Ch14

• Special senses


  Senses whose sensory receptors are located in large, complex organs in the head
• The five special senses

  • Taste
  • Smell
  • Hearing
  • Equilibrium
  • Vision
• Sensation


  The conscious or unconscious awareness of external or internal stimuli
• Perception


  The conscious awareness and interpretation of sensations
• Sensory adaptation


  The process by which a sensory receptor becomes less stimulated following continuous stimuli
• All sensory receptors, except nociceptors, adapt to continuous stimuli (i.e. undergo sensory adaptation)
• Receptor types


  • Free nerve ending
  • Encapsulated ending
  • Receptor cell
• Free nerve ending


  Dendrites embedded in tissue that would receive a sensation
• Free nerve ending


  • Pain and temperature receptors in dermis of skin
• Encapsulated ending


  Sensory nerve endings are encapsulated in connective tissue that enhances their sensitivity
• Encapsulated ending


  • Respond to pressure and touch embedded in dermis
• Receptor cell


  Has distinct structural components that interpret a specific type of stimulus
• Receptor cell


  • Photoreceptors in the retina
• Exteroceptor


  A receptor that is located near a stimulus in the external environment, detect changes at the body's surface: touch, pressure, temperature
• Interoceptor


  A receptor that detects changes from internal organs and tissues, such as the receptors that sense the increase in blood pressure in the aorta or carotid sinus
• Proprioceptor


  Receptor that detect changes in muscles, tendons, and body position
• Functional receptor types

  • Chemoreceptor
  • Osmoreceptor
  • Nociceptor
  • Thermoreceptor
  • Mechanoreceptor
• Chemoreceptor


  Interprets chemical stimuli, such as an object's taste or smell
• Osmoreceptor


  Respond to solute concentrations of body fluids
• Nociceptor


  Detects pain is primarily a chemical sense that interprets the presence of chemicals from tissue damage, or similar intense stimuli
• Thermoreceptor


  Sensitive to temperatures above (heat) or below (cold) normal body temperature
• Mechanoreceptor


  Interprets physical stimuli, such as pressure and vibration, as well as the sensation of sound and body position (balance)
• Gustation sensation: Taste


  Provides information about the foods and liquids we consume
• Basic tastes

  • Sweet
  • Salty
  • Sour
  • Bitter
  • Umami
• Sweet


  Stimulated by sugars, alcohols, saccharin, and some amino acids
• Salty


  Stimulated by sodium chloride and other inorganic salts
• Sour


  Stimulated by acids
• Bitter


  Stimulated by alkaloids commonly found in bitter tasting plants such as quinine, tobacco, coffee, tannins, hops, chocolate, etc.
• Umami


  Stimulated by amino acids, responsible for the "savory" taste of meat, the twang of aging cheese, and the flavor of the food additive MSG
• Cranial nerves that innervate taste


  CN VII, CN IX, and CN X
• Facial nerve (VII)


  Innervates the anterior 2/3 of the tongue
• Glossopharyngeal nerve (IX)


  Innervates the posterior 1/3 of the tongue
• Vagus nerve (X)


  Innervates the taste buds scattered on the pharynx and epiglottis
• Aguesia


  Loss or impairment of the taste sense
• Taste is 80% smell. When olfactory receptors are blocked, food tastes bland.
• Although not considered taste, the trigeminal nerve (CN V) is able to relay information regarding the texture, the temperature, and the "spicy" nature of food. Spicy is detected by pain receptors – not taste receptors.
• Olfactory sensations: Smell


  The sense of smell, or olfaction, is provided by the paired olfactory organs located in the nasal cavity
• Olfactory epithelium


  Composed of three kinds of cells
• Olfactory nerve


  The axons of the olfactory receptor cells collect into 20 or more bundles that penetrate the cribriform plate of the ethmoid and constitute the filaments of the olfactory nerve that first synapse within the olfactory bulb
• Olfactory bulbs


  Transmit the impulse towards the brain via the olfactory tracts to reach the olfactory cortex located within the temporal lobe of the cerebrum, the hypothalamus, and portions of the limbic system