31.1 The Neuron

The nervous system collects information about the body's internal and external environment, processes that information, and responds to it.

Nervous system impulses are transmitted by cells called neurons.

An impulse begins when a neuron is stimulated by another neuron or by the environment.

• peripheral nervous system (896)

• central nervous system (896)

• myelin sheath (897)

• resting potential (898)

• action potential (898)

• cell body (897)

• threshold (899)

• dendrite (897)

• synapse (900)

• axon (897)

• neurotransmitter (900)

31.2 The Central Nervous System

Each of the major areas of the brain—the cerebrum, cerebellum, and brain stem—are responsible for processing and relaying information.

The spinal cord is the main communication link between the brain and the rest of the body.

The brain reacts to excessive dopamine levels by reducing the number of receptors for the neurotransmitter. As a result, normal activities no longer produce the sensations of pleasure they once did.

• reflex (901)

• hypothalamus (903)

• cerebrum (902)

• cerebellum (903)

• cerebral cortex (902)

• brain stem (903)

• thalamus (903)

• dopamine (904)

31.3 The Peripheral Nervous System

The sensory division of the peripheral nervous system transmits impulses from sense organs to the central nervous system.

The motor division of the peripheral nervous system transmits impulses from the central nervous system to muscles or glands. The motor division is divided into the somatic nervous system and the autonomic nervous system.

• somatic nervous system (907)

• autonomic nervous system (908)

• reflex arc (907)

31.4 The Senses

Different sensory receptors in the body respond to touch, temperature, and pain.

Sensations of smell and taste are both the result of impulses sent to the brain by chemoreceptors.

Mechanoreceptors found in parts of the ear transmit impulses to the brain. The brain translates the impulses into sound and information about balance.

Vision occurs when photoreceptors in the eyes transmit impulses to the brain, which translates these impulses into images.

• taste bud (910)

• pupil (912)

• cochlea (911)

• lens (912)

• semicircular canals (911)

• retina (913)

• cornea (912)

• rods (913)

• iris (912)

• cones (913)

Think Visually Develop a graphic organizer to show the relationship between the different divisions of the nervous system.