Unit 11 The Senses PDF

14.1 Sensory Perception Figure 14.2 - Receptor Classification by Cell Type Free nerve endings (dendrites) Encapsulated nerve ending Specialized nerve ending  Sensitive Respond to Respond to Inform brain to p...

14.1 Sensory Perception Figure 14.2 - Receptor Classification by Cell Type Free nerve endings (dendrites) Encapsulated nerve ending Specialized nerve ending  Sensitive Respond to Respond to Inform brain to pain- stimuli from stimuli arising of one's causing outside in internal movements stimuli body viscera and Most blood vessels special sense organs ▪ Respond to stimuli arising outside body ▪ Receptors in skin for touch, pressure, pain, and temperature ▪ Most special sense organs ▪ Respond to stimuli arising in internal viscera and blood vessels ▪ Sensitive to chemical changes, tissue stretch, and temperature changes ▪ Sometimes cause discomfort but usually person is unaware of their workings. ▪ Respond to stretch in skeletal muscles, tendons, joints, ligaments, and connective tissue coverings of bones and muscles ▪ Inform brain of one's movements.  Modified dendritic endings of sensory neurons Found throughout body Vision, hearing, equili- brium, smell, and taste All are housed in complex sense organs ▪ General senses include tactile sensations (touch, pressure, stretch, vibration), temperature, pain, and muscle sense. No “one-receptor-one-function” relationship Receptors can respond to multiple stimuli  : discriminative touch : deep pressure and vibration : deep and continuous pressure : muscle stretch tendon stretch monitor joint position and motion  Sensation Perception the awareness of the conscious changes in the interpretation of internal and external those stimuli environment ▪ Generating a signal ▪ Pathways of neurons conduct sensory impulses received from receptors upward to appropriate cortical regions ▪ Interpretation of sensory input depends on specific location of target neurons in sensory cortex Everybody perceives pain at same stimulus intensity ▪ Pain tolerance varies ▪ “Sensitive to pain” means low pain tolerance, not low pain threshold ▪ Genes help determine pain tolerance as well as response to pain medications ▪ - stimulation of visceral organ receptors o Felt as vague aching, gnawing, burning o Activated by tissue stretching, ischemia, chemicals, muscle spasms ▪ - pain from one body region perceived as coming from different region o Visceral and somatic pain fibers travel along same nerves. Ex: left arm pain during heart attack ▪ NMDA (N-methyl-D-aspartate) receptors are activated by long-lasting or intense pain o Allow spinal cord to “learn” hyperalgesia o Early pain management critical to prevent pain felt in limb that has been amputated ▪ Epidural anesthesia during surgery to reduce phantom pain 28  29 Senses: Maintain homeostasis, by providing information about the outside world and the internal environment Two types of senses: Receptors that are widely distributed General throughout the body senses: Skin, various organs, and joints Specialized receptors confined to Special structures in the head senses: Eyes, ears, nose, and mouth  30 Sensory receptors: 1. Collect information from the environment, and relay it to the CNS on sensory neurons 2. Link nervous system to internal and external changes or events. 3. Can be specialized cells or multicellular structures 33  34 Special senses of the body include: Vision Taste Smell Hearing Equilibrium All use special sensory receptor cells localized in the head region The sense of touch is one of the general senses, mediated by general receptors  35 70% of body’s sensory receptors are in the eye. Half of cerebral cortex* is involved in visual processing *Associated with higher level processes: consciousness, thought, emotion, reasoning, language, and memory  36 Eyebrow Only one-sixth of surface Eyelid visible Eyelashes Mostly enclosed and Conjunctiva protected by fat cushion merges with cornea and bony orbit Palpebral fissure Consists of accessory Lateral structures and the commissure eyeball Iris Eyelid Pupil Sclera Lacrimal Medial caruncle commi ssure Levator palpebrae superioris muscle 37 Orbicularis oculi muscle Eyebrow Tarsal plate Accessory structures include: Palpebral conjunctiva Eyebrows Tarsal glands Cornea Eyelids (palpebrae) Palpebral fissure Conjunctiva Lacrimal apparatus Eyelashes Bulbar conjunctiva Extrinsic eye muscles Conjunctival sac Orbicularis oculi muscle  38 1 Lacrimal gland 2 Excretory ducts of the lacrimal gland. Tears flow Lacrimal gland and ducts down and 3 that drain into nasal cavity across the eyeball. Lacrimal secretion (tears): 4 Lacrimal canaliculi Dilute saline solution Lacrimal punctum 5 Lacrimal sac Mucus Lacrimal canaliculus Antibodies 6 Nasolacrimal Antibacterial lysozyme duct Inferior meatus of nasal cavity Nostril  39 Six strap-like extrinsic eye muscles Superior oblique tendon ▪ Originate from bony orbit and insert on eyeball Superior oblique muscle ▪ Follow moving objects, maintain Superior rectus muscle shape, and hold it in orbit Lateral rectus Four rectus muscles muscle ▪ Superior, inferior, lateral, and medial Lateral view right eye Two oblique muscles Inferior rectus Inferior oblique ▪ Superior and inferior  40 Trochlea Superior Superior oblique rectus Lateral Medial rectus rectus Inferior Inferior oblique rectus Anterior view right eye  41 Wall of eyeball contains three layers ▪ Fibrous layer: Cornea and Sclera ▪ Vascular layer ▪ Inner layer Internal cavity filled with fluids called humors Lens separates internal cavity into anterior and posterior segments  Ora serrata Cornea Ciliary body ▪ Transparent anterior Ciliary zonule 1/6th of fibrous layer o Lets light enter and Cornea bends light as it enters Iris eye Pupil ▪ Epithelium covers both surfaces Anterior segment o Outer surface protects (contains aqueous humor) from abrasions o Inner layer contains Lens sodium pumps. Scleral venous sinus Posterior segment (vitreous humor) Sclera ▪ Sclera Choroid o Opaque posterior region Retina o Protects and shapes eyeball Macula lutea o Anchors extrinsic eye muscles Fovea centralis o Posteriorly, sclera is continuous with dura mater of brain Optic nerve Optic disc  Choroid Ora serrata Vascular layer Ciliary body ▪ Middle pigmented Ciliary zonule layer of eye (uvea) Cornea ▪ Three regions: Iris choroid, ciliary body, and iris Pupil o Choroid region Anterior segment Supplies blood (contains aqueous humor) Brown pigment Lens prevents Scleral venous sinus scattering of light Posterior segment (vitreous humor)  Choroid Ora serrata Ciliary body Ciliary body ▪ Anteriorly, choroid Ciliary zonule becomes ciliary body Cornea ▪ Ring of tissue Iris surrounding lens Pupil ▪ Smooth ciliary muscles control shape Anterior segment of lens (contains aqueous humor) ▪ Ciliary zonule (suspensory ligament) Lens holds lens in position Scleral venous sinus Posterior segment (vitreous humor)  Choroid Ora serrata Iris Ciliary body ▪ Colored part of eye Ciliary zonule that lies between cornea and lens, Cornea continuous with Iris ciliary body Pupil ▪ Pupil: central opening that regulates amount Anterior segment (contains aqueous humor) of light entering eye Lens Scleral venous sinus Posterior segment (vitreous humor)  47 Parasympathetic + Sympathetic + Sphincter pupillae Iris (two muscles) Dilator pupillae muscle contracts: Sphincter pupillae muscle contracts: Pupil constricts Dilator pupillae Pupil dilates (size decreases). (size increases).  48 o P: Pupils; how much light enters your eye o E: Pupils are equal in size o R: Pupils are round o L: Pupils react to light when your doctor shines a bright light in your eyes o A: Pupils react to accommodation, which is your eyes' ability to change focus.  49 Inner layer (retina) ▪ Retina originates as an outpocketing of brain ▪ Contains: o Photoreceptor cells o Neurons o Glial cells ▪ Delicate two-layered membrane o Outer pigmented layer o Inner neural layer  50 Retina detachment Photo: Richard Leung/Kings College Hospital. Community Eye Health Journal Vol. 19 No. 57 MARCH 2006  51 Retina: Neural layer of the retina Neural layer Pigmented layer ▪ Anterior end has Choroid Choroid serrated edges called Optic disc ora serrata Sclera ▪ Three main types of neurons: o Photoreceptors, Optic bipolar cells, ganglion nerve cells ▪ Optic disc o Site where optic nerve leaves eye (blind spot)  52 Retina: Pigmented layer of the Neural layer Pigmented layer retina Choroid ▪ Single-cell-thick lining next to choroid Sclera ▪ Functions: o Absorbs light and prevents its scattering Optic o Phagocytizes nerve photoreceptor cell fragments o Stores vitamin A  53 Photoreceptors Bipolar Rod Ganglion cells Cone cells Axons of Rods ganglion ▪ Dim light, peripheral vision cells receptors ▪ More numerous and more sensitive to light than cones ▪ No color vision or sharp images Cones ▪ Vision receptors for bright light ▪ High-resolution color vision Amacrine cell Pathway of signal output Horizontal Pathway of light cell Pigmented layer of retina  Choroid 54 Outer segments Nuclei of of rods and cones ganglion cells 120 million photoreceptors (rods) and 6 million photoreceptors (cones) Axons of Pigmented ganglion cells Nuclei Nuclei of layer of retina of bipolar rods and cells cones  55 Central ▪ Macula lutea artery area at posterior and vein emerging pole lateral to from the blind spot optic disc o Contains mostly cones Optic disc ▪ Fovea centralis: tiny pit in center Macula lutea of macula lutea region with Retina best visual Lateral Medial acuity 56 57 58 59 Smell (olfaction) and taste (gustation): Complementary senses that let us know whether a substance should be savored or avoided. Chemoreceptors are used by these systems Smell receptors detect chemicals dissolved in nasal fluids Chemicals must be dissolved in aqueous solution Taste receptors respond to chemicals dissolved in saliva Olfactory epithelium ▪ Roof of nasal cavity ▪ Covers superior nasal conchae  Mitral cell Olfactory (output cell) tract Glomeruli Olfactory bipolar neurons: Olfactory bulb Cribriform plate o Covered by mucus of ethmoid bone (solvent for odorants) Filaments of olfactory nerve Lamina propria Olfactory connective tissue gland Olfactory axon Olfactory stem cell Fascicles: Olfactory sensory Olfactory Make up filaments neuron epithelium Supporting cell Dendrite of olfactory nerve Mucus Olfactory cilia (cranial nerve I) Route of inhaled air containing odor molecules  Mitral cell Olfactory (output cell) tract Glomeruli Olfactory bulb Cribriform plate Lamina propria of ethmoid bone connective tissue Filaments of olfactory nerve Olfactory gland Olfactory axon Olfactory stem cell Olfactory sensory Olfactory neuron epithelium Supporting cell Dendrite Mucus Olfactory cilia Route of inhaled air containing odor molecules 66 Humans have ~400 “smell” genes active in nose ▪ Each encodes a unique receptor protein ▪ Each odor binds to several different receptors ▪ Each receptor has one type of receptor protein Pain and temperature receptors are also in nasal cavities ▪ Respond to irritants, such as ammonia, or can “smell” hot or cold (chili peppers, menthol) In order to smell substance, it must be volatile ▪ Must be in gaseous state ▪ Odorant must also be able to dissolve in olfactory epithelium fluid Odorant binds to its receptor.  Receptor G protein Adenylate cAMP opens a cation activates G activates cyclase channel, allowing Na+ protein (Golf). adenylate converts ATP to and Ca2+ influx and cyclase cAMP. causing depolarization.      Olfactory Mitral cell tract (output cell) Filaments of olfactory Glomeruli nerves synapse with mitral Olfactory bulb cells at glomeruli Sent to frontal lobe Filaments of olfactory nerve Smell interpreted and identified Olfactory stem cell Olfactory sensory neuron Sent to hypothalamus, amygdala, limbic system Olfactory cilia Emotional response Route of inhaled air containing odor molecules Figure 14.3 – The Tongue  Epiglottis Sensory organs for taste Palatine tonsil Most located on tongue Lingual in papillae tonsil Foliate o Fungiform papillae papillae o Foliate papillae Vallate papillae o Vallate papillae Few on soft palate, cheeks, pharynx, epiglottis Fungiform papillae  Vallate papilla Each consists epithelial cells of two types: 1. Gustatory epithelial cells ▪ Have microvilli called gustatory hairs ▪ Some release serotonin or ATP as neurotransmitter and others lack synaptic vesicles 2. Basal epithelial cells - stem cells Taste buds Connective tissue Gustatory Taste fibers Hair (microvilli) of cranial nerve Taste receptors adapt rapidly: Partial – 3-5 sec Complete – 1-5 min Taste pore Stratified squamous epithelium of tongue Basal Gustatory epithelial epithelial cells cells Taste bud (210×) Five basic taste sensations: 1. Sweet sugars, saccharin, alcohol, some amino acids, some lead salts 2. Sour hydrogen ions in solution 3. Salty metal ions (inorganic salts); sodium chloride tastes saltiest 4. Bitter alkaloids such as quinine and nicotine, caffeine, and nonalkaloids such as aspirin 5. Umami amino acids glutamate and aspartate; example: beef (meat) or cheese taste, and monosodium glutamate Possible sixth taste - taste for long-chain fatty acids from lipids “Tastants” must: ▪ Be dissolved in saliva. ▪ Diffuse into taste pores. ▪ Contact gustatory “hairs” Two main cranial nerve pairs carry taste impulses from tongue to brain: 1. Facial nerve (VII) carries impulses from anterior two- thirds of tongue 2. Glossopharyngeal (IX) carries impulses from posterior one-third and pharynx ▪ Vagus nerve transmits from epiglottis and lower pharynx Fibers synapse in the solitary nucleus of the medulla, then travel to thalamus, and then to gustatory cortex in the insula Hypothalamus and limbic system allow us to determine appreciation of taste Taste is 80% smell Major areas: External (outer) ear Hearing ONLY Middle ear (tympanic cavity) Hearing ONLY Internal (inner) ear Hearing AND Equilibrium Receptors for hearing and balance respond to separate stimuli and are activated independently.  Middle Internal ear External ear ear (labyrinth) Auricle (pinna) Helix Lobule External Tympanic Pharyngotympanic acoustic membrane (auditory) tube meatus  Oval window Entrance to Semicircular mastoid antrum canals Malleus Vestibule Auditory Incus ossicles Vestibular Stapes nerve Cochlear Tympanic nerve membrane Cochlea Round window Pharyngotympanic (auditory) tube: Connects middle ear to nasopharynx  Malleus Incus Epitympanic Superior recess Lateral Anterior View ▪ Malleus: the “hammer” ▪ Incus: the “anvil” ▪ Stapes: the “stirrup” Pharyngo- Tensor Tympanic Stapes Stapedius tympanic tympani membrane muscle tube muscle (medial view) Located in temporal bone behind eye socket Two major divisions: ▪ Bony labyrinth: o Vestibule, semicircular canals, cochlea, fluid ▪ Membranous labyrinth: respond to gravity and o series of membranous sacs changes in position of head and ducts. Semicircular canals ▪ Three canals oriented in three planes of space: anterior, lateral, and posterior ▪ Ampulla: enlarged area of ducts of each canal that houses equilibrium receptor region called the crista ampullaris. Receptors respond to angular (rotational) movements of the head Figure 14.7 – Cross Section of the Cochlea Contains mechanoreceptor hair cells Organ of Corti Scala vestibuli Scala tympani  Figure 14.8 – Hair Cells Tectorial membrane stereocilia hair cells The stereocilia are tethered together by proteins that The tectorial membrane amplifies auditory stimuli by open ion channels when the array is bent toward the deflecting the stereocilia of the outer hair cells. Sound tallest member of their array and closed when the array is waves cause the tectorial membrane to shear against bent toward the shortest member of their array. the hair cells, which displaces the stereocilia and triggers the flow of transducer currents. Figure 14.10 - Frequency Coding in the Cochlea Figure 14.11 - Linear Acceleration Coding by Maculae Otoliths stereocilia Otoliths Motion and head position Each crista has supporting cells and hair cells that extend into gel-like mass called ampullary cupula. Cristae respond to changes in velocity of rotational movements of head. Inertia in ampullary cupula causes endolymph in semicircular ducts to move in direction opposite body’s rotation, causing hair cells to bend.  Ampullary cupula Crista ampullaris Endolymph Hair bundle (kinocilium plus stereocilia) Crista Hair cell Membranous ampullaris labyrinth Supporting Fibers of vestibular nerve cell Figure 14.12 - Rotational Coding by Semicircular Canals