Untitled Quiz

Professor Information

• Professor: Rebecca Polich, PhD
• Pronouns: She/Hers/Her
• Email: [email protected]
• Office: R224
• Office Hours: by appointment, Zoom and in-person available

Course Outline

• My philosophy on teaching (and life)
• Why the rules are in place
• Anatomy terms and roots (and why "mispronouncing" words aren't funny)
• How the class is organized and why
• Nursing Department
• Review of Canvas pages
• Class vs. lab
• Resources available in each
• Review of Mastering A&P homework
• Syllabus review
• Share out/getting to know each other session
• Lecture: the special senses: vision

Syllabus Agreement Activity

• 3 Canvas participation activities to complete
• Syllabus quiz
• Cheating rules acknowledgement
• Missed exam and lab acknowledgement
• Disability and chronic illness communication acknowledgement
• Found in the Week 1 module
• Must be completed to access later modules

Who I Am (Professor)

• B.S. from UC Davis, 2012
• PhD from Iowa State University, 2017
• Former Professor at Rocky Mountain College
• Taught A&P
• Daughter
• Sister
• Wife
• Cat mom

Share Out

• Find a partner or two in the class
• Talk about your background
• What college are you a student in?
• What year in school and major?
• Your career path and why you chose it
• Share out/getting to know each other session

Chapter 15: The Special Senses

Chapter 15 - Learning Objectives (Vision)

• Explain how light is directed to the fovea centralis of the retina.
• Describe the process by which images are focused on the retina.
• Describe the structure and function of the retina's layers of cells.
• Explain the distribution of rods and cones and their relation to visual acuity.
• Describe the structure of the photoreceptors and how we are able to distinguish color.
• Explain photoreception and how visual pigments are activated.
• Explain how the visual pathways distribute information to their destinations in the brain.
• Describe disorders of vision and their possible treatments.

Chapter 15 - Learning Objectives (Equilibrium and Hearing)

• Describe the structures and functions of the bony labyrinth and membranous labyrinth.
• Describe the functions of hair cells in the semicircular ducts, utricle, and saccule.
• Describe the structures and functions of the spiral organ.
• Explain the anatomical and physiological basis for pitch and volume sensations for hearing.
• Trace the pathways for the sensations of equilibrium and hearing to their destinations in the brain.
• Describe age-related disorders of olfaction, gustation, vision, equilibrium, and hearing.

Chapter 15 - Learning Objectives (Olfaction and Gustation)

• Explain the roles of generation potentials and depolarization in sensory neurons and receptor cells.
• Trace the olfactory pathways to their destinations in the cerebrum and explain how olfactory perception occurs.
• Describe gustatory reception. Be able to answer questions about the physiological processes involved in taste.
• Trace the gustatory pathways.

Eye Layers and Cavities - Fibrous Layer

• Outermost layer of the eye
• Consists of cornea (clear) and sclera (white)
• Joined at the corneoscleral junction
• Supports and protects the eye
• Attachment site for extrinsic eye muscles
• Curvature of the cornea aids in focusing process (light enters through cornea)

Eye Layers and Cavities - Vascular Layer

• Contains many blood vessels, lymphatic vessels, and intrinsic (smooth) muscles
• Includes iris, ciliary body, and choroid
• Provides route for blood vessels/lymphatics to eye tissues
• Regulates amount of light entering eye (iris)
• Secretes/reabsorbs aqueous humor (fluid) circulating in eye chambers
• Controls shape of lens (ciliary body) needed for focusing

Eye Layers and Cavities - Inner Layer (Retina)

• Innermost layer of the eye
• Outer pigmented layer absorbs light
• Thick, inner neural layer contains photoreceptors (cells sensitive to light)

The Three Layers of the Eye and Associated Structures

• Diagram showing the fibrous layer, vascular layer, and inner layer (retina).

Eye Layers and Cavities - Aqueous Humor

• Transports nutrients and wastes
• Forms fluid cushion
• Helps retain eye shape
• Stabilizes position of the retina

Iris (part of the vascular layer)

• Colored part of the eye
• Blood vessels and pigment cells (melanocytes)
• Two layers of smooth muscle-contract to change pupil diameter to control light
• Ciliary body-thickened region bulging into the interior of the eye
• Ring of fibers connects ciliary body and lens
• Choroid—vascular layer under sclera, which has an extensive capillary network supplying oxygen/nutrients to neural layer

Eye Structures - Cornea

• Allows light to enter the eye—transparent and clear
• Dense matrix of multiple layers of collagen fibers (clear)
• Avascular, receives oxygen and nutrients from tears

Eye Structures - Lens

• Posterior to cornea
• Anchored by ciliary zonule of ciliary body
• Primary function: changes shape to focus image on photoreceptors

Eye Structures - Choroid

• Middle layer
• Blood vessels nourish all eye structures
• Sclera-dense fibrous connective tissue with collagen and elastic fibers
• Stabilizes eye shape
• Insertion for extrinsic eye muscles

Eye Structures - Optic Nerve

• Conveys visual information to the brain

Eye Structures - Ciliary Body

• Supports lens, controls its shape
• Tension in ciliary zonule resists tendency of lens to ball up
• Retina-contains photoreceptors, pigment cells, supporting cells, neurons

Eye Structures - Pupil

• Opening in iris through which light passes
• Two pupillary muscles of iris regulate amount of light entering eye
• Dilator pupillae muscles-enlarge pupil/supplied by the sympathetic system
• Sphincter pupillae muscles-make pupil smaller/supplied by parasympathetic NS

Eye Structures - Visual Axis

• Imaginary line drawn from the center of an object you are looking at, through center of cornea and lens to retina.
• Fovea centralis-central part of macula
• Has the highest concentration of photoreceptors
• Point of sharpest vision

Retina-Photoreceptors, Pigment

• Photoreceptors in inner neural portion; type/density varies by area
• Macula-patch of retina with high density of photoreceptors
• Fovea centralis-central part of macula
• Highest concentration of photoreceptors
• Sharpest vision
• Rods and cones synapse with bipolar cells to ganglion synapses

Photoreceptor Distribution

• Cones: ~6 million per eye, most dense in fovea centralis of macula (no rods)

Rods

• Highly sensitive to very dim light
• No color discrimination-only black-and-white
• 125 million per eye

Cones

• Color vision
• Sharper, clearer images in very bright light
• Require more intense light
• Rods and cones synapse with bipolar cells

Photoreceptors (Rods & Cones)

• Rods and cones detect photons (basic units of light)
• Our visible spectrum: 400-700 nm

Photoreception

• Visual pigments transduce light
• Derived from rhodopsin (visual purple)

Photoreceptor Structure

• Pigmented epithelium adjacent to photoreceptors
• Absorbs photons not absorbed by visual pigments, phagocytizes old discs

Photoreceptor structure (continued)

• Outer segment: flattened membranous discs containing visual pigment
• Cones: plasma membrane infoldings, tappers to a blunt point
• Rods-discs separate, elongated cylinder
• Inner segment: contains organelles for all cell functions except photoreception, synapses with bipolar cell

Photoreception - Color Vision

• Rods all contain same opsin, react to blue-green light
• Three types of cones: Blue (16%), Green (10%), and Red (74%)
• If all three cones are stimulated equally, perceived light is white
• Different opsin in different cones, which makes the types sensitive to different wavelengths, with some overlap. If all three types are stimulated equally, white is viewed.

Photoreception - Color blindness

• Nonfunctional cones
• Inability to distinguish specific colors
• One or more cone types not working or aren't using necessary visual pigment
• Most common is red-green color blindness (lack of red cones)
• Often inherited—more common in males
• 10% males, 0.67% females

Photoreception Process (Resting State)

• Chemically gated sodium ion channels in outer segment; stay open if cGMP is present
• Inner segment continuously pumps sodium ions from cytosol

Photoreception Process-Activation

• Retinal molecule changes shape (activation) from bent 11-cis form to linear 11-trans from
• Opsin activates transducin
• Transducin activates phosphodiesterase (PDE)

Photoreception Process-Deactivation

• Phosphodiesterase breaks down cGMP, inactivating gated sodium channels
• Sodium entry decreases

Photoreception Process - Active State

• Decreased sodium entry reduces dark current
• Membrane potential drops to -70mV (hyperpolarized)

Photoreception process - Activation (cont'd)

• Hyperpolarization decreases neurotransmitter release
• Decreased neurotransmitter signals bipolar cell that photoreceptor has absorbed a photon.

Photoreception Process - Bleaching (cont'd)

• Rhodopsin cannot respond to another photon until the original shape of retinal is regained
• Three-step process: Bleaching, Retinal converted back to cis shape, Opsin and retinal reassembled as rhodopsin

Visual Pathways

• Photoreceptors to bipolar cells to ganglion cells
• ~1 Million axons from ganglion cell converge at optic disc to head toward diencephalon as optic nerve (II)

Visual Pathways

• Two optic nerves (one from each eye) reach diencephalon at the optic chiasm
• From optic chiasm, continue along optic tracts
• About half of fibers go to the lateral geniculate nucleus on the same side of the brain; other half cross over to the opposite side

Visual Pathways - Optic radiation

• Bundle of projection fibers linking each lateral geniculate body with visual cortex.
• Collaterals from fibers synapse in lateral geniculate bodies and go to subconscious processing centers in diencephalon and brainstem.

Visual Pathways - Pupillary Reflexes

• Pupillary reflexes and others triggered by collaterals going to superior colliculi

Visual Pathways - Depth Perception

• Ability to judge depth/distance by interpreting 3-D relationships
• Perceived by comparing relative positions of objects in images received by both eyes
• Images from left and right eyes overlap with each eye receiving slightly different image

Internal Ear Sensory Receptors

• Equilibrium and hearing receptors in internal ear are isolated and protected from external environment
• Receptors are located in internal ear.
• Information is integrated locally and forwarded to CNS.

Internal Ear Sensory receptors (Hair cells)

• Free surfaces covered with specialized nonmotile processes (stereocilia)
• Stereocilia-resemble long microvilli
• Kinocilium-a single large cilium
• Hair cells act as mechanoreceptors-sensitive to contact/movement
• External force distorts plasma membranes
• Modifies neurotransmitter release; provides info on direction/strength of stimulus; monitored by dendrites of sensory neurons.

Internal Ear Sensory Receptors - Structure & Function

• Complex 3-D structure in internal ear determines what stimuli can reach hair cells
• Hair cells in one region respond only to gravity or acceleration.
• Hair cells in other regions respond only to rotation or to sound.

External Ear

• Auricle (elastic cartilage): collects/directs soundwaves
• External acoustic meatus (passageway in temporal bone) • Ceruminous glands: secrete earwax, keeping foreign bodies out, slows growth of microorganisms • Hairs: trap debris

Middle Ear

• Tympanic membrane (tympanum, eardrum): thin, semitransparent sheet separating external and middle ear.
• Auditory ossicles: three tiny bones (malleus, incus, stapes); connect tympanic membrane and inner ear

Middle Ear - Auditory Tube

• (pharyngotympanic tube, eustachian tube): connects middle ear to nasopharynx; allows equalizing pressures across tympanic membrane; can allow microorganisms into middle ear.

Anatomy of the Ear - Internal Ear

• Contains sensory organs (hearing and equilibrium)
• Receives amplified sound waves from middle ear
• Established by layer of dense bone = bony labyrinth

The Anatomy of the Internal Ear

• Bony labyrinth: shell of dense bone surrounding membranous labyrinth
• Filled with perilymph (liquid similar to CSF)
• Three parts: semicircular canals, vestibule, cochlea

Labyrinths of the Internal Ear - Membranous Labyrinth

• Collection of fluid-filled tubes/chambers
• Houses receptors for hearing and equilibrium
• Contains fluid called endolymph

Labyrinths of the Internal Ear - Three Parts

• Semicircular ducts (within canals): receptors stimulated by head rotation
• Utricle and saccule (within vestibule): provide sensations of gravity and linear acceleration
• Cochlear duct (within cochlea): sandwiched between pair of perilymph-filled chambers, resembles snail shell, receptors stimulated by sound

Hair Cells in the Semicircular Ducts

• Respond to rotation
• Three ducts (anterior, posterior, lateral)
• Continuous with utricle, filled with endolymph
• Ampulla-enlarged part of duct with receptors
• Ampullary crest-region in wall of ampulla with receptors
• Ampullary cupula-gelatinous structure extending through ampulla with kinocilia and stereociliaEmbedded in hair cells.

Receptors for Equilibrium

• Head rotating in plane of a duct moves endolymph, which pushes ampullary cupula to side
• Distorting receptor processes
• Movement causes stimulation, opposite movement inhibits
• Ampullary cupula rebounds

Receptors for Equilibrium - Utricle and Saccule

• Provide equilibrium sensations
• Utricle and saccule contain hair cells clustered in maculae
• Macula in utricle senses horizontal movement;
• Macula of saccule senses vertical movement.
• Hair cell processes embedded in gelatinous otolithic membrane

Cochlear Duct (scala media)

• Filled with endolymph
• Between two chambers with perilymph
• Scala vestibuli (vestibular duct)
• Scala tympani (tympanic duct)

Cross-Sections of the Cochlea

• Diagram of the cochlea showing scala vestibule, scala media, and scala tympani.

Receptors for Hearing (Spiral Organ)

• Hair cells lack kinocilia
• Stereocilia are in contact with overlying tectorial membrane
• Bulk of each hair cell is embedded in basilar membrane

Receptors for Hearing (Spiral Organ-cont'd)

• Sound waves create pressure waves in perilymph
• Pressure waves cause basilar membrane to vibrate up and down
• Vibrations of basilar membrane press stereocilia into tectorial membrane, distorting them

Receptors for Hearing (Spiral Organ - cont'd)

• Distortion triggers nerve impulse
• Sensory neurons relay signals through spiral ganglion to cochlear branch of vestibulocochlear nerve (VIII)

External and Cross-Sectional Views of the Cochlea

• Diagram showing external and cross-sectional views of the cochlea including the scala vestibuli, cochlear duct, and scala tympani.

Anatomy of the Spiral Organ

• Diagram of spiral organ.

Physiology of Hearing

• Hearing: perception of sound
• Sound = waves of pressure
• Pressure wave in air, causes compressed/separated molecules
• Wavelength of sound = distance between adjacent wave crests.

Physiology of Hearing - Frequency

• Frequency = Number of waves (cycles) passing a fixed point in a given time = pitch
• High frequency (short wavelength) = high pitch

Physiology of Hearing - Intensity (Loudness)

• Intensity (loudness) = amount of energy in sound waves
• Amplitude of sound wave reflects amount of energy (intensity)
• Greater energy = larger amplitude = louder sound; measured in decibels (dB)

Intensity of Representative Sounds

• Chart showing typical decibel levels for various sounds (quiet library to rocket launch).

Physiology of Hearing - Stapes Pushing on Oval Window

• Stapes pushing on oval window moves causing distortion of basilar membrane toward the round window.

Physiology of Hearing (continued)

• Flexibility of basilar membrane varies with its length
• Different sound frequencies affect different parts of the membrane
• Location of vibration interpreted as pitch
• Number of stimulated hair cells interpreted as volume

Events Involved in Hearing

• Movement of sound waves arrives at tympanic membrane, which displaces auditory ossicles.
• Movement of stapes causes pressure waves in perilymph of scala vestibuli
• Pressure waves distort basilar membrane and cause hair cells to vibrate and tectorial membrane
• Sensory information is relayed to the CNS (through cranial nerve VIII).

Neural Pathways for the Sense of Equilibrium (Continued)

• Summary/description of the neural pathways to interpret the sense of equilibrium.

Functions of the Vestibular Nuclei

• Integrating sensory information about equilibrium from both ears
• Relaying information to cerebellum
• Relaying information to cerebral cortex
• Sending commands to motor nuclei

Vestibulocochlear Nerve Function - Hearing

• Nerve signals for hearing carried on cochlear nerve and the vestibulocochlear nerve
• Stimulation of hair cells activates sensory neurons (hearing)

Neural Pathways for the Sense of Hearing

• Stimulation of hair cells activates sensory neurons, delivering information relayed via the cochlear nerve of the vestibulocochlear nerve (VIII)
• Information carried on cochlear nerve to cochlear nuclei in the medulla oblongata
• Neuronal pathways coordinate responses to auditory stimuli and relay impulses to the brainstem, pons, midbrain, and thalamus.
• Projection fibers deliver information to locations within the auditory cortex of the temporal lobe.

Vestibulocochlear Nerve Function (Continued)

• Most auditory info from one cochlea projects to auditory cortex on the opposite side.
• Some info from cochlea reaches the auditory cortex on the same side.

A Generator Potential-Depolarization of Sensory Membranes

• Five special senses: Olfaction, Gustation, Vision, Equilibrium, and Hearing
• All senses originate with specialized sensory receptor cells.
• Dendrites of specialized neurons/specialized cells synapse with sensory neurons
• Depolarization of sensory neuron = generator potential

Generator Potential - Olfactory Receptors

• Dissolved odorants bind to olfactory receptors, causing depolarization (a generator potential).
• Strong enough stimulus triggers action potentials to the CNS.

Generator Potential - Receptors for Taste, Vision, Equilibrium, and Hearing

• Specialized cells with inexcitable membranes synapse with sensory neurons
• Stimulation triggers graded depolarization

Generator Potential - Graded Depolarization Triggers Neurotransmitter Release

• Graded depolarization of receptor cell triggers neurotransmitter release
• Neurotransmitters depolarize sensory neurons and cause generator potentials that can trigger action potentials.
• Action potentials are propagated to CNS.

Olfaction (sense of smell)

• Odorants = dissolved chemicals that stimulate olfactory neurons
• Bind membrane receptors on olfactory receptor cells
• Generally small organic molecules.
• As few as four molecules can activate a receptor cell.

Olfactory Reception Process

• Odorant binds to receptor protein, activates adenylate cyclase
• cAMP opens sodium channels, starts depolarization
• If enough depolarization, action potential is triggered and relayed to CNS.

The Process of Olfaction

• Diagram describing olfaction process.

Olfactory Pathway

• Bundled axons penetrate cribriform plate of ethmoid bone, bulb, and olfactory tract
• Olfactory information carried to limbic system and hypothalamus (as well as olfactory cortex)

Gustation (taste)

• Taste receptors (gustatory receptor cells)
• Most important receptors are on superior surface of tongue
• Also in adjacent parts of pharynx, larynx, epiglottis
• Numbers decrease with age

Gustation (continued)

• Lingual papillae = epithelial projections on tongue surface
• Contain taste buds-sensory structures with taste receptors that respond to various chemical stimuli.

The Tongue

• Diagram showing location of taste buds on different parts of the tongue.

Gustation (continued)

• Four primary taste sensations: sweet, salty, sour, bitter

Gustation (continued)-Umami

• Umami = pleasant, savory taste characteristic of broths, cheese
• Binds receptors for amino acids, small peptides, nucleotides.

Gustation (continued) - Water Receptors

• Concentrated in pharynx
• Output goes to hypothalamus
• Affects water balance and regulation of blood volume
• Prevent over-ingesting H₂O

Gustation (continued) - Taste buds, Gustatory Cells, Basal Cells

Gustatory Reception-Taste Reception

• Two types of gustatory reception: Salt, and Sour receptors.
• Binding to receptors for sweet, bitter, and umami; activate G-protein complexes

Gustatory Reception

• Gustatory receptor cells bind dissolved chemicals, generator potential occurs
• Triggers action potentials
• Information relayed on cranial nerves (facial, glossopharyngeal, vagus)

Gustatory Pathway (continued)

• Sensory afferents synapse in solitary nucleus of medulla oblongata
• Axons of postsynaptic neurons cross over, enter medial lemniscus of medulla oblongata
• Synapse in thalamus; information to gustatory cortex of insula

Gustatory reception - Taste

• Conscious perception of taste processing of primary somatosensory cortex
• Integrated with other sensory data—texture of food
• Taste-related sensations (peppery or burning hot—carried by trigeminal nerve (V))

Disorders of the Special Senses-Olfaction

• Head injury: damage to olfactory nerve
• Age changes: olfactory receptors regularly replaced, but number declines and sensitivity decreases with age.

Disorders of the Special Senses-Gustation

• Problems with receptors - decreased smell dulls taste
• Damaged taste buds — mouth infection or inflammation
• Damaged cranial nerves (VII, IX, X) - trauma or compression
• Natural age-related changes

Disorders of the Special Senses-Vision

• Senile cataracts: lens loses transparency-natural aging, surgically correctable, progresses-person needs more light to read, acuity may decline to blindness
• Presbyopia: age-related farsightedness due to loss of lens elasticity.

Disorders of the Special Senses-Equilibrium

• Vertigo: false perception of spinning
• Internal ear receptor complex
• Vestibular nerve
• Sensory nuclei & CNS pathways
• Can be due to vision problems / drug use (including alcohol.)

Disorders of the Special Senses - Vertigo (cont'd)

• Vertigo (Continued): stimulated by anything that sets endolymph in motion
• Motion sickness: most common cause • Symptoms: headache, sweating flushing of face, nausea, vomiting.

Disorders of the Special Senses - Hearing

• Partial hearing deficit: affects ~37.5 million in U.S.
• Two types: conductive and sensorineural
• Conductive hearing loss: problem conducting sound waves

Disorders of the Special Senses - Conductive Hearing Loss

• Causes: • Impacted earwax • Infection • Perforated tympanic membrane

Disorders of the Special Senses - Sensorineural Hearing Loss

• Damage to cochlea or nerve pathways from internal ear to brain
• Causes: exposure to loud noise, head trauma, and aging
• Age changes: • Tympanic membrane loses flexibility • Articulations between auditory ossicles stiffen • Round window may start to ossify

Participation 6/12

• Find a partner in class
• Answer questions from the Participation 6/12 activity (found in Week 1 Module)
• Name the two photoreceptors of the eye, and where they are found
• Explain the significance of the fovea centralis.