Preview
IB DP Biology — C: Interaction and Interdependence | SL | C3.1 Integration of Body Systems
📋 What You Will Learn
- Identify the structural components of a neuron and explain how their form relates to their function in signal transmission
- Explain how resting potential and action potential are generated and propagated along a neuron
- Describe synaptic transmission and explain how neurotransmitters mediate communication between neurons
- Explain how the nervous system integrates sensory input and coordinates motor output through reflex arcs and voluntary pathways
- Analyse data from nerve conduction studies and synaptic experiments to draw conclusions about nervous system function
- Apply understanding of nervous system integration to evaluate the effects of drugs, toxins, and disease on signal transmission
🔍 Guiding Question How does the nervous system integrate information from the environment and the body to produce coordinated responses, and what does this reveal about the relationship between structure and function at the cellular and systems level?
🌍 Why This Matters When a sprinter hears the starting pistol, their muscles contract within 150 milliseconds — faster than conscious thought. This is the nervous system operating at its most elegant: detecting a stimulus, integrating the signal, and generating a precisely coordinated motor response. Understanding how this works at the molecular level is fundamental to treating neurological disorders from Parkinson's disease to multiple sclerosis.
📋 What You Will Learn
- Identify the structural components of a neuron and explain how their form relates to their function in signal transmission
- Explain how resting potential and action potential are generated and propagated along a neuron
- Describe synaptic transmission and explain how neurotransmitters mediate communication between neurons
- Explain how the nervous system integrates sensory input and coordinates motor output through reflex arcs and voluntary pathways
- Analyse data from nerve conduction studies and synaptic experiments to draw conclusions about nervous system function
- Apply understanding of nervous system integration to evaluate the effects of drugs, toxins, and disease on signal transmission
The Problem the Nervous System Had to Solve
Imagine being a multicellular organism. You have trillions of cells, each doing something different — contracting, secreting, absorbing. The moment you need them to act together, you face an engineering problem: how do you send a signal fast enough, precisely enough, and with enough specificity to coordinate all of them? The nervous system is evolution's answer. It is a biological electrical network, capable of transmitting signals at speeds up to 120 metres per second, with exquisite specificity down to a single target cell.
The solution required a specialised cell type — the neuron — whose structure is inseparable from its function. Before we can understand how the nervous system integrates information, we need to understand the unit it is built from.
📖 Key Definition — Neuron A neuron is a specialised cell of the nervous system that is adapted to receive, integrate, and transmit electrical signals. Neurons are the structural and functional units of the nervous system.
Structure of a Neuron
Every neuron is a story of form following function. The cell body (soma) contains the nucleus and most of the metabolic machinery — it is the command centre. Branching from it are dendrites, short extensions that receive incoming signals from other neurons or sensory receptors. A single long projection, the axon, carries the signal away from the cell body toward the next neuron or effector. At its far end, the axon branches into axon terminals, which form the junctions with the next cell.
Dendrites
Dendrites are highly branched extensions of the cell body that dramatically increase the surface area available for receiving signals. A single motor neuron may receive input from thousands of other neurons simultaneously across its dendritic tree. This convergence of inputs is the physical basis of integration — the neuron must "decide" whether to fire based on the sum of all incoming signals.
Cell Body (Soma)
The soma contains the nucleus, rough endoplasmic reticulum (for protein synthesis), mitochondria, and ribosomes. It is the metabolic hub of the neuron. Crucially, it also performs integration — summing excitatory and inhibitory inputs arriving from dendrites to determine whether an action potential will be generated at the axon hillock.
Axon and Myelin Sheath
The axon is a single elongated projection that conducts the action potential away from