Special Senses

1. Special Senses Vision, Hearing, Equilibrium, Small, and Taste

5. Physiology of Equilibrium • Vestibular Apparatus • Vestibule & Semicircular canals • Responds to head movements • Works w/sight, muscles, and tendons to provide info used to control balance in cerebellum • Static Equilibrium • Receptors report on position of head w/respect to gravity when body is not moving • Determines which way is up/down • Keeps head upright • Dynamic Equilibrium • Receptors in semicircular canals respond to angular or rotary movements of the head • 3 canals (one in ea/plane) • Transmits up vestibular nerve to cerebellum • When moving at a constant rate receptors stop sending impulses

6. Physiology of Hearing • Sound waves transmit via vibrations tympanic membrane auditory ossicles oval window  fluids of cochlea • Fluid bends hair cells which act as hearing receptors in the Organ of Corti (inside the cochlear duct) • High pitched sounds disturb short hair fibers close to the oval window • Low pitch sounds affect the longer hair fibers further along the cochlea • Hairs transmit impulse via cochlear nerve to auditory cortex in temporal lobe • Sound reaches ea/ear at different times therefore we hear “in-stereo” and detect location of sound • When same sounds or tones keep reaching ears the auditory receptors stop responding to the sounds

7. Deafness • Deafness – hearing loss of any degree • 2 types: • Conduction • Something interferes w/conduction of sound vibrations (i.e. earwax build up) • Hearing aids helpful • Sensorineural • Damage to receptor cells in organ of Corti, the cochlear nerve, or auditory cortex (i.e. damage due to repeated loud sounds)

9. Smell • Sense of smell – provided by a pair of olfactory organs • In nasal cavity on either side of nasal septum • Olfactory receptor cells found in olfactory epithelium • Underlying olfactory glands secrete mucus (keep nostrils moist and debris free) • Tips of receptor cells have cilia that extend into mucus • The binding of an odorant changes permeability of receptor membrane producing an action potential • Signal sent to olfactory bulbs  olfactory cortex of cerebrum & hypothalamus • Smell is the only sensory info that doesn’t synapse with the thalamus first, explains profound emotional and behavioral responses certain smells produce • http://www.youtube.com/watch?v=H_WFlTtPZmE

10. Taste • Gustatory receptors are distributed on tongue, pharynx, and larynx • Taste buds – taste receptors, well protected (from mech. stress), found along sides of epithelial projections called papillae • Dissolved chums change the memb. potential of taste cells  action potential of sensory neurons medulla oblongata thalamus  primary sensory cortex • 4 taste sensations: Sweet, Salty, Sour, Bitter • No difference in structure of taste buds • Extremely sensitive to sour (acids) and bitter (bio toxins) than sweet and salty • 2 additional tastes recently discovered: • Umami – pleasant taste (beef & chxn broth, parmesan cheese) • Water – (in pharynx) – water balance and blood volume • Sensitivity to tastes increases as olfactory function increases • http://www.youtube.com/watch?v=FSHGucgnvLU&feature=related