special senses the eyes n.
Skip this Video
Download Presentation
Special Senses: The Eyes

Loading in 2 Seconds...

play fullscreen
1 / 24

Special Senses: The Eyes - PowerPoint PPT Presentation

  • Uploaded on

Special Senses: The Eyes. By the end of this class you should understand:. The general structure of a sensory neuron and the types found in the body The properties of light as it relates to vision The major parts of the eye and their roles in focusing light

I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
Download Presentation

PowerPoint Slideshow about 'Special Senses: The Eyes' - gautam

Download Now An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.

- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
by the end of this class you should understand
By the end of this class you should understand:
  • The general structure of a sensory neuron and the types found in the body
  • The properties of light as it relates to vision
  • The major parts of the eye and their roles in focusing light
  • The different types of photoreceptors in the eye and their functions
the six senses
The Six Senses
  • Classically, humans are thought to have five senses
  • Reality is we have many!
    • Vision
    • Hearing
    • Taste
    • Smell
    • Touch (actually many kinds of senses)
    • Balance (vestibular sense)
sensory neuron
Sensory Neuron
  • All sensory neurons, or receptors, have some type of molecule that causes them to receive signals from the environment
  • These signals create action potentials (depolarizations of membrane)
  • The axon sends this action potential to the spinal cord and ultimately the brain
types of receptors
Types of Receptors
  • Mechanoreceptor
    • Responds to mechanical stress such as pressure or stretching
  • Thermoreceptor
    • Reponds to high or low temperatures
  • Nociceptor
    • Pain receptor that signals damage to cells
  • Chemoreceptor
    • Responds to chemical stimulus
  • Photoreceptor
    • Reponds to light
  • Mechanoreceptors generate our sense of touch
  • They also are responsible for hearing and balance (more on that next class)
  • Typically, when something pushes on the cell it opens mechanically gated ion channels
    • When ions move into the cell it depolarizes the membrane and creates an action potential
  • Thermoreceptors are embedded in our skin and organs
  • Relate information about heat and cold
  • Only function within a certain range and can be killed by extreme temperatures
    • Frostbite and burns often begin with numbness until pain receptors kick in
  • Nociceptors detect imbalances in tissues and send action potentials as a result
    • Combination mechanoreceptor and chemoreceptor
  • Potassium is one stimulus that they respond to
    • Potassium is supposed to be inside cells, so a large amount of potassium is often caused by cell lysis
  • Responsible for itching and pain
  • Chemoreceptors send action potentials in response to having chemicals bind to the cell membrane
  • Responsible for senses of smell and taste
    • Taste: only five flavors (sweet, sour, bitter, salt, savory)
    • Over 1000 smell receptor types
    • Much of “taste” is smell, which is why food tastes bland when you have a cold
  • Photoreceptors respond to light by sending action potentials
    • Found only in the eye
  • Produce the sense of sight
  • The eye’s function is to focus light onto these photoreceptors so they can send action potentials to the brain
    • The human eye has three types of cone and one type of rod, all different kinds of photoreceptors
properties of light
Properties of Light
  • Light is made up of particles called photons that are so small and move so fast they also behave as waves
  • The more energy a photon has, the faster its frequency
  • The perceived color of a particle of light depends on what frequency it has
wavelengths of light
Wavelengths of Light
  • Only particles of light with certain energies are visible light
    • These are the frequencies that activate our photoreceptors
  • Higher-energy particles such as UV light and X-rays pass through without stimulating our photoreceptors
  • Lower-energy particles such as infrared, microwaves and radio waves don’t have enough energy to stimulate our photoreceptors
the structure of the eyeball
The Structure of the Eyeball
  • The eye has one function: to focus light on the retina which is a tissue filled with photoreceptors
  • The light is allowed in through a small hole called the pupil and is focused (bent) by the lens
    • The lens can change its thickness to change the focus to be closer or farther away
  • All the other parts of the eye are protection and support for these active parts
outer protection of eye
Outer Protection of Eye
  • Sclera
    • Also known as the “white” of the eye
    • Fibrous connective tissue that envelops the eye
  • Conjunctiva
    • A thin transparent membrane around the outside of the sclera
  • Cornea
    • The portion of the conjunctiva in front of the pupil
    • Bends light (Lasik surgery changes the shape of the cornea)
inner structure of eye
Inner Structure of Eye
  • Pupil
    • The hole though which light enters
  • Iris
    • The colored part of the eye
    • Changes size to allow more or less light in
  • Humors (liquids)
    • Aqueous humor is between the pupil and lens
    • Vitreous humor fills main eyeball and keeps it round and taut
focusing of light
Focusing of Light
  • Light is focused by the lens and the cornea
  • The eye’s shape is vital for this focusing to work
    • Anyone who has tried wearing the wrong glasses prescription can tell you so!
  • The retina lines the back of the eyeball
  • Filled with rods and cones
  • The very center of the retina is called the macula and is filled primarily with cones
  • The rest of the retina is filled primarily with rods
blind spot
Blind Spot
  • The optic disk on the retina is where the axons from all the interneurons of the photoreceptors meet and become the optic nerve
  • This produces a blind spot that our visual cortex (in the occipital lobe) fills in
rods and cones
Rods and Cones
  • Rods are sensitive to many different wavelengths of light
    • Since action potentials are all-or-none, rods do not distinguish between different colors of light and produce only grayscale vision
  • Most humans have three types of cones (red, green and blue)
    • They require much more light to function than rods but produce color vision
two rods converged
Two Rods Converged
  • Rods also have a property called convergence
    • Many rods are attached to the same interneuron
    • When any of those rods fire, the interneuron fires
    • Produces a fuzzy picture
  • Cones do not have convergence
    • They produce clear images but require a lot of light
    • This is why they are concentrated in the macula
activation of photoreceptors
Activation of Photoreceptors
  • Rods and cones all have different versions of the same molecule, rhodopsin
  • Rhodopsin is a protein with a pigment called retinal contained inside
  • Retinal is made from vitamin A
    • Eat your carrots!
  • Different retinal structures respond to different frequencies of light but all of them change shape when struck by the right photon
  • The change in shape causes the rhodopsin to alter the behavior of sodium channels
  • This ultimately creates action potentials in the interneurons of the eye which go to the brain
thursday the ear
Thursday: the Ear!
  • And after that: prep for lecture exam #2!