11: Sensory Perception #

Sensation #

Detection and capacity to respond to some signal; Property of all living organism

• Microorganisms can detect and respond to physical stimuli
  • Chemotaxis (reaction to chemicals, i.e sugar) has been observed in ecoli through movement by ‘swimming’ with runs and tumbles
• Phototaxis: Moving toward light (e.x. bacteria)
• Phototropism: Bending towards light (e.x. plant)

Perception #

The experience of said a signal; constructive process occurring with our nervous system

• Depends on…
  • ..what is ‘out there’ (objective; profound assumption)
  • ..processing that occurs in our brain/mind
  • ..physics of our sensory receptors (can also be out of our range of sensation)
    • Visible light is just the range (~400 - 700 nm) of light we can sense on the electromagnetic spectrum
      • These colors or not objective and is a product of our human body
      • No reason to assume aliens would perceive them similarly
    • Ultraviolet is below (shorter) our range, infrared is above (longer)
      • Increasing wavelength, decreasing energy
      • These are clearly there, but we are unable to experience them (perceive them)
• Naive realism: Common sense theory of perception; what we experience is what there is - Illusions can easily disprove this

Animals #

• Karl von Frisch asked how to honeybees see flowers colors?
  • Colors one sugar-sample blue; bees routinely came back to it
    • Only possible if they could see color; impossible if they say black-and-white
    • Discovered that bees communicated information to hive mates
  • Received Nobel Prize in 1973 for said research
    • Only prize awarded thus far for behavioral work
  • Some flowers also have a UV ’landing-guide’
• Pit vipers can view infrared
  • ‘Images’ similar to our eyes in their nostril
  • Enables them to hunt in complete darkness
  • Animals emit heat which can be seen by them

Light #

Can be thought of as vibrating wave; posses wavelength, velocity, energy (amplitude), and polarization (the plane in which wave is propagating)

• Light from sun is unpolarized and varies with position in sky
  • Bees, ants, beetles, and other insects are able to perceive this
  • Enables them to navigate their environment form this
• Polarized filters only allow certain planes through
• Water also acts as a filter

Audition #

• We can hear~ 20-20,000 hertz (vibrations per second)
• Elephants, pigeons, dolphins, whales are able able to hear low frequency noises < 10 Hz
• Bats, dolphins, whales, moths can hear >50,000 Hz
  • Use as a bio-sonar to practice echolocation
    • Sonar = sound navigation and ranging

Electroreception #

• Ability to sense electric fields
• Occurs passively (only detecting, not producing) in sharks
  • Shown in study in 60s by showing sharks find/eat buried fish that they can otherwise no sense (smell)
  • Fish have some field due to their nervous system, creating a field
    • Field is especially strong in water
    • Can sense this to feel it’s surroundings – active electroreception
• Platypus also has this capacity
  • Bill has electroreceptors
  • Used to detect bioelectric fields of invertebrate prey
  • Also passive
• Magnetic field detection
  • Earth produces a magnetic field everywhere
  • Birds, Fish, sea turtles, bees, and many other animals posses this, use to navigate
    • Pigeons are taken from home then released
      • Overcast days inhibit a birds ability to orient themselves (versus a nice, sunny day)
  • We don’t really know how!

12: Nose and Smell #

Olfaction #

Our ability to sense volatile molecules, resulting in smell

• Olfactory receptor cells are found in the nasal cavity, extending nerve fibers containing olfactory receptor proteins
  • Proteins are GPCRs
  • Fish have ~ 100 gene types
  • Mammals have ~ 1000 gene types
  • Mice have ~ 1300 gene types
  • Humans have ~ 350 gene types (with ~ 650 nonfunctional pseudogenes)
    • We can still discriminate ~100,000 odors
• Cilia are the ‘fingers’ that extend out, increasing the surface area
  • They arise from a mucus layer which helps molecules stick
• Signals are then generated and sent through the olfactory bulb in the brain
  • One path goes to thalamus, orbitofrontal cortex
    • Standard route
    • Involved in identification
  • Second path goes to amygdala, temporal cortex, hypothalamus (limbic system)
    • Associated with emotional response
    • Causes innate reaction
• Olfactory stem cells replace dying cells often - We smell a lot of chemicals that may harm/cause error in our existing receptor cells

Aromatic Odor #

The flavor component of plants; the ’essence’ of the plant (from ’esse’, to be)

• Essential oil (i.e perfumes, spices) are concentrates (often through distillation) are made up of numerous aromatic molecules
• Small changes in the composition of these molecules results in radically different sensations
  • Stick slightly differently to GPCRs receptors

• Thiols indicate sulfur
  • Stinky! Found in skunks and ‘asparagus smell’ in urine
  • Not everyone can smell this though, there are genetic differences
    • Anosmia – Specific: deficit in specific gene change in olfactory GPCR, the case here
    • Anosmia – General: deficit occurs at a higher level of perception

Pheromones #

Chemicals used for intraspecies social communication

• Found in insects and some vertibraes
  • Rodents have an vomeronasal organ (VMO) and pathway in vertebrate animals for pheromone detection
• Used for territorial marking, sex, social status, identity, mate attraction
• Some of these chemicals are found in nature as well
• It appears us humans have a vestigial VMO that’s not active
  • Menstrual synchrony in women is thought to be mediated by subtle aromatics
  • Sexual attraction is speculated to be partially mediated by human leukocyte antigen genes
  • Tears carry several molecules as well that may contribute as well

13: Tongue and Taste #

• Taste buds are made up of..
  • Microvilli, adjacent to cilia, that increase surface area
  • Stem cells gustatory cells to replenish cells
  • Taste receptor cells fall into these types with the associated proteins:
    1. Salt: ion channel sensitive to Na+
    2. Sour: acidic, ion channel sensitive to H+
    3. Bitter: Group of ~30 different GPCR receptors
       • Variety of molecules are bitter, typically poisonous
    4. Sweet: GPCR heterodimer receptor; sucrose/fructose/glucose/stevioside (~300x sweeter than sucrose!)
    5. Umami: ‘Savory’; glutamate
• Gustatory neural pathways are analogous to their olfaction counterparts..
  • (Identification) Tongue to brainstem to thalamus to insula + somatosensory cortex
  • (Reaction/emotion) Tongue to brainstem to hypothalamus + amygdala
• Capsicum annum: Chili pepper
  • Capsaicin: Molecular component associated with ‘hotness’
    • Same receptor protein (TRPV1 receptor; Ca++ channel) is also activated with heat
    • All over our skin as well as tongue
    • TRPA1 activated by mustard, horseradish, wasabi
      • How pit vipers see heat (infared)! Wow
    • TRPV1 activated by (crushed) garlic
• Menthol: ‘Cool’ mint sensation; Opposite than capsicum
  • Activates Ca++ channels to cause cell depolarization
  • Menthol receptor (TRPM8) also activated by cold temperatures
• These TRP ion channels are tetramer (4 proteins) subunits surrounding a Ca++ channel
• Flavor is the amalgamation of taste, smell, pungency, texture, and other qualities (metallic, fatty)

14: Eyes and Vision #

• The human eye, like all vertebrate eyes, contain the…
  • Retina: Photosensitive material
    • Photoreceptor cells:
      • Rods: Ideal for dim light, nighttime
        • Most responsive at 498 nm wavelength
        • Most concentrated around fovea, with none at the fovea itself; ‘donut’
      • Cones: Ideal for colorful, bright light
        • Multiple types; S at 420nm, M at 530nm, L at 560nm
        • The amalgamation of these 3 enables color
        • Most concentrated at the fovea, and drop off rapidly
    • Retinal achromatopsia: loss of color perception, due to loss of cones
    • Retinal (vitamin A) absorbs light of the right wavelength, changes via Photoisomerization from cis (bent) to trans (straight), altering the amino acid, activating a GPCR receptor to hyperpolarize
      • Retinal needs beta-carotene (from carrots, etc.)
    • Retina: bipolar cells, ganglion cells
    • Retina: horizontal cells, amacrine cells
  • Fovea: Where the light is directly focused, in the center
    • Latin “pit”
    • Where our vision is best
  • Blind spot: Where all the axons come bundled together
    • No rods nor cones
• Receptive field: the region of space from which a stimulus elicits a neural response
• From the retina, the signal goes to the diencephalon containing the thalamus where the Lateral Geniculate Nucleus (LGN) parses the information, then onto the visual cortex (occipital, posterior parietal, posterior temporal lobes)
  • Visual cortex (V1-5) are areas maps to the visual world
  • Basically, nearly every cortex is connected bidirectionally to every other cortex
• Disordrs
  • Scotoma: Dark region, blind spot in certain region; due to lesion in V1 - Hemianopia: blindness of one hemisphere
  • Cortical achromatopsia: Loss of color, sometimes confined to only a certain region; Lesion in V4
  • Superior colliculus: Loss of ability to see color; Lesion in V5
  • Prosopagnosia: difficulty in recognizing faces; due to fusiform gyrus; spectrum condition
  • Agnosia: difficulty in recognizing objects