Source: A Brain-Mind Odyssey, Ch. 2
Tags: nervous system, neurons, glia, cerebral cortex, brain anatomy, vertebrate brain, meninges, CSF, Descartes, Golgi, Ramón y Cajal, neuron theory, reticular theory, MCB C61
The nervous system is the body's network for rapid communication, built from neurons and glial cells. The human brain contains roughly 100 billion neurons and at least as many glia. This chapter covers brain anatomy (cerebrum, cerebellum, brainstem, cortex, meninges), the historical development of neuroscience from Descartes through Galvani to Golgi and Cajal, and the foundational debate between reticular theory and neuron theory.
Neuron (nerve cell)
The primary cellular unit of signal transmission in the nervous system. Components include dendrites (receive signals), a cell body (soma), an axon (transmits signals), and axon terminals (release neurotransmitters).
Glial cell (glia)
Non-neuronal cells in the brain, at least as numerous as neurons. Astrocyte glia are now known to be directly involved in signalling. Glia also provide structural support, insulation, and other functions.
Nervous system
A network within the body specialised for manipulating external and internal information and for rapid communication of signals throughout the body. The brain is its central control structure.
Cerebrum
The largest part of the brain. In many mammals, its surface is highly folded, producing bumps (gyri) and grooves (sulci).
Cerebral cortex
The outer layer of the cerebrum, roughly 3 mm thick in humans. If unfolded and laid flat, it would cover about 2.5 square feet, roughly the size of an opened small newspaper.
Gyri (singular: gyrus)
The bumps or ridges on the surface of the cerebrum, created by folding of the cortex.
Sulci (singular: sulcus)
The grooves or valleys between the gyri on the cerebral surface.
Cerebellum
A brain structure involved in motor coordination, located at the back of the brain beneath the cerebrum.
Brainstem
Collectively refers to the medulla, pons, and midbrain. Some definitions also include part or all of the diencephalon and the cerebellum.
Corpus callosum
A bundle of approximately 200 million nerve fibres connecting the right and left cerebral hemispheres.
Cerebral lobes
The four major divisions of each cerebral hemisphere: occipital, parietal, temporal, and frontal.
Meninges
Three protective membranes covering the brain: the dura mater (tough outer layer), the arachnoid (middle, web-like layer), and the pia mater (soft, innermost layer).
Cerebrospinal fluid (CSF)
A liquid found in the subarachnoid space (between the arachnoid and pia layers) that cushions the brain inside the skull and transports soluble substances throughout the central nervous system.
Meningitis
Inflammation of the meninges, typically caused by infection. Extremely serious because of the meninges' proximity to the brain.
Ventricles
Fluid-filled internal spaces in the brain, formed from the interior of the embryonic neural tube.
Animals need nervous systems to facilitate movement through the world
Collection and analysis of sensory information must be coordinated with the mechanisms of movement
Plants and fungi do not move in the animal fashion and have evolved non-neural ways to flourish
Caenorhabditis elegans (a nematode worm) has exactly 302 neurons, all of which have been mapped for location, connectivity, and developmental history
Despite its simplicity, C. elegans demonstrates behavioural sophistication, navigating soil using olfactory and thermal cues
All vertebrate brains share the same basic structure: forebrain, midbrain, hindbrain, and spinal cord
Vertebrate classes include fish, amphibians, reptiles, birds, and mammals
The vertebrate brain develops from a neural tube that folds, closes, and expands at one end
Interior spaces of the tube become the ventricles
Major divisions: cerebrum, cerebellum, brainstem
The diencephalon (thalamus and hypothalamus) sits between the cerebral cortex base and the midbrain
The cerebral cortex is a sheet of neural tissue, folded to fit inside the skull
The corpus callosum connects the two hemispheres via ~200 million nerve fibres
Four cerebral lobes per hemisphere: frontal, parietal, temporal, occipital
Beneath the skull lies the dura mater ("hard mother"), a tough skin-like sheet
Under the dura is the arachnoid ("like a spider web"), a delicate layer
Closest to the brain is the pia mater ("soft mother")
Between the arachnoid and pia is the subarachnoid space, filled with cerebrospinal fluid
CSF cushions the brain and transports soluble substances
William James (1890): wrote The Principles of Psychology, arguing that if nervous communication is severed between brain and body, the experiences of those parts are lost to the mind
Andreas Vesalius: published De Humani Corporis Fabrica (On the Fabric of the Human Body), a spectacularly illustrated anatomy text based on human dissections
René Descartes: key figure in Western philosophy and science, interested in how the body works, how we perceive the world, and how bodily actions relate to subjective mental experiences. Proposed mind-body dualism (res extensa and res cogitans), effectively setting the mind aside so science could focus on the physical world
Luigi Galvani (1737–1798): demonstrated that severed frog legs twitch when electrically stimulated, proposing that muscles move via internal electrical forces. Published his findings in 1791
Camillo Golgi: developed the Golgi stain (la reazione nera, "the black reaction") in 1873, which made neurons and their dendrites and axons visible under the microscope. Advocated reticular theory (the brain as a single continuous network)
Santiago Ramón y Cajal: used Golgi's stain to argue for neuron theory, proposing that neurons are discrete cells that receive and send signals in a consistent direction
Reticular theory (Golgi): the nervous system is a single continuous network of fused cells
Neuron theory (Cajal): the nervous system is composed of discrete individual cells (neurons) that communicate at junctions
Neuron theory prevailed and is the foundation of modern neuroscience
⚠️ Know the difference between reticular theory and neuron theory, and who championed each
⚠️ Be able to label the four cerebral lobes and define gyri vs. sulci
⚠️ The three meninges (dura, arachnoid, pia) and their order from outside in are commonly tested
⚠️ Understand why C. elegans is a model organism: fully mapped 302-neuron nervous system
⚠️ Descartes' dualism (res extensa / res cogitans) set the stage for modern scientific method by separating mind from body investigation
⚠️ Know that there are ~100 billion neurons and at least as many glia in the human brain
Q: How many neurons does C. elegans have, and why is this organism important for neuroscience?
A: 302 neurons. Every neuron's location, connectivity, and developmental history has been mapped, making it a key model for understanding nervous system function.
Q: What is the Golgi stain and what did it reveal?
A: A staining technique developed by Camillo Golgi in 1873 (la reazione nera) that made individual neurons, including their dendrites and axons, visible under the microscope.
Q: What is the difference between reticular theory and neuron theory?
A: Reticular theory (Golgi) held that the brain was a single continuous network. Neuron theory (Cajal) held that the brain is composed of discrete individual cells. Neuron theory is the accepted view.
Q: Name the three meninges from outermost to innermost.
A: Dura mater, arachnoid, pia mater.
Q: What is cerebrospinal fluid and where is it found?
A: CSF is a liquid found in the subarachnoid space (between the arachnoid and pia layers). It cushions the brain and transports soluble substances throughout the central nervous system.
Q: What did Descartes' dualism propose, and how did it shape the practice of science?
A: Descartes divided reality into res extensa (the extended material domain) and res cogitans (the mental/knowing domain). This encouraged scientists to set the mind aside and focus on investigating the physical world through mechanism, a practice that has shaped science ever since.
Q: Approximately how large is the human cerebral cortex if unfolded?
A: About 2.5 square feet, roughly the size of a small opened newspaper. It is approximately 3 mm thick.
neurons, glia, astrocytes, nervous system, cerebrum, cerebellum, brainstem, cerebral cortex, gyri, sulci, corpus callosum, meninges, dura mater, arachnoid, pia mater, CSF, cerebrospinal fluid, ventricles, William James, Descartes, dualism, Galvani, Golgi stain, Ramón y Cajal, reticular theory, neuron theory, C. elegans, vertebrate brain, MCB C61, PSYCH C61