SENSES

• Sense


  Ability to perceive stimuli
• Sensation


  Conscious awareness of stimuli received by sensory neurons
• Sensory receptors


  Sensory nerve endings that respond to stimuli by developing action potentials
• Types of Senses


  • General senses (touch, pressure, pain, temperature, itch)
  • Somatic senses (provide information about body and environment)
  • Visceral senses (provide information about internal organs)
  • Special senses (smell, taste, sight, hearing, balance)
• Types of Receptors


  • Mechanoreceptors (detect movement)
  • Chemoreceptors (detect chemicals)
  • Photoreceptors (detect light)
  • Thermoreceptors (detect temperature changes)
  • Nociceptors (detect pain)
• Types of Touch Receptors

  • Merkel's disk (detect light touch and pressure)
  • Hair follicle receptors (detect light touch)
  • Meissner corpuscle (deep in epidermis, localizing tactile sensations)
  • Ruffini corpuscle (deep tactile receptors, detect continuous pressure in skin)
  • Pacinian corpuscle (deepest receptors, associated with tendons and joints, detect deep pressure, vibration, position)
• Pain


  An unpleasant perceptual and emotional experience
• Types of Pain


  • Localized (sharp, pricking, cutting pain, rapid action potential)
  • Diffuse (burning, aching pain, slower action potentials)
• Local anesthesia


  Action potentials suppressed from pain receptors in local areas
• General anesthesia


  Loss of consciousness, chemicals affect reticular formation
• Referred pain


  Originates in a region that is not the source of the pain stimulus, felt when internal organs are damaged or inflamed
• Olfaction


  The sense of smell, occurs in response to odorants, receptors located in superior portion of nasal cavity
• Olfaction process


  Odors dissolve in mucous, olfactory neurons detect odor, depolarize, and carry signal to olfactory bulb, frontal and temporal lobes process odor
• Taste buds


  Sensory structures that detect taste, located on papillae on tongue, hard palate, throat, each contains 40 taste cells with taste hairs
• Taste process


  Taste molecules/ions bind to receptors on taste hairs, initiate action potentials, sensory neurons carry signals to insula of cerebral cortex
• Types of Tastes


  • Sweet
  • Sour
  • Salty
  • Bitter
  • Umami
• Accessory structures of the eye

  Eyebrow, eyelid, eyelashes, conjunctiva, lacrimal apparatus, extrinsic eye muscles
• Lacrimal apparatus


  Produces tears
• Extrinsic eye muscles


  Help move the eyeball
• Anatomy of the eye

  Hollow, fluid filled sphere, composed of 3 layers (tunics), divided into chambers
• Fibrous tunic


  Outermost tunic, includes sclera and cornea
• Vascular tunic


  Middle tunic, contains blood supply, includes choroid, ciliary body, and iris
• Nervous tunic


  Innermost tunic, includes retina with photoreceptors (rods and cones)
• Macula and fovea centralis

  Small spot near center of retina, where light is focused when looking directly at an object, only contains cones
• Optic disk


  White spot medial to macula, where blood vessels enter eye and axons exit as optic nerve, no photoreceptors
• Chambers of the eye

  Anterior chamber (aqueous humor), posterior chamber (aqueous humor), vitreous chamber (vitreous humor)
• Functions of the eye

  Works like a camera, iris allows light through pupil, cornea/lens/humors focus light onto retina, retina produces action potentials relayed to brain, light refraction and image focusing are important
• Light refraction


  Bending of light, focal point is anterior to retina, object is inverted
• Accommodation


  Changes in shape of lens to focus image on retina, enables focusing on objects closer than 20 feet
• Posterior chamber


  Located behind anterior chamber, contains aqueous humor
• Vitreous chamber


  Located in retina region, filled with vitreous humor: jelly-like substance, helps maintain pressure, holds lens and retina in place, refracts light
• Functions of the Eye

  • The eye functions much like a camera. The iris allows light into the eye through the pupil, which is focused by the cornea, lens, and humors onto the retina. The light striking the retina produces action potentials that are relayed to the brain. Light refraction and image focusing are two important processes in establishing vision.
• Light Refraction


  Bending of light, focal point: point where light rays converge, occurs anterior to retina, object is inverted
• Focusing Images on Retina

  Accommodation: Changes in shape of the lens so image can be focused on retina, enables eye to focus on images closer than 20 feet
• Rhodopsin


  Photosensitive pigment in rod cells
• Opsin


  Colorless protein in rhodopsin
• Retinal


  Yellow pigment in rhodopsin, requires vitamin A
• Effects of Light on Rhodopsin

  Light strikes rod cell, Retinal changes shape, Opsin changes shape, Retinal dissociates from opsin, Change in rhodopsin shape stimulates response in rod cell which results in vision, Retinal detaches from opsin, ATP required to reattach retinal to opsin and return rhodopsin to original shape
• Optic nerve


  Leaves eye and exits orbit through optic foramen to enter cranial cavity
• Optic chiasm


  Where 2 optic nerves connect