CHAPTER 15-THE NERVOUS SYSTEM
I. THE NERVOUS SYSTEM-directs and regulates the functions of all the human body
systems.
A. The Nervous System is subdivided into two sections: The Central Nervous System
(CNS) which includes the brain and spinal cord and The Peripheral Nervous System
(PNS), which includes the nerves of the body.
B. Neurons-nerve cells; these are the basic functional elements of the nervous system.
1. They come in a variety of shapes and sizes but all neurons are capable of
generating and carrying electrical signals known as Impulses.
2. Three Primary Parts of a Neuron:
a. The Cell Body-contains the nucleus and organelles.
b. Dendrites-small branches off of the cell body. These carry impulses to
the cell body.
c. Axons-larger branches off of the cell body. These carry impulses away
from the cell body. Many axons are covered by a fatty protective
covering known as a Myelin Sheath.
1) Terminal End Fibers-located at the end of an axon. Impulses
pass through here to leave the neuron. Impulses can move from
neurons to:
a) Other neurons
b) Glands and organs
c) Muscles
2) Synapses-the space between adjacent neurons or the space
between neurons and organs and muscles. In many cases,
impulses are carried through the synapse by neurotransmitters.
3. 2 Properties of all Neurons
a. Excitability-the ability to respond to a stimulus by producing an impulse.
b. Conductivity-the ability to transmit an impulse to other structures.
4. 2 Major Types of Neurons:
a. Motor (Effferent) Neurons-carry impulses from the CNS to the body.
b. Sensory (Afferent) Neurons-carry impulses from the body to the CNS.
C. Neuroglial Cells-support cells in the nervous system. Types:
1. Astrocytes-regulate nutrient levels in the nervous system.
2. Oligodendrocytes-produce myelin sheaths.
3. Microglia-phagocytic, remove microbes, debris in the nervous system.
II. THE CENTRAL NERVOUS SYSTEM-includes the brain and spinal cord. The central
nervous system regulates all bodily activities.
A. The Brain-weighs about 3 pounds and contains more than a 100 billion neurons.
1. The brain is surrounded and protected by the skull and the meninges.
a. The meninges are three layers of connective tissue that attach to and
protect the brain. The three meninges are:
1) The dura mater-outer bag around the brain. It is separated from the
skull by the epidural space.
2) The arachnoid layer-separated from the dura mater by the subdural
space.
3) The pia mater-attaches directly to and protects the brain.
b. Cerebrospinal fluid-surrounds and runs through the brain. This fluid carries
nutrients and other necessary compounds to and from the brain.
2. There are 4 major parts or sections to the brain: the brain stem, the cerebrum,
the cerebellum and the diencephalon.
3. The Brain Stem-base of the brain, this portion of the brain regulates activities such
as heart and lung functions and sight. The brain stem is made up of the medulla
oblongata, the midbrain and the pons. Damage to this portion of the brain is often
fatal.
4. The Cerebellum-posterior, inferior portion of the brain. The cerebellum regulates
activities related to muscular movement, balance and posture.
5. The Cerebrum-the upper, largest area of the brain. The cerebrum is divided into 2
hemispheres (sides). The hemispheres are held together by the corpus callosum.
a. The outer covering of the cerebrum (known as the cortex) is composed of
many folds and fissures. The cortex is divided into four major lobes: the
frontal lobe, the occipital lobe, the parietal lobes and the temporal lobes.
b. The cerebrum is the decision-making portion of the brain and it
plays a key role in providing us with memory.
c. The deeper layers of the cerebrum are composed of neurons that help
regulate muscle activity.
6. The Diencephalon-the deepest portion of the brain, is superior to the brain stem.
a. The diencephalon contains two major regions: the thalamus and the
hypothalamus.
b. The thalamus and hypothalamus work together to regulate the normal
functioning of the body, including regulating blood pressure, body
temperature and the autonomic nervous system.
III. THE PERIPHERAL NERVOUS SYSTEM-includes the nerves of the body.
A. This system is made up of 12 pairs of cranial nerves that attach directly to the brain
and 31 pairs of spinal nerves that attach to the spinal cord.
B. There are 12 cranial nerves that attach to the brain and oversee several major functions in
the body.
C. Parts of the Peripheral Nervous System
1. Somatic Nervous System-carries information between the brain and the skin
and skeletal muscles.
2. The Autonomic Nervous System-regulates involuntary processes in the body.
This part of the nervous system is divided into two major portions:
a. The Parasympathetic Division-regulates digestion and those processes that
allow us to generate and conserve energy.
b. The Sympathetic Division-regulates processes that expend energy in the
body. This includes fight or flight responses and phobias.
IV. THE SPINAL CORD-runs from the base of the brain to near the second lumbar veretbra.
A. Externally, the cord is protected by the vertebral column. It is also covered by the spinal
meninges (connective tissue coverings). These meninges are continuous with the cranial
meninges; therefore, the spinal meninges have the same three layers as described earlier.
B. Internally, the spinal cord is composed of a series of nerve bundles known as tracts.
C. Tracts contain both motor and sensory nerve fibers.
D. The spinal cord plays a key role in connecting the body to the brain and the brain to the
body.
E. The spinal cord also helps to oversee and regulate many of the reflexes associated with
skeletal muscle in the body.
F. The end of the cord is known as the Conus Medullaris. The Filum terminale extends from
the end of the cord and attaches to the coccyx.
V. MEDICAL WORD ELEMENTS-pages 507-510
VI. PATHOLOGY
A. Cerebrovascular Disease
1. Ischemic stroke
2. Hemiplegia
3. TIA
B. Seizure Disorders
C. Parkinson Disease
D. Multiple Sclerosis
E. Alzheimer Disease
F. Mental Illness
VII. DISEASES AND CONDITIONS-pages 515-523
VIII. PHARMACOLOGY-pages 524-525