Biology 223 Autonomic Nervous System PDF

# Biology 223 ## Autonomic Nervous System ### Chapter 16: Overview of the ANS - The sympathetic division - The parasympathetic division ### Functional Organization of the Nervous System - **Central Nervous System** - Brain and Spinal Cord - **Peripheral Nervous System** (peripheral nerves and...

# Biology 223 ## Autonomic Nervous System ### Chapter 16: Overview of the ANS - The sympathetic division - The parasympathetic division ### Functional Organization of the Nervous System - **Central Nervous System** - Brain and Spinal Cord - **Peripheral Nervous System** (peripheral nerves and ganglia) - **Afferent sensory system** - General & special senses - **Efferent motor system** - Somatic nervous system controlling skeletal muscles - Autonomic nervous system controlling smooth muscles, cardiac muscles, glands ### Autonomic Nervous System (ANS) - Operates without conscious control via reflex centers in spinal cord & brainstem controlled by **hypothalamus** - Regulated by higher brain centers that affect the hypothalamus - Limbic system, thalamus, cerebral cortex - Coordinates processes that maintain homeostasis - cardiovascular, respiratory, digestive, urinary, reproductive etc. ### Divisions of the ANS - **Sympathetic division** - Expenditure of energy - Dominant under conditions of physical or emotional stress ("Fight or flight responses") - **Parasympathetic division** - Conserve and restore body energy, rest and recovery - Dominant control during rest ### Effectors with dual innervation = opposing sympathetic & parasympathetic effects - Heart - Sympathetic increases heart rate, Parasympathetic decreases heart rate - Pupils - Sympathetic dilates pupils, Parasympathetic constricts pupils - Digestive tract - Symp. decreases motility and secretions, Parasymp. increases - Bronchioles - Sympathetic dilates airways, Parasympathetic constricts airways ### Effectors with single innervation - **Effectors with sympathetic input only** - Sweat glands (increased secretion) - Arrector pili muscles (contraction) - Blood vessels of skeletal muscle, heart, lungs, brain (dilation) - Blood vessels of digestive viscera and kidney (constriction) - **Effectors with parasympathetic input only** - Lacrimal glands (increased secretion) ### Structure of the ANS Efferent pathway is two neuron pathway 1. Motor neurons in CNS send axons (preganglionic) to synapse on motor neurons in autonomic ganglia in PNS 2. Motor neurons in autonomic ganglia (ganglionic cells) send axons (postganglionic axons) to synapse on effector ### Differences between structure of sympathetic and parasympathetic - **Sympathetic (Thoraco-lumbar division)** - Preganglionic cell body in lateral horn of spinal cord segments T1-L2 - Preganglionic axon typically shorter - Ganglion typically closer to CNS - Sympathetic chain ganglia - Collateral ganglia - Adrenal medulla - **Parasympathetic (Cranio-sacral division)** - Preganglionic cell body in nuclei of CN III, VII, IX, X and lateral horn of spinal cord segments S2, S3, S4 - Preganglionic axon typically longer - Ganglion typically near or in effector organ, so postganglionic axon is short ### Organization and anatomy of the sympathetic division - SC segments T1-L2 - ventral roots contain preganglionic axons - Some axons synapse on cells of chain ganglia - Some axons pass through going to collateral ganglia and adrenal medulla ### Sympathetic division #### Thoraco-lumbar division of ANS - **Sympathetic chain ganglia** - 2 Chains of ganglia - one on each side of the vertebral column - Innervate head, body wall, limbs, and viscera of thoracic cavity (heart, lungs) ### Sympathetic division #### Thoraco-lumbar division of ANS - **Collateral ganglia** - Located close to large abdominal arteries - Celiac, superior mesenteric, inferior mesenteric ganglia - Preganglionic pass through chain ganglia and form splanchnic nerves to reach collateral ganglia - Innervate abdominal and pelvic viscera - Sympathetic activation decreases blood flow, decreased digestive activity, and releases stored energy molecules ### Sympathetic division #### Thoraco-lumbar division of ANS - **Adrenal medulla** - Central portion of the adrenal gland - Preganglionic fibers pass through chain ganglia and splanchnic nerve to celiac ganglia passes through to reach adrenal gland - Postganglionic cells in adrenal medulla are modified neurons that secrete into blood rather than onto effector ### Parasympathetic division #### Cranio-sacral division of ANS - Preganglionic neurons in the brainstem and sacral segments of spinal cord - Ganglionic neurons in peripheral ganglia located near or within target organs - Effects produced by the parasympathetic division include relaxation, food processing, energy absorption ### Organization and anatomy of the parasympathetic division - SC segments S2, S3, S4 - Pelvic nerves carry preganglionic axons to parasympathetic. intramural ganglia located in wall of viscera in inferior portion of abdominal pelvic cavity - Short postganglionic axon innervate effectors ### Organization and anatomy of the parasympathetic division - Cranial nerve III (Oculomotor) - parasympathetic control of pupil and lens - Cranial nerve VII (Facial) - lacrimal and salivary glands - Cranial nerve IX (Glossopharyngeal) - salivary glands - Cranial nerve X (Vagus) - Carries 75% of all parasympathetic output - Parasympathetic control of heart, lungs, digestive tract and all other thoracic and abdominal viscera, except most inferior portions ### Autonomic Activation Sympathetic & parasympathetic divisions are activated by different stimuli. ### Sympathetic Activation Has widespread effect on body due to: - Sympathetic innervation is through out body and has systemic effects. - Each preganglionic axon branches to synapse onto 24 or more ganglionic cells - Adrenal medulla releases mostly **epinephrine**, but some norepinephrine, into blood stream affecting tissues not innervated by ANS ### Parasympathetic Activation Has localized effect - Innervation limited to head and viscera, does not innervate body wall, skin - Each preganglionic axon branches to synapse on to only 6-8 ganglionic cells - Less divergent than the sympathetic. - Postganglionic axons generally go to a single effector ### Neurotransmitter release and effects on target organs and tissues - Synapse of preganglionic axon onto ganglionic cell in autonomic ganglion - Neurotransmitter is ACh in both sympathetic and parasympathetic ganglia - Synapse of postganglionic axon to effector - All parasympathetic postganglionic axons release ACh onto effectors - Sympathetic postganglionic axons to dual innervated viscera release NE onto effectors ### Neurotransmitters of ANS - Postsynaptic receptor properties determines effect of neurotransmitter on postsynaptic cell - Many neurotransmitters have more than one type of post synaptic receptor ### Cholinergic Synapses post synaptic receptors - Nicotinic cholinergic receptors - Skeletal muscles, autonomic ganglia - Excitatory - Muscarinic cholinergic receptors - excitatory or inhibitory - Visceral muscles, cardiac muscle, CNS ### Adrenergic Synapses post synaptic receptors - Alpha (a) adrenergic receptors - Alpha-1: Excitatory effect on smooth muscles of blood vessels of skin & viscera, causes constriction - Alpha-2: Inhibitory effects on digestion tract - Beta (B) adrenergic receptors - Beta-1: excitatory on cardiac muscle - Beta-2: inhibitory on smooth muscles of respiratory tract, causes relaxation - Beta-3: excitatory effects on adipocytes, releases lipids to blood stream ### Neurotransmitters and Sympathetic function Sympathetic postganglionic axons to: - viscera that have dual innervation:(release norepinephrine (NE) onto effectors (adrenergic synapses) - viscera that receive only sympathetic input:(release NE or ACh or NO onto effectors - Sympathetic postganglionic cells of adrenal medulla (release epinephrine (E) and norepinephrine (NE) into the blood stream ### Neurotransmitters and sympathetic function - Sympathetic postganglionic NE axons end in branching network with multiple varicosities filled with neurotransmitter - Removal of NE after release is slower - Reuptake and reuse - Breakdown by monoamine oxidase (MAO) and catechol-O-methyltransferase (COMT) in surrounding tissue and in liver ### Adrenergic Synapses post synaptic receptors - NE stimulates a receptors more than ẞ receptors - E stimulates both a and ẞ receptors - Localized sympathetic activity from NE release at varicosities - primarily affects & receptors near the active varicosities - Generalized sympathetic activity and release of E by adrenal medulla - affect Ot and ẞ receptors through out body ### Alpha Adrenergic Receptors activated by both NE & E - Alpha 1 (α1) - excitatory - Found through out body - Examples of effects - Constriction of peripheral BV - Closure of sphincters along digestive tract - Alpha 2 (α2)-inhibitory - Directly counteracts parasympathetic innervation of digestive viscera - Examples of effects: IPSP's by causeing a reduction in CAMP - Reduces motility and secretions in Gi tract ### Beta Adrenergic Receptors activated by E more than NE - Beta 1 (β1) - excitatory - Heart, kidney, adipose tissue - Examples of effects - Increase heart rate & force of contraction - Beta 2 (β2)-inhibitory - Bronchioles, BV of heart & skeletal muscle - Examples of effects - Increased blood flow in heart & skeletal muscle - Dilation of airways for increased respiration ### Pharmacology and the ANS - Propranolol (beta-1 and beta-2 blocker) - Metroprolol (beta-1 specific blocker) - Albuterol (beta-2 specific agonist) - Nicotine (nicotinic cholinergic agonist) - Atropine (muscarinic cholinergic blocker) ### Dual Innervations | Effector Organ | Receptor Type and Sympathetic Effect | Receptor Type - Parasymp. Effect | |---|---|---| | Eyes (Iris Muscle) | Alpha 1-Contracts Beta 1 | MC.-Contracts (small) | | Heart (SA Node) | Alpha 1 Beta 2-dilates | M.C.- Decreases heart rate | | Arterioles (coronary) | Alpha 1-Increases Beta 2-dilates | MG.-Dilates | | Bronchiole Muscles | Beta 2-Relax (dilates) | MC- Constricts (contract) | ### Sympathetic Only | Effector Organ | Receptor Type and Sympathetic Effect | Receptor Type - Parasymp. Effect | |---|---|---| | Kidneys | Beta 1 - Increase Secretion α1 & Beta 1- gluconeogenesis | None | | Skin (Smooth muscle of BV) | Alpha 1-constricts | None | | Skin (Arrector pili Muscles) | Alpha 1-contracts | None | ### Integration and Control of Autonomic Functions - Operates without conscious control via reflex centers in autonomic ganglia, spinal cord, and brainstem - Reflex centers are controlled by **hypothalamus** - Regulated by higher brain centers that affect the hypothalamus - Limbic system, thalamus, cerebral cortex ### Integration and Control of Autonomic Functions #### Autonomic Tone - Background level of activity - Activation of sympathetic and/or parasympathetic input can increase or decrease activity - Examples - Heart rate-dual innervation - Blood vessel diameter - sympathetic innervation only ### Integration and Control of Autonomic Visceral reflexes Functions - Afferent input from sensory receptor/neuron - Processing center with one or more interneurons - Efferent pathway to effectors #### Reflex processing centers - Short reflexes (occur in autonomic ganglia) - Long reflexes (occur in CNS) ### Short reflexes - Bypass the CNS entirely - Involve sensory neurons and interneurons with cell bodies located in the autonomic ganglia, control ganglionic motor neurons - Typically control very simple motor responses with localized effects whereas long reflexes coordinate activity of an entire organ ### Short reflexes (Enteric Nervous System) - Extensive network of intramural ganglia and nerve networks in walls of digestive tract - Influenced by sympathetic and parasympathetic input but many complex visceral reflexes are initiated and coordinated locally without instructions from CNS ### Long reflexes - Autonomic equivalent of polysynaptic reflexes in somatic system - Sensory input - Visceral sensory neurons such as chemoreceptors, baroreceptors, etc. - General senses such as pain, touch, temperature, etc. - Special senses (smell, taste, vision, etc.) - Processing steps involve interneurons with in CNS ### Integration and Control of Autonomic Functions - Simple reflexes in SC provide relatively rapid and stereotypic responses to stimuli - Processing centers in medulla and pons provide more complex sympathetic and parasympathetic reflexes - Cardiovascular - Digestive secretions - Salivation - Swallowing - Peristalsis - Urinary function ### Medulla Oblongata and Pons ### Autonomic reflexes-Parasympathetic - Typically affect individual organs/systems reflecting the relatively specific, restricted pattern of parasympathetic innervation - Defecation reflex - Urination reflex - Direct light and consensual light reflex - Swallowing reflex - Coughing reflex - Baroreceptor blood pressure reflex - Sexual arousal ### Autonomic reflexes-Sympathetic - Some affect individual organs - Cardioacceleratory reflex - Vasomotor reflex - Pupil dilation reflex - Ejaculation of semen - Sympathetic division typically activated as a whole - release of NE and E as hormones produces widespread long lasting peripheral effects ### Higher levels of autonomic control - Reflex centers are subject to regulation by **hypothalamus** - Hypothalamus interacts with all other portions of the brain - Activity in the limbic system, thalamus, cerebral cortex effect autonomic function - biofeedback ### Hypothalamus - Controls autonomic function - Regulates body temperature - Coordinates circadian cycles of activity - Produces emotions and behavioral drives - Coordination of voluntary, emotional, and autonomic functions - Coordinates activities of the endocrine and nervous systems - Secretes hormones