Rucete ✏ Campbell Biology In a Nutshell
Unit 7 ANIMAL FORM AND FUNCTION — Concept 49.4 Changes in Synaptic Connections Underlie Memory and Learning
Learning and memory arise from physical changes at synapses. During development, neurons compete for survival and form connections. After birth, these connections are refined through activity, and experiences continue shaping the nervous system throughout life via neuronal plasticity.
1. Nervous System Development and Synapse Elimination
- Neurons form in specific embryonic regions due to regulated gene expression and signal transduction
- They compete for growth-supporting factors; failed connections lead to programmed cell death
- Each neuron initially forms many synapses—more than necessary
- Synaptic pruning eliminates unused connections and refines networks
- This pruning continues into childhood and adolescence
2. Neuronal Plasticity
- Neuronal plasticity: remodeling of synapses based on activity
- Used synapses are strengthened; unused ones are weakened
- Plasticity changes either synapse number or signal strength
- Like adding/removing highway ramps to control neural traffic
- Disruption linked to autism spectrum disorder (ASD)
- ASD may involve impaired activity-dependent synapse remodeling
- No link exists between ASD and vaccines—claims have been debunked
3. Memory and Learning
- Short-term memory: uses hippocampus links for temporary storage
- Long-term memory: involves rewiring of cortical circuits, consolidated during sleep
- Hippocampus damage prevents new long-term memory formation
- Early Alzheimer’s often involves hippocampal degradation
4. Learning Types
- Associative memory: connects new info with existing memory (e.g., learning card games)
- Motor skills: learned by repetition (e.g., riding a bike)
- Declarative memory: facts like names and dates; forms quickly and involves synapse strength changes
5. Long-Term Potentiation (LTP)
- Strengthens synapses with frequent use; important for learning
- Discovered in hippocampus using glutamate
- Involves two receptor types:
- NMDA: normally blocked by Mg²⁺
- AMPA: inserted after NMDA activation
- Requires:
- Rapid presynaptic neuron firing
- Postsynaptic depolarization
- Results in more AMPA receptors, boosting future signal strength
- Stronger postsynaptic response can trigger action potentials more easily
In a Nutshell
Memory and learning arise from activity-dependent changes in synaptic strength and structure. During development, neurons are sculpted by pruning and survival signals. After birth, neuronal plasticity continues shaping brain function. Long-term potentiation (LTP) is a key cellular mechanism for memory, strengthening synapses in response to experience and forming the neural basis of learning.