The brain’s internal orgalllzation makes performances like the orchestra’s possible. Resembling Russian dolls that nest one inside another, the systems of the brain are organized with greater or lesser degrees of scale, but with the same principles.

At the brain’s behavioral level-the largest doll-humans carry out actions originating in the cortex. These behaviors include speech and written language.

At the next level, the microscopic, behavioral activity is processed by the sum of electrochemical signals pinging among the brain’s billions of neurons.

At a still smaller, molecular, level, behavior is influenced by the neurotransmitters that pass information across the synaptic clefts that separate individual neurons.

For communication to occur through, say, language, every level has to operate in harmony and virtually simultaneously. Electrochemical processes must pass information from neuron to neuron; neural pathways must interact; and those interactions must come together to create speech.


The very concept of the brain’s whole being greater than its parts continues throughout the nervous system. The body contains only one nervous system, but for purposes of study it often is divided into parts, each of which has smaller and smaller divisions.

Thanks to evolution's hard wiring for survival, gazelles in Botswana react without thinking when a lioness attacks.
Thanks to evolution’s hard wiring for survival, gazelles in Botswana react without thinking when a lioness attacks.

The nervous system’s two biggest parts are the central nervous system and the peripheral nervous system. The former consists of the brain and the spinal cord.

It interprets sensations and issues commands in the form of motor responses, which are based on current sensations, reflexes, and experiences. The peripheral consists mainly of the axons that branch out of the brain and spinal cord, carrying nerve impulses to and fro.

Spinal nerves send impulses to and from the spinal cord, while cranial nerves do the same for the brain itself. All cranial nerves terminate in the head and neck except for the vagus nerve, which extends into the chest and abdomen. Cranial nerves in the head include those that interact with eyes, ears, nose, and tongue.

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