science F3 1.2

• Definition  Stimulus and Response in Humans

  Sensory organs are organs that can detect stimuli
• The function of eyes:

  • Focusing on objects near and far
  • Produces continuous images that are sent directly to the brain
  • As a sense of sight

  
• The mechanism of vision:

  • Light from an object enters the eye through the pupil
  • Light is refracted by the cornea, aqueous humor, eye lens, and vitreous humor
  • Inverted and small images are formed on the retina
  • The retina produces nerve impulses and the optic nerve transmits them to the brain
  • The brain translates impulses and produces upright images
• The function of ears:

  • To keep our balance and hearing
  • As a sense of sound
• The structure of ears:

  
• The structure of ears

  Ossicles

  Amplifies the vibration of sound and sends it to the oval window

  Earlobe

  Receives sound waves

  Ear canal

  Transmits sound waves to the eardrum

  The eardrum

  Vibrates when sound waves hit it

  Semicircular canal

  Controls body balance

  The auditory nerve

  Sends impulses from the cochlea to the brain

  Cochlea

  Converts sound vibrations into impulses

  Oval window

  Transmits sound vibrations from the middle ear to the inner ear

  Eustachian tube

  Balances the air pressure on both sides of the eardrum
• The mechanism of hearing:

  • Sound waves enter the ear canal
  • The eardrum receives sound waves and vibrates
  • The vibrations are amplified by the ossicle bone and transmitted to the oval window
  • The oval windows vibrated
  • The cochlea converts vibrations into impulses
  • Impulses are carried by the auditory nerve to the brain
  • The brain interprets it as sound
• The function of the nose:

  • Provides air for breathing
  • Filters and cleans foreign debris during respiration
  • As a sense of smell
• The structure and mechanism of the nose:

  
• The function of the tongue:

  • As a digestive organ with ease of movement of food during chewing and swallowing
  • As a sense of taste
• The structure and mechanism of the tongue:

  • The surface of the tongue is covered by taste buds that contain many taste receptors and are scattered on the surface of the tongue
  • Taste receptors are sensitive to chemicals in food
  • The tongue has 5 types of taste receptors, namely sweet, sour, bitter, and umami (savory taste).
• The function of the skin:

  • Protect us from microbes
  • Allows sensations of touch, temperature, and pressure
  • As a sense of touch
• The structure of skin:

  
• Skin sensitivity:

  • The concentration of the skin depends on the number of receptors present and the thickness of the epidermis
  • The more receptors, the more sensitive that part of the skin is
  • The thinner the epidermis, the more sensitive the skin is to stimuli
  • Blind people read Braille using their fingertips
  • Very sensitive parts of the skin: Fingertips, back of neck, lips, and earlobes
  • Part of the skin that is less sensitive: Elbows and knees
• • The sensory organs are interconnected with each other and can balance the human body on a single daily basis
• The limit of sensory:

  • Limits our sensory ability to detect a stimulus
  • Caused by sensory organ defects or the aging process
• The visual sensory limitations:

  • The eye cannot detect an image that falls on a blind spot
  • Human vision can also be affected due to long-sightedness, short-sightedness, astigmatism, and presbyopia(老花）
• The structure of the normal eye, long-sightedness, and short-sightedness:

  
• • Short-sightedness cannot see distant objects clearly because light from the object is focused in front of the retina
  • Requires a concave lens
  • Long-sightedness cannot see near objects clearly because light from the object focuses behind the retina
  • Requires a convex lens
• The structure of the astigmatism eye:

  • Images are blurred and unclear because light from objects is separated and focused at different points on the retina
  • Requires a cylindrical lens or undergoes surgery

  
• The structure of the presbyopia eye:

  • Not being able to see distant objects and close objects clearly is common among the elderly
  • Requires a dual focus lens to see near and far objects clearly

  
• Hearing sensory limitations:

  • Humans can only hear between 20Hz to 20,000Hz
  • Deafness is caused by the ossicle bones joining together due to infection, the aging process or exposure to loud noise for a long period of time
  • Only surgery or hearing aids can help deaf people
• Limitation of vision

  • Magnifying glass & microscope
  • Can see art/small objects
  • Binoculars & telescopes
  • Can see distant objects
• Limitation of hearing

  Stethoscope

  Amplifies the sound of the heartbeat

  Loudspeaker 

  Amplifies the sound