The Cyprus International Institute for the Environment and Public Health In collaboration with the Harvard School of Public Health Introduction
• Peripheral Nervous System Lecture 4 • Afferent Division • Sends information from the PNS to the CNS • Efferent Division The Peripheral Nervous System • Send information from the CNS to the PNS • Afferent Division (181-240) • Visceral afferents (subconscious input) • Pressure, O2, temperature, etc. • Sensory afferents (conscious input) Excluded: adaptation of pacinian corpuscle (185), labeled lines • Somatic sensation (186), acuity (186-187), phototransduction (200-203), on- off- center • Somesthetic sensation from skin • Proprioception from muscle joints, skin and ganglion cells (205) inner ear • Special senses • Vision, hearing, taste and smell • Efferent Division • Autonomic Nervous System Constantinos Pitris, MD, PhD • Cardiac muscle, smooth muscle, most exocrine glands, some endocrine glands, Assistant Professor, University of Cyprus adipose tissue [email protected] • Somatic Nervous system http://www.eng.ucy.ac.cy/cpitris/courses/CIIPhys/ • Skeletal muscle 2
Introduction Receptor Physiology
• Sensation ≠ Perception • Receptors • Detect stimulus (detectable change) from different modalities (energy forms) • Perception • e.g. light, heat, sound, pressure, chemical changes • Our understanding (conscious • Adequate stimulus = the stimulus to which the receptor is most sensitive interpretation) of the physical world • Convert forms of energy into electrical signals (action potentials) • An interpretation of the senses • Process is called transduction • Different from what is out there • Types of receptors because • Photoreceptors • Responsive to visible wavelengths of light • Our receptors detect limited number • Mechanoreceptors of existing energy forms • Sensitive to mechanical energy • The information does not reach our • Thermoreceptors brain unaltered. Some features are • Sensitive to heat and cold accentuated and some are • Osmoreceptors suppressed • Detect changes in concentration of solutes in body fluids and resultant changes in osmotic activity • The brain interprets the information • Chemoreceptors and often distorts it (“completes the • Sensitive to specific chemicals picture” or “feels in the gaps”) to • Include receptors for smell and taste and receptors that detect O2 and CO2 concentrations in blood extract conclusions. and chemical content of digestive tract •Nociceptors • Interpretation is affected by cultural, • Pain receptors that are sensitive to tissue damage or distortion of tissue social and personal experiences stored in our memory 3 4 Receptor Physiology Receptor Physiology
• Receptors may be • May adapt slowly or rapidly to • Specialized ending of an afferent neuron Chemically gated Diffusion sustained stimulation Æ receptor potential channels chemical • Separate cell closely associated with messenger • Types of receptors according to Receptor Slowly peripheral ending of a neuron Æ their speed of adaptation potential adapting generator potential (mV) • Potential generation • Tonic receptors • Separate receptor • Do not adapt at all or adapt slowly Afferent • Muscle stretch receptors, joint • Stimulus causes release of chemical neuron fiber Stimulus messenger Receptor proprioceptors (to continuously strength (separate cell) • Specialized afferent nerve ending receive information regarding Stimulus Stimulus on off • Stimulus alters receptor’s permeability posture and balance) Time which leads to graded receptor potential Voltage-gated channels • Phasic receptors • Usually causes nonselective opening of Rapidly all small ion channels Æreceptor • Rapidly adapting receptors adapting Off response (generator) potentials. • Tactile receptors in skin (the reason • The magnitude of the receptor potential Receptor you don’t “feel” your clothes or potential represents the intensity of the stimulus. watch) (mV) • A receptor potential of sufficient magnitude can produce an action • Adaptation is not the same as Afferent potential. neuron fiber habituation (synapse changes in Receptor Stimulus • This action potential is propagated along (separate cell) the CNS) strength an afferent fiber to the CNS. Stimulus Stimulus 5 6 on off Time
Pain Pain
• Pain • Three categories of nociceptors • Primarily a protective mechanism meant • Mechanical nociceptors • Respond to mechanical damage such as to bring a conscious awareness that cutting, crushing, or pinching tissue damage is occurring or is about to • Thermal nociceptors occur • Respond to temperature extremes • Storage of painful experiences in • Polymodal nociceptors memory helps us avoid potentially • Respond equally to all kinds of damaging harmful events in future stimuli • Presence of prostaglandins (released • Sensation of pain is accompanied by after tissue injury) motivated behavioral responses and • Lowers nociceptors threshold for activation emotional reactions • Greatly enhances receptor response to • Subjective perception can be influenced noxious stimuli by other past or present experiences • Aspirin-like drugs inhibit their synthesis Æ (Are you afraid of your dentist?) analgesic effect • Nociceptors do not adapt to sustained or repetitive stimulation
7 8 Pain Pain
• Characteristics of pain • Two best known pain neurotransmitters Fast Pain Slow Pain • Substance P Somatosensory (Location of pain) Other cortical (Experience and Occurs on stimulation of mechanical Occurs on stimulation of polymodal • Glutamate cortex areas deliberation of pain) and thermal nociceptors nociceptors
Higher (Perception of pain) Thalamus Carried by small, myelinated A-delta Carried by small, unmyelinated C fibers • Substance P brain fibers • Activates ascending (Behavioral and Hypothalamus emotional responses Produces sharp, prickling sensation Produces dull, aching, burning pathways that limbic system to pain) sensation transmit nociceptive Brain Reticular ( Alertness) signals to higher formation Easily localized Poorly localized stem Noxious levels for further stimulus Occurs first Occurs second, persists for longer time, more unpleasant processing Spinal cord Provoked and sustained by release of bradykinin Afferent pain fiber Substance P Nociceptor
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Pain Pain
• Glutamate • Brain has built in analgesic system • Suppresses transmission in pain pathways as they enter • Major excitatory spinal cord neurotransmitter • Suppress release of Substance P • Causes hypersensitivity in the • Depends on presence of opiate receptors • Endogenous opiates (morphine like substances) – area endorphins, enkephalins, dynorphin • Protection mechanism for • Factors which modulate pain healing and against further • Exercise (“runner’s high”) • Stress (survival mechanism) damage • Acupuncture • How does a sunburn feel? No perception of pain Periagueductal To thalamus gray matter
Opiate Reticular receptor formation Noxious stimulus
Endogenous opiate Transmission of pain impulses to brain blocked Afferent pain fiber Substance P 11 12 Nociceptor Vision Vision
• Eye • Eye • Sensory organ for vision • Spherical, fluid-filled structure enclosed by three tissue layers Suspensory ligament Extrinsic eye muscle • Mechanisms that help protect • Sclera/cornea Choroid eyes from injury • Sclera – tough outer layer of Ciliary body Lacrimal Glands connective tissue; forms visible white • Eyeball is sheltered by bony Retina (under eyelid) part of the eye Conjunctiva socket in which it is positioned Sclera • Cornea – anterior, transparent outer
•Eyelids layer through which light rays pass into Iris • Act like shutters to protect eye interior of eye Fovea from environmental hazards • Choroid/ciliary body/iris • Eyelashes • Choroid - middle layer underneath Pupil sclera which contains blood vessels • Trap fine, airborne debris such that nourish retina Lens as dust before it can fall into • Choroid layer is specialized anteriorly eye Cornea to form ciliary body and iris Optic nerve • Tears Aqueous humor • Retina Optic disc Canal for tear Pupil Sclera • Continuously produced by • Innermost coat under choroid Vitreous humor drainage Iris Blood vessels lacrimal glands • Consists of outer pigmented layer and • Lubricate, cleanse, bactericidal inner nervous-tissue layer • Rods and cones
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Vision Vision
• Eye • Convex structures of eye • Pupil produce convergence of • Round opening through which light enters the eye diverging light rays that reach •Iris • Controls amount of light entering eye eye • Contains two sets of smooth muscle networks • Two structures most • Circular (or constrictor) muscle • Radial (or dilator) muscle important in eye’s refractive • Pigment in iris is responsible for eye color ability are • Unique for each individual • Basis for latest identification technology • Cornea Parasympathetic stimulation Sympathetic stimulation • Contributes most extensively to + + eye’s total refractive ability • Refractive ability remains constant because curvature never changes • Lens • Refractive ability can be adjusted by changing curvature Circular Circular Radial Pupil Iris Radial as needed for near or far vision (constrictor) muscle muscle (dilator) muscle runs of iris of iris muscle runs (accommodation) circularly radially 15 Pupillary constriction 16 Pupillary dilation Vision Vision
• Accommodation Far source Near source Normal eye (Emmetropia) Ciliary muscle Far source focused on retina without • Change in strength and shape of lens accommodation Lens • Accomplished by action of ciliary Pupillary Near source focused on retina with muscle and suspensory ligaments opening accommodation in front No accommodations Accommodations • Age-related reduction in of lens Nearsightedness (Myopia)– Suspensory accommodation ability - presbyopia ligaments Eyeball too long or lens too strong 1. 1. Uncorrected Image Focus Sympathetic Sympathetic Far source focused in front of stimulation out of retina (where retina would be in stimulation focus eye of normal length) Relaxed ciliary Contracted Near source focused on retina Iris muscle ciliary No accommodations No accommodations with accommodations muscle Farsightedness (Hyperopia)– Flattened 1. Image Eyeball too short or lens too weak Cornea weak Rounded out of lens strong focus 1. Uncorrected lens Far source focused on retina with accommodations Taut suspensory ligaments Slackened Focus Near source focused behind retina even with accommodations suspensory Accommodations Accommodations ligaments 17 18
Vision Vision
Back of retina • Retina • Photoreceptors Cells of pigment layer • Several layers of cells • Rod and cone cells Cone Rod • Receptor containing • Photopigments on the disk Outer portion is actually an membranes segment Discs extension of the CNS • Rod Æ one type Outer Mitochondria segment • Fovea • one pigment, high sensitivity Direction of light Optic nerve Pigment layer • Cones Æ three different types • Pinhead-sized depression Inner Inner Retina Choroid layer • Red, green, blue sensing Direction of retinal visual processing segment Nuclei segment in exact center of retina Sclera pigments, lower sensitivity • Point of most distinct • Undergo chemical alterations Dendrites vision of bipolar when activated by light Synaptic cells Synaptic terminal terminal • Has only cones Front Back • Change the receptor potential of of Front retina retina • Induce action potentials of retina • Unlike other receptors, photoreceptors hyperpolarize! Direction Fibers of Ganglion Amacrine Bipolar Horizontal Cone Rod the optic cell cell cell cell of nerve Photoreceptor light cells 19 Retina 20 Vision Vision
• Color Vision Blue cone Green cone Red cone • Properties of Rod and Cone Vision • Perception of color • Depends on the ratio of stimulation of three different Rods Cones cones 100 million per retina 3 million per retina • Different absorption of cone Vision in shades of gray Color vision pigments High sensitivity to light Low sensitivity to light • Coded and transmitter by Much convergence in retinal pathways Little convergence in retinal pathways different pathways Color perceived Night vision (from sensitivity and convergence) Day vision (lack sensitivity and convergence) • Processed in color vision center Low acuity High acuity of primary visual cortex Wavelength of light (nm) Visible More numerous in periphery Concentrated in fovea • Color blindness spectrum • Defective cone • Colors become combinations of two cones • Most common = red-green color blindness 21 22
Vision Vision
• The sensitivity of the eyes varies through dark and light adaptation • Dark adaptation • Can gradually distinguish objects as you enter a dark area. • Due to the regeneration of rod photopigments that had been broken down by previous light exposure. • Light adaptation • Can gradually distinguish objects as you enter an area with more light. • Due to the rapid breakdown of cone photopigments. • Along with pupillary reflexes increase the range of vision
23 24 Vision Vision
• Visual field • >30% of cortex participates in • Area which can be seen without Left Right moving the head) Æ overlap visual information processing between eyes • “What” and “where” pathways • Visual Pathway • Optic nerve Left Right • Optic chiasm eye eye • Depth Perception • Thalamus Optic 1 nerve • Visual field of two eyes slightly • Sorts information to appropriate areas for processing Optic different • Optic radiation chiasm • Depth perception with one eye • Primary visual cortex (occipital lobe) Optic tract 2 • Other cues (such as size, • Higher processing areas Lateral 3 geniculate location, experience) • Information arrives altered at the nucleus of primary visual cortex thalamus Optic radiation • Upside down and backward because of the lens • The left and right halves of the brain receive information from Optic lobe the left and right halves of the visual field 25 26
Hearing Hearing
Region of Region of • Hearing compression rarefaction • Characteristics of sound • Neural perception of sound • Pitch (tone) of sound energy • Depends on frequency of air waves • Involves two aspects • Intensity (loudness) • Identification of the sounds • Depends on amplitude of air waves (“what”) • Timbre (quality) • Localization of the sounds • Determined by overtones (“where”) • Sound waves • Traveling vibrations of air • Consist of alternate regions of compression and rarefaction of air molecules
27 28 Hearing Hearing
Pinna of Tympanic Auditory • Ear external ear membrane ossicles Semicircular • Sound Wave Transmission (eardrum) canals Basilar membrane • Consists of three parts Utricle • Tympanic membrane Vestibular membrane Tectorial membrane and saccule • External ear • Vibrates when struck by sound Cochlea Organ of Corti • Consists of pinna, external Oval window waves auditory meatus, and tympanum Helicotrema Vestibulocochlear nerve • Middle ear • Transmits airborne sound waves Cochlea • Transfers vibrations through Malleus Incus to fluid-filled inner ear Round window Stapes • Amplifies sound energy ossicles (malleus, incus, stapes) at oval to oval window (entrance into fluid- window • Middle ear Eustachian filled cochlea) • Transmits airborne sound waves tube • Amplify the pressure 20x to fluid-filled inner ear Scala vestibuli External • Large surface of the tympanic • Amplifies sound energy auditory meatus membrane transferred to the (ear canal) To pharynx • Inner ear smaller oval window Scala tympani • Houses two different sensory • Lever action of the osscicles External Middle Inner Scala media systems ear ear ear • Small muscles change the stifness • Cochlea (Contains receptors for of the tympanic membrane conversion of sound waves into External Middle ear Round window nerve impulses which makes • Protection mechanism auditory cavity hearing possible) • Slow action (40 msec) Æ protects meatus • Vestibular apparatus (Necessary for only from prolonged sounds Tympanic membrane sense of equilibrium)
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Hearing Hearing
Vestibular membrane • Sound Wave Transmission Basilar membrane • Sound Transduction Tectorial membrane • Inner ear Vestibular membrane Tectorial membrane • Organ of Corti Cochlea Scala Organ of Corti Scala • Sound dissipates in cochlea • Hair cells with ~ 100 sterocilia media vestibuli • Waves in cochlear fluid Helicotrema each (cochlear (endolymph) set basilar • Inner hair cells are tilted as duct) Incus membrane in motion Malleus basilar membrane oscillates Auditory Basilar Stapes nerve membrane at oval • Sound converted to electrical window • Mechanically gated channels signals by the Organ of Corti open and close Æ graded potentials Scala tympani Scala vestibuli • Communicate via chemical Hairs Outer signals with the nerves which (stereocilia) hair cells Scala tympani form the auditory nerve Tectorial membrane • Outer hair cells Æ adjust length Scala media with respond to electrical Inner hair cells External Middle ear Round window stimulus (electromotility) Æ auditory cavity meatus accentuate motion of basilar Tympanic membrane membrane and fine tune response Supporting cell 31 32 Nerve fibers Basilar membrane Hearing Hearing
• Auditory pathway • Pitch discrimination • Hair cells • Basilar membrane does not have uniform mechanical properties • Auditory nerve • Narrow and stiff to wide and flexible •Brain stem • Different regions vibrate maximally at different frequencies • Signals cross over to opposite site • Frequency (or frequencies) are discriminated by the location of hair cells (unlike visual signals) firing • Thalamus
• Sorts and relays signals to cortical High frequency regions Wide, flexible end •Cortex of basilar membrane • Cortical Processing near helicotrema • Primary auditory cortex in the Medium frequency temporal lobe
• Tonotopically mapped (i.e. Narrow, stiff end mapped according to tone) of basilar membrane near oval window • Higher cortical processing Low frequency • Separates coherent and meaningful patterns 33 34
Hearing Hearing
• Loudness discrimination • Localization Comparison to Loudness • Exquisitely sensitive organ faintest audible • Up-Down localization (elevation) Sound in decibels (motion less than a molecule of sound (hearing • External ear (Pinna) shape (dB) Hydrogen) Æ easily damaged threshold) changes sound timbre and • Wide range (every 10 dB Rustle of 10 dB 10 x louder intensity slightly according to means 10-fold increase in leaves elevation intensity) Ticking of 20 dB 100 x • Left-right localization (azimuth) watch • Higher intensity causes larger • Sound arriving to proximal ear Hush of 30 dB 1000 x arrives basilar membrane movement Library • Slightly earlier (~ 0.5 msec) • Stronger graded potential of Normal 60 dB 1 million x • Slightly stronger conversation hair cells • Brain uses the electrical activity • Faster rate of action potentials Food Blender 90 dB 1 billion x changes to these two cues to from auditory nerve cells Loud rock 120 dB 1 trillion x localize the direction concert • Anything > 100 dB can cause Takeoff of jet 150 dB 1 quadrillion x permanent damage plane
35 36 Hearing Equilibrium
• Deafness • Detection of position • Conductive and motion • Sound waves not adequately • Posture and conducted through external and coordination middle portions of ear • Vestibular apparatus • Blockage, rupture of ear drum, middle ear infection, iddle ear • Fluid filled tunnels In adhesions the inner ear • Hearing aids might help • Semicircular canals • Senosineural • Three circular tunnels • Sound waves conducted but not arranged on translated into electrical signals perpendicular planes • Neural presbycusis, certain • Otolith organs (Utricle antibiotics, poisoning and saccule) • Cochlear implants might help • Two bulges arranged • Electrical devices stimulating in perpendicular the auditory nerve directly directions
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Equilibrium Equilibrium
Direction of • Semicircular canals • Semicircular canals head rotation • Three circular tunnels arranged on perpendicular planes • Signal transduction • Detect rotational acceleration or deceleration in any direction • Head is rotated • Hair cells • Two of the canals are rotated around their axis in opposite directions • On a ridge in the ampulla • Endolymph moves opposite to the • Have on kinocilium and several sterocilia (mikrovilli) direction of motion (inertia) • Embedded in gelatinous material, the cupula • Cupula leans in that direction + Vestibular • Cilia bent and K channels open or apparatus close Semicircular Cupula canals Vestibular • The haircells are depolarized or nerve Auditory hyperpolarized Utricle nerve • Neurotransmitter realize from the hair Endolymph Saccule cells is modified Left Direction Direction of Right Perilymph • Firing of the vestibular nerve is horizontal of fluid bending of horizontal modified semicircular movement in cupula and semicircular canal semicircular hairs of canal Ampulla Hair canals receptor hairs cells cell
Oval window Support Kinocilium cell Round window Ridge in Stereocilia ampulla Hairs of hair cell; Cochlea Vestibular 39 kinocilium (red) 40 Hair cell nerve fibers and stereocilia (blue) Equilibrium Equilibrium
• Vestibular pathway Head motion • Otolith Organs • Vestibular nuclei in brain stem • Detect changes in rate of linear movement in • Motor neurons for controlling Eye Movement any direction eye movement, perceiving • Arranged in perpendicular directions motion and orientation • Provide information important for determining • E.g. vestibuloocular reflex head position in relation to gravity • Cerebellum for use in • Hair cells maintaining balance and • As described before posture, • In addition, calcium carbonate crystals (otoliths) • The vestibular system detects are embedded in within the gelatinous layer acceleration • Increased inertia • Sensitivity to gravity • Speed is calculated by integrating circuitry in the brain stem Endolymph Motion
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Equilibrium Taste and Smell
• Otolith Organs • Taste (gustation) and smell • Signal transduction (olfaction) • Utricle Æ Forward or backward • Receptors are chemoreceptors motion or tilt (motion due to • In association with food intake, gravitational force) influence flow of digestive juices and • Saccule Æ vertical motion affect appetite • Endolymph and gelatinous • Stimulation of receptors induces mass with otoliths move in the pleasurable or objectionable opposite direction sensations and signals presence of something to seek or to avoid • Cilia bent and K+ channels open • In lower animals also play a role in or close Gravitational force finding direction, seeking prey, • The haircells are depolarized or avoiding predators and sexual hyperpolarized attraction to a mate • Neurotransmitter realize from • Less developed and important in the hair cells is modified humans • Firing of the vestibular nerve is • Really? How much do you spend on modified perfumes and colognes
43 44 Taste (Gustation) Taste (Gustation)
• Chemoreceptors housed in • Signal transduction taste buds • Tastant (taste-provoking • Present in oral cavity and chemical) Papilla throat • Binding of tastant with receptor • Taste receptors have life span cell of about 10 days • Alters cell’s ionic channels to produce depolarizing receptor • Taste bud consists of potential • Taste pore Tongue • Receptor potential releases • Opening through which fluids in Taste bud neurotransmitter mouth come into contact with surface of receptor cells • Initiates action potentials within terminal endings of afferent nerve • Taste receptor cells fibers with which receptor cell • Modified epithelial cells with synapses surface folds called microvilli Surface Sensory of the tongue nerve fiber • Signals conveyed via synaptic • Plasma membrane of microvilli contain receptor sites that bind Taste pore stops in brain stem and thalamus selectively with chemical Taste receptor to cortical gustatory area molecules cell Supporting cell 45 46
Taste (Gustation) Taste (Gustation)
• Five primary tastes • Taste Perception •Salty • Influenced by information • Stimulated by chemical salts, derived from other receptors, especially NaCl especially odor • Sour • Temperature and texture of food • Caused by acids which contain a influence taste free hydrogen ion, H+ • Psychological experiences • Sweet associated with past • Evoked by configuration of glucose experiences with food influence • Bitter taste • Brought about by more chemically • How cortex accomplishes diverse group of tastants perceptual processing of taste • Examples – alkaloids, toxic plant sensation is currently unknown derivatives, poisonous substances • Umami • Meaty or savory taste (MSG receptor!) 47 48 Smell (Olfaction) Smell (Olfaction)
• Olfactory receptors in nose • Odorants are specialized endings of • Molecules that can be smelled renewable afferent neurons • Act through second-messenger systems Brain Brain to open Na+ channels and trigger action • Olfactory mucosa Olfactory bulb potentials Olfactory bulb 2 •3cmof mucosa in ceiling of • To be smelled, substance must be Mitral cells nasal cavity Bone • Sufficiently volatile that some of its Glomeruli To limbic system Olfactory tract Olfactory molecules can enter nose in inspired air and cerebral cortex • Contains three cell types bulb • Sufficiently water soluble that it can Nasal cavity • Olfactory receptor cell dissolve in mucus coating the olfactory Afferent mucosa • Afferent neuron whose Soft palate nerve fibers receptor portion is in olfactory (olfactory • 5 million olfactory receptors mucosa in nose and afferent nerve) • 1000 different types axon traverses into brain Basal • Afferent signals are sorted according • Axons of olfactory receptor cell to scent component by glomeruli cells collectively form olfactory within olfactory bulb nerve Olfactory • Two routes to the brain • Supporting cells receptor Olfactory cell • Subcortical (limbic system) •Secrete mucus mucosa • Through the thalamus to the cortex Cilia Olfactory receptors •Basal cells Supporting • The olfactory system adapts quickly • Precursors of new olfactory cell receptor cells (replaced about and odorants are rapidly cleared (by odor-eating enzymes) every two months) Mucus Cilia 49 layer 50
Smell (Olfaction) PNS – Efferent Division
• Vomeronasal Organ (VNO) • Communication link by which CNS controls • Common in mammals but until activities of muscles and glands recently was thought to nonexistent in humans • Two divisions of PNS • Governs emotional responses • Autonomic nervous system (ANS) and sociosexual behaviors • Involuntary branch of PNS • Located about half an inch • Innervates cardiac muscle, smooth muscle, most exocrine glands, inside human nose next to some endocrine glands, and adipose tissue vomer bone • Detects pheromones • Somatic nervous system • Nonvolatile chemical signals • Subject to voluntary control passed subconsciously from • Innervates skeletal muscle one individual to another • Role in human behavior has not been validated • “Good chemistry” and “love at first sight” 51 52 Autonomic Nervous System Autonomic Nervous System
• Autonomic nerve pathway Sympathetic Parasympathetic • Extends from CNS to an innervated organ Nervous System Nervous System Brain • Two-neuron chain ACh ACh Effector Fibers originate in Fibers originate from organs • Preganglionic fiber (synapses with cell body of second neuron) Terminal thoracic and lumbar cranial and sacral Cardiac ganglion • Postganglionic fiber (innervates effector organ) regions of spinal areas of CNS muscle • Postganglionic fibers end in varicosities cord Spinal ACh NE • Two subdivisions cord Most preganglionic Preganglionic fibers • Sympathetic nervous system Sympathetic ganglion chain fibers are short are longer Smooth • Parasympathetic nervous system muscle Thoracolumbar Long postganglionic Very short sympathetic nerves Central nervous Preganglionic Preganglionic fibers postganglionic fibers system neurotransmitter neurotransmitter Preganglionic fibers Preganglionic fibers Adrenal medulla Blood release release acetylcholine E,NE Craniosacral ACh Varicosity acetylcholine (Ach) (Ach) parasym- NE pathetic Most exocrine Most postganglionic Postganglionic fibers nerves Collateral ganglion glands fibers release release acetylcholine and some noradrenaline ACh Preganglionic fiber ACh endocrine Preganglionic fiber (norepinephrine) glands Terminal 53 Autonomic ganglion Effector organ 54 ganglion
Autonomic Nervous System Autonomic Nervous System
• Most visceral organs innervated by both sympathetic and parasympathetic fibers • In general produce opposite effects in a particular organ • Dual innervation of organs by both branches of ANS allows precise control over organ’s activity • Sympathetic system dominates in emergency or stressful (“fight-or-flight”) situations • Promotes responses that prepare body for strenuous physical activity • Parasympathetic system dominates in quiet, relaxed (“rest-and-digest”) situations • Promotes body-maintenance activities such as digestion 55 56 Autonomic Nervous System Autonomic Nervous System
• Exceptions to general rule of • Adrenal medulla is a dual reciprocal innervation by modified part of Spinal cord the two branches of sympathetic nervous system autonomic nervous system Sympathetic = Acetylcholine • Modified sympathetic • Beyond the scope of this course preganglionic = Norepinephrine ganglion that does not give fiber = Epinephrine rise to postganglionic fibers Adrenal • What is the one activity that • Stimulation of preganglionic medulla requires sympathetic / fiber prompts secretion of hormones into blood parasympathetic • About 20% of hormone Sympathetic coordination? release is norepinephrine postganglionic fiber Blood • About 80% of hormone released is epinephrine (adrenaline) • Reinforces the activity of the sympathetic response • More long-acting and sustained Target organs 57 58
Autonomic Nervous System Autonomic Nervous System
• Tissues innervated by autonomic • Andrenergic receptors – bind to nervous system have one or more of norepinephrine and epinephrine
several different receptor types for • Alpha (α) receptors (α1, α2)
postganglionic chemical messengers • α1 Æ excitatory • In most sympathetic target tissues • Cholinergic receptors – bind to ACh • E.g. Constriction of skin and GI arterioles, dilation of pupils, etc. • Nicotinic receptors (bind nicotine) • α2 Æ inhibitory • Found on postganglionic cell bodies of all • Decreased motility in digestive tract autonomic ganglia • Beta (β) receptors (β , β ) • Opens cation channels Æ Na+ flow is higher 1 2 • β Æ excitatory Æ AP 1 • Primarily in the heart (increased heart • Muscarinic receptors (bind mushroom rate and force of contraction) poison) • β2 Æ inhibitory • Found on effector cell membranes (e.g. • Dilation of skeletal muscle arterioles and smooth muscle, cardiac muscle, glands) bronchioles
• Several (five) types • β3 Æ ιin adipose tissue Amanita muscaria • Lipolysis 59 60 Sympathetic Paraympathetic Action Receptor Action Receptor General -stress response (fight or flight) -maintains homeostasis Homeostasis -expends energy -conserves energy Autonomic Nervous System Heart Cardiac muscle -↑ rate β1 -↓ rate (atria only) M2 -↑ contractility β1 -↓ contractility (atria only) M2 Smooth muscle Blood vessels • Agonists -skeletal m. -dilation β2 -skin -constriction α • Bind to same receptor as -penis and clitoris -constriction α -dilation M neurotransmitter Spleen -contraction α • Elicit an effect that mimics that Bronchi -dilation β2 -constriction M3 of neurotransmitter G.I. tract -walls -↓ motility α2 & β2 -↑ motility M3 •E.g. -sphincters -contraction 1 -relaxes M3 α • Salbutamol Genitourinary tract -bladder wall -relaxation β2 -contraction M3 • Activates β2 receptors -sphincter -contraction α2 -relaxation M3 • Treatment of asthma -penis -ejaculation α -erection M • Phenylephrine Glands • Stimulates both α1 & α2 Salivary -↑viscous secretion (small amounts) α1 -↑ watery secretion receptors Sweat • Vasoconstrictor -Thermoregulation -↑ secretion M -Stress -↑ secretion α • Used as nasal decongestant Metabolism • Pilocarpine Liver -glycogenolysis α, β2 • Stimulates muscarinic Adipose -lipolysis β3 receptors Kidney -renin release β1 • Useful for both narrow and Eye wide angle glaucoma Iris -dilation α1 -constriction M3 • Side effects include sweating. Ciliary61 muscle -contraction M3 62
Autonomic Nervous System Autonomic Nervous System
• Antagonists • Regions of CNS Involved in Control of Autonomic • Bind with receptor Activities • Block neurotransmitter’s • Prefrontal association complex response • Influences through its involvement with emotional expression •E.g. characteristic of individual’s personality (e.g. blushing) • Succinylcholine • Hypothalamus • Binds to the nicotinic receptor • Plays important role in integrating autonomic, somatic, and endocrine • Causes prolonged responses that automatically accompany various emotional and depolarization marked first by behavioral states (e.g. anger or fear) muscle fasciculations followed by flaccid paralysis • Medulla (within brain stem) • Atenolol • Region directly responsible for autonomic output (cardiovascular,
• Selective β1 blocker respiratory, digestive tract) • Blockage produces •Spinal Cord bradycardia and decrease in blood pressure • Some autonomic reflexes, such as urination, defecation, and erection, are integrated at spinal cord level but control by higher levels of consciousness
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Neuromuscular Physiology (240-249, 253-267,270-286,288-297)
Excluded: muscle length, tension, contraction and velocity, phosphorylation of myosin
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