Senses

• Sensing


  Sensory cells translating stimuli (chemical, electromagnetic, mechanical) into action potentials that our nervous system can integrate
• General sensory receptors


  Modified nerve endings of sensory neurons
• Touch


  A general (somatic) sense that relates to our ability to detect pressure, pain, temperature, and tension through a variety of general sensory receptors
• Special senses


  Vision, smell, taste, hearing, and equilibrium
• Special sensory receptor cells

  In sensory organs (like your ear and eye) and/or epithelial structures (like your taste buds and olfactory epithelium) in your head
• Vision


  • The dominant sense of humans
  • Light = electromagnetic waves
  • Photoreceptors in our eyes convert light energy to electrical energy (APs) that then travel to the brain
• Eye


  • Surrounded by protective fat and the bony orbits in the skull
  • Accessory structures: Eyebrows, Eyelids and Eyelashes, Lacrimal apparatus
  • Accessory structures: Extrinsic eye muscles

  
• Eye


  • Internally hollow with fluids (humors) that hold its shape
  • Wall of the eyeball is made of 3 layers: Fibrous layer, Vascular layer, Inner layer (retina)

  
• Retina


  • 2 layers: Outer pigmented layer, Inner neural layer
  • Millions of photoreceptors that convert light energy to APs that travel through the optic nerve to the thalamus, and then the visual cortex in the brain
  • 2 types of photoreceptors: Rods and Cones
• Eye


  • Lens focuses the light that is allowed in and projects it onto the retina
  • Vitreous humor fills the posterior segment
  • Aqueous humor fills the anterior segment

  
• Smell (olfaction) and taste (gustation)

  Chemical senses that use chemoreceptors to detect molecules in the air (dissolved in fluids from our nasal membranes) and our food (dissolved in saliva)
• Odor


  The gaseous molecules we smell
• Smell (olfaction)


  1. Molecules bind to receptors

  2. APs down the olfactory nerve into the ethmoid bone, and eventually to the olfactory bulb that connects to our brain

  3. Signal gets sent to the olfactory cortex and the emotional pathway in our limbic system
• Taste (gustation)


  • Gustatory epithelial cells are the taste receptor cells
  • Basal epithelial cells are stem cells that make new gustatory epithelial cells
  • Taste buds are the sensory organ of taste
• Taste (gustation)


  1. Sensory receptor cells

  2. APs

  3. Signal to the gustatory cortex of brain

  4. Release of digestive enzymes to break down the food
• Ear


  • Designed to receive mechanical waves and convert them to nerve signals that our brains can interpret
  • Sound creates vibrations in the air that hit our eardrums and cause tiny bones (auditory ossicles) to move internal fluid against a membrane
  • This triggers tiny "hair" cells to stimulate neurons to APs to the brain
• Ear


  • 3 parts: (1) outer/external and (2) middle ear for hearing, (3) inner ear for hearing and maintaining equilibrium
• External (outer) ear


  • Pinna (auricle), External acoustic meatus (auditory canal)
  • Function: Catch sound waves and pass them deeper into the ear through the auditory canal
• Middle ear


  • Tympanic cavity = relay station between outer and inner ear
  • 3 tiny bones = the auditory ossicles (malleus, incus, and stapes)
  • Function: Amplify sound waves to make stronger for when they get to inner ear
• Inner ear


  • Labyrinth (bony and membranous)
  • Both divisions are filled with fluid that help conduct the sound vibrations that allow us to hear and respond to changes in our equilibrium
  • Function: Turn physical vibrations into electrical impulses (APs) to travel to brain
• Inner ear


  • Semicircular canals aid in maintaining balance when head rotates
  • Cochlea contains hair cells that vibrate at different frequencies stimulating the organ of Corti to send AP through cochlear nerve to the auditory cortex in the brain
  • Vestibule is a key structure for maintaining balance