sensory systems

• structure of the eye


  • Pupil is the opening in the middle of the eye through which light passes.
  • Iris is the visible coloured ring at the front of the eye. It adjusts to control the amount of light entering the eye through the pupil.
  • Tear glands (lacrimal glands) produce tears to clean and lubricate the front of the eye. The fluid contains salt and has natural antiseptic properties to defend against infection.
  • Aqueous and vitreous humours (or fluids) are the watery, jelly-like fluids that fill the eye. They keep the eye in shape and nourish it.
• structure of the eye


  • Conjunctiva is a thin membrane that protects the cornea.
  • Cornea is at the front of the eye and is transparent; light rays pass through the cornea to the retina.
  • Retina is the inner lining of the eye; it contains light-sensitive cells called rods and cones.
  • Macula has a very high concentration of photoreceptor cells; these detect light and send signals to the brain, which interprets them as images.
  • Optic nerve is where the nerve cells exit the eye. There are no rods or cones there and so this is called the 'blind spot'.
• structure of the eye

  • Ciliary muscle enables the lens to change shape for focusing. It contracts to stretch the lens, making it flatter and thinner.
  • Suspensory ligaments attach the lens to the ciliary muscle.
  • Lens focuses light entering the eye.
• structure of the ear

  • Eardrum (or tympanic membrane) is a thin layer of tissue that receives sound vibrations and transmits them to the middle ear cavity.
  • Stapes/incus/malleus ear bones (also known as stirrup, anvil and hammer) are small bones that amplify the sound waves and transmit the vibrations across the middle ear to the cochlea.
  • Cochlea contains a jelly-like fluid in a coiled tube that resembles a snail's shell. Vibrations pass though the fluid and are converted to neural messages and passed on to the brain via the auditory nerve.
• structure of the ear

  • Organ of corti is located in the cochlea; it is sometimes called the body's microphone and is lined with rows of hair cells that convert sound vibrations into nerve impulses.
  • Eustachian tube connects the middle ear to the throat. It ensures that the pressure in the middle ear is equal to the pressure outside the ear.
  • Round window is a drum-like membrane. Vibrations from the oval window pass through it to the cochlea.
• structure of the ear

  • Auditory nerve is a bundle of nerve fibres that carry hearing information between the cochlea and the brain.
  • Semi-circular canals and ampullae are tiny fluid-filled tubes in the inner ear that help with balance. They have nothing to do with hearing. They are lined with cilia and as the movements of the cilia are communicated to the brain they work as a kind of motion sensor to help you keep your balance.