Guided Notes for the Nervous System

Part One

Three Overlapping Functions of the Nervous System

A. Uses millions of sensory receptors to monitor stimuli inside and outside the body (sensory input)

B. Processes and intercepts sensory input and makes decisions (integration)

C. Effects a response by activating muscles or glands (motor output)

2. The nervous system works with the endocrine system to regulate and maintain homeostasis. While the nervous system controls with rapid electrical nerve impulses, the endocrine system organs produce hormones that are released into the blood.

3. The central nervous system consists of the brain and the spinal cord, which act as the integrating and command centers of the nervous system. They interpret incoming sensory information and issue instructions based on past experience and current conditions.

4. The peripheral nervous system consists mainly of the nerves that extend from the brain and spinal cord. Spinal nerves carry impulses to and from the spinal cord. Cranial nerves carry impulses to and from the brain.

5.There are two subdivisions of the PNS. The sensory, or afferent, division consists of nerve fibers that convey impulses to the central nervous system from sensory receptors located in various parts of the body. The motor, or efferent, division carries impulses from the CNS to effector organs, the muscles and glands.

6. The motor division has two subdivisions. The somatic nervous system allows us to consciously, or voluntarily, control our skeletal muscles. The autonomic nervous system regulates events that are automatic, or involuntary, such as the activity of smooth and cardiac muscles and glands.

Major Differences Between Neuroglia and Neurons

Neuroglia are not able to transmit nerve impulses

Neuroglia never lose their ability to divide

8. Schwann cells are supporting cells in the PNS. They form the myelin sheaths around nerve fibers that are found in the PNS.

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

10. The cell body contains the organelles and is the metabolic center of the neuron. Neuron processes that convey incoming messages toward the cell body are called dendrites. Processes that generate nerve impulses away from the cell body are axons. Neurons may have hundreds of branching dendrites, but each neuron has only one axon.

11. Most long nerve fibers are covered with a whitish, fatty material called myelin, which has a waxy appearance.

12. Myelin protects and insulates nerve fibers and increases the transmission rate of nerve impulses.

13. Axons outside the CNS are myelinated by Schwann cells.

A myelin sheath is a tight coil of wrapped membranes of Schwann cells which encloses the axon.

14. Instead of Schwann cells, neurons in the CNS are myelinated by oligodendrocytes, which form CNS myelin sheaths.

15. In people with multiple sclerosis (MS), the myelin sheaths around nerve fibers are gradually destroyed and converted to hardened sheaths called scleroses.

16. Functional classification groups neurons according to the direction the nerve impulse is traveling relative to the CNS. Sensory neurons are neurons carrying impulses from sensory receptors to the CNS. They are also called afferent neurons. Sensory neurons keep us informed about what is happening both inside and outside the body.

17. The dendrite endings of the sensory neurons are usually associated with specialized receptors that are activated by specific changes occurring nearby.

18. Neurons carrying impulses from the CNS to the viscera, muscles, or glands are called motor, or efferent neurons.

19. Structural classification is based on the number of processes extending from the cell. If there are several, the neuron is multipolar. This is the most common type because all motor and association neurons are multipolar.

20. Neurons with only two processes, an axon and a dendrite are called bipolar neurons. In adults, they are found only in some special sense organs (eye, ear).

21. Unipolar neurons have a single process emerging from the cell body. Sensory neurons found in PNS ganglia are unipolar.

22. Neurons have two major functional properties: irritability, which is the ability to respond to a stimulus and convert it into a nerve impulse, and conductivity, the ability to transmit the impulse to other neurons, muscles and glands.

23. Reflexes are rapid, predictable, and involuntary responses to stimuli. Reflexes that occur over neural pathways are called reflex arcs.

24. Autonomic reflexes regulate the activity of smooth muscles, the heart, and glands.

25. Somatic reflexes include all reflexes that stimulate the skeletal muscles.