Neuroscience Cellular and molecular neuroscience Neuroanatomy Systems neuroscience

The astonishing hypothesis • • • Perception Thought Emotion Memory Consciousness • Material processes

Perception • • • Where physics meets psychology Vision Hearing Touch Etc.

Light • Photon energy = Planck’s constant x frequency • Wavelength x frequency =

Electromagnetic spectrum Visible light Violet Higher energy Red Wavelength (nm) Figure by MIT OCW.

Why is “visible” where it is? • Notch in water absorption spectrum • “Visible”

Reflection and absorption • Lightness - Dark objects absorb more than light ones •

$Refraction Figure by MIT OCW.$

Functions of the eye • Forming a stable image on the retina • Emphasizing

Gross anatomy of the eye Figure by MIT OCW. After figure 9. 4 in:

Opthalmoscopic view Image removed due to copyright reasons. Please see figure 9. 5 in:

Blind spot demo Figure by MIT OCW. After Box 9. 1 in: Bear, Mark

Filling in Figure by MIT OCW. After Box 9. 1 in: Bear, Mark F.

Cross-sectional anatomy Figure by MIT OCW. After: Bear, Mark F. , Barry W. Connors,

$Refraction by the cornea Focal Distance Refractive Power (Dlopters) Focal Distance (m) Figure by$

Accommodation Figure by MIT OCW. After figure 9. 8 in: Bear, Mark F. ,

Visual field Retinal images are inverted. Figure by MIT OCW. After figure 9. 9

Visual angle • Distance on the retina corresponds to visual angle. • 20/20 vision=

Retinal circuitry Ganglion cell axons Projecting to forebrain Output Direct pathway Ganglion cells Amacrine

Laminar organization Ganglion Cell Layer Inner Plexiform Layer Inner Nuclear Layer Outer Plexiform Layer

Rods and cones Synaptic terminals Cell bodies Inner segments Scotopic/night Vision 1000 x more

Spatial organization • Photoreceptors less dense in periphery • Ratio of photoreceptors to ganglion

Fovea in cross section Lateral displacement of ganglion cells at fovea improves acuity Figure

Neurotransmission and phototransduction Figure by MIT OCW. After figures 9. 16 a and b

Response to light • Dark current due to open sodium channels • Light depletes

Rhodopsin photoactivation Opsin has seven transmembrane alpha helices, like other GPCRs Figure by MIT

Signaling cascade Images removed due to copyright reasons. Please see figures 9. 19 a

Chemical amplification • Each rhodopsin activates many G-proteins • Each PDE converts many c.

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Neuroscience • Cellular and molecular neuroscience • Neuroanatomy • Systems neuroscience

The astonishing hypothesis • • • Perception Thought Emotion Memory Consciousness • Material processes in vast networks of neurons • “You’re nothing but a pack of neurons. ”

Perception • • • Where physics meets psychology Vision Hearing Touch Etc.

Light • Photon energy = Planck’s constant x frequency • Wavelength x frequency = speed of light Wavelength Amplitude Figure by MIT OCW.

Electromagnetic spectrum Visible light Violet Higher energy Red Wavelength (nm) Figure by MIT OCW. Lower energy AC circuits Broadcast bands Radar Infrared rays Ultra-violet rays X-rays Gamma rays • White = superposition of all frequencies.

Why is “visible” where it is? • Notch in water absorption spectrum • “Visible” light is what is available in the ocean. • Evolution has exploited this fact. Image removed due to copyright reasons. Please see figure on page 291 in: Jackson, John David. Classical Electrodynamics. 3 rd ed. New York: Wiley, 1999. ISBN: 047130932 X.

Reflection and absorption • Lightness - Dark objects absorb more than light ones • Color - Frequency-dependent absorption Reflection Absorption Figure by MIT OCW.

$Refraction Figure by MIT OCW.$

Refraction Figure by MIT OCW.

Functions of the eye • Forming a stable image on the retina • Emphasizing spatial and temporal differences in images

Gross anatomy of the eye Figure by MIT OCW. After figure 9. 4 in: Bear, Mark F. , Barry W. Connors, and Michael A. Paradiso. Neuroscience: Exploring the Brain. 2 nd ed. Baltimore, Md. : Lippincott Williams & Wilkins, 2001. ISBN: 0683305964.

Opthalmoscopic view Image removed due to copyright reasons. Please see figure 9. 5 in: Bear, Mark F. , Barry W. Connors, and Michael A. Paradiso. Neuroscience: Exploring the Brain. 2 nd ed. Baltimore, Md. : Lippincott Williams & Wilkins, 2001. ISBN: 0683305964.

Blind spot demo Figure by MIT OCW. After Box 9. 1 in: Bear, Mark F. , Barry W. Connors, and Michael A. Paradiso. Neuroscience: Exploring the Brain. 2 nd ed. Baltimore, Md. : Lippincott Williams & Wilkins, 2001. ISBN: 0683305964. Further reading: V. S. Ramachandran and S. Blakeslee, Phantoms in the Brain

Filling in Figure by MIT OCW. After Box 9. 1 in: Bear, Mark F. , Barry W. Connors, and Michael A. Paradiso. Neuroscience: Exploring the Brain. 2 nd ed. Baltimore, Md. : Lippincott Williams & Wilkins, 2001. ISBN: 0683305964. Moral: perception is an active process. “Seeing is believing. ” “Believing is seeing. ”

Cross-sectional anatomy Figure by MIT OCW. After: Bear, Mark F. , Barry W. Connors, and Michael A. Paradiso. Neuroscience: Exploring the Brain. 2 nd ed. Baltimore, Md. : Lippincott Williams & Wilkins, 2001. ISBN: 0683305964.

$Refraction by the cornea Focal Distance Refractive Power (Dlopters) Focal Distance (m) Figure by$

Refraction by the cornea Focal Distance Refractive Power (Dlopters) Focal Distance (m) Figure by MIT OCW. After figure 9. 7 in: Bear, Mark F. , Barry W. Connors, and Michael A. Paradiso. Neuroscience: Exploring the Brain. 2 nd ed. Baltimore, Md. : Lippincott Williams & Wilkins, 2001. ISBN: 0683305964.

Accommodation Figure by MIT OCW. After figure 9. 8 in: Bear, Mark F. , Barry W. Connors, and Michael A. Paradiso. Neuroscience: Exploring the Brain. 2 nd ed. Baltimore, Md. : Lippincott Williams & Wilkins, 2001. ISBN: 0683305964.

Visual field Retinal images are inverted. Figure by MIT OCW. After figure 9. 9 in: Bear, Mark F. , Barry W. Connors, and Michael A. Paradiso. Neuroscience: Exploring the Brain. 2 nd ed. Baltimore, Md. : Lippincott Williams & Wilkins, 2001. ISBN: 0683305964.

Visual angle • Distance on the retina corresponds to visual angle. • 20/20 vision= resolution of 1/12 degree Figure by MIT OCW. After figure 9. 10 in: Bear, Mark F. , Barry W. Connors, and Michael A. Paradiso. Neuroscience: Exploring the Brain. 2 nd ed. Baltimore, Md. : Lippincott Williams & Wilkins, 2001. ISBN: 0683305964.

Retinal circuitry Ganglion cell axons Projecting to forebrain Output Direct pathway Ganglion cells Amacrine cell Bipolar cell Horizontal cell Photoreceptors Input Figure by MIT OCW. After figure 9. 11 in: Bear, Mark F. , Barry W. Connors, and Michael A. Paradiso. Neuroscience: Exploring the Brain. 2 nd ed. Baltimore, Md. : Lippincott Williams & Wilkins, 2001. ISBN: 0683305964.

Laminar organization Ganglion Cell Layer Inner Plexiform Layer Inner Nuclear Layer Outer Plexiform Layer Outer Nuclear Layer of Photoreceptor Outer Segments Pigmented Epithelium Figure by MIT OCW. After figure 9. 12 in: Bear, Mark F. , Barry W. Connors, and Michael A. Paradiso. Neuroscience: Exploring the Brain. 2 nd ed. Baltimore, Md. : Lippincott Williams & Wilkins, 2001. ISBN: 0683305964.

Rods and cones Synaptic terminals Cell bodies Inner segments Scotopic/night Vision 1000 x more Light sensitive Photopic/day vision Color vision Cone Photorecepto Outer segments photoreceptor Figure by MIT OCW. After figure 9. 13 in: Bear, Mark F. , Barry W. Connors, and Michael A. Paradiso. Neuroscience: Exploring the Brain. 2 nd ed. Baltimore, Md. : Lippincott Williams & Wilkins, 2001. ISBN: 0683305964.

Spatial organization • Photoreceptors less dense in periphery • Ratio of photoreceptors to ganglion cells higher in the periphery • Acuity is lower, sensitivity higher in the periphery Images removed due to copyright reasons. Please see figures 9. 14 a and b in: Bear, Mark F. , Barry W. Connors, and Michael A. Paradiso. Neuroscience: Exploring the Brain. 2 nd ed. Baltimore, Md. : Lippincott Williams & Wilkins, 2001. ISBN: 0683305964.

Fovea in cross section Lateral displacement of ganglion cells at fovea improves acuity Figure by MIT OCW. After figure 9. 15 in: Bear, Mark F. , Barry W. Connors, and Michael A. Paradiso. Neuroscience: Exploring the Brain. 2 nd ed. Baltimore, Md. : Lippincott Williams & Wilkins, 2001. ISBN: 0683305964.

Neurotransmission and phototransduction Figure by MIT OCW. After figures 9. 16 a and b in: Bear, Mark F. , Barry W. Connors, and Michael A. Paradiso. Neuroscience: Exploring the Brain. 2 nd ed. Baltimore, Md. : Lippincott Williams & Wilkins, 2001. ISBN: 0683305964.

Response to light • Dark current due to open sodium channels • Light depletes c. GMP, closing sodium channels Figure by MIT OCW. After figures 9. 17 a and b: Bear, Mark F. , Barry W. Connors, and Michael A. Paradiso. Neuroscience: Exploring the Brain. 2 nd ed. Baltimore, Md. : Lippincott Williams & Wilkins, 2001. ISBN: 0683305964.

Rhodopsin photoactivation Opsin has seven transmembrane alpha helices, like other GPCRs Figure by MIT OCW. After figure 9. 18 in: Bear, Mark F. , Barry W. Connors, and Michael A. Paradiso. Neuroscience: Exploring the Brain. 2 nd ed. Baltimore, Md. : Lippincott Williams & Wilkins, 2001. ISBN: 0683305964.

Signaling cascade Images removed due to copyright reasons. Please see figures 9. 19 a and b in: Mark F. Bear, Barry W. Connors, Michael A. Paradiso. Neuroscience: Exploring the Brain. 2 nd ed. Baltimore, Md. : Lippincott Williams & Wilkins, 2001. ISBN: 0683305964.

Chemical amplification • Each rhodopsin activates many G-proteins • Each PDE converts many c. GMPs • Detection of a single photon is possible! Further reading: B. Sakitt, Counting every quantum, J. Physiol. (London) 223: 131 -150, 1972. P. B Detwiler et al. , Engineering aspects of enzymatic signal transduction: photoreceptors in the retina, Biophys. J. 79: 2801 -17 (2000). R. W. Rodieck, The first steps in seeing, Sinauer (1998).