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Lecture IX. Brain Pathways: Sensation Bio 3411 Wednesday September 29, 2010 September 29, 2010 Lecture IX. Brain Pathways: Sensation 1 What the last lecture was about Spinal Cord Peripheral Nerves Spinal Nerves Spinal Reflexes Introduction to Pathways September 29, 2010 Lecture IX. Brain Pathways: Sensation 2 “Readings” (background only) Neuroscience 4th ed Page(s) 207 231 253 289 313 343 363 381 Feature Touch Pain Eye Central Visual Pathways Auditory Function Vestibular Function Olfactory receptors Taste buds & receptors Page(s) 182-183 186-187 41, 45 192-193 196-197 198-199 194-195 190-191 Feature Dorsal Column/Medial Leminscus – Touch & Position Spinothalamic Tract – Crude touch, Pain & Temperature Brain stem showing optic pathway Visual Pathways Auditory Pathways Vestibular Pathways Olfactory Pathways Taste Pathways The Brain Atlas 3rd ed September 29, 2010 Lecture IX. Brain Pathways: Sensation 3 References †Cox, J. J., Reimann, F., Nicholas, A. K., Thornton, G., Roberts, E., Springell, K., Karbani, G., Jafri, H., Mannan, J., Raashid, Y., Al-Gazali, L., Hamamy, H., Valente, E. M., Gorman, S., Williams, R., McHale, D. P., Wood, J. N., Gribble, F. M., & Woods, C. G. (2006). An SCN9A channelopathy causes congenital inability to experience pain. Nature, 444(7121), 894-898. †Goodwin, G. M., McCloskey, D. I., & Matthews, P. B. (1972). Proprioceptive illusions induced by muscle vibration: contribution by muscle spindles to perception? Science, 175(28), 1382-1384. †Mogil, J. S., Yu, L., & Basbaum, A. I. (2000). Pain genes?: natural variation and transgenic mutants. Annu Rev Neurosci, 23, 777-811. †Thyrion, C., & Roll, J-P. (2009) Perceptual integration of illusory and imagined kenesthetic images. J Neurocsci, 29(26):8483-8492. _________________ †(pdfs on course websites: [http://artsci.wustl.edu/~bio3411/] & [http://www.nslc.wustl.edu/courses/Bio3411/bio3411.html] September 29, 2010 Lecture IX. Brain Pathways: Sensation 4 What the last lecture was about: Spinal Cord - Segmental organization Peripheral Nerves - Compound action potential (Erlanger & Gasser Prix Nobel 1944) Spinal Nerves - Dermatomes, motor neuron pools (nuclei) and motor units Spinal reflexes - stretch (knee jerk); withdrawal/ crossed extensor Introduction to Pathways - 1 sensory (DC-ML); 1 motor (CST) September 29, 2010 Lecture IX. Brain Pathways: Sensation 5 Overview Sensation Sensory Transduction Receptive Fields Adaptation Feature Detection Maps September 29, 2010 Lecture IX. Brain Pathways: Sensation 6 Charles Scott Sherrington Edgar Douglas Adrian 1857 – 1957 1889 – 1977 (Prix Nobel 1932) (Prix Nobel 1932) September 29, 2010 Lecture IX. Brain Pathways: Sensation 7 The Five Senses • Touch: e.g., fine, muscle/position, pain • Smell: e.g., odorants, “taste”, opposite sex • Taste: bitter, sweet, sour, salt, ?(glutamate/umami) • Hearing/Balance: e.g., frequency & amplitude; linear & angular acceleration • Sight: light/dark, color (chromatic) September 29, 2010 Lecture IX. Brain Pathways: Sensation 8 Domains • Exteroception vs Interoception • Distance vs Direct September 29, 2010 Lecture IX. Brain Pathways: Sensation 9 Sensory Transduction • Single fiber recording (E. Adrian, Prix Nobel 1932) • Transduction is the conversion of a relevant physical stimulus into altered membrane potential, the currency of the nervous system. • Stimuli: – radiant – light and thermal – mechanical – pressure and sound – chemical – molecules and ions September 29, 2010 Lecture IX. Brain Pathways: Sensation 10 General Scheme for Sensory Transduction Interaction with Cell Conductance Change Stimulus Na+ Na+Na+ + Na Na+ Na+ Na+ Na+ Receptor Potential Neural Activation September 29, 2010 Lecture IX. Brain Pathways: Sensation 11 Transducers • Direct: by neurons • Mediated: by extensions, cell filters, receptor cells, complex organs • Code: onset, duration, intensity, change September 29, 2010 Lecture IX. Brain Pathways: Sensation 12 Touch “Receptors” in Skin There are many different kinds of sensory endings in the skin. They are relatively more sensitive to movement (amplified by the lever of a hair (B)), vibration, light pressure, pain, temperature etc. September 29, 2010 Lecture IX. Brain Pathways: Sensation 13 September 29, 2010 Lecture IX. Brain Pathways: Sensation 14 Photoreceptors in Eye - Sight The sensors in the eye contain “visual pigments” that change chemically when exposed to light of different colors and intensities. Photoreceptors sensitive to red, blue and green are called cones (C) while those sensitive to low light levels are rod like (R). September 29, 2010 Lecture IX. Brain Pathways: Sensation 15 Hair Cells in Ear The sensors in the ear are modified “touch” receptors. Sound causes the membrane on which these “hair cells” (because they have cell protrusions that look like hairs) rest to move and this causes the hairs to bend. When the hairs bend the hair cells depolarize and release transmitter to activate the sensory nerve endings. September 29, 2010 Lecture IX. Brain Pathways: Sensation 16 With respect to neurons: • Threshold (the magnitude of a stimulus sufficient to depolarize the sensory neuron) • Adequate Stimulus (the form of energy to which a particular sensory cell is most sensitive - light, touch, sound, etc.) • Law of specific nerve energies (depolarization of neurons in a pathway is interpreted as a particular form of stimulation - pressure to the eyes or direct electrical activation of the visual cortex are both interpreted as a change in light) September 29, 2010 Lecture IX. Brain Pathways: Sensation 17 Thresholds by Location The threshold to pressure differs over the body. The lips and the ends of the fingers are most sensitive. In part, this reflects different innervation densities (higher in the fingers and lips). Similar differences innervation density associated with high acuity vision and speech sounds are found in the eye and the ear respectively. September 29, 2010 Lecture IX. Brain Pathways: Sensation 18 Thresholds by Fiber Type The thresholds to mechanical force (mbars) differ for endings associated with different fiber sizes. Smaller forces activate myelinated faster conducting fibers (A - b) while greater forces are required to activate unmyelinated C and thin myelinated slower conducting fibers (A -d). September 29, 2010 Lecture IX. Brain Pathways: Sensation 19 Receptive Fields • Mainly about change • Tuning and fidelity • Organization - orientation, direction September 29, 2010 Lecture IX. Brain Pathways: Sensation 20 Receptive Fields - Endings Single sensory neurons innervating the hand have different receptive fields depending on the kind of ending they are associated with. These different endings (here named for famous guys in Italy or Germany) respond to very localized stimulation (Meissner & Merkel) or to more widely placed stimuli (Pacini and Ruffini). September 29, 2010 Lecture IX. Brain Pathways: Sensation 21 Receptive Fields - Retina (Center/Surround) The neurons projecting from the eye to the rest of the brain (ganglion cells) respond stimuli in the center of their receptive fields by increasing depolarization (which will increase firing) while stimuli in the periphery of the receptive field will hyperpolarize them (which will make the cell less likely to fire). The cell fires best when the stimulus covers only the central excitatory part of the receptive field as shown in the histogram at the bottom. September 29, 2010 Lecture IX. Brain Pathways: Sensation 22 Receptive Fields - Visual Cortex (Orientation & Length) A neuron in the visual cortex that responds best to stimuli of a particular lengths, in a particular orientation, moving in a particular direction at a prefered speed. (The bar in A is the right length. The one in B is too long and the cell fires less.) September 29, 2010 Lecture IX. Brain Pathways: Sensation 23 General Scheme for Neuron “Adaptation” Sensory Neuron Rapidly Adapting Rapidly/ Slowly Adapting Slowly Adapting September 29, 2010 Lecture IX. Brain Pathways: Sensation 24 Sensation September 29, 2010 Lecture IX. Brain Pathways: Sensation 25 Maps • Somatotopic, Visuotopic, Tonotopic, etc. • All Levels • Distortions ≈ innervation density September 29, 2010 Lecture IX. Brain Pathways: Sensation 26 Dorsal Column – Medial Lemniscus Pathway This pathway carries fine discriminative and active touch, body and joint position, and vibration sense. September 29, 2010 Lecture IX. Brain Pathways: Sensation 27 THE BRAIN ATLAS, 3rd ed, p 185 Face Hand Body Foot September 29, 2010 Lecture IX. Brain Pathways: Sensation 28 This is a sketch of the left cerebral hemisphere of a monkey brain. The body parts to which neurons in the cerebral cortex of the monkey best respond are organized in 2 systematic maps (Sm I and Sm II) in the parietal lobe. September 29, 2010 Lecture IX. Brain Pathways: Sensation 29 The whiskers on the mouse’s face are innervated by sensory neurons that project to a pathway ending in the somatosensory cortex. In sections parallel to the surface of the cortex, simple stains show a “visible” map of the whiskers and easily identify groups of cells which fire when the homologous whisker is moved. September 29, 2010 Lecture IX. Brain Pathways: Sensation 30 Visual Pathways These pathways convey visual information for recognizing scenes and objects, directing gaze, controlling light levels on the retina, and modulating body function with changes in the length of the day. September 29, 2010 Lecture IX. Brain Pathways: Sensation 31 THE BRAIN ATLAS, 3rd ed, pp. 192-193 Eye Optic nerve Hypothalamus Optic chiasm Optic Tract Pretectum Lateral geniculate nucleus Optic Radiation Superior Colliculus (Optic Tectum) Visual Cortex September 29, 2010 Lecture IX. Brain Pathways: Sensation 32 Innervation of Visual Cortex from One Eye (via LGN) The axons to the visual cortex of monkeys that represent one eye are separate from those from the other eye. A technique was used that labeled axons from one eye. The image above cuts through the thickness of the visual cortex showing patches; the one below was reconstructed from sections cut in the plane of the cortex showing that the patches above are actually stripes (ocular dominance stripes). September 29, 2010 Lecture IX. Brain Pathways: Sensation 33 The map of the visual world (right) onto the visual cortex of the monkey (dark area in the box to the left). September 29, 2010 Lecture IX. Brain Pathways: Sensation 34 Orientation Map in the Monkey Visual Cortex (Optical Imaging) The different colors represent areas responding to bars of light in different parts of the visual field in different orientations as indicated in the key on the left of the figure. September 29, 2010 Lecture IX. Brain Pathways: Sensation 35 The 6th Sense September 29, 2010 Lecture IX. Brain Pathways: Sensation 36 Motor Unit - A motor neuron and the muscle fibers it innervates. September 29, 2010 Lecture IX. Brain Pathways: Sensation 37 September 29, 2010 Lecture IX. Brain Pathways: Sensation 38 Demonstration September 29, 2010 Lecture IX. Brain Pathways: Sensation 39 September 29, 2010 Lecture IX. Brain Pathways: Sensation 40 Loss of myelin in dorsal columns in late stage Syphilis – Tabes Dorsalis September 29, 2010 Lecture IX. Brain Pathways: Sensation 41 Two Clinical Findings in Tabes Dorsalis: 1)Difficulty walking over uneven surfaces in the dark. 2)Reduced or absent knee jerk reflexes. September 29, 2010 Lecture IX. Brain Pathways: Sensation 42 What this Lecture was About Sensory Transduction Receptive Fields Adaptation Feature Detection Maps Sensory Integration September 29, 2010 Lecture IX. Brain Pathways: Sensation 43 END September 29, 2010 Lecture IX. Brain Pathways: Sensation 44