Biology 211 Anatomy & Physiology I

1. Biology 211Anatomy & Physiology I The Special Senses

2. Special Senses • Receptors all located in the head 2. Highly specialized cells form those receptors 3. These specialized receptor cells are located in highly specialized sensory organs 4. All special senses reach the brain through cranial nerves

3. Special Senses Specialized Receptor Cells Specialized Organ. . . . . TASTE: SMELL: VISION: HEARING: EQUILIBRIUM: Gustatory Cells Taste Buds Olfactory Cells Olfactory Epithelium Rods & Cones Eye (Retina) Hair Cells Cochlea Hair Cells Vestibular Apparatus

4. Let’s start with taste Specialized Receptor Cells Specialized Organ. . . Gustatory Cells Taste Buds

5. Most, but not all, taste buds are located on projections from the surface of the tongue called papillae Some taste buds are also located on the palate and the oropharynx,as far down as the epiglottis

6. Each taste bud contains three types of cells: Gustatory cells (50-100) Supporting cells Basal cells Each taste bud also has a small hole, or taste pore, on its free surface (facing the inside of the mouth).

7. Each gustatory cell has long microvillus, called a gustatory hair, which extends out of the taste pore into the saliva of the mouth. This gustatory hair contains receptors on its plasma membrane which can detect specific chemicals in the saliva. At the other end, each gustatory cell is surrounded by dendrites of sensory neurons which form part of a cranial nerve

8. Gustatory cells within taste buds can detect thousands of different types of molecules, but these are grouped into five general categories: • Sweet tastes: sugars (glucose, fructose, lactose, sucrose) saccharin, aspartame, sucralose, xylitol, etc. • Salty tastes: sodium, potassium, lithium, many others c) Sour tastes: citric acids, carbonic acid, hydrochloric acid, malic acid, tartaric acid, many others • Bitter tastes: quinine, fatty acids, many others • Umami taste: glutamate

9. Substances must be dissolved in saliva or other liquid before they can stimulate the gustatory cells. Each gustatory cell can respond to only one substance (sodium, glucose, etc.) BUT each taste bud contains many different types of gustatory cells. We used to think that taste buds on certain regions of the tongue were specialized for particular tastes, but we now know that taste buds with gustatory cells for different types of tastes are located in all regions of the tongue.

10. Each gustatory cell has a separate threshold: concentrations below this do not stimulate the receptors. In general: Sweet & salty substances have high thresholds Sour and umami substances have moderate thresholds Bitter substances have low thresholds

11. Taste signals from the anterior part of the tongue travel in the facial nerve. Taste signals from the posterior part of the tongue travel in the glossopharyngeal nerve. Taste signals from the palate and pharynx travel in the vagus nerve. Taste signals in all three nerves reach a nucleus in the medulla oblongata, then get sent to the thalamus From the thalamus, these signals get relayed to the “gustatory region” on the parietal and frontal lobes of the cerebral cortex.

12. These afferent neurons carry information for conscious perception of tastes. They also form afferent limbs of reflexes whose efferent limbs stimulate: saliva production, secretion of enzymes by stomach, liver, pancreas if necessary, gagging & vomiting

13. Special Senses Specialized Receptor Cells Specialized Organ . TASTE: SMELL: VISION: HEARING: EQUILIBRIUM: Gustatory Cells Taste Buds Olfactory Cells Olfactory Epithelium Rods & Cones Eye (Retina) Hair Cells Cochlea Hair Cells Vestibular Apparatus

14. Olfactory receptor cells are part of the olfactory epithelium (mucosa) located high in the nasal cavity, just inferior to the cribriform plate of the ethmoid bone.

15. Each olfactory cell has long microvillus, called an olfactory hair, which extends into a layer of mucous on its free surface This olfactory hair contains receptors on its plasma membrane which can detect specific chemicals in the mucous.

16. The axons of these olfactory cells (neurons) form the olfactory nerve which passes through the cribriform plate to synapse with neurons in the olfactory bulb of the brain.

17. Substances must dissolve from the air into the mucous before they can stimulate the olfactory cells. Each olfactory cell appears to be able to respond to many different substances. Each olfactory cell has a separate threshold, but these are generally very low: just a few molecules of a substance may stimulate the olfactory cells.

18. Olfactory Pathways: Axons of olfactory receptor cells pass through the cribriform plate of the ethmoid bone as the olfactory nerve, then synapse with afferent neurons in the olfactory bulb which lies just superior to it.

19. Olfactory Pathways: Axons of olfactory receptor cells pass through the cribriform plate of the ethmoid bone as the olfactory nerve, then synapse with afferent neurons in the olfactory bulb which lies just superior to it. Axons of these afferent neurons pass through the olfactory tract to: • The thalamus and the olfactory cortex on the medial surface of the temporal lobe. This provides conscious perception and interpretation of smells

20. Olfactory Pathways: Axons of olfactory receptor cells pass through the cribriform plate of the ethmoid bone as the olfactory nerve, then synapse with afferent neurons in the olfactory bulb which lies just superior to it. Axons of these afferent neurons pass through the olfactory tract to: • The hypothalamus and • amygdala (limbic system). • This provides reflexes • (salivation, avoidance, etc.) and "associative responses" (activation of autonomic pathways, sexual responses, emotional responses, etc.)

21. Special Senses Specialized Receptor Cells Specialized Organ..... TASTE: SMELL: VISION: HEARING: EQUILIBRIUM: Gustatory Cells Taste Buds Olfactory Cells Olfactory Epithelium Rods & Cones Eye (Retina) Hair Cells Cochlea Hair Cells Vestibular Apparatus

22. Anterior view of the eye Sclera Medial angle (canthus) Lateral angle (canthus) Iris Pupil

24. The eyeball has three layers or "tunics: Fibrous Tunic: Sclera and cornea Strong connective tissue Protects the eye Holds shape of eye Insertion of extraoccular muscles Vascular Tunic: Choroid, ciliary body, iris Contains blood vessels Pigmented Smooth muscle cells in ciliary body &iris Sensory Tunic: Retina Contains rod and cone cells and Other neurons to transmit visual information to brain

25. Layers ("tunics") of the eyeball Fibrous Layer Vascular Layer Sensory Layer Ciliary Body Sclera Iris Choroid Retina Cornea

26. Internal Structure of the Eye

27. Vitreous Humor Lens Aqueous Humor Suspensory Ligaments ("Zonules") Ciliary Body

28. Focus: Majority of light refraction (bending) occurs in cornea. Not adjustable "Fine tuning" of light refraction occurs in lens: Thicker lens = more refraction Thinner lens = less refraction

30. Rods:~ 6 million Cones:~ 20 million Detect black , white, gray Highly sensitive in low-light conditions Low resolution Detect motion Detect color Less sensitive in low light conditions High resolution

32. The cornea and lens focus light onto the macula lutea and fovea centralis, which has only cones. This provides high resolution and color vision but requires brighter light. Other regions of the retina have mostly rods. This provides black/white/gray vision in dimmer light, and detects movement.

33. Optic Chiasm Optic Nerve Midbrain (superior colliculus) Optic Tract Optic Radiations Thalamus (lateral geniculate nucleus)

34. Optic nerve Optic chiasm Optic tract

35. Next: Hearing Specialized Receptor Cells Specialized Organ . HEARING Hair Cells Cochlea Located in inner ear. Outer ear and middle ear transmit and regulate the volume of sound reaching the inner ear.

36. Auricle or Pinna Inner Ear Outer Ear Middle Ear

37. The inner ear contains two complex fluid-filled structures, the bony labyrinth and the membranous labyrinth, which are embedded in the temporal bone. The outer ear channels air vibrations (sound) to the tympanic membrane (eardrum). The middle ear is an air-filled chamber containing three ossicles, the malleus, the incus, & the stapes, which transmit vibrations to the inner ear.

38. The tympanic membrane is attached to the malleus, which is attached to the incus, which is attached to the stapes, which is attached to the oval window of the inner ear. The inner ear is fluid-filled.

39. Therefore: Vibrations of air (sound) in the outer ear vibrate the tympanic membrane Which makes the ossicles vibrate Which makes the oval window vibrate Which makes the fluid of the inner ear vibrate This is how the vibrations get transmitted from the air of the outer ear to the receptor cells of the cochlea in the inner ear

40. The inner ear actually consists of two sets of tubes, one inside the other. The outer tube, or bony labyrinth, is filled with a fluid called perilymph, while the inner tube, the membranous labyrinth, is filled with fluid called endolymph.

41. At one end of inner ear, these two tubes (one inside the other) coil about 2 & 2/3 times to form the cochlea. Vibrations of the oval window make the perilymph vibrate. This must be transmitted to the endolymph within the cochlea before the hair cells can detect it.

42. Scala vestibuli (perilymph) Cochlear duct (endolymph) Scala tympani (perilymph)

43. Structure of cochlea if it could be uncoiled

44. Vibration of oval window causes vibration of perilymph of scala vestibuli and scala tympani, which causes vibration of endolymph in cochlear duct

45. Vibration of the endolymph in the cochlear duct causes bending of hair cells in the spiral organ of Corti. When these hair cells bend, they send electrical signals through the vestibulocochlear nerve to the brain Vestibulocochlear nerve Hair cells

46. Hearing involves two aspects of bending hair cells: Which hair cells bend determines the pitch of the sound How farhair cells bend determines volume of the sound

47. The membranous labyrinth of the inner ear also houses the specialized receptor cells for equilibrium - both position of the head ("static equilibrium") and movement of the head ("dynamic equilibrium").

48. Special Senses Specialized Receptor Cells Specialized Organ..... TASTE: SMELL: VISION: HEARING: EQUILIBRIUM: Gustatory Cells Taste Buds Olfactory Cells Olfactory Epithelium Rods & Cones Eye (Retina) Hair Cells Cochlea Hair Cells Vestibular Apparatus

49. The parts of the membranous labyrinth responsible for equilibrium are the saccule, the utricle, and three semicircular canals which lie at right angles to each other. Semicircular Canals Utricle Saccule

50. The saccule and the utricle are responsible for detecting the position of the head ("static equilibrium"). Each of them contain a region of hair cells called a macula