Nervous System — Reading Comprehension Lesson

Reading Passage

Nervous System

The nervous system is the body’s master control and communication network. It collects information from inside and outside the body, processes that information, and coordinates the body’s responses. The nervous system controls voluntary actions (like walking, writing, and speaking), involuntary functions (like heartbeat, breathing, and digestion), thought, memory, emotion, and sensation. The nervous system is divided into two main parts: the central nervous system (CNS), consisting of the brain and spinal cord, and the peripheral nervous system (PNS), consisting of all the nerves that branch out from the CNS to the rest of the body.

The basic unit of the nervous system is the neuron, or nerve cell. Neurons are specialized cells designed to transmit electrical signals called nerve impulses. A neuron consists of a cell body, short branching extensions called dendrites that receive signals from other neurons, and a long fiber called an axon that transmits signals to other neurons or to muscles and glands. Axons can be very short or extremely long — the axon of a single neuron can extend from the spinal cord all the way to the tip of the toes. Many axons are coated in a fatty insulating layer called myelin that greatly speeds up signal transmission.

The brain is the most complex organ in the body and the command center of the nervous system. It is divided into several regions with specialized functions. The cerebrum, the largest part, is responsible for conscious thought, voluntary movement, language, memory, and sensory processing. It is divided into two hemispheres, each controlling the opposite side of the body. The cerebellum at the back of the brain coordinates movement, balance, and posture. The brainstem, at the base of the brain, controls vital automatic functions like breathing, heart rate, blood pressure, and swallowing. The brain contains about 86 billion neurons, each connected to thousands of others, forming a network of staggering complexity.

The spinal cord is a column of nervous tissue that runs from the brainstem down through the spine, serving as the main communication highway between the brain and the body. Nerves branch off from the spinal cord and extend to every part of the body. The spinal cord also controls reflex arcs — automatic responses to stimuli that bypass the brain for speed. When you touch something painfully hot and immediately pull your hand away before you are consciously aware of the pain, that is a spinal reflex. The signal travels only as far as the spinal cord before the motor response is initiated, saving precious fractions of a second. Damage to the spinal cord can interrupt communication between the brain and body, causing paralysis below the point of injury.

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