1. The Senses Ch. 13

2. Receptor Classification by Stimulus Type
Mechanoreceptors
Thermoreceptors
Photoreceptors
Chemoreceptors
Nociceptors
Mechanoreceptors – respond to touch, pressure, vibration, stretch, and itch
Thermoreceptors – sensitive to changes in temperature
Photoreceptors – respond to light energy (e.g., retina)
Chemoreceptors – respond to chemicals (e.g., smell, taste, changes in blood chemistry)
Nociceptors – sensitive to pain-causing stimuli

3. Receptor Class by Location
Exteroceptors –general senses and special senses
Interoceptors – internal viscera, blood vessels
Proprioceptors – skeletal muscles, tendons, joints, ligaments, CT coverings of bones & muscles
Exteroceptors: Respond to stimuli arising outside the body;Found near the body surface
Sensitive to touch, pressure, pain, and temperature;Include the special sense organs
Interoceptors: Respond to stimuli arising within the body;Found in internal viscera and blood vessels;Sensitive to chemical changes, stretch, and temperature changes
Proprioceptors: Respond to degree of stretch of the organs they occupy; Found in skeletal muscles, tendons, joints, ligaments, and connective tissue coverings of bones and muscles
Constantly “advise” the brain of one’s movements

4. Receptor Classification by Structural Complexity
Receptors are structurally classified as either simple or complex
Most receptors are simple and include encapsulated and unencapsulated varieties
Complex receptors are special sense organs

5. The Simple Receptors General Senses Touch and Stretch

6. Simple Receptors: Nonencapsulated
Tactile (Merkel) Discs:
Hair follicle receptors
Free Nerve endings
Merkel Discs :Modified free nerve endings for light pressure.
Found in basal layer of epidermis.
Hair Follicle receptors: Mechanoreceptors (hair bending), rapidly adapting.
In and around hair follicles.
Free nerve endings
Thermoceptors (warm & cool), chemoreceptors (itch, pH), mechanoreceptor (pressure), nociceptors (pain, hot, cold, pinch)
Found in most body tissues.

7. Simple Receptors: Encapsulated
Muscle spindles
Tactile (Meissner’s) corpuscles
Lamellar (Pacinian) corpuscles
Muscle spindles
mechanoreceptors - muscle stretch and length
skeletal muscles
Meissner’s corpuscles
Mechanoreceptors (light pressure, vibration of low frequency)
dermal papillae of hairless skin
Pacinian corpuscles
Mechanoreceptors (deep pressure, vibration of high frequency)
dermis and hypodermis, ligaments, tendons, joints, thick skin.

8. Organization of the Somatosensory System
Sensory input comes from exteroceptors, proprioceptors, and interoceptors
The three main levels of neural integration in the somatosensory system are:
Receptor level – sensory receptors
Circuit level – ascending pathways in CNS
Perceptual level – neuronal circuits in the cerebral cortex

10. Adaptation of Sensory Receptors
Receptor membranes become less responsive, receptor potentials decline in frequency or stop
Of the various receptors,
pressure, touch, and smell receptors adapt quickly (Phasic receptors). Interoceptors that respond to chemical levels in the blood adapt more slowly.
Pain receptors and proprioceptors adapt very slowly or not all (tonic receptors).
After an extended period of a repetitive sensory stimulus, we no longer notice it - we “tune it out” unless someone points it out to us
Examples: clothes, hair accessories, jewelry, humming fans or lights, even perfumes/colognes
Receptor membranes become less responsive
Receptor potentials decline in frequency or stop
Of the various receptors,
pressure, touch, and smell receptors adapt quickly
Merkel’s discs, Ruffini’s corpuscles, and interoceptors that respond to chemical levels in the blood adapt slowly.
Pain receptors and proprioceptors do not adapt at all.

11. The Chemical Senses

12. Chemical Senses
Chemoreceptors detect chemicals dissolved in aqueous solutions, and send signals to brain for interpretation.
Taste, gustation– taste buds detect substances dissolved in saliva
Smell, olfaction – olfactory receptors detect substances dissolved in fluids of the nasal membranes

13. Gustation

14. Taste Bud Locations
tongue, soft palate, interior lining of cheeks, epiglottis, pharynx and larynx.
about 10,000.
Tongue taste buds in papillae
Fungiform papillae: mushroom-like, all over tongue surface.
Vallate (Circumvallate) papillae form a “V” in the back of the tongue.
Follate papillae are found on the sides of the tongue.

15. Taste Buds (Fig. 13.20 p. 458 A&P 5th Ed.)

16. Taste Buds - electron microscope view

17. Anatomy of a Taste Bud
Onion-shaped, epithelial cells of two types:
Gustatory epithelial cells – taste cells with chemoreceptors on gustatory hairs (microvilli) projecting from a taste pore. Exposed to friction and burns from hot food.
Basal epithelial cells – stem cells that replace gustatory cells every 7-10 days.

18. The Five Basic Taste Sensations
Sweet –sugars, saccharin, alcohol, and some amino acids
Salt –Metal ions (inorganic salts) Na+ and K+ ions
Sour –H+ ions (acids)
Bitter –alkaloids such as quinine and nicotine, caffeine, and other complex organic chemicals like aspirin.
Umami – savory taste caused by glutamate, also found in cheese, fish and chocolate.

19. Gustatory Pathway
Cranial nerves involved: Facial Nerve (anterior 2/3 of tongue), Glossopharyngeal (posterior 1/3 of tongue), and Vagus nerve (deep taste buds)
Those cranial nerves carry impulses from taste buds to the solitary nucleus of the medulla oblongata.
These impulses then travel to the thalamus, from which fibers branch off to the:
Gustatory cortex of insula (taste)
Hypothalamus and limbic system (appreciation or disapproval of taste)

20. Gustatory Pathway (illustration)

21. What makes up taste? Taste is 80% smell
Thermoreceptors, mechanoreceptors, nociceptors
Temperature and texture
Taste is 80% smell
Thermoreceptors, mechanoreceptors, nociceptors also influence tastes
Temperature and texture enhance or detract from taste

22. Olfaction

23. Sense of Smell
olfactory epithelium on superior nasal concha (pseudostratified).
Olfactory sensory neurons receptor cells are bipolar neurons with olfactory cilia, and are replaced every days (unusual among neurons).
Replaced by stem cells in the olfactory epithelium
The organ of smell is the olfactory epithelium, which covers the superior nasal concha. This epithelium is pseudostratified.
Olfactory receptor cells are bipolar neurons with olfactory cilia, and are replaced every 2 months.
Olfactory receptors are surrounded and cushioned by supporting cells
Basal cells lie at the base of the epithelium and give rise to either supporting cells or olfactory receptors.

24. Sense of Smell (Fig 13.19 p 457 A&P 5th Ed.)
Axons of bipolar cells pass through the cribiform plate.
They synapse with mitral cells in the olfactory bulb. Mitral cells process odor signals.
The axons of mitral cells make the olfactory nerve, sending impulses to the olfactory cortex, the hypothalamus, amygdala, and limbic system.
Adjacent granule cells are inhibitory and may help make smells more distinct by closing down neighboring mitral cells.
They may also play a part in olfactory adaptation.

25. Role of the limbic system
Limbic system triggers sympathetic and parasympathetic responses.
Hunger-smell response is a hypothalamic function
Limbic system is involved in “primitive pathways,” triggering sympathetic and parasympathetic responses.
Hunger triggered by smell is a hypothalamic function

26. Homeostatic Imbalances
Anosmias
Uncinate fits (uns-ih-nate)
Olfactory auras
Anosmias = inability to smell
Uncinate fits (uns-ih-nate) = olfactory hallucinations
Olfactory auras = transient uncinate fits that may be experienced by epileptics just before a seizure.

27. Smells
We can distinguish 10,000 odors, we have 400 genes for smell active only in the nose
One gene codes for unique receptor protein (one type per cell), which responds to one or more odors
Very sensitive
Each odor binds with several different receptor types.
Anything smelled must be volatile & able to dissolve in mucus lining.
1000 genes for smell (out of a total of 30,000-50,000 genes)
One receptor protein type per olfactory receptor cell
Very sensitive
Work in combinations, or guilds.
Things to be smelled must be volatile chemicals with both polar and non-polar properties, able to dissolve in mucus lining.

29. The Eye and Vision

30. Eye and Associated Structures
70% of all sensory receptors in the body are in the eyes
Most of the eye is protected by a cushion of fat and the bony orbit
Accessory structures include eyebrows, eyelids, conjunctiva, lacrimal apparatus, and extrinsic eye muscles

31. Palpebrae (Eyelids) Palpebral fissure Canthi (commissures)
Lacrimal caruncle
Tarsal plates
Levator palpebrae superioris
Blink every 3-7 sec
Eyelashes
Lubricating glands: tarsal (Meibomian), ciliary glands
Palpebrae Close the eyes and protect the eye anteriorly
Orbicularis oculi muscle
Palpebral fissure – separates eyelids
Canthi – where the eyelids meet at the medial and lateral angles (commissures)
Lacrimal caruncle (“piece of flesh”) – medial corner contains glands that secrete a whitish, oily secretion (forms that crusty “Sandman’s eye sand” after sleep)
Tarsal plates of dense irregular connective tissue support the eyelids internally
The plates anchor the orbicularis oculi as well as the levator palpebrae superioris (levator gives the upper eyelid mobility)
Blinking is the result of orbicularis oculi contractions, every 3-7 seconds.
Eyelashes project from the free margin of each eyelid and initiate reflex blinking
Lubricating glands associated with the eyelids
Tarsal (aka Meibomian) glands and sebaceous glands - ducts open posterior to eyelashes
Ciliary glands lie between the hair follicles

32. Palpebrae (Fig. 13.3 p 438 A&P 5th Ed)

33. Conjunctiva Transparent membrane: palpebral conjunctiva (eyelids)
bulbar (ocular) conjunctiva (on “white” of eyes)
On anterior sclera, but not on the cornea
Lubricates and protects
Conjunctivitis = inflammation of conjunctiva by irritants, bacteria or viruses.
Transparent membrane that:
Lines the eyelids as the palpebral conjunctiva
Covers the whites of the eyes as the bulbar (ocular) conjunctiva
It is on the anterior sclera, but not on the cornea
Lubricates and protects the eye
When infected, called conjunctivitis

34. Lacrimal Apparatus lacrimal gland and associated ducts
superior/lateral location
Tears contain mucus, antibodies, and lysozyme (anti-bacterial). Travel as follows:
superolateral excretory ducts and drain downward and across to the median canthus  lacrimal puncta  lacrimal canaliculi  lacrimal sac  nasolacrimal duct inferior nasal meatus.
Consists of the lacrimal gland and associated ducts
It is located in the superior/lateral region just above the eye.
Lacrimal glands secrete tears, which contain mucus, antibodies, and lysozyme (anti-bacterial).
Tears travel through superolateral excretory ducts and drain downward and across to the median canthus  lacrimal puncta  lacrimal canaliculi  lacrimal sac  nasolacrimal duct inferior nasal meatus.

35. Lacrimal Apparatus (Fig 13.4 p 438 in A&P 5th Ed)

36. Extrinsic Eye Muscles Allow eye to follow moving objects
Maintain the shape of the eyeball
Common tendinous (annular) ring
Six straplike extrinsic eye muscles: Four are rectus muscles (rectus=straight), two are oblique muscles (oblique=at an angle)
Enable the eye to follow moving objects
Maintain the shape of the eyeball
The four rectus muscles originate from the annular ring
The two oblique muscles move the eye in the vertical plane

37. Extrinsic Eye Muscles (fig. 13.5 p 440 in A&P 5th Ed)

38. Summary of Cranial Nerves and Muscle Actions
Names, actions, and cranial nerve innervation of the extrinsic eye muscles (Fig 13.5 c)

39. Strabismus (cross-eyed)
Caused by weakness of the extrinsic eye muscles
Attempts can be made to strengthen the weaker eye
Surgery to shorten a tendon may be employed in extreme cases.

40. Structure of the Eyeball
Three tunics form wall – fibrous, vascular, and sensory
Humors fill cavity
lens separates cavity into anterior and posterior segments
A slightly irregular hollow sphere with anterior and posterior poles
The wall is composed of three tunics – fibrous, vascular, and sensory
The internal cavity is filled with fluids called humors
The lens separates the internal cavity into anterior and posterior segments

41. Structure of the Eyeball

42. Fibrous Tunic
Fibrous tunic is made of dense avascular connective tissue:
White, opaque sclera is tendon-like. Continuous with the dura mater of the brain (at the optic nerve)
Clear cornea has a lot of nerve endings, and its outer parts covered by epithelium.
External sheet is stratified squamous epithelium;
Inner face is simple squamous epithelium.

43. Vascular Tunic (Uvea): Choroid Region
Uvea (“grape”), the vascular layer, is made of loose connective tissue: choroid, ciliary body, and iris
Choroid region: Pigmented (melanocytes), supplies nutrients to retina and blood to all eye tunics
Ciliary body: surrounds lens, made of smooth muscle bundles (ciliary muscles) and the ciliary process
Muscles regulate shape of lens.
Ciliary process: loose connective tissue, capillaries, & ciliary zonule (suspensory ligament). Produces aqueous humor.
Is made of loose connective tissue and has three regions: choroid, ciliary body, and iris
Choroid region
A dark brown membrane that forms the posterior portion of the uvea. Melanocytes are abundant and act to absorb excess light.
Supplies nutrients to the retina and blood to all eye tunics
A thickened ring of tissue surrounding the lens
Composed of smooth muscle bundles (ciliary muscles) and the ciliary process
The ciliary muscles act to regulate the shape of the lens.
The ciliary process consists of loose connective tissue and capillaries, and zonule fibers extend from here to form the suspensory ligaments. The ciliary process produces aqueous humor.

44. Suspensory ligaments Support the lens Project from the ciliary process
Relax with the contraction of the ciliary muscle.
Tighten with the relaxation of the ciliary muscle.

45. Vascular Tunic: Iris
The pigmented region of the eye contains fibroblasts and melanocytes.
Pupil – central opening of the iris
Regulates the amount of light entering the eye during:
Close vision and bright light – pupils constrict
Distant vision and dim light – pupils dilate
Changes in emotional state – pupils dilate when the subject matter is appealing or requires problem-solving skills

46. Pupil Dilation and Constriction (Fig 13.7, p 442)

47. Sensory Tunic: Retina
The ora serrata - saw-tooth pattern border between retina and choroid
Retina has 2 layers:
Pigmented layer
Neural layer, with:
Photoreceptors
Bipolar cells
Ganglion cells
The ora serratae retinae is where the retina meets the ciliary body in a saw-tooth pattern. The retina itself is a delicate two-layered membrane:
Pigmented layer – the outer layer that absorbs light and prevents its scattering
Neural layer, an extension of the optic nerve, which contains:
Photoreceptors that transduce light energy
Bipolar cells and ganglion cells
Amacrine and horizontal cells

48. Sensory Tunic: Retina (Fig.13.8 p 443)

49. The Retina: Ganglion Cells and the Optic Disc
Ganglion cell axons:
Run along the inner surface of the retina
Leave the eye as the optic nerve
The optic disc:
Is the site where the optic nerve leaves the eye
Lacks photoreceptors (the blind spot)

50. The Retina: Ganglion Cells & Optic Disc

51. The Retina: Photoreceptors
Rods
Cones
Macula lutea and fovea centralis (fine focus).
Rods: Respond to dim light, gray scale photoreceptors and are used for peripheral vision and night vision.
Cones: Respond to bright light and have high-acuity color vision
The macula lutea is an elevated region that contains the ganglion and bipolar cells of the fovea centralis.
Fovea centralis only contains cones, with no interference of bipolar or ganglion cells. The spot for fine focus.

52. Blood Supply to the Retina
The neural retina receives its blood supply from two sources
The outer third receives its blood from the choroid
The inner two-thirds is served by the central artery and vein
Small vessels radiate out from the optic disc and can be seen with an ophthalmoscope

53. Inner Chambers and Fluids
Anterior and posterior segments separated by lens.
posterior segment filled with vitreous humor. Never replaced. At birth it’s all we get.
Anterior segment filled with aqueous humor. Produced by the ciliary process (recycled from blood) and drains via the scleral venous sinus, which returns it to the blood stream.
The lens separates the internal eye into anterior and posterior segments
The posterior segment is filled with a clear gel called vitreous humor, a substance that is never replaced. We are born with all the vitreous humor we’ll ever have. It:
Transmits light
Supports the posterior surface of the lens
Holds the neural retina firmly against the pigmented layer and contributes to intraocular pressure
Region in front of the lens.
Filled with aqueous humor, a plasma-like fluid produced by the ciliary process and recycled from blood.
Aqueous fluid drains via the canal of Schlemm (aka scleral venous sinus), which returns it to the blood stream.
Aqueous fluid supports, nourishes, and removes wastes

54. Glaucoma This is caused by an excessive build up of aqueous humor
The build up of aqueous humor results in increased intraocular pressure.
The increased pressure may damage the retina.
Anyone over the age of 40 should get yearly check-ups for glaucoma.
Treatment: eye drops that increase rate of aqueous humor drainage or decrease its production

55. Anterior Segment (fig. 13.10 p. 445)

56. Lens Allows precise focusing of light onto the retina
Made of epithelium (cuboidal cells) and lens fibers derived from the epithelium and containing transparent protein crystallin
With age, the lens becomes more compact and dense and loses its elasticity
A biconvex, transparent, flexible, avascular structure that:
Allows precise focusing of light onto the retina
Is composed of epithelium (cuboidal cells) and lens fibers derived from the epithelium.
The lens fibers form the bulk of the lens and consists of cells filled with the transparent protein crystallin
With age, the lens becomes more compact and dense and loses its elasticity

57. Cataract Clouding of the lens
The risks of developing this increases with
Diabetes mellitus
Heavy smoking
Frequent exposure to intense sunlight
Treatment: replacement of lens with artificial one

58. So, how do eyes work?

59. We need to learn about how LIGHT works, first.

60. Light
Electromagnetic radiation – all energy waves from short gamma rays to long radio waves, 10-5nm to 103m wavelength.
Visible spectrum, nm wavelength.
Different cones in the retina respond to different wavelengths of the visible spectrum

61. Light (Fig p 446)
From Webvision (University of Utah)

62. Refraction and Lenses
Refraction = light bends when passing through materials of differing density
Light passing through a convex lens (as in the eye) refracts so that the rays converge to a focal point.
When a convex lens forms an image, the image is upside down and reversed right to left
When light passes from one transparent medium to another more denser medium its speed changes and it bends. This bending is called refraction.
Light passing through a convex lens (as in the eye) is bent so that the rays converge to a focal point.
When a convex lens forms an image, the image is upside down and reversed right to left

63. Refraction and Lenses (fig. 13.12 p 447)

64. Focusing Light on the Retina
Pathway of light entering the eye: cornea, aqueous humor, lens, vitreous humor, and the neural layer of the retina to the photoreceptors
Light is refracted: 1) at the cornea (most); 2) entering the lens; and 3) leaving the lens
The lens curvature and shape allow for fine focusing of an image
The focal point is where refracted light rays cross.

65. Focusing for Distant Vision
Light from a distance needs little adjustment for proper focusing
When the ciliary muscles relax, the suspensory ligaments get tight. Distance vision occurs.
Far point vision is the farthest point that you can see clearly. It is the distance beyond which the lens does not need to change shape to focus (20 ft.)

66. Focusing for Distant Vision (Fig. 13.13 p 447)

67. Focusing for Close Vision
Near point vision is the closest point that you can see clearly. Close vision requires:
Accommodation – changing the lens shape
Constriction – the pupillary reflex
Convergence – medial rotation of the eyeballs toward the object being viewed
Near point vision is the closest point that you can see clearly. Close vision requires:
Accommodation – changing the lens shape by ciliary muscles to increase refractory power. As the lens gets fatter, the focal point becomes closer, allowing us to see close objects.
Constriction – the pupillary reflex constricts the pupils to prevent divergent light rays from entering the eye
Convergence – medial rotation of the eyeballs toward the object being viewed

68. Focusing for Close Vision (Fig. 13.13 p 447)

69. Problems of Refraction
Emmetropic eye – normal eye with light focused properly (20/20)
Myopic eye (nearsighted) – the focal point is in front of the fovea centralis. It is corrected with a concave lens.
Hyperopic eye (farsighted) – the focal point is behind the fovea centralis. The eyeball is too short. It is corrected with a convex lens
Presbyopia (“old eyes”) - cannot accommodate due to the loss of flexibility in the lens.

70. Problems of Refraction (fig 24.3 lab manual 11th ed)

71. Photoreception
Photoreception – process by which the eye detects light energy
A photoreceptor cell (rod or cone) consists of two segments:
The outer segment is imbedded in the pigmented retina. Visual pigments (photopigments) are arranged in disk-like structures and change shape as they absorb light.
The inner segment contains cytoplasm rich in mitochondria and is connected to the cell body.

72. Photoreceptors (Fig. 13.14 p 449)

73. Rods Sensitive to dim light and best suited for night vision
Receptor field is about 100:1 (many rods feed into 1 ganglion cell)
Absorb all wavelengths of visible light but perceives gray scale vision only.
Results in fuzzy and indistinct images

74. Cones
Need bright light for activation (have low sensitivity, higher threshold than rods)
Receptor field is 1:1. Each cone synapses with a single ganglion cell
Have pigments that provide a vivid color view
Vision is detailed and has high resolution, particularly in the fovea centralis where there is nothing but cones.

75. Cones and Rods (Fig p 443)

76. Chemistry of Visual Pigments
Retinal is a light-absorbing molecule
Combines with opsins to form visual pigments
Similar to and is synthesized from vitamin A
Two isomers: cis isomer and trans isomer
Isomerization of retinal initiates electrical impulses in the optic nerve

77. Chemistry of Visual Pigments (Fig. 13.15 p 451)

78. Excitation of Rods
The visual pigment of rods is rhodopsin. The cis isomer of retinal is bound to opsin. (opsin + 11-cis retinal)
Light phase
When light hits the rhodopsin, it is converted to the trans isomer of retinal which detaches from opsin, triggering “bleaching” of the pigment.
In bright daylight all the rods bleach out and recover at night.

79. Excitation of Rods Dark phase
The reconversion to cis-retinal and rhodopsin occurs in the pigmented retina and requires ATP and isomerase enzyme.

80. Excitation of Rods (Fig. 13.15 p. 451)

81. Excitation of Cones
Visual pigments in cones are similar to rods (retinal + opsins)
There are three types of cones: blue, green, and red
Intermediate colors are perceived by activation of more than one type of cone
Method of excitation is similar to rods

82. Color Blindness Inability to see certain colors or all colors.
Often sex-linked, 8-10% males are color blind.
Green/red color blindness is more common among color blind individuals. People will see green in the presence of red or vice versa.
Some color blind see everything in gray scale, in which case the person may have only rods, or may have rods + nonfunctional cones.

83. Other colors we see:
Yellow is the combination of activating green and red cones.
Orange involves activation of more red than green cones.
White is seen when all cones bleach (all cones fire)
Black is caused by the lack of cones firing.

84. Adaptation
When we go from darkness to light, rods must bleach out before the cones become functional. Adaptation to bright light occurs within 60 seconds and involves:
Dramatic decreases in retinal sensitivity – rod function is lost
Cones take over, visual acuity is gained and color vision reaches peak within 5-10 minutes.
Adaptation to dark is the reverse, but takes minutes to hours to achieve.
Cones stop functioning in low light
Rods accumulate Rhodopsin in the dark and retinal sensitivity is eventually restored

85. Nyctalopia or Night Blindness
This is the inability to see in low light.
Where malnutrition is a problem, often it is due to lack of Vitamin A.
Cones can function in low levels of Vitamin A, but rods require high levels to function.
Where malnutrition is not a big problem, degenerative diseases are more common. Failure to recycle the tips of the rods as they slough off.

86. Good Sources of Vitamin A (RAE= Retinol Activity Equivalents)
Food Serving Size RAE %RDA men* % RDA women*
Sweet Potato 1/2 C
Carrot medium
Kale, boiled 1/2 C
Mango /2 medium
Turnip Greens 1/2 C
Spinach, raw 1 C
Papaya /2 medium
Red Bell Pepper /2 medium
Apricot
Cantaloupe 1/2 C
Milk, Fat Free 1 C
Romaine 1 C
Egg, large
Milk, whole 1 C
Tomato, raw medium
Broccoli 1/2 C
Green Bell Pepper 1/2 C
Orange medium
*RDA for men is 900 RAE. RDA for women is 700 RAE.

87. Visual Pathways (Fig 13.18 p 455 A&P 5th Ed)

88. Depth Perception
Achieved by both eyes viewing the same image from slightly different angles
Three-dimensional vision results from cortical processing of the slightly different images
If only one eye is used, depth perception is lost and the observer must rely on learned clues to determine depth

89. The Ear & Hearing

90. Parts of the Ear
The three parts of the ear are the inner, outer, and middle ear
The outer and middle ear are involved with hearing
The inner ear functions in both hearing and equilibrium
Receptors for hearing and balance respond to separate stimuli and re activated independently

91. The Ear

92. Outer Ear
The auricle (pinna) includes the helix (rim), the lobule (earlobe), and the tragus (hard flap anterior to the external auditory canal)
External auditory canal
ceruminous glands, produce cerumen (earwax).
Tympanic membrane (eardrum)
Thin CT membrane transfers sound energy to the ossicles & marks the boundary between outer and middle ears
The auricle (pinna) includes the helix (rim), the lobule (earlobe), and the tragus (hard flap anterior to the external auditory canal)
External auditory canal is a short, curved tube that provides a path for sound to travel to the inner ear.
Filled with ceruminous glands, modified sebaceous glands that produce cerumen (earwax).
Cerumen prevents foreign objects from entering the ear.
Tympanic membrane (eardrum)
Thin connective tissue membrane that vibrates in response to sound
It transfers sound energy to the ossicles.
Marks the boundary between outer and middle ears

93. Middle Ear (Tympanic Cavity)
Air-filled, mucosa-lined cavity between tympanic membrane, oval and round windows.
Tympanic membrane connected to the malleus (the first of three ossicles) here.
Epitympanic recess
Pharyngotympanic tube – connects the middle ear to the nasopharynx. Usually collapsed, equalizes pressure in the middle ear cavity with the external air (yawning or chewing opens it)
A small, air-filled, mucosa-lined cavity. Lateral boundary is the eardrum, medial boundary is marked by the oval and round windows.
On this side the eardrum is connected to the malleus (the first of three ossicles).
Epitympanic recess – superior portion of the middle ear
Pharyngotympanic tube – connects the middle ear to the nasopharynx. It equalizes pressure in the middle ear cavity with the external air pressure
It is typically collapsed. Yawning and chewing are actions that open these tubes.

94. Otitis media Inflammation of the middle ear.
May be due to excessive fluid or pus due to bacterial infection.
Most of the non-infectious cases are due to food allergies.

95. Middle Ear - Tympanic Cavity (Fig 13.21 p 461)

96. Oval and Round windows
The oval window is a membrane that allows sound to enter the inner ear, and it is attached to the stapes (the 3rd of the three ossicles).
The round window is a membrane that allows sound to exit the inner ear (back into the middle ear). It is not associated with any ossicles.

97. Ear Ossicles: Three small bones
The malleus (hammer) attaches to the tympanic membrane and vibrates as the membrane vibrates.
The incus (anvil) attaches to the malleus and vibrates when the malleus vibrates.
The stapes (stirrup) attaches to the oval window and vibrates when the incus vibrates.

98. Ear Ossicles (illustration)

99. Regulatory Muscles
Tensor tympani and stapedius muscles contract upon very loud sounds to prevent neurological hearing loss.
Tensor tympani:
Origin: wall of the auditory tube
Insertion: malleus
Stapedius muscle:
Origin: posterior wall of the middle ear.
Insertion: stapes

100. Inner Ear
Bony labyrinth is a bony coiled channel within the inner ear, housed within the temporal bone.
Contains the vestibule, the cochlea, and the semicircular canals
Filled with perilymph
Membranous labyrinth is a membranous coil within the bony labyrinth.
Series of membranous sacs filled with endolymph, a potassium-rich fluid similar to cytoplasm.
The membranous labyrinth is surrounded by perilymph.

101. Inner Ear (Fig p 462)

102. The Cochlea
A snail-shaped bony cavity that contains the membranous and bony labyrinths.
Coils around a bony pillar called the modiolus
Contains the cochlear duct, which ends at the cochlear apex
Contains the spiral organ of Corti (hearing receptors are here)

103. The Cochlea The cochlea is divided into three chambers:
Scala vestibuli - perilymph region that begins at the oval window.
Scala media - endolymph region contained within the membranous labyrinth.
Scala tympani - perilymph region that ends at the round window.
The Helicotrema connects the scala vestibuli and the scala tympani.

104. Cochlear membranes
The vestibular membrane separates the scala vestibuli from the scala media.
The basilar membrane separates the scala tympani from the scala media.
The tectorial membrane is the membrane within the scala media that holds the stereocilia of the spiral organ of Corti in place.

105. The Cochlea (Fig p. 463)

106. Sound, Pitch and Amplitude
A sound wave is a series of pressure disturbances - alternating areas of high pressure (compressions) and low pressure (rarefactions). Sound travels in any elastic medium and travels better in water than in air.
Pitch (frequency) is determined by the distance between wavelengths of sound. High frequency is high pitch, low frequency is low pitch. We hear ,000 Hz.
Amplitude is loudness or intensity of sound, proportional to its energy. Loudness is measured in decibels (dB). Conversation= 50 dB; A rock concert = 120 dB. Severe hearing loss happens at >90 dB!

107. How do we hear?
Sound is amplified by the auricle, enters the external auditory canal, then vibrates the eardrum
The eardrum vibrates the malleus, which vibrates the incus, which vibrates the stapes. The vibration of the stapes causes vibration of the oval window
Oval window vibration sends sound waves through the perilymph of scala vestibuli.
The waves cross the scala vestibuli to the endolymph of scala media at a given region depending on pitch. High pitch sounds cross earliest. Crossing results in vibration of the vestibular membrane.

108. What happens next?
As the vestibular membrane vibrates, sound waves pass through the endolymph.
The basilar membrane vibrates, and displaces the organ of Corti from its position on the tectorial membrane.
This movement sets up shearing forces that pull on hair cells.
The moving hair cells stimulates the cochlear nerve that sends impulses to the brain.

109. What finally happens to the sound energy?
Sound travels through the perilymph of the scala tympani
Sound travels out the round window and into the middle ear.
By this time the sound waves are finally dampened or “depleted” in the middle ear and so do not cause vibrations of the oval window or ossicles.

110. Resonance of the Basilar Membrane
A better way to explain the “crossing of sound” mentioned earlier: resonance of basilar membrane.
Sound waves of low frequency (inaudible): travel around the helicotrema and do not excite hair cells
Audible sound waves: penetrate through the cochlear duct, vibrate the basilar membrane, and excite specific hair cells according to frequency of the sound

111. Sound frequencies (Fig 13.25 p 466)

112. The Organ of Corti
Is composed of supporting cells and outer and inner hair cells
Afferent fibers of the cochlear nerve attach to the base of hair cells
The stereocilia (hairs) protrude into the endolymph and touch the tectorial membrane.

113. Excitation of Hair Cells in Organ of Corti

114. Auditory Processing
Pitch is perceived by:
The primary auditory cortex
Cochlear nuclei
Loudness is perceived by:
Varying thresholds of cochlear cells
The number of cells stimulated
Localization is perceived by superior olivary nuclei that determine sound

115. Deafness
Conduction deafness – sound is not able to conduct to the fluids of the inner ear (e.g., impacted earwax, perforated eardrum, osteosclerosis of the ossicles)
Sensory-neural deafness – results from damage to the neural structures at any point from the cochlear hair cells to the auditory cortical cells
Tinnitus – ringing or clicking sound in the ears in the absence of auditory stimuli
Meniere’s syndrome – labyrinth disorder that affects the cochlea and the semicircular canals, causing vertigo, nausea, and vomiting. Balance problem and really loud tinnitis. Cause is uncertain.

116. The Ear & Equilibrium

117. The Vestibule The central egg-shaped cavity of the bony labyrinth
Suspended in its perilymph are two sacs: the saccule and utricle. These sacs house equilibrium receptors called maculae, which respond to gravity and changes in the position of the head
The saccule extends into the cochlea and is involved in vertical equilibrium.
The utricle extends into the semicircular canals and is involved in horizontal equilibrium.

118. The Vestibule

119. The Semicircular Canals
Three canals that each define two-thirds of a circle and lie in the three planes of space
Membranous semicircular ducts line each canal and communicate with the utricle
The ampulla is the swollen bulge at the base of each canal and it houses equilibrium receptors in a region called the crista ampullaris
These receptors respond to angular movements of the head (dynamic equilibrium).

120. The Semicircular Canals

121. Mechanisms of Equilibrium and Orientation
Vestibular apparatus – equilibrium receptors in the semicircular canals and vestibule
Maintains our orientation and balance in space
Vestibular receptors monitor static equilibrium (standing still)
Semicircular canal receptors monitor dynamic equilibrium (moving)

122. Anatomy of Maculae
Maculae are the sensory receptors for static equilibrium
Contain supporting cells and hair cells
Each hair cell have numerous stereocilia and a single kinocilium embedded in the otolithic membrane
Otolithic membrane – jellylike mass studded with tiny CaCO3 stones called otoliths
Utricular hairs respond to horizontal movement
Saccular hairs respond to vertical movement

123. Anatomy of Maculae (Fig. 13.26 p 468)

124. Effect of Gravity on Utricular Receptor Cells
As the head tilts, the jelly slides over the macula and tugs on the hair cells & kinocilium. This triggers the vestibulocochlear nerve and lets the brain know the position of the head.
Otolithic movement in the direction of the kinocilia increases the number of action potentials generated
Movement in the opposite direction hyperpolarizes vestibular nerve fibers and reduces the rate of impulse propagation
From this information, the brain is informed of the changing position of the head

125. Crista Ampullaris and Dynamic Equilibrium
The crista ampullaris (or crista) is the receptor for dynamic equilibrium (angular movement) and is located in the ampulla at the base of each semicircular canal
Each crista has hair cells and kinocilium that extend into a gel-like mass called the cupula. The base of the hair cells are surrounded by dendrites of vestibular nerve fibers.
When the body turns, endolymph and perilymph turn within the body and cause the kinocilium to bend with the cupula. The result is that the brain is informed of rotational movements of the head

126. Crista Ampullaris and Dynamic Equilibrium

127. Crista Ampullaris in Ampulla
Cupula

128. Balance and Orientation Pathways
There are three modes of input for balance and orientation
Vestibular receptors
Visual receptors
Somatic receptors
These receptors allow our body to respond reflexively

129. Balance Disorders
Vestibular nystagmus: complex jerking eye movements that occur after rotation. Accompanied by a dizzy feeling. The eyes are trying to compensate for the movement of fluid in the semicircular canals.
Motion sickness: sensory system is confused. The vestibular apparatus detects movement, which contradicts visual assessment. The sympathetic system causes nausea.

130. Doesn’t this photo make your head hurt?