IAS27 Nervous System and Autonomic Regulation 2024.pdf

Introduction to the Art and Science of Medicine (IASM) Nervous System and Autonomic Regulation Michael M. Manio, MD, MHPED, PhD Lecturer: School of Biomedical Sciences Learning Outcomes: Describe the organization of the nervous system into central nervous system (...

Introduction to the Art and Science of Medicine (IASM) Nervous System and Autonomic Regulation Michael M. Manio, MD, MHPED, PhD Lecturer: School of Biomedical Sciences Learning Outcomes: Describe the organization of the nervous system into central nervous system (CNS) peripheral nervous system (PNS). Identify the structures and functions of the central nervous system (CNS) and peripheral nervous system (PNS). Learning Outcomes: Describe how the autonomic nervous system (ANS) functions and differentiate between its sympathetic and parasympathetic divisions. Explore the differences in organization between the autonomic nervous system and the nervous system. Learning Outcomes: Discuss the neurotransmitters involved in the autonomic nervous system and their roles in mediating responses on target organs and tissues Apply the knowledge of the autonomic nervous system to real life scenarios or clinical scenarios. Nervous System a complex network of specialized cells that transmit information throughout the body. responsible for controlling and coordinating all bodily functions and processes. Nervous System Central Nervous System (CNS) brain and spinal cord Peripheral Nervous System (PNS) all nerves outside CNS Central Nervous System (CNS) central processing unit of the nervous system integrating and coordinating sensory information and motor commands. brain thoughts, emotions, and behaviors, spinal cord a pathway for nerve signals between the brain and the rest of the body. Peripheral Nervous System (PNS) consists of all the nerves that branch out from the CNS to connect it with other parts of the body muscles, organs, and sensory receptors. Divided into: somatic nervous system autonomic nervous system Somatic Nervous System (SNS) controls voluntary movements and carries sensory information from the body's sensory receptors to the CNS. enables us to interact with our environment and consciously control our skeletal muscles. Autonomic Nervous System (ANS) regulates involuntary functions heart rate, digestion, breathing, and glandular activity. sympathetic parasympathetic work in opposition to maintain homeostasis in the body. Somatic and Autonomic Nervous System Organization of the SNS and ANS  Divisions of the ANS 1. Sympathetic division activated in times of stress, danger, or excitement. "fight or flight" stimulate tissue metabolism and increase alertness increasing heart rate, dilating the airways, redirecting blood flow to muscles, and releasing adrenaline  Divisions of the ANS 2. Parasympathetic division responsible for promoting activities that occur during periods of rest, relaxation, and normal bodily functions "rest and digest"  Divisions of the ANS Two divisions may work independently and most often have opposing effects. Two divisions may work together, with each controlling one stage of a complex process. Overall Organization of the Sympathetic Division Sites of Ganglia in Sympathetic Pathways Sites of Ganglia in Sympathetic Pathways  Sympathetic Varicosities specialized structures found along sympathetic nerve fibers sites of neurotransmitter release play a crucial role SNS enabling widespread and diffuse communication with target cells in the sympathetic nervous system. Sympathetic Varicosities Sympathetic pre-ganglionic neurons release acetylcholine (ACh) at synapses with ganglionic neurons Cholinergic synapses always excitatory release of acetylcholine stimulates the postganglionic neurons to propagate action potentials norepinephrine (noradrenaline) as the primary neurotransmitter at the specific target Sympathetic Varicosities The synaptic terminals form a branching network, resembling a string of pearls Each pearl is packed with neurotransmitter vesicles Varicosity How are norepinephrine and epinephrine synthesized and released? NE and Epinephrine activate adrenergic receptors (α and β receptors, both are G protein‐coupled receptors (GPCRs). How are norepinephrine and epinephrine synthesized and released? Norepinephrine (NE) and epinephrine synthesized from the amino acid tyrosine in a series of enzymatic reactions within the adrenal medulla and sympathetic nerve terminals. Tyrosine is converted to dopamine by the enzyme tyrosine hydroxylase. Dopamine is then converted to norepinephrine by the enzyme dopamine beta-hydroxylase. Norepinephrine can be further converted to epinephrine by the enzyme phenylethanolamine N-methyltransferase. Once synthesized, norepinephrine and epinephrine are stored in vesicles within the nerve terminals. How are norepinephrine and epinephrine synthesized and released? Upon stimulation of the sympathetic nervous system, action potentials trigger the release of norepinephrine or epinephrine into the synaptic cleft. Norepinephrine or epinephrine released from the nerve terminals binds to adrenergic receptors on target cells, initiating physiological responses. After exerting their effects, norepinephrine and epinephrine can be taken back up into the nerve terminals for recycling or degraded by enzymes like monoamine oxidase (MAO) and catechol-O-methyltransferase (COMT).  Basic Mode of Operations of GPCRs G protein-coupled receptors (GPCRs) are a large and diverse family of cell surface receptors that play a crucial role in signal transduction in cells.  Basic Mode of Operations of GPCRSs In the inactive state, the α subunit of the G‐protein binds GDP. When activated by a GPCR, the GDP is exchanged for GTP. The activated G‐protein splits, both Gα and Gβγ activate effector proteins Gα slowly removes phosphate from GTP, terminating the activity.  2 Main Classes of Adrenergic Receptors Alpha-adrenergic receptors: α1(most common) Gq/11 family of G proteins is involved in signaling pathways mediated by certain G protein-coupled receptors (GPCRs) activation of Gq/11 proteins leads to the activation of phospholipase C (PLC), which in turn cleaves phosphatidylinositol 4,5-bisphosphate (PIP2) into inositol trisphosphate (IP3) and diacylglycerol (DAG). release of intracellular calcium ions; excitatoryeffect on the target cell.  Opposite Effects of β and α2 receptors Alpha-adrenergic receptors: α2: Binding of norepinephrine to the α2 receptor activates Gi, which inhibits adenylyl cyclase Beta receptors: β1‐3: Binding of norepinephrine to the β receptor activates Gs, which in turn activates adenylyl cyclase to generate cAMP for PKA activation. Organization of the Parasympathetic Division of ANS Distribution of Parasympathetic Innervation Parasympathetic Stimulation and ACh Release All parasympathetic neurons release ACh as a neurotransmitter. Effects varies widely, depending the types of receptors (nicotinic or muscarinic receptors) and the nature of second messenger Nicotinic receptors: works by opening chemically gated channels in the membrane ganglionic cells both parasympathetic and sympathetic ACh short live excitation of the ganglionic neuron or target Parasympathetic Stimulation and ACh Release Muscarinic receptors: GPCRs in the parasympathetic division stimulation produces longer lasting effects than nicotinic receptors. response can be excitatory or inhibitory Anatomical Differences between Two ANS Divisions Sympathetic division widespread impact Parasympathetic division innervates visceral structures Some organs are innervated by just one division, but most receive dual innervation  Summary SNS includes voluntary movement of the muscles and organs, while ANS makes routine and unconscious homeostatic adjustment in physiological systems. The sympathetic division consists of short preganglionic neurons (ACh) and long ganglionic neurons (NE/E) involved in using energy and increasing metabolic rates. The parasympathetic division consists of long preganglionic neurons (ACh) and short ganglionic neurons (ACh) involved in conserving energy and lowering metabolic rate. References QUESTIONS? Email: [email protected] Office No. 39179433