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Sensory Information Processing Notes

Somatosensory Cortex

  • Different areas of the brain are dedicated to processing different sensory information.
  • The amount of brain area dedicated to a body part correlates with its importance for sensory perception.
  • Areas like the hip, trunk, neck, shoulder, and upper limbs have relatively small dedicated areas.
  • Index finger and lips have large dedicated areas, reflecting their high sensitivity.
    • The size is indicative of how much of this brain area we dedicate to that sensory information.
  • Areas sensitive to information:
    • Lips
    • Face
    • Index finger
  • Areas less sensitive to information:
    • Hips
    • Trunk

Vision

  • Vision involves both neural and optical components.
  • The eye refracts light to focus it on the retina.
  • Light coming straight doesn't need refraction.
  • Light at an angle is refracted to focus on a single point.
  • Ideal refraction:
    • Light focuses on the back of the eyeball, where optical and neural processing meet.
  • Ciliary muscles control the lens shape to adjust refraction based on the object's distance.
    • Relaxed ciliary muscles:
      • Flat lens.
      • Distant objects.
      • Light rays nearly parallel.
    • Constricted ciliary muscles:
      • Round lens.
      • Close objects.
      • Stronger refraction.
  • Vision correction involves adding lenses to compensate for focusing issues.
    • Nearsightedness (myopia):
      • Ciliary muscles contract too much.
      • Focal point is in front of the retina.
      • Corrected with a concave lens to diverge light before it enters the eye.
    • Farsightedness (hyperopia):
      • Insufficient refraction.
      • Focal point is behind the retina.
      • Corrected with a convex lens to converge light before it enters the eye.
  • Neural and chemical pathways:
    • Ganglion cells:
      • First cells to be hit when the light activated or when the light comes into our eyeball.
      • React to external light and cause a chemical response.
    • Rods:
      • Responsible for reacting to pigment.
      • Enable color vision.
    • Cones:
      • React to levels of light (light vs dark).
      • Adapt to varying light levels by firing action potentials.

Photoreceptor Process

light \rightarrow G \text{ coupled protein response} \rightarrow \text{cyclic GMP} \rightarrow \text{regular GMP}

  • Processes are favored by light or dark conditions, adapting the eye.

Binocular Vision

  • Each eye has a right and left field of vision.
  • Overlapping binocular zone provides depth perception.
  • Information from each visual field goes to the opposite side of the brain.
  • Right eye:
    • Left visual field projects to the right side of the eye.
    • Right visual field projects to the left side of the eye.
  • Information from each eye goes to both the left and right visual cortex in the occipital lobe.
  • Lateral geniculate nucleus (LGN) processes and cleans up visual information.
  • This is where we start to clean up that information and put it into a way that our visual cortex can understand.
  • Visual information is initially chemical (neurotransmitters).

Electromagnetic Spectrum and Color Vision

  • Different animals may perceive different colors based on the rods they possess.
  • Human cones:
    • Long wavelength:
      • Red and orange.
    • Medium wavelength:
      • Green and yellow.
    • Short wavelength:
      • Blue and purple.

Eye Movement

  • Lens movement adjusts focus.
  • Six skeletal muscles control eye movements:
    • Saccades:
      • Fast, jerking movements.
      • Allow quick shifts in gaze.
    • Slow eye movements:
      • Track objects in space.

Hearing

  • Sound waves are created by compression and relaxation of air molecules.
  • Sound travels better through higher density.
    • Higher density attenuates sound.
  • Sound is characterized by pitch (frequency) and amplitude (loudness).
    • Pitch = Frequency.
    • Loudness = Amplitude.
  • Increase frequency:
    • Increase amount of cycles per second.
    • Increases the pitch.
  • Increase amplitude:
    • You make something sound louder.

Ear Anatomy

  • External ear: funnels sound waves.
    • Auditory canal.
    • Cartilage help guide waves, but not essential.
  • Middle ear:
    • Tympanic membrane (eardrum).
    • Malleus, incus, and stapes (smallest bones in the body).
      • Transmit vibrations.
      • Transition sound waves.
  • Inner ear:
    • Semicircular canals (balance).
    • Cochlea (hearing).
      • Attached to vestibular cochlear nerve.

Cochlea function

  • The cochlea is a fluid-filled sac within the inner ear.
  • The malleus, incus, and stapes are all connected to that tympanic membrane, there's actual movement of those bones because of the sound waves.
  • Vibrations of the tympanic membrane cause movement of the malleus, incus, and stapes, which transmit vibrations to the oval window of the cochlea.
  • This creates liquid waves within the cochlea.
  • Organ of Corti contains hair cells that connect to afferent neurons.
  • Movement of liquid in the cochlea causes hair cells to bend, activating afferent neurons.

Wave Properties

  • High-frequency at the point of stimulus.
  • Then changes over time.
  • High-pitched, loud sounds are sensed at the front of the cochlea.
  • Low, deep, soft sounds are sensed later in the cochlea.
  • The eighth nerve is going down the after the pressure waves cause a change in the hair movement.
  • Pressure waves eventually reach the round window of the middle ear.
  • Ear popping is due to pressure changes in the inner ear, releasing pressure.
  • Very loud sounds can cause the stapes to damage the oval window.

Hair Cell Activation

  • Stereocilia on hair cells bend in response to pressure waves.
  • Bending in one direction activates the cell.
    Spherical \; cell \rightarrow Depolarization \rightarrow Vesicles \rightarrow \text{Excitatory Neurotransmitters}
  • Bending in The another direction inhibits the cell.
  • Hair cell orientation may contribute to pitch discrimination; conflicting research exists.

Decibel Levels

  • Breathing: 10 dB
  • Quiet conversation: 50-60 dB
  • Chainsaws/concerts: 100-110 dB
  • Pain: 125 dB
  • Hearing loss likely: 130 dB
  • Eardrum rupture: 150 dB

Semicircular Canals

  • Fluid filled structure.
  • Position of head in space.
  • Connected to the cochlea, also connected to vestibulochochlear nerve.
  • Detect head position and movement.
  • Hair cells respond to fluid movement caused by head movement.
    • Resting \; Activity \rightarrow \text{Semicircular canal moves} \rightarrow hair \; cells \; depolarize
  • In low/zero gravity, lack of pressure on semicircular canals disrupts spatial orientation.
  • Vestibular information controls eye movement, posture, balance, and spatial awareness.
  • Information travels to the parietal lobe.

Taste and Smell

  • External chemicals binding to chemoreceptors are responsible for taste and smell.
  • Taste buds contain gustatory (taste) cells.
  • Taste cell has chemicals to come to taste buds
  • Basal cells convert food chemicals into neurotransmitters at the base of the cell turning it into intnernal chemical information.
  • Taste receptors:
    • Sweet
    • Sour
    • Salty
    • Bitter
    • Umami
  • Olfactory receptor neurons are in the olfactory epithelium.
  • The sense of smell is closely tied to memory because of the proximity of the olfactory bulb to the memory center in the brain.