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
  • Special senses
• General senses


  • Receptors over large part of body that sense touch, pressure, pain, temperature, and itch
  • Somatic senses provide information about body and environment
  • Visceral senses provide information about internal organs
• Special senses


  • Smell, taste, sight, hearing, and balance
• Types of receptors


  • Mechanoreceptors
  • Chemoreceptors
  • Photoreceptors
  • Thermoreceptors
  • Nociceptors
• Mechanoreceptors


  Detect movement
• Mechanoreceptors


  • Touch, pressure, vibration
• Chemoreceptors


  Detect chemicals
• Chemoreceptors


  • Odors and taste
• Photoreceptors


  Detect light
• Thermoreceptors


  Detect temperature changes
• Nociceptors


  Detect pain
• Types of touch receptors

  • Merkel's disk
  • Hair follicle receptors
  • Meissner corpuscle
  • Ruffini corpuscle
  • Pacinian corpuscle
• 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, detects continuous pressure in skin
• Pacinian corpuscle


  Deepest receptors, associated with tendons and joints, detect deep pressure, vibration, position
• Pain


  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, chemicals are injected near sensory nerve
• General anesthesia


  Loss of consciousness, chemicals affect reticular formation
• Referred pain


  Originates in a region that is not source of pain stimulus, felt when internal organs are damaged or inflamed, sensory neurons from superficial area and neurons of source pain converge onto same ascending neurons of spinal cord
• Olfaction is the sense of smell, occurs in response to odorants, receptors are located in superior portion of the nasal cavity, we can detect 10,000 different smells
• Olfaction process


  1. Nasal cavity contains a thin film of mucous where odors become dissolved

  2. Olfactory neurons are located in the mucous, dendrites pick up odor, depolarize, and carry odor to axons in olfactory bulb (cranial nerve I)

  3. Frontal and temporal lobes process odor
• Taste buds


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


  1. Taste cells send taste stimuli to taste hairs

  2. Dissolved molecules or ions bind to receptors on the taste hairs and initiate action potentials

  3. Sensory neurons carry signals to the insula of the cerebral cortex
• Types of tastes


  • Sweet
  • Sour
  • Salty
  • Bitter
  • Umami
• Certain taste buds are more sensitive to certain tastes, taste is also linked to smell
• Accessory structures of the eye

  • Eyebrow
  • Eyelid/Eyelashes
  • Conjunctiva
  • Lacrimal apparatus
  • Extrinsic eye muscles
• Eyebrow


  Protects from sweat, shade from sun
• Eyelid/Eyelashes


  Protects from foreign objects, lubricates by blinking
• Conjunctiva


  Thin membrane that covers inner surface of eyelid
• Lacrimal apparatus


  Produces tears
• Extrinsic eye muscles


  Help move eyeball
• The eye is a hollow, fluid filled sphere composed of 3 layers (tunics) and divided into chambers
• Layers of the eye

  • Fibrous tunic
  • Vascular tunic
  • Nervous tunic
• Sclera


  Firm, white outer part that helps maintain eye shape, provides attachment sites for muscles, protects internal structures