The General and Special Senses

The General and Special Senses
9 The General and Special Senses

Chapter 9 Learning Outcomes
9-1 Explain how the organization of receptors for the general senses and the special senses affects their sensitivity. 9-2 Identify the receptors for the general senses, and describe how they function. 9-3 Describe the sensory organs of smell, and discuss the processes involved in olfaction. 9-4 Describe the sensory organs of taste, and discuss the processes involved in gustation. © 2013 Pearson Education, Inc.

Chapter 9 Learning Outcomes
9-5 Identify the internal and accessory structures of the eye, and explain their functions. 9-6 Explain how we form visual images and distinguish colors, and discuss how the central nervous system processes visual information. 9-7 Describe the parts of the external, middle, and internal ear, and the receptors they contain, and discuss the processes involved in the senses of equilibrium and hearing. 9-8 Describe the effects of aging on smell, taste, vision, and hearing. © 2013 Pearson Education, Inc.

Sensory Receptors (9-1) Can be special cell processes
Or separate cells Monitor conditions both inside and outside the body © 2013 Pearson Education, Inc.

Free Nerve Endings (9-1) The simplest receptors
Are modified dendritic endings Examples: Touch receptors Pain receptors Heat receptors Taste receptors © 2013 Pearson Education, Inc.

Separate Receptor Cells (9-1)
Complex structures Associated with supportive cells Examples: Visual receptors in the eyes Auditory receptors in the ears © 2013 Pearson Education, Inc.

The Receptive Field (9-1)
The area monitored by a single receptor The smaller the field, the more precise the sensory information © 2013 Pearson Education, Inc.

Sensation and Perception (9-1)
Occurs in the brain The action potential from the afferent pathway arrives in sensory cortex Perception Awareness and interpretation of sensory input by the integration areas of cerebral cortex © 2013 Pearson Education, Inc.

Adaptation (9-1) A reduction in sensitivity due to a constant stimulus
Some sensory receptors adapt quickly (e.g., jumping into a cold lake) Some are slow to adapt or do not adapt at all, like pain receptors © 2013 Pearson Education, Inc.

General Senses (9-1) Temperature Pain Touch Pressure Vibration
Proprioception (body position) Occur throughout the body © 2013 Pearson Education, Inc.

Special Senses (9-1) Olfaction (smell) Gustation (taste) Vision
Equilibrium (balance) Hearing Concentrated in the sense organs and located in the head © 2013 Pearson Education, Inc.

Figure 9-1 Receptors and Receptive Fields.
© 2013 Pearson Education, Inc.

Checkpoint (9-1) What is adaptation?
Receptor A has a circular receptive field with a diameter of 2.5 cm. Receptor B has a circular receptive field 7.0 cm in diameter. Which receptor provides more precise sensory information? List the five special senses. © 2013 Pearson Education, Inc.

Classes of General Sensory Receptors (9-2)
Classified by type of stimulus that activates them Nociceptors respond to pain Thermoreceptors respond to temperature Mechanoreceptors respond to touch, pressure, and body position Chemoreceptors respond to chemical stimuli © 2013 Pearson Education, Inc.

Nociceptors (9-2) Free nerve endings that adapt very slowly
Can respond to extremes of temperature, mechanical damage, dissolved chemicals Fast pain transmitted to CNS through myelinated axons Slow pain transmitted by unmyelinated axons and is burning or aching Referred pain is perception of pain in an unrelated area of the body © 2013 Pearson Education, Inc.

Heart Liver and gallbladder Stomach Ureters Appendix Colon
Figure 9-2 Referred Pain. Heart Liver and gallbladder Stomach Small intestine Ureters Appendix Colon © 2013 Pearson Education, Inc.

Thermoreceptors (9-2) Free nerve endings Cold receptors
In dermis, skeletal muscles, liver, and hypothalamus Cold receptors More numerous than warm receptors, although there is no known difference in structure They use the same pathway as pain receptors, but thermoreceptors are adaptive © 2013 Pearson Education, Inc.

Three Classes of Mechanoreceptors
Tactile receptors Touch Baroreceptors Pressure Proprioceptors Position © 2013 Pearson Education, Inc.

Tactile Receptors (9-2) Include fine touch and pressure receptors and crude touch and pressure receptors Six types of tactile receptors in the skin Free nerve endings responding to temperature and pain Root hair plexus Tactile (Merkel) disc Tactile (Meissner) corpuscle Lamellated (pacinian) corpuscle Ruffini corpuscle © 2013 Pearson Education, Inc.

Figure 9-3 Tactile Receptors in the Skin.
Tactile disc (innervating Merkel cell) Tactile corpuscle Free nerve ending Dendrites Hair Sensory nerve fiber Free nerve endings Ruffini corpuscle Root hair plexus Dendrite Lamellated corpuscle Sensory nerves Ruffini corpuscle Dermis Lamellated corpuscle Root hair plexus Dendrites Merkel cells Tactile disc Dermis Tactile discs innervating Merkel cells Tactile corpuscle © 2013 Pearson Education, Inc.

Baroreceptors (9-2) Monitor changes in pressure in the viscera
Adapt readily Found in the major blood vessels, lungs, digestive, and urinary tracts © 2013 Pearson Education, Inc.

Figure 9-4 Baroreceptors and the Regulation of Autonomic Functions.
Baroreceptors of Carotid Sinus and Aortic Sinus Baroreceptors of Lung Baroreceptors of Digestive Tract Baroreceptors of Colon Baroreceptors of Bladder Wall © 2013 Pearson Education, Inc.

Proprioceptors (9-2) Monitor position, tension in tendons and ligaments, state of muscle contraction Nonadaptive and include: Free nerve endings that monitor joint capsule pressure, tension, and movement Golgi tendon organs that monitor strain on tendons Muscle spindles that monitor the length of a muscle © 2013 Pearson Education, Inc.

Chemoreceptors (9-2) Respond to chemicals in solution in body fluids
Include CNS receptors that monitor CSF, plasma concentrations of carbon dioxide, and pH Key peripheral chemoreceptors for plasma carbon dioxide and pH are in the carotid bodies and aortic bodies © 2013 Pearson Education, Inc.

Figure 9-5 Locations and Functions of Chemoreceptors.
Chemoreceptors in and near Respiratory Centers of Medulla Oblongata Trigger reflexive adjustments in depth and rate of respiration Chemoreceptors of Carotid Bodies Cranial nerve IX Cranial nerve X Trigger reflexive adjustments in respiratory and cardiovascular activity Chemoreceptors of Aortic Bodies © 2013 Pearson Education, Inc.

Checkpoint (9-2) List the four types of general sensory receptors, and identify the nature of the stimulus that excites each type. Identify the three classes of mechanoreceptors. What would happen if information from proprioceptors in your legs were blocked from reaching the CNS? © 2013 Pearson Education, Inc.

Special Sense of Olfaction (9-3)
Olfactory organs found in the nasal cavity Olfactory epithelium, containing olfactory receptor cells, supporting cells, and stem cells, lines the nasal cavity Olfactory glands, which are deeper, secrete mucus Air is warmed and moisturized as it is inhaled © 2013 Pearson Education, Inc.

Special Sense of Olfaction (9-3)
Olfactory receptor cells Modified neurons with chemical receptors called odorant-binding proteins on the cilia Odorants are chemicals in the air that bind to the proteins Respond to over 1000 unique smells © 2013 Pearson Education, Inc.

Olfactory Pathways (9-3)
Axons projecting from the olfactory epithelium Bundled and pass through the cribriform plate of the ethmoid bone and into olfactory bulb Olfactory tracts extend back to the olfactory cortex of the cerebrum, the hypothalamus, and the limbic system Olfaction is the only sense that is NOT routed through the thalamus © 2013 Pearson Education, Inc.

Figure 9-6a 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 right side of the nasal septum. © 2013 Pearson Education, Inc.

Figure 9-6b The Olfactory Organs.
Basal cell: divides to replace worn-out olfactory receptor cells To olfactory bulb Olfactory gland Cribriform plate Olfactory nerve fibers Areolar tissue Developing olfactory receptor cell Olfactory receptor cell Olfactory epithelium Supporting cell Mucous layer Olfactory cilia: surfaces contain receptor proteins Substance being smelled An olfactory receptor is a modified neuron with multiple cilia extending from its free surface. © 2013 Pearson Education, Inc.

Checkpoint (9-3) Define olfaction.
How does repeated sniffing help to identify faint odors? © 2013 Pearson Education, Inc.

Special Sense of Gustation (9-4)
Gustatory receptors Found in the gustatory cells of the taste buds, which are found on the sides of the papillae Circumvallate papillae most numerous and on the front 2/3 of the tongue Gustatory cells have microvilli (taste hairs) that extend out through the taste pore © 2013 Pearson Education, Inc.

Special Sense of Gustation (9-4)
Taste hairs respond to chemicals in solution Trigger a change in the membrane potential of the taste cells Primary taste sensations Sweet, sour, bitter, salty, and umami Also receptors in the pharynx for water © 2013 Pearson Education, Inc.

The Taste Pathway (9-4) Extends from the taste cell axons found in:
Facial nerve (N VII) Glossopharyngeal (N IX) Vagus (N X) Fibers synapse in the medulla oblongata Those neurons extend into the thalamus Neurons project to the primary sensory cortex © 2013 Pearson Education, Inc.

Figure 9-7 Gustatory Receptors.
Water receptors (pharynx) Umami Taste buds Taste buds Sour Bitter Salty Sweet Circumvallate papilla Taste buds LM x 280 Supporting cell Gustatory cell Tastes are detected by gustatory receptors within taste buds, which form pockets along the sides of epithelial projections called papillae. Taste hairs (microvilli) Taste pore A diagrammatic view of the structure of a taste bud, showing gustatory receptor cells and supporting cells. © 2013 Pearson Education, Inc.

Checkpoint (9-4) Define gustation.
If you completely dry the surface of your tongue and then place salt or sugar crystals on it, you cannot taste them. Why not? © 2013 Pearson Education, Inc.

The Accessory Structures of the Eye (9-5)
Eyelids and associated exocrine glands The superficial epithelium of the eye Structures associated with the production, secretion, and removal of tears The extrinsic eye muscles © 2013 Pearson Education, Inc.

The Eyelids (9-5) Also called palpebrae
Upper and lower eyelids join at the medial canthus and lateral canthus At the medial canthus, glands that secrete gritty "sleep" are found in the lacrimal caruncle Have sebaceous glands that can become infected, known as a sty © 2013 Pearson Education, Inc.

Conjunctiva (9-5) Inner surface of the eyelids
And the outer, white surface of the eye, up to the edge of the cornea Irritation or damage to the conjunctiva is called conjunctivitis, or pinkeye © 2013 Pearson Education, Inc.

The Lacrimal Apparatus (9-5)
Produces essential tears, distributes them across the eye, and removes them The lacrimal gland secretes the tears and is superior and lateral to the eyeball Tears drain through two pores at the medial canthus called the lacrimal canals and into the nasolacrimal duct PLAY ANIMATION The Eye: Accessory Structures © 2013 Pearson Education, Inc.

Figure 9-8a The Accessory Structures of the Eye.
Sclera Lateral canthus Eyelashes Pupil Palpebra (eyelid) Iris Medial canthus Lacrimal caruncle Gross and superficial anatomy of the accessory structures © 2013 Pearson Education, Inc.

Figure 9-8b The Accessory Structures of the Eye.
Lacrimal gland Lacrimal gland ducts Lacrimal pores Superior lacrimal canal Lacrimal sac Inferior lacrimal canal Nasolacrimal duct Opening of duct into nasal cavity The organization of the lacrimal apparatus © 2013 Pearson Education, Inc.

The Extrinsic Eye Muscles (9-5)
Control the position of the eye and include: Inferior rectus Medial rectus Superior rectus Lateral rectus Inferior oblique Superior oblique © 2013 Pearson Education, Inc.

Figure 9-9 The Extrinsic Eye Muscles.
Superior rectus Superior oblique Frontal bone Trochlea Optic nerve Trochlea Superior rectus Superior oblique Lateral rectus Medial rectus Inferior oblique Inferior rectus Lateral rectus Inferior rectus Maxilla Inferior oblique Anterior view, right eye Lateral surface, right eye © 2013 Pearson Education, Inc.

Table 9-1 The Extrinsic Eye Muscles

The Eye (9-5) Found in the orbit with the:
Lacrimal glands Extrinsic eye muscles Cranial nerves Blood vessels Orbital fat cushions the eye © 2013 Pearson Education, Inc.

The Eyeball (9-5) The eyeball is hollow and divided into two cavities
Posterior cavity Filled with jellylike vitreous body Anterior cavity has two subdivisions The anterior and posterior chambers Filled with aqueous humor © 2013 Pearson Education, Inc.

The Fibrous Layer of the Eyeball (9-5)
The sclera The white of the eye Supportive dense connective tissue The cornea Transparent Allows light to enter the eye © 2013 Pearson Education, Inc.

The Vascular Layer of the Eyeball (9-5)
Contains blood and lymphatic vessels, and the intrinsic eye muscles Functions Providing a route for vessels supplying the tissue Adjusting the amount of light entering the eye Providing a route for secreting and reabsorbing aqueous humor Controlling the shape of the lens © 2013 Pearson Education, Inc.

The Vascular Layer of the Eyeball (9-5)
Structures The iris, with pupillary muscles that change the size of the pupil, the "window" into the eye The ciliary body, which contains the ciliary muscle and ciliary processes, and the suspensory ligaments, which adjust the shape of the lens for focusing The choroid, a highly vascular tissue PLAY ANIMATION The Eye: Cilliary Muscles © 2013 Pearson Education, Inc.

Figure 9-10a The Sectional Anatomy of the Eye.
Eyelash Optic nerve Conjunctiva Cornea Lens Pupil Iris Fovea Sagittal section of left eye © 2013 Pearson Education, Inc.

Figure 9-10b The Sectional Anatomy of the Eye.
Fibrous layer Vascular layer Cornea Anterior cavity Iris Sclera Ciliary body Choroid Posterior cavity Inner layer (retina) Neural part Pigmented part Horizontal section of right eye © 2013 Pearson Education, Inc.

Figure 9-10c The Sectional Anatomy of the Eye.
Visual axis Anterior cavity Posterior chamber Anterior chamber Cornea Iris Edge of pupil Suspensory ligament of lens Nose Lacrimal pore Conjunctiva Lower eyelid Lacrimal sac Lens Ciliary muscle Ciliary body Sclera Choroid Retina Posterior cavity Medial rectus muscle Lateral rectus muscle Optic disc Fovea Optic nerve Orbital fat Central artery and vein Horizontal dissection of right eye © 2013 Pearson Education, Inc.

Figure 9-11 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 © 2013 Pearson Education, Inc.

The Inner Layer (9-5) Also called the retina The inner layer includes:
A pigmented part, which absorbs light A neural part that contains the photoreceptors Supportive cells and neurons Blood vessels © 2013 Pearson Education, Inc.

Photoreceptors (9-5) Rods Cones Used in dim light
Found on the periphery of retinal surface Cones Used in bright light and detect color Found in the macula, the center of which is the fovea, or fovea centralis © 2013 Pearson Education, Inc.

The Inner Layer (9-5) Rods and cones synapse with bipolar cells, which synapse with ganglion cells Ganglion cells These axons leave the back of the eye through the optic disc, the origin of the optic nerve The blind spot is where there are no photoreceptors on the retina PLAY ANIMATION The Eye: The Retina © 2013 Pearson Education, Inc.

Figure 9-12a Retinal Organization.
Horizontal cell Cone Rod Choroid Pigmented part of retina Rods and cones Amacrine cell Bipolar cells Ganglion cells Retina LM x 350 Nuclei of ganglion cells Nuclei of rods and cones Nuclei of bipolar cells LIGHT The cellular organization of the retina. The photoreceptors are closest to the choroid, rather than near the posterior cavity (vitreous chamber). © 2013 Pearson Education, Inc.

Figure 9-12b Retinal Organization.
Pigmented part of retina Neural part of retina Central retinal vein Optic disc Central retinal artery Optic nerve Sclera Choroid The optic disc in diagrammatic sagittal section. © 2013 Pearson Education, Inc.

Figure 9-12c Retinal Organization.
Optic disc (blind spot) Fovea Central retinal artery and vein emerging from center of optic disc Macula A photograph of the retina as seen through the pupil. © 2013 Pearson Education, Inc.

Figure 9-13 A Demonstration of the Presence of a Blind Spot.

The Chambers of the Eye (9-5)
Anterior cavity Anterior chamber extends from the cornea to the iris Posterior chamber between the iris and the lens Filled with aqueous humor produced by the ciliary processes Maintains pressure in eye Drains out through the scleral venous sinus © 2013 Pearson Education, Inc.

The Chambers of the Eye (9-5)
Problems with fluid and pressure is a condition called glaucoma Posterior cavity Filled with the vitreous body Holds the retina in place © 2013 Pearson Education, Inc.

Figure 9-14 The Circulation of Aqueous Humor.
Cornea Pupil Anterior cavity Anterior chamber Scleral venous sinus Posterior chamber Body of iris Ciliary process Conjunctiva Lens Ciliary body Suspensory ligaments Sclera Pigmented epithelium Posterior cavity (vitreous chamber) Choroid Retina © 2013 Pearson Education, Inc.

The Lens (9-5) Posterior to cornea
Held in place by suspensory ligaments Cells Are wrapped in concentric circle Elastic fibers make lens spherical Changes shape to accommodate for focus © 2013 Pearson Education, Inc.

Light Refraction and Accommodation (9-5)
Light is bent or refracted as it enters the cornea and lens Light rays converge on retina at focal point Focal distance is between lens and focal point For far-away objects, the ciliary muscles relax, flattening the lens For close objects, the lens accommodates by rounding when the ciliary muscles contract PLAY ANIMATION The Eye: Light Path © 2013 Pearson Education, Inc.

Figure 9-15a-c Focal Point, Focal Distance, and Visual Accommodation.
Close source Focal point Light from distant source (object) Lens The closer the light source, the longer the focal distance The rounder the lens, the shorter the focal distance © 2013 Pearson Education, Inc.

Figure 9-15d-e Focal Point, Focal Distance, and Visual Accommodation.
Lens rounded Lens flattened Focal point on fovea Ciliary muscle contracted Ciliary muscle relaxed For Close Vision: Ciliary Muscle Contracted, Lens Rounded For Distant Vision: Ciliary Muscle Relaxed, Lens Flattened © 2013 Pearson Education, Inc.

Figure 9-16 Image Formation.
Light rays projected from a vertical object show why the image arrives upside down. (Note that the image is also reversed.) 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 representations are not drawn to scale.) © 2013 Pearson Education, Inc.

Figure 9-17 Accommodation Problems (1 of 3)
A camera focuses an image by moving the lens toward or away from the film. This method cannot work in our eyes, because the distance from the lens to the macula cannot change. We focus images on the retina by changing the shape of the lens to keep the focal distance constant, a process called accommodation. The eye has a fixed focal distance 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 or semiconductor device. © 2013 Pearson Education, Inc.

Emmetropia (normal vision) In the healthy eye, when the ciliary muscle is relaxed and the lens is flattened, a distant image will be focused on the retina’s surface. This condition is called emmetropia (emmetro-, proper + opia, vision). © 2013 Pearson Education, Inc.

Myopia (nearsightedness) If the eyeball is too deep or the rest- ing 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. 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 on 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). Myopia corrected with a diverging, con- cave lens Hyperopia corrected with a converging, convex lens Diverging lens Converging lens © 2013 Pearson Education, Inc.

Checkpoint (9-5) Which layer of the eye would be the first to be affected by inadequate tear production? When the lens is more rounded, are you looking at an object that is close to you or far from you? As Malia enters a dimly lit room, most of the available light becomes focused on the fovea of her eye. Will she be able to see very clearly? © 2013 Pearson Education, Inc.

Photoreceptors Respond to Photons (9-6)
Photons are units of visible light Red, orange, yellow, green, blue, indigo, violet Color determined by wavelength Photons of red have longest wavelength, least energy Photons of violet have shortest wavelength, most energy © 2013 Pearson Education, Inc.

Photoreceptors in the Eye (9-6)
Rods Respond to presence or absence of photons regardless of wavelength Very sensitive, therefore effective in dim light Cones Three different types Blue cones, green cones, red cones Contain pigments sensitive to blue, green, or red wavelengths of light Less sensitive, therefore function only in bright light © 2013 Pearson Education, Inc.

Color Blindness (9-6) Occurs when one or more types of cone is not functioning or is missing Most common is red-green color blindness where red cones are missing More common in males (10 percent) than females (0.67 percent) Total color blindness is extremely rare (1 person in 300,000) © 2013 Pearson Education, Inc.

Figure 9-18 A Standard Test for Color Vision.

The Structure of Photoreceptors (9-6)
Outer segment contains hundreds to thousands of flattened discs Contain visual pigments that absorb photons and initiate photoreception Made of compound rhodopsin that contains opsin and retinal (derived from vitamin A) Retinal is the same in rods and cones, opsin is different Inner segment contains organelles, synapses with bipolar cells © 2013 Pearson Education, Inc.

Figure 9-19a The Structure of Rods and Cones.
Pigment Epithelium Absorbs photons not absorbed by visual pigments. Melanin granules Outer Segment Visual pigments are contained in membrane discs. Discs Connecting stalks Inner Segment Mitochondria Site of major organelles and cell functions other than photoreception. It also releases neurotransmitters. Golgi apparatus Nuclei Cone Rods Each photoreceptor synapses with a bipolar cell. Bipolar cell LIGHT © 2013 Pearson Education, Inc.

Figure 9-19b The Structure of Rods and Cones.
Rhodopsin molecule Retinal Opsin Structure of rhodopsin molecule © 2013 Pearson Education, Inc.

Photoreception (9-6) Photon strikes rhodopsin
Retinal and opsin break apart, referred to as bleaching Alters rate of neurotransmitter release into synapse with bipolar cell For rod or cone to be able to respond to light again, the opsin and retinal must recombine © 2013 Pearson Education, Inc.

Figure 9-20 Bleaching and Regeneration of Visual Pigments.
Photon Retinal changes shape Retinal and opsin are reassembled to form rhodopsin Bleaching (separation) Regeneration enzyme Retinal restored Opsin Opsin Opsin inactivated © 2013 Pearson Education, Inc.

The Visual Pathways (9-6)
Photoreceptor  bipolar cell  ganglion cell Axons from optic nerves (N II)  optic chiasm Medial fibers cross, lateral fibers do not cross Optic tracts  thalamic nuclei Superior colliculi of midbrain controls eye reflexes Thalamic axons  visual cortex of cerebrum © 2013 Pearson Education, Inc.

The Visual Pathways (9-6)
Combined Visual Field Left side Right side Left eye only Right eye only Binocular vision The Visual Pathway Retina Photoreceptors in retina Optic disc Optic nerve (N II) Optic chiasm Optic tract Thalamic nucleus Hypothalamus, pineal gland, and reticular formation Projection fibers Visual cortex of cerebral hemispheres Superior colliculus Left cerebral hemisphere Right cerebral hemisphere © 2013 Pearson Education, Inc.

Anatomy of the Ear (9-7) External ear Middle ear Internal ear
Visible portion, collects sound waves Middle ear Chamber with structures that amplify sound waves Internal ear Contains sensory organs for hearing and equilibrium PLAY ANIMATION The Ear: Ear Anatomy © 2013 Pearson Education, Inc.

Figure 9-22 The Anatomy of the Ear.
External Ear Middle Ear Internal Ear Elastic cartilages Auditory ossicles Oval window Semicircular canals Temporal bone Auricle Facial nerve (N VII) Vestibulocochl- ear nerve (N VIII) Bony labyrinth of internal ear Cochlea Auditory tube To nasopharynx External acoustic meatus Tympanic membrane Round window Vestibule © 2013 Pearson Education, Inc.

The External Ear (9-7) Auricle or pinna is fleshy "cup" directing sound into ear External acoustic meatus or auditory canal Contains ceruminous glands, secreting earwax Tympanic membrane or eardrum Thin sheet that vibrates when sound waves strike it © 2013 Pearson Education, Inc.

The Middle Ear (9-7) Also called the tympanic cavity Auditory tube
Air-filled chamber Auditory tube Also called pharyngotympanic or Eustachian tube Leads to the pharynx, making a path for microorganisms to trigger otitis media, an infection Allows for pressure equalization on either side of eardrum © 2013 Pearson Education, Inc.

The Auditory Ossicles (9-7)
Three small bones in middle ear that connect tympanic membrane to internal ear Malleus attaches to eardrum Incus attaches malleus to innermost bone Stapes has a base that nearly fills the oval window into the internal ear © 2013 Pearson Education, Inc.

Auditory Ossicles Malleus Incus Stapes Temporal bone Connections to
Figure The Middle Ear. Auditory Ossicles Malleus Incus Stapes Temporal bone Connections to mastoid air cells Stabilizing ligament Oval window Muscles of the Middle Ear Branch of facial nerve VII (cut) Tensor tympani muscle External acoustic meatus Stapedius muscle Round window Tympanic membrane Auditory tube © 2013 Pearson Education, Inc.

The Internal Ear (9-7) Sensory structures protected by bony labyrinth
Contains fluid perilymph between bony and membranous labyrinths Inside bony labyrinth is membranous labyrinth Tubes that follow contours of bony labyrinth Filled with fluid endolymph © 2013 Pearson Education, Inc.

Three Parts of the Bony Labyrinth (9-7)
Vestibule Contains membranous saccule and utricle with receptors for gravity and linear acceleration Semicircular canals Contain membranous semicircular ducts with receptors for rotational acceleration Vestibular complex is the combination of the first two, providing sense of balance © 2013 Pearson Education, Inc.

Three Parts of the Bony Labyrinth (9-7)
Cochlea Contains the membranous cochlear duct Sensory receptors for hearing Oval window is covered with thin membrane separating perilymph in cochlea from air in middle ear Round window is opening in the bone of the cochlea © 2013 Pearson Education, Inc.

Hair Cells (9-7) Sensory receptors in internal ear
Surrounded by supporting cells Synapse with dendrites of sensory neurons Free surface covered with stereocilia Movement of stereocilia alters neurotransmitter release Bending stereocilia in one direction triggers depolarization; in the other direction, hyperpolarization © 2013 Pearson Education, Inc.

Figure 9-24a The Internal Ear and a Hair Cell.
KEY Membranous labyrinth Bony labyrinth Perilymph Bony labyrinth Endolymph Membranous labyrinth A section through one of the semicircular canals, showing the relationship between the bony and membranous labyrinths, and the locations of perilymph and endolymph. © 2013 Pearson Education, Inc.

Figure 9-24b The Internal Ear and a Hair Cell.
Semicircular Ducts KEY Membranous labyrinth Anterior Bony labyrinth Lateral Vestibule Posterior Crista ampullaris Maculae Endolymphatic sac Semicircular canal Cochlea Utricle Saccule Scala vestibuli Cochlear duct Scala tympani Spiral organ The bony and membranous labyrinths. Areas of the membranous labyrinth containing sensory receptors (cristae, maculae, and spiral organ) are shown in purple. © 2013 Pearson Education, Inc.

Figure 9-24c The Internal Ear and a Hair Cell.
Displacement in this direction stimulates hair cell Displacement in this direction inhibits hair cell Stereocilia Hair cell Sensory neuron Supporting cell A representative hair cell (receptor) from the vestibular complex. Bending the stereocilia in one direction depolarizes the cell and stimulates the sensory neuron. Displacement in the opposite direction inhibits the sensory neuron. © 2013 Pearson Education, Inc.

Equilibrium (9-7) Dynamic equilibrium Static equilibrium
Maintaining balance while in motion Monitored by semicircular ducts Static equilibrium Maintaining balance and posture while motionless Monitored by saccule and utricle © 2013 Pearson Education, Inc.

The Semicircular Ducts (9-7)
Three ducts Anterior Posterior Lateral Organized in three planes Transverse Frontal Sagittal © 2013 Pearson Education, Inc.

The Semicircular Ducts (9-7)
Each contains the ampulla, which contains the sensory receptors The crista ampullaris contains hair cells that are embedded in gelatinous structure called the cupula When head rotates, endolymph pushes against the cristae and activates hair cells © 2013 Pearson Education, Inc.

The Vestibule (9-7) Saccule receptors Utricle receptors
Respond to gravity and linear acceleration Utricle receptors Respond to horizontal acceleration Hair cells clustered in maculae Project into gelatinous membrane with otoliths Gravity pulls on otoliths, pulling on hair cells © 2013 Pearson Education, Inc.

Figure 9-25a The Vestibular Complex.
The locations of equilibrium receptors, a crista ampullaris and a macula. © 2013 Pearson Education, Inc.

Figure 9-25b The Vestibular Complex.
Ampulla filled with endolymph Cupula Hair cells Crista ampullaris Supporting cells Sensory nerve A cross section through the ampulla of a semicircular duct showing the crista ampullaris. © 2013 Pearson Education, Inc.

Figure 9-25c The Vestibular Complex.
Direction of rotation Direction of endolymph movement Direction of rotation Semicircular duct Cupula At rest Endolymph movement along the axis of the semicircular duct moves the cupula and stimulates the hair cells. © 2013 Pearson Education, Inc.

Figure 9-25d The Vestibular Complex.
Otoliths Gelatinous layer forming otolithic membrane Hair cells Nerve fibers The structure of an individual macula. © 2013 Pearson Education, Inc.

Figure 9-25e The Vestibular Complex.
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 . © 2013 Pearson Education, Inc.

Pathways for Equilibrium Sensations (9-7)
Hair cells of vestibule and semicircular ducts Synapse with neurons of vestibular branch of N VIII These synapse with neurons in the vestibular nuclei of the pons and medulla oblongata Information is relayed to: Cerebellum Cerebral cortex Motor nuclei in brain stem and spinal cord PLAY ANIMATION The Ear: Balance © 2013 Pearson Education, Inc.

Hearing (9-7) Vibrations of sound waves determine stimulus
Tympanic membrane vibrates the ossicles Pressure pulses travel through perilymph of cochlea Pitch (frequency) determined by which part of cochlear duct is stimulated Volume (intensity) determined by how many hair cells are activated at that site © 2013 Pearson Education, Inc.

The Cochlear Duct (9-7) Sectional view shows three chambers
Scala vestibuli (the vestibular duct) Scala media (the cochlear duct) Scala tympani (the tympanic duct) Scala vestibuli and scala tympani are filled with perilymph and are a continuous chamber © 2013 Pearson Education, Inc.

The Spiral Organ of Corti (9-7)
Located in cochlear duct on basilar membrane Hair cell stereocilia project into tectorial membrane, attached to wall of cochlear duct Waves strike basilar membrane, moving it up and down Hair cells are pushed against tectorial membrane, bending stereocilia © 2013 Pearson Education, Inc.

Figure 9-26a The Cochlea and Spiral Organ.
Bony 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 © 2013 Pearson Education, Inc.

Figure 9-26b The Cochlea and Spiral Organ.
Cochlear duct (scala media) Tectorial membrane Vestibular membrane Tectorial membrane Outer hair cell Scala tympani Basilar membrane Hair cells of spiral organ Spiral ganglion cells of cochlear nerve Basilar membrane Inner hair cell Nerve fibers Spiral organ LM x 125 Diagrammatic and sectional views of the receptor hair cell complex of the spiral organ © 2013 Pearson Education, Inc.

Six Steps of Hearing (9-7)
Sound waves strike tympanic membrane Tympanic membrane vibrates auditory ossicles Vibration of stapes applies pressure to perilymph Pressure distorts basilar membrane Movement of basilar membrane distorts hair cells against tectorial membrane, altering neurotransmitter release Impulses travel to CNS through N VIII © 2013 Pearson Education, Inc.

Figure 9-27 Sound and Hearing.
External acoustic meatus Cochlear branch of cranial nerve VIII Malleus Incus Stapes Oval window Scala vestibuli (contains perilymph) Vestibular membrane Movement of sound waves Cochlear duct (contains endolymph) Basilar membrane Scala tympani (contains perilymph) 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. 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. © 2013 Pearson Education, Inc.

Auditory Pathways (9-7) Cochlear branch of vestibulocochlear nerve (N VIII) axons arise from spiral ganglion To cochlear nuclei of medulla oblongata To inferior colliculi of midbrain To nuclei in thalamus To auditory cortex of temporal lobes © 2013 Pearson Education, Inc.

Figure 9-28 Pathways for Auditory Sensations.
Projection fibers then deliver the information to specific locations within the auditory cortex of the temporal lobe. Stimulation of hair cells at a specific location along the basilar membrane activates sensory neurons. High- frequency sounds Low-frequency sounds Thalamus Cochlea Ascending acoustic information synapes at a nucleus of the thalamus. Low-frequency sounds High-frequency sounds Vestibular branch The inferior colliculi direct a variety of unconscious motor responses to sounds. 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) Information ascends from each cochlear nucleus to the inferior colliculi of the midbrain. KEY Primary pathway Secondary pathway Motor output Motor output to spinal cord © 2013 Pearson Education, Inc.

Checkpoint (9-7) If the round window were not able to bulge out with increased pressure in the perilymph, how would sound perception be affected? How would the loss of stereocilia from the hair cells of the spiral organ affect hearing? © 2013 Pearson Education, Inc.

Aging and the Special Senses (9-8)
Olfaction and gustation decrease with decrease in number and sensitivity of receptors Hearing decreases with age due to loss of elasticity of tympanic membrane © 2013 Pearson Education, Inc.

Checkpoint (9-8) How can a given food be both too spicy for a child and too bland for an elderly individual? Explain why we have an increasingly difficult time seeing close-up objects as we age. © 2013 Pearson Education, Inc.

The General and Special Senses

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The General and Special Senses

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