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

• White = superposition of all frequencies.

Gam

ma

rays

X-r

ays

Ultr

a-vi

olet

rays

Infr

ared

rays

Rad

ar

Bro

adca

stba

nds

AC

circ

uits

Visiblelight

Violet Red

Higherenergy

LowerenergyWavelength (nm)

Figure by MIT OCW.

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. 3rd ed. New York: Wiley, 1999. ISBN: 047130932X.

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.

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 MichaelA. Paradiso. Neuroscience: Exploring the Brain.2nd 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. 2nd 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. 2nd 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. 2nd 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. 2nd ed. Baltimore, Md.: Lippincott Williams & Wilkins,2001. ISBN: 0683305964.

Refraction by the cornea

Figure by MIT OCW. After figure 9.7 in: Bear, Mark F., Barry W. Connors, and Michael A. Paradiso.Neuroscience: Exploring the Brain. 2nd ed. Baltimore, Md.: Lippincott Williams & Wilkins, 2001.ISBN: 0683305964.

Focal Distance

Refractive Power (Dlopters)

Focal Distance (m)

Accommodation

Figure by MIT OCW. After figure 9.8 in: Bear, Mark F., Barry W. Connors, and Michael A. Paradiso.Neuroscience: Exploring the Brain. 2nd ed. Baltimore, Md.: Lippincott Williams & Wilkins, 2001.ISBN: 0683305964.

Visual field

Figure by MIT OCW. After figure 9.9 in: Bear, Mark F., Barry W. Connors, and Michael A. Paradiso.Neuroscience: Exploring the Brain. 2nd ed. Baltimore, Md.: Lippincott Williams & Wilkins, 2001.ISBN: 0683305964.

Retinal images are inverted.

Visual angle

Figure by MIT OCW. After figure 9.10 in: Bear, Mark F., Barry W. Connors,and Michael A. Paradiso. Neuroscience: Exploring the Brain. 2nd ed.Baltimore, Md.: Lippincott Williams & Wilkins, 2001. ISBN: 0683305964.

• Distance on the retina corresponds to visual angle.

• 20/20 vision= resolution of 1/12 degree

Retinal circuitryOutput

Ganglion cell axonsProjecting to forebrain

Amacrinecell

Bipolarcell

Horizontalcell

Direct pathway

Ganglion cells

Photoreceptors

Input

Figure by MIT OCW. After figure 9.11 in: Bear, Mark F., Barry W. Connors, andMichael A. Paradiso. Neuroscience: Exploring the Brain. 2nd ed.Baltimore,Md.: Lippincott Williams & Wilkins, 2001. ISBN: 0683305964.

Laminar organization

Figure by MIT OCW. After figure 9.12 in: Bear, Mark F., Barry W. Connors, and Michael A. Paradiso.Neuroscience: Exploring the Brain. 2nd ed. Baltimore, Md.: Lippincott Williams & Wilkins,2001. ISBN: 0683305964.

Ganglion Cell Layer

Inner Plexiform Layer

Inner Nuclear Layer

Outer Plexiform Layer

Outer Nuclear Layer

Layer of Photoreceptor Outer Segments

Pigmented Epithelium

Rods and cones

Figure by MIT OCW. After figure 9.13 in: Bear, Mark F., Barry W. Connors, and Michael A.Paradiso. Neuroscience: Exploring the Brain. 2nd ed. Baltimore, Md.: Lippincott Williams & Wilkins,2001. ISBN: 0683305964.

Cell bodies

Scotopic/nightVision 1000 x moreLight sensitive

photoreceptor

Synapticterminals

Inner segments

Photopic/day visionColor vision

Outer segments

ConePhoto-recepto

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., BarryW. Connors, and Michael A. Paradiso. Neuroscience: Exploring the Brain. 2nd ed. Baltimore, Md.:Lippincott Williams & Wilkins, 2001. ISBN:0683305964.

Fovea in cross section

Figure by MIT OCW. After figure 9.15 in: Bear, Mark F., Barry W. Connors, and Michael A. Paradiso.Neuroscience: Exploring the Brain. 2nd ed. Baltimore, Md.: Lippincott Williams & Wilkins, 2001.ISBN: 0683305964.

Lateral displacement of ganglion cells at fovea improves acuity

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. 2nd ed. Baltimore, Md.: Lippincott Williams & Wilkins,2001. ISBN: 0683305964.

Response to light

• Dark current due to open sodium channels

• Light depletes cGMP, 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. 2nd ed. Baltimore, Md.: Lippincott Williams & Wilkins,2001. ISBN: 0683305964.

Rhodopsin photoactivation

Figure by MIT OCW. After figure 9.18 in: Bear, Mark F., Barry W. Connors, and Michael A. Paradiso.Neuroscience: Exploring the Brain. 2nd ed. Baltimore, Md.: Lippincott Williams & Wilkins, 2001.ISBN: 0683305964.

Opsin has seven transmembrane alpha helices, like other GPCRs

Signaling cascade

Images removed due to copyright reasons. Please see figures 9.19 a and b in: Mark F. Bear, BarryW. Connors, Michael A. Paradiso. Neuroscience: Exploring the Brain. 2nd ed. Baltimore, Md.:Lippincott Williams & Wilkins, 2001. ISBN: 0683305964.

Chemical amplification

• Each rhodopsin activates many G-proteins

• Each PDE converts many cGMPs

• 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).