2017-09-20 08:12:47
Visualizing the microanatomy of the brain (4:29)
Announcements
- Exam 1 next Friday, 9/22
- 40 questions
Today's Topics
- Cells of the nervous system
- Glia
- Neurons
- How do these cells communicate?
How many neurons and glia?
- Old "lore": ~100 billion neurons
- New estimate (Azevedo et al. 2009)
- ~86 +/- 8 billion neurons
- ~85 +/- 9 billion glia
- 100-500 trillion synapses, 1 billion/mm^3
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."
Neurons by brain mass
Non-neuronal cells by brain mass
The Human Advantage
Glia (neuroglia)
- "Glia" means glue
- Functions
- Structural support
- Metabolic support
- Brain development
- Neural plasticity?
Astrocytes
- "Star-shaped"
- Physical and metabolic support
- Blood/brain barrier
- Ion (Ca++/K+) buffering
- Neurotransmitter (e.g., glutamate) buffering
Astrocytes
- Shape brain development, synaptic plasticity
- Regulate local blood flow
- Regulate/influence communication between neurons, (Bazargani and Attwell 2016)
- Disruption linked to cognitive impairment, disease (Chung et al. 2015)
Astrocytes
Myelinating cells
- Produce myelin or myelin sheath
- White, fatty substance
- Surrounds many neurons
- The "white" in white matter
- Provide electrical/chemical insulation
- Make neuronal messages faster, less susceptible to noise
Types of myelin-producing 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
- Prune synapses in normal development and disease
- Disruptions in microglia pruning -> impaired functional brain connectivity and social behavior, (Zhan et al. 2014)
Microglia
Neurons
Fun facts about neurons
- Specialized for electrical & chemical communication
- Post-mitotic – don't divide
- Most born early in life, (Bhardwaj et al. 2006)
- Among longest-lived cells in body, may scale with organism lifespan (Magrassi, Leto, and Rossi 2013)
- Can extend over long distances
Macrostructure of neurons
Structure of neurons
Dendrites
- Branch-like "extrusions" from cell body
- Majority of input to neuron
- Cluster close to cell body/soma
- Usually receive info
- Passive (do not regenerate electrical signal) vs. active (regenerate signal)
- Spines
Dendrites
Dendritic Spines
Soma (cell body)
- Varied shapes
- Nucleus
- Chromosomes
- Organelles
- Mitochonrdria
- Smooth and Rough Endoplasmic reticulum (ER)
Soma
Axons
- Another branch-like "extrusion" from soma
- Extend farther than dendrites
- Usually transmit info
Axons
- Parts
- Initial segment (closest to soma, unmyelinated)
- Nodes of Ranvier (unmyelinated segments along axon)
- Terminals, axon terminals, terminal buttons, synaptic terminals, synaptic boutons
Axons
Synaptic bouton (terminal button)
- Synapse (~5-10K per neuron)
- Presynaptic membrane (sending cell) and postsynaptic (receiving cell) membrane
- Synaptic cleft – space between cells
- Synaptic vesicles
- Pouches of neurotransmitters
- Autoreceptors (detect NTs); transporters (transport NTs across membrane)
Synaptic bouton (terminal button)
Classifying neurons
- Functional role
- Input (sensory), output (motor/secretory), interneurons
- Anatomy
- Unipolar
- Bipolar
- Multipolar
Classifying neurons
- By specific anatomy
- Pyramidal cells
- Stellate cells
- Purkinje cells
- Granule cells
Neurons by type
Next time
- Neural communication
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.
Bazargani, Narges, and David Attwell. 2016. “Astrocyte Calcium Signaling: The Third Wave.” Nature Neuroscience 19 (2): 182–89. doi:10.1038/nn.4201.
Bhardwaj, Ratan D., Maurice A. Curtis, Kirsty L. Spalding, Bruce A. Buchholz, David Fink, Thomas Björk-Eriksson, Claes Nordborg, et al. 2006. “Neocortical Neurogenesis in Humans Is Restricted to Development.” Proceedings of the National Academy of Sciences 103 (33): 12564–8. doi:10.1073/pnas.0605177103.
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.
Magrassi, L., K. Leto, and F. Rossi. 2013. “Lifespan of Neurons Is Uncoupled from Organismal Lifespan.” Proceedings of the National Academy of Sciences 110 (11): 4374–9. doi:10.1073/pnas.1217505110.
Zhan, Yang, Rosa C. Paolicelli, Francesco Sforazzini, Laetitia Weinhard, Giulia Bolasco, Francesca Pagani, Alexei L. Vyssotski, et al. 2014. “Deficient Neuron-Microglia Signaling Results in Impaired Functional Brain Connectivity and Social Behavior.” Nature Neuroscience 17 (3): 400–406. doi:10.1038/nn.3641.