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1 Chapter 16 The Special Senses. 2  Chemical senses  Taste (gustation)  Smell (olfaction)  Vision  The ear  Hearing  Equilibrium.

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Presentation on theme: "1 Chapter 16 The Special Senses. 2  Chemical senses  Taste (gustation)  Smell (olfaction)  Vision  The ear  Hearing  Equilibrium."— Presentation transcript:

1 1 Chapter 16 The Special Senses

2 2  Chemical senses  Taste (gustation)  Smell (olfaction)  Vision  The ear  Hearing  Equilibrium

3 3 Touch The sense of touch is part of the General somatic senses____ This chapter deals with the Special category of the two left sensory boxes

4 4 TASTE  Taste buds: mostly on tongue  Two types  Fungiform papillae (small, on entire surface of tongue)  Circumvallate papillae (inverted “V” near back of tongue)

5 5  Taste buds of epithelial cells each  Taste receptor cells (gustatory cells)  Microvilli through pore, bathed in saliva  Dissolved molecules bind & induce receptor cells to generate impulses in sensory nerve fibers

6 6  Types of taste  Sweet  Sour  Salty  Bitter  Umami “beef taste”- elicited by Glutamine  Gustatory (taste) pathway to brainstem & cerebral cortex via two cranial nerves:  VII (Facial n.) – anterior 2/3 of tongue  IX (Glossopharyngeal n.) – posterior 1/3 tongue and pharynx

7 7 Olfactory epithelium in roof of nasal cavity  Has millions of bipolar neurons = olfactory receptor cells Only neurons undergoing replacement throughout adult life Olfactory hair (cilia) bind odor molecules  Mucus captures & dissolves odor molecules Each receptor cell has an axon - are bundled into “filaments” of olfactory nerve  Penetrate cribriform plate of ethmoid bone & enter olfactory bulb Smell (olfaction)

8 8  Olfactory bulb is in forebrain  In bulb nerve axons branch and synapse with mitral cells (neurons in clusters of “glomeruli”)  Mitral cells send signals via olfactory tract Olfactory bulb__ _______Olfactory tract Filaments of Olfactory nerve (CN I) * *

9 9

10 10 Anosmia: absence of the sense of smell  Trauma  Colds or allergies producing excessive mucus  Polyps causing blockage  1/3 are from zinc deficiency  Head injury  Aging

11 11 The Eye and Vision  Vision is the dominant sense in humans  70% of sensory receptors in humans are in the eyes  40% of the cerebral cortex is involved in processing visual information  The eye (or eyeball) is the visual organ  Diameter 2.5 cm (1 inch)  Only anterior 1/6 visible  Lies in bony orbit  Surrounded by a protective cushion of fat

12 12 Accessory structures of the eye  Eyebrows  Eyelids or palpebrae  Upper & lower separated by palpebral fissure  Corners: medial & lateral canthi  Eyelashes

13 13  Eyelid tarsal plates give structure  Where orbicularis oculi muscles attach (close eyes)  Levator palpebrae superioris muscle  Lifts upper lid voluntarily (inserts on tarsal plate)

14 14  Tarsal glands – modified sebaceous (oil) glands in tarsal plates  Conjunctiva - transparent mucus membrane of stratified columnar epithelium  Palpebral conjunctiva  Bulbar conjunctiva  Covers white of eye but not the cornea (transparent tissue over the iris and pupil)

15 15 Lacrimal apparatus  Responsible for tears  The fluid has mucus, antibodies and lysozyme  Lacrimal gland in orbit superolateral to eye  Tears pass out through puncta into canaliculi into sac into nasolacrimal duct  Empty into nasal cavity (sniffles)

16 16 Extraocular (extrinsic) eye muscles: 6 in #  Four are rectus muscles (straight)  Lateral rectus, medial rectus, superior rectus, and inferior rectus.  Two are oblique: superior and inferior

17 When Extrinsic Eye Muscles Contract  Superior oblique- eyes look out and down  Superior rectus- eyes looks up  Lateral rectus- eyes look outward  Medial rectus- eyes look inward  Inferior rectus- eyes looks down  Inferior oblique- eyes look in and up

18 18

19 19 Extraocular (extrinsic) eye muscles Cranial nerve innervations:  Lateral rectus: VI (Abducens nerve)  Medial, superior, inferior rectus & inferior oblique: III (Oculomotor nerve.)  Superior oblique: IV (Trochlear n.)

20 20 3 Layers form the external wall of the eye 1.(outer) Fibrous: dense connective tissue  Sclera – white of the eye  Cornea  Clear because regular alignment  Role in light bending  Avascular but DOES have pain receptors  Regenerates 2.(middle) Vascular:  Choroid – blood rich, dark pigmented  Ciliary body – attaches lens  Iris (colored part: see next slide) 3.(inner) Sensory  Retina and optic nerve

21 21 1.(outer layer) Fibrous: dense connective tissue  Sclera – white of the eye  Cornea 2.(middle) Vascular: uvea  Choroid – blood rich, has dark pigmented that prevents light scattering  Ciliary body  Muscles – control lens shape  Processes – secrete aqueous humor  Zonule (attaches lens)  Iris 3.(inner layer) Sensory  Retina and optic nerve

22 22 Layers of external wall of eye continued 1.(outer) Fibrous: dense connective tissue  Sclera – white of the eye  Cornea 2.(middle) Vascular: uvea  Choroid – posterior, pigmented  Ciliary body  Iris  Opening is called PUPIL: lets in light  Acts like the diaphragm of a camera lens.  Regulates the amount of light that enters by contracting or dilating to see clearly.  Dark to dim light = dilation  Bright light and close vision = contraction 3.(inner) Sensory  Retina

23 23 Layers of external wall of eye continued 1.(outer) Fibrous: dense connective tissue  Sclera – white of the eye  Cornea 2.(middle) Vascular: uvea  Choroid – posterior, pigmented  Ciliary body  Iris 3.(inner) Sensory  Retina will cover after the chambers and lens

24 24 some pictures…

25 25 Chambers and fluids  Vitreous humor in posterior segment  Jellylike  Forms in embryo and lasts life-time  Anterior segment filled with aqueous humor – liquid, replaced continuously  Anterior chamber between cornea and iris  Posterior chamber between iris and lens  Glaucoma when problem with drainage resulting in increased intraocular pressure (see previous pics)

26 26 Lens: thick, transparent biconvex disc  Changes shape for precise focusing of light on retina  Onion-like avascular fibers, increase through life  Cataract if becomes clouded Note lens below, but in life it is clear Cataract below: the lens is milky and opaque, not the cornea

27 27 Cataract (opaque lens)

28 28 (to a lesser degree, not shown here, the cornea also) a.Resting eye set for distance vision: parallel light focused on retina b.Resting eye doesn’t see near objects because divergent rays are focused behind retina c.Lens accommodates (becomes rounder) so as to bend divergent rays more sharply, thereby allowing convergence on the retina Note: images are upside down and reversed from left to right, like a camera The eye is an optical device: predominantly the lens

29 Lens Accommodation  Light must be focused to a point on the retina for optimal vision  The eye is set for distance vision (over 20 ft away)  20/20 vision- at 20 feet, you see what a normal eye would see at 20 feet (20/100- at 20, normal person would see at 100)  The lens must change shape to focus for closer objects

30 30 Retina: develops as part of the brain Retina is 2 layers  Outer thin pigmented layer:  Melanocytes (prevent light scattering)  Inner thicker neural layer  Plays a direct role in vision  Three type of neurons: 1. (outer layer) Fibrous: dense connective tissue Sclera – white of the eye Cornea 2. (middle layer) Vascular: uvea Choroid – posterior, pigmented Ciliary body Iris 3. (inner layer) Sensory Retina and optic nerve Remember the 3 layers of the external eye? 1.Photoreceptors 2.Bipolor cells 3.Ganglion cells

31 31 Light passes through pupil in iris, through vitreous humor, through axons, ganglion cells and bipolar cells, to photoreceptors next to pigmented layer

32 32 Photoreceptor neurons signal bipolar cells, which signal ganglion cells to generate (or not) action potentials: axons run on internal surface to optic nerve which runs to brain *Know that axons from the retina form the optic nerve, CN II

33 33 Photoreceptors: 2 types  Rod cells  More sensitive to light - vision permitted in dim light but only gray and fuzzy  Only black and white and not sharp  Cone cells  High acuity in bright light  Color vision  3 sub-types: blue, red and green light cones *Know that rods are for B & W and cones are for color


35 Cone Sensitivity  There are three types of cones  Different cones are sensitive to different wavelengths - red- long - green- medium - blue- short  Color blindness is the result of lack of one or more cone type

36 COLORBLINDNESS - An inherited trait that is transferred on the sex chromosomes (23 rd pair)- sex-linked trait - Occurs more often in males - Can not be cured or corrected Comes from a lack of one or more types of color receptors. Most are green or red or both and that is due to a lack of red receptors. Another possibility is to have the color receptors missing entirely, which would result in black and white vision.

37 37 One of the Ishihara charts for color blindness Commonly X-linked recessive: 8% males and 0.4% females

38 38

39 39 If you want more detail, it’s fascinating…

40 40 Retina through ophthalmoscope  Macula: at posterior pole  Fovea: maximal visual acuity (most concentrated cones)  Optic disc: optic nerve exits  Vessels

41 Images Formed on the Retina If the image is focused at the spot where the optic disk is located, nothing will be seen. This is known as the blind spot. There are no photoreceptors there, as nerves and blood vessels pass through this point.

42 42 Visual pathways Green is area seen by both eyes, and is the area of stereoscopic vision At optic chiasm, medial fibers from each eye (which view lateral fields of vision) cross to opposite side of the brain. Optic tracts (of crossed and uncrossed fibers, sensing opposite side of visual field of both eyes) synapse with neurons in the thalamus. These axons form the optic radiation and terminate in the primary visual cortex in the occipital lobe. Left half of visual field perceived by right cerebral cortex, and vice versa.

43 Visual Pathway  Photoreceptors of the retina  Optic nerve  Optic nerve crosses at the optic chiasma  Optic tract  Thalamus  Visual Cortex of Occipital Lobe

44 44 Visual field defects print this out and follow from the fields to the visual cortex using 4 colors remember: fields are reversed and upside down 1. Optic nerve ipsilateral (same side) blind eye 2. Chiasmatic (pituitary tumors classically) lateral half of both eyes gone 3. Optic tract opposite half of visual field gone 4. & 5. Distal to geniculate ganglion of thalamus: homonymous superior field (4) or homonymous inferior field (5) defect Visual cortex Visual fields Location of lesion:

45 45  Double vision: diplopia (what the patient experiences)  Eyes do not look at the same point in the visual field  Misalignment: strabismus (what is observed when shine a light: not reflected in the same place on both eyes) – can be a cause of diplopia  Cross eyed  Gaze & movements not conjugate (together)  Medial or lateral, fixed or not  Many causes  Weakness or paralysis of extrinsic muscle of eye –Surgical correction necessary  Oculomotor nerve problem, other problems  Lazy eye: amblyopia  Cover/uncover test at 5 yo  If don’t patch good eye by 6, brain ignores lazy eye and visual pathway degenerates: eye functionally blind NOTE: some neurological development and connections have a window of time - need stimuli to develop, or ability lost

46 Geometrical illusions

47 Successive contrast : afterimages... what do you see? fixate the black dot in the center for 60 seconds... … and then look at a the black dot in the right panel !



50 50 Terminology, remember…  Optic – refers to the eye  Otic – refers to the ear  Getting eyedrops and ear drops mixed up is probably not a good idea

51 Anatomy of the Ear  The ear is divided into three areas  Outer (external) ear  Middle ear  Inner ear  (Add C. “INNER EAR” to notes)

52 The External Ear  Involved in hearing only  Structures of the external ear  Pinna (auricle)- collects sound  External auditory canal- channels sound inward

53 The External Auditory Canal  Narrow chamber in the temporal bone- through the external auditory meatus  Lined with skin  Ceruminous (wax) glands are present  Ends at the tympanic membrane (eardrum)

54 The Middle Ear or Tympanic Cavity  Air-filled cavity within the temporal bone  Only involved in the sense of hearing

55 The Middle Ear or Tympanic Cavity  Two tubes are associated with the inner ear  The opening from the auditory canal is covered by the tympanic membrane (eardrum)  The auditory tube connecting the middle ear with the throat (also know as the eustacian tube)  Allows for equalizing pressure during yawning or swallowing  This tube is otherwise collapsed

56 Bones of the Tympanic Cavity  Three bones span the cavity  Malleus (hammer)  Incus (anvil)  Stapes (stirrip)


58 Bones of the Tympanic Cavity  Vibrations from eardrum move the malleus  These bones transfer sound to the inner ear

59 Inner Ear or Bony Labyrinth  Also known as osseous labyrinth- twisted bony tubes  Includes sense organs for hearing and balance  Filled with perilymph

60 Inner Ear or Bony Labryinth  3 Subdivisions  Cochlea  Upper chamber is the scala vestibuli  Lower chamber is the scala tympani  Vestibule  Semicircular canals

61 Chochlea  Spiral organ of Corti  Receptors = hair cells on the basilar membrane Scala tympani Scala vestibuli

62  Gel-like tectorial membrane is capable of bending hair cells (endolymph in the membranous labyrinth of the cochlear duct flows over it and pushes on the membrane) Organ of Corti Scala tympani Scala vestibuli

63 Organs of Hearing  Organ of Corti  Cochlear nerve attached to hair cells transmits nerve impulses to auditory cortex on temporal lobe Scala tympani Scala vestibuli

64 Mechanisms of Hearing  Vibrations from sound waves move tectorial membrane (pass through the endolymph fluid filling the membranous labyrinth in the cochlear duct)  Hair cells are bent by the membrane

65 65

66 Mechanisms of Hearing  An action potential starts in the cochlear nerve  The signal is transmitted to the midbrain (for auditory reflexes and then directed to the auditory cortex of the temporal lobe)

67  Continued stimulation can lead to adaptation (over stimulation to the brain makes it stop interpreting the sounds) Mechanisms of Hearing

68 Organs of Equilibrium  Receptor cells are in two structures  Vestibule  Semicircular canals

69 Organs of Equilibrium  Equilibrium has two functional parts  Static equilibrium- in the vestibule  Dynamic equilibrium- in the semicircular canals

70 Static Equilibrium  Maculae – receptors in the vestibule  Report on the position of the head  Send information via the vestibular nerve

71 Static Equilibrium  Anatomy of the maculae  Hair cells are embedded in the otolithic membrane  Otoliths (tiny stones) float in a gel around the hair cells

72 Function of Maculae  Movements cause otoliths to bend the hair cells (gravity moves the “rocks” over and pulls the hairs)


74 Dynamic Equilibrium  Whole structure is the ampulla  Crista ampullaris – receptors in the semicircular canals  Tuft of hair cells  Cupula (gelatinous cap) covers the hair cells

75 Dynamic Equilibrium  Action of angular head movements  The cupula stimulates the hair cells  Movement of endolymph pushes the cupula over and pulls the hairs  An impulse is sent via the vestibular nerve to the cerebellum



78 Hearing loss- due to disease (ex. meningitus), damage, or age related Conduction deafness- prevention or blocking sounds from entering inner ear. Ex. ear wax, ruptured ear drum, middle ear inflammation (otis media), and otosclerosis (hardening of the ossicles of the ear) Sensoneural deafness- damage to the neural structures from any point from the cochlear hair cells to and including the auditory cortical cells Partial or complete deafness, or gradual loss over time

79 Tinnitus- ringing or clicking sound in the absence of auditory stimuli; 1 st symptom of cochlear nerve degeneration may result from inflammation of the inner or middle ear side effect from medicine such as aspirin Symptoms- vertigo, nausea, hearing loss Meniere's Syndrome- labyrinth disorder; effects both semicircular canals and cochlea

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