Special Senses

1. Special Senses Chapter 15

2. Anatomy of an Eyeball • Accessory structures • 3 tunics (layers) • Fibrous (cornea & sclera) • Vascular (choroid) • Sensory (retina) • Segments • Anterior divided into chambers • Posterior • Filled with humors (fluid) • Lens

3. Accessory Eye Structures • Eye muscles • Rectus as named; oblique opposite and lateral • Diplopia: muscle weakness/alcohol • Strabismus: uncontrolled rotation • Eyebrows • Eyelids • Blink to spread secretions • Eyelashes trigger blinking • Conjunctiva • Mucus prevents drying out • Conjunctivitis • Lacrimal apparatus • Tears clean, protect, and moisten • Excess secretions • Emotional tears unique to humans • Stuffy/runny nose when cry • Watery eyes with cold

4. Fibrous Tunic • Avascular CT • Sclera (white of the eye) • Protects and shapes • Muscle attachment • Continuous with dura mater • Cornea (transparent) • Outer stratified squamous, why? • Inner simple squamous maintain clarity • Innervated • Transplants not rejected between people

5. Vascular Tunic • Choroid • Vascularized to supply nutrients • Melanocytes to absorb light • Ciliary body • Smooth muscle ring  ciliary muscles control lens shape • Ciliary processes secrete aqueous humor • Suspensory ligaments hold lens in place • Iris • Colored portion of ciliary body • Brown pigment only (varies) • Less scatters light = blues/greens/grays (babies) • Encircles the pupil (2 smooth muscle layers)

6. Sensory Tunic • Pigmented layer (outer) • Prevents light scattering • Phagocytize damaged photoreceptors • Neural layer (inner) • Photoreceptors, bipolar cells, ganglion cell • Rods and cones • Blind spot (optic disc) filled • Macula lutea and fovea centralis • Rapid eye movement for rapid scene changes • Vascular supply from choroid and central vein/artery • Opthalmologist examines • Retinal detachment when layers separate • Vitreous humor seeps in • Photoreceptors lose nutrients = blindness

7. Humors • Anterior segment with aqueous humor • Similar to CSF • Continual development • Nutrients & O2 to lens, cornea, & retina • Blocked drainage = up pressure = glaucoma • Posterior segment with vitreous humor • Transmits light, support lens, & intraocular pressure • Unchanged from embryonic development

8. The Functioning Eye • Light enters the pupil, regulated by the iris • Passes through a convex lens • Avascular • Lens fibers added through life • Cataracts = clouding of lens due to loss of nutrients • Lens is shaped by the ciliary body to focus light on the retina (accommodation) • Refraction of light converges to a focal point • Real image forms upside down and reversed

9. Visual Pathway • Visual field • Overlap to provide depth perception = 3D vision • Ganglion cells • Optic nerve • Optic chiasm • Nasal and temporal visual field • Optic tract • Thalamus • LGN • Primary visual cortex • Conscious perception of images

10. Olfactory Receptors • Ciliated bipolar cells • Located in olfactory epithelium (pseudostratified ciliated) • Mucus captures and dissolves odorants • Pass through cribriform plates • Synapse in olfactory bulbs • Odorant detection • Humans can distinguish 10,000 odors • Some is pain (ammonia, chili, methanol) • Combinations of different odorant/receptor binding • Replaceable, but responsiveness declines with age

11. Olfactory Neural Pathway • Olfactory receptors synapse with mitral cells • Contained in glomeruli • Receptor type specific • Refines smell • Mitral cells signal via olfactory tracts • 2 pathways • Olfactory cortex • Hypothalamus, limbic system = emotional connection

12. Gustation • Taste buds detect molecules in solution • About 10,000 • Four familiar and 1 other found in papillae • Sweet: organic substances • Alcohol, sugar, amino acids • Sour : acids, H+ in solution • Salty: inorganic salts • Bitter: alkaloids • Aspirin, nicotine, caffeine • Umami: glutamate & aspartate • Meats, cheeses, and protein-rich foods (MSG) • Each receptor responsive to a particular type of substance • Often mixes • Many ‘tastes’ (80%) are really smell (head colds)

13. Papillae • Fungiform • Mushroom shaped • Tops of, all over tongue • Foliate • Fold in side walls • Circumvallate • Largest, fewest, back of tongue • Filiform • Hair like projections all over tongue • Do not have taste buds • Roughness

14. Gustatory Neural Pathway • Cranial nerves (VII and IX) carry sensations to medulla • Relay through the thalamus into primary gustatory cortex • Pathway initiates digestive process too

15. Regions of the Ear • Outer ear • Pinna, external auditory canal, and tympanic membrane (separates) • Middle ear • Pharyngotympanic tube equalizes pressure b/w middle ear and atmosphere (‘pop’) • Function of tympanic membrane • Ossicles (malleus, incus, & stapes) amplify signal • Inner ear • Membranous labyrinths w/i bony labryinth • Cochlea houses the hearing organ • Vestibule report on changes of head position • Saccule and utricle for gravity and acceleration • Semicircular canals for rotation of head

16. The Cochlea • Scalavestibuli • Perilymph: like CSF • Oval window • Scala Tympani • Perilymph • Round window • Scala media (Cochlear duct) • Endolymph: K+ rich intracellular fluid • Organ of Corti • Contains hair cells embedded in a basilar membrane • Vestibular membrane • Tectorial membrane bends cells as basilar membrane moves • Signal to auditory nerve

17. Frequency and Amplitude • Sounds detected as changes in AP’s • Pitch depends on frequency • High pitch = higher frequency • Basilar membrane responsive to certain frequencies • 20 to 20,000 Hz; 1500 – 4000 most sensitive • Loudness depends on amplitude • Louder sounds = higher amplitude • Vigorous vibrations in cochlea = more bending = more AP’s • Hair cells easily damaged due to prolonged exposure to certain frequencies

18. Physiology of Hearing • Pinna collects sound waves • Travel down auditory canal to tympanic membrane • Moves ossicles with vibrations • Stapes pushes on oval window, in and out • Creates fluid pressure waves in scalavestibuliperilymph • Pressure waves deform scala tympani to push round window in and out • Pressure changes move endolymph • Highest frequency at base (oval window), lowest at apex • Pressure changes in endolymph, from perilymph changes, moves the basilar membrane • Hair cells on Organ of Cortibend as they move against the tectorial membrane • Generates nerve impulses that leave via the cochlear nerve

19. Auditory Pathway • AP signals from cochlea to medulla • Cochlear nuclei • Some fibers cross to olives (collection of nuclei in the medulla) , all ascend into MGN(medial geniculate nucleus) in the thalamus • Pass through inferior colliculi(reflex area) • Interactions with superior colliculi to turn toward sound • Synapse in primary auditory cortex • Localization utilizes relative intensity and timing http://openlearn.open.ac.uk/file.php/3373/SD329_1_027i.jpg

20. Dynamic Equilibrium • Maintain body position after initiation of mov’t • Within semicircular canals • Rotation within 1 of 3 planes • Endolymph moves opposite direction of mov’t • Reverse to signal stop • Dizzy feeling

21. Static Equilibrium • Linear changes only • E.g. elevator changes or car acceleration/deceleration • Vestibule • Saccule: vertical, hairs horizontal • Utricle: horizontal, hairs vertical • Maculae overlaid by otoliths • Mov’t displaces in opposite direction

22. Motion Sickness • Results from conflict between eyes and equilibrium sensors in the inner ear • Feeling motion, but not seeing it (inside structure) • One system is hallucinating, implying toxins in system = vomiting • Dramamine inhibits input from equilibrium sensors • Astronauts learn to control