Senses Other Than Vision Hearing The Kinesthetic Senses Touch The Chemical Senses Hearing (Audition) Sound begins as pressure waves in a medium (usually air). The frequency of the pressure waves corresponds to the pitchof the sound. The amplitude of the pressure waves corresponds to the intensity of the sound. The particular mixture corresponds to the timbre of the sound. Transmission of Vibrations Basilar membrane Pressure waves in the air vibrate the tympanic membrane (ear drum), Which sets into motion the three bones or ossicles of the middle ear, Which vibrates the oval window of the cochlea. Which drives the fluid within the cochlea, driving the basilar membrane. 1
The Cochlea and Pitch Perception The Cochlea resembles a snail shell. The shell gets wider as one moves along the coils toward the inner end. Because of this shape, standing pressure waves are created whose peaks depend on the frequency of the vibrations high frequency near the oval window, low frequency near the tip. The perceived pitch of the sound depends on where along the basilar membrane the vibrations are greatest. The Cochlear Implant The bending of the basilar membrane stimulates hair cells, which in turn affect the rate of firing of the associated auditory neurons. If the hair cells are destroyed, deafness occurs. Surgeons can correct this problem by inserting an electrode array into the cochlea. An electronic device stimulates different electrodes depending on the sound frequencies entering a microphone, artificially stimulating the appropriate neurons. The Kinesthetic Senses The kinesthetic senses include: The vestibular senses (via the semi-circular canals) A sense of down Senses of rotation (angular acceleration): pitch, yaw, and turn The proprioceptive senses Joint angle Muscle length and tension These allow us to know where are various limbs are and how the body is moving through space. 2
The Chemical Senses The chemical senses are so called because they are based on the chemical properties of the materials being sensed. Two senses fall into this category: Smell Taste Smell Breathing in conveys odorant molecules to the olfactory bulb. There, olfactory receptors recognize odorant molecules. Activated receptors affect the firing of olfactory neurons. The brain interprets combinations of neural activity as particular smells. Receptors for Smell At one time there was a theory around, based on analysis of the way people categorize various smells, that there might be perhaps seven smell receptors. These were given names like floral, pungent, and putrid. However, recent evidence from DNA studies suggests that there may be as many as 100 to 1000 different smell receptor protiens. 3
Organs of Taste Taste receptors are located in the taste buds of the tongue. There are four kinds of taste receptors known and now possibly a fifth. The Primary Tastes Sweet Sugars Sour Weak Acids Salty Salts Bitter Alkaloids And maybe one more... Umami or savory Certain amino acids Taste = Taste + Smell What we often call the taste of food is actually the combination of its taste and smell. You can check this for yourself: While holding your nose, try munching on: A raw potato A raw onion The two have a similar crunchy texture and bland taste. With your nose held, you will have trouble telling them apart! 4
Touch Touch actually includes a number of specific sensory qualities, including: Light pressure Deep pressure Hot Cold There are specialized receptors for each of these qualities. Aristotle s Five Senses The ancient Greek philosopher Aristotle held that there are five senses: Sight, hearing, touch, taste, and smell. We are still taught in primary school that there are only five senses. But old Aristotle missed some important ones, including the kinesthetic senses and various forms of pain. And if we classified each type of sensory receptor as providing a different sense, we would have to say that there are hundreds, perhaps thousands of senses. 5