Autonomic Nervous System Flashcards
All pre-ganglionic neurons use what neurotransmitter?
cholinergic = ACh – binds post-ganglionic nAChR
What is the function of the autonomic nervous system?
controls all vegetative (involuntary) functions: heart rate, BP, GI motility, iris diameter.
separate from voluntary (somatic) motor system.
entirely efferent (conducting outwards or away from something), but is regulated by afferent inputs
Where do the sympathetic nerves originate from?
originate from lateral horn of thoracic and lumbar region
Which is fight or flight + rest and digest?
Fight or flight: sympathetic
Rest and digest: parasympathetic
What is the sympathetic nerve structure?
Short pre-ganglionic, long post-ganglionic - Ganglia are located in paravertebral chain close to spinal cord
Name the sympathetic receptors
Receptors –> a1, a2, b1, b2 (GCPRs)
Where do the parasympathetic nerves originate from?
originate from lateral horn of medullary and sacral region
What is the parasympathetic nerve structure?
Long pre-ganglionic, short post-ganglionic - Ganglia are located within innervated tissues
What is the parasympathetic post-ganglionic neurotransmitter?
Post-ganglionic = cholinergic: ACh - bind muscarinic receptors (GPCR, M1, M2, M3)
What is the sympathetic post-ganglionic neurotransmitter?
Post-ganglionic = noradrenergic NA - bind adrenergic receptors (GPCRs, A1, A2, B1, B2)
highly branching axonal network, numerous varicosities: specialized site for Ca2+-dependent noradrenaline release
Name the parasympathetic receptors
Receptors –> M1, M2, M3 (GCPRs)
Describe the ANS within the adrenal glands
Sympathetic post-ganglionic neurons diff to form neurosecretory chromaffin cells (prod noradrenalin) = can be considered as postganglionic sympathetic neurons that do not project to a target tissue.
Noradrenalin –> adrenaline (catalysed by phenylethanolamine N- methyltransferase)
Outline the steps in neurotransmission
1) uptake of precursors
2) synthesis of transmitter
3) vesicular storage of transmitter
4) degradation of transmitter
5) depolarization by propagated action potential
6) depolarization-dependent influx of Ca2+
7) exocytotic release of transmitter
8) diffusion to post-synaptic membrane
9) interaction with post-synaptic receptors
10) inactivation of transmitter
11) re-uptake of transmitter
12) interaction with pre-synaptic receptors
How is ACh synthesised?
acetyl CoA + choline –> ACh + coenzyme A (catalysed by choline acetyltransferase)
How is ACh degraded?
ACh –> acetate + choline (catalysed by acetylcholinesterase)
What is SLUDGE?
pathological side effects indicative of massive discharge of parasympathetic nervous system, Usually in drug overdose (mushrooms), Insecticides = covalently deactivate acetylcholinesterase = raise Ach.
S --> salivation L --> lacrimation U --> urination D --> defecation G --> gastrointestinal upset: diarrhoea E --> emesis: vomiting
Outline 2 noradrenergic therapeutic interventions
β2-adrenoceptor-selective agonists (salbutamol) used in asthma to reverse/oppose bronchoconstriction, beta receptors in heart and lungs = selectivity important as it limits possible cardiovascular side-effects.
α1-adrenoceptor-selective antagonists (doxazosin) and β1-adrenoceptor-selective antagonists (atenolol) = treat cardiovascular disorders: hypertension
Outline the pathophysiology of asthma
1) eosinophils accumulate/infiltrate bronchial smooth muscle = mucosal oedema
2) swelling = narrowing
3) release of cytotoxic mediators damage respiratory epithelial layer
4) damage = exposure of sensory nerves = bronchial hyper-responsiveness
5) = smooth muscle spasms = narrowing
6) Inflammation = hyper secretion of mucus = plug = further narrowing
Describe the innervation of airways
Autonomic innervation of the airway = parasympathetic = Ach –> Stimulation of β 2 adenoceptors = activates AC, formation cAMP, activation PKA, low Ca2= conc = bronchodilation
What is an asthma reliever?
bronchodilators: β agonists (salbutamol), montelukast blocks leukotriene D4 which is a major bronchoconstrictor mediator
What is an asthma preventer?
anti-inflam drugs: glucocorticosteroids (dexamethasone): down regulate genes involved in mediating inflame response. Sodium cromoglicate: reduces release of histamine from mast cells
How is hypertension regulated?
sympathetic NS, renin angiotensin aldosterone system RAAS
How is hypertension treated?
1) ACE inhibitors –> medications that inhibit activity of enzyme ACE = decreases prod of angiotensin II = blood vessels dilate, BP reduced
2) Ca channel blockers –> prevent release of Ca stores = smooth muscle vasodilators
3) Diuretics –> increase Na and water loss, reduces ECF = lowers blood volume = lowers BP
4) β-adrenoceptors blockers (antagonist) –> reduce cardiac output (reduce ionotropy/force and chromotropy/ rate of heart), reduce renin production = less aldosterone = increase kidney secretion
5) α-adrenoceptor blockers (antagonist) –> vasodilator
Where are the following receptor found: α1, α2, β1, β2, M1, M2, M3?
A1 = Smooth muscle cells of blood vessels. A2 = Liver cells, platelets, and the smooth muscle of blood vessels. B1 = Heart, Kidney. B2 = Bronchioles of the lungs and the arteries of the skeletal muscles. M1 = Exocrine glands. M2 = Heart. M3 = Lungs
What is the function of the thyroid?
T3, T4: regulate metabolic rate. Low levels = hypo releases TRH –> pituitary releases TSH –> thyroid. High T3, T4 = -ve feedback = stops prod. Hypo = underactive. Hyper = overactive. Thyroid hormones upregulate the number of adrenoceptors in the body
What is thyrotoxicosis and how is it treated?
Thyrotoxicosis = clinical symptoms due to high levels of thyroid hormone in blood. Treatment = propranolol non-selective β-adrenoceptor antagonist, IV given in thyrotoxic crisis (storm), Iodine = blocks release of hormones as reduces conversion of T4 to T3
What are the 2 divisions of the ANS
sympathetic and parasympathetic
What parasympathetic nerve regulates the heart?
vagus nerve
What is the term for disorders of the ANS?
dysautonomia
What are catecholamines disorders?
cancer cell release NA and adrenaline constantly = always fight or flight
Activation of M2 receptors in the heart causes?
bradycardia
Activation of B1 receptors in the heart causes?
tachycardia
Activation of A1 receptors cause?
arteriolar contraction
Explain what activation of B2 receptors causes?
bronchiole relaxation
What is trimethaphan used for?
ganglion blocking cholinergic drug, given during surgery to sustain hypotension
