Chapter 16 Special Senses Essentials of Human Anatomy & Physiology Seventh Edition Elaine N. Marieb Chapter 16 Special Senses Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

The Senses General senses of touch Special senses Temperature Pressure Pain Special senses Smell Taste Sight Hearing Equilibrium Slide 8.1 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

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 Slide 8.34 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Taste Sensations Sweet receptors Sugars Saccharine Some amino acids Sour receptors Acids Bitter receptors Alkaloids Salty receptors Metal ions Umami (“taste good”)– elicited by the amino acid glutamate (MSG) Slide 8.41 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

The Sense of Taste Taste buds house the receptor organs Location of taste buds Most are on the tongue Soft palate Cheeks Figure 8.18a, b Slide 8.37 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

The Tongue and Taste The tongue is covered with projections called papillae Filiform papillae – sharp with no taste buds Fungifiorm papillae – rounded with taste buds Circumvallate papillae – large papillae with taste buds Taste buds are found on the sides of papillae Slide 8.38 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Structure of Taste Buds Gustatory cells are the receptors Have gustatory hairs (long microvilli) Hairs are stimulated by chemicals dissolved in saliva Slide 8.39a Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Physiology of Taste In order to be tasted, a chemical: Must be dissolved in saliva Must contact gustatory hairs Binding of the food chemical: Depolarizes the taste cell membrane, releasing neurotransmitter Initiates a generator potential that elicits an action potential

Structure of Taste Buds Impulses are carried to the gustatory complex by several cranial nerves because taste buds are found in different areas Facial nerve Glossopharyngeal nerve Vagus nerve Slide 8.39b Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Anatomy of Taste Buds Slide 8.40 Figure 8.18 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Influence of Other Sensations on Taste Taste is 80% smell Thermoreceptors, mechanoreceptors, nociceptors (pre-pain) also influence tastes Temperature and texture enhance or detract from taste

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 Slide 8.35 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Olfactory Epithelium Slide 8.36 Figure 8.17 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

The Eye and Vision 70 percent of all sensory receptors are in the eyes, only see 1/6th of eye Each eye has over a million nerve fibers Protection for the eye Most of the eye is enclosed in a bony orbit A cushion of fat surrounds most of the eye Slide 8.2 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Accessory Structures of the Eye Eyelids Meets at medial and lateral canthus Eyelashes Figure 8.1b Slide 8.3a Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Accessory Structures of the Eye Eyelashes =Meibomian glands modified sebacious glands produce an oily secretion to lubricate the eye Figure 8.1b Slide 8.3b Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Accessory Structures of the Eye Ciliary glands – modified sweat glands between the eyelashes Figure 8.1b Slide 8.3c Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Accessory Structures of the Eye Conjunctiva Membrane that lines the eyelids Connects to the surface of the eye Secretes mucus to lubricate the eye Slide 8.4a Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Accessory Structures of the Eye Lacrimal apparatus Glands, ducts, (eye), canals, sac, nasolacrimal duct Tears: antibodies, lysozymes, stress? Figure 8.1a Slide 8.4b Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Extrinsic Eye Muscles Muscles attach to the outer surface of the eye Produce eye movements Figure 8.2 Slide 8.6 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Structure of the Eye The wall is composed of three tunics Sclera&Cornea fibrous outside layer Choroid – middle layer Sensory tunic – (retina) inside layer Figure 8.3a Slide 8.7 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

The Fibrous Tunic Sclera Cornea 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 Slide 8.8 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Choroid Layer Blood-rich nutritive tunic Pigment prevents light from scattering Modified interiorly into two structures Cilliary body – smooth muscle Iris Pigmented layer that gives eye color Pupil – rounded opening in the iris Slide 8.9 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

The Iris Visible colored part of the eye Attached to the ciliary body Composed of smooth muscle Pupil – the round, central opening Sphincter pupillae muscle (constrictor or circular) Dilator pupillae muscle (dilator or radial) Act to vary the size of the pupil

Pupillary dilation and constriction

Sensory Tunic (Retina) Contains receptor cells (photoreceptors) Rods- low levels of light, any color Cones- need more intense light, detect color Signals pass from photoreceptors and leave the retina toward the brain through the optic nerve Slide 8.10 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Neurons of the Retina Slide 8.11 Figure 8.4 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Neurons of the Retina and Vision Rods Most are found towards the edges of the retina Allow dim light vision and peripheral vision Perception is all in gray tones Lower resolution images Slide 8.12a Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Neurons of the Retina and Vision Cones – 3 types detect different colors (red, green, blue) Densest in the center of the retina Fovea centralis – area of the retina with only cones Lack of one type = color blindness Higher resolution images No photoreceptor cells are at the optic disk, or blind spot Slide 8.12b Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Normal Opthalmoscopic View of Eye

Lens Biconvex crystal-like structure Held in place by a suspensory ligament attached to the ciliary body Figure 8.3a Slide 8.14 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Internal Chambers and Fluids Figure 16.8

Internal Eye Chamber Fluids Aqueous humor in Anterior Segment Watery fluid found in chamber between the lens and cornea Similar to blood plasma Helps maintain intraocular pressure Provides nutrients for the lens and cornea Reabsorbed into venous blood Blocked drainage = glaucoma Slide 8.15a Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Internal Eye Chamber Fluids Vitreous humor in Posterior Segment Gel-like substance behind the lens Keeps the eye from collapsing Lasts a lifetime and is not replaced Slide 8.15b Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Lens Accommodation Light must be focused to a point on the retina for optimal vision The eye is set for distance vision (over 20 ft away) The lens must change shape to focus for closer objects Slide 8.16 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Figure 8.9

Correcting the Eye Correct Focus = emmetropia Nearsightedness = myopia Focus of light in front of retina Eyeball too long or lens too strong Distant objects are blurry Farsightedness = hyperopia Focus of light beyond the retina Short eyeball or lazy lens Near objects are blurry.

Emmetropia

Hyperopia

Astigmatism Unequal curvatures in cornea & lens

The Ear Houses two senses Receptors are mechanoreceptors Hearing Equilibrium (balance) Receptors are mechanoreceptors Slide 8.20 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Anatomy of the Ear The ear is divided into three areas Outer (external) ear Middle ear Inner ear Figure 8.12 Slide 8.21 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

The External Ear Involved in hearing only Structures of the external ear Pinna (auricle) External auditory canal Figure 8.12 Slide 8.22 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

The External Auditory Canal Narrow chamber in the temporal bone Lined with skin Ceruminous (wax) glands are present Ends at the tympanic membrane Slide 8.23 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

The Middle Ear or Tympanic Cavity Air-filled cavity within the temporal bone Only involved in the sense of hearing Slide 8.24a Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

The Middle Ear or Tympanic Cavity Two tubes are 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 Slide 8.24b Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Bones of the Tympanic Cavity Three bones span the cavity Malleus (hammer) Incus (anvil) Stapes (stirrip) Figure 8.12 Slide 8.25a Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Bones of the Tympanic Cavity Vibrations from eardrum move the malleus These bones transfer sound to the inner ear Figure 8.12 Slide 8.25b Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Inner Ear or Bony Labyrinth Includes sense organs for hearing and balance Filled with perilymph Figure 8.12 Slide 8.26a Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Inner Ear or Bony Labrynth A maze of bony chambers within the temporal bone Cochlea Vestibule Semicircular canals Figure 8.12 Slide 8.26b Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Organs of Hearing Organ of Corti Located within the cochlea Receptors = hair cells on the basilar membrane Gel-like tectorial membrane is capable of bending hair cells Cochlear nerve attached to hair cells transmits nerve impulses to auditory cortex on temporal lobe Slide 8.27a Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Organs of Hearing Slide 8.27b Figure 8.13 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Mechanisms of Hearing Vibrations from sound waves move tectorial membrane Hair cells are bent by the membrane An action potential starts in the cochlear nerve Continued stimulation can lead to adaptation Slide 8.28 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Mechanisms of Hearing Slide 8.29 Figure 8.14 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Organs of Equilibrium Receptor cells are in two structures Vestibule Semicircular canals Figure 8.16a, b Slide 8.30a Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Organs of Equilibrium Equilibrium has two functional parts Static equilibrium – sense of gravity at rest Dynamic equilibrium – angular and rotary head movements Figure 8.16a, b Slide 8.30b Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Static Equilibrium - Rest Maculae – receptors in the vestibule Report on the position of the head Send information via the vestibular nerve Anatomy of the maculae Hair cells are embedded in the otolithic membrane Otoliths (tiny stones) float in a gel around the hair cells Movements cause otoliths to bend the hair cells Slide 8.31 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Function of Maculae Slide 8.32 Figure 8.15 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Anatomy and Function of the Maculae Figure 16.21b

Dynamic Equilibrium - Movement Crista ampullaris – receptors in the semicircular canals Tuft of hair cells Cupula (gelatinous cap) covers the hair cells Figure 8.16c Slide 8.33a Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Dynamic Equilibrium Action of angular head movements The cupula stimulates the hair cells An impulse is sent via the vestibular nerve to the cerebellum Figure 8.16c Slide 8.33b Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Disorders of Equilibrium and Hearing: Motion Sickness Motion sickness – carsickness, seasickness Popular theory for a cause – a mismatch of sensory inputs

Disorders of Equilibrium and Hearing: Conduction Deafness Sound vibrations cannot be conducted to the inner ear Ruptured tympanic membrane, otitis media, otosclerosis Ruptured tympanic membrane Otitis media Normal tympanic membrane

Disorders of Equilibrium and Hearing: Sensorineural Deafness Results from damage to any part of the auditory pathway mild severe

Developmental Aspects of the Special Senses Formed early in embryonic development Eyes are outgrowths of the brain All special senses are functional at birth Slide 8.42 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings