lesson 8

• Five Sensory Receptors


  • Photoreceptors
  • Mechanoreceptors
  • Chemoreceptors
  • Thermoreceptors
  • Pain receptors
• Photoreceptors


  Respond to light
• Mechanoreceptors


  Respond to physical stimuli such as sound or touch
• Chemoreceptors


  Detect chemicals
• Thermoreceptors


  Respond to temperature
• Pain receptors


  Detect possible tissue damage
• Types of eyes that have evolved in the animal kingdom


  • Eye cups in flatworms and other invertebrates
  • Compound eyes in insects and arthropods
  • Single lens eyes in squid
• Sclera


  • Outermost layer of the eyeball
  • Forms the white of the eye
  • Has a transparent cornea in front
• Conjunctiva


  • Lines the eyelids and the front of the eyeball
  • Helps keep the eyes moist
• Choroid


  • Surrounds the sclera
  • The iris is formed from the choroid
• Vision


  1. Light passes through the pupil

  2. Light focused by the transparent lens

  3. Light hits the retina

  4. Photoreceptor cells transduce light energy into action potentials

  5. Nerve impulses travel along the optic nerve

  6. Image formed in the brain
• Iris


  Gives the eye its color
• Pupil


  Opening in the center of the iris that allows light to enter the eye
• Retina


  Contains photoreceptor cells
• Optic nerve


  Carries nerve impulses from the retina to the brain
• Photoreceptor cells


  • Rods and cones
• Rod cells


  • Use the pigment rhodopsin
  • Used for night vision
  • Can only detect shades of gray, not color
• Cone cells


  • Distinguish various colors
  • Sensitive to bright light
• Outer ear


  • Lobes catch sound waves and channel them to the eardrums
• Middle ear


  1. Amplifies the sound wave vibrations to three small bones-the hammer, anvil and stirrup

  2. Sound waves travel to the oval window
• Eustachian tube


  Equalizes air pressure in the middle ear and outer ear
• Inner ear


  • Hearing organ composed of several channels of fluid wrapped in a spiral cochlea
  • Encased in the bones of the skull
• Hearing process


  1. Vibrations in the oval window produce pressure waves

  2. Pressure waves travel through the upper canal to the tip of the cochlea, enter the lower canal and fade away

  3. Pressure waves of the upper canal push down to the middle canal and the membrane below this canal vibrates

  4. Vibrations stimulate hair cells attached to the membrane by moving them against the overlying tissue

  5. Hair cells develop receptor potentials causing release of neurotransmitters that induce action potentials in the auditory neurons
• Ear structures


  • External canals
  • Tympanic membrane
  • Malleus
  • Incus
  • Stapes
  • Oval window
  • Round window
  • Eustachian tube
  • Cochlea
  • Vestibular nerve
  • Cochlear nerve
• Odor and Taste organs


  • membrane
  • Round Eustachian tube
  • window
  • Stimuli vibrations
• The senses of odor and taste are interrelated
• Chemoreceptors in the nose


  • Detect molecules
  • Differentiated into numerous types of odor
• In the upper portion of the nasal cavity, there are olfactory chemoreceptors
• Odor molecules enter the nose and bind to specific receptor molecules
• Chemoreceptors in taste buds

  Detect salty, bitter, sweet and sour tastes
• Taste perception is due to similar signal mechanisms as mentioned above for smell
• What one "tastes" is actually "smell" or odor
• The common cold (due to a virus)

  Can disrupt our sense of smell, thus, we lose taste for the food
• Systems that control the ability to move

  • Skeletal system
  • Muscle system
  • Nervous system
• Skeletal system


  Consists of bones that act as levers
• Muscle system


  Delivers force needed to move bones
• Nervous system


  Delivers signals for muscle contraction
• Skeletomuscular system


  Connected by fibrous tissue
• Ligaments


  Attach bones to bones
• Tendons


  Attach muscles to bones