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Field notes · chapter 43

Sensory Systems

Rebuilt from the standard chapter outline — no photos available

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Check this chapter against your book. No photos of it exist in your folders, so these notes were rebuilt from the standard textbook outline rather than transcribed from your own pages.

Cram sheet

27 points
  1. Sensory transduction = converting stimulus energy into a change in membrane potential. Stimulus → receptor potential (graded) → if it reaches threshold, action potentials fire down a sensory neuron. Watch The Sensory System on YouTube, from Bozeman Science
  2. Perception happens in the brain, not the receptor. The brain uses the labeled line principle: it knows what a signal means from which neuron carried it, not from the signal itself. Press on your eyeball and you see light.
  3. Stimulus intensity is coded two ways: higher action-potential frequency, and recruitment of more receptors. Action potential size never changes — it is all-or-none. Watch Peripheral somatosensation | Organ Systems | MCAT | Khan Academy on YouTube, from khanacademymedicine
  4. Tonic receptors adapt slowly and keep firing (pain, proprioception — things you must not ignore). Phasic receptors adapt fast and stop firing (smell, light touch — you stop noticing your clothes). Watch Sensory adaptation | Processing the Environment | MCAT | Khan Academy on YouTube, from khanacademymedicine
  5. Receptor classes by stimulus: mechanoreceptors, chemoreceptors, thermoreceptors, photoreceptors, electroreceptors, nociceptors (pain). Watch Peripheral somatosensation | Organ Systems | MCAT | Khan Academy on YouTube, from khanacademymedicine
  6. Exteroceptors sense the outside world; interoceptors sense the body itself (proprioceptors, baroreceptors, internal chemoreceptors). Watch Peripheral somatosensation | Organ Systems | MCAT | Khan Academy on YouTube, from khanacademymedicine
  7. Hair cells are the mechanoreceptor behind hearing, balance, and the fish lateral line. Bending stereocilia toward the tallest one depolarizes; bending away hyperpolarizes. Watch 2-Minute Neuroscience: The Cochlea on YouTube, from Neuroscientifically Challenged
  8. Middle ear bone order — malleus → incus → stapes — then the stapes hits the oval window. They amplify because the tympanic membrane is much larger than the oval window. Watch Hearing & Balance: Crash Course Anatomy & Physiology #17 on YouTube, from CrashCourse
  9. Pitch is coded by place on the basilar membrane: the base is stiff and narrow → high frequency; the apex is wide and floppy → low frequency. Loudness is coded by amplitude. Watch Hearing & Balance: Crash Course Anatomy & Physiology #17 on YouTube, from CrashCourse Watch 2-Minute Neuroscience: The Cochlea on YouTube, from Neuroscientifically Challenged
  10. Balance: utricle and saccule (otoliths) detect gravity and linear acceleration; the three semicircular canals detect rotational/angular acceleration. Watch 2-Minute Neuroscience: Vestibular System on YouTube, from Neuroscientifically Challenged
  11. Five tastes: sweet, sour, salty, bitter, umami. Salty and sour act directly through ion channels; sweet, bitter, umami act through G-protein-coupled receptors. Watch Taste & Smell: Crash Course Anatomy & Physiology #16 on YouTube, from CrashCourse
  12. Smell is the only major sense that reaches the cortex without relaying through the thalamus first. Each olfactory neuron expresses one receptor type. Watch 2-Minute Neuroscience: Olfaction on YouTube, from Neuroscientifically Challenged Watch Taste & Smell: Crash Course Anatomy & Physiology #16 on YouTube, from CrashCourse
  13. Rods = many, super sensitive, no color, peripheral, night vision. Cones = fewer, need bright light, give color and sharp detail, packed in the fovea. Watch Photoreceptors (rods vs cones) | Processing the Environment | MCAT | Khan Academy on YouTube, from khanacademymedicine
  14. THE classic trick question: light hyperpolarizes photoreceptors. Light → retinal isomerizes → transducin → phosphodiesterase → cGMP falls → Na+ channels close → cell hyperpolarizes → less glutamate released. Watch 2-Minute Neuroscience: Phototransduction on YouTube, from Neuroscientifically Challenged
  15. Visual path: retina → optic nerve → optic chiasm → lateral geniculate nucleus of the thalamus → visual cortex in the occipital lobe. The optic disc has no photoreceptors — that is your blind spot. Watch Vision: Crash Course Anatomy & Physiology #18 on YouTube, from CrashCourse
  16. The vertebrate retina is wired "backwards": light passes through ganglion cells and bipolar cells before reaching the rods and cones at the very back. The signal then travels back out the way the light came in. Watch Vision: Crash Course Anatomy & Physiology #18 on YouTube, from CrashCourse
  17. Cone types are tuned to roughly blue 420 nm, green 530 nm, red 560 nm. Color is computed from the ratio of their responses, not from any one cone. Watch Photoreceptors (rods vs cones) | Processing the Environment | MCAT | Khan Academy on YouTube, from khanacademymedicine
  18. Rhodopsin = retinal (made from vitamin A) + the protein opsin. Vitamin A deficiency → night blindness, because rods fail first. Watch 2-Minute Neuroscience: Phototransduction on YouTube, from Neuroscientifically Challenged
  19. Red–green color blindness is X-linked recessive, so it is far more common in males. Watch Vision: Crash Course Anatomy & Physiology #18 on YouTube, from CrashCourse
  20. Skin receptors, fast-adapting vs slow: Meissner (light touch, fast) and Pacinian (deep pressure and vibration, very fast) vs Merkel (sustained touch, slow) and Ruffini (stretch, slow). Free nerve endings handle pain and temperature. Watch Overview of Sensation and Meissner's Corpuscle | NCLEX-RN | Khan Academy on YouTube, from khanacademymedicine
  21. Two-point discrimination measures receptor density — millimetres on a fingertip, centimetres on your back. Watch Overview of Sensation and Meissner's Corpuscle | NCLEX-RN | Khan Academy on YouTube, from khanacademymedicine
  22. Muscle spindles sit parallel to muscle fibers and sense stretch (knee-jerk reflex). Golgi tendon organs sit in tendons and sense tension (overload protection). Watch Neurology | Spinal Cord: Stretch Reflex | Muscle Spindle on YouTube, from Ninja Nerd
  23. The cochlea has three chambers: scala vestibuli, scala media (cochlear duct), scala tympani. The organ of Corti sits on the basilar membrane and its hair cells shear against the tectorial membrane. Watch 2-Minute Neuroscience: The Cochlea on YouTube, from Neuroscientifically Challenged
  24. The round window bulges to release the pressure wave; the Eustachian tube equalizes middle-ear pressure with the throat. Hair cells do not regenerate in mammals — noise damage is permanent. Watch Hearing & Balance: Crash Course Anatomy & Physiology #17 on YouTube, from CrashCourse
  25. Compound eyes (arthropods) are built from many ommatidia giving a mosaic image that is superb at detecting motion. Single-lens eyes evolved independently in vertebrates and cephalopods — classic convergent evolution. Watch Ancestral & Weird Senses: Crash Course Zoology #8 on YouTube, from CrashCourse
  26. Each olfactory neuron expresses just one of ~1000 receptor types, and all neurons sharing a receptor converge on one glomerulus. That combinatorial code lets a few hundred receptors distinguish thousands of odors. Watch 2-Minute Neuroscience: Olfaction on YouTube, from Neuroscientifically Challenged
  27. Beyond the human senses: pit organs (infrared, pit vipers), ampullae of Lorenzini (electric fields, sharks and rays), and magnetite-based magnetoreception in migrating birds and sea turtles. Watch Ancestral & Weird Senses: Crash Course Zoology #8 on YouTube, from CrashCourse