Autonomic Nervous System Student Notes PDF

Jacqueline Mobley, DVM AHS 2202  The Autonomic Nervous System  Questions we will answer in today’s lecture.. ▪ What is the autonomic nervous system? ▪ What are the 2 branches of the autonomic nervous...

Jacqueline Mobley, DVM AHS 2202  The Autonomic Nervous System  Questions we will answer in today’s lecture.. ▪ What is the autonomic nervous system? ▪ What are the 2 branches of the autonomic nervous system? ▪ What do they do? ▪ Where do they originate in the CNS? ▪ What are the types of neurotransmitters and receptors associated with components of the autonomic nervous system?   What is the The part of the nervous system autonomic that controls many subconscious nervous body functions system? The autonomic nervous system is divided into Sympathetic Parasympathetic nervous system nervous system  Fight-or-flight Sympathetic nervous system (SNS) = fight-or-flight Associated with survival in emergency situations Energy expenditure  Rest-and-digest (rest-and-restore) Parasympathetic nervous system (PSNS) – rest & digest Associated with processes that occur in the normal resting state Energy conserving  Clinical signs associated with activation of the autonomic nervous system ▪ Fight-or-flight? ▪ What do your muscles need? ▪ What does your heart need? ▪ What do your lungs need? ▪ What do your eyes need? ▪ What body functions are less important in that moment?   Effects of Sympathetic & Parasympathetic Nervous Systems Sympathetic Parasympathetic Heart rate Increases Decreases Force of heart contraction Increases No significant effect Diameter of bronchioles Increases (dilates) Decreases (constricts) Diameter of pupil Increases (dilates) Decreases (constricts) GI motility & function Decreases Increases Diameter of skin blood Decreases No significant effect vessels Diameter of muscle blood Increases No significant effect vessels Diameter of blood vessels Decreases No significant effect to kidney   Structure of the Autonomic  Nervous System   Where exactly are the nervesfor the autonomic nervous system? ▪ Sympathetic nervous system ▪ Thoracic and lumbar vertebral regions in the back ▪ Referred to as the “thoracolumbar system” ▪ Parasympathetic nervous system ▪ Brain and sacral vertebral regions in the back ▪ Referred to as the “cranial- sacral system” Efferent motor nerves are a  sequence of 2 neurons ▪ First neuron (preganglionic neuron): ▪ 1st neuron cell bodies are in the CNS ▪ Its axon extends to a cluster of nerve cell bodies called autonomic ganglion ▪ Second neuron (postganglionic neuron): ▪ 2nd neuron cell bodies are in the ganglion ▪ The axon of 1st neuron synapses with one or more second neurons ▪ Second neurons synapse with the target organ (muscle, gland) This Ph oto by Unknown Author is licensed und er CC BY  Sympathetic efferent motor nerves  ▪ 1st neuron is located in the the TL spinal cord ▪ Outside the spinal cord, a chain of autonomic ganglia are present, called the sympathetic ganglion chain ▪ The 1st neuron synapses with a ganglion in the chain or synapses with a neuron past the ganglion chain ▪ Each 1st neuron synapses with multiple ganglia in the chain or even outside the chain ▪ ***SNS activation affects multiple organ systems simultaneously***   Sympathetic efferent motor nerves cont.. ▪ 2nd spinal neuron then synapses with the target organ ▪ The postganglionic neuron is much longer than the preganglionic neuron in the SNS  Parasympathetic motor nerves ▪ PSNS preganglionic neuron is long ▪ Originates from ▪ Nuclei (clusters of neurons) in the brain of cranial nerves ▪ Sacral region of the spinal cord ▪ Terminates at ▪ Its target organ ▪ Synapses with a short postganglionic neuron at the target organ   Sympathetic nervous system neurotransmitters  & receptors   Neurotransmitters & Receptors ▪ Sympathetic Nervous System ▪ Norepinephrine is the primary neurotransmitter for the SNS ▪ “Catecholamines” include norepi, epi, dopamine ▪ Epinephrine is formally known as “adrenaline” ▪ Norepinephrine is formally known as “noradrenaline” ▪ Neurons that release norepi are referred to as “adrenergic” neurons   Where do norepinephrine & epinephrine Adrenergic come from? postganglionic neurons Adrenal medulla Directly released into bloodstream  ▪ Adrenergic receptors are receptors for norepinephrine & epinephrine Types of adrenergic ▪ Alpha1 adrenergic receptors receptors ▪ Alpha2 adrenergic receptors ▪ Beta1 adrenergic receptors ▪ Beta2 adrenergic receptors   Alpha1 adrenergic Blood vessels receptors Cause vasoconstriction with sympathetic stimulation Skin GI Kidney   Beta1 adrenergic receptors Increases heart rate Increases force of heart contraction  Beta2 adrenergic receptors ▪ Bronchodilation   Parasympathetic Neurotransmitters ▪ Acetylcholine is the parasympathetic neurotransmitter ▪ Acetylcholine is also the neurotransmitter at the synapse between 1st & 2nd neurons ▪ Neurons that release ACh are referred to as ”cholinergic” neurons ▪ What’s weird about cholinergic neurons… ▪ All preganglionic neurons are considered cholinergic ▪ The postganglionic neuron is the one that determines if the effect is sympathetic or parasympathetic   Cholinergic receptors ▪ There are 2 types of cholinergic receptors ▪ Nicotinic ▪ Muscarinic   Nicotinic receptors ▪ Found on ▪ The second neuron (he postganglionic neurons) in both sympathetic & parasympathetic nervous systems ▪ Between motor neurons and muscle in the somatic (voluntary) system   Muscarinic receptors ▪ Found on ▪ Target organs and tissues supplied by postganglionic neurons of the PSNS  Summary of impulses in the autonomic nervous system ▪ Presynaptic (preganglionic) neurons extend to autonomic ganglia ▪ Presynaptic neurons release acetylcholine into the synaptic cleft ▪ ACh binds to nicotinic ganglionic receptors on postganglionic neurons ▪ Postsynaptic (postganglionic) neurons transmit impulses to end organs ▪ Release norepinephrine (Sympathetic neurons) ▪ Release acetylcholine (Parasympathetic neurons)  Transmission continued: Sympathetic ▪ Norepinephrine are released from postganglionic neuron into the synaptic cleft ▪ Norepinephrine binds to a receptor ▪ Alpha 1 ▪ Alpha 2 ▪ Beta 1 ▪ Beta 2  Transmission continued: Parasympathetic ▪ Nerve transmission occurs between the preganglionic & postganglionic neuron (ACh binds to nicotinic receptors) ▪ The postganglionic nerve synapses with the target organ and releases ACh ▪ ACh binds to target receptors ▪ Nicotinic muscle receptors on muscle cells causes muscle contraction (somatic motor) ▪ Muscarinic receptors on other target organs results in muscle activity or release of secretions  Drugs that Affect the autonomic nervous system ▪ Some drugs can be used to enhance neurotransmission ▪ Receptor agonists ▪ Agents that induce neurotransmitter release ▪ Drugs which prevent transmitter breakdown by enzymes ▪ Some drugs can be used to suppress neurotransmission ▪ Presynaptic nerve blockers ▪ Receptor antagonists ▪ Ganglion blockers   Sympathomimetics Sympathomimetics act like catecholamines Frequently used to treat life threatening conditions Anaphylaxis Cardiac arrest Heart failure Shock   Clinical Relevance: CPR ▪ Cardiopulmonary arrest ▪ Treatment: chest compressions, respirations, drugs ▪ Epinephrine – sympathomimetic ▪ Adrenaline ▪ Vasoconstriction, increased heart rate & contractility, bronchodilation ▪ Atropine – anticholinergic ▪ Directly blocks muscarinic receptors ▪ Prevents bradycardia and respiratory secretions ▪ Blocks “rest & digest”   The End