Zoology 120 Sensory Physiology Lecture Notes PDF

20373-X: ZOOLOGY 120 ANIMAL PHYSIOLOGY | LECTURE SENSORY PHYSIOLOGY 2ND SEMESTER 2023-2024 LECTURER: BRIAN ALLISON MARTOS DATE OF LECTURE: MAY 2, 2024 II. I. ○ ○ ○ ○ Roles of Sensors or Receptors Afferent Nervous System Receptor/Sensor – present in sense organs that will detect information from our...

20373-X: ZOOLOGY 120 ANIMAL PHYSIOLOGY | LECTURE SENSORY PHYSIOLOGY 2ND SEMESTER 2023-2024 LECTURER: BRIAN ALLISON MARTOS DATE OF LECTURE: MAY 2, 2024 II. I. ○ ○ ○ ○ Roles of Sensors or Receptors Afferent Nervous System Receptor/Sensor – present in sense organs that will detect information from our environment Visceral Afferents ○ Subconscious input ○ Blood pressure ○ CO2 concentration ○ Etc. Sensory Afferents ○ Conscious awareness ○ Somatic (body) sensations Somesthetic – external stimuli perceived by body surface Proprioception ○ Special Senses Eyes Ears Tongue Nose II. Sensory Cells Receptor Cell Physiology Sensory cells – have ion channels and receptor proteins with specific modalities. ○ Receives the external stimuli ○ Should contain ion channels to process the information; entry and exit of ions based on the type of sensory organ ○ Stimulus from environment vary Transduction – conversion of one form of energy (external stimulus) into electrical energy ○ Our nervous systems can pass on electric signals ○ External signals must be converted to electrical signals that can be processed or integrated by the nervous system ○ Opening and closing of ion channels often due to actions of receptor proteins Entry or exit of ions will cause depolarization or repolarization Types of Gated Channels ○ Mechanically-gated ○ Chemically-gated ○ Voltage-gated ○ Thermally-gated Classification based on modalities or the kind of stimulus they react to: ○ Mechanoreceptors ○ Chemoreceptors ○ Thermoreceptors JA N A H Receptors may be: ○ Specialized ending of an afferent neuron Channels → stimulus binding to the receptors → opening of ion(Na+) channels → influx of Na+ ions → depolarization → passive flow (axonal area) → threshold potential → formation of AP → opening of voltage–gated Na+ channels Generator potential ○ Separate cell closely associated with peripheral ending of a neuron Stimulus binds to the receptor → opening of ion(Na+) channels → influx of Na+ ions → more positive(depolarization) → in terminal knobs, when there is AP, it opens Ca2+ gated channels → entry of Ca2+ → exocytosis of neurotransmitters(have receptors for afferent neuron) → binding → opening of nonspecific-cation channels → entry of Na+ ions(chemically-gated channels) → threshold potential → formation of AP → transmitted towards CNS Stimulus alters receptor’s permeability which leads to graded receptor potential Usually causes nonselective opening of all small ion channels This change in membrane permeability can lead to the influx of sodium ions. The magnitude of the receptor potential represents the intensity of the stimulus. A receptor potential of sufficient magnitude can produce an action potential. This action potential is propagated along an afferent fiber to the CNS. Receptors may adapt slowly or rapidly to sustained stimulation Types of receptors according to their speed of adaptation ○ Tonic receptors Do not adapt at all or adapt slowly Muscle stretch receptors, joint proprioceptors When these adapt rapidly, a person won’t be able to move ○ Phasic receptors Rapidly adapting receptors Tactile receptors in skin Receptor potential — Generator potential — A N G EL IK A Interoreceptors – information regarding the body fluids ○ Blood pressure, internal organs Proprioceptors – Information regarding movement and position Exteroreceptors – Information regarding the “classic” external sensations Receptor Cell Physiology Afferent Nervous System Photoreceptors Electroreceptors Magnetoreceptors Nociceptors A N TO N IO OUTLINE Afferent Nervous III. Classification of Sensors System or Receptors A. Afferent Nervous A. Mechanoreceptor System s Receptor Cell Physiology B. Chemoreceptors A. Sensory Cells C. Thermoreceptors B. Roles of Sensors D. Photoreceptors or Receptors E. Electroreceptors C. Receptor Cell F. Magnetoreceptors Physiology G. Nociceptors D. Adaptation vs. Habituation I. TRANSCRIBED BY: JANAH ANGELIKA R. ANTONIO | BIOLOGY 1 LECTURE 4 - SENSORY PHYSIOLOGY | ANIMAL PHYSIOLOGY Uses of Information from Receptors Afferent input(stimulus) from receptors, is essential for the control of efferent output, both for regulating motor behavior in accordance with external circumstances and for coordinating internal activities directed at maintaining homeostasis. Processing of sensory input by the reticular activating system in the brain stem is critical for cortical arousal and consciousness. Central processing of sensory information gives rise to our perceptions of the world around us. Selected information delivered to the CNS may be stored for future reference(storage of memory based on experiences). Sensory stimuli can have a profound impact on our emotions. Integument Adaptation vs. Habituation Adaptation ○ Intrinsic mechanism of adaptation of Pacinian corpuscle mechanical and electrical intrinsic components ○ Intrinsic mechanism of adaptation of olfactory receptors Activation of proteins that closes Ca2+ channels ○ Extrinsic mechanism of adaptation in hearing Release of GABA via the brain’s efferent neuron Proprioception – detection of motion and position Higher animals: mechanoreceptors are function for the integument Types of sensory cells in the integument UNENCAPSULATED 1. Merkel Cells ○ Epithelial tactile cells for light touch sensation and sensation of texture 2. Free Nerve Endings ○ Respond to high and low temperatures, pain, itching, and tactile functions 3. Root Hair Plexuses ○ Detect movement of hairs A N G EL IK A Mechanoreceptors ○ Integument ○ Muscles, tendons, joints ○ Statocysts ○ Lateral line system ○ Vestibular apparatus ○ Cochlea A N TO N IO JA N A H ENCAPSULATED 1. Meissner Corpuscles ○ initiate impulses when deformed due to light touch or low-frequency stimuli 2. Pacinian Corpuscles ○ for sensing coarse touch, pressure, and vibrations 3. Krause End Bulbs ○ sense low frequency vibrations in penis and clitoris 4. Ruffini Corpuscles ○ stimulated by stretch (tension) or twisting (torque) in skin III. Classification of Sensors or Receptor Mechanoreceptors Detection of physical forces Touch and pressure Lower animals ○ Detected by leg bristles Connected by dendrite; opening of ion channel in dendrites; receptors are mechanically-gated Statocyst Simplest organ for equilibrium Gravity receptors ○ Statoliths Grains in lobsters Statocyst is consist of hollow chamber CDC UNIVERSITY OF THE PHILIPPINES BAGUI O 2 LECTURE 4 - SENSORY PHYSIOLOGY | ANIMAL PHYSIOLOGY ○ ○ ○ ○ Lateral Line System Somesthetic and proprioceptive mechanoreceptor system A N G EL IK A Each stereocilia have mechanically gated channels In a normal situation, some mechanically gated channels are open which allow the entry of K+ ions → more positive → trigger the formation of AP → entry of Ca2+ ions Sterocilum bending towards kinocilium: opening of mechanically gated channels in the stereocilia and kinocilia → K+ ions will enter → faster → exocytosis of neurotransmitter Sterocilum bending away from kinocilium: closing of mechanically gated channels in the stereocilia and kinocilia → no entry of K+ ions → no AP A N TO N IO with sensory neurons in the form of sensory hair cells; connected to statolith Composed of sand grains Statolith is floating → magagalaw yung position ni statolith → sensory hair cells will bend → transmitted as electrical signal going towards the brain CaCO3 Ca2+ channels (fish) Vestibular Apparatus JA N A H Neuromast organ – part of the lateral line organs in a fish; provides the fish with spatial orientation and the ability to navigate in unknown waters. ○ Dome shaped ○ Hair cell (stereocilia, kinocilium) – found at the base of neuromas Stereocilia – microvilar processes Kinocilium – tallest stereocilia Cupula – a small, inverted cup or dome-shaped gelatinous cap over a structure where microvilar processes protrude Tip links (CAMs) ○ Each stereocilia is connected by tip links Balance, equilibrium and coordinating head movement in higher vertebrates proprioceptive structure essential for equilibrium and posture COMPONENTS OF VESTIBULAR APPARATUS 1. Semicircular Canals ○ Detect rotational or angular acceleration or deceleration of the head (equilibrium). ○ Arranged 3 Dimensionally in planes that are 90° perpendicular to each other ○ Endolymph – fluid inside the semicircular canals i. Law of inertia – rotation of head make the fluid appears as if it is at rest ○ When rotation of the head stops, the fluid will still move in the same direction which makes you feel dizzy ○ Hair cells will have cilium that projects to the cupula CDC UNIVERSITY OF THE PHILIPPINES BAGUI O 3 Otolith Organs ○ Provide position of the head relative to gravity and changes in rate of linear motion. i. Utricle – detect horizontally directed linear acceleration and deceleration ii. Saccule – vertically directed linear acceleration and deceleration ○ Otoliths (CaCO3) Alcohol: render the cupula lighter compared to its original state. Initially, the cupula is lighter Ears and Hearing Mechanoreception of Sound Waves Invertebrates and lower vertebrates ○ Sound waves(source of the stimuli) → body → otolith (inner ear) ○ The otolith, aside from being functional for equilibrium, will also function to process sound from their environment. Fish ○ Gas bladder(initial processing; contains gas where sound waves travel faster) → Weber bone → inner ear Vertebrates(mammals) ○ Action of cilia in sensory cell → action potential Anatomy of the Ear ○ Three Division of Ear in Mammals External: Pinna — localization of sound waves; cartilage covered by epithelium External auditory meatus (ear canal) — Tympanic membrane (eardrum) — initial processing of sound in vertebrates; first to receive the sound waves/stimulus Middle: Ossicles: Mallus, Incus, and Stapes Inner: Cochlea — where the sense organ for sound will be found JA N A H TRANSMISSION OF SOUND WAVES Tympanic membrane — sound waves will cause vibration in the membrane; sends the vibrations to the malleus Incus → Stapes Stapes — connected to the inner ear via the oval window Cochlea — ○ Three fluid compartments: i. Scala vestibuli — contains perilymph; connected to scala tympani via helicotrema; ————VESTIBULAR MEMBRANE———— ii. Scala media — aka cochlear duct, contains endolymph Organ of Corti — sense organ for sound; situated above the basilar membrane; composed of hair cells that have projections called hairs that are connected to a tectorial membrane. ○ Tectorial membrane — stationary; where hairs of the hair cells are attached to. —————BASILAR MEMBRANE————— iii. Scala tympani — contains perilymph A N G EL IK A 2. A N TO N IO LECTURE 4 - SENSORY PHYSIOLOGY | ANIMAL PHYSIOLOGY SOUND PATHWAY 1. Sound waves will cause the vibration of tympanic membrane → CDC UNIVERSITY OF THE PHILIPPINES BAGUI O 4 LECTURE 4 - SENSORY PHYSIOLOGY | ANIMAL PHYSIOLOGY 2. Vibration of the ossicles → *Stapes is connected to the cochlea via the oval window 3. Vibration of the oval window → *Oval window leads to the scala vestibuli Fluid movement(perilymph) within the cochlea → 5A. From the scala vestibuli, the sound waves will just travel through the helicotrema → 5B.1. From the scala vestibuli, the sound waves will vibrate towards the scala media → A N TO N IO 4. 5B.2. The scala media houses the Organ of Corti, which will vibrate as well → *the tectorial membrane will not move 6B. Bending of hair cells → 7A. The sound energy will dissipate through the vibration of the round window. 7B. Triggering of action potential given that the sound waves are enough JA N A H *it will not be processed as sound in the brain A N G EL IK A 6A. Then it will travel to the scala tympani (has round window which is covered with membrane) → Chemoreceptors Chemical stimulus having specific receptors; detecting chemicals to generate neural signals. ○ Exteroreceptors and interoreceptors Gustation (taste) and Olfaction (smell) Functions of taste and smell ○ in association with food intake in some species, it can influence the flow of digestive juices and affect appetite ○ permit social recognition of kin (organisms that secrete pheromones) ○ induce pleasurable or objectionable sensations CDC UNIVERSITY OF THE PHILIPPINES BAGUI O 5 LECTURE 4 - SENSORY PHYSIOLOGY | ANIMAL PHYSIOLOGY ○ have a major role in finding direction, finding shelter, seeking prey, avoiding predators, and sexual attraction to a mate Gustation GUSTATORY PATHWAY Facial (VII) nerve: anterior two-thirds of the tongue Glossopharyngeal (IX) nerve: posterior one-third of the tongue; Vagus (X) nerve: throat and epiglottis Most of the taste buds are located in the tongue region A N TO N IO Taste — detection of molecules in objects in contact with the taste cells Taste buds – chemoreceptors found in different regions (tongue, digestive tract, lungs, etc.); houses the taste receptor cells that are connected to the nerve sensory fibers Tastant – substance that alters the cell’s ionic channels to produce a depolarizing receptor potential Bitter Taste ○ Stimulated by alkaloids ○ Employ various signaling pathways to bring about a receptor potential ○ G-protein (gustducin) coupled mechanism Umami Taste ○ Stimulated by amino acid (Glutamate) ○ G-protein coupled mechanism ○ Details of pathway unknown JA N A H A N G EL IK A TRANSDUCTION PATHWAYS Salt Taste ○ Stimulated by chemical salts (NaCl) ○ Na+ enters via specialized ion channels (regulated by antidiuretic hormone and aldosterone) Na+ essential for the formation of action potential ○ Depolarization Sour Taste ○ Stimulated by acids; H+ can also pass through specialized ion channels ○ H+ direct entry; can also pass through specialized ion channels ○ H+ blocks K+ channels ○ Depolarization: K+ ions cannot exit Na+ ions enter via the leak channels; continuous entry Sweet Taste ○ Stimulated by glucose When glucose will bind to a receptor in the taste cell receptors, it will activate the G-protein pathway ○ G-protein coupled mechanism cAMP pathway — activation of adenylyl cyclase that will function to convert ATP to cAMP → activation of protein kinase → Phosphorylation of K+ channels → Blockage of K+ channels → no exit of K IP3 pathway — binding to a receptor of ER → receptors for IP3 → opening of Ca2+ ion channels → efflux of Ca2+ ions → Taste receptor cell have ER → Ca2+ efflux from ER → release of neurotransmitter from taste receptor cells → binding of neurotransmitters to the receptors of sensory nerve fibers ○ Depolarization (Na+ entry) Nerve innervations of the tongue Olfaction Olfactory receptors are specialized endings of renewable afferent neurons. Smell sensation ○ Olfactory mucosa found in the nasal fossae ○ Olfactory nerve — axons of the cells that comprise the olfactory mucosa Olfactory Epithelium Cells ○ Supporting cells(Bowman's gland) — produces mucus ○ Olfactory receptor cells — receives stimulus, particularly the odorant molecules; continuously being replaced via the mitosis of basal cells ○ Basal cells — replenishment of olfactory receptor cells Odorant ○ Sufficiently volatile that some of its molecules can enter the nose in inspired air. CDC UNIVERSITY OF THE PHILIPPINES BAGUI O 6 LECTURE 4 - SENSORY PHYSIOLOGY | ANIMAL PHYSIOLOGY ○ Sufficiently water soluble that it can dissolve in mucus coating the olfactory mucosa. OLFACTORY ADAPTATION Reduced sensitivity or habituation ○ Intrinsic receptor adaptation ○ Extrinsic adaptation in the CNS Lingering of smell ○ “Odor-eating” enzymes ○ Similar property to detoxifying liver enzymes A N TO N IO PATHWAY 1. Odorant molecule will have specific factors in the olfactory receptor cells 2. Activation of G-protein mechanism 3. Activation of the adenylyl cyclase 4. Conversion of ATP to cAMP 5. cAMP will act on Na+ channels 6. Influx of Na+ ions → depolarization of generator potential → depolarization of olfactory receptor cell membrane Olfactory tract Subcortical route Regions of the limbic system (primary olfactory cortex of the temporal lobes) ○ Behavioral reactions associated with feeding, mating, and direction orienting Thalamic-cortical route ○ With hypothalamic involvement for conscious perception and fine discrimination of smell VOMERONASAL ORGAN Vomeronasal Organ (VNO) – in mammals including humans Jacobson’s Organ – in nonavian reptiles “Sexual nose” – governs reproductive and social behaviors Pheromones – odorless substances affecting reproductive and social behaviors ○ Female: (z)-7-dodecenyl acetate, copulins ○ Male: darcin, androstenone ○ Flehman position (horse’s laugh) ○ Lordosis A N G EL IK A Thermoreceptors JA N A H OLFACTORY TRANSDUCTION AND PROCESSING Odors are dissected into components. Each part of an odor is detected by one of a thousand receptors. Spatial summation Olfactory bulb ○ Glomeruli — “smell files” ; where synapses form between the terminals of the olfactory nerve and the mitral cells ○ Mitral cells — receive information from the axons of olfactory receptor neurons, forming synapses in glomeruli. Ability to detect environmental temperature Three kinds ○ Mammalian skin and tongue Cold sensors: respond to decrease in temperature Cold-gated channels: TRPA1 (ice-cold temperature) and TRPM8 (8oC and 28oC) Warmth sensors: respond to increase in temperature Heat-gated channels: TRPV1 (42oC), TRPV2 (52oC), TRPV3 (33oC) ○ Pit vipers, some phytons, and boas Infrared sensors: respond to infrared radiation TRPA1 Photoreceptors Vertebrate Eyes Eye – spherical, fluid-filled structure enclosed by three tissue layers ○ Outer: sclera and cornea(anterior) ○ Middle: choroid, ciliary body, and iris ○ Inner: retina Sensory organ for vision; receives light rays Mechanisms that help protect eyes from injury ○ Eyeball – sheltered by a bony socket in which it is positioned. ○ Eyelids – act like shutters to protect eye from environmental hazards ○ Eyelashes – trap fine, airborne debris such as dust before it can fall into eye ○ Tear – Continuously produced by lacrimal glands; Lubricate, cleanse, bactericidal Sclera/cornea ○ Sclera – tough outer layer of connective tissue; forms visible white part of the eye ○ Cornea – anterior, transparent outer layer through CDC UNIVERSITY OF THE PHILIPPINES BAGUI O 7 LECTURE 4 - SENSORY PHYSIOLOGY | ANIMAL PHYSIOLOGY which light rays pass into interior of eye Choroid, ciliary body, iris ○ Choroid — middle layer underneath sclera which contains blood vessels that nourish retina ○ Choroid layer is specialized anteriorly to form ciliary body and iris ○ Iris — composed of muscle members Circular muscles Radial muscles Radial muscle Circular muscle Pupil Parasympath etic Nervous System relaxation contraction constriction (less light) Sympathetic Nervous System contraction relaxation dilation (more light) Retina – innermost coat under choroid ○ consists of outer pigmented layer and inner nervous-tissue layer ○ rods and cones Interior consists of two fluid-filled cavities separated by the lens ○ Posterior cavity Larger cavity between lens and retina Contains vitreous humor Important in maintaining the spherical shape of eyeball ○ Anterior cavity Anterior cavity between cornea and lens Contains aqueous humor Carries nutrients for cornea and lens Produced by capillary network within ciliary body Vertebrate proprioception IRIS AND PUPIL Iris – controls amount of light entering eye ○ contains two sets of smooth muscle networks circular (or constrictor) muscle radial (or dilator) muscle ○ Pigment in iris is responsible for eye color ○ Unique for each individual Basis for latest identification technology Pupil – Round opening through which light enters the eye CORNEA AND LENS Two structures most important in eye’s refractive ability ○ Cornea — 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 as needed for near or far vision Accommodation – ability to adjust the lens strength in order to focus both near and distant objects ○ For humans, if the light source is >6m, the light rays would be parallel already; focal point is at the clear image ○