17- Lab The Special Senses

An Introduction to the Special Senses Learning Outcomes 17-1 Describe the sensory organs of smell, trace the olfactory pathways to their destinations in the brain, and explain the physiological basis of olfactory discrimination. 17-2 Describe the sensory organs of taste, trace the gustatory pathways to their destinations in the brain, and explain the physiological basis of gustatory discrimination. 17-3 Identify the internal and accessory structures of the eye, and explain the functions of each.

An Introduction to the Special Senses Learning Outcomes 17-4 Explain color and depth perception, describe how light stimulates the production of nerve impulses, and trace the visual pathways to their destinations in the brain. 17-5 Describe the structures of the external, middle, and internal ear, explain their roles in equilibrium and hearing, and trace the pathways for equilibrium and hearing to their destinations in the brain.

An Introduction to the Special Senses Five Special Senses Olfaction Gustation Vision Equilibrium Hearing

17-1 Smell (Olfaction) Olfactory Organs Olfactory epithelium Provide sense of smell Located in nasal cavity on either side of nasal septum Made up of two layers Olfactory epithelium Lamina propria

17-1 Smell (Olfaction) Layers of Olfactory Organs Olfactory epithelium contains: Olfactory receptors Supporting cells Basal (stem) cells

17-1 Smell (Olfaction) Layers of Olfactory Organs Lamina propria contains: Areolar tissue Blood vessels Nerves Olfactory glands

Figure 17-1a The Olfactory Organs Olfactory Pathway to the Cerebrum Olfactory epithelium Olfactory nerve fibers (N I) Olfactory bulb Olfactory tract Central nervous system Cribriform plate Superior nasal concha The olfactory organ on the left side of the nasal septum 8

Figure 17-1b The Olfactory Organs Basal cell: divides to replace worn-out olfactory receptor cells To olfactory bulb Olfactory gland Cribriform plate Olfactory nerve fibers Lamina propria Developing olfactory receptor cell Olfactory receptor cell Olfactory epithelium Supporting cell Mucous layer Knob Olfactory cilia: surfaces contain receptor proteins (see Spotlight Fig. 173) Subsance being smelled An olfactory receptor is a modified neuron with multiple cilia extending from its free surface. 9

17-1 Smell (Olfaction) Olfactory Glands Olfactory Receptors Secretions coat surfaces of olfactory organs Olfactory Receptors Highly modified neurons Olfactory reception Involves detecting dissolved chemicals as they interact with odorant-binding proteins

17-2 Taste (Gustation) Gustation Taste Receptors (Gustatory Receptors) Provides information about the foods and liquids consumed Taste Receptors (Gustatory Receptors) Are distributed on tongue and portions of pharynx and larynx Clustered into taste buds

17-2 Taste (Gustation) Taste Buds Associated with epithelial projections (lingual papillae) on superior surface of tongue

17-2 Taste (Gustation) Three Types of Lingual Papillae Filiform papillae Provide friction Do not contain taste buds Fungiform papillae Contain five taste buds each Circumvallate papillae Contain 100 taste buds each

17-2 Taste (Gustation) Taste Buds Contain: Basal cells Gustatory cells Extend taste hairs through taste pore Survive only 10 days before replacement Monitored by cranial nerves that synapse within solitary nucleus of medulla oblongata Then on to thalamus and primary sensory cortex

Figure 17-3a Gustatory Receptors Water receptors (pharynx) Umami Sour Bitter Salty Sweet Landmarks and receptors on the tongue 15

Figure 17-3b Gustatory Receptors Taste buds Circumvallate papilla Fungiform papilla Filiform papillae The structure and representative locations of the three types of lingual papillae. Taste receptors are located in taste buds, which form pockets in the epithelium of fungiform or circumvillate papillae. 16

Figure 17-3c Gustatory Receptors Taste buds Taste buds LM  280 Nucleus of transitional cell Nucleus of gustatory cell Nucleus of basal cell Taste bud LM  650 Transitional cell Gustatory cell Taste hairs (microvilli) Basal cell Taste pore Taste buds in a circumvallate papilla. A diagrammatic view of a taste bud, showing gustatory (receptor) cells and supporting cells. 17

17-2 Taste (Gustation) Gustatory Discrimination Sweet Salty Sour Four primary taste sensations Sweet Salty Sour Bitter

17-2 Taste (Gustation) Additional Human Taste Sensations Umami Water Characteristic of beef/chicken broths and Parmesan cheese Receptors sensitive to amino acids, small peptides, and nucleotides Water Detected by water receptors in the pharynx

17-2 Taste (Gustation) Gustatory Discrimination Dissolved chemicals contact taste hairs Bind to receptor proteins of gustatory cell Salt and sour receptors Chemically gated ion channels Stimulation produces depolarization of cell Sweet, bitter, and umami stimuli G proteins Gustducins

Figure 14-21 Cranial Nerves Controlling the Extra-Ocular Muscles Superior rectus muscle OPTIC NERVE (N II) Optic chiasm OCULOMOTOR NERVE (N III) TROCHLEAR NERVE (N IV) Superior oblique muscle Trochlea Levator palpebrae superioris muscle Trigeminal nerve (N V), cut Inferior oblique muscle Vestibulocochlear nerve (N VIII), cut Facial nerve (N VII), cut Inferior rectus muscle Medial rectus muscle Ciliary ganglion Lateral rectus muscle (cut) ABDUCENS NERVE (N VI) 21

Extrinsic Eye Muscles External muscles that rotate the eyeball Originate on surface of the eyeball (sclera) 4 rectus muscles – attach straight behind the eyeball Superior rectus (N III) Inferior rectus (N III) Medial rectus (N III) Lateral rectus (N VI) 2 oblique muscles – attach from the side of the eyeball Superior oblique (N IV) – along medial wall, passes through trochlea (loop on medial wall of orbit) and turns laterally Inferior oblique (N III) – from lateral wall of orbit, on inferior side of eyeball

Extrinsic Eye Muscles Figure 11–5c

Extrinsic Eye Muscles Figure 11–5a, b

Summary: Extrinsic Eye Muscles Table 11–3

17-3 Accessory Structures of the Eye Provide protection, lubrication, and support Include: The palpebrae (eyelids) The superficial epithelium of eye The lacrimal apparatus

17-3 Accessory Structures of the Eye Eyelids (Palpebrae) Continuation of skin Blinking keeps surface of eye lubricated, free of dust and debris Palpebral fissure Gap that separates free margins of upper and lower eyelids

17-3 Accessory Structures of the Eye Eyelids (Palpebrae) Medial canthus and lateral canthus Where two eyelids are connected Eyelashes Robust hairs that prevent foreign matter from reaching surface of eye

17-3 Accessory Structures of the Eye Eyelids (Palpebrae) Tarsal glands Secrete lipid-rich product that helps keep eyelids from sticking together

17-3 Accessory Structures of the Eye Superficial Epithelium of Eye Lacrimal caruncle Mass of soft tissue Contains glands producing thick secretions Contributes to gritty deposits that appear after good night’s sleep Conjunctiva Epithelium covering inner surfaces of eyelids (palpebral conjunctiva) and outer surface of eye (ocular conjunctiva)

Figure 17-4a External Features and Accessory Structures of the Eye Eyelashes Pupil Lateral canthus Palpebra Sclera Palpebral fissure Medial canthus Lacrimal caruncle Corneal limbus Gross and superficial anatomy of the accessory structures 31

17-3 Accessory Structures of the Eye Lacrimal Apparatus Produces, distributes, and removes tears Fornix Pocket where palpebral conjunctiva joins ocular conjunctiva Lacrimal gland (tear gland) Secretions contain lysozyme, an antibacterial enzyme

17-3 Accessory Structures of the Eye Tears Collect in the lacrimal lake Pass through: Lacrimal puncta Lacrimal canaliculi Lacrimal sac Nasolacrimal duct To reach inferior meatus of nose

Figure 17-4b External Features and Accessory Structures of the Eye Superior rectus muscle Tendon of superior oblique muscle Lacrimal gland ducts Lacrimal punctum Lacrimal gland Lacrimal caruncle Ocular conjunctiva Superior lacrimal canaliculus Lateral canthus Medial canthus Lower eyelid Inferior lacrimal canaliculus Orbital fat Inferior rectus muscle Lacrimal sac Nasolacrimal duct Inferior oblique muscle Inferior nasal concha Opening of nasolacrimal duct The organization of the lacrimal apparatus. 34

17-3 The Eye Three Layers of the Eye Outer fibrous layer Intermediate vascular layer Deep inner layer

17-3 The Eye Eyeball Is hollow Is divided into two cavities Large posterior cavity Smaller anterior cavity

Figure 17-5a The Sectional Anatomy of the Eye Fornix Palpebral conjunctiva Optic nerve Eyelash Ocular conjunctiva Ora serrata Cornea Lens Pupil Iris Limbus Fovea Retina Choroid Sclera Sagittal section of left eye 37

Figure 17-5b The Sectional Anatomy of the Eye Fibrous layer Vascular layer (uvea) Cornea Anterior cavity Iris Sclera Ciliary body Choroid Posterior cavity Neural layer (retina) Neural part Pigmented part Horizontal section of right eye 38

Figure 17-5c The Sectional Anatomy of the Eye Visual axis Anterior cavity Cornea Posterior chamber Anterior chamber Edge of pupil Iris Suspensory ligament of lens Nose Corneal limbus Lacrimal punctum Conjunctiva Lacrimal caruncle Lower eyelid Medial canthus Lateral canthus Ciliary processes Lens Ciliary body Ora serrata Sclera Choroid Retina Posterior cavity Ethmoidal labyrinth Lateral rectus muscle Medial rectus muscle Optic disc Fovea Optic nerve Orbital fat Central artery and vein Horizontal dissection of right eye 39

17-3 The Eye The Fibrous Layer Sclera (white of the eye) Cornea Corneal limbus (border between cornea and sclera)

17-3 The Eye Vascular Layer (Uvea) Functions Provides route for blood vessels and lymphatics that supply tissues of eye Regulates amount of light entering eye Secretes and reabsorbs aqueous humor that circulates within chambers of eye Controls shape of lens, which is essential to focusing

Figure 17-5c The Sectional Anatomy of the Eye Visual axis Anterior cavity Cornea Posterior chamber Anterior chamber Edge of pupil Iris Suspensory ligament of lens Nose Corneal limbus Lacrimal punctum Conjunctiva Lacrimal caruncle Lower eyelid Medial canthus Lateral canthus Ciliary processes Lens Ciliary body Ora serrata Sclera Choroid Retina Posterior cavity Ethmoidal labyrinth Lateral rectus muscle Medial rectus muscle Optic disc Fovea Optic nerve Orbital fat Central artery and vein Horizontal dissection of right eye 42

17-3 The Eye The Vascular Layer Iris Contains papillary muscles Change diameter of pupil

Figure 17-6 The Pupillary Muscles Pupillary constrictor (sphincter) Pupil Pupillary dilator (radial) The pupillary dilator muscles extend radially away from the edge of the pupil. Contraction of these muscles enlarges the pupil. The pupillary constrictor muscles form a series of concentric circles around the pupil. When these sphincter muscles contract, the diameter of the pupil decreases. Decreased light intensity Increased sympathetic stimulation Increased light intensity Increased parasympathetic stimulation 44

17-3 The Eye The Vascular Layer Ciliary Body Extends posteriorly to level of ora serrata Serrated anterior edge of thick, inner portion of neural tunic Contains ciliary processes, and ciliary muscle that attaches to suspensory ligaments of lens

17-3 The Eye The Vascular Layer The choroid Vascular layer that separates fibrous and inner layers posterior to ora serrata Delivers oxygen and nutrients to retina

17-3 The Eye The Inner Layer Outer layer called pigmented part Inner called neural part (retina) Contains visual receptors and associated neurons Rods and cones are types of photoreceptors Rods Do not discriminate light colors Highly sensitive to light Cones Provide color vision Densely clustered in fovea, at center of macula

Figure 17-5c The Sectional Anatomy of the Eye Visual axis Anterior cavity Cornea Posterior chamber Anterior chamber Edge of pupil Iris Suspensory ligament of lens Nose Corneal limbus Lacrimal punctum Conjunctiva Lacrimal caruncle Lower eyelid Medial canthus Lateral canthus Ciliary processes Lens Ciliary body Ora serrata Sclera Choroid Retina Posterior cavity Ethmoidal labyrinth Lateral rectus muscle Medial rectus muscle Optic disc Fovea Optic nerve Orbital fat Central artery and vein Horizontal dissection of right eye 48

Figure 17-7a The Organization of the Retina Horizontal cell Cone Rod Pigmented part of retina Rods and cones Amacrine cell Bipolar cells Ganglion cells LIGHT The cellular organization of the retina. The photoreceptors are closest to the choroid, rather than near the posterior cavity (vitreous chamber). 49

Figure 17-7a The Organization of the Retina Choroid Pigmented part of retina Rods and cones Bipolar cells Ganglion cells Retina LM  350 Nuclei of ganglion cells Nuclei of rods and cones Nuclei of bipolar cells The cellular organization of the retina. The photoreceptors are closest to the choroid, rather than near the posterior cavity (vitreous chamber). 50

Figure 17-7b The Organization of the Retina Pigmented part of retina Neural part of retina Central retinal vein Optic disc Central retinal artery Sclera Optic nerve Choroid The optic disc in diagrammatic sagittal section. 51

Figure 17-7c The Organization of the Retina Optic disc (blind spot) Fovea Macula Central retinal artery and vein emerging from center of optic disc A photograph of the retina as seen through the pupil. 52

17-3 The Eye Inner Neural Part Bipolar cells Horizontal cells Neurons of rods and cones synapse with ganglion cells Horizontal cells Extend across outer portion of retina Amacrine cells Comparable to horizontal cell layer Where bipolar cells synapse with ganglion cells

17-3 The Eye Horizontal and Amacrine Cells Optic Disc Facilitate or inhibit communication between photoreceptors and ganglion cells Alter sensitivity of retina Optic Disc Circular region just medial to fovea Origin of optic nerve Blind spot

Figure 17-8 A Demonstration of the Presence of a Blind Spot 55

17-3 The Eye The Chambers of the Eye Ciliary body and lens divide eye into: Large posterior cavity (vitreous chamber) Smaller anterior cavity Anterior chamber Extends from cornea to iris Posterior chamber Between iris, ciliary body, and lens

17-3 The Eye Aqueous Humor Intraocular Pressure Fluid circulates within eye Diffuses through walls of anterior chamber into scleral venous sinus (canal of Schlemm) Re-enters circulation Intraocular Pressure Fluid pressure in aqueous humor Helps retain eye shape

Figure 17-9 The Circulation of Aqueous Humor Cornea Pupil Anterior cavity Anterior chamber Posterior chamber Scleral venous sinus Body of iris Conjunctiva Ciliary process Lens Ciliary body Suspensory ligaments Sclera Pigmented epithelium Posterior cavity (vitreous chamber) Choroid Retina 58

17-3 The Eye Large Posterior Cavity (Vitreous Chamber) Vitreous body Gelatinous mass Helps stabilize eye shape and supports retina

17-3 The Eye The Lens Lens fibers Cataract Cells in interior of lens No nuclei or organelles Filled with crystallins, which provide clarity and focusing power to lens Cataract Condition in which lens has lost its transparency

17-5 The Ear The External Ear Auricle Surrounds entrance to external acoustic meatus Protects opening of canal Provides directional sensitivity

17-5 The Ear The External Ear External acoustic meatus Ends at tympanic membrane (eardrum) Tympanic membrane Is a thin, semitransparent sheet Separates external ear from middle ear

Figure 17-21 The Anatomy of the Ear External Ear Middle Ear Internal Ear Elastic cartilages Auditory ossicles Oval window Semicircular canals Petrous part of temporal bone Auricle Facial nerve (N VII) Vestibulocochlear nerve (N VIII) Bony labyrinth of internal ear Cochlea Tympanic cavity Auditory tube To nasopharynx External acoustic meatus Tympanic membrane Round window Vestibule 63

17-5 The Ear The External Ear Ceruminous glands Integumentary glands along external acoustic meatus Secrete waxy material (cerumen) Keeps foreign objects out of tympanic membrane Slows growth of microorganisms in external acoustic meatus

17-5 The Ear The Middle Ear Also called tympanic cavity Communicates with nasopharynx via auditory tube Permits equalization of pressures on either side of tympanic membrane Encloses and protects three auditory ossicles Malleus (hammer) Incus (anvil) Stapes (stirrup)

Figure 17-22a The Middle Ear Auditory Ossicles Malleus Incus Stapes Temporal bone (petrous part) Stabilizing ligaments Oval window Muscles of the Middle Ear Branch of facial nerve VII (cut) Tensor tympani muscle External acoustic meatus Stapedius muscle Tympanic cavity (middle ear) Round window Tympanic membrane Auditory tube The structures of the middle ear. 66

Figure 17-22b The Middle Ear Malleus attached to tympanic membrane Tendon of tensor tympani muscle Malleus Incus Base of stapes at oval window Stapes Stapedius muscle Inner surface of tympanic membrane The tympanic membrane and auditory ossicles 67

17-5 The Ear Vibration of Tympanic Membrane Converts arriving sound waves into mechanical movements Auditory ossicles conduct vibrations to inner ear Tensor tympani muscle Stiffens tympanic membrane Stapedius muscle Reduces movement of stapes at oval window

17-5 The Ear The Internal Ear Contains fluid called endolymph Bony labyrinth surrounds and protects membranous labyrinth Subdivided into: Vestibule Semicircular canals Cochlea

Figure 17-23b The Internal Ear KEY Semicircular ducts Membranous labyrinth Anterior Bony labyrinth Lateral Posterior Vestibule Cristae within ampullae Maculae Endolymphatic sac Semicircular canal Cochlea Utricle Saccule Vestibular duct Cochlear duct Tympanic duct Spiral organ The bony and membranous labyrinths. Areas of the membranous labyrinth containing sensory receptors (cristae, maculae, and spiral organ) are shown in purple. 70

Figure 17-23a The Internal Ear Perilymph KEY Membranous labyrinth Bony labyrinth Endolymph Bony labyrinth Membranous labyrinth A section through one of the semicircular canals, showing the relationship between the bony and membranous labyrinths, and the boundaries of perilymph and endolymph. 71

17-5 The Ear The Internal Ear Vestibule Encloses saccule and utricle Receptors provide sensations of gravity and linear acceleration Semicircular canals Contain semicircular ducts Receptors stimulated by rotation of head

17-5 The Ear The Internal Ear Cochlea Contains cochlear duct (elongated portion of membranous labyrinth) Receptors provide sense of hearing

17-5 The Ear The Internal Ear Round window Oval window Thin, membranous partition Separates perilymph from air spaces of middle ear Oval window Formed of collagen fibers Connected to base of stapes

17-5 The Ear Stimuli and Location Sense of gravity and acceleration From hair cells in vestibule Sense of rotation From semicircular canals Sense of sound From cochlea

17-5 The Ear Equilibrium Sensations provided by receptors of vestibular complex Hair cells Basic receptors of inner ear Provide information about direction and strength of mechanical stimuli

17-5 The Ear The Semicircular Ducts Are continuous with utricle Each duct contains: Ampulla with gelatinous cupula Associated sensory receptors Stereocilia – resemble long microvilli Are on surface of hair cell Kinocilium – single large cilium

Figure 17-24a The Semicircular Ducts Vestibular branch (N VIII) Semicircular ducts Anterior Cochlea Ampulla Posterior Lateral Endolymphatic sac Endolymphatic duct Utricle Saccule Maculae An anterior view of the right semicircular ducts, the utricle, and the saccule, showing the locations of sensory receptors 78

Figure 17-24b The Semicircular Ducts Ampulla filled with endolymph Cupula Hair cells Crista Supporting cells Sensory nerve A cross section through the ampulla of a semicircular duct 79

Figure 17-24c The Semicircular Ducts Direction of duct rotation Direction of relative endolymph movement Direction of duct rotation Semicircular duct Ampulla At rest Endolymph movement along the length of the duct moves the cupula and stimulates the hair cells. 80

Figure 17-24d The Semicircular Ducts Displacement in this direction stimulates hair cell Displacement in this direction inhibits hair cell Kinocilium Stereocilia Hair cell Sensory nerve ending Supporting cell A representative hair cell (receptor) from the vestibular complex. Bending the sterocilia toward the kinocilium depolarizes the cell and stimulates the sensory neuron. Displacement in the opposite direction inhibits the sensory neuron. 81

17-5 The Ear The Utricle and Saccule Provide equilibrium sensations Are connected with the endolymphatic duct, which ends in endolymphatic sac

17-5 The Ear The Utricle and Saccule Maculae Oval structures where hair cells cluster Statoconia Densely packed calcium carbonate crystals on surface of gelatinous mass Otolith (ear stone) = gelatinous matrix and statoconia

Figure 17-25ab The Saccule and Utricle The location of the maculae Otolith Gelatinous material Statoconia Hair cells Nerve fibers The structure of an individual macula 84

Figure 17-25c The Saccule and Utricle Head in normal, upright position Gravity Head tilted posteriorly Gravity Otolith moves “downhill,” distorting hair cell processes Receptor output increases A diagrammatic view of macular function when the head is held horizontally and then tilted back 1 2 85

17-5 The Ear Pathways for Equilibrium Sensations Vestibular receptors Activate sensory neurons of vestibular ganglia Axons form vestibular branch of vestibulocochlear nerve (VIII) Synapse within vestibular nuclei

17-5 The Ear Hearing Cochlear duct receptors Provide sense of hearing

Vestibulocochlear nerve (N VIII) Figure 17-27a The Cochlea Round window Stapes at oval window Scala vestibuli Cochlear duct Scala tympani Semicircular canals Cochlear branch Vestibular branch KEY From oval window to tip of spiral Vestibulocochlear nerve (N VIII) From tip of spiral to round window The structure of the cochlea 88

Diagrammatic and sectional views of the cochlear spiral Figure 17-27b The Cochlea Temporal bone (petrous part) Vestibular membrane Scala vestibuli (contains perilymph) Tectorial membrane Cochlear duct (contains endolymph) Basilar membrane From oval window Spiral organ Spiral ganglion To round window Scala tympani (contains perilymph) Cochlear nerve Vestibulocochlear nerve (N VIII) Diagrammatic and sectional views of the cochlear spiral 89

Diagrammatic and sectional views of the cochlear spiral Figure 17-27b The Cochlea Vestibular membrane Basilar membrane Temporal bone (petrous part) Scala vestibuli (contains perilymph) Cochlear duct (contains endolymph) Spiral organ Spiral ganglion Scala tympani (contains perilymph) Cochlear nerve Cochlear spiral section LM  60 Diagrammatic and sectional views of the cochlear spiral 90

17-5 The Ear Hearing Auditory ossicles Convert pressure fluctuation in air into much greater pressure fluctuations in perilymph of cochlea Frequency of sound Determined by which part of cochlear duct is stimulated Intensity (volume) Determined by number of hair cells stimulated

17-5 The Ear Hearing Cochlear duct receptors Basilar membrane Separates cochlear duct from tympanic duct Hair cells lack kinocilia Stereocilia in contact with overlying tectorial membrane

Figure 17-28a The Spiral Organ Body cochlear wall Scala vestibuli Spiral ganglion Vestibular membrane Cochlear duct Tectorial membrane Basilar membrane Scala tympani Spiral organ Cochlear branch of N VIII A three-dimensional section of the cochlea, showing the compartments, tectorial membrane, and spiral organ 93

Figure 17-28b The Spiral Organ Tectorial membrane Outer hair cell Basilar membrane Inner hair cell Nerve fibers Diagrammatic and sectional views of the receptor hair cell complex of the spiral organ 94

Figure 17-28b The Spiral Organ Cochlear duct (scala media) Vestibular membrane Tectorial membrane Scala tympani Basilar membrane Hair cells of spiral organ Spiral ganglion cells of cochlear nerve Spiral organ LM  125 Diagrammatic and sectional views of the receptor hair cell complex of the spiral organ 95