1 Special Senses sensory receptors are within large, complex sensory organs in the head smell in olfactory organs taste in taste buds hearing and equilibrium in ears sight in eyes connected

2 Sense of Smell Olfactory Receptors chemoreceptors respond to chemicals dissolved in liquids Olfactory Organs contain olfactory receptors and supporting epithelial cells cover parts of nasal cavity, superior nasal conchae, and a portion of the nasal septum

3 Olfactory Receptors

4 Olfactory Nerve Pathways Once olfactory receptors are stimulated, nerve impulses travel through olfactory nerves olfactory bulbs olfactory tracts limbic system (for emotions-mom’s apple pie….) and olfactory cortex (for interpretation)

5 Olfactory Stimulation Olfactory Code hypothesis odor that is stimulated by a distinct set of receptor cells and its associated receptor proteins (the variety stimulated determines the smell) olfactory organs located high in the nasal cavity above the usual pathway of inhaled air olfactory receptors undergo sensory adaptation rapidly sense of smell drops by 50% within a second after stimulation

6 Sense of Taste Taste Buds organs of taste located on papillae of tongue, roof of mouth, linings of cheeks and walls of pharynx Taste Receptors chemoreceptors taste cells – modified epithelial cells that function as receptors taste hairs –microvilli that protrude from taste cells; sensitive parts of taste cells

7 Taste Receptors

8 Taste Sensations Four Primary Taste Sensations sweet – stimulated by carbohydrates sour – stimulated by acids salty – stimulated by salts bitter – stimulated by many organic compounds Spicy foods activate pain receptors (and sour)

9 Taste Nerve Pathways Sensory impulses from taste receptors travel along cranial nerves to medulla oblongata to thalamus to gustatory cortex (for interpretation)

10 Hearing Ear – organ of hearing Three Sections External Middle Inner

11 External Ear auricle collects sounds waves external auditory meatus lined with ceruminous glands carries sound to tympanic membrane terminates with tympanic membrane tympanic membrane vibrates in response to sound waves

12 Middle Ear tympanic cavity air-filled space in temporal bone auditory ossicles vibrate in response to tympanic membrane malleus, incus, and stapes oval window opening in wall of tympanic cavity stapes vibrates against it to move fluids in inner ear

13 Auditory Tube eustachian tube connects middle ear to throat helps maintain equal pressure on both sides of tympanic membrane (think altitude-pop) usually closed by valve-like flaps in throat

14 Inner Ear complex system of labyrinths osseous labyrinth bony canal in temporal bone filled with perilymph membranous labyrinth tube within osseous labyrinth filled with endolymph

15 Inner Ear Three Parts of Labyrinths cochlea functions in hearing semicircular canals functions in equilibrium vestibule functions in equilibrium

16 Cochlea Scala vestibuli upper compartment leads from oval window to apex of spiral part of bony labyrinth Scala tympani lower compartment extends from apex of the cochlea to round window part of bony labyrinth

17 Cochlea Cochlear duct portion of membranous labyrinth in cochlea Vestibular membrane separates cochlear duct from scala vestibuli Basilar membrane separates cochlear duct from scala tympani

18 Organ of Corti group of hearing receptor cells (hair cells) on upper surface of basilar membrane different frequencies of vibration move different parts of basilar membrane particular sound frequencies cause hairs of receptor cells to bend Ca influx causes NT release onto sensory nerve AP generated-to medulla-to thalamus-to auditory cortex (temporal) Some crossover occurs

19 Organ of Corti

20 Auditory Nerve Pathways

21 Summary of the Generation of Sensory Impulses from the Ear

22 Equilibrium Static Equilibrium vestibule sense position of head when body is not moving Dynamic Equilibrium semicircular canals sense rotation and movement of head and body

23 Vestibule Utricle communicates with saccule and membranous portion of semicircular canals Saccule communicates with cochlear duct Mucula hair cells of utricle and saccule

24 Macula responds to changes in head position bending of hairs results in generation of nerve impulse

25 Semicircular Canals three canals at right angles ampulla swelling of membranous labyrinth that communicates with the vestibule crista ampullaris sensory organ of ampulla hair cells and supporting cells rapid turns of head or body stimulate hair cells

26 Crista Ampullaris