THE SPECIAL SENCES- Unlocking the Wonders of the Special Senses: Sight, Sound, Smell, Taste, and Balance

Title: Unlocking the Wonders of the Special Senses: Sight, Sound, Smell, Taste, and Balance

Introduction:

Welcome to our captivating SlideShare presentation on the Special Senses, where we delve into the extraordinary capabilities that allow us to perceive and interact with the world around us. Join us on a sensory journey as we explore the intricate structures and functions of sight, sound, smell, taste, and balance.

The special senses are our primary means of experiencing and interpreting the environment, each sense providing unique and vital information that shapes our perceptions and responses. These senses are facilitated by highly specialized organs and complex neural pathways, enabling us to see a vibrant sunset, hear a symphony, savor a delicious meal, detect a fragrant flower, and maintain our equilibrium.

In this presentation, we will:

Visual System (Sight): Dive into the anatomy and physiology of the eye, exploring how light is converted into electrical signals and processed by the brain to create the images we see. Understand common vision disorders and the mechanisms behind corrective measures like glasses and contact lenses.

Auditory System (Hearing): Examine the structures of the ear and the process of sound wave transduction, from the outer ear to the cochlea and auditory nerve. Learn about hearing loss, auditory processing, and the advances in hearing aid technology.

Olfactory System (Smell): Discover the olfactory receptors and pathways that enable the detection of thousands of different odors. Explore the connection between smell and memory and the impact of olfactory disorders on quality of life.

Gustatory System (Taste): Uncover the taste buds and the five basic tastes – sweet, salty, sour, bitter, and umami. Delve into the interplay between taste and smell and the factors influencing our food preferences and eating habits.

Vestibular System (Balance): Investigate the inner ear structures responsible for balance and spatial orientation. Understand how the vestibular system helps maintain posture and coordination, and explore common vestibular disorders and their effects.

Through engaging visuals, interactive diagrams, and insightful explanations, we aim to illuminate the complexities of the special senses and their profound impact on our daily lives. Whether you're a student, educator, or simply curious about how we perceive the world, this presentation will provide valuable insights into the remarkable capabilities of the human sensory system.

Join us as we unlock the wonders of the special senses and gain a deeper appreciation for the intricate mechanisms that allow us to experience the richness of our environment.

1. ANATOMY $ PHYSIOLOGY OF SENSORY SYSTEM MR. SAGAR PANDYA ASSISTANT PROFESSOR M.Sc. Nursing (Child Health Nursing )

2. SENSATION Sensation is the conscious or subconscious awareness of changes in the external & internal environment. Thus, sensation may occur without perception . Perception is the conscious awareness and interpretation of sensations and is primarily function of the cerebral cortex Sensory Modality- Each unique type of sensation e.g. touch, pain, vision, hearing. Modalities can be grouped into two classes: * General Senses : - Somatic senses - Visceral Senses * Special Senses

3. General Senses *Somatic senses Tactile sensation: Touch, Pressure, Vibration, Itch. Thermal Sensation: Warm & Cold. Pain Sensation Proprioceptive Sensation (Perception of moving Or non moving limbs parts or head) *Visceral Senses Provide information about conditions within internal organs like pressure stretch chemical nausea hunger & temperature.

4. Special Senses Vision Hearing Taste Smell Equilibrium or Balance

5. The Process of Sensation A sensory receptor responds only to a particular type of stimulus (a property known as selectivity). Four events in sensation: Stimulation of the sensory receptor. Transduction of the stimulus. Generation of nerve impulses. Integration of sensory input.

6. TYPES OF SENSORY RECEPTORS

7. Sensory Receptors in the Skin

8. A Muscle Spindle and a Tendon Organ

9. THE SPECIAL SENSE ORGANS (SENSORY ORGANS)

10. The Sensory System The central nervous system receives information from the internal and external environment via the sensory organs. Sensory organs are able to “sense” this information because of specialized receptors. When a receptor is triggered, it causes an action potential in the sensory neuron.

11. Sensory Organs Sense Organ Touch Skin (external) Taste Tongue Smell Nose Hearing/Equilibrium Ears Sight Eyes

12. Visual receptors account for ~ 70% of all sensory input in the body. 40% of the cerebral cortex in involved in processing visual perception. Eye balls are the sense organs for vision Eye is a sphere ~ 1” in diameter and is located in the orbital cavity of the skull. Our visual perception is dependent on the eye, its accessory structures, the optic tracts, and the 1 o visual cortex and it’s association areas. Vision is possible because of photoreceptors that detect light. Visible light: 400-700 nm. The Eye and Vision

13. Each eye has over a million nerve fibers Protection for the eye Most of the eye is enclosed in a bony orbit A cushion of fat surrounds most of the eye Accessory Structures of Eye Eyebrows Eyelids with tarsal and ciliary glands. Eyelashes Lateral and medial canthus (angles at corner of eye) Conjunctiva Lacrimal apparatus Extrinsic eye muscles (6)

14. Eyelids Eyelids “ palpebrae ” protect eyes from foreign objects and bright light. Meets at medial and lateral canthus (crease) Angle of eyes is canthus - medial and lateral canthi Lacrimal caruncle is at median canthus Levator palpebrae muscle raises and lowers eye lids Tarsal glands in eyelids secrete oily substance that keeps eyes moist. Eyelashes on the margin of each lid help to keep substances from entering eye; ciliary glands open into lash follicle. Eyelashes

15. Meibomian Glands (Tarsal glands)- Modified sebaceous glands produce an oily secretion to lubricate the eye. Ciliary Glands – Modified sweat glands between the eyelashes Conjunctiva - Transparent mucous membrane covering inner surface of eyelids ( palpebral conjunctiva) and anterior surface of eye (bulbar conjunctiva), but not the cornea. It made up of stratified columnar epithelium with numerous goblet cells that secrete mucous and keep eyeball and lids moist. When eye is closed a slit-like space forms conjunctival sac. When inflamed, conjunctivitis

16. Lacrimal apparatus Keeps surface of eye moist with tears from lacrimal glands. From upper lateral position, tears washover eyes when you blink eyes and move to medial canthus to drain into lacrimal puncta → → canaliculi → lacrimal sac and → nasolacrimal duct → nasal cavity. Lacrimal fluid “tears” contain mucus, antibodies and lysozymes that destroy bacteria.

17. Extrinsic Eye Muscles Muscles attach to the outer surface of the eye. Produce eye movements. Six muscles :

18. Extrinsic Eye Muscles Superior rectus Lateral rectus Inferior rectus Medial rectus Superior oblique Inferior oblique

19. The eye is a sphere with a bulge (cornea) at the front and a stem at the back (optic nerve). The outside is covered by a tough outer covering called fibrous tunic. Consists of 3 tunics (fibrous, vascular and sensory) and 2 chambers (anterior and posterior) separated by a lens and iris. The anterior chamber is filled with aqueous humor. Posterior chamber is filled with vitreous body. Eye anatomy

20. The visual receptor field (retina) occupies the major portion of the posterior wall of the eye and light reaching the retina is regulated by the iris. Fibrous tunic The fibrous tunic consists of the cornea and sclera. Cornea is avascular and transparent and allows light to pass through. It is made of 100’s of sheets of collagen fibers sandwiched between two layers of epithelium. Highly innervated and sensitive to touch or particles on it.

21. Sclera is the white of the eye which protects, shapes and serves as the anchor site for the extrinsic eye muscles. Limbus is junction between sclera and cornea- stem cells here between cornea and conjunctiva allow for continual renewal of cornea. Scleral venous sinus allows for drainage of aqueous humor.

22. Vascular tunic Consists of three parts: choroid, ciliary body, iris and pupil. Choroid highly vascular dark brown pigmented layer that covers 5/6 of posterior chamber. Melanocytes produce melanin that accounts for dark brown color of choroid. Prevents light scattering within the eye. Ciliary body anterior to choroid consists of ciliary muscle (sm. m.), and the ciliary process. Radiating off of ciliary process are fine fibrils that attach to the iris and control its thickness.

23. Lens is attached; contains muscles that change the lenses shape. Iris is the colored portion of the eye and constricts and dilates to regulate the amount of light entering into the eye. Pigmented ring of muscular tissue composed of circular and radial muscles. Reflex contraction of circular muscle in bright light (small dia of pupil) Reflex contraction of radial muscle in dim light (large dia of pupil) Pupil- central hole in iris. 

24. sclera iris pupil tear drainage canal cornea Medial commisure lateral commisure palpabre palpabre Lacrimal caruncle

25. Bright light N ormal light D im light Pupil

26. Sensory tunic “Retina” Consists of two layers; thin pigmented layer and a thick neural layer Outer layer – Pigmented layer - Beginning of visual pathway to brain Inner layer – Neural layer contains rods and cones - Layer where light rays are deciphered and converted into an impulse to be relayed to brain. Ganglion cells- synapse with bipolar cells and make a 90 degree turn on retinal surface to go into optic nerve.

27. Bipolar cells- synapse with rod and cone receptors to synapse with ganglion cells. Optic disc- blind spot because its where optic nerve leaves the eyeball (no rods or cones) Macula lutea - It containing the fovea centralis . Small flat yellowish spot in exact center of posterior eye. Contains only CONES, and no bipolar or ganglion cells to scatter light. Macula lutea is the area of highest visual acuity .

28. Optic disc Fovea centralis Macula lutea Fovea centralis - In center of macula lutea , contains only cones, area of greatest visual acuity.

29. The Photoreceptors RODS- Receptor for black and white light (dim light, contains pigment rhodopsin ). Location – (~ 250 million) in the pigmented layer of the retina. Functions – low light and peripheral vision receptors. CONES- Receptors for colored light (color vision, not evenly distributed, concentrated in fovea).

30. Location – (~6 million) in the pigmented layer of retina and macula lutea . Functions – operate in bright light and are high acuity color receptors.

31. The LENS Defined: composed of proteins called crystallins arranged in layers much like an onion. It is completely transparent and lacks any blood vessels. Attachments: Lens is enclosed in a clear connective tissue capsule and is held in place by encircling zonular fibers which attach it to the ciliary processes. Biconvex structure, flexible. Attached by suspensory ligaments to ciliary body. Focuses image onto retina

32. Changes lens thickness to allow light to be properly focused onto retina. Lens divides the eyeball into two cavities: Anterior cavity and Posterior cavity. Anterior cavity- Further divided into anterior and posterior chambers. Both are filled with aqueous humor. Anterior chamber – Lies between the cornea and iris It is filled with aqueous humor a watery fluid that

33. nourishes the lens and cornea. Posterior chamber – Lies between the iris and in front of the zonular fibers and lens Posterior cavity (vitreous chamber)- Filled with vitreous humor.

34. Fluid In the eye Vitreous Humor & Aqueous Humor Vitreous humor - Behind lens, gel-like substance with fine collagenic fibrils imbedded in as viscous ground substance- binds with water. Keeps the eye from collapsing Lasts a lifetime and is not replaced Functions: Transmits light

35. Supports the posterior surface of the lens and holds the neural retina firmly against pigmented layer. Contributes to intraoccular pressure, helping to counter act the pulling force of the extrinsic eye muscles. Aqueous humor - In front of lens, anterior segment, watery fluid. Helps maintain intraocular pressure Provides nutrients for the lens and cornea Reabsorbed into venous blood Functions: Supplies cornea and lens with nutrients.     

36. Helps to maintain the shape of the eye. Produced and renewed every 4 hrs by the cilliary body . 

37. Lens Accommodation Light must be focused to point on retina for optimal vision The eye is set for distance vision (over 20 ft away) The lens must change shape to focus for closer objects

38. Refraction of Light Rays : Refraction is the bending of light rays. The cornea and lens refract light rays.

39. Accommodation and the Near Point of Vision : Increase in the curvature of the lens for near vision is called accommodation. Near point of vision is the minimum distance from the eye that an object can be clearly focused.

40. Refraction Abnormalities and their Correction : Nearsightedness (myopia)- Close objects seen clearly. Image is focused in front of the retina. Correction- use of concave lens. Farsightedness ( hyperopia )- Distant objects seen clearly. Image is focused behind the retina. Correction- use of convex lens.

41. Vision & Corrective Lenses

42. Color Blindness and Night Blindness Color blindness- I nherited inability to distinguish between certain colors. Result from the absence of one of the three types of cones. Most common type: red-green color blindness. Night blindness or Nyctalopia - vitamin A deficiency.

43. Processing of Visual Input Receptor potential in rods and cones→ graded potentials in bipolar neurons and horizontal cells→ nerve impulses in ganglion cells→ optic nerve→ optic chiasm→ optic tract→ thalamus→ primary visual area of cerebral cortex in occipital lobe.

44. Visual Pathway Fibers partially cross over in optic chiasm. Right half of brain interprets image from left eye and vice versa.

45. Visual field of left eye Temporal half Visual field of right eye Temporal half Nasal half Midbrain Left eye Temporal retina Optic radiations Left eye and its pathways Primary visual area of cerebral cortex (area 17) in occipital lobe Lateral geniculate nucleus of the thalamus Optic radiations Midbrain Temporal retina Nasal retina Right eye Right eye and its pathways Nasal half Nasal retina 1 1 Visual field of left eye Temporal half Visual field of right eye Temporal half Nasal half Midbrain Left eye Temporal retina Optic radiations Left eye and its pathways Primary visual area of cerebral cortex (area 17) in occipital lobe Lateral geniculate nucleus of the thalamus Optic radiations Midbrain Temporal retina Nasal retina Right eye Right eye and its pathways Nasal half Nasal retina 1 1 2 2 Visual field of left eye Temporal half Visual field of right eye Temporal half Nasal half Midbrain Left eye Temporal retina Optic radiations Left eye and its pathways Primary visual area of cerebral cortex (area 17) in occipital lobe Lateral geniculate nucleus of the thalamus Optic radiations Midbrain Temporal retina Nasal retina Right eye Right eye and its pathways Nasal half Nasal retina 1 1 2 2 3 3 Visual field of left eye Temporal half Visual field of right eye Temporal half Nasal half Midbrain Left eye Temporal retina Optic radiations Left eye and its pathways Optic tract Primary visual area of cerebral cortex (area 17) in occipital lobe Lateral geniculate nucleus of the thalamus Optic radiations Midbrain Temporal retina Nasal retina Right eye Right eye and its pathways Nasal half Nasal retina 1 1 2 2 4 4 3 3 Visual field of left eye Temporal half Visual field of right eye Temporal half Nasal half Midbrain Left eye Temporal retina Optic radiations Left eye and its pathways Optic tract Primary visual area of cerebral cortex (area 17) in occipital lobe Lateral geniculate nucleus of the thalamus Optic radiations Midbrain Temporal retina Nasal retina Right eye Right eye and its pathways Nasal half Nasal retina 1 1 2 2 4 4 5 5 3 3 Visual field of left eye Temporal half Visual field of right eye Temporal half Nasal half Midbrain Left eye Temporal retina Optic radiations Left eye and its pathways Optic tract Primary visual area of cerebral cortex (area 17) in occipital lobe Lateral geniculate nucleus of the thalamus Optic radiations Midbrain Temporal retina Nasal retina Right eye Right eye and its pathways Nasal half Nasal retina 1 1 2 3 2 4 3 4 5 5 6 6

46. THE EAR (Hearing and Equilibrium) The ear is the organ of hearing and is also involve in balance. It is supplied by the 8 th cranial nerve : Vestibulocochlear nerve, which is stimulated by vibrations caused by sound waves. These structures are all embedded in the temporal bones of the cranium. Hearing involves the perception of sound waves entering the external auditory canal which is received by the middle ear and relayed to the inner ear where it is then registered in the cochlea.

47. Equilibrium is maintained and perceived by the structures in the semi-circular canals of the inner ear. Hearing and equilibrium mediated through the structures of the inner ear. Sound Frequency (Pitch) Frequency is measured in hertz (Hz). A person who has hearing within the normal range can hear sounds that have frequencies between 20 and 20,000 Hz. The most important sounds we hear every day are in the 250 to 6,000 Hz range.

48. Anatomy of the Ear Three main regions: External (outer) ear:- A uricle or Pinna , External auditory canal, Tympanic membrane and ceruminous glands. Middle ear:- Auditory ossicles ( malleus , incus or stapes) & Auditory ( eustachian ) tube. Internal (inner) ear:- Labyrinth: bony and membranous. Bony labyrinth- Perilymph Membranous labyrinth- Endolymph

49. Oval window and round window (membranous regions) The semicircular canals, the vestibule (both contain receptors for equilibrium) and the cochlea (contains receptors for hearing).

50. The Middle Ear and the Auditory Ossicles

51. The Internal Ear

52. EXTERNAL EAR Pinna – auricle covered with skin and made of elastic cartilage; helix and lobule. External auditory meatus - ear canal lined with skin and ceruminous glands passes through temporal bone. Tympanic membrane – “ear drum” separates outer ear from middle ear and is innervated with sensory fibers from trigeminal and vagus nerves. Responds to air vibrations or sound waves and transfers energy to middle ear ossicles .

53. Middle ear Three middle ear ossicles joined together: Malleus (Hammer) – looks like a hammer attaches to tympanic membrane and connected to the incus . Incus (Anvil) - Looks like an anvil and connected to the stapes. Stapes (Stirrup) - looks like a stirrup – footplate attaches to oval window of inner ear where it creates ossicilations in the scala vestibuli Middle ear muscles: stapedius inserts on stapes; tensor tympani inserts on malleus . Contract during loud noises and relieve tension on ossicles to protect inner ear. Eustachian tube connects middle ear to nasopharynx .

54. Inner ear anatomy Housed in a maze of temporal bone passages called the bony labyrinth. Bony labyrinth is filled with perilymph and is lined with periosteum ; perilymph is continuous with CSF Bony labyrinth consists of: -a). vestibule, b). cochlea and c). semicircular canals Membranous labyrinth lines inside of bony labyrinth. It is lined with epithelium and is filled with endolymph (high in Na+, K+). Consists of semicircular ducts, utricle and saccule and the cochlear duct.

55. The Vestibule: Expanded part nearest to the middle ear. The oval and round windows are located in its lateral wall. It contain two membranous sacs: the utricle and the saccule, which are important in balance. The Semicircular Canals: These are three tubes arranged so that one is situated in each of the three planes of space. Lateral semicircular canal Anterior semicircular canal Posterior semicircular canal They are continuous with the vestibule and are also important in balance.

56. Structures of hearing Cochlea –spiraling chamber of bony labyrinth. Looks like a snails shell, and spirals around modiolus . Lined with a membranous labyrinth with 3 separate chambers: Scala vestibuli –filled with perilymph abuts oval window. Cochlear duct –filled with endolymph and contains organ of Corti Scala tympani –filled with perilymph abuts round window. Scala vestibuli and scala tympani are joined by heliocotrema at the apex of cochlea.

57. Organ of Corti

58. Structures of hearing

59. Innervation from CN-VIII

60. Physiology of Hearing Audible sound range: 20-20,000 Hz. Sound waves→ auricle→ external auditory canal→ tympanic membrane→ malleus → incus → stapes→ oval window→ perilymph of the scala vestibuli → vestibular membrane→ endolymph in the cochlear duct→ basilar membrane →hair cells against tectorial membrane → bending of hair cell stereocilia → receptor potential→ nerve impulse. Sound wave → scala tympani→ round window.

61. Scala vestibuli Cochlear duct (contains endolymph) Scala tympani Perilymph Basilar membrane Cochlea Sound waves Helicotrema Stapes vibrating in oval window Malleus Incus External auditory canal Tympanic membrane Secondary tympanic membrane vibrating in round window Auditory tube Vestibular membrane Middle ear Tectorial membrane Spiral organ (organ of Corti) 1 Scala vestibuli Cochlear duct (contains endolymph) Scala tympani Perilymph Basilar membrane Cochlea Sound waves Helicotrema Stapes vibrating in oval window Malleus Incus External auditory canal Tympanic membrane Secondary tympanic membrane vibrating in round window Auditory tube Vestibular membrane Middle ear Tectorial membrane Spiral organ (organ of Corti) 1 2 Scala vestibuli Cochlear duct (contains endolymph) Scala tympani Perilymph Basilar membrane Cochlea Sound waves Helicotrema Stapes vibrating in oval window Malleus Incus External auditory canal Tympanic membrane Secondary tympanic membrane vibrating in round window Auditory tube Vestibular membrane Middle ear Tectorial membrane Spiral organ (organ of Corti) 1 2 3 Scala vestibuli Cochlear duct (contains endolymph) Scala tympani Perilymph Basilar membrane Cochlea Sound waves Helicotrema Stapes vibrating in oval window Malleus Incus External auditory canal Tympanic membrane Secondary tympanic membrane vibrating in round window Auditory tube Vestibular membrane Middle ear Tectorial membrane Spiral organ (organ of Corti) 1 2 3 4 Scala vestibuli Cochlear duct (contains endolymph) Scala tympani Perilymph Basilar membrane Cochlea Sound waves Helicotrema Stapes vibrating in oval window Malleus Incus External auditory canal Tympanic membrane Secondary tympanic membrane vibrating in round window Auditory tube Vestibular membrane Middle ear Tectorial membrane Spiral organ (organ of Corti) 1 2 3 4 5 Scala vestibuli Cochlear duct (contains endolymph) Scala tympani Perilymph Basilar membrane Cochlea Sound waves Helicotrema Stapes vibrating in oval window Malleus Incus External auditory canal Tympanic membrane Secondary tympanic membrane vibrating in round window Auditory tube Vestibular membrane Middle ear Tectorial membrane Spiral organ (organ of Corti) 1 2 3 4 5 6 Scala vestibuli Cochlear duct (contains endolymph) Scala tympani Perilymph Basilar membrane Cochlea Sound waves Helicotrema Stapes vibrating in oval window Malleus Incus External auditory canal Tympanic membrane Secondary tympanic membrane vibrating in round window Auditory tube Vestibular membrane Middle ear Tectorial membrane Spiral organ (organ of Corti) 1 2 3 4 5 6 7 Scala vestibuli Cochlear duct (contains endolymph) Scala tympani Perilymph Basilar membrane Cochlea Sound waves Helicotrema Stapes vibrating in oval window Malleus Incus External auditory canal Tympanic membrane Secondary tympanic membrane vibrating in round window Auditory tube Vestibular membrane Middle ear Tectorial membrane Spiral organ (organ of Corti) 1 2 3 4 5 6 7 8 8 Scala vestibuli Cochlear duct (contains endolymph) Scala tympani Perilymph Basilar membrane Cochlea Sound waves Helicotrema Stapes vibrating in oval window Malleus Incus External auditory canal Tympanic membrane Secondary tympanic membrane vibrating in round window Auditory tube Vestibular membrane Middle ear Tectorial membrane Spiral organ (organ of Corti) 1 2 3 4 5 6 7 8 8 9

62. Physiology of Equilibrium Two types of equilibrium: Static- maintenance of the body position relative to the force of gravity. Dynamic- maintenance of body position (mainly head) in response to rotational acceleration and deceleration. Receptors for equilibrium are hair cells in the utricle, saccule and semicircular canals and are collectively called vestibular apparatus.

63. Otolithic Organs: Saccule and Utricle Macula- small thickened regions within the saccule and utricle. Sensory structures for static equilibrium. Also detect linear acceleration and deceleration. Contain hair cells and supporting cells. Stereocilia and kinocilium together called hair bundle. Otolithic membrane rests on the hair cells and contain otoliths . Macculae structure in utricle and saccule. Respond to: - Static equilibrium - Linear acceleration

64. Location and Structure of Receptors in the Maculae

65. Semicircular Ducts Semicircular canals are lined with a membranous semicircular duct. Ampullae is bulge at each end of semicircular canals. These receptors detect head rotation or angular rotation and dynamic equilibrium. Crista , a small elevation in the ampulla contain hair cells and supporting cells. Cupula , a mass of gelatinous material covering the crista . Semicircular ducts with ampullae and Crista Ampullaris.Respond to: -Detect angular rotation -Dynamic equilibrium

66. Location and Structure of the Semicircular Ducts

67. Cupula in Still Position versus Rotation

68. Olfaction: Sense of Smell Olfactory epithelium contains 10-100 million receptors. Chemoreceptor's located in superior nasal concha and septum in the olfactory epithelium (nasal mucosa). Olfactory epithelium is pseudo-stratified columnar Odors must be in liquid state to be perceived, thus they mix with mucus prior to be sensed by receptors. ~ 10,000 different odor molecules and ~ 1,000 different receptor types.

69. Olfactory receptor: A bipolar neuron with cilia called olfactory hairs. It is situated in cribriform plate of ethmoid bone. Function: Respond to chemical stimulation of an odorant molecule. Supporting cells: Provide support and nourishment. Basal cells: Replace olfactory receptors.

70. Physiology of Olfaction Can detect about 10,000 different odors. Odorant binds to the receptor of an olfactory hair→ G-protein activation→ activation of adenylate cyclase → production of cAMP → opening of Na+ channels→ inflow of Na+ →generator potential→ nerve impulse through olfactory nerves→ olfactory bulbs→ olfactory tract→ primary olfactory area of the cerebral cortex. Smell is perceived in the limbic system, hypothalamus and olfactory cortex (areas 28 & 34) of the piriform lobe.

71. Olfactory tract Olfactory bulb Nasal conchae Route of inhaled air Olfactory epithelium

72. Olfactory pathway

73. Gustation : Sense of Taste Taste and smell are involved with specific receptor cells called chemoreceptors . Olfactory and gustatory (taste) impulses travel not only to the cerebral cortex, but also to the limbic system. Respond to chemicals in an aqueous solution Food dissolved in saliva. Airborne chemicals dissolved in mucous membrane.

74. Tastes are senses by taste bud or papillae (taste receptors ) found on tongue. Taste is perceived by taste receptors than relayed to brain via: CN VII (Facial), IX ( Glossopharyngeal ) and X ( Vagus ) nerves. VII = Anterior 2/3 tongue IX = Posterior 1/3 tongue and pharynx X = Pharynx and Epiglottis Taste is highly dependent on smell for full perception of the odor, without smell we lose much of our taste.

75. Five Basic Taste Umami - S avory/Meaty Bitter- Alkaloid Sour- H + Salty- Metallic ions Sweet- Sugar

76. Anatomy of Taste Buds and Papillae Humans have 10,000 taste buds located on papillae of tongue, roof of mouth, cheek linings, walls of pharynx. Taste buds are found in the papillae. Taste bud- made of three types of epithelial cells: supporting cells, gustatory receptor cells and basal cells. About 50 gustatory cells per taste bud. Each one has a gustatory hair that projects through the taste pore. Chemoreceptors housed in taste buds.

77. Taste receptors have life span of about 10 days. Taste bud consists of: Taste pore: Opening through which fluids in mouth come into contact with surface of receptor cells Taste receptor cells: Modified epithelial cells with surface folds called microvilli . Plasma membrane of microvilli contain receptor sites that bind selectively with chemical molecules. ~50 receptor cells surrounded by supporting cells.

78. Basal cells develop into supporting cells then receptor cells. Gustatory hairs project through the taste pore. The tongue is covered with 4 types of projections called papillae. Sharp or Filiform papillae Fungifiorm papillae Foliate papillae Circumvallate papillae

79. The Tongue

80. 1) Filiform Papillae Filiform papillae cover the entire surface of the tongue. They are pointed, threadlike structures that contain tactile receptors but no taste buds. They increase friction between the tongue and the food, making it easier for the tongue to move food into the oral cavity.

81. Filiform Papillae

82. 2) Fungiform Papillae The Fungiform (mushroom like) papillae are mushroom shaped elevations scattered over the entire surface of the tongue. They contain about 5 taste buds each. 3)Foliate Papillae The foliate ( leaflike ) papillae are located in small trenches on the lateral margins of the tongue, but most of their taste buds degenerate in early childhood.

83. Fungiform or Foliate Papillae

84. 4) Vallate (Circumvallate) Papillae Large papillae with taste buds. About 12 very large circular Vallate papillae form an inverted V-shaped row at the back of the tongue. Each of these papillae contains approximately 100-300 taste buds.

85. Physiology of Taste In order to be tasted, a chemical: Must be dissolved in saliva Must contact gustatory hairs Binding of the food chemical: Depolarizes the taste cell membrane, releasing neurotransmitter Initiates a generator potential that elicits an action potential

86. Taste Transduction The stimulus energy of taste is converted into a nerve impulse by: Na + influx in salty tastes H + in sour tastes (by directly entering the cell, by opening cation channels, or by blockade of K + channels) Gustducin in sweet and bitter tastes

87. Gustatory Pathway Cranial Nerves VII and IX carry impulses from taste buds to the solitary nucleus of the medulla These impulses then travel to the thalamus, and from there fibers branch to the: Gustatory cortex (taste) Hypothalamus and limbic system (appreciation of taste)