Source: Chapter 2, Lecture slides
Tags: William James, neuron, glial cell, synapse, neuron doctrine, Golgi stain, Ramón y Cajal, vertebrate brain, cerebral cortex, sulci, gyri, cerebral lobes, meninges, CSF, Descartes, Galvani, nervous system evolution
This unit covers the basic building blocks of the nervous system (neurons, glia, synapses) and the gross anatomy of the brain (lobes, landmarks, views, slices). It traces the evolution of nervous system complexity across species and introduces key historical figures who shaped our understanding of neural structure and signalling.
William James
Pioneer of the modern scientific study of the mind. Wrote The Principles of Psychology (1890). Advocated studying the mind through behaviour, biology, and mental experience. His key insight: if nervous communication is cut off between brain and body, experience of those parts is lost; if the brain is injured, consciousness is altered even when every other organ is intact.
Neuron (nerve cell)
An electrically excitable cell that receives, processes, and transmits information through electrical and chemical signals. Estimated 100 billion neurons in the human brain. The cellular unit of signal transmission.
Sensory neuron
Responds to a specific type of stimulus (touch, sound, light) and converts it into an electrical signal via transduction, which is sent to the spinal cord or brain.
Motor neuron
Receives signals from the brain and spinal cord to cause muscle contractions and affect glandular outputs.
Interneuron
Connects neurons to other neurons within the same region of the brain or spinal cord, forming neural networks.
Glial cell (glia)
At least 100 billion in the human brain, making them the most abundant cell type in the CNS. They surround neurons, provide support and insulation, and are also involved in signalling (especially astrocyte glia).
Schwann cell
Produces myelin in the peripheral nervous system (PNS).
Oligodendrocyte
Produces myelin in the central nervous system (CNS), by wrapping around axons.
Synapse
A structure that permits a neuron to pass an electrical or chemical signal to another neuron or target cell. Chemical synapses use neurotransmitter molecules across a gap. Electrical synapses use channel proteins (gap junctions) that allow current to flow directly.
Neuron doctrine
Proposed by Santiago Ramón y Cajal. Neurons are discrete, autonomous entities that communicate with each other but are not physically continuous.
Reticular theory
Proposed by Camillo Golgi. Neurons do not function autonomously but rather as one large, interconnected network.
Golgi stain
A technique using silver chromate crystals to stain neurons completely, revealing minute structures. Only stains about 1% of neurons, but those it does stain become exquisitely visible, including dendrites and axons. Still not known why only some neurons take up the stain.
Cerebrum
The principal, most anterior part of the brain in vertebrates. Two hemispheres separated by a fissure. Integrates complex sensory and neural functions, coordinates voluntary activity. In birds and mammals, the cerebrum is proportionally larger than in fish, reptiles, and amphibians.
Cerebellum
Located at the back of the skull. Coordinates and regulates muscular activity. Also involved in motor control, attention, language, and regulation of fear and pleasure responses.
Brainstem
Central trunk of the mammalian brain: medulla oblongata, pons, and midbrain. Continues downward to form the spinal cord. Regulates cardiac and respiratory function, consciousness, sleep cycle, heart rate, breathing, and eating.
Cerebral cortex
The outer layer of neural tissue on the cerebrum. A highly folded structure with sulci (grooves) and gyri (bumps). If laid flat, roughly the size of a newspaper of varying thickness.
Sulci (singular: sulcus)
The grooves on the surface of the cerebrum.
Gyri (singular: gyrus)
The bumps or ridges on the surface of the cerebrum.
Corpus callosum
A broad band of approximately 200 million nerve fibres spanning the longitudinal fissure and connecting the two cerebral hemispheres.
Meninges
Three protective layers surrounding the brain: dura mater ("hard mother"), arachnoid, and pia mater ("soft mother"). Inflammation of the meninges is called meningitis.
Cerebrospinal fluid (CSF)
A liquid found in the subarachnoid space (between the arachnoid and pia layers) that cushions the brain and transports soluble substances through the CNS.
Gray matter
Cell bodies, found in the peripheral cortex.
White matter
Nerve fibres (axons) connecting regions of the cerebrum, covered in myelin.
Sponges: no nerve cells or nervous system at all
Cnidarians (Hydra): simple, loosely connected nerve net for basic signalling. Jellyfish are similar.
Roundworm (C. elegans): studied since the 1970s, only 302 neurons, but shows behavioural complexity (navigates using olfactory and thermal cues)
Planaria (flatworms): extended network of interconnected neurons with two clusters at the head (possibly a primitive brain)
Arthropods: insects have complex brains and complex behaviours (e.g. Drosophila fruit fly)
Molluscs/cephalopods: nervous system and intelligent brain (octopus, squid, cuttlefish)
The vertebrate brain develops from the neural tube in the embryo, which folds, closes off, and expands; the interior spaces become ventricles
Three main divisions:
Forebrain: cerebrum
Midbrain: optic tectum
Hindbrain: medulla, cerebellum, brainstem (medulla, pons, midbrain)
The cerebrum has characteristic bumps (gyri) and grooves (sulci) because it is highly folded
Sulci and gyri are seen in capybaras, dogs, cats, and all primates
Not seen in mice, rats, or squirrels
Occipital lobe: visual cortex
Parietal lobe: somatosensory cortex (touch)
Temporal lobe: auditory cortex, language, memory (hippocampus)
Frontal lobe: motor cortex, decision making, emotion, attention
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 right and left cerebral hemispheres
The boundary between occipital, temporal, and parietal lobes is less clearly defined
Dorsal (top), ventral (bottom), lateral (side), medial (inside, revealed by cutting along the longitudinal fissure)
Slices: coronal (front-to-back vertical), sagittal (side-to-side vertical), axial (horizontal)
Dura mater: tough, skin-like outer layer
Arachnoid: delicate middle layer
Pia mater: delicate layer closest to the brain
Meningitis: inflammation of the meninges due to infection, extremely serious
CSF sits in the subarachnoid space, cushions the brain, transports substances
Gray matter: cell bodies (cortex). White matter: myelinated nerve fibres connecting regions.
Andreas Vesalius: published De Humani Corporis Fabrica (1543), beautifully illustrated anatomical drawings from human dissections
René Descartes (1596–1650): early thinker on nervous system signalling, interested in perception, body-mind relations. Published Le Monde and L'Homme. Treatise on Man (1662) includes eye dissection drawings.
Luigi Galvani: Italian physician who found that frog legs twitch when electrically stimulated (published 1791). Hypothesised that muscles move via internal electrical forces triggered by external stimulation.
Camillo Golgi (1843–1926): developed the Golgi stain, proposed the reticular theory
Santiago Ramón y Cajal (1852–1934): used the Golgi stain to draw neurons in exquisite detail, proposed the neuron doctrine (neurons are discrete, autonomous, unidirectional)
Electrical synapses (gap junctions): fast, bidirectional, but cannot build highly compartmentalised systems
Chemical synapses: cells are electrically isolated, use neurotransmitters, allow for more complexity
Some neurotransmitters depolarise the postsynaptic cell, others hyperpolarise it
Some have transient effects (~1 ms), others are long-lasting (~100 ms)
Evolution favoured chemical synapses because they enable more complex, compartmentalised systems
Earth: ~4.6 billion years old
Oldest life: >3 billion years ago
Nervous systems: >600 million years ago
Homo sapiens: ~200,000 years ago
~600 million years ago, a proliferation of species occurred, enabling multicellular organisms
Nearly 99% of body mass: oxygen, carbon, hydrogen, nitrogen, calcium, phosphorus
Another ~0.85%: potassium, sulphur, sodium, chlorine, magnesium
All 11 are necessary for life; remaining elements are trace elements
⚠️ Know the difference between the neuron doctrine (Cajal) and reticular theory (Golgi), and who proposed each.
⚠️ Be able to match each cerebral lobe with its primary function (occipital = vision, parietal = touch, temporal = auditory/memory, frontal = motor/decision/emotion).
⚠️ Know the three meningeal layers in order from outside in: dura, arachnoid, pia.
⚠️ Understand why evolution favoured chemical synapses over electrical synapses (compartmentalisation, variable effects, complexity).
⚠️ Know which animals have sulci/gyri and which do not.
⚠️ Be able to distinguish the three brain slice orientations: coronal, sagittal, axial.
Q: What is the neuron doctrine, and who proposed it?
A: The neuron doctrine, proposed by Santiago Ramón y Cajal, states that neurons are discrete, autonomous entities that send signals unidirectionally to one another, rather than forming one continuous network.
Q: How many neurons and glial cells are estimated to be in the human brain?
A: Approximately 100 billion neurons and at least 100 billion glial cells.
Q: What are the three divisions of the vertebrate brain?
A: Forebrain (cerebrum), midbrain (optic tectum), and hindbrain (medulla, cerebellum, brainstem).
Q: Name the four cerebral lobes and one primary function of each.
A: Occipital (vision), parietal (somatosensory/touch), temporal (auditory, language, memory), frontal (motor cortex, decision making, emotion, attention).
Q: What is the corpus callosum?
A: A broad band of about 200 million nerve fibres connecting the two cerebral hemispheres across the longitudinal fissure.
Q: Why did evolution favour chemical synapses over electrical ones?
A: Chemical synapses allow electrically isolated cells, variable effects (depolarisation or hyperpolarisation), and both transient and long-lasting signalling, enabling more complex and compartmentalised nervous systems.
William James, neuron, nerve cell, glia, glial cell, astrocyte, Schwann cell, oligodendrocyte, myelin, synapse, chemical synapse, electrical synapse, gap junction, neuron doctrine, reticular theory, Golgi stain, Ramón y Cajal, Camillo Golgi, cerebrum, cerebellum, brainstem, forebrain, midbrain, hindbrain, cerebral cortex, sulcus, gyrus, corpus callosum, meninges, dura mater, arachnoid, pia mater, CSF, cerebrospinal fluid, gray matter, white matter, meningitis, Descartes, Galvani, Vesalius, C. elegans, Drosophila, MCB C61, UC Berkeley