Unit 11 Somatic Senses and Special Senses

Objectives: Overview of Sensations Definition of Sensation Characteristics of Sensations Types of Sensory Receptors

General Senses: Somatic and Visceral Tactile: Touch, Pressure, Vibration Thermal (warm, cold) Pain Proprioception Visceral: Internal organ conditions

Definition of Sensation Conscious or subconscious awareness of change in external or internal environment Requires Stimulus Sensory receptor Neural pathway Brain region for integration

Characteristics Perception: Conscious awareness Occurs in cerebral cortex Adaptation: Decreased receptor response during prolonged stimulation Decreased perception Adaptation speed varies with receptor Rapid adaptation: Pressure, Touch, Smell Slow adaptation: Pain, Body position, Chemical levels in blood

Sensory Receptors: Structural Types Free nerve endings Pain, thermal, tickle, itch, some touch receptors Encapsulated nerve endings Touch pressure, and vibration Separate, specialized cells Hair cells in inner ear Photoreceptors in retina of eye

Sensory Receptors: Functional Types Mechanoreceptors Cell deformation: Stretching or bending Touch, Pressure, Vibration Thermoreceptors: Temperature Nociceptors: Pain Photoreceptors: Light Chemoreceptors: Taste, Smell Osmoreceptors Osmotic pressure of body fluid

Objectives: Somatic Senses Tactile Sensations Thermal Sensations Pain Sensations Proprioceptive Sensations

Somatic Senses Somatic receptors in skin, mucous membranes, muscles, tendons, and joints Distributed unevenly: Dense concentration of receptors in very sensitive areas Fingertips, Lips, Tip of tongue Include tactile, thermal, pain, proprioceptive

Tactile Sensations Touch, pressure, vibration Itch and tickle Encapsulated mechanoreceptors Itch and tickle Free nerve endings

Touch Rapidly adapting receptors for touch Meissner corpuscles Hair root plexuses: Detect hair movement Slowly adapting receptors for touch Type I Mechanoreceptors: Merkel discs or Tactile discs Surface receptors: In epidermis Type I Mechanoreceptors: Ruffini corpuscles Deep in dermis and tendons

Pressure and Vibration Pacinian (lamellated) corpuscles: Layers like onion Rapid adapting Widely distributed: In dermis, subcutaneous, around joints, tendons, muscles, periosteum Vibration Response to rapidly repetitive stimuli Receptors: Meissner and Pacinian

Structure and Location of Sensory Receptors Copyright 2010, John Wiley & Sons, Inc.

Itch and Tickle Itch: Chemical stimulation of Free nerve endings Bradykinin from inflammation response Tickle: From Free nerve endings and Pacinian corpuscles Tickle requires stimulus from outside of self Effects of attempts to tickle oneself are blocked by signals to/from cerebellum

Thermal Sensations Two kinds of Thermoreceptors Cold receptors: 10˚– 40˚ C (50 – 105˚ F) Located in epidermis Warm receptors: 32˚– 48˚ C (90 – 118˚ F) Located in dermis Both adapt rapidly but continue slow signals during prolonged stimulus Outside these ranges: Nociceptors detect pain

Pain Sensations Nociceptors Types of pain Free nerve endings in every tissue except brain Can respond to any excessive stimulus Minimal adaptation Types of pain Fast pain: acute, sharp pain Well localized Slow pain: chronic, burning, aching, throbbing More diffuse (not localized) Analgesic drugs – Block formation of chemicals that stimulate nociceptors Referred pain is visceral pain displaced to surface

Distribution of Referred Pain Copyright 2010, John Wiley & Sons, Inc.

Proprioception (Kinesthesia) Awareness of Body position, movements, weight of objects Sites of receptors Muscles (muscle spindles) Tendons (tendon organs) Joint kinesthetic receptors (synovial joints) Inner ear (hair cells): head position Tracts to Somatosensory area of cerebral cortex and Cerebellum Slight adaptation

Functional Areas of the Cerebrum Copyright 2010, John Wiley & Sons, Inc.

Objectives: Special Senses Olfaction: Sense of Smell

Special Senses Smell (Olfaction) Taste (Gustation) Vision Balance Hearing

Smell: Olfaction Site of olfactory receptors In mucosa of superior region of nose Three types of olfactory cells Olfactory receptors Consist of olfactory hairs with chemoreceptors These are first order neurons of olfactory pathway Supporting cells Epithelial cells: Support, Protect Basal cells: Stem cells that produce new neurons (receptors) throughout life. Rare!

Copyright 2010, John Wiley & Sons, Inc. Smell: Olfaction Copyright 2010, John Wiley & Sons, Inc.

Stimulation of Receptors Genetic evidence: 100’s of primary odors exist Binding of chemical odorants stimulates receptor Recognition of 10,000 odors from combination of primary receptor input Rapid adaptation by 50% in 1 second

Olfactory Pathway First-order neurons Second-order neurons Olfactory receptors are neurons in nasal mucosa Axons form olfactory nerves (Cranial nerve I) Extend through cribriform plate into cranium to olfactory bulb Second-order neurons Neuron cell bodies in olfactory bulb Olfactory tract: Axons extend from olfactory bulb to cerebral cortex (Temporal lobe) Limbic system: Emotional response to odors

Copyright 2010, John Wiley & Sons, Inc. Olfactory Receptors Copyright 2010, John Wiley & Sons, Inc.

Objectives: Special Senses Gustation: Sense of Taste

Taste: Gustation Five primary tastes: Salt, Sweet, Sour, Bitter, and Umami Perception of what is called “Taste” includes olfactory input Receptors in 10,000 taste buds Located on tongue, pharynx, epiglottis In structures called Papillae Vallate (posterior) Fungiform (all over) Filiform: Touch receptors only

Copyright 2010, John Wiley & Sons, Inc. Taste: Gustation Copyright 2010, John Wiley & Sons, Inc.

Copyright 2010, John Wiley & Sons, Inc. Taste: Gustation Copyright 2010, John Wiley & Sons, Inc.

Structure of Taste Bud Contains 3 types of Epithelial cells Supporting cells that surround Gustatory receptor cells Gustatory hair projects from receptor through taste pore Basal cells Stem cells that produce supporting cells that develop into receptor cells (10-day life span)

Copyright 2010, John Wiley & Sons, Inc. Taste: Gustation Copyright 2010, John Wiley & Sons, Inc.

Stimulation of Taste Receptors Sequence of events Tastant dissolves in saliva  Enters taste pore  contacts gustatory hair  Electrical signal produced  Causes gustatory cell to release neurotransmitter That activates dendrites of first-order neurons Adaptation occurs within minutes Different tastes arise from activation of different groups of taste neurons

Gustatory Pathway Cranial nerves transmit impulses Facial (CN VII) from Anterior of tongue Glossopharyngeal (CN IX) from Posterior Vagus (CN X) from Pharynx, Epiglottis To medulla oblongata  Thalamus  Primary gustatory area of cerebral cortex  Limbic system or hypothalamus

Objectives: Special Senses Vision: Sense of Sight

Vision: Eyes Accessory structures Eyebrows, eyelashes: Protection Eyelids: Protection and Lubrication (blinking) Extrinsic muscles: Move eyeball Superior, Inferior, Lateral and Medial rectus Superior and Inferior oblique Lacrimal apparatus: Produces tears Lysozyme – Bacteria killing enzyme in tears Lacrimal glands  lacrimal ducts  surface of upper eyelid  surface of eye  Lacrimal canals  lacrimal sac  nasolacrimal duct  nasal cavity

Copyright 2010, John Wiley & Sons, Inc. Vision: Eyes Copyright 2010, John Wiley & Sons, Inc.

Layers of Eyeball First layer: Fibrous tunic Anteriorly: Cornea (clear, colorless) Posteriorly: Sclera (“white of eye”) Second layer: Vascular tunic consists of Choroid: Lines most of internal surface of eye Contains blood vessels that nourish the eye Ciliary body consists of Ciliary processes: Secrete aqueous humor Ciliary muscles: Changes lens shape for focusing Iris: Pigmented part of eye (blue, brown, green) Smooth muscle that dilates or constricts pupil Pupil: Hole for passage of light

Layers of Eyeball Third layer: Retina—composed of 2 layers Neural layer: Outgrowth of brain Photoreceptor layer: Rods and Cones Bipolar cell layer Ganglion cell layer: Axons of neurons form optic nerve (CN II) that exits eye at Optic disc (“blind spot” - no rods/cones) Pigmented layer: Helps absorb stray light Between choroid and neural layer

Pupil Response to Light Copyright 2010, John Wiley & Sons, Inc.

Copyright 2010, John Wiley & Sons, Inc. Layers of Eyeball Copyright 2010, John Wiley & Sons, Inc.

Photoreceptors: Rods and Cones Rods: Black-and-white vision; 120 million Cones: Color sensitive; 6 million cones Three types: Sensitive to blue, green or red light Color vision results from combined input Cones mostly in Central Fovea in center of Macula Lutea Point of highest visual acuity (sharpness) Visual pathway Photoreceptor cells (rods or cones)  Bipolar layer  Ganglion cells; their axons form Optic nerve

Photoreceptors: Rods and Cones Copyright 2010, John Wiley & Sons, Inc.

Interior of Eyeball Two cavities separated by the lens Anterior cavity filled with Aqueous humor Clear, colorless fluid secreted from capillaries in ciliary body Completely replaced every 90 min Establishes intraocular pressure, maintains eye shape; nourishes lens and cornea Drains into blood in scleral venous sinus (canal of Schlemm) Vitreous chamber: Filled with gel-like vitreous body (not replaced) Holds retina back against choroid

Physiology of Vision: Three Steps Formation of image on retina Stimulation of photoreceptors (rods and cones) Visual pathway: Nerve impulses pass to cerebral cortex

A. Formation of Image on Retina: Four Steps Refraction (bending) of light rays to focus them on retina Accommodation: Change of lens shape to focus for near (or far) vision Constriction (narrowing) of pupil to control amount of light entering the eye Convergence of eyeballs: For binocular vision

Step 1: Refraction of Light Definition: Bending of light rays as they pass from medium of one density to another of different density 75% occurs at cornea; Lens also helps focus light on retina Image is inverted but brain adjusts and interprets distance and size

Step 1: Refraction of Light Copyright 2010, John Wiley & Sons, Inc.

Step 1: Refraction of Light Copyright 2010, John Wiley & Sons, Inc.

Step 1: Refraction of Light Copyright 2010, John Wiley & Sons, Inc.

Step 2: Accommodation Lens adjusts shape for distance to allow image to focus on retina For distant objects, ciliary muscle relaxes  Flat lens For closeup vision, ciliary muscle contracts  Fat lens (rounder = more convex) Visual disorders Myopia (nearsightedness): Can see near but not far objects Eyeball is too long so lens cannot accommodate enough to focus images of distant objects onto retina

Step 2: Accommodation Visual disorders Hyperopia (Farsightedness): Can see far but not near Eyeball is too short so lens cannot accommodate enough to focus images of near objects onto retina Astigmatism: irregular curvature of cornea or lens Presbyopia: aging change  loss of elasticity of lens  farsightedness  reading glasses These disorders can be corrected with lenses or LASIK (laser-assisted in situ keratomileusis)

Copyright 2010, John Wiley & Sons, Inc. Step 2: Accommodation Copyright 2010, John Wiley & Sons, Inc.

Steps 3 and 4: Constriction and Convergence Constriction of pupil Autonomic (parasympathetic) reflex to prevent excessive light rays from entering eye By contraction of circular muscles of iris Convergence Eyes rotate inward for binocular vision By contraction of extrinsic eye muscles

B. Stimulation of Photoreceptors Photoreceptors: Light  neural signal In rods light is absorbed by a photopigment (rhodopsin) which splits into opsin + retinal and leads  receptor potential Vitamin A deficiency decreases rhodopsin production and leads to night blindness. In cones light is absorbed by 3 opsins  receptor potential for color vision In Colorblindness, red or green cones are missing.

C. Visual Pathway Rods or cones  Bipolar cells  ganglion cells (their axons form optic nerve = CN II) About 50% of these axons cross over to opposite side of brain in optic chiasm Axons continue on into optic tract   Terminate/synapse in Thalamus   Occipital lobes of cerebral cortex Right brain sees left side of object Left brain sees right side of object

Physiology of Vision: Three Steps Copyright 2010, John Wiley & Sons, Inc.

Visual Disease/Disorder Conjunctivitis – Pinkeye Cataracts – Loss of transparency of lens Ophthalmology – Science that focuses on eyes and disorders https://www.youtube.com/watch?v=nBNNgeHsPxQ

Objectives: Special Senses Hearing & Equilibrium

Hearing and Equilibrium: Ear Structure Outer ear: Auricle External auditory canal Canal contains hairs and ceruminous glands Tympanic membrane (ear drum) Middle ear: Eustachian tube Ossicles Malleus, Incus, Stapes

Inner ear: Bony labyrinth + Membranous labyrinth filled with endolymph Cochlea: Sense organ of hearing, Vestibule and semicircular canals: Organs of balance

Hearing and Equilibrium: Ear Structure Copyright 2010, John Wiley & Sons, Inc.

Inner Ear Structure: Three Regions Vestibule includes Two sacs: Utricle and Saccule Semicircular canals: at right angles Contain membranous semicircular ducts Each ends in a swelling known as Ampulla Cochlea: 3 levels Cochlear duct: Membranous, has Endolymph Contains Spiral organ (sensory organ for hearing) Above: Scala Vestibuli: ends at Oval window Below: Scala Tympani: ends at Round window

Copyright 2010, John Wiley & Sons, Inc. Inner Ear Structure Copyright 2010, John Wiley & Sons, Inc.

Spiral Organ Sits on Basilar membrane Floor of cochlear duct Contains supporting cells + hair cells Hair cells Covered with jellylike Tectorial membrane Receptors for Auditory sensations Synapse with sensory neurons in cochlear branch of Vestibulocochlear nerve cranial nerve VIII)

Copyright 2010, John Wiley & Sons, Inc. Inner Ear Structure Copyright 2010, John Wiley & Sons, Inc.

Physiology of Hearing Sound waves in air  Auditory canal Tympanic membrane  Ossicle movement  Stapes strikes oval window Creates pressure waves in Perilymph Conveyed from Scala Vestibuli  Scala Tympani Pressure waves in Endolymph cause Hair cells bend against tectorial membrane Neurotransmitter released to sensory neurons Pitch (wavelength): Location in cochlea Volume (loudness): Intensity of waves

Scala vestibuli Cochlear duct (contains endolymph) tympani Perilymph Basilar membrane Cochlea Sound waves Helicotrema Stapes vibrating in oval window Malleus Incus External auditory canal Tympanic Secondary tympanic membrane vibrating in round window Auditory tube Vestibular membrane Middle ear Tectorial membrane Spiral organ (organ of Corti) 1 2 3 4 5 6 7 Scala vestibuli Cochlear duct (contains endolymph) tympani Perilymph Basilar membrane Cochlea Sound waves Helicotrema Stapes vibrating in oval window Malleus Incus External auditory canal Tympanic Secondary tympanic membrane vibrating in round window Auditory tube Vestibular membrane Middle ear Tectorial membrane Spiral organ (organ of Corti) 1 2 3 4 5 6 7 8 Scala vestibuli Cochlear duct (contains endolymph) tympani Perilymph Basilar membrane Cochlea Sound waves Helicotrema Stapes vibrating in oval window Malleus Incus External auditory canal Tympanic Secondary tympanic membrane vibrating in round window Auditory tube Vestibular membrane Middle ear Tectorial membrane Spiral organ (organ of Corti) 1 2 3 4 5 6 7 8 9 Scala vestibuli Cochlear duct (contains endolymph) tympani Perilymph Basilar membrane Cochlea Sound waves Helicotrema Stapes vibrating in oval window Malleus Incus External auditory canal Tympanic Secondary tympanic membrane vibrating in round window Auditory tube Vestibular membrane Middle ear Tectorial membrane Spiral organ (organ of Corti) 1 2 3 4 5 6 Scala vestibuli Cochlear duct (contains endolymph) tympani Perilymph Basilar membrane Cochlea Sound waves Helicotrema Stapes vibrating in oval window Malleus Incus External auditory canal Tympanic Secondary tympanic membrane vibrating in round window Auditory tube Vestibular membrane Middle ear Tectorial membrane Spiral organ (organ of Corti) 1 2 3 4 5 Scala vestibuli Cochlear duct (contains endolymph) tympani Perilymph Basilar membrane Cochlea Sound waves Helicotrema Stapes vibrating in oval window Malleus Incus External auditory canal Tympanic Secondary tympanic membrane vibrating in round window Auditory tube Vestibular membrane Middle ear Tectorial membrane Spiral organ (organ of Corti) 1 2 Scala vestibuli Cochlear duct (contains endolymph) tympani Perilymph Basilar membrane Cochlea Sound waves Helicotrema Stapes vibrating in oval window Malleus Incus External auditory canal Tympanic Secondary tympanic membrane vibrating in round window Auditory tube Vestibular membrane Middle ear Tectorial membrane Spiral organ (organ of Corti) 1 2 3 Scala vestibuli Cochlear duct (contains endolymph) tympani Perilymph Basilar membrane Cochlea Sound waves Helicotrema Stapes vibrating in oval window Malleus Incus External auditory canal Tympanic Secondary tympanic membrane vibrating in round window Auditory tube Vestibular membrane Middle ear Tectorial membrane Spiral organ (organ of Corti) 1 2 3 4 Scala vestibuli Cochlear duct (contains endolymph) tympani Perilymph Basilar membrane Cochlea Sound waves Helicotrema Stapes vibrating in oval window Malleus Incus External auditory canal Tympanic Secondary tympanic membrane vibrating in round window Auditory tube Vestibular membrane Middle ear Tectorial membrane Spiral organ (organ of Corti) 1

Auditory Pathway Cochlear neurons (cranial nerve VIII) end in medulla On same side: R ear  R side medulla  Midbrain  Thalamus  Auditory cortex in Temporal lobe Each side of brain receives input from both ears Tinnitus – ringing in the ears

Physiology of Equilibrium Static equilibrium: senses position relative to gravity As when head is tilted or a car is speeding up or slowing down Dynamic equilibrium: senses position in response to head movement As in spinning movements

Static Equilibrium Sensed in Maculae of Utricle and Saccule Mechanism Gravity pulls on otoliths in otolithic membrane Bends hair cells in otolithic membrane Triggers nerve impulses in vestibular branch of Vestibulochochlear nerve (VIII)

Copyright 2010, John Wiley & Sons, Inc. Static Equilibrium Copyright 2010, John Wiley & Sons, Inc.

Copyright 2010, John Wiley & Sons, Inc. Static Equilibrium Copyright 2010, John Wiley & Sons, Inc.

Dynamic Equilibrium Semicircular canals (3) At right angles to each other Cristae in each ampulla contain Hair cells embedded in jellylike cupula Supporting cells Mechanism When head turns, hair cells move Endolymph lags and bends hair cells  Nerve impulses in Vestibular branch

Copyright 2010, John Wiley & Sons, Inc. Dynamic Equilibrium Copyright 2010, John Wiley & Sons, Inc.

Copyright 2010, John Wiley & Sons, Inc. Dynamic Equilibrium Copyright 2010, John Wiley & Sons, Inc.

Equilibrium Pathways Axons from vestibular branch  Medulla or Cerebellum Medulla  motor control: eye, head, neck  Spinal cord tracts for adjusting muscle tone and postural muscles