Human Anatomy Chapter 8 PDF

# Special Senses **PowerPoint® Lecture Slide Presentation** * **by Patty Bostwick-Taylor** * Florece-Darlington Technical College ## Essentials of Human Anatomy & Physiology * Ninth Edition * **ELAINE N. MARIEB** **Part A** * Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummi...

# Special Senses **PowerPoint® Lecture Slide Presentation** * **by Patty Bostwick-Taylor** * Florece-Darlington Technical College ## Essentials of Human Anatomy & Physiology * Ninth Edition * **ELAINE N. MARIEB** **Part A** * Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings ## The Senses * Special senses * Smell * Taste * Sight * Hearing * Equilibrium ## Structure of The Eye ### Structure of The Eye: The Fibrous Layer * **Sclera** * White connective tissue layer * Seen anteriorly as the "white of the eye" * **Cornea** * Transparent, central anterior portion * Allows for light to pass through * Repairs itself easily * The only human tissue that can be transplanted without fear of rejection ### Structure of The Eye: Vascular Layer * **Choroid** is a blood-rich nutritive layer in the posterior of the eye * Pigment prevents light from scattering * **Modified anteriorly into two structures:** * **Ciliary body** - smooth muscle attached to lens * **Iris** - regulates amount of light entering eye * Pigmented layer that gives eye color * Pupil - rounded opening in the iris ### Structure of The Eye: Sensory Layer * **Retina** contains two layers: * Outer pigmented layer * Inner neural layer * Contains receptor cells (photoreceptors): * Rods * Cones * Signals leave the retina toward the brain through the optic nerve * **Optic disc** (blind spot) is where the optic nerve leaves the eyeball * Cannot see images focused on the optic disc * Neurons of the retina and vision * **Rods** * Most are found towards the edges of the retina * Allow dim light vision and peripheral vision * All perception is in gray tones * **Cones** * Allow for detailed color vision * Densest in the center of the retina * **Fovea centralis** - area of the retina with only cones * No photoreceptor cells are at the optic disc, or blind spot * **Cone sensitivity** * Three types of cones * Different cones are sensitive to different wavelengths * Color blindness is the result of the lack of one cone type ## Sensitivities of Cones to Different Wavelengths * **Visible light** * **Light absorption by cone populations** * **Wavelength (nanometers)**: 380, 450, 500, 550, 600, 650, 700, 750 * **560nm (red cones)** * **530nm (green cones)** * **420nm (blue cones)** ## Lens * **Biconvex crystal-like structure** * Held in place by a suspensory ligament attached to the ciliary body * **Cataracts** result when the lens becomes hard and opaque with age * Vision becomes hazy and distorted * Eventually causes blindness in affected eye ## Two Segments, or Chambers, of The Eye * **Anterior (aqueous) segment** * Anterior to the lens * Contains aqueous humor * **Posterior (vitreous) segment** * Posterior to the lens. * Contains vitreous humor ## Anterior Segment * **Aqueous humor** * Watery fluid found between lens and cornea * Similar to blood plasma * Helps maintain intraocular pressure * Provides nutrients for the lens and cornea * Reabsorbed into venous blood through the scleral venous sinus, or canal of Schlemm ## Posterior Segment * **Vitreous humor** * Gel-like substance posterior to the lens * Prevents the eye from collapsing * Helps maintain intraocular pressure ## Pathway of Light Through The Eye * Light must be focused to a point on the retina for optimal vision * The eye is set for distance vision (over 20 feet away) * **Accommodation** - the lens must change shape to focus on closer objects (less than 20 feet away) * Image formed on the retina is a real image * **Real images are:** * Reversed from left to right * Upside down * Smaller than the object ## Images Formed on The Retina ## A Closer Look * **Emmetropia** - eye focuses images correctly on the retina * **Myopia** (nearsighted) * Distant objects appear blurry * Light from those objects fails to reach the retina and are focused in front of it. * Results from an eyeball that is too long * **Hyperopia** (farsighted) * Near objects are blurry while distant objects are clear * Distant objects are focused behind the retina * Results from an eyeball that is too short or from a "lazy lens" * **Astigmatism** * Images are blurry * Results from light focusing as lines, not points, on the retina due to unequal curvatures of the cornea or lens ## Homeostatic Imbalances of The Eyes * **Night blindness** - inhibited rod function that hinders the ability to see at night * **Color blindness** - genetic conditions that result in the inability to see certain colors * Due to the lack of one type of cone (partial color blindness) * **Cataracts** - when lens becomes hard and opaque, our vision becomes hazy and distorted * **Glaucoma** - can cause blindness due to increasing pressure within the eye * **Hemianopia** - loss of the same side of the visual field of both eyes; results from damage to the visual cortex on one side only ## The Ear * Houses two senses: * Hearing * Equilibrium (balance) * **Receptors** are mechanoreceptors * Different organs house receptors for each sense ## Anatomy of The Ear * The ear is divided into three areas: * **External (outer) ear** * **Middle ear** (tympanic cavity) * **Inner ear** (bony labyrinth) * **External (outer) ear** * **Auricle** (pinna) * **External acoustic meatus** (auditory canal) * Narrow chamber in the temporal bone * Lined with skin and ceruminous (wax) glands * Ends at the tympanic membrane * **Middle ear** (tympanic cavity) * Air-filled cavity within the temporal bone * Only involved in the sense of hearing * **Two tubes associated with the inner ear:** * The opening from the auditory canal is covered by the tympanic membrane * The auditory tube connecting the middle ear with the throat * Allows for equalizing pressure during yawning or swallowing * This tube is otherwise collapsed * **Bones of the middle ear (tympanic cavity):** * Three bones (ossicles) span the cavity: * Malleus (hammer) * Incus (anvil) * Stapes (stirrup) * **Function** * Vibrations from eardrum move the malleus → anvil → stirrup → inner ear * **Inner ear (bony labyrinth)** * Includes sense organs for hearing and balance * A maze of bony chambers within the temporal bone: * Cochlea * Vestibule (static eqilibrium - position of head) * Semicircular canals (dynamic equilibrium - movement of head) ## Organs of Equilibrium * **Semicircular canals** * Vestibular nerve * **Vestibule** * **Ampulla** * **Endolymph** * **Cupula of crista ampullaris** ## Mechanism of Hearing * **EXTERNAL EAR** * Pinna * Auditory canal * Ear-drum * **MIDDLE EAR** * Hammer, anvil, stirrup * Oval window * **INTERNAL EAR** * Fluids in cochlear canals * Upper & middle * Lower * Spiral organ of Corti stimulated ## Olfaction - The Sense of Smell * **Olfactory receptors** are in the roof of the nasal cavity * Neurons with long cilia * Chemicals must be dissolved in mucus for detection * Impulses are transmitted via the **olfactory nerve** * Interpretation of smells is made in the **cortex** ## The Sense of Taste * **Taste buds** house the receptor organs * **Location of taste buds:** * Most are on the tongue * Soft palate * Cheeks ## Taste Sensations * **Sweet receptors** (sugars) * Saccharine * Some amino acids * **Sour receptors** * Acids * **Bitter receptors** * Alkaloids * **Salty receptors** * Metal ions ## Chemical Senses: Taste and Smell * Both senses use **chemoreceptors** * Stimulated by chemicals in solution * Taste has four types of receptors * Smell can differentiate a large range of chemicals * Both senses complement each other and respond to many of the same stimuli ## Developmental Aspects of The Special Senses * Formed early in embryonic development * Eyes are outgrowths of the brain * All special senses are functional at birth