2017-09-13 15:42:03

Announcements

  • Quiz 1 Friday
    • 13 questions/15 points
    • Take-home, take 30 min

Today's Topics

  • Cells of the nervous system
    • Glia
    • Neurons

Visualizing the microanatomy of the brain

Crowd-sourcing anatomy research with EyeWire

How many neurons and glia?

  • Old "lore": ~100 billion neurons
  • New estimate (Azevedo et al. 2009):
    • ~86 +/- 8 billion neurons
    • 85 +/- 9 billion glia

How many neurons and glia?

"These findings challenge the common view that humans stand out from other primates in their brain composition and indicate that, with regard to numbers of neuronal and nonneuronal cells, the human brain is an isometrically scaled-up primate brain."

(Azevedo et al. 2009)

Mass, Neurons, Non-Neurons

Neurons by brain mass

Non-neuronal cells by brain mass

brain %>% ggplot() +
  aes(x=mass_g, b_nonneurons, color=portion) +
  geom_point() +
  xlab("Mass in g") +
  ylab("Billions of cells")

The Human Advantage

Could you count to 170 billion?

  • How many years to count to 170 billion?
  • 60 s/min * 60 min/hr * 24 hrs/day * 365 days/ yr = 31,536,000 s/yr
  • 1e11/31,536,000 = 5,390 years

Glia (neuroglia)

  • Functions
    • Structural support
    • Metabolic support
    • Brain development

Astrocytes

  • "Star-shaped"
  • Most numerous cell type in CNS
  • Physical and metabolic support
    • Blood/brain barrier
    • Ion (Ca++/K+) buffering
    • Neurotransmitter (e.g., glutamate) buffering
    • Regulate local blood flow

Astrocytes

Astrocytes

Myelinating cells

  • Oligodendrocytes
    • In brain and spinal cord (CNS)
    • 1:many neurons
  • Schwann cells
    • In PNS
    • 1:1 neuron
    • Facilitate neuro-regeneration

Oligodendrocytes

Schwann Cells

Microglia

  • Phagocytosis
  • Clean-up damaged, dead tissue
  • Role in 'pruning' of synapses in normal development

Microglia

What makes neurons "special"?

  • Long-lived (most generated b/w 3-25 weeks gestational age)
  • Extended branching (dendrites and axons)
  • Electrically excitable
  • Connect to small #s of other cells via synapses
  • Release neurotransmitters

Macrostructure of neurons

  • Dendrites
  • Soma
  • Axons
  • Terminal buttons (boutons)

Structure of neurons

Dendrites

  • Majority of input to neuron
  • Passive vs. active
  • Spines

Dendrites

Dendritic Spines

Soma (cell body)

  • Varied shapes
  • Nucleus
    • Chromosomes
  • Organelles
    • Mitochonrdria
    • Smooth and Rough Endoplasmic reticulum (ER)

Soma

Axons

  • Initial segment
  • Nodes of Ranvier
  • Terminals

Axons

Synaptic bouton (terminal button)

  • Synapse (~5-10K per neuron)
  • Pre and postsynaptic membranes
  • Synaptic cleft
  • Synaptic vesicles
    • Store/release neurotransmitters
  • Autoreceptors & transporters

Synaptic bouton (terminal button)

Classifying neurons

  • Functional role
    • Input (sensory), output (motor/secretory), interneurons
  • Anatomy
    • Unipolar
    • Bipolar
    • Multipolar

Branching types

Classifying neurons

  • By specific anatomy
    • Pyramidal cells
    • Stellate cells
    • Purkinje cells
    • Granule cells

Neurons by type

Morphology, physiology, gene transcription

Next time

  • Quiz 1 (available after class)
  • Neurophysiology

References

Azevedo, Frederico AC, Ludmila RB Carvalho, Lea T Grinberg, José Marcelo Farfel, Renata EL Ferretti, Renata EP Leite, Roberto Lent, Suzana Herculano-Houzel, and others. 2009. “Equal Numbers of Neuronal and Nonneuronal Cells Make the Human Brain an Isometrically Scaled-up Primate Brain.” Journal of Comparative Neurology 513 (5). Wiley Online Library: 532–41. doi:10.1002/cne.21974.

Chung, Won-Suk, Christina A. Welsh, Ben A. Barres, and Beth Stevens. 2015. “Do Glia Drive Synaptic and Cognitive Impairment in Disease?” Nature Neuroscience 18 (11): 1539–45. doi:10.1038/nn.4142.