BVMS1

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Author:
mkusiak
ID:
51679
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BVMS1
Updated:
2010-11-28 07:06:29
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Physiology
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Autonomic Nervous System
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  1. Autonomic nervous system (breif)
    • control of involuntary activities
    • cardiovascular responses
    • respiration
    • endocrine secretion
    • gastrointestinal motility and secretions
    • reproductive and urogenital control
  2. regulation of the ANS
    limbic cortex--> spinal cord, brain stem, hypothalamus---> AMS--->sympathetic or parasympathetic
  3. ANS- structure
    • receptors
    • Afferent pathways (using visceral and somatic nerves)
    • dorsal root ganglion
    • CNS
    • efferent pathway
    • paraveterbral (sympathetic)
    • prevetebral (sympathetic)
    • pre-ganglionic (parasympathetic)
    • post-ganglionic (parasympathetic)
  4. Sympathetic outflow
    • each lower motor pathway has 2 neurones to organs
    • 1) short finely myelinated PRE-GANGLIONIC fibres leave with notor roots of spinal nerves
    • 2) LONG POST-GANGLIONIC fibres pass to organs
    • (see image)
  5. Parasympathetic outflow
    • Each lower motor pathway has 2 neurones to organs
    • 1) long finely myelinated PRE-GANGLIONIC fibres leave w/ the cranial nerves
    • 2) Short non-myelinated POST-GANGLIONIC fibres pass to organs
    • (75% via vagus nerve (cranial X)
    • more localized effect than sympathetic
  6. Chemical transmission at autonomic junctions
    • Parasympathetic NS: cholinergic/Ach/Cholinergic/Ach
    • Ach removed from synapses by cleavage (achase) and reuptake
    • Sympathetic NS: Cholinergic/ach/Adrenergic (most)/NA
    • NA removed by reuptake, diffusion, enzymatic destruction (monoamine oxidase, catechol-O-methyl transferase)
  7. Transmitter and receptor phenotypes in autonomic neurones (parasympathetic)
    • Ach--> nicotinic receptor-->Ach--> muscarinic receptor
    • increased exocrine gland secretion
    • increased GI smooth muscle contraction, decreased heart rate
  8. Transmitter and receptor phenotypes in autonomic neurones (sympathetic)
    • Ach-->N-->ach-->M
    • (increase sweating, dilate skeletal muscle blood vessels)
    • Ach-->N (Adrenal medulla)--> A, NA via blood
    • Ach-->N---> NA---> alpha or Beta
    • (increased slenic contraction, increased cardiac efficiency, decreased contraction of GI smooth muscle, constrict peripheral blood vessels, dilate airways)
  9. Transmitter and receptor phenotypes in autonomic neurones (somatic NS)
    somatic NS--> Ach--> N (skeletal muscle)
  10. Types of Receptors
    • Nicotinic (Nn, Nm)
    • Muscarinic (M1, M2, M3, M4, M5)
    • adrenoreceptors (alpha (a1[a1a, a1b, a1d], a2 [a2a, a2b, a2c]), Beta (B1, B2, B3, B4)
  11. Adrenal medulla
    • secretes:
    • Noradrenaline (20%)
    • Adrenaline (80%)
    • longer effect than neural stimulation, as NA/A not degraded as quickly
    • (acts on a & B receptors)
    • Adrenaline, generally has the same effects as NA but...
    • greater effect at B receptors, increase effect on heart rate, decrease effect on vascular in muscle
    • adrenaline has 5-10x effect of NA on metabolism adrenaline can double metabolic rate
    • why!?= parallel system (saftey), metabolic regulation is non innervated organs
  12. Tone
    • both divisions of the ANS are continually active
    • basal rate- tone
    • adrenal gland cont. secretes low levels of NA and A- adrenal tone
  13. Co-transmission
    • transmitters released from nerve terminals other than Ach and noradrenaline
    • non-peptides (ATP, GABA....)
    • peptides
    • ex: ATP is released from postganglionic sympathetic nerve terminals in conjunction with noradrenaline
  14. Autonomic reflexes
    • Cardiovascular: several reflexes
    • Baroreceptor reflex: pressure- monitored by receptors in major arteries, signal sent to brainstem- changes sympathetic impulses to heart and blood vessels
    • Bladder reflex- stretch- impulses to sacral cord contration of bladder and relaxation of sphincter
    • sexual reflex- psychological and physical stimulation- activation of Parasympathetic NS- erection, stimulation of the glans penis- activation of sympathetic NS- ejaculation
  15. Drug Action (Adrenergic Agonists/ Non-selective)
    • same effect as Sympathetic stimulation
    • Noradrenaline
    • adrenaline (a & B- cardiac arrest, anaphylaxis)
    • Dopamine- effects dependent upon dose, due to ability to interact w/ different receptor subtypes
    • isoprenaline- non selective B adrenergic agonist- chronotropic/inotropic actions (does not bind with a)
    • phenylpropanolamine- a adrenergic agonist- urinary incontinence in dogs (does not bind to B)
    • ephedrine- induces the release or noradrenaline (therefore non-selective)
    • usualy used in emergency situations
  16. Drug action (Adrenergic agonists/ selective)
    • Dobutamine- B1, agonist- chronotropic/inotropic cardiac effects
    • Clenbuterol- B2, agonist- bronchodilater
    • Phenylephtine- a1, agonist- vasocontriction
    • Clonidine- a2, agonist- Central sedative effect
  17. Drug action (adrenergic antagonists)
    • block the effects of sympathetic stimulation
    • phenoxybenzamine- a1, irreversible antagonist- laminitis and urinary retention
    • Yohimbine- a2, antagonist- reverse sedation
    • metoprolol- B1 antagonist- cardiac effect
    • propranodol- mixed B antagonist
  18. Drug action (cholinergic agonists)
    • same effect as parasympathetic stimulation
    • Acteylcholine- rapid broken down
    • Methacholine- M>N- cardiovascular system
    • Carbochol- M receptors in GI- Glaucoma
    • Pilocarpine- M effects- Glaucoma
  19. Drug action (Anti cholinesterase agents)
    • Prolong/ increase effects as parasympathetic stim.
    • Reversible: Phytostigmine, Neostigmine (reversal agent for non depolarising muscle relaxants. myasthenia gravis)
    • Irreversible: organophosphates (parathion, malathion)
  20. Drug actions (muscarinic and Nicotinic antagonists)
    • muscarinic antagonists: Atropine (prevents salivation. antidote for OP poisoning), Hyoscine (antiemetic)
    • Nicotinic antagonists: N receprots are present at autonomic ganglia and muscle end plate but different subtypes at each location. therefore targeted tx is important.
    • non depolarising- Curare, Atracurium
    • Depolarising- suxamethonium
  21. Enteric nervous system
    • system of neurones contained w/in the gut begin in the esophagus and end at anus
    • control GI function movement and secretion
    • contains 100 milliion neurones= spinal cord!
  22. Myenteric plexus (ENS)
    • regulates movement
    • tonic contraction of gut wall
    • intensity of rhythmical contractions
    • rate of rhythmical contractions
    • speed of peristaltic waves
  23. Submucosal plexus (local functions)
    • absorption
    • secrection
  24. Neurotransmitters in ENS
    • lots!
    • Ach, NA, ATP, seratonin, Dopamine substance P, VIP, Somatostatin the specific functions of which are not known!
  25. ENS interactions w/ ANS
    • Post gangionic fibres of the Parasympathetic (activated) incorporated into myenteric and submucosal
    • stimulation increases activity of the enteric
    • Cell bodies of post ganglionic sympathetic fibres present w/in the prevertebral ganglia, fibres terminate on both GI smooth muscle and enteric NS
    • Stimulation decreases activity of the enteric (sympathetic)
  26. 3 types of enteric reflex
    • W/in the enteric (GI secretions, peristalsis)
    • GI/prevertebral/GI (gastrocholic- signal from the stomach causes evacuation of the colon) (Enterogastric- signal from the colon and small intestine to inhibit stomach motility and secretion)
    • GI/Spinal cord-brain stem/GI (control of gastric motor and secretory activity via signals generated in the stomach and duodenum, pain reflexes- inhibit entire tract, defecation reflexes)

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