Lecture 6 - Organisation of the Autonomic Nervous System PDF

Organisation of the autonomic nervous system (ANS) Dr. Bruno Sil dos Santos Overview The nervous system Central and Peripheral nervous systems The Autonomic Definition, Sympathetic / Parasympathetic, Nervous System neurotransmission and drugs ...

Organisation of the autonomic nervous system (ANS) Dr. Bruno Sil dos Santos Overview The nervous system Central and Peripheral nervous systems The Autonomic Definition, Sympathetic / Parasympathetic, Nervous System neurotransmission and drugs  TNS – ANS Autonomic nervous system Concepts The nervous system is a complex network of nerves and cells that carry messages to and from the brain and spinal cord to various parts of the body. The nervous system includes both the Central nervous system and Peripheral nervous system. The Central nervous system is made up of the brain and spinal cord. The Peripheral nervous system is made up of the Somatic and the Autonomic nervous systems. https://www.news-medical.net/health/What-is-the-Nervous-System.aspx  TNS – ANS Autonomic nervous system The nervous system – Then and now https://web.stanford.edu/class/history13/earlysciencelab/body/brainpages/brain.html  TNS – ANS Autonomic nervous system The nervous system All multicellular animals have a nervous system of some sort (varying complexities). Means of coordinating involuntary and voluntary actions based on environment. Includes: sensory nerves (afferent neurons) and motor nerves (efferent neurons). http://people.eku.edu/ritchisong/301notes2b.html  TNS – ANS Autonomic nervous system The nervous system Coordination of involuntary and voluntary actions occurs via a NEURONAL NETWORK (CNS and PNS). A series of interconnected neurons which relocate a signal from the brain to a target organ or muscle Use of charged ions to create a current which passes from one neuron to the other. Current is passed on from neuron to neuron by a biochemical bridge called a synapse. http://people.eku.edu/ritchisong/301notes2b.html  TNS – ANS Autonomic nervous system The nervous system How do neurons communicate? DEPOLARISATION followed by SYNAPTIC release of NEUROTRANSMITTERS to cause DEPOLARISATION of the next neuron. If neurotransmitters are involved, THEN DRUGS CAN BE USED!  TNS – ANS Autonomic nervous system The nervous system The PNS coordinates the automatic control of ALL the visceral organs Heart, lung, liver, intestines, kidneys etc. etc.  TNS – ANS Autonomic nervous system The nervous system VISCERAL: body cavity CNS SOMATIC: “bodily” Sensory Motor impulse impulse “ANS” EFFERENT Rest/digest and PNS Feed/breed PARA AFFERENT SYMPATHETIC Somatic Visceral Motor division Motor division SYMPATHETIC Fight or flight Sensory Smooth muscle Receptors Skeletal Cardiac muscle muscle Glands TISSUE VOLUNTARY INVOLUNTARY  TNS – ANS Autonomic nervous system The ANS Visceral motor control in the ANS is coordinated by pairs of neurons (remember, signal originates from CNS). Neuron 1 – projects from the spinal cord. Neuron 2 – projects to target organ (smooth muscle etc.). GANGLIA: Anatomical structure where ANS neuron 1 meets ANS neuron 2 Target organ  TNS – ANS Autonomic nervous system The ANS (Structure) ANS Sympathetic Para – sympathetic Homeo- GANGLIA stasis  TNS – ANS Autonomic nervous system The ANS (Neuron lengths and synapse locations) SYMPATHETIC DIVISION (flight or fight) Location of synapse (neuron NEURON Length terminus) PREganglionic neuron Short Close to spinal cord (neuron 1) POSTganglionic neuron Long Close to target organ (effector) (neuron 2) PARASYMPATHETIC DIVISION (breed/feed, rest/digest) Location of synapse (neuron NEURON Length terminus) PREganglionic neuron Long Away from spinal cord (neuron 1) POSTganglionic neuron Short Close to target organ (effector) (neuron 2)  TNS – ANS Autonomic nervous system The ANS (Preganglionic neurons) Vagus nerve Sympathetic: Parasympathetic: Preganglionic Preganglionic neurons project from neurons project from the thoracic regions the cranial and of the spinal cord sacral regions of the spinal cord  TNS – ANS Autonomic nervous system The ANS (Vagus nerve)  TNS – ANS Autonomic nervous system The ANS (The sympathetic trunk) Neuron 1 Neuron 2 Paravertebral ganglia, sympathetic trunk, sympathetic chain  TNS – ANS Autonomic nervous system The ANS (Neurotransmitters and receptors) The ANS controls many vital organs via neuronal “innervation” (stimulus). Signals inform organs to continue/increase or stop/decrease certain activities (e.g. heart rate). Neuronal synaptic transmission in the ANS is controlled by two neurotransmitters: 1. NORADRENALINE (norepinephrine). 2. ACETYLCHOLINE.  TNS – ANS Autonomic nervous system The ANS (Neurotransmitters and receptors) Noradrenaline binds to ADRENERGIC RECEPTORS (α, β). Acetylcholine binds to CHOLINERGIC RECEPTORS (muscarinic(m) AChR and nicotinic(n) AChR). ALL preganglionic neurons (neuron 1) synapse with postganglionic neurons (neuron 2) via ACETYLCHOLINE and nAChR. Postganglionic neurons (interact with tissue) synapse via NORADRENALINE (αR or βR) or ACETYCHOLINE (mAChR).  TNS – ANS Autonomic nervous system The ANS (Sympathetic) SYMPATHETIC ANS “Ganglia” Preganglionic PARASYMPATHETIC ANS ACh/nAChR Postganglionic ACh/nAChR Target... organ Target... organ NORADRENALINE / ACETYLCHOLINE/ ADRENERGIC RECEPTOR MUSCARINC ACh RECEPTOR  TNS – ANS Autonomic nervous system The ANS (Sympathetic – exception) The only sympathetic, postganglionic neuron to synapse via ACh and mAChRs is that associated with sweat gland innervation.  TNS – ANS Autonomic nervous system The ANS (Neurotransmitters and the ANS) Sympathetic Parasympathetic Somatic Spinal cord Preganglionic ACh neuron nAChR ACh nAChR Postganglionic ACh ACh ACh or neuron Nor/Adr Tissue Adrenergic Muscarinic Nicotinic receptor Muscarinic  TNS – ANS Autonomic nervous system The ANS (Pharmacological intervention) Remember, nervous transmission via the ANS controls all the visceral organs: Heart, lung, intestines etc. Pharmacological intervention of the receptors involved in ANS neuronal transmission (adrenergic and cholinergic) can alter visceral organ activity. i.e. to increase heart rate, we can pharmacologically “switch on” the receptors involved in controlling it.  TNS – ANS Autonomic nervous system The ANS (Example – The heart) Sympathetic innervation: increases heart rate via NORADRENALINE and β adrenergic receptors Parasympathetic innervation: decreases heart rate via ACETYLCHOLINE and muscarinic AChR (cholinergic receptors)  TNS – ANS Autonomic nervous system The ANS (Example – The heart) Sympathetic innervation: increases heart rate via NORADRENALINE and β adrenergic receptors Parasympathetic innervation: decreases heart rate via ACETYLCHOLINE and muscarinic AChR (cholinergic receptors) By using drugs which either inhibit or activate β adrenergic receptors, we can modulate cardiac activity artificially (block = decrease, stimulate = increase) Likewise, by BLOCKING muscarinic AChR (e.g. ATROPINE), we can INCREASE heart rate – atropine is used to resuscitate slow beating hearts in emergency scenarios. REMEMBER, normally, ACh and mAChR DECREASE heart rate  TNS – ANS Autonomic nervous system The ANS (Drugs) Drugs which alter ANS activity can be categorised depending on their action. Most of these drugs aim receptors on the target organ. A few target receptors in the ganglia. Drug type Action Receptor target Parasympatholytic INHIBIT parasympathetic nerves mAChR (antagonist) Parasympathomimetic STIMULATE parasympathetic nerves mAChR (agonist) Sympatholytic INHIBIT sympathetic nerves αR βR (antagonist) Sympathomimetic STIMULATE sympathetic nerves αR βR (agonist)  TNS – ANS Autonomic nervous system The ANS (Drugs) Most drugs in these categories block ligand-receptor binding events (AChR, α/βR). Some increase/block neurotransmitter recycling/breakdown, e.g. cocaine – blocks reuptake of NA from synaptic cleft.  TNS – ANS Autonomic nervous system The ANS (Drugs) Sympathomimetic Sympatholytic Parasympatho-mimetic Parasympatholytic Noradrenaline Bucindolol Acetylcholine Atropine Adrenaline Carteolol Bethanechol Benztropine (Cogentin) Isoprenaline Carvedilol Carbachol Biperiden Phenylephrine Labetalol Methacholine Dicyclomine (Dicycloverine) Methylnoradrenaline Nadolol Arecoline Glycopyrrolate (Robinul) Clonidine Penbutolol Nicotine Ipratropium (Atrovent) Salbutamol Pindolol Muscarine Orphenadrine Dobutamine Alprenolol Pilocarpine Oxitropium (Oxivent) Prenalterol Propranolol Donepezil Oxybutynin (Ditropan) Phenoterol Acebutolol Edrophonium Tolterodine (Detrol) Albuterol Atenolol Neostigmine Tiotropium (Spiriva) Terbutaline Betaxolol Physostigmine Trihexyphenidyl Metapreterenol Bisoprolol Pyridostigmine Scopolamine Phenylephedrine Celiprolol Rivastigmine Solifenacin Ephedrine Esmolol Tropicamide Pseudoephedrine Amphetamine Metoprolol Doxacurium Methamphetamine Nebivolol Hexamethonium Cocaine Tubocurarine Methylphenidate (Ritalin) Summary The ANS is split into two divisions – sympathetic and parasympathetic. The ANS controls visceral organ activity. Neuronal transmission in the ANS is governed by the neurotransmitters, Noradrenaline and Acetylcholine (and their appropriate receptors). Drugs can be administered to manipulate ANS neuronal transmission and therefore visceral organ activity.