Brain Biology Lecture Notes: Neurons, Synapses, Pruning, Synaptogenesis, and Schema
Course Context and Learning Orientation
The class has had scheduling challenges: Day Friday section and starting on Wednesday, with Tuesday/Thursday and Wednesday/Friday sections; two sections this week and one, causing coordination difficulties. The instructor plans to cover most material today and finish next Wednesday.
The brain biology lecture stands alone but is foundational for this course; Tuesday/Thursday content will be integrated later in fall break week.
The session begins with a 60-second paired discussion about an image to engage students emotionally (limbic system) as a learning trigger.
Neurons: Anatomy and Basic Function
A neuron is the basic cell of the brain; the key parts are:
Dendrite
Cell body (which includes the nucleus)
Axon (long projection)
Synaptic terminals (referred to as synapses in quizzes)
The image shown is not required to be replicated; it is used to highlight the four main parts and their roles.
Focus word: dendrite (receives neurotransmitters from previous neurons).
The four pieces to know and understand: cell body, nucleus, axon, synapses.
The neuron’s arrangement is relevant to understanding thought and learning as a network of electrochemical processes.
When we say “thought,” we mean a series of electrochemical reactions triggered by sensory input and processed in the brain.
How Neurons Work: Transmission of Signals
A thought or sensation begins when a stimulus is detected (e.g., sensory input like touch on the arm).
Nerve cells translate sensory information into an electrochemical signal that travels along a chain of neurons.
The electrical impulse travels down the axon and, when it reaches the synapse, triggers the production and release of neurotransmitters.
Neurotransmitters cross the synapse and bind to receptors on the next neuron’s dendrites, initiating a new electrical impulse in that neuron.
This cycle continues across many neurons to produce perception, memory, and thought.
Analogy: electricity flowing along an axon is paralleled by chemical signaling (neurotransmitters) at the terminal end.
Neurotransmitters discussed include serotonin and cortisol; some people may take prescriptions to modulate these chemicals.
The process emphasizes that your thoughts and actions are the result of thousands of electrical impulses and chemical signaling.
Neurochemistry: Neurotransmitters and Signaling
Neurotransmitters are chemicals released at the end of the neuron into the synapse.
They are detected by neighboring neurons via dendrites, which then generate new electrical impulses.
Examples of neurotransmitters mentioned: serotonin and cortisol.
The presence or absence of these chemicals can be influenced by medications or personal health conditions, affecting mood, stress, and cognition.
Brain Plasticity: Pruning and Synaptogenesis
Pruning (synaptic pruning) refers to the loss of neurons and synapses that are not frequently used.
Peak neuron number happens early in life; by about age two, the brain begins to prune away unused connections as it prioritizes commonly used pathways.
Increased use strengthens connections: more dendrites and synaptic terminals develop, reducing the distance neurotransmitters must travel and speeding signaling.
Repetitive use leads to a massively stronger and more complex neural path for frequently exercised skills and behaviors (e.g., smiling when fed reinforces that pathway).
The principle: use it, build it; use it less, it withers away (neural pruning) to make room for other functions (neural reallocation).
Synaptogenesis is the process of creating new synapses in response to new information, enabling learning and adaptation.
The brain’s neural structure is dynamic and shaped by experience: new information can create new neural pathways; neglected information gets pruned to free resources.
A note on interpretation: in everyday life, gun ownership discussions illustrate how neural networks around concepts like guns can reflect prior experiences and training; environments that emphasize certain beliefs shape the neural schema for related ideas.
Schema: Mental Models and Neural Organization
A schema is a neural model or organized network surrounding a concept; it governs how we interpret new information and experiences.
Schemas are sources of bias, but also of expertise and wisdom; they guide interpretation and reasoning.
When a concept is invoked (e.g., civil war, baseball, chess), our brains automatically activate a set of associated emotions, beliefs, facts, and memories, which can differ between individuals.
The idea that schema guides perception explains why people with different backgrounds can have productive but divergent viewpoints in discussion.
The “baseball” and “chess” analogy shows how related concepts activate overlapping neural networks, illustrating how schemas are interconnected.
The schema around a topic acts as a filter for information, influencing how new data is received and interpreted.
When discussing controversial topics, it’s common to experience conflicts in viewpoint due to differing schemas and emotional associations.
A practical exercise: compare two people’s schemas about civil war by having them describe what comes to mind when they hear the term, then compare the resulting associations to highlight differing perspectives.
Plato’s mug metaphor is used to illustrate how even simple concepts are bounded by our schema.
Assimilation vs Accommodation: Integrating New Ideas
When a person encounters a new idea, there are two possible outcomes regarding their schema:
Assimilation: the new information fits into the existing schema with minimal modification.
Accommodation: the new information challenges the existing schema, requiring modification or restructuring of the schema.
Assimilation example: new research aligns with an existing belief about Civil War causes, causing only a slight adjustment to the schema.
Accommodation example: new evidence contradicts a long-held belief about Civil War causes, prompting major schema revision; this process can be uncomfortable but is essential for growth.
The instructor uses analogies to illustrate the difference:
Doctor/Dad model (assimilation) vs Borg collective (accommodation) to show how some processes resist change versus how others disrupt and reorganize identities.
A practical demonstration: if a teacher asserts a specific interpretation of slavery as a primary cause, students might assimilate if it aligns with their schema, or accommodate if it conflicts with their established understanding and evidence.
The “mug” analogy (Plato) reinforces that even simple concepts are constrained by our schema, which can limit or empower understanding.
Application to Learning and Discussion
Before engaging with new material or opinions, pause to consider your own schema around the concept.
When a new idea arrives, ask: Does it fit my current schema (assimilation) or does it force me to adjust my schema (accommodation)?
When challenging beliefs, recognize the emotional component of belief and be prepared for cognitive discomfort as schemas are revised.
The discussion goal is understanding and growth, not simply proving a point or erasing someone else’s beliefs.
Quick Facts and Activity Reminders
Provocative images in learning can engage the limbic system, triggering emotional arousal that helps learning and memory.
Attendance and grading policies were discussed in the session; important to note for planning but not the primary learning content.
Neurological development considerations: significant neural growth occurs early in life; by around age two, pruning accelerates, refining neural networks that are frequently used.
Takeaways: Linking Neurobiology to Learning and Society
Learning is underpinned by neural plasticity: synaptogenesis builds new connections when we encounter new information, and pruning removes unused connections.
Repetition and practice strengthen neural pathways, making recall and task performance faster and more efficient.
Our schemas influence how we interpret new ideas and engage in dialogue; recognizing this can improve communication and reduce conflict.
Ethical and practical implications: understanding schemas can inform education, policy debates, and ways to engage constructively with others who hold different viewpoints.
The biology of learning supports educational strategies that encourage deliberate practice, exposure to diverse perspectives, and reflective discussion to foster accommodation where appropriate.