Chapter 31Chapter 31Nervous SystemNervous System

31.1 The Neuron31.1 The NeuronFunctions of the Nervous System

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

– The peripheral nervous system consists of nerves and supporting cells. It collects information about the body’s internal and external environment.

– The central nervous system consists of the brain and spinal cord. It processes information and creates a response that is delivered through the peripheral nervous system.

Neurons •Nervous system impulses are transmitted by cells called neurons. •The three types of neurons are sensory, motor, and interneurons. •All neurons have certain features:

– The cell body contains the nucleus and much of the cytoplasm.– Dendrites receive impulses from other neurons and carry impulses to the cell body.– The axon is the long fiber that carries impulses away from the cell body. In some

neurons, the axon is surrounded by an insulating membrane called the myelin sheath.

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The cell body contains the nucleus and much of the cytoplasm.Dendrites receive impulses from other neurons and carry impulses to the cell body.The axon is the long fiber that carries impulses away from the cell body. In some neurons, the

axon is surrounded by an insulating membrane called the myelin sheath.

31.2 The Central Nervous System31.2 The Central Nervous SystemThe Brain and Spinal Cord •The central nervous system consists of the brain and spinal cord.•Some kinds of information, including some reflexes, are processed directly in the spinal cord. •A reflex is a quick, automatic response to a stimulus.

• The largest region of the human brain is the cerebrum, which controls learning, judgment, and voluntary actions of muscles.

• The cerebrum is divided into right and left hemispheres. Each deals primarily with the opposite side of the body.

• The outer layer of the cerebrum is the cerebral cortex.

• It processes information from the sense organs and controls body movements

• The limbic system controls functions such as emotion, behavior, and memory.

• The thalamus receives messages from sensory receptors throughout the body and sends the information to the proper region of the cerebrum for processing.

• The hypothalamus controls the recognition and analysis of hunger, thirst, fatigue, anger, and body temperature. It helps coordinate the nervous and endocrine systems.

• The cerebellum is the second largest region of the brain. It receives information about muscle and joint position and coordinates the actions of these muscles.

• The brain stem connects the brain and spinal cord. It regulates the flow of information between the brain and the rest of the body.

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31.3 The Peripheral Nervous 31.3 The Peripheral Nervous SystemSystemThe Sensory Division

•The peripheral nervous system consists of all the nerves and associated cells that are not part of the brain or spinal cord. •It is made up of the sensory division and the motor division.•The sensory division transmits impulses from sense organs to the central nervous system.

Sensory receptors are cells that transmit information about changes in the internal and external environment.

– Chemoreceptors respond to chemicals.

– Photoreceptors respond to light.– Mechanoreceptors respond to touch,

pressure, vibrations, and stretch.– Thermoreceptors respond to

temperature change. – Pain receptors respond to tissue

injury.

The Motor Division •The motor division, which is divided into the somatic and autonomic nervous systems, transmits impulses from the central nervous system to muscles and glands.•The somatic nervous system regulates processes under voluntary control.•Actions of the somatic nervous system called reflexes occur automatically. The impulses controlling these actions travel on a pathway called a reflex arc.

• The autonomic nervous system regulates activities that are involuntary.

• It consists of two parts, – the sympathetic nervous system and the– parasympathetic nervous system.

• In general, the sympathetic nervous system prepares the body for intense activity.

• It prepares the body to “fight or flee” in response to stress.

• The parasympathetic nervous system causes the “rest and digest” response.

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