PHYSIO (ANS)

• Neurotransmission and disposition of NT in the synapse
• The Autonomic Nervous System (ANS) is divided into the Parasympathetic Nervous System (PSNS) which conserves and restores energy, and the Sympathetic Nervous System (SNS) which strengthens the body’s defense against adverse conditions by expenditure of energy.
• The Parasympathetic Nervous System (PSNS) is often referred to as the rest and digest system.
• The Sympathetic Nervous System (SNS) is often referred to as the fight or flight system.
• The Autonomic Nervous System (ANS) consists of the Somatic Nervous System (SNS) which is responsible for conscious perception and voluntary motor responses, and the Autonomic Nervous System (ANS) which maintains homeostasis by controlling visceral organs and glandular secretions.
• The Autonomic Nervous System (ANS) innervates and controls smooth muscles (visceral), glands and cardiac function.
• Most viscera receive a dual sympathetic and parasympathetic innervation, but some are innervated solely by the sympathetic division (e.g., sweat gland, vascular smooth muscle of skeletal muscle, skin, and arrector pili) or parasympathetic division (e.g., pupillary sphincter muscle, ciliary muscle).
• Autonomic motor control have slower and longer-lasting effects compared to somatic motor control which is fast.
• The Autonomic Nervous System (ANS) action on the gastrointestinal tract is to modulate its intrinsic neural system.
• The Hypothalamus controls the Autonomic Nervous System (ANS) and acts as an integrator for autonomic functions.
• The Autonomic Nervous System (ANS) is composed of the Sympathetic Nervous System (SNS) which requires a two neuron chain between the nucleus of origin in the CNS and the peripheral target organ, and the Parasympathetic Nervous System (PSNS) which requires a three neuron chain between the nucleus of origin in the CNS and the peripheral target organ.
• The organization of the Autonomic Nervous System (ANS) is different from the Somatic Nervous System (SNS) which is composed of only one neuron.
• Sympathetic pre ganglionic neurons are cholinergic nerves while the post ganglionic nerve fibers are adrenergic since norepinephrine is released from these neurons.
• Cholinergic receptors are receptors in the ganglia or target organs which responds to the binding of the neurotransmitter Acetylcholine.
• Epinephrine stimulates adrenergic receptors throughout the body and causes a massive adrenergic response.
• Cholinergic nerves are nerve fibers that secrete acetylcholine neurotransmitter at their endings, while adrenergic nerves are nerve fibers that secrete noreadrenaline (norepinephrine) neurotransmitter at their nerve endings.
• There are two major neurochemical transmitters that are released at the synapses and at the neuroeffector junctions in the autonomic nervous system: Norepinephrine (noreadrenaline) and Acetylcholine.
• There are two types of receptors found in the post ganglionic neurons and target organs in the autonomic nervous system, cholinergic and adrenergic receptors.
• The preganglionic nerve fiber are short and synapse with the cell bodies of the post ganglionic neurons in the sympathetic chain ganglia, post ganglionic nerve fiber are long and ends on the organs innervated.
• Acetylcholine is the transmitter released at the peripheral motor portions of the autonomic nervous system which include: postganglionic parasympathetic fibers at the neuroeffector junction, preganglionic parasympathetic fibers, preganglionic sympathetic nerve fibers, and splanchnic nerve terminals in the adrenal medulla.
• The parasympathetic nervous system pre and post ganglionic nerves are cholinergic nerves since acetylcholine is released from these neurons.
• Norepinephrine (noreadrenaline) is the major transmitter at the terminals of the postganglionic fibers* in the neuroeffector junction in the sympathetic division, with exceptions being those innervating the sweat glands and blood vessels of the skeletal muscles which secrete acetylcholine.
• Nicotinic Receptors are found in the autonomic ganglia at the synapses between the preganglionic and postganglionic neurons of both the sympathetic and parasympathetic systems, and are specifically stimulated by nicotine, a substance derived from tobacco.
• Chromaffin cells in the adrenal medulla are modified adrenergic nerves, when stimulated by splanchnic nerve causes a release of epinephrine into the blood circulation.
• The parasympathetic nervous system predominates in states of rest where energy is conserved, while the sympathetic nervous system predominates during fight or flight conditions where massive discharge of energy is needed by the body.
• The Parasympathetic Nervous System (PSNS) preganglionic neuron cell body originates from the brain and sacral region and has long preganglionic nerve fiber.
• The cell bodies of the postganglionic neurons in the Parasympathetic Nervous System (PSNS) are on the wall of organs in which the preganglionic nerve fiber synapse with it.
• The short postganglionic nerve fiber in the Parasympathetic Nervous System (PSNS) leave the organ and innervates the tissues of the organ.
• The Sympathetic Nervous System (SNS) cell bodies of the preganglionic neurons arise from the thoracolumbar area.
• If all present, epinephrine will be the more effective excitant.
• D3 dopaminergic receptor is involved in cognition, impulse control, attention, sleep.
• Stimulation of nicotinic receptors produces nicotinic effects.
• Norepinephrine excites mainly alpha receptors but excites the beta receptors to a lesser extent as well.
• Overstimulation of sympathetic and parasympathetic ganglia occurs. Nicotinic receptors
• Alpha receptors are mostly excitatory and induce vasoconstriction of most blood vessels, raising blood pressure, constricting sphincters of the gastrointestinal tract, contracting urethral smooth muscle, and dilating the pupils.
• In the synthesis of cathecolamines, dopamine is one of the intermediate product.
• Beta receptors in the heart (cardiac muscle, pacemakers) increase heart rate and contraction force.
• β2-adrenergic receptor is also present in the vascular smooth muscle of the heart and skeletal muscle, as well as bronchiolar smooth muscle.
• Organophosphate (OP) Poisoning results in clinical signs due to the persistent binding of Ach with nicotinic and muscarinic receptors.
• Stimulation of muscarinic receptors produces muscarinic effects such as increased secretion in glands, generally enhanced contraction in smooth muscles, and depressed activity in cardiac muscles.