Parasympathetic NS

• Parasympathetic NS

  keeping energy use low (blood pressure, heart rate)

  gastrointestinal activity high - "rest and digest"
• Parasympathetic craniosacral outflow

  ganglia lie near to effector organs or within their walls small ganglia

  CRANIAL:

  postganglionic fibres in effector organ

  SACRAL:

  sacral nerves form pelvic plexuses containing scattered ganglia

  some ganglia within tissue

  
• Parasympathetic pathway

  preganglionic longer than post

  AcH with nicotinic receptors

  muscarinic effector cell

  
• cholinergic synapse

  ACh acts postsynaptically on nicotinic receptors at ganglionic synapses

  ACh acts postjunctionally on muscarinic receptors at effector cell

  Muscarinic receptors of receptor cell

  -  In varicosities – Ach synthesised by acetyl coA and choline by choline acetyltransferase

  -          Packaged into vesicles

  -          AP – triggers release

  -          Two ach molecules to trigger a receptor

  -          Sodium ions flood in
• ACh receptors

  Nicotinic - at ganglia

  ionotropic - ion channel receptor - regulates transport of NA+/K+

  muscarinic: at autonomic target tissues

  metabotropic: G- protein couples to second messenger
• Ionotropic nicotinic ACh recpetor

  ion channel -> ion transport (Na+ and K+) -> response
• muscarinic ACh receptor - metabotropic

  Attaches to G protein -> 2nd messenger system -> enzyme activation/ ion transport -> response
• parasympathetic drugs

  PARASYMPATHOMIMETIC: cholinomimetic - mimics actions of parasympathetic NS - increases PNS

  PARASYMPATHOLYTIC: antagonists - inhibit effects of PNS

  CHOLINESTERASE INHIBITORS: enhances effects of PNS

  GANGLIONIC BLOCKING DRUGS : Nicotinic antagonist – blocks both sympathetic & parasympathetic ganglia
• Parasympathetic control of heart

  reduces cardiac function - releases ACh -acts on M2 muscarinic receptors in the heart

  cardiac arrest - atropine - resuscitation - blocks M2 receptors

  
• parasympathetic control of pupil diameter

  M3 receptors
• Parasympathetic control of pupil diameter

  M3 receptors

  releases ACh onto circular muscles

  causes muscle t contract

  pupil becomes smaller (miosis)

  muscarinic antagonist (atropine)

  blocks circular muscle contraction

  puipil dilation - mydriasis
• parasympathetic control of focussing

  suspensory ligaments are attached to ciliary muscles

  ciliary muscles relaxed - moved out - ligaments under tension - pulls and flattens lens

  PNS ACTIVATED

  contracts ciliary muscles - ligaments relaxed - lens bulges - FOCUSSES ON NEAR THINGS - called accommodation
• parasympathetic cotransmission

  Vasoactive intestinal polypeptide (VIP)  : released when AP alongside Ach – need high frequency