Source: A Brain-Mind Odyssey, Chapter 2 | MCB C61, UC Berkeley
Tags: vertebrate brain, cerebrum, cerebellum, brainstem, cerebral cortex, sulci, gyri, corpus callosum, frontal lobe, parietal lobe, temporal lobe, occipital lobe, meninges, dura mater, arachnoid, pia mater, cerebrospinal fluid, CSF, meningitis, neural tube, Descartes, Galvani, Golgi stain, Ramón y Cajal, Vesalius
All vertebrate brains share a common three-part plan (forebrain, midbrain, hindbrain) that develops from the embryonic neural tube. In mammals the forebrain expands massively into the cerebrum, whose folded outer layer (the cerebral cortex) is divided into four lobes. The brain is protected by three membrane layers (meninges) and cushioned by cerebrospinal fluid. Key historical figures, from Descartes to Ramón y Cajal, progressively revealed the electrical and cellular nature of nervous system signalling.
Neural tube
The embryonic structure that folds in, closes off, and expands at one end to form the brain. Its three initial swellings become the forebrain, midbrain, and hindbrain.
Forebrain
The anterior division of the vertebrate brain. Dominated by the cerebrum in mammals. Expands dramatically across vertebrate evolution.
Midbrain
The middle division of the vertebrate brain. Contains the optic tectum. Part of the brainstem.
Hindbrain
The posterior division of the vertebrate brain. Includes the medulla and the cerebellum.
Brainstem
Collective term for the medulla, pons, and midbrain. Sits beneath the cerebrum and connects the brain to the spinal cord.
Cerebrum
The largest part of the mammalian brain, dominating the forebrain. Its relative size increases from older to more recent vertebrate lineages.
Cerebellum
A hindbrain structure involved in motor coordination. Sits at the back of the brain, beneath the cerebrum.
Cerebral cortex
The outer layer of the cerebrum. In many mammals it is highly folded rather than smooth.
Gyri (singular: gyrus)
The ridges or bumps on the surface of the cerebral cortex.
Sulci (singular: sulcus)
The grooves or furrows between gyri on the cerebral cortex.
Central sulcus
The landmark groove that separates the frontal lobe from the parietal lobe.
Lateral fissure (Sylvian fissure)
The groove that separates the temporal lobe from the frontal and parietal lobes.
Longitudinal fissure
The deep groove that divides the right and left cerebral hemispheres.
Corpus callosum
A bundle of approximately 200 million nerve fibres connecting the right and left cerebral hemispheres. The primary communication bridge between the two sides of the brain.
Cerebral lobes
The four divisions of the cerebral cortex: frontal, parietal, temporal, and occipital.
Meninges
The three protective membrane layers surrounding the brain: dura mater (outermost), arachnoid (middle), and pia mater (innermost).
Dura mater
The tough, skin-like outermost membrane covering the brain.
Arachnoid
The delicate middle membrane, sitting beneath the dura mater.
Pia mater
The innermost membrane, closely adherent to the brain surface.
Subarachnoid space
The gap between the arachnoid and pia mater layers. Filled with cerebrospinal fluid.
Cerebrospinal fluid (CSF)
A clear liquid that cushions the brain within the skull and transports soluble substances throughout the central nervous system.
Meningitis
Inflammation of the meninges, usually caused by infection. Extremely serious owing to the meninges' proximity to the brain.
Golgi stain (la reazione nera, the black reaction)
A staining technique developed by Camillo Golgi that makes neurons, including all their dendrites and axons, visible under the microscope. Stains only a random subset of neurons, which is what makes the dense tissue readable.
All vertebrates (fish, amphibians, birds, reptiles, mammals) share the same basic brain organisation.
The brain develops from the neural tube: the tube folds in, closes off, and expands at one end.
Three embryonic regions form and later expand into the mature brain:
Forebrain – dominated by the cerebrum
Midbrain – contains the optic tectum
Hindbrain – includes the medulla and cerebellum
Across vertebrate evolution, the cerebrum has grown proportionally larger relative to the rest of the brain.
The medulla, pons, and midbrain are collectively called the brainstem.
Connects the higher brain structures to the spinal cord.
Handles vital autonomic functions.
In many mammals the cerebrum's surface is folded rather than smooth.
The ridges are called gyri; the grooves are called sulci.
The outer layer of the cerebrum is the cerebral cortex, where much of higher-order processing occurs.
Three landmark grooves to know:
Central sulcus – separates the frontal lobe from the parietal lobe
Lateral fissure – separates the temporal lobe from the frontal and parietal lobes
Longitudinal fissure – divides the left and right cerebral hemispheres
A massive fibre bundle of roughly 200 million axons.
Connects the left and right cerebral hemispheres, enabling communication between them.
Frontal lobe – anterior, in front of the central sulcus
Parietal lobe – behind the central sulcus, above the lateral fissure
Temporal lobe – below the lateral fissure, on the side of the brain
Occipital lobe – at the very back of the brain
Three membranes wrap the brain in layers:
Dura mater (outermost) – tough, skin-like
Arachnoid (middle) – delicate
Pia mater (innermost) – delicate, directly on the brain surface
The subarachnoid space (between arachnoid and pia) is filled with cerebrospinal fluid.
Meningitis occurs when these membranes become inflamed, typically from infection. It is dangerous precisely because the meninges sit so close to brain tissue.
Clear liquid found in the subarachnoid space and the brain's ventricles.
Two main roles: cushions the brain inside the skull, and transports soluble substances throughout the central nervous system.
Andreas Vesalius
Physician who lived and taught in Italy.
Wrote De Humani Corporis Fabrica, containing some of the most detailed and beautiful anatomical drawings ever produced.
René Descartes
One of the earliest thinkers on signalling in the nervous system.
Central interest: perception. How do we sense the world, and how do physical sensations become subjective mental experiences?
Treatise on Man includes drawings of eye dissections and speculation on eye-to-brain connections.
Also wrote Le Monde (L'Homme).
Luigi Galvani
Studied the effects of electrical stimulation on animal muscles.
Proposed that muscles move through internal electrical forces that can be triggered by external electrical stimulation. This was an early step toward understanding the electrical basis of nervous system function.
Camillo Golgi
Demonstrated the elaborate interconnectivity of nerve cells in the brain.
Developed the Golgi stain (la reazione nera, the black reaction), which made neurons and all their dendrites and axons visible under the microscope.
The stain is inefficient (it labels only a random subset of neurons), but that sparseness is what makes the dense neural tissue interpretable.
Santiago Ramón y Cajal
Used and refined Golgi's staining technique to illustrate and map the brain in extraordinary detail.
His work was foundational to the neuron doctrine: the idea that the nervous system is made up of discrete individual cells rather than a continuous network.
Vertebrate brain organisation (anterior → posterior):
Forebrain (cerebrum) → Midbrain (optic tectum) → Hindbrain (medulla + cerebellum) → Spinal cord
Meningeal layers (outside → inside):
Skull → Dura mater → Arachnoid → Subarachnoid space (CSF) → Pia mater → Brain surface
Cerebral lobe boundaries:
Central sulcus: frontal | parietal. Lateral fissure: temporal | frontal + parietal. Longitudinal fissure: left hemisphere | right hemisphere.
⚠️ Know the three-part embryonic brain plan (forebrain, midbrain, hindbrain) and what each becomes in the mature brain. This comes up constantly.
⚠️ Be able to name each sulcus/fissure and the lobes it separates. Central sulcus (frontal from parietal), lateral fissure (temporal from frontal/parietal), longitudinal fissure (left from right hemisphere).
⚠️ The corpus callosum connects the hemispheres with approximately 200 million fibres. Know the number and its function.
⚠️ Meningeal layers from outside in: dura, arachnoid, pia. CSF sits in the subarachnoid space. Meningitis is inflammation of these layers.
⚠️ Golgi vs. Ramón y Cajal: Golgi developed the stain; Cajal used it to map the brain and support the neuron doctrine. Both shared the 1906 Nobel Prize. They are easy to confuse on exams.
⚠️ Galvani's contribution: establishing that the nervous system uses electrical signalling. His muscle experiments were the key evidence.
Q: What are the three embryonic divisions of the vertebrate brain, and what major structures does each give rise to?
A: Forebrain (becomes the cerebrum), midbrain (contains the optic tectum, part of the brainstem), and hindbrain (becomes the medulla and cerebellum).
Q: Name the three structures that collectively form the brainstem.
A: The medulla, pons, and midbrain.
Q: What is the central sulcus, and which lobes does it separate?
A: The central sulcus is a prominent groove on the cerebral cortex that separates the frontal lobe (anterior) from the parietal lobe (posterior).
Q: What is the corpus callosum, and approximately how many nerve fibres does it contain?
A: The corpus callosum is a fibre bundle connecting the right and left cerebral hemispheres. It contains approximately 200 million nerve fibres.
Q: List the three meningeal layers from outermost to innermost.
A: Dura mater (outermost), arachnoid (middle), pia mater (innermost).
Q: Where is cerebrospinal fluid found, and what are its two main functions?
A: CSF is found in the subarachnoid space (between the arachnoid and pia mater). It cushions the brain within the skull and transports soluble substances throughout the central nervous system.
Q: What was the Golgi stain, and why was it important despite being inefficient?
A: The Golgi stain (la reazione nera) was a technique developed by Camillo Golgi that made neurons, dendrites, and axons visible under the microscope. It stained only a random subset of neurons, but this sparseness was precisely what made the dense tissue readable, allowing researchers to trace individual cells.
Q: What did Luigi Galvani contribute to our understanding of the nervous system?
A: Galvani studied electrical stimulation of animal muscles and hypothesised that muscles move through internal electrical forces triggered by external stimulation. This was early evidence that the nervous system operates via electrical signalling.
Q: How did Ramón y Cajal build on Golgi's work?
A: Cajal used and refined Golgi's staining technique to produce detailed maps of the brain, providing evidence for the neuron doctrine: the idea that the nervous system consists of discrete individual cells rather than a continuous network.
vertebrate brain, neural tube, forebrain, midbrain, hindbrain, cerebrum, cerebellum, brainstem, medulla, pons, optic tectum, cerebral cortex, gyri, sulci, central sulcus, lateral fissure, longitudinal fissure, corpus callosum, frontal lobe, parietal lobe, temporal lobe, occipital lobe, meninges, dura mater, arachnoid, pia mater, subarachnoid space, cerebrospinal fluid, CSF, meningitis, Andreas Vesalius, De Humani Corporis Fabrica, René Descartes, Treatise on Man, Luigi Galvani, bioelectricity, Camillo Golgi, Golgi stain, la reazione nera, Santiago Ramón y Cajal, neuron doctrine, MCB C61, brain-mind odyssey