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49 Cards in this Set
- Front
- Back
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draw a classification of nervous systems including CNS and PNS |
check on note |
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what does Somatic Nervous System control? |
It innervates the voluntary movements of skeletal muscle, posture and breathing |
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What does ANS control? |
It innervates involuntary movements of all structures of the body except skeletal muscles (such as heart, blood vessels, glands, visceral organs and smooth muscle) for the maintenance of homeostasis |
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what is the major anatomical difference between the ANS and Sometic NS? |
Somatic: a single efferent nerve fiber connects the CNS to the skeletal muscle fiber Motor nerves are myelinated ANS: the efferent nerve pathway consists of two sets; preganglionic and postganglionic fibers Preganglionic - myelinated postganglionic- generally not. |
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what is the type of nerves of preganglionic sympathetic and parasympathetic fibers ? |
Cholinergic (release ACh) |
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Which types of fibers are cholinergic as postganglionic ? |
All postganglionic parasympathetic fibers Sweat and piloerector muscles in the skin; postganlionic sympathetic fibers |
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what is piloerector? |
muscle causing erection of hair (goose pimples) |
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the majority of postganglionic sympathetic fibers release...? |
they release noradrenaline onto adorenoreceptors (either α or β). |
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where do sympathetic preganglionic fibers arise from? |
sympathetic preganglionic fibers arise from the lateral horn of the thoracic and upper lumbar regions of the spinal cord these fibers are short, lying either side of the spinal cord, ganglionic nicotinic receptor sites |
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where do parasympathetic preganglionic fibers arise from? |
parasympathetic preganglionic fibers arise from cells in the midbrain/ medulla or in the sacral region of the spinal cord these fibers are long; they emerge in |
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How does the system of adrenal medulla work? |
Adrenal medulla is part of the sympathetic activities secreting catecholamines. It receives ACh directly (without ganlia) from the spinal cord |
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what are the ratio of pre/post ganglionic nerves in parasympathetic and sympathetic? |
Parasympathetic: pre/pose = 1:2 as distribution is much limited and usually subserves discrete local conditions Sympathetic: pre/ post = 1:20 or more, enabling more diffuse and fast actions |
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The activities of sympathetic and parasympathetic are usually opposed. What are the exceptions? |
Salivary glands; both system increase secretion Sweat glands; by sympathetic Ciliary muscle of the eye; mainly parasympathetic Lacrimal glands; parasympathetic adrenal medulla; sympathetic |
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Automic innervation of the iris muscle of the eye What are the two muscles involved in the control of the pupil diameter? |
pupillary constrictor muscle fibers pupillary dilator muscle |
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How does ANS control these muscles? |
pupillary constrictor muscle fibers; only receive parasympathetic from the oculomotor nerve, to cause pupillary constriction and a reduction in pupil diameter pupillary dilator muscle consists of radial fibers controlled by the sympathetic from the superior cervical ganglion, to cause radial fiber contraction and increase in pupil diameter |
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Autonomic innervation of the ciliary muscle of the eye what is ciliary body? what does ciliary body consist of? |
The ciliary body is a separate circular shaped structure in the eye, which is nothing to do withthe iris and pupil diameter!! It consists of ciliary muscle fibres, responsible for controllingthe shape of the lens of the eye. T |
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How does ANS control ciliary muscle fibers? what is this process called? |
This process is called accommodation The ciliary muscles receive parasympathetic, they contract. The zonule fibers relax, the tension on the lens is released and the lense becomes fatter, allowing to focus for near vision. The ciliary muscles receive sympathetic, they relax. It tightens the zonule fibers, making the lens flatter for long range focus. |
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Sympathetic Nervous System: Adorenoreceptors what tissues have alpha receptors? |
- Blood vessels in skin and abdominal viscera - Radial muscle of iris - Gut sphincters - Smooth muscle of gut wall - Salivary glands - Sex organs |
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what are subtypes of alpha receptors for each tissue? Muscle contraction or relaxation? |
- Blood vessels in skin and abdominal viscera;
alpha 1, constriction - Radial muscle of iris; alpha 1, contraction - Gut sphincters; alpha 1, contraction - Smooth muscle of gut wall; alpha 1&2, relaxation - Salivary glands; alpha 1, thick viscous saliva - Sex organs; alpha 1, ejaculation |
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Sympathetic, adrenoreceptors what are the tissues with beta-receptors? |
- Heart - Smooth muscle of the gut wall - Blood vessels in skeletal muscle - Smooth muscle of bronchioles and trachea - Salivary glands - Fat cells |
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what are the subtypes of beta receptors for each tissue? muscle reactions? |
- Heart; beta 1, increase in heart rate and contraction
- Smooth muscle of the gut wall; beta 1&2, decrease motility and tone - Blood vessels in skeletal muscle; beta 2, dilation but no direct innervation - Smooth muscle of bronchioles and trachea; beta2, relaxation but no direct innervation - Salivary glands; beta 1, thick viscous saliva - Fat cells; beta 3, lipolysis |
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what are the agonists of alpha receptors? selectivity? |
Noradrenaline (alpha 1&2) Adrenaline (alpha 1&2) Methoxamine (alpha 1&2) Phenylephrine (alpha 1) Clonidine (alpha 2, partial agonist) |
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what are the antagonists of alpha receptors? selectivity? |
Phentolamine (alpha 1&2) Phenoxybenzamine (alpha 1&2) Prazosin (alpha 1) Yohimbine (alpha 2) |
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what are the agonists of beta receptors? selectivity? |
Isoprenaline (beta 1&2) Salbutamol (beta 2) Salmeterol (beta 2) Dobutamine (beta 1) |
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what are the antagonists of beta receptors? selectivity? |
Propranolol (beta 1&2) Atenolol (beta 1) Butoxamine (beta 2) Labetalol (mixed antagonist for both alpha and beta) |
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what are the two main neurotransmitters operating in the ANS? |
ACh, acetylcholine and NA, noradrenaline |
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How does cholinergic nerve terminals synthesize ACh? |
- the acetylation of choline - choline can be normal dietary constituent, or synthesized naturally from the amino acid serine. - the acetyl group is provided by Acetyl-CoA - the conjugation is catalysed by choline acetyltransferase present within the neuronal cytoplasm |
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How is ACh stored? |
ACh is stored in synaptic vesicles, and synchronously discharged from these vesicles on arrivalof a nerve impulse at the terminal |
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what is the drug blocking the vesicular ACh transporter? |
Vesamicol |
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How is destruction of ACh release is accomplished? |
Destruction of the ACh released is accomplished by acetylcholinesterase (AChE) - whichhydrolyses ACh to choline and acetate [within milliseconds at skeletal NMJ]. AChE ispresent at the surface of postjunctional membranes [and also nerve terminal membranes]. Thefree choline is largely retaken up into the cholinergic nerve terminal by a special cholinetransport system
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what drugs block the destruction of ACh? |
hemicholinium |
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How is NA synthesized? |
NA from the amino acid precursor L-tyrosine, which isactively transported into the nerve ending. Within the cytosol, tyrosine hydroxylase catalysesconversion of tyrosine to DOPA (dihydroxyphenylanaline); DOPA is then converted todopamine by DOPA decarboxylase (also within the cytosol). The final conversion ofdopamine to noradrenaline occurs within noradrenergic vesicles/storage granules via theenzyme dopamine-β-hydroxylase [also released along with NA!]. This form of the transmitteris in equilibrium with NA outside the storage granules - the cytoplasmic pool
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How is NA removed from synapses? |
NA can be taken up within the granules by an active carrier system |
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What drug blocks the re-uptake of NA? |
reserpine |
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How is NA broken down? |
The cytoplasmic pool of NA is susceptible to breakdown by the mitochondrial enzymemonoamine oxidase (MAO), whereas released NA is metabolised (methylated) by the enzymecatechol-O-methyl-transferase (COMT) present in the liver.
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what is the main mechanism of removal of NA from its receptor sites? |
, the main mechanism responsible for the removal of NA from its receptor sites is theactive reuptake by sympathetic nerve terminals (U1: high affinity carrier) and also bynon-neural tissues such as smooth muscle, cardiac muscle, endothelium (U2: low affinitycarrier; the latter mechanism is more important for clearing adrenaline from the bloodstream).
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How is the release of NA regulated? |
Noradrenaline can regulate its own release by acting on presynaptic α-adrenoreceptors presenton the noradrenergic terminals. This inhibitory feedback mechanism operates via α2-receptors
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what drug selectively activate the release of NA? |
clonidine, used as antihypertensive |
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what are the drugs affecting cholinergic neurotransmission? |
anticholinesterases, ganglion blockingagents and muscarinic agonists/antagonists
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what are the drugs affecting sympathetic neurotransmission? |
Methyldopa Guanethidine Indirectly acting sympathomimetic amines Noradrenaline uptake inhibitors cocaine MAOIs |
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What is Methyldopa? mechanism of action? |
Used as treatment of hypertension: Methyldopa is taken up bynoradrenergic nerve endings, and competes with DOPA in the NA synthetic pathway, to form a'false' transmitter α-methyl-noradrenaline, which is somewhat less active than NA on α1receptors, therefore less effective in causing vasoconstriction. It is also more active than NAon presynaptic α2 receptors, therefore reduces transmitter release below normal. A central α2stimulant effect of α-methyl-noradrenaline is also believed to contribute to the hypotensiveaction. |
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what is Guanethidine? mechanism of action? |
Adrenergic neurone blocker to prevent release of NA from sympathetic nerve terminals. It is first accumulated by noradrenergic nerve terminals bymeans of uptake 1, then gets stored in synaptic vesicles and ultimately inhibits NA release.Although guanethidine is a powerful antihypertensive agent, it is not often used clinically dueto severe side effects associated with the loss of sympathetic reflexes - postural hypotension,diarrhoea, nasal congestion and failure of ejaculation. |
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what are indirectly acting sympathomimetic amines? |
tyramine, ephedrine and emphetamine |
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what is the mechanism of sympathomimetic amines? |
They promote therapid release of NA from sympathetic nerve terminals [not theadrenal medulla] thereby producing an indirect sympathomimetic effect. Like guanethidine,they are transported into the nerve terminal via uptake 1, but once inside, they displace NAfrom the vesicles, which then leaks out to act on postsynaptic receptors. Eventually, theydeplete the releasable store of NA. They have no effective (legal!) clinical uses, althoughephedrine can be used as a nasal decongestant. |
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what is noradrenaline uptake inhibitors? mechanism of action? |
many drugs can inhibit the noradrenaline U1 uptakeprocess and thereby enhance the effects of sympathetic nerve activity. The main class ofdrugs with this property are the so-called tricyclic antidepressants - imipramine, desipramine- which have their major effects in the CNS.
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what is cocaine? |
local anaesthetic also has this unusual further property of inhibitingnoradrenaline uptake, but note: other local anaesthetics do not have this effect! The centralpsychoactive actions of cocaine are due to its ability to inhibit the reuptake of released |
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what are the examples of MAOIs? |
tranylcypromine andphenelzine (used as antidepressants) |
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what is the mechanism of MAOIs? |
They irreversibly inhibit the intracellular (cytosolic)breakdown of free NA by MAO [both MAO-A and MAO-B isoforms selegiline that is used in the treatment of early-stage Parkinson’s disease |
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what is the interaction with MAOIs? |
MAO inhibition with these early MAOIdrugs does, however, enhance the effects of the indirectly acting sympathomimetic amines e.g.amphetamine or tyramine (normally a substrate for MAO). Thus, ingestion of tyramine-richfoods such as cheese, Bovril, OXO, wines or broad beans, could induce a sudden anddangerous rise in blood pressure.
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