Copyright © 2007 Pearson Prentice Hall, Inc.

The Brain

The Nervous System

Overview: The nervous system is composed of both the CNS & PNS

The Central Nervous System

• The brain and spinal cord are protected by the bones of the vertebral column and skull, three connective tissue membranes that form the meninges, and cerebrospinal fluid

• Inflammation of the meninges is called meningitis

The Brain

• The cerebrum consists of two hemispheres which receive sensory information from and direct the movements of the opposite side of the body

The corpus callosum connects the two cerebral hemispheres

• The sensory, motor, and association areas are in the cerebral cortex

• The primary somatosensory area receives sensory information from the body while the primary motor area controls the skeletal muscles

The Brain

• Association areas communicate with the sensory and motor areas, and with other parts of the brain

• The most complex of these areas is the prefrontal cortex which enables us to reason and think in the abstract

• The thalamus is the relay station of the brain for all sensory information except smell. It also directs motor activity, cortical arousal and memory

• The hypothalamus maintains homeostasis by regulating blood pressure, heart rate, breathing rate, digestion and body temperature

• The hypothalamus coordinates the nervous and endocrine systems through its connection to the pituitary gland– It is a center for emotions

and serves as the master biological clock

• The cerebellum integrates information from the motor cortex and sensory pathways to produce movements – It also stores memories of learned motor skills.

• The medulla oblongata contains reflex centers to regulate the rhythm of breathing, force and rate of the heartbeat, and blood pressure

– It serves as the pathway for all sensory messages to the higher brain centers and motor messages leaving the brain

• The limbic system, which includes several brain structures, is largely responsible for emotions

•The reticular activating system (RAS) filters sensory input and keeps the cerebral cortex in an alert state (Green arrows)

• Spinal nerves arise from the cord and exit through the openings between the stacked vertebrae of the vertebral column

The spinal cord conducts messages between the brain and the body and serves as a reflex center

The Spinal Cord

• A reflex action is an automatic response to a stimulus in a pre-wired circuit called a reflex arc

The Peripheral Nervous System

• The body has 31 pairs of spinal nerves

The Peripheral Nervous System

• The body has12 pairs of cranial nerves

The Peripheral Nervous System

• The peripheral nervous system includes the sensory receptors, the peripheral nerves and ganglia, and specialized motor endings that stimulate the effectors

The Peripheral Nervous System

• The peripheral nervous system is divided into the somatic nervous system, which governs conscious sensations and voluntary movements, and the autonomic nervous system, which is concerned with our unconscious, involuntary internal activities

The Peripheral Nervous System

• The autonomic nervous system can be divided into the sympathetic and parasympathetic nervous systems, two branches with antagonistic actions

The Peripheral Nervous System

• The sympathetic nervous system gears up the body for stressful or emergency situations while the parasympathetic nervous system adjusts body functioning so that energy is conserved during nonstressful times

Disorders of the Nervous System Vary in Health Significance

• Headaches are usually caused by tension in the neck or by dilation of the blood vessels of the head

• Migraine headaches are caused by an imbalance in the brain’s chemistry

Disorders of the Nervous System

• A stroke results when the brain is deprived of blood and nerve cells die

• The extent and location of the damage caused by a stroke depends on the affected region of the brain

Disorders of the Nervous System

• A coma is caused by trauma to neurons in regions of the brain responsible for stimulating the cerebrum

• A comatose person is totally unresponsive to all sensory input and cannot be awakened

Disorders of the Nervous System

• A spinal cord injury results in loss of function below the site of injury