2024-25 Autonomic Nervous System 1-2 PDF

Physiology School of Medicine Founded in 1845 2024-25 AUTONOMIC NERVOUS SYSTEM 1-2 Course: MD137 Principles of Lecturer: Professor AM Wheatley Physiology...

Physiology School of Medicine Founded in 1845 2024-25 AUTONOMIC NERVOUS SYSTEM 1-2 Course: MD137 Principles of Lecturer: Professor AM Wheatley Physiology Email: [email protected]  Autonomic nervous system (ANS) The sweating sunbather lying quietly on the beach The racing heart and “hair-standing on end” sensation one feels at a horror movie What do these responses have in common?  Autonomic nervous system (ANS) The sweating sunbather lying quietly on the beach The racing heart and “hair-standing on end” sensation one feels at a horror movie What do these responses have in common? Examples of body responding automatically to physical and emotional environment Actions occur without conscious action – autonomic nervous system (ANS) Autonomic: “self” “law”  Autonomic nervous system (ANS) Functions of the ANS Maintaining homeostatic conditions within the body Coordinating the body’s responses to exercise and stress Assisting the endocrine system to regulate reproduction  Autonomic nervous system (ANS) Functions of the ANS Maintaining homeostatic conditions within the body Coordinating the body’s responses to exercise and stress Assisting the endocrine system to regulate reproduction ANS exerts its activity by regulating the functions of the involuntary organs: -heart -blood vessels -exocrine glands (secrete substances onto an epithelial cell surface by way of a duct) -visceral organs  Autonomic nervous system (ANS) The autonomic nervous system (ANS) is divided into 3 divisions -sympathetic -parasympathetic -enteric (see GI System module, semester 2) The sympathetic and parasympathetic divisions of the ANS are the major efferent pathways controlling target organs other than skeletal muscle  Autonomic nervous system (ANS) Sympathetic division An increase in output of the sympathetic division occurs during: -stress -anxiety -physical activity -fear -excitement -use of metabolic resources  Autonomic nervous system (ANS) Sympathetic division An increase in output of the sympathetic division occurs during: -stress -anxiety -physical activity -fear -excitement -use of metabolic resources Fight or flight response!  Autonomic nervous system (ANS) Parasympathetic division An increase in output of the parasympathetic division occurs during: -sedentary activity -eating -restoration of the body’s reserves -elimination of waste products  Autonomic nervous system (ANS) Parasympathetic division An increase in output of the parasympathetic division occurs during: -sedentary activity -eating -restoration of the body’s reserves -elimination of waste products Rest and digest!  NERVOUS(SYSTEM Central(nervous( Peripheral( system nervous(system Somatic Brain Spinal( Autonomic( nervous( cord nervous(system system Sympathetic( Parasympathetic nervous(system nervous(system  NERVOUS(SYSTEM Central(nervous( Peripheral( system nervous(system Somatic Brain Spinal( Autonomic( nervous( cord nervous(system system Sympathetic( Parasympathetic nervous(system nervous(system  Autonomic nervous system (ANS) Enteric nervous system The enteric division of the ANS is a system of neurons that form a networks (plexuses) that surround the GI tract It can function as a separate and independent nervous system but normally it is controlled by the sympathetic and parasympathetic nervous systems. (The enteric nervous system will be dealt with in the GI module (MD124) in semester 2)  Neurons Neuron: A nerve cell (axon) that sends and receives electrical signals over long distances within the body Afferent neurons: convey information from tissues/organs to the CNS (sensory receptor at end) Efferent neurons: convey information from the CNS from the to the tissues/organs Interneurons: connects neurons within the CNS  Neurons Neuron: A nerve cell (axon) that sends and receives electrical signals over long distances within the body Afferent neurons: convey information from tissues/organs to the CNS (sensory receptor at end) Efferent neurons: convey information from the CNS from the to the tissues/organs Interneurons: connects neurons within the CNS  Neurons Neuron: A nerve cell (axon) that sends and receives electrical signals over long distances within the body Afferent neurons: convey information from tissues/organs to the CNS (sensory receptor at end) Efferent neurons: convey information from the CNS from the to the tissues/organs Interneurons: connects neurons within the CNS  Somatic nervous system The somatic nervous system contains -sensory pathway (afferent) from the skin, muscle, joints to the CNS, special senses to CNS (sight) -motor pathway (efferent) from the CNS to muscles Efferent division of the peripheral nervous system Somatic nervous system ACh The efferent pathway in the somatic nervous system is made up of nerve fibres going directly from the CNS to the skeletal muscle cells (motor neuron) The neurotransmitter released from the nerve endings is acetylcholine The acetlycholine receptor is nicotinic  Efferent division of the peripheral nervous system Autonomic nervous system (ANS) The efferent pathway in the autonomic nervous system is made up of 2 neurons in series that connect the CNS and the effector cells The first neuron comes from the CNS and forms a connection with the second neuron in structure called a ganglion (preganglionic neuron) 1 Synapse 2 The second neuron connect the first neuron with the effector cells (postganglionic neuron) The connection between the 2 neurons in the ganglion is called a synapse Synapses are also present between neurons and the effector organ Synapse A synapse is an anatomically specialised junction between 2 neurons – in which 2 neurons are physically not chemically separated from each other by a space called the synaptic cleft The synapse includes parts of the presynaptic and postsynaptic neurons and the cleft Signals are transmitted across the synaptic cleft by a chemical messenger called a neurotransmitter Transmitter is stored in the presynaptic cell while the receptor for the neurotransmitter is on the postsynaptic cell  Efferent division of the peripheral nervous system Autonomic nervous system (ANS) The efferent pathway in the autonomic nervous system is made up of 2 neurons in series that connect the CNS and the effector cells The first neuron comes from the CNS and forms a connection with the second neuron in structure called a ganglion (preganglionic neuron) 1 Synapse 2 The second neuron connect the first neuron with the effector cells (postganglionic neuron) The connection between the 2 neurons in the ganglion is called a synapse Synapses are also present between neurons and the effector organ  Neurotransmitters in the autonomic nervous system Figure 6.46 ACh nicotinic Parasympathetic Preganglionic-postganglionic : acetylcholine (ACh) released and binds to acetylcholine receptor -acetylcholine receptor type: nicotinic  Nicotinic acetylcholine receptors Ionotropic receptor - when activated, directly affects the activity of a cell by opening ion Ligand-gated channel channels (ligand-gated channels) when activated – increased ligand permeability to Na+ and K+ rapid depolarisation of the postganglionic neuron ligand There are 2 types of nicotinic receptors -muscle type (neuromuscular junction) -ganglionic type (ANS ganglia) Rhoades & Bell 3rd Ed, Fig 3.3,p40  Neurotransmitters in the autonomic nervous system Figure 6.46 ACh nicotinic Parasympathetic Preganglionic-postganglionic : acetylcholine (ACh) released and binds to acetlylcholine receptor -acetlycholine receptor type: nicotinic  Neurotransmitters in the autonomic nervous system Figure 6.46 ACh nicotinic Parasympathetic Preganglionic-postganglionic : acetylcholine (Ach) released and binds to acetylcholine receptor -acetylcholine receptor type: nicotinic Nicotinic receptor ligand-gated ion channel (ionotropic) activated by ACh (or nicotine) when activated – increased permeability to Na+ and K+ rapid depolarisation of the postganglionic neuron  Neurotransmitters in the autonomic nervous system Figure 6.46 ACh muscarinic nicotinic Parasympathetic Preganglionic-postganglionic : acetylcholine (Ach) released and binds to acetylcholine receptor -acetylcholine receptor type: nicotinic Postganglionic-effector cell: acetylcholine -acetylcholine receptor type: muscarinic  Acetylcholine muscarinic receptor There are 5 types of muscarinic receptors: M1, M2, M3, M4, M5 M1, M4 & M5: : found in the CNS M2 (inhibitory): found in heart, stimulation slows heart rate M3 (excitatory) : found in smooth muscles and glandular tissues - smooth muscle in bronchi (respiratory tract) and GI tract: contraction - smooth muscle in bladder: contraction - pupil: constriction (get smaller) – response to bright light - secretion of glands (increased): salivary glands, sweat glands, mucous glands in the respiratory and GI tract Stimulation of vascular smooth muscle contraction Taken from MD121 Cardiovascular System Stimulation of vascular smooth muscle contraction Voltage-gated channel Taken from MD121 Cardiovascular System Stimulation of vascular smooth muscle contraction Ligand-gated channel Inotropic receptor Taken from MD121 Cardiovascular System  Stimulation of vascular smooth muscle contraction Metabotropic receptor G proteins: a family of proteins that couple cell surface receptors to intracellular signalling pathways Taken from MD121 Cardiovascular System  Metabotropic receptor A metabotropic receptor is a type of receptor found on the surface of cells, that is involved in cellular signalling through a second messenger system rather than directly controlling ion channels Metabotropic receptors are typically G protein-coupled receptors When a neurotransmitter or other signalling molecule binds to a metabotropic receptor, it triggers the activation of G proteins inside the cell. These G proteins influence various intracellular signalling pathways, involving the production of second messengers: - cyclic AMP (cAMP) - inositol trisphosphate (IP₃) - diacylglycerol (DAG) These second messengers can modulate a variety of cellular processes Metabotropic receptors tend to produce slower but longer-lasting effects compared to ionotropic receptors.  Metabotropic receptor Type of membrane receptors that acts through a second messenger The signal transduction mechanism is often mediated by G-protein coupled receptor G-protein types: STIMULATORY -Gas: stimulates production of cAMP (from ATP) -Gaq/11: activates phospholipase C (PLC) which then cleaves PIP2 (a minor membrane phosphoinositol) into two second messengers, IP3 and diacylglycerol (DAG) INHIBITORY Gai: inhibits production of cAMP The acetylcholine muscarinic receptor is a metabotropic receptor  Neurotransmitters in the autonomic nervous system Figure 6.46 ACh muscarinic nicotinic Parasympathetic Preganglionic-postganglionic : acetylcholine (Ach) released and binds to acetylcholine receptor -acetylcholine receptor type: nicotinic Postganglionic-effector cell: acetylcholine -acetylcholine receptor type: muscarinic  Neurotransmitters in the autonomic nervous system Figure 6.46 Sympathetic Preganglionic-postganglionic : acetylcholine (Ach) released and binds to acetlycholine receptor -acetlycholine receptor type: nicotinic ACh NA Ach receptor adrenergic (nicotinic) receptor  Neurotransmitters in the autonomic nervous system Figure 6.46 Sympathetic Preganglionic-postganglionic : acetylcholine (Ach) released and binds to acetlycholine receptor (nicotinic) -acetlycholine receptor type: nicotinic Postganglionic-effector cell: noradrenaline (norepinephrine) -adrenergic receptor ACh NA Ach receptor adrenergic (nicotinic) receptor  Sympathetic – adrenal medulla Figure 6.46 One set of postganglionic sympathetic neurons never develops into a neuron- instead they form an endocrine organ – the adrenal medulla Preganglionic-adrenal medulla : acetylcholine (Ach) released and binds to acetylcholine receptor The adrenal medulla contains the hormone adrenaline (epinephrine) which is released into the bloodstream Adrenaline is transported to the effector organ where it binds to adrenergic receptors ACh Ach receptor adrenergic (nicotinic) A receptor Adrenal medulla The adrenal medulla Neuroendocrine gland (inner core of the adrenal gland) Cells innervated by preganglionic sympathetic fibres Fibres terminate on chromaffin cells (modified ganglionic cells) Chromaffin cells synthesise both adrenaline and noradrenaline in a ratio of 8:1 and stores them in secretory vesicles Adrenaline is a hormone When stimulated, the chromaffin cells release adrenaline (mostly) into the blood stream Adrenaline mimics the action of sympathetic stimulation at both α-adrenergic and β- adrenergic receptors Adrenaline can also stimulate adrenergic receptors on cells that receive little or no direct sympathetic innervation (eg, liver and adipose cells for mobilizing glucose and fatty acids)  Sympathetic – adrenal medulla Figure 6.46 One set of postganglionic sympathetic neurons never develops into a neuron- instead they form an endocrine organ – the adrenal medulla Preganglionic-adrenal medulla : acetylcholine (Ach) released and binds to acetylcholine receptor The adrenal medulla contains the hormone adrenaline (epinephrine) which is released into the bloodstream Adrenaline is transported to the effector organ where it binds to adrenergic receptors ACh Ach receptor adrenergic (nicotinic) A receptor Adrenal medulla  Sympathetic – adrenergic receptors Figure 6.46 There are 2 main families of adrenergic receptors èAlpha-adrenergic (α-adrenergic) èBeta-adrenergic (β-adrenergic) adrenergic receptor α-adrenergic β- adrenergic  Figure 6.46 α-adrenergic vs β-adrenergic stimulation Both α-adrenergic and β-adrenergic receptors are found in blood vessel walls Stimulation of α-adrenergic receptors causes vasoconstriction (reduced blood flow) A α α α adrenergic Ach receptor ACh receptor (nicotinic)  Figure 6.46 α-adrenergic vs β-adrenergic stimulation Both α-adrenergic and β-adrenergic receptors are found in blood vessel walls Stimulation of β-adrenergic receptors causes vasodilation A β β adrenergic Ach receptor ACh receptor (nicotinic)  Figure 6.46 α-adrenergic vs β-adrenergic stimulation Both α-adrenergic and β-adrenergic receptors are found in blood vessel walls Stimulation of β-adrenergic receptors causes vasodilation Thus, adrenaline will cause vasoconstriction of blood vessels in some organs and vasodilation in others Adrenergic receptor A Ach receptor ACh α-adrenergic β-adrenergic (nicotinic)  Figure 6.46 α-adrenergic vs β-adrenergic stimulation Thus, adrenaline will cause vasoconstriction of blood vessels in some organs and vasodilation in others -vasoconstriction: skin, kidneys (α-adrenergic receptors) -vasodilation: cardiac (heart) muscle, skeletal muscle (β-adrenoreceptors) β? A Ach receptor ? adrenergic ACh (nicotinic) α receptor  Figure 6.46 α-adrenergic vs β-adrenergic stimulation Thus, adrenaline will cause vasoconstriction of blood vessels in some organs and vasodilation in others -vasoconstriction: skin, kidneys (α-adrenergic receptors) -vasodilation: cardiac (heart) muscle, skeletal muscle (β-adrenoreceptors) A adrenergic Ach receptor ACh (nicotinic) α receptor  Figure 6.46 α-adrenergic vs β-adrenergic stimulation Thus, adrenaline will cause vasoconstriction of blood vessels in some organs and vasodilation in others -vasoconstriction: skin, kidneys (α-adrenergic receptors) -vasodilation: cardiac (heart) muscle, skeletal muscle (β-adrenoreceptors) β A adrenergic Ach receptor ACh receptor (nicotinic) Sympathetic stimulation: high ⍺-adrenergic receptor density - SM contraction ⍺-adrenergic receptor β-adrenergic receptor Sympathetic stimulation: high ⍺-adrenergic receptor density - SM contraction ⍺-adrenergic receptor β-adrenergic receptor Sympathetic stimulation: high ⍺-adrenergic receptor density - SM contraction ⍺-adrenergic receptor β-adrenergic receptor Sympathetic stimulation: high β-adrenergic receptor density - SM relaxation  Adrenoceptors (adrenergic receptors) Figure 6.46 Alpha-adrenergic (-adrenergic) - alpha1 (α1) - contraction of smooth muscle in blood vessels - alpha2 (α2) - preganglionic nerve ending – inhibits NE release Beta-adrenergic (β-adrenergic) -beta1 (β1) - cardiac muscle contraction -beta2 (β2) - relaxation of smooth muscle in blood vessels adrenergic receptor  Heart rate control by the autonomic nervous system Frequently stimulation by the sympathetic and parasympathetic systems have opposite effects A good example of this is the control of heart rate (the frequency with which the heart beats)  Heart rate control by the autonomic nervous system The site of heart rate control in the heart is found in the atria (sino-atrial node, SA node) The SA node is innervated by both parasympathetic and sympathetic fibres Parasympathetic stimulation…………………………………… Sympathetic stimulation………………………………………….  Heart rate control by the autonomic nervous system The site of heart rate control in the heart is found in the atria (sino-atrial node, SA node) The SA node is innervated by both parasympathetic and sympathetic fibres Parasympathetic stimulation decreases heart rate Sympathetic stimulation increases heart rate Downloaded from: StudentConsult (on 22 November 2010 01:56 PM) © 2005 Elsevier Downloaded from: StudentConsult (on 22 November 2010 01:56 PM) © 2005 Elsevier Downloaded from: StudentConsult (on 22 November 2010 01:56 PM) © 2005 Elsevier α1: effector organ α2: preganglionic nerve ending – inhibits NE release β1: cardiac (effector organ) β2: blood vessels, liver (effector) Downloaded from: StudentConsult (on 22 November 2010 01:56 PM) © 2005 Elsevier  Adrenergic receptor signalling Receptor G protn Stimulatory/ IC messenger Action Inhibitory Alpha(α)1 adrenergic : Gq Stimulatory éIP3/DAG éSM contractn Beta(β) 1 or 2 adrenergic : Gs Stimulatory écAMP éheart muscle contractn ésmooth muscle relaxn  Adrenergic receptor signalling Receptor G protn Stimulatory/ IC messenger Action Inhibitory Alpha(α)1 adrenergic : Gq Stimulatory éIP3/DAG éSM contractn Beta(β) 1 or 2 adrenergic : Gs Stimulatory écAMP éheart muscle contractn ésmooth muscle relaxn (Cardiac muscle and vascular smooth muscle contraction and relaxation will be dealt with in the CVS module (MD121) in semester 2) α1: effector organ α2: preganglionic nerve ending – inhibits NE release β1: cardiac (effector organ) β2: blood vessels, liver (effector) Downloaded from: StudentConsult (on 22 November 2010 01:56 PM) © 2005 Elsevier Exception to the rule: Sympathetic stimulation of sweat gland is mediated by postganglionic fibres that release ACh that binds to a muscaric receptors Downloaded from: StudentConsult (on 22 November 2010 01:56 PM) © 2005 Elsevier Note 1. The sudomotor is a branch of the SNS that innervates sweat glands – postsynaptic transmitter is ACh. ACh stimulates the production of sweat (cooling by evaporation). Components of sweat (nitric oxide [NO]) elicit a vasodilation in the local skin Exception to the rule: Sympathetic stimulation of sweat gland is mediated by postganglionic fibres that release ACh that binds to a muscaric receptors Downloaded from: StudentConsult (on 22 November 2010 01:56 PM) © 2005 Elsevier Downloaded from: StudentConsult (on 22 November 2010 01:56 PM) © 2005 Elsevier  Adrenoceptors (adrenergic receptors) Figure 6.46 Alpha-adrenergic (-adrenergic) - alpha1 (α1) - contraction of smooth muscle in blood vessels - alpha2 (α2) - preganglionic nerve ending – inhibits NE release Beta-adrenergic (β-adrenergic) -beta1 (β1) - cardiac muscle contraction -beta2 (β2) - relaxation of smooth muscle in blood vessels adrenergic receptor Sympathetic: thoracic (chest) and lumbar (back) regions of the spinal cord  Most of the sympathetic ganglia lie close to the spinal cord and form 2 chains of ganglia called the sympathetic trunk (Paravertebral sympathetic ganglia)  Most of the sympathetic ganglia lie close to the spinal cord and form 2 chains of ganglia called the sympathetic trunk (Paravertebral sympathetic ganglia) The sympathetic trunk forms an interconnected chain located on either side of the vertebral column – these ganglia extend above and below the thoracic and lumbar spinal regions  Most of the sympathetic ganglia lie close to the spinal cord and form 2 chains of ganglia called the sympathetic trunk Other sympathetic ganglia are in the abdominal cavity closer to the innervated organ (coeliac, superior mesenteric, inferior mesenteric ganglia)  Most of the sympathetic ganglia lie close to the spinal cord and form 2 chains of ganglia called the sympathetic trunk Other sympathetic ganglia are in the abdominal cavity closer to the innervated organ (coeliac, superior mesenteric, inferior mesenteric ganglia) Organisation of the sympathetic division The sympathetic nervous system is larger and more complex and innervates more structures than the parasympathetic nervous system The preganglionic cell bodies are located in the intermediolateral horn cells of the thoracic and upper lumbar segments of the spinal cord The axons exit the and enter the paravertebral sympathetic ganglia The post-ganglionic axons consist of multiple regions specialized for neurotransmitter release called varicosities Neurotransmitters are released from varicosities into the extracellular fluid where they diffuse the short distance to effector cells/receptors Varicosities enable a stimulated fiber to simultaneously release neurotransmitter in multiple areas of the effector organ, resulting in a greater coordinated impact on the organ Synapse A synapse is an anatomically specialised junction between 2 neurons – in which 2 neurons are physically not chemically separated from each other by a space called the synaptic cleft The synapse includes parts of the presynaptic and postsynaptic neurons and the cleft Signals are transmitted across the synaptic cleft by a chemical messenger called a neurotransmitter Transmitter is stored in the presynaptic cell while the receptor for the neurotransmitter is on the postsynaptic cell Organisation of the sympathetic division The sympathetic nervous system is larger and more complex and innervates more structures than the parasympathetic nervous system The preganglionic cell bodies are located in the intermediolateral horn cells of the thoracic and upper lumbar segments of the spinal cord The axons exit the and enter the paravertebral sympathetic ganglia The post-ganglionic axons consist of multiple regions specialized for neurotransmitter release called varicosities Neurotransmitters are released from varicosities into the extracellular fluid where they diffuse the short distance to effector cells/receptors Varicosities enable a stimulated fiber to simultaneously release neurotransmitter in multiple areas of the effector organ, resulting in a greater coordinated impact on the organ Organisation of the sympathetic division Axons of preganglionic neurons emerge from the spinal cord at the level of their cell bodies (T1 to T12 & L1 to L3) Most of the neurons enter the sympathetic paravertebral chain and synapse with one or more postganglionic neurons in the ganglia of the chain Some enter the chain and run up and down and synapse with other ganglia that form part of the chain Some preganglionic axons can pass through the chain without synapsing and go on to form the splanchnic nerves which synapse in the prevertebral ganglia (celiac, superior mesenteric, inferior mesenteric ganglia) Organisation of the sympathetic division Axons of preganglionic neurons emerge from the spinal cord at the level of their cell bodies bodies (T1 to T12 & L1 to L3) Most of the neurons enter the sympathetic paravertebral chain and synapse with one or more postganglionic neurons in the ganglia of the chain Some enter the chain and run up and down and synapse with other ganglia that form part of the chain Some preganglionic axons can pass through the chain without synapsing and go on to form the splanchnic nerves which synapse in the prevertebral ganglia (celiac, superior mesenteric, inferior mesenteric ganglia) Organisation of the sympathetic division Axons of preganglionic neurons emerge from the spinal cord at the level of their cell bodies Most of the neurons enter the sympathetic paravertebral chain and synapse with one or more postganglionic neurons in the ganglia of the chain Some enter the chain and run up and down and synapse with other ganglia that form part of the chain Some preganglionic axons can pass through the chain without synapsing and go on to form the splanchnic nerves which synapse in the prevertebral ganglia (superior mesenteric, inferior mesenteric ganglia) Organisation of the sympathetic division Axons of preganglionic neurons emerge from the spinal cord at the level of their cell bodies (short) Most of the neurons enter the sympathetic paravertebral chain and synapse with one or more postganglionic neurons in the ganglia of the chain Some enter the chain and run up and down and synapse with other ganglia that form part of the chain Some preganglionic axons can pass through the chain without synapsing and go on to form the splanchnic nerves which synapse in the prevertebral ganglia - celiac ganglion - superior mesenteric ganglion - inferior mesenteric ganglion Convergence and Divergence Convergence: Divergence: Convergence and Divergence Convergence: Many preganglionic axons (4-15) may synapse on a single post ganglionic neuron Stimulation by a single neuron is insufficient, summation is required for activation (fine control) Divergence: Convergence and Divergence Convergence: Many preganglionic axons (4-15) may synapse on a single post ganglionic neuron Stimulation by a single neuron is insufficient, summation is required for activation (fine control) Divergence: Relatively few preganglionic axons synapse with many post ganglionic neurons The ratio of pre- to post-ganglionic neurons may be 1:10 to 1:100 Numerical amplification allows for massive activation of multiple sympathetic targets under extreme conditions (eg, fight or flight response) Parasympathetic : brain stem and sacral portions of the spinal cord  Autonomic nervous system (ANS) An increase in output of the sympathetic division occurs during: -stress -anxiety -physical activity -fear -excitement - use of metabolic resources Fight or flight response!  Autonomic nervous system (ANS) An increase in output of the parasympathetic division occurs during: -sedentary activity -eating -restoration of the body’s reserves -elimination of waste products Rest and digest! Eye SNS: Dilates pupil and elevates eyelid PNS: Constricts pupil Eye SNS: Dilates pupil and elevates eyelid PNS: Constricts pupil In response to light, the PNS causes the pupil to constrict) Eye SNS: Dilates pupil and elevates eyelid PNS: Constricts pupil Lacrimal gland SNS: - PNS: Secretes tears Salivary glands SNS: Reduces secretion PNS: Increases secretion (abundant watery secretion) Cool Hand Luke (1967) Paul Newman Skin Blood flow SNS: alters blood flow increased SNS: reduced blood flow decreased SNS: increased blood flow PNS: - Skin Blood flow SNS: alters blood flow PNS: - Piloerector muscle SNS: Causes erection of hair PNS: - Skin Blood flow SNS: alters blood flow PNS: - Piloerector muscle SNS: Causes erection of hair PNS: - Goose bumps Skin Blood flow SNS: alters blood flow PNS: - Piloerector muscle SNS: Causes erection of hair PNS: - Sweat gland SNS: stimulates secretion PNS: - Downloaded from: StudentConsult (on 22 November 2010 01:56 PM) © 2005 Elsevier Skin Blood flow SNS: alters blood flow PNS: - Piloerector muscle SNS: Causes erection of hair PNS: - Sweat gland SNS: stimulates secretion PNS: - Lungs SNS: relaxes airways PNS: constricts airways Heart Heart rate SNS: increases HR PNS: reduces HR Heart Heart rate SNS: increases HR PNS: reduces HR Strength of muscle contraction SNS: increases PNS: - Stomach SNS: inhibits digestion PNS: stimulates digestion Liver SNS: stimulates glucose production and release PNS: - GI tract SNS: inhibits GI function PNS: stimulates GI function Urinary bladder SNS: relaxes bladder, constricts urinary sphincter (reduces urination) PNS: contracts bladder, relaxes urinary sphincter (increases urination) Male reproductive organ SNS: ejaculation PNS: penile erection (nitric oxide mediated) Female reproductive organs SNS: uterine contraction PNS: increased secretions  Many autonomic mechanisms can be inhibited by voluntary control An example of this is the bladder emptying reflex