLC; as are the dopamine, glutamate, GABA, and serotonin transporters
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major inhibitory transmitter in CNS
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GABA
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major excitatory transmitter in CNS
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glutamate
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primary acetylcholine receptor subtypes
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muscarinic and nicotinic receptors
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adrenoceptor
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receptors that respond to catecholamines like norepinephrine
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cholinoceptor
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receptors that respond to acetylcholine
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adrenergic and cholinergic describe
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nerves that supply them
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capsaicin
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neurotoxin from chili peppers that can cause release of transmitter from neurons that do not have cholinergic or adrenergic receptors (NANC neurons)
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trophotropic
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rest and digest, in general parasympathetic
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ergotropic
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fight or flight, in general sympathetic
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sensory carotid sinus baroreceptor fibers in glossopharyngeal nerve
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major influence on sympathetic outflow from vasomotor center
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parasympathetic sensory fibers in wall of urinary bladder
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significantly influence inhibitory sympathetic inhibitory outflow
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primary controlled variable in cardiovascular fxn
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mean arterial P
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reflex to norepinephine infusion
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powerful increase in parasympathetic discharge at SA node
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what Is response to norepinephine infusion mediated by
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increased firing by baroreceptor nerves of carotid sinus and aortic arch
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a2 receptor located on noradrenergic nerve terminals presynaptic feedback inhibitory control mechanism
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activated by norepinephrine, activation diminishes further release; G-protein mediated
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What does the G-protein mediated effect do
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inhibition of inward calcium current that causes vesicular fusion and transmitter release
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autoreceptrs
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presynaptic receptors that respond to primary transmitter substance released; usually inhibitory
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heteroreceptors
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activated by substances released from other nerve terminals that synapse with the nerve ending
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example of heteroreceptor
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vagal fibers in myocardium synapse on sympathetic noradrenergic nerve terminals and inhibit norepineprine release
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extreme example of up-regulation
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denervation causes supersensitivity of tissue to activators of that receptor tyoe due to proliferation of receptors
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what is up regulated after denervation of skeletal muscle
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nicotinic cholinoceptors
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what occurs after prolonged administration of large doses of reserpine (norepinephrine depleter)
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increased sensitivity of smooth muscle and cardiac muscle effector cells due to depleted sympathetic fibers
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how are postganglionic cells activated
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bindng of appropriate ligand to neuronal nicotinic acetylcholine receptor
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hyperpolarization afterpotential
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slow inhibitory postsynaptic potential (IPSP); opening of K+ channels linked to M1 cholinoceptors
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selectivity of drugs that block action potential propagation
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very nonselective in action (act on process common to all neurons); local anestetics are an example
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parasympathetic nerve activity and muscarinic cholinomimetics mediate contraction of what in the eye
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circular pupillary constrictor muscle and ciliary muscle
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what causes miosis (reduction in pupil size)
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contraction of pupillary constriction muscle
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what is present in patients exposed to large systemic or small topical doses of cholinomimetics
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miosis
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example of cholinomimetic
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organophosphate cholinesterase inhibitors
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cyclospasm
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marked contraction of the ciliary muscle
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how can the effect of a cholinomimetic be reverse
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muscarinic blocking drugs like atropine
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how can cyclospasm be beneficial to glaucoma patients
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puts tension on trabecular meshwork, opening pores and facilitating outflow of aqueous humor into canal of schlemm…reducing intraocular P
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what regulates the contration of radially oriented pupillary dilator muscle
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alpha adrenoceptors
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mydriasis
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pupil dilation
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apla-agonist drug example
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phenylephrine
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what do beta-adrenoceptors on ciliarry epithelium facilitate
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secretion of aqueous humor
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