CHAPTER 7a

SCHWANN CELLS

Most long nerve fibers are covered with a whitish, fatty material, called myelin, which has a waxy appearance. Myelin protects and insulates the fibers and increases the transmission rate of nerve impulses. Axons outside the Central Nervous System (CNS) are myelinated by _____ ______, specialized supporting cells that wrap themselves tightly around the axon jelly-roll fashion.

SENSORY (division)

The _______ division or afferent division consists of nerve fibers that convey impulses to the Central Nervous System (CNS) from sensory receptors located in various parts of the body.

MOTOR (division)

The _______ division, or efferent, division carries impulses from the Central Nervous System (CNS) to effector organs, the muscles and glands. These impulses activate muscles and glands; that is, they effect (bring about) a response.

CENTRAL (nervous)

The _______ nervous system consists of the brain and spinal cord, which occupy the dorsal body cavity and act as the integrating and command centers of the nervous system

SOMATIC (nervous)

The ________ nervous system allows us to consciously, or voluntarily, control our skeletal muscles. Hence, this subdivision is often referred to as the voluntary nervous system. However, not all skeletal muscle activity controlled by this motor division is voluntary. Skeletal muscle reflexes, like stretch reflex for example, are initiated involuntarily by these same fibers.

AUTONOMIC (nervous)

The ________ nervous system regulates events that are automatic, or involuntary, such as the activity of smooth and cardiac muscles and glands.

PERIPHERAL (nervous)

The ________ nervous system, the part of the nervous system outside the CNS, consist mainly of the nerves that extend from the brain and spinal cord. Spinal nerves carry impulses to and from the spinal cord. The cranial nerves carry impulses to and from the brain.

NEURONS

_______, also called nerve cells, are highly specialized to transmit messages (nerve impulses) form one part of the body to another.

ASTROCYTES

_________ are star-shaped cells and account for nearly half of the neural tissue. Their numerous projections have swollen ends that cling to neurons, bracing them and anchoring them to their nutrient supply lines, the blood capillaries. _________ form a living barrier between capillaries and neurons, and play a role in making exchanges between the two. This helps to protect neurons from harmful substances that might be in the blood

OLIGODENDROCYTES

___________ are glia cells that wrap their flat extensions tightly around nerve fibers, producing fatty insulation coverings called myelin sheaths. The _________ form these myelin sheaths around nerve fibers in the CNS