Organs of Hearing Organ of Corti - Located within the cochlea Receptors = hair cells on the basilar membrane Gel-like tectorial membrane is capable of bending hair cells Cochlear nerve is attached to hair cells transmits nerve impulses to auditory cortex on temporal lobe

Organs of Hearing Figure 8.15

Mechanisms of Hearing Figure 8.16a–b

The Process of Hearing 1) Vibrations from sound waves move through a medium to the Pinna and into the auditory canal of the outer ear. 2) The vibrations reach the middle ear and vibrate the eardrum. The malleus bone which is attached to the eardrum is vibrated and it is sent to the incus and to the stapes bones. 3) The vibrations are amplified as they travel through the three bones 4) The stapes is attached to the cochlea at the oval window of the inner ear and it vibrates the fluid inside called endolymph.

The Process of Hearing 5) In the Cochlea the Organ of Corti has hair (receptor) cells touching the tectorial membrane 6) The hair cells are bent by the membrane and an action potential starts in the cochlear nerve sending signals to the auditory cortex. 7) Continued stimulation can lead to adaptation Ex: like tuning out the furnace in the room http://www.youtube.com/watch?v=pCCcFDoyBxM http://www.youtube.com/watch?v=xMUl5CCoW6Y

Homeostatic Imbalances Conduction Deafness – some kind of interference with the conduction of sound vibrations to the fluids of the inner ear (could be as simple as ear wax) Otosclerosis – fusion of ossicle bones (hammer, anvil, stirrup) Hearing aides – can help overcome conduction deafness; conducts sounds through the skull Sensorineural Deafness – occurs from damage to the receptor cells in the Organ of Corti, cochlear nerve, or auditory cortex in the brain (nerve structures) Often caused by exposure to loud noises (MUSIC, guns, jackhammer, etc.) http://www.youtube.com/watch?v=dMU-VckZY0A http://www.youtube.com/watch?v=gnKwqeAwspI&NR=1 https://www.youtube.com/watch?v=uJIoVXJ4RJU

Organs of Equilibrium Receptor cells are in two structures Vestibule 2) Semicircular canals https://www.youtube.com/watch?v=S5lmQEBQ6mE Figure 8.14a–b

Organs of Equilibrium Equilibrium has two functional parts Static equilibrium (Vestibule) = body NOT moving Dynamic equilibrium (Semi-circular canals) = body moving Figure 8.14a–b

Static Equilibrium and Functon of Maculae Maculae – receptors in the vestibule that report on the position of the head Sends info to the cerebellum via the vestibular nerve to help keep our head erect. Anatomy of the maculae Hair cells are embedded in the otolithic membrane which is a jelly-like material containing Otoliths Otoliths (tiny calcium stones) float in a gel around the hair cells Movements due to changes in gravity cause otoliths to bend the hair cells … kind of messing with yourself when you headbang!

Function of Maculae Figure 8.13a–b

Dynamic Equilibrium and function of Crista Ampullaris Crista ampullaris – receptors in the semicircular canals with Tufts of hair cells Cupula (gelatinous cap) covers the hair cells Figure 8.14c

Dynamic Equilibrium and function of Crista Ampullaris Action of angular head movements (Boat, roller coaster, merry-go-round) 1) The cupula stimulates the hair cells 2) An action potential is sent via the vestibular nerve to the cerebellum 3) Static and dynamic equilibrium have different receptors but they work together with many other receptors to keep your balance. http://www.youtube.com/watch?v=CpLa5FgD52w Figure 8.14c

Chemical Senses – Taste and Smell Both senses use chemoreceptors and are stimulated by chemicals in solution Both senses complement each other and respond to many of the same stimuli

Olfaction – The Sense of Smell Olfactory receptors - Neurons with long cilia in the roof of the nasal cavity Chemicals must be dissolved in mucus for detection Impulses are transmitted via the olfactory nerve Interpretation of smells is made in the cortex Olfactory pathways are tied to the limbic system (emotions). Certain smells bring back memories.

Olfactory Epithelium Figure 8.17

The Sense of Taste Taste buds house the receptor organs for taste Most are on the tongue and some are on the soft palate and Cheeks Figure 8.18a–b

The Tongue and Taste The tongue is covered with projections called papillae Filiform papillae – sharp with no taste buds Fungifiorm papillae – rounded with taste buds Circumvallate papillae – large papillae with taste buds Taste buds are found on the sides of papillae

Structure of Taste Buds Gustatory cells – taste receptors with gustatory hairs (long microvilli) Hairs are stimulated by chemicals dissolved in saliva

Structure of Taste Buds Impulses are carried to the gustatory complex by several cranial nerves because taste buds are found in different areas 1) Facial nerve 2) Glossopharyngeal nerve 3) Vagus nerve

Anatomy of Taste Buds Figure 8.18

Taste Sensations Sweet receptors : Sugars, Saccharine, Some amino acids Sour receptors : Acids Bitter receptors: Alkaloids (bases) Salty receptors: Metal ions Umami: amino acid glutamate; “beef taste” of steak located in the pharynx

Developmental Aspects of the Special Senses Formed early in embryonic development Eyes are outgrowths of the brain All special senses are functional at birth