17 The Special Senses.

17 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.

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.

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

17-1 Smell (Olfaction) Olfactory Pathways
Axons leaving olfactory epithelium Collect into 20 or more bundles Penetrate cribriform plate of ethmoid Reach olfactory bulbs of cerebrum where first synapse occurs

17-1 Smell (Olfaction) Olfactory Pathways
Axons leaving olfactory bulb: Travel along olfactory tract to reach olfactory cortex, hypothalamus, and portions of limbic system Arriving information reaches information centers without first synapsing in thalamus

17-1 Smell (Olfaction) Olfactory Discrimination
Can distinguish thousands of chemical stimuli CNS interprets smells by the pattern of receptor activity Olfactory Receptor Population Considerable turnover Number of olfactory receptors declines with age

Figure 17-2 Olfactory and Gustatory Receptors
Olfaction and gustation are special senses that provide us with vital information about our environment. Although the sensory information provided is diverse and complex, each special sense originates at receptor cells that may be neurons or specialized receptor cells that communicate with sensory neurons. Stimulus Dendrites Specialized olfactory neuron Stimulus removed Action potentials Stimulus Threshold Generator potential to CNS 14

Olfactory reception occurs on the surface membranes of the olfactory cilia. Odorantsdissolved chemicals that stimulate olfactory receptorsinteract with receptors called odorant- binding proteins on the membrane surface. In general, odorants are small organic molecules. The strongest smells are associated with molecules of either high water or high lipid solubilities. As few as four odorant molecules can activate an olfactory receptor. The binding of an odorant to its receptor protein leads to the activation of adenylyl cyclase, the enzyme that converts ATP to cyclic-AMP (cAMP). The cAMP then opens sodium channels in the plasma membrane, which, as a result, begins to depolarize. If sufficient depolarization occurs, an action potential is triggered in the axon, and the information is relayed to the CNS. MUCOUS LAYER Odorant molecule Closed sodium channel Depolarized membrane Inactive enzyme Active enzyme RECEPTOR CELL Sodium ions enter 15

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 20

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. 21

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. 22

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

17-2 Taste (Gustation) End Result of Taste Receptor Stimulation
Release of neurotransmitters by receptor cell Dendrites of sensory afferents wrapped by receptor membrane Neurotransmitters generate action potentials in afferent fiber

17-2 Taste (Gustation) Taste Sensitivity
Exhibits significant individual differences Some conditions are inherited For example, phenylthiocarbamide (PTC) 70% of Caucasians taste it but 30% do not Number of taste buds Begins declining rapidly by age 50

Receptor cell Stimulus Stimulus removed Stimulus Receptor cell Threshold Receptor depolarization Synapse Axon of sensory neuron Axon Action potentials Stimulus Synaptic delay to CNS Generator potential 28

Salt and Sour Receptors Sweet, Bitter, and Umami Receptors Salt receptors and sour receptors are chemically gated ion channels whose stimulation produces depolarization of the cell. Receptors responding to stimuli that produce sweet, bitter, and umami sensations are linked to G proteins called gustducins (GUST-doos- inz)protein complexes that use second messengers to produce their effects. Sweet, bitter, or umami Sour, salt Gated ion channel Membrane receptor Resting plasma membrane Inactive G protein Active G protein Channel opens Depolarized membrane Active G protein Active 2nd messenger Inactive 2nd messenger Depolarization of membrane stimulates release of chemical neurotransmitters. Activation of second messengers stimulates release of chemical neurotransmitters. 29

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

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

Eyelids (Palpebrae) Medial canthus and lateral canthus Where two eyelids are connected Eyelashes Robust hairs that prevent foreign matter from reaching surface of eye

Eyelids (Palpebrae) Tarsal glands Secrete lipid-rich product that helps keep eyelids from sticking together

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 35

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

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. 38

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 41

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 42

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 43

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

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 48

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 17-7a 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). 53

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). 54

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. 55

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. 56

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
59

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 62

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

17-3 The Eye Light Refraction Bending of light by cornea and lens
Focal point Specific point of intersection on retina Focal distance Distance between center of lens and focal point

Figure 17-10 Factors Affecting Focal Distance
Close source Focal point Light from Lens distant source (object) The closer the light source, the longer the focal distance The rounder the lens, the shorter the focal distance 66

17-3 The Eye Light Refraction of Lens Accommodation
Shape of lens changes to focus image on retina Astigmatism Condition where light passing through cornea and lens is not refracted properly Visual image is distorted

Figure 17-11 Accommodation
For Close Vision: Ciliary Muscle Contracted, Lens Rounded Lens rounded Focal point on fovea Ciliary muscle contracted For Distant Vision: Ciliary Muscle Relaxed, Lens Flattened Lens flattened Ciliary muscle relaxed 68

Figure 17-11a Accommodation
For Close Vision: Ciliary Muscle Contracted, Lens Rounded Lens rounded Focal point on fovea Ciliary muscle contracted 69

Figure 17-11b Accommodation
For Distant Vision: Ciliary Muscle Relaxed, Lens Flattened Lens flattened Ciliary muscle relaxed 70

17-3 The Eye Light Refraction of Lens Image reversal Visual acuity
Clarity of vision “Normal” rating is 20/20

Figure 17-12a Image Formation
Light from a point at the top of an object is focused on the lower retinal surface. 72

Figure 17-12b Image Formation
Light from a point at the bottom of an object is focused on the upper retinal surface. 73

Figure 17-12c Image Formation
Light rays projected from a vertical object show why the image arrives upside down. (Note that the image is also reversed.) 74

Figure 17-12d Image Formation
Light rays projected from a horizontal object show why the image arrives with a left and right reversal. The image also arrives upside down. (As noted in the text, these representa- tions are not drawn to scale.) 75

Figure 17-13 Accommodation Problems
The eye has a fixed focal length and focuses by varying the shape of the lens. A camera lens has a fixed size and shape and focuses by varying the distance to the film. 76

Emmetropia (normal vision) 77

Myopia (nearsightedness) If the eyeball is too deep or the resting curvature of the lens is too great, the image of a distant object is projected in front of the retina. The person will see distant objects as blurry and out of focus. Vision at close range will be normal because the lens is able to round as needed to focus the image on the retina. Myopia corrected with a diverging, concave lens Diverging lens 78

Hyperopia (farsightedness) If the eyeball is too shallow or the lens is too flat, hyperopia results. The ciliary muscle must contract to focus even a distant object o the retina. And at close range the lens cannot provide enough refraction to focus an image on the retina. Older people become farsighted as their lenses lose elasticity, a form of hyperopia called presbyopia (presbys, old man). Hyperopia corrected with a converging, convex lens Converging lens 79

Surgical Correction Variable success at correcting myopia and hyperopia has been achieved by surgery that reshapes the cornea. In Photorefractive keratectomy (PRK) a computer-guided laser shapes the cornea to exact specifications. The entire procedure can be done in less than a minute. A variation on PRK is called LASIK (Laser-Assisted in-Situ Keratomileusis). In this procedure the interior layers of the cornea are reshaped and then re-covered by the flap of original outer corneal epithelium. Roughly 70 percent of LASIK patients achieve normal vision, and LASIK has become the most common form of refractive surgery. Even after surgery, many patients still need reading glasses, and both immediate and long-term visual problems can occur. 80

17-4 Visual Physiology Visual Physiology Rods Cones
Respond to almost any photon, regardless of energy content Cones Have characteristic ranges of sensitivity

17-4 Visual Physiology Anatomy of Rods and Cones
Outer segment with membranous discs Inner segment Narrow stalk connects outer segment to inner segment

17-4 Visual Physiology Anatomy of Rods and Cones Visual pigments
Is where light absorption occurs Derivatives of rhodopsin (opsin plus retinal) Retinal synthesized from vitamin A

Figure 17-14a Structure of Rods, Cones, and Rhodopsin Molecule
Pigment Epithelium In a cone, the discs are infoldings of the plasma membrane, and the outer segment tapers to a blunt point. Melanin granules In a rod, each disc is an independent entity, and the outer segment forms an elongated cylinder. Outer Segment Discs Connecting stalks Inner Segment Mitochondria Golgi apparatus Nuclei Cone Rods Each photoreceptor synapses with a bipolar cell. Bipolar cell LIGHT Structure of rods and cones. 84

Figure 17-14b Structure of Rods, Cones, and Rhodopsin Molecule
In a rod, each disc is an independent entity, and the outer segment forms an elongated cylinder. Rhodopsin molecule Retinal Opsin Structure of rhodospin molecule. 85

17-4 Visual Physiology Color Vision
Integration of information from red, green, and blue cones Color blindness Inability to detect certain colors

Figure 17-15 Cone Types and Sensitivity to Color
Rods Red cones Blue cones Green cones Light absorption (percent of maximum) W A V E L E N G T H (nm) Violet Blue Green Yellow Orange Red 87

Figure 17-16 A Standard Test for Color Vision
88

17-4 Visual Physiology Photoreception
Photon strikes retinal portion of rhodopsin molecule embedded in membrane of disc Opsin is activated Bound retinal molecule has two possible configurations 11-cis form 11-trans form

Figure 17-17 Photoreception
Opsin activation occurs The bound retinal molecule has two possible configurations: the 11-cis form and the 11-trans form. Photon Rhodopsin 11-cis retinal 11-trans retinal Opsin Normally, the molecule is in the 11-cis form; on absorbing light it changes to the more linear 11-trans form. This change activates the opsin molecule. 90

Opsin activates transducin, which in turn activates phosphodiestease (PDE) Transducin is a G proteina membrane-bound enzyme complex PDE Transducin Disc membrane In this case, transducin is activated by opsin, and transducin in turn activates phosphodiesterase (PDE). 91

Cyclic-GMP levels decline and gated sodium channels close Phosphodiesterase is an enzyme that breaks down cGMP. GMP cGMP The removal of cGMP from the gated sodium channels results in their inactivation. The rate of Na entry into the cytoplasm is then decreased. 92

IN LIGHT ACTIVE STATE Dark current is reduced and rate of neurotransmitter release declines 93

17-4 Visual Physiology Recovery after Stimulation Bleaching
Rhodopsin molecule breaks down into retinal and opsin Night blindness Results from deficiency of vitamin A

Figure 17-18 Bleaching and Regeneration of Visual Pigments
On absorbing light, retinal changes to a more linear shape. This change activates the opsin molecule. Opsin activation changes the Na permeability of the outer segment, and this changes the rate of neurotransmitter release by the inner segment at its synapse with a bipolar cell. Na Na 11-trans retinal 11-cis retinal and opsin are reassembled to form rhodopsin. Photon Once the retinal has been converted, it can recombine with opsin. The rhodopsin molecule is now ready to repeat the cycle. The regeneration process takes time; after exposure to very bright light, photoreceptors are inactivated while pigment regeneration is under way. ADP ATP Changes in bipolar cell activity are detected by one or more ganglion cells. The location of the stimulated ganglion cell indicates the specific portion of the retina stimulated by the arriving photons. Neuro- transmitter release enzyme 11-trans retinal Opsin 11-cis retinal Opsin Bipolar cell After absorbing a photon, the rhodopsin molecule begins to break down into retinal and opsin, a process known as bleaching. Ganglion cell The retinal is converted to its original shape. This conversion requires energy in the form of ATP. 95

17-4 Visual Physiology Light and Dark Adaptation Dark Light
Most visual pigments are fully receptive to stimulation Light Pupil constricts Bleaching of visual pigments occurs

17-4 Visual Physiology The Visual Pathways Begin at photoreceptors
End at visual cortex of cerebral hemispheres Message crosses two synapses before it heads toward brain Photoreceptor to bipolar cell Bipolar cell to ganglion cell

17-4 Visual Physiology Ganglion Cells
Monitor a specific portion of a field of vision M Cells Are ganglion cells that monitor rods Are relatively large Provide information about: General form of object Motion Shadows in dim lighting

17-4 Visual Physiology Ganglion Cells P cells
Are ganglion cells that monitor cones Are smaller, more numerous Provide information about edges, fine detail, and color

17-4 Visual Physiology Ganglion Cells On-center neurons
Are excited by light arriving in center of their sensory field Are inhibited when light strikes edges of their receptive field Off-center neurons Inhibited by light in central zone Stimulated by illumination at edges

Figure 17-19 Convergence and Ganglion Cell Function
Retinal surface (contacts pigment epithelium) Receptive field of ganglion cell Receptive field Photoreceptors Horizontal cell Bipolar cell Amacrine cell Ganglion cell 101

17-4 Visual Physiology Central Processing of Visual Information
Axons from ganglion cells converge on optic disc Penetrate wall of eye Proceed toward diencephalon as optic nerve (II) Two optic nerves (one for each eye) reach diencephalon at optic chiasm

17-4 Visual Physiology Visual Data
From combined field of vision arrive at visual cortex of opposite occipital lobe Left half arrive at right occipital lobe Right half arrive at left occipital lobe Optic radiation Bundle of projection fibers linking lateral geniculate with visual cortex

17-4 Visual Physiology The Field of Vision Depth perception
Obtained by comparing relative positions of objects between left-eye and right-eye images

17-4 Visual Physiology The Brain Stem and Visual Processing
Circadian rhythm Is tied to day-night cycle Affects other metabolic processes

Figure 17-20 The Visual Pathways
Combined Visual Field Left side Right side Left eye Right eye only Binocular vision only The Visual Pathway Photoreceptors in retina Retina Optic disc Optic nerve (N II) Optic chiasm Optic tract Suprachiasmatic nucleus Diencephalon and brain stem Lateral geniculate nucleus Projection fibers (optic radiation) Visual cortex of cerebral hemispheres Superior colliculus Left cerebral hemisphere Right cerebral hemisphere 106

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 109

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. 112

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 113

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. 116

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. 117

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 124

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 125

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. 126

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. 127

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 130

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 2 131

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 Four Functions of Vestibular Nuclei
Integrate sensory information about balance and equilibrium from both sides of head Relay information from vestibular complex to cerebellum Relay information from vestibular complex to cerebral cortex Provide conscious sense of head position and movement Send commands to motor nuclei in brain stem and spinal cord

Figure 17-26 Pathways for Equilibrium Sensations
To superior colliculus and relay to cerebral cortex Red nucleus N III Vestibular ganglion N IV Semicircular canals Vestibular branch Vestibular nucleus N VI To cerebellum Vestibule Cochlear branch N XI Vestibulocochlear nerve (N VIII) Vestibulospinal tracts 134

17-5 The Ear Eye, Head, and Neck Movements
Reflexive motor commands From vestibular nuclei Distributed to motor nuclei for cranial nerves Peripheral Muscle Tone, Head, and Neck Movements Instructions descend in vestibulospinal tracts of spinal cord

17-5 The Ear Eye Movements Sensations of motion directed by superior colliculi of the midbrain Attempt to keep focus on specific point If spinning rapidly, eye jumps from point to point Nystagmus Have trouble controlling eye movements Caused by damage to brain stem or inner ear

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 138

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 139

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 140

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 143

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 144

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 145

17-5 The Ear An Introduction to Sound Pressure Waves
Consist of regions where air molecules are crowded together Adjacent zone where molecules are farther apart Sine waves S-shaped curves

17-5 The Ear Pressure Wave Wavelength Frequency
Distance between two adjacent wave troughs Frequency Number of waves that pass fixed reference point at given time Physicists use term cycles instead of waves Hertz (Hz) number of cycles per second (cps)

17-5 The Ear Pressure Wave Pitch Amplitude
Our sensory response to frequency Amplitude Intensity of sound wave Sound energy is reported in decibels

Figure 17-29a The Nature of Sound
Wavelength Tympanic membrane Tuning fork Air molecules Sound waves (here, generated by a tuning fork) travel through the air as pressure waves. 149

Figure 17-29b The Nature of Sound
1 wavelength Amplitude A graph showing the sound energy arriving at the tympanic membrane. The distance between wave peaks is the wavelength. The number of waves arriving each second is the frequency, which we perceive as pitch. Frequencies are reported in cycles per second (cps), or hertz (Hz). The amount of energy in each wave determines the wave’s amplitude, or intensity, which we perceive as the loudness of the sound. 150

Figure 17-31a Frequency Discrimination
Stapes at oval window Cochlea 16,000 Hz 6000 Hz 1000 Hz Round window Basilar membrane The flexibility of the basilar membrane varies along its length, so pressure waves of different frequencies affect different parts of the membrane. 151

Figure 17-31b Frequency Discrimination
Stapes moves inward Basilar membrane distorts toward round window Round window pushed outward The effects of a vibration of the stapes at a frequency of 6000 Hz. When the stapes moves inward, as shown here, the basilar membrane distorts toward the round window, which bulges into the middle-ear cavity. 152

Figure 17-31c Frequency Discrimination
Stapes moves outward Round window pulled inward Basilar membrane distorts toward oval window When the stapes moves outward, as shown here, the basilar membrane rebounds and distorts toward the oval window. 153

Figure 17-30 Sound and Hearing
External acoustic meatus Malleus Incus Stapes Oval window Movement of sound waves Tympanic membrane Round window Sound waves arrive at tympanic membrane. Movement of the tympanic membrane causes displacement of the auditory ossicles. Movement of the stapes at the oval window establishes pressure waves in the perilymph of the scala vestibuli. 154

Figure 17-30 Sound and Hearing
Cochlear branch of cranial nerve VIII Scala vestibuli (contains perilymph) Vestibular membrane Cochlear duct (contains endolymph) Basilar membrane Scala tympani (contains perilymph) The pressure waves distort the basilar membrane on their way to the round window of the scala tympani. Vibration of the basilar membrane causes vibration of hair cells against the tectorial membrane. Information about the region and the intensity of stimulation is relayed to the CNS over the cochlear branch of cranial nerve VIII. 155

17-5 The Ear Auditory Pathways Cochlear branch
Formed by afferent fibers of spiral ganglion neurons Enters medulla oblongata Synapses at dorsal and ventral cochlear nuclei Information crosses to opposite side of brain Ascends to inferior colliculus of midbrain

17-5 The Ear Auditory Pathways Ascending auditory sensations
Synapse in medial geniculate nucleus of thalamus Projection fibers deliver information to auditory cortex of temporal lobe

Figure 17-32 Pathways for Auditory Sensations
Stimulation of hair cells at a specific location along the basilar membrane activates sensory neurons. KEY Primary pathway Secondary pathway Motor output Cochlea Low-frequency sounds High-frequency sounds Vestibular branch Sensory neurons carry the sound information in the cochlear branch of the vestibulocochlear nerve (VIII) to the cochlear nucleus on that side. Vestibulocochlear nerve (VIII) 158

Figure 17-32 Pathways for Auditory Sensations
Projection fibers then deliver the information to specific locations within the auditory cortex of the temporal lobe. High- frequency sounds Low-frequency sounds Thalamus Ascending acoustic information goes to the medial geniculate nucleus. The inferior colliculi direct a variety of unconscious motor responses to sounds. To cerebellum To reticular formation and motor nuclei of cranial nerves Information ascends from each cochlear nucleus to the inferior colliculi of the midbrain. KEY Primary pathway Motor output to spinal cord through the tectospinal tracts Secondary pathway Motor output 159

17-5 The Ear Hearing Range From softest to loudest represents trillionfold increase in power Never use full potential Young children have greatest range

Table 17-1 Intensity of Representative Sounds
161

17-5 The Ear Effects of Aging on the Ear With age, damage accumulates
Tympanic membrane gets less flexible Articulations between ossicles stiffen Round window may begin to ossify

17 The Special Senses.

Similar presentations

Presentation on theme: "17 The Special Senses."— Presentation transcript:

Similar presentations

About project

Feedback

Log in

Auth with social network:

17 The Special Senses.

Similar presentations

Presentation on theme: "17 The Special Senses."— Presentation transcript:

Similar presentations

About project

Feedback