Taste/Gustation • Transduced on taste buds • Four basic tastes • Sweet • Salty • Sour • Bitter. • Spice is not a taste… It is PAIN!! • Different people have different tastes based on genetics, culture, learning
Taste: Savoury Sensations • Papillae • Knoblike elevations on the tongue, containing the taste buds (Singular: papilla). • Taste buds • Nests of taste-receptor cells.
Taste Buds • Photograph of tongue surface (top), magnified 75 times. • 10,000 taste buds line the tongue and mouth. • Taste receptors are down inside the “bud” • Children have more taste buds than adults.
Taste and Smell Work Together Much of the taste of an onion is odor, not flavor. If you did not have the sense of smell, an onion and an apple would taste the same
Smell Like taste, smell is a chemical sense. Odorants enter the nasal cavity to stimulate 5 million receptors on the olfactory epitheleum to sense smell. Unlike taste, there are many different forms of smell.
Smell: The Sense of Scents • Airborne chemical molecules enter the nose and circulate through the nasal cavity. • Vapors can also enter through the mouth and pass into the nasal cavity. • Receptors on the roof of the nasal cavity detect these molecules.
Age, Gender, and Smell Ability to identify smell peaks during early adulthood, but steadily declines after that. Women are better at detecting odors than men.
Smell and Memories The brain region for smell (in red) is hard wired into brain regions involved with memory (limbic system – amygdala and the hippocampus). That is why strong memories are made through the sense of smell.
Smell • Anosmia • Complete loss of the ability to smell • Pheromones • Used by animals as a form of communication • Provides information about identity • Also provides information about sexual receptivity • Pheromones stimulate the vomeronasal organ (VNO) • Information from the VNO is sent to a special part of the olfactory bulb used for pheromonal communication
Pheromones Chemical signals released by organisms to communicate with other members of the species Relies on receptors of the vomeronasal organ
The Skin Senses • Skin is the largest sense organ • There are receptors for pressure, temperature, and pain • Touch appears to be important not just as a source of information, but as a way to bond with others • Touch Localization • Touch localization depends on the relative lengths of the pathways from the stimulated parts to the brain.
Fast fibers vs. Slow fibers • Fast fibers deliver most of the sensory information to the brain • (on the small nerve fibers) • Very intense stimuli (pain) send strong signals on the slow fibers • (on the large nerve fibers)
Pain Pain tells the body that something has gone wrong. Usually pain results from damage to the skin and other tissues. A rare disease exists in which the afflicted person feels no pain. AP Photo/ Stephen Morton Ashley Blocker (right) feels neither pain nor extreme hot or cold.
Gate-Control Theory Melzak and Wall (1965, 1983) proposed that our spinal cord contains neurological “gates” that either block pain or allow it to be sensed. Gary Comer/ PhototakeUSA.com
Gate-Control Theory of Pain • Experience of pain depends (in part) on whether the pain impulse gets past neurological “gate” in the spinal cord and thus reaches the brain.
Gate Control Theory • Spinal cord contains small nerve fibers that conduct most pain signals • It also contains larger fibers that conduct most other sensory signals • When tissue is injured small nerve fibers activate and open the neural gate • Large fiber activity shuts that gate • Thus if you stimulate gate closing activity by massage electrical signal or acupuncture you can disrupt the pain message. • The brain can close this gate too!
Neuromatrix Theory of Pain • Theory that the matrix of neurons in the brain is capable of generating pain (and other sensations) in the absence of signals from sensory nerves.
The Environment Within • Kinesthesis • The sense of body position and movement of body parts; also called kinesthesia. • Equilibrium • The sense of balance. • Semicircular Canals • Sense organs in the inner ear, which contribute to equilibrium by responding to rotation of the head.
Vestibular Senses • Vestibular senses provide information about equilibrium and body position • Fluid moves in two vestibular sacs • Vestibular organs are also responsible for motion sickness • Motion sickness may be caused by discrepancies between visual information and vestibular sensation