Lecture 16

1. Lecture 16 Senses

2. What do we respond to? • Stimulus: • Pain • Mechanical • Temperature • Chemicals • Electromagnetic • Awareness of stimulus = _______________ • Where are sensory receptors located? • Interoceptors: • Exteroceptors:

3. An interoceptor which monitors changes in blood pressure • What kind of stimulus do these respond to? • A chemoreceptor monitoring changes in hydrogen ion concentration within the body

4. Mechanoreceptors • Respond to distortion of cell membrane • Baroreceptors – changes in internal pressure • Proprioceptors – position of limbs, extension of muscle • Hearing and equilibrium – inner ear • Tactile – touch, etc. integument

5. Receptors in the Integument • Nonencapsulated • Naked nerve endings • Merkel Discs • Encapsulated • Meissner’s Corpuscles • Tactile • Dermal papillae – hairless skin • Pacinian corpuscles – lamellated corpuscles • Dermis/hypodermis – deep pressure • Joint capsules • Ruffini endings – flattened capsule • Deep dermis, joints • Continuous deep pressure

7. Pain Sensations • Nociceptors = pain receptors • Tissue injury compounds • Free nerve endings • Stimulus: • excessive distension, muscle spasm, & inadequate blood flow • Little adaptation occurs • Acute (fast) vs. chronic (slow)

8. Exteroceptors - Chemoreception • Taste - Gustatory • Tongue, mouth pharynx and larynx • 4-5 chemical categories • Olfactory • Nasal passages • Response to many different compounds

9. Smell - Olfactory • Olfactory cells - epithelium in the upper nasal cavity • bind to specific odor molecules • cerebral cortex processes input • Limbic associations occur (‘It smells like…’)

10. Numbers- 5 million olfactory receptors. Size and Shape- similar to a postage stamp. Location- roof of the nasal cavity. Cell Division- replaced every 60 days. Sensitivity- 1,000 different types of receptors

11. Odorants bind to receptors Depolarization • Olfactory glands  mucus • Rapid adaptation: • 50% 1 min • Highly sensitive

12. Gustatory – Taste: • Dissolved substances • 10,000 taste buds found on tongue, soft palate & larynx • sides of circumvallate & fungiform papillae • 3 cell types: supporting, receptor & basal cells • Four + responses: • Sweet – okay • Salty - okay • Sour ?? • Bitter ?! – poison? • umami • water

14. Gustatory Pathway • First-order gustatory fibers found in cranial nerves • VII (facial) serves anterior 2/3 of tongue • IX (glossopharyngeal) serves posterior 1/3 of tongue • X (vagus) serves palate & epiglottis • Signals travel to thalamus or limbic system & hypothalamus • Taste fibers extend from the thalamus to the primary gustatory area on parietal lobe of the cerebral cortex • providing conscious perception of taste

15. Ear -Mechanoreceptors • Sound - hearing • Orientation and motion in space – equilibrium • Gravitational equlib • rotational equilibrium • VIII cranial nerve • ? name

16. Ear: 3 regions • External ear • Auricle: • External acoustic meatus  ear drum • Ceruminous glands  cerumen • Middle ear • Tympanic membrane • Auditory ossicles • Auditory tube • Inner ear • Bony labyrinth encloses membranous labyrinth

18. Middle ear: • Ossicles – malleus, incus, stapes •  oval window of inner ear • Auditory tube

19. Inner Ear: • Bony labrynth w/i petrous portion of temporal bone • Membranous labrynth – contain endolymph • Vestibular complex • Utricle + saccule: static + gravitational equilib. • Hair cells located at maculae – embedded in gelatinous mass containing CaCO3 crystals = otoliths • Semicircular canals: rotational equilibrium • Hair cells in ampullae – cilia embedded in cupula

21. Cristae – within ampulla • When head moves, the attached semicircular ducts and hair cells move with it • endolymph fluid does not • Cilia of hair cells enclosed cupula bend

22. Close-up of Macula • Otolithic membrane slides  Movement of stereocilia + kinocilium alters release of neurotransmitter onto the vestibular branches of the vestibulocochler nerve

23. Cochlea: 3 fluid filled channels • scala vestibuli, scala tympani and cochlear duct • Sound tranduced by Organ of Corti

24. Section thru one turn of Cochlea • Partitions that separate the channels are Y shaped • bony shelf of central modiolus • vestibular membrane above & basilar membrane below form the central fluid filled chamber (cochlear duct) • Fluid vibrations affect hair cells in cochlear duct

25. Motion in vestibular/tympanic duct  basilar membrane moved  distortion of sterocilia against tectoral membrane  neural impulse • Pitch: where in cochlea • Amplitude: force of motion

26. Eye – Eyeball + Accessory Structures • Accessory Structures • Eyelids = palpebrae • Tarsal glands secrete sebum • Extrinsic muscles (6 of them) • Lacrimal glands • Conjunctiva – epithelial layers covering anterior edges of eye – eyelid to eyeball

28. Eye muscles • Superior and Inferior rectus • Lateral and medial rectus • Superior and inferior oblique • Control: CN III, IV, VI

29. Conjunctiva Palpebral conjunctiva Bulbar conjunctiva Stratified squamous epith Mucous membrane Conjunctiva palpebrae

30. Eyeball: Three Tunics • Fibrous Tunic (outer layer) • Sclera and cornea • Vascular Tunic (middle layer) • Iris and choroid • Nervous Tunic (inner layer) • Retina Cavities • Anterior cavity – aqueous humor • Two cavities • Drained via Canal of Schlemm • lens • Posterior cavity (vitreous chamber) – vitreous humor

32. Radial muscles – sympathetic – dilate pupil • Circular muscles: parasympathetic – constrict pupil

33. Avascular, crystalline protein • Suspensory ligaments attach lens to ciliary process • Ciliary muscle controls tension on ligaments & lens

34. Cataracts • Leading cause worldwide of blindness. • A lens becomes cloudy or opaque. • Caused by • Natural aging. 50 or over. • Drug reactions. • Injury. • Diabetes. • UVB damage. • At risk • Smokers (2X). • Guys named “Phil” or “Rupert”. • Treatment- surgery, removal and replacement of the lens.

36. Nervous Tunic -- Retina • Posterior 3/4 of eyeball • Optic disc • optic nerve exiting back of eyeball = blindspot • Central retina BV • fan out to supply nourishment to retina • visible for inspection • hypertension & diabetes • Detached retina • trauma (boxing) • fluid between layers • distortion or blindness View with Ophthalmoscope

37. Rods & Cones--Photoreceptors • Rods----rod shaped – 120 million • shades of gray in dim light • discriminates shapes & movements • distributed along periphery • Cones----cone shaped – 6 million • sharp, color vision • Concentrated at fovea of macula lutea

38. Major Processes of Image Formation • Refraction of light • by cornea & lens • light rays must fall upon the retina • Accommodation of the lens • changing shape of lens so that light is focused • Constriction of the pupil • less light enters the eye

39. Visual fields • Left occipital lobe receives visual images from right side of an object through impulses from nasal 1/2 of the right eye and temporal 1/2 of the left eye • Left occipital lobe sees right 1/2 of the world • Fibers from nasal 1/2 of each retina cross in optic chiasm

40. Accommodation & the Lens • Convex lens refract light rays towards each other • Lens of eye is convex on both surfaces • View a distant object • lens is nearly flat by pulling of suspensory ligaments • View a close object • ciliary muscle is contracted & decreases the pull of the suspensory ligaments on the lens • elastic lens thickens as the tension is removed from it • increase in curvature of lens is called accommodation

41. Abnormalities of the Eye Distance Vision Nearsighted Close objects are seen clearly. Long eyeball causes image to focus in front of the retina. Farsighted Distant objects are seen clearly. Short eyeball causes image to focus behind retina. Astigmatism Image is blurred. Irregular curvature of the cornea or lens causes light rays to focus unevenly.

43. Abnormalities of the Eye Color blindness Colors cannot be distinguished. 75% of people have poor green perception. 8-10% of males, <1% females. X-Linked. A lack of or reduced number of one of the cone types.

44. Color Blindness Test – do you see pink elephants?

47. TheEnd.