Lesson 6: Vegetative Nervous System PDF

Lesson 6 Vegetative Nervous System 3° Medicine Professor: Vittoria Carrabs PhD Academic year: 2024/25 SUMMARY 1. Bases of vegetative nervous system. Nomenclature 2. ANS functions. 3. Chemical transmission. 4. Neurotransmitter concept. Main transmitters. 5. Drugs...

Lesson 6 Vegetative Nervous System 3° Medicine Professor: Vittoria Carrabs PhD Academic year: 2024/25 SUMMARY 1. Bases of vegetative nervous system. Nomenclature 2. ANS functions. 3. Chemical transmission. 4. Neurotransmitter concept. Main transmitters. 5. Drugs affecting neurotransmission 2 1. BASES OF VEGETATIVE NERVOUS SYSTEM. 1. Bases of vegetative nervous system The Autonomic Nervous System is characterized by regulating most visceral functions of organs and tissues, without the intervention of consciousness (hence the name autonomous) 4  1. Bases of vegetative nervous system 1. Neuron communication: Enabled by synapses. 2. Bioelectrical signal: Initiated at a synapse and travels along the axon to the axonal terminal. 3. Conversion to chemical signal: At the terminal, the electrical signal is converted into a neurotransmitter (chemical signal). 4. Diffusion across the synapse: The neurotransmitter diffuses across the synaptic cleft to the neighboring neuron. 5. Conversion in the postsynaptic neuron: The chemical signal is converted back into an electrical signal in the postsynaptic neuron. 6. Basis of brain processing: This process forms the 5 foundation for information processing in the brain.  1. Bases of vegetative nervous system. Nomenclature Synapse is the junction across which a nerve impulse passes from an axon to another neuron. Nerve fibers carrying the signal into a Synapse are: presynaptic. Nerve fibers carrying the signal out of a Synapse are: postsynaptic.  1. Bases of vegetative nervous system. Nomenclature Ganglion is a group of nerve cells forming a nerve center, especially one located outside the brain of spinal cord. Nerve fibers carrying the signal into a ganglion are: Preganglionic. Nerve fibers carrying the signal out of a ganglion are: Postganglionic.  1. Bases of vegetative nervous system. Nomenclature The neurons transmitting the neuronal message out of the CNS to the periphery are efferent fibers. The neurons transmitting the neuronal message from periphery to the CNS are afferent fibers. The fibers that control voluntary movements are somatic nerves.  1. Bases of vegetative nervous system. Division of the ANS: Ø sympathetic or adrenergic system Ø parasympathetic or cholinergic system Ø enteric system (gastrointestinal tract). – The sympathetic and parasympathetic systems provide a link between the central nervous system and peripheral -The enteric nervous system includes the intrinsic nerve plexuses of the gastrointestinal tract. 9 SUMMARY 1. Bases of vegetative nervous system. Nomenclature 2. ANS functions. 3. Chemical transmission. 4. Neurotransmitter concept. Main transmitters. 5. Drugs affecting neurotransmission 1 0  2. ANS FUNCTIONS The autonomic system controls smooth muscle (visceral and vascular), exocrine (and some endocrine) secretions, rate and force of contraction of the heart, and certain metabolic processes (e.g. glucose utilisation). Sympathetic and parasympathetic systems have opposing actions in some situations (e.g. control of heart rate, gastrointestinal smooth muscle), but not in others (e.g. salivary glands, ciliary muscle.. – Sympathetic activity increases in stress (‘fight or flight’ response) – Parasympathetic activity predominates during satiation and sleep. Both systems exert a continuous physiological control of specific organs under normal conditions, when the body is at neither extreme. sleep rest myosis 11 SUMMARY 1. Bases of vegetative nervous system. Nomenclature 2. ANS functions. 3. Chemical transmission. 4. Neurotransmitter concept. Main transmitters. 5. Drugs affecting neurotransmission  3. CHEMICAL TRANSMISSION Sympathetic Nervous System The autonomic efferent pathway consists of two neurons arranged in series: preganglionic and postganglionic. – In the sympathetic nervous system, the intermediate synapses are located in the autonomic ganglia, which are situated outside the CNS and contain the nerve endings of preganglionic fibres and the cell bodies of postganglionic neurons. 17  3. CHEMICAL TRANSMISSION Sympathetic Nervous System Some actions controlled by the SNS: ↑ Pupil dilation (mydriasis) ↑Heart rate (tachycardia) ↑ Glucose release ↑ Bronchodilation ↑ Liver activity ↓Saliva production (inhibition of salivary secretion) ↓ GI Activity ↓ Diuresis (relaxes bladder muscle) 3. CHEMICAL TRANSMISSION Parasympathetic Nervous System The autonomic efferent pathway consists of two neurons arranged in series: preganglionic and postganglionic. – In parasympathetic pathways, the postganglionic cells are mainly found in the target organs. 18 3. CHEMICAL TRANSMISSION Parasympathetic Nervous System Some actions controlled by the PNS: ↓ Pupil dilation (miosis) ↓ Heart rate ↓ Glucose release ↑ Bronchoconstriction ↓ Liver activity ↑ GI Activity ↑ Diuresis (contracts bladder muscle) 3. CHEMICAL TRANSMISSION Somatic Motor System Somatic motor system a single motor neuron connects the central nervous system directly to the skeletal muscle fibre. 19 SUMMARY 1. Bases of vegetative nervous system. Nomenclature 2. ANS functions. 3. Chemical transmission. 4. Neurotransmitter concept. Main transmitters. 5. Drugs affecting neurotransmission 1 9  4. MAIN TRANSMITTERS What is a neurotransmitter? These are chemical molecules released from nerve terminals, which are recognised by specific receptors located on the membranes of postsynaptic cells. As a consequence of this binding, an excitatory or inhibitory response is triggered.  Peripheral Nervous System Sympathetic Parasympathetic Somatic Preganglionic neuron Ach Ach Ganglion Postganglionic neuron Nicotinic Receptor Nicotinic Receptor N.A. Ach Ach Adrenergic Receptor Muscarinic Receptor Nicotinic Receptor (Skeletal muscle) Effector organs 4. MAIN TRANSMITTERS Transmitters other than noradrenaline and acetylcholine (NANC transmitters) are also abundant in the autonomic nervous system. The main ones are nitric oxide and vasoactive intestinal peptide (parasympathetic), ATP and neuropeptide Y (sympathetic). Others, such as 5-hydroxytryptamine, GABA and dopamine, also play a role. serotonine SUMMARY 1. Bases of vegetative nervous system. Nomenclature 2. ANS functions. 3. Chemical transmission. 4. Neurotransmitter concept. Main transmitters. 5. Drugs affecting neurotransmission 2 6 5. DRUGS AFFECTING NEUROTRANSMISSION AUTONOMIC NERVOUS SYSTEM The drugs used in the ANS must follow the requirements below: a) Drugs that mimic the action of the ANS are agonist drugs: mimic the action of acetylcholine (Ach) parasympathomimetics or cholinergics noradrenaline (NA) sympathomimetic or adrenergic b) Drugs that inhibit the action of the ANS are Antagonists. (parasympatholytic or anticholinergic; sympatholytic or anti-adrenergic) c) Drugs that interfere with the synthesis, storage or metabolization of the neurotransmitter, either facilitating these processes or inhibiting them. They are indirect methods. 5. DRUGS AFFECTING NEUROTRANSMISSION SYMPATHETIC (ADRENERGIC) SYSTEM The transmission of the nerve impulse takes place by: Ø the release of neurotransmitters: Noradrenaline (NA) or norepinephrine, Acetylcholine (Ach) Ø The pharmacological modification of the activity of the ANS is based on the use of substances capable of mimicking the actions of the neurotransmitter (NT). Ø Adrenergic receptors (a1, a2 ; b1, b2, b3 ) 5. DRUGS AFFECTING NEUROTRANSMISSION PARASYMPATHETIC (CHOLINERGIC) SYSTEM Ø The NT is Acetylcholine. Ø There are 2 types of R: Ø Nicotinic Ø Muscarinic (in effector organs) (M1-M5) Ø Parasympathetic or cholinergic drugs reproduce the effects of stimulation of the Parasympathetic N.S. Ø Muscarinic actions = parasympathetic stimulation Ø Parasympatholytic or anticholinergic drugs block the effects derived from the stimulation of parasympathetic N.S.  5. DRUGS AFFECTING NEUROTRANSMISSION NEUROMUSCULAR JUNCTION Motor plate or neuromuscular plate is a specialized area of skeletal muscle fiber rich in cholinergic receptors that is part of the neuromuscular junction. Motor nerves stimulate the muscle by releasing Ach at muscle plate receptors. An electrical potential is then triggered which activates the muscle fibre contraction. ANTAGONISTS Nicotinic receptor Drugs that block the motor plate produce complete muscle relaxation with no effect on the CNS. The patient will be left in apnea and conscious  5. DRUGS AFFECTING NEUROTRANSMISSION NEUROTRASMISSION BLOCKERS Tetrodotoxin, batrachotoxin, and snake venom share some similarities in their effects on neuromuscular function, but they act through different mechanisms: Neuromuscular Effects: leading to symptoms such as paralysis, muscle weakness, and difficulties with respiration. Toxic Effects on Nerve or Muscle Cells: They all interfere with the normal function of nerve or muscle cells, which can disrupt muscle contraction and nerve signal transmission. Tetrodotoxin, – is a potent neurotoxin. (Tetraodontiformes order). – Mechanism: Blocks sodium channels on nerve and muscle cell membranes. – Effect: Prevents action potentials by stopping sodium ion influx, leading to paralysis and potentially respiratory failure.  5. DRUGS AFFECTING NEUROTRANSMISSION NEUROTRASMISSION BLOCKERS Batrachotoxin (BTX) is an extremely potent cardiotoxic and neurotoxic found in certain species of frogs, and birds Mechanism: Keeps sodium channels open, preventing them from closing. Effect: Causes continuous sodium influx, leading to persistent depolarization of nerves and muscles, resulting in convulsions, spasms, and paralysis. Snake venom depending on the specific toxin but generally includes: Acetylcholine Receptor Blockade: Some toxins block acetylcholine receptors at the neuromuscular junction preventing muscle contraction. Acetylcholine Degradation: Some toxins contain enzymes that degrade acetylcholine, reducing nerve-muscle communication and causing muscle weakness. Effect: Causes paralysis by interfering with neuromuscular transmission through different mechanisms, including receptor blockade or enzyme activity. Questions?????