AR

chapter 1 overview

Summary: Brain Adaptability & Nervous System Overview

1. Brain Cell Numbers & Adaptability

  • Human brain: ~86 billion neurons (Herculano-Houzel, 2009).

  • ~80% in the cerebellum, yet people missing a cerebellum can function relatively normally — sometimes undetected until adulthood.

  • Similar findings in individuals missing other large brain areas or the corpus callosum (main connection between hemispheres).

  • These cases show brain plasticity — other regions can compensate for damaged or missing areas.

Key takeaway: Unlike machines, the brain doesn’t depend on every part being intact to function. Removing major hardware from a computer/car disables it; in humans, neural networks can reorganize.

2. Brain Function Is Network‑Based

  • While certain functions localize to specific brain areas, most complex processes (learning, memory, reasoning, emotions) involve multiple, interconnected regions.

  • Functions are not strictly one-to-one with brain regions — networks overlap and can reorganize after injury.

  • Plasticity allows reassignment of functions to new regions when needed.

3. Defining the Nervous System

  • Still debated among neuroscientists/philosophers.

  • In simplest terms: input-output device responding to internal & external stimuli.

  • But also:

    • Anticipates, fine‑tunes responses.

    • Stores information short‑ and long‑term.

    • Maintains an internal model of the world to guide “educated guesswork” (Dr. David Eagleman).

  • Reality perception involves constant updating of this internal model from sensory and internal data.

4. Major Divisions

  • Central Nervous System (CNS): Brain + spinal cord (processing, integrating, command center).

  • Peripheral Nervous System (PNS): Nerves & ganglia outside CNS (sensory input to CNS; motor output from CNS).

  • Together: Receive/send, process, interpret, and regulate all behavior and physiology — from breathing to reasoning.

Key Points to Remember

  • The brain is resilient and adaptable; functions can be redistributed after damage.

  • Networked processing underlies most human cognitive and emotional life.

  • Plasticity differentiates brain function from mechanical systems.

  • Nervous system is more than stimulus-response — it anticipates and predicts.

  • Divided into CNS and PNS, which integrate to control all actions and thoughts.