PSYC 380 Week 1 DB Forum 1 Example

Discussion Board Forum 1: Thread and Two Replies

PSYC 380 Physiological Psychology, Discussion Board Forum 1 (thread and two replies)

Thread by [Student Name]

The prompt and the classmates' posts are composites standing in for the course's own forum; the textbook and the two journal articles are real and described from their published sources; the requirements follow Liberty's public course guide for PSYC 380.

Thread

Open almost any older introduction to the brain and you will read of a hundred billion nerve cells, outnumbered tenfold by glia. Both figures sound precise, but neither came from a direct count of a whole brain. Earlier estimates multiplied cell densities in small samples of tissue by the volume of each region, an approach that can go badly wrong because density varies so much from place to place; the cerebellum alone packs neurons far more tightly than the cortex above it.

Herculano-Houzel (2009) described a different method. Instead of counting cells in thin slices, her group dissolved brain tissue into a uniform suspension of free cell nuclei, stained them and counted samples of the suspension, then used a marker found only in neurons to separate neurons from other cells. When the method was applied to adult human brains, the neuron total came to roughly 86 billion, and the other cells, glia included, turned out to be about as numerous, so the ratio sits near one to one, not ten to one. She also reported that the cerebral cortex holds only about 19% of the brain's neurons, a share similar to other mammals.

The number matters less than what glia do. Carlson (2014) explains that astrocytes provide physical and nutritional support to neurons and clean up debris, oligodendrocytes form the myelin sheaths around axons in the central nervous system, and microglia serve as the brain's immune cells. Allen and Barres (2009) argued that glia had been treated for too long as passive filler. They described evidence that astrocytes help form and remove synapses, regulate blood flow and influence how strongly synapses transmit signals, so that brain function depends on partnerships between neurons and glia.

Classmates: which other textbook number would you most like to see checked against a direct measurement?

Reply to Dana

Dana, you mentioned that we use only 10% of our brains, which is one of the most persistent myths about the brain. Carlson (2014) describes how damage to almost any region produces some deficit, which would not happen if most of the brain were idle. Imaging studies also show activity across the whole brain over the course of a day, even during sleep. There is also an energy argument: the brain uses roughly a fifth of the body's resting energy, and an organ that costly would not have evolved with nine tenths of its tissue unused. The myth may survive because it offers hope that we have hidden potential, but learning works by strengthening connections among cells we already use.

Reply to Marcus

Marcus, you suggested that humans are smarter than other animals because our brains are bigger. Herculano-Houzel (2009) found something more interesting. Brain size alone is a poor guide, because rodent and primate brains follow different scaling rules; a rodent brain enlarged to human size would hold far fewer neurons than ours. Among primates, whose brains pack neurons economically, the human brain is simply the largest, so it contains the most neurons. Elephants have bigger brains, yet she argued that neuron number, not mass, may be the better measure. Carlson (2014) would add that connections and glial support matter too, so counting cells is a start, not a full explanation of what a brain can do.

References

Allen, N. J., & Barres, B. A. (2009). Glia: More than just brain glue. Nature, 457(7230), 675-677. https://doi.org/10.1038/457675a

Carlson, N. R. (2014). Foundations of behavioral neuroscience (9th ed.). Pearson.

Herculano-Houzel, S. (2009). The human brain in numbers: A linearly scaled-up primate brain. Frontiers in Human Neuroscience, 3, Article 31. https://doi.org/10.3389/neuro.09.031.2009