CHAPTER 19 NERVOUS SYSTEM Lesson 1 Cerebrospinal fluid Dementia Epilepsy Impulse Intracranial Ischemia Meninges Myelography Neurotransmitter Polyneuritis Reflex Regenerate Senile Journal question: What are the functions of the nervous system?

Chapter 19 Learning Objectives Define at least 10 terms relating to the nervous system. Describe the function of the nervous system. Identify at least 10 structures of the nervous system. Remind students that the learning objectives are the goals of the chapter – what the student is expected to know or learn from the chapter. Turning each objective into a question will help the student better understand the objective. As a pre-test, challenge the class to give possible answers to these learning objectives. Ask the students to write their answers on a sheet of paper. When the chapter is completed, have the students go back and re-visit their initial answers to these questions.

Structure and Function The nervous system is divided into two major parts: Central nervous system (CNS) Peripheral nervous system (PNS) The nervous system senses, interprets, and responds to internal and external environmental changes to maintain the body’s homeostasis. The nervous system transmits messages to the brain at 180 miles per hour. How does the nervous system help maintain homeostasis in the human body?

Central Nervous System Parts of the CNS Brain Spinal cord Coordinates body’s full nervous system Contains nerves that control connections between impulses to and from the brain and the rest of the body The human brain is very soft, like butter. The human spinal cord is about 17 to 18 inches long and is longer in men than in women.

Central Nervous System The CNS plays a critical role in maintaining a healthy, normally functioning body. Meninges (tough membranes) protect the nervous tissues. Surrounding the human brain is a liquid that helps cushion it as we move our heads.

Central Nervous System Human brains require a continuous supply of oxygen to survive and sugar in the form of glucose for the neurons to function. FIGURE 19-1 Divisions of the nervous system. A, The central nervous system. (From Sorrentino SA: Mosby’s textbook for nursing assistants, ed 7, St. Louis, 2008, Mosby.)

Peripheral Nervous System The PNS contains 12 pairs of cranial nerves Originate in the brain 31 pairs of spinal nerves Act independently from the brain in some reflex reactions Refer to Slide 9 for the location of the cranial and spinal nerves or Figure 19-1B in the students’ textbook and to Slide 10 (Table 19-1 in students’ textbook) for the functions.

Peripheral Nervous System FIGURE 19-1 Divisions of the nervous system. B, The peripheral nervous system. (From Sorrentino SA: Mosby’s textbook for nursing assistants, ed 7, St. Louis, 2008, Mosby.)

Functions of the Peripheral Nervous System

Organs of the Peripheral Nervous System PNS organs contain Afferent (sensory) neurons Carry messages from the sensory cell of the body to the brain Efferent (motor) neurons Carry messages from the brain to the body organs or parts Classified as somatic (voluntary) or automatic (involuntary) There are about 13,500 neurons in the human spinal cord.

Divisions of the Nervous System FIGURE 19-5 The nervous system may be divided into parts on the basis of their functions.

Spinal Reflex Arc The most sensitive nerves are found at the base of the spinal cord. FIGURE 19-3 The spinal reflex arc. The motor response to injury is a reflex action controlled by the spinal nerves.

Neurons The basic structural unit of the nervous system is the nerve. A nerve is a bundle of fibers that carries impulses (messages) to and from the body’s organs. Nerve fibers consist of neurons (cells). Three main types of neurons Afferent (sensory) Efferent (motor) Interneuron Interneurons connect sensory impulses to motor impulses.

Autonomic Nervous System Sympathetic system Sympathetic nerves are stimulated in situations that require action (e.g., fight-or-flight reaction). Parasympathetic system Parasympathetic nerves respond to normal, everyday situations.

Neurons Important parts of a neuron Dendrites Cell body Axon Receive impulses and transmits them to the cell body Cell body Transmits impulses to the axon Axon Transmits impulse away from the cell body to the dendrite of the next neuron Myelin (white matter) White, fatty substance covering the axon Arranged in bundles called Schwann cells The term dendrites is from the Greek word meaning “tree.” Dendrites are the branched projections of a neuron. Myelin is referred to as white matter because of the color of its fatty substance. Schwann cells are named after the German physiologist, Theodor Schwann. Schwann cells keep peripheral nerve fibers alive.

Neurons FIGURE 19-6 Neuron.

Glia Special nervous tissue cells that act as “glue” to support, bind, repair, and protect neurons Five major types Astrocyte cells Oligodendroglia Microglia Ependymal cells Neuroglia

Synapse Space between two neurons Impulses from one neuron are transmitted across the synapse to another neuron by a chemical called a neurotransmitter. Most common neurotransmitters Acetylcholine Norepinephrine Neurons may be as close as one millionth of an inch to each other but still not touch. More than 100 chemical messengers used by the nervous system have been identified.

Ganglia Groups of nerve cell bodies Located outside of the CNS Increased ability to transmit impulses because they are clustered in the ganglion Ganglia means “glue” in the Greek language.

Plexus and Dermatome Plexus Dermatomes Four major networks of interwoven spinal nerves Cervical Brachial Lumbar Sacral Provides impulses to specific regions of the body Dermatomes Spinal nerves that control sensations on the skin surface

Brain Largest structure of the nervous system and one of the largest organs of the body Weighs 2 to 3 pounds Covered by three layers of membranes called meninges Dura mater Arachnoid Pia mater Only 4% of the brain cells work, and the remaining cells are kept in reserve. Any damage to brain cells cannot be repaired completely. The human body can function without a brain.

The Brain The human brain is made of 60% white matter and 40% gray matter. It is estimated that there are more than one hundred quadrillion connections in the human brain. Men listen with the left side of their brain, and women use both sides of the brain. FIGURE 19-8 The parts of the brain. (From Patton KT, Thibodeau GA: Anatomy & physiology, ed 7, St. Louis, 2010, Mosby.)

Parts of the Brain Your brain is about 2% of your total body weight but uses 20% of your body's energy. The energy used by the brain is enough to light a 25-watt bulb. FIGURE 19-8 The parts of the brain. (From Patton KT, Thibodeau GA: Anatomy & physiology, ed 7, St. Louis, 2010, Mosby.)

Functions of the Brain

Summary The function of the nervous system is to sense, interpret, and respond to internal and external environmental changes to maintain homeostasis. Structures of the nervous system include the CNS and PNS and their parts.

Review The term cerebrospinal, with regard to the nervous system, pertains to: a. Inflammation of the meninges b. An incision into the skull c. Study of the nerve d. The brain and spine e. A small brain

Review The term cerebrospinal, with regard to the nervous system, pertains to: a. Inflammation of the meninges b. An incision into the skull c. Study of the nerve d. The brain and spine e. A small brain