Chapter 8 Special Senses Essentials of Human Anatomy & Physiology Seventh Edition Elaine N. Marieb Chapter 8 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

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 (crease) 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 eyelids Connects to the surface of eye Secretes mucus to lubricate eye When inflamed, conjunctivitis 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

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 Ciliary 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

Sensory Tunic (Retina) Contains receptor cells (photoreceptors) Rods- Most are found towards the edges of the retina Allow dim light vision and peripheral vision Perception in gray tones Cones – 3 types detect different colors Densest in the center of the retina Fovea centralis – area of the retina with only cones Lack of one type = color blindness Signals pass from photoreceptors; leave the retina toward the brain through the optic nerve No photoreceptor cells are at the optic disk, or blind spot

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

Lens Biconvex crystal-like structure Held in place by a suspensory ligament attached to the ciliary body

Internal Eye Chamber Fluids Aqueous humor in Anterior Segment Watery fluid found in chamber between lens and cornea Similar to blood plasma Helps maintain intraocular pressure Provides nutrients for the lens and cornea Reabsorbed into venous blood Blocked drainage = inc pressure = glaucoma

Internal Eye Chamber Fluids Vitreous humor in Posterior Segment Gel-like substance behind 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 point on 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

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 3 areas Outer (external) ear Middle ear Inner ear

The External Ear Involved in hearing only Structures of external ear Pinna (auricle) External auditory canal

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

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

The Middle Ear or Tympanic Cavity 2 tubes are associated with the ear opening from auditory canal is covered by the tympanic membrane auditory tube (Eustachian tube) connecting middle ear with throat equalizing pressure during yawning or swallowing otherwise collapsed

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

Bones of the Tympanic Cavity Vibrations from eardrum move malleus These bones transfer sound to 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 (liquid) Figure 8.12 Slide 8.26a Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Inner Ear or Bony Labrynth Maze of bony chambers within temporal bone Cochlea Vestibule Semicircular canals

Organs of Hearing Organ of Corti Located within cochlea Receptors = hair cells on basilar membrane Gel-like tactorial membrane is capable of bending hair cells Cochlear nerve attached to hair cells transmits nerve impulses to auditory cortex on temporal lobe

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

Mechanisms of Hearing Uncoiled cochlea: sound waves below level of hearing travel w/o exciting hair cells 1- Higher pitched sounds make pressure waves that penetrate through cochlea and reach scala tympani 2- Membrane vibrates and response to frequencies of sound, stimulating hair cells Figure 8.14 Slide 8.29 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 position of head Send information via vestibular nerve Anatomy of the maculae Hair cells are embedded in otolithic membrane Otoliths (tiny stones) float in a gel around hair cells Movements cause otoliths to bend 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

Dynamic Equilibrium - Movement Crista ampullaris – receptors in the semicircular canals Tuft of hair cells Cupula (gelatinous cap) covers 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 hair cells An impulse is sent via vestibular nerve to cerebellum Figure 8.16c Slide 8.33b Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Chemical Senses Taste and Smell Both senses use chemoreceptors Both stimulated by chemicals in solution Taste has 4 types of receptors Smell can differentiate a large range of chemicals Both senses complement each other and respond to many of same stimuli! Slide 8.34 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Olfaction – The Sense of Smell Olfactory receptors are in roof of the nasal cavity Neurons with long cilia Chemicals must be dissolved in mucus for detection

Olfaction – The Sense of Smell Impulses are transmitted via olfactory nerve Interpretation of smells made in cortex

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 w/ projections,or papillae Filiform papillae sharp w/ no taste buds Fungifiorm papillae rounded w/ taste buds Circumvallate papillae large w/ taste buds

The Tongue and Taste Taste buds are found on the sides of papillae

Structure of Taste Buds Gustatory cells are the receptors Have gustatory hairs (long microvilli) Hairs stimulated by chemicals dissolved in saliva

Facial, Glossopharyngeal & Vagus nerves Structure of Taste Buds Impulses carried to gustatory complex by several cranial nerves b/c taste buds found in different areas Facial, Glossopharyngeal & Vagus nerves

Taste Sensations Sweet receptors Sugars Saccharine Some amino acids indicates energy-rich nutrients Slide 8.41 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Taste Sensations Sour receptors Acids Slide 8.41

Taste Sensations Bitter receptors allows sensing diverse natural toxins

Taste Sensations Salty receptors allows modulating diet for electrolyte balance

Developmental Aspects of All Special Senses Formed early in embryonic development Eyes are outgrowths of the brain All special senses are functional at birth

Short taste intro Relationship between smell and taste