Lecture on the Parasympathetic Nervous System

LO:

1. Describe the synthesis of acetylcholine (ACh) in ANS nerves 

2. Describe the metabolism of ACh released from ANS nerves

3. Outline the main types of cholinergic (ACh) receptors, including 3 types of muscarinic receptors and their distribution in target tissues

4. Outline the parasympathetic control of the heart, eye and smooth muscle tissues in the body, including drugs used medically to treat disorders of the eye

5. Outline parasympathetic cotransmission of ACh and vasoactive intestinal polypeptide (VIP)

Hard shiz:

• the drugs are quite hard
• not very well described in notes so her ethey be
• parasympathominetic such as macarine, pilocarpine and nicrotine increase PNS
• parasympatholytic such as atropine - decrease PNS action - this is the main one to know
• cholinesterase inhibitors - physostigmine increase PNS action
• and ganlionic blocking drugs - work on both PNS and SNS (sympathetic) by decreasing both
• also learn what Parasympathomimetic Drugs and Parasympatholitic Drugs mean

Overview

• Focus on the parasympathetic nervous system (PNS).
• Synthesis and metabolism of acetylcholine (ACH) in autonomic nervous system nerves.
• Types of cholinergic receptors (muscarinic and nicotinic).
• Distribution of muscarinic receptors in various tissues.
• Parasympathetic control of the heart and eye.
• Clinical use of drugs for eye disorders.
• Introduction to the co-transmitter vasoactive intestinal polypeptide (VIP).

Parasympathetic Division

• Also known as the craniosacral division.
  • First neuron's cell body located in cranial or sacral regions of the spinal cord.
• Functions to keep body energy use low.
  • Lowers blood pressure, heart rate, and respiratory rates.
  • Increases gastrointestinal activity.
  • Involved in "rest and digest" response.

Organization

• Two neurons in series:
  • Preganglionic (longer, located in cranial/sacral region).
  • Postganglionic (shorter, near target tissue).
• Major cranial nerves:
  • Oculomotor nerve (eye muscles).
  • Facial nerve (facial glands).
  • Glossopharyngeal nerve (salivary glands).
  • Vagus nerve (various target tissues).
• Sacral nerves synapse in pelvic region ganglia.

Neurotransmitters

• Acetylcholine used exclusively in PNS:
  • Acts on nicotinic receptors (ion channels) at ganglia.
  • Acts on muscarinic receptors (G-coupled) at target tissues.

Receptors

• Nicotinic Receptors: Ionotropic, present at ganglia and neuromuscular junctions.
• Muscarinic Receptors: Metabotropic, present in target tissues like heart, lungs, glands.
  • M1: Gastrointestinal tract (promotes gastric secretion).
  • M2: Heart (reduces heart rate).
  • M3: Glands, smooth muscle.

Acetylcholine Synthesis and Metabolism

• Synthesis from acetyl-CoA and choline via choline acetyltransferase.
• Packaged in vesicles and released upon action potential.
• Broken down by acetylcholine esterase; choline recycled.

Clinical Drug Use

• Parasympathomimetic Drugs: Mimic acetylcholine (e.g., pilocarpine, muscarine).
• Parasympatholitic Drugs: Muscarinic antagonists (e.g., atropine).
• Choline Esterase Inhibitors: Increase acetylcholine by preventing breakdown.
• Ganglion Blocking Drugs: Nicotinic antagonists affecting both PNS and SNS.

Parasympathetic Control of the Heart

• Acetylcholine reduces heart rate and force, slows impulse conduction.
• Clinical use of atropine to block these effects, useful in resuscitation.

Parasympathetic Control of the Eye

• Pupil Diameter:
  • Acetylcholine causes constriction (meiosis).
  • Atropine causes dilation (mydriasis) for clinical inspection or surgery.
• Focus and Accommodation:
  • Ciliary muscle relaxation and contraction affect lens shape.
  • Accommodation for near vision, inhibited by atropine (cycloplegia).
• Clinical Uses:
  • Mydriatic drugs for inspection, glaucoma treatments.

Co-Transmission

• VIP acts alongside acetylcholine in some PNS pathways.
• Co-transmission involves different neurotransmitters like ATP and nitric oxide.

Summary

• Key topics covered: synthesis, metabolism, and receptors of acetylcholine.
• Detailed exploration of parasympathetic control mechanisms in heart and eye.
• Introduction to clinical drug applications and co-transmitters such as VIP.