The Brain

Added October 2020

The mind is a product of the endocrine system, which releases hormones, and the nervous system. The peripheral nervous system includes the somatic nervous system, which enables voluntary control of our skeletal muscles, and the autonomic nervous system, which controls our heartbeat and digestion, including the stress response. The central nervous system, the body’s decision-maker, is composed of the brain and spinal cord.

Parts of the brain

The oldest parts of the brain are the brainstem (controls heartbeat and breathing), thalamus (hub for sensory information), reticular formation (linked to arousal), and cerebellum (“little brain”; coordinates movement, enables nonverbal learning and memory). The limbic system, between the oldest and newest brain areas, includes the amygdala (linked to emotion); the hypothalamus (linked to reward); and the hippocampus (processes explicit memories).

The upper brain is made up of the two hemispheres of the cerebrum, which are covered by the cerebral cortex (“bark”), and linked by the corpus callosum. Each hemisphere is divided into four lobes: frontal, parietal, occipital, and temporal.

The motor cortex, at the back of the frontal lobes, produces motor commands, while the somatosensory cortex, at the front of the parietal lobes, processes sensory information. The prefrontal cortex, in the frontal lobes, is associated with judgment and planning. However, many functions are not localized entirely to any one part of the brain, and most of the cerebral cortex is made up of uncommitted “association areas.”


The nervous system is made up of perhaps 40 billion neurons, which have trillions of connections between them. When a neuron is stimulated, it fires an electrical impulse, or action potential, to either excite or inhibit other neurons from firing. A neuron sends an impulse through its axons, which link to the dendrites of other neurons, separated by a tiny gap called a synapse. Neurotransmitter molecules cross this gap in order to unlock channels on the receiving neuron through which electrically charged atoms can enter.

How do we study the brain?

We study the brain using EEGs, and PET and MRI scans. An EEG is a readout of magnetic signals using electrodes on the subject’s head. A subject undergoing a PET scan is first fed radioactive glucose; the scanner then detects which parts of the brain consume the most of this glucose during particular tasks or stimuli. (The brain, though only 2% of the body’s mass, consumes 20% of its calorie intake.) An MRI scanner uses powerful magnets to align the spinning atoms in a person’s brain, then detects signals emitted by the atoms when they return to normal.

Resource: Myers and Dewall 2015