special senses

• describe sensory signal transduction.
• describe how the special senses differ other sensory apparatus
• describe the anatomical structures and functions of the eye
• what are the structures and functions associated with the different layers of the eye?
• what are the specialized cell types associated with vision?
• what are the properties fo light?
• describe visual accommodation
• what are some common errors associated with vision?
• how are visual signals sent to the brain and processed?
• transduction: physical or chemical stimulus is converted into action potential that can be interpreted by brain

  • general senses: touch, temperature, pain
  • special senses: detect stimuli (light, chemicals, sounds)
  • sensory signals are then passed to association areas for further interpretation and integration
• special senses: sensory stimuli

  • smell (olfaction)
  • taste (gustation)
  • vision
  • hearing (audition)
  • vestibular (balance)
• special and general senses differ in:

  1. stimuli detected:
  2. general = detection touch, pain, temperature
  3. special = detection light, sound, head movements, chemicals (tastes and smells)
  4. structure of sensory receptors:
  5. any special senses rely on receptors that are not neurons
  6. general sensory receptors are receptive ends of sensory neurons
  7. olfaction is only special sense exception
  8. location of sensory nerves:
  9. special sensory organs are confined to head
  10. all information travels on axons of various cranial nerves
  11. general sensory information travels on axons of both cranial and spinal nerves
• vision

  • accessory structures
  • eyebrows: shade the eye from sunlight; prevent perspiration reaching eyes
  • eyelids/palpebrae: separated by palpebral fissure; protect eyeballs
  • eyelashes: innervated hairs at rid of eyelid; reflex blinking when stimulated
• conjunctiva: transparent mucous membrane

  • lines the eyelid
  • palpebral conjunctiva
  • secretes mucus that lubricates eye
  • pink eye = conjunctivitis
• lacrimal apparatus: produces tears

  • lacrimal gland: produces lacrimal secretions/tears
  • helps "clean" the eye
  • lubricates the eye
  • lacrimal sac
  • drains the canaliculi into the nasolacrimal duct
  • reason why your nose runs when you cry
• extrinsic eye muscles: allows eye to follow objects

  1. rectus muscles: moving up and down, left and right
  2. oblique muscles: move the eye vertically, when eye is turned

  innervations

  1. abducens
  2. trochlear
  3. oculomotor
• layers of the eyeball:

  1. fibrous layer (sclera and cornea)
  2. vascular layer (iris, ciliary body, choroid)
  3. neural layer (retina)
• fibrous layer

  • sclera: tough, white portion of the eye
  • cornea: transparent layer
  • allows light into the eye
  • innervated with many nociceptors that can make us feel stuff in our eye
• vascular layer

  • choroid: heavily vascularized and pigmented
  • ciliary body: encircles the lens
  • ciliary muscle: smooth muscles, encircles the lens and control shape
  • ciliary processes: secrete fluid that fills anterior portion of eye
  • suspensory ligament / ciliary muscle: hold the lens in an upright position
  • iris: colored portion of eye
  • pupil: opening allows light to enter
  • pupillary sphincter muscle
  • contracts to make pupil smaller
  • parasympathetic control
  • increased light intensify
  • pupillary dilater muscle
  • contracts to make pupil larger
  • sympathetic control
  • decreased light intensify
• neural layer

  • photoreceptor cells: detect & transduce light stimuli into electrical signals
  • rods: black & white vision in low light levels & also peripheral vision
  • cones: high acuity color vision in higher light levels
  • macula lutae: yellowish central region of fovea; large # of photoreceptors
  • fovea centralis: central region of macula lutae; large # of cones tightly packed together; allows for detailed vision & ability to focus on objects
  • optic disc: location where axons of optic nerve exit from retina; does not contain photoreceptors; does not capture visual images (blind spot)
• macular degeneration: leads to progressive loss of visual activity in macula lutae, particularly in center of visual field; may also cause visual distortion & changes in color perception
• layers of retina are in contact with each other but are not physically linked by desmosomes or tight junctions

  • certain conditions (trauma, diabetes, or abnormally shaped eyeball) can pull inner layer away from pigmented epithelium (detached retina)
  • isolates photoreceptors from blood supply; permanent loss of vision can occur if not corrected within several days