CHAPTER PREVIEW
As we journey into the nervous system, we need language to navigate quickly around and through nervous system structures. To prepare for this journey, we will learn about the various planes of space, directional terms, and muscle actions relevant to neuroanatomy. In addition, we will survey how various neuroscientists have organized the nervous system, which allows for the better conceptualization of this complex system.
IN THIS CHAPTER
In this chapter, we will ...
■ Learn how to navigate around the nervous system using anatomical orientation terms
■ Explore three approaches to organizing the nervous system
■ Identify which of the three approaches this text will take
LEARNING OBJECTIVES
1. The learner will be able to list and define anatomical orientation terms to navigate nervous system structures.
2. The learner will list and briefly describe the three approaches to organizing the nervous system.
CHAPTER OUTLINE
■ Introduction
■ Navigation of the Nervous System
• Anatomical Terms
• The Anatomical Position
• Anatomical Versus Clinical Orientation
• Body Planes
• Directional Terms
• Muscle Actions
■ Organizational Approaches to the Nervous System
• An Anatomical Approach
• A Functional Approach
• A Developmental Approach
• The Approach of This Text
■ Conclusion
■ Summary of Learning Objectives
■ Key Terms
■ Draw It to Know It
■ Questions for Deeper Reflection
■ Case Study
■ Suggested Projects
■ References
► Introduction
The journalist William F. Allman (1990) has described the brain as “a beautiful, monstrous mess.” What he is referring to is the fact that the nervous system is a very complex system. How can one ever grasp and understand its complexity? Neuroscientists have developed several different grids by which to categorize and begin to understand this daunting system. In this chapter, various terms and concepts will be introduced to help in navigating through the nervous system system and its structures. In addition, three organizational approaches will be surveyed: the anatomical, functional, and developmental approaches.
► Navigation of the Nervous System
In looking at a nervous system structure like the brain, how does one navigate around it quickly and using only language? A picture is worth a thousand words, but sometimes pictures are not available and clinicians need to describe structures verbally. To help in this task, this section introduces key anatomical terms and concepts, including the anatomical position, anatomical versus clinical orientation, body planes, directional terms, and muscle actions.
Anatomical Terms
Many of the terms used in neuroanatomy have Greek and Latin origins. Education in these languages was a standard part of American and British education but fell into disfavor in the 1960s. Students prior to the 1960s who learned these languages had an advantage when learning anatomy in general, and neuroanatomy specifically, in that they already had a foundation for the Latin and Greek roots, prefixes, and suffixes used in these fields. Today, students report that unfamiliarity with these terms is sometimes a barrier to their learning and a disadvantage when taking standardized tests, like the SAT or GRE. For those without a background in Greek or Latin, TABLE 2-1 is a valuable tool for navigating the terms that will be encountered in this text.
The Anatomical Position
The anatomical position is pictured in FIGURE 2-1. It serves as the starting position to describe anatomical features and positions. In this position, the body is erect, the palms face out, and the arms and face are forward. Why has this position become standard and not some other configuration? The anatomical position grew out of the world of human dissection and represents the position a cadaver lying on the dissection table.
TABLE 2-1 Summary of Some Prefixes and Suffixes Used in Neuroanatomy
|
Prefix or Suffix |
Definition |
Example |
|
|
a- |
Without |
Aphasia—without speech |
|
|
ab- |
Away from |
Abduction—to move structures away from each other |
|
|
ad- |
Toward |
Adduction—to move structures toward each other |
|
|
-algia |
Pain |
Neuralgia—nerve pain |
|
|
an- |
Without |
Anoxia—without oxygen |
|
|
angio- |
Related to blood vessels |
Angiography—neuroimaging technique for blood vessels |
|
|
ante-/antero- |
Before |
Anterograde amnesia—not remembering what happened before |
|
|
bi- |
Two |
Bilateral—occurs on both sides |
|
|
brachy- |
Short |
Brachycephaly—having a flat or short head |
|
|
brady- |
Slow |
Bradykinesia—slow movements |
|
|
cephalo- |
The head |
Cephalocaudal—growth from head to tail |
|
|
contra- |
Opposite |
Contralateral—opposite sided |
|
|
cranio- |
Skull |
Cranium—the skull |
|
|
-culus |
Small |
Homunculus—little man |
|
|
de- |
Cessation |
Denervation—nerve supply loss |
|
|
di- |
Two |
Diplopia—double vision |
|
|
dys- |
Impaired |
Dysarthria—impaired articulation |
|
|
ecto- |
Outer |
Ectoderm—an embryo's outermost layer of tissue |
|
|
-ectomy |
Removal |
Craniectomy—surgical removal of part of the cranium |
|
|
endo- |
Inner |
Endoderm—an embryo's innermost layer of tissue |
|
|
ep-/epi- |
Above |
Epidural—above the dura mater |
|
|
extra- |
In addition to |
Extrapyramidal tract—a nerve tract in addition to (or that complements) the pyramidal tract |
|
|
-gen/-genic |
Origin or beginning |
Neurogenic—of a neurological origin |
|
|
hemi- |
One-sided or half |
Hemiplegia—one-sided paralysis |
|
|
hyper- |
Too much |
Hypertonia—too much muscle tone |
|
|
hypo- |
Too little |
Hypotonia—too little muscle tone |
|
|
infra- |
Below |
Infrahyoid muscles—muscles found below the hyoid bone |
|
|
inter- |
Between |
Interhemispheric communication—communication between the left and right hemispheres |
|
|
intra- |
Within |
Intracranial—within the cranium |
|
|
ipsi- |
Same |
Ipsilateral—same sided |
|
|
itis |
Inflammation |
Meningitis—inflammation in the meninges |
|
|
kine- |
Movement |
Kinesiology—the study of movement |
|
|
latero- |
Side |
Lateroversion—turning to one side |
|
|
medio- |
Middle |
Mediopontine—the middle portion of the pons |
|
|
micro- |
Small |
Microcephaly—abnormally small head |
|
|
my-/myo- |
Muscle |
Myotrophy—nutrition of a muscle |
|
(continues)
TABLE 2-1 Summary of Some Prefixes and Suffixes Used in Neuroanatomy (continued)
|
Prefix or Suffix |
Definition |
Example |
|
neo- |
New |
Neoplasm—new growth (i.e., tumor) |
|
neuro- |
Nerve |
Neurology—the study of the nervous system |
|
oculo- |
Eye |
Oculomotor nerve—a cranial nerve that controls the eye muscles |
|
-oma |
Tumor |
Neuroma—a tumor on a nerve |
|
-osis |
A condition |
Neurosis—a mild mental illness |
|
patho- |
Abnormal |
Pathology—the study of disease states |
|
-pathy |
Disease |
Neuropathy—disease of the nervous system |
|
peri- |
Around |
Periventricular—around the cerebral ventricles |
|
-phage/-phagia |
Eating |
Dysphagia—swallowing disorder |
|
-plasia |
Growth |
Hyperplasia—excessive growth |
|
-plasty |
Mold or repair |
Cranioplasty—surgical repair of a skull defect |
|
pseudo- |
Not genuine |
Pseudoscience—beliefs mistakenly thought to be based in science |
|
quadra-/quadri- |
Four |
Quadriplegia—paralysis in all four limbs |
|
re- |
Again, repeat |
Recurrent laryngeal nerve—a branch of the vagus nerve that descends to the chest then back up to larynx |
|
sclerosis |
Scarring, hardening |
Multiple sclerosis—chronic disease of the brain due to patchy demyelination of the central nervous system |
|
semi- |
Half |
Semicircular canals—part of the vestibular or balance system; three half-circle structures in the inner ear |
|
soma-/ somato- |
Body |
Somatosensory—the part of the nervous system that conveys sensory information to the brain for interpretation |
|
tetra- |
Four |
Tetraplegia—same as quadriplegia (paralysis in four limbs) |
|
-tomy |
Cutting |
Craniotomy—surgical removal of part of the skull |
|
-trophic |
Nourishment |
Amyotrophic lateral sclerosis—a progressive motor neuron disease |
|
-trophy |
Growth |
Atrophy—muscle wasting |
|
uni- |
One |
Unilateral—on one side |
FIGURE 2-1 The anatomical position.
Anatomical Versus Clinical Orientation
There are two orientations to be aware of as you navigate images in neuroanatomy. The first is anatomical orientation, in which you view the brain as if you were standing looking at the top of someone’s head (FIGURE 2-2A). In this view, the left side of the brain is on your left, and the right side of the brain is on your right. This is the view used in drawings and photos of the brain. The opposite of anatomical orientation is clinical orientation, in which you are looking at the brain from the person’s feet rather than the top of the head (FIGURE 2-2B). The right side of the brain is on your left, and the left side is on your right. This is the orientation to use when viewing magnetic resonance imaging (MRI) or computed tomography (CT) scans of the brain. As you navigate images in this text, keep these two orientations in mind.
Body Planes
There are three different ways to cut up the body, which grew out of the world of dissection (FIGURE 2-3A and B). The first is the sagittal (Latin for “arrow”) section or plane. This term likely takes its name from the world of warfare, where an arrow or sword could cut or divide things into left and right portions (e.g., think of the legend of William Tell shooting an apple from the top of his son’s head). The sagittal section cuts the body or a specific anatomical structure into left and right portions. If this plane is right in the middle, it is called a midsagittal plane. If it is not in the middle, it is called a parasagittal plane. The second plane is the coronal (Latin for “crown”) or frontal section that splits a structure into front and back portions. This term most likely came into existence from the act of lowering a crown onto a new king’s head through a ceremony known as a coronation. The third and final body section is a transverse or axial plane, which splits a structure into top and bottom portions. Those familiar with the Star Wars universe will remember that Obi-Wan Kenobi used his light saber to make a transverse section of Darth Maul’s body in The Phantom Menace. TABLE 2-2 provides a summary of these planes.
FIGURE 2-2 A. Anatomical orientation. If a subject's body was lying in the supine position, the observer would be viewing the brain from a superior angle. The observer's and subject's left and right sides would be aligned. B. Clinical orientation. If a subject's body was lying in the supine position, the observer would be viewing the brain from an inferior angle. The observer's and subject's left and right sides would be reversed.
These three sections can be applied to the brain as well as the body (FIGURE 2-3C). A sagittal section divides the brain into left and right portions. In fact, the longitudinal fissure, a deep groove between the left and right cerebral hemispheres, essentially does this. Of course, this division can be made at any place in the left or right cerebral hemispheres, depending on what someone wants to see in the brain. The coronal section divides the brain into front and back portions, which allows viewing of not only the gray matter at the surface on the cerebral hemispheres, but also the deeper white matter along with deep gray matter structures, like the thalamus and basal ganglia. A transverse section cuts the brain into upper and lower portions and, again, can be made anywhere in the brain to see structures such as the brain ventricles better.
Directional Terms
How does one quickly move around an anatomical structure using language only? Directional terms are very useful tools for accomplishing this task and will be used heavily in this text. Some of these terms are useful for navigating around the body in general, and others are useful for navigating around the nervous system specifically.
The first set of these terms is superior and inferior. Superior means from a high position, whereas inferior means the opposite—from a low position. The second set is anterior and posterior. Anterior (FIGURE 2-4A) means toward the stomach and posterior toward the back (FIGURE 2-4B). The term ventral is sometimes used as a synonym for anterior and dorsal for posterior (think of a dolphin’s dorsal fin). A third set is lateral and medial. Think of an imaginary line that runs through the center of the body (i.e., a midline); lateral would mean away from midline, whereas medial would refer to toward midline (or the middle of the body). Proximal and distal are the fourth set of directional terms, and these have to do with limbs. Proximal refers to the point nearest a limb’s attachment, whereas distal refers to the part of the limb farthest from its attachment. The fifth set includes peripheral (i.e., toward the outer surface) and central (i.e., toward the center). Think of a computer system as an analogy. Peripherals include items such as a printer or keyboard, whereas the processor is central and is appropriately termed the central processing unit. A sixth set is ipsilateral and contralateral. Ipsilateral means same sided, whereas contralateral means opposite sided (FIGURE 2-5). For example, your right arm and your right leg are on the same side of the body and thus are ipsilateral to each other. However, your right arm is contralateral to your left arm. Some nerve pathways are ipsilateral tracts, whereas others are contralateral. The point where a contralateral tract crosses from left to right (or right to left) is called the point of decussation or crossing. These sets of directional terms are summarized in TABLE 2-3.
FIGURE 2-3 A. Sections applied to the body. B. Planes in three-dimensional view. C. Sections applied to the brain. Note that the body in parts A and B is facing anteriorly, and the brain in part C is a lateral view.
© Brand X Pictures/Thinkstock.
TABLE 2-2 Summary of the Three Body Planes
|
Plane Name |
Alternative Name |
Definition |
Example |
|
Sagittal |
Lateral |
Splits structure into right and left portions |
The halves of an apple |
|
Coronal |
Frontal |
Splits structure into front and back portions |
Slices of bread |
|
Transverse |
Horizontal |
Splits structure into upper and lower portions |
The layers of a hamburger |
FIGURE 2-4 A. Directional terms applied to the body in an anterior view. B. Directional terms applied to the body in a lateral view.
We have been discussing how these directional terms apply to the body, but now it is time to explore how they apply to the brain. It is helpful to first consider how some of these terms would be applied to a four-legged animal, like a dog, whose brain and spinal cord are organized in a horizontal direction (FIGURE 2-6A). Dorsal refers to the dog’s back as well as the top of its brain, whereas ventral directs us to the dog’s belly and the bottom of its brain. The term rostral (Latin for “beak” or “nose”) helps us orient to the front of the dog as well as the front of the brain. The term caudal (Latin for “tail”) directs us to the tail end of the dog and the back of the brain. FIGURE 2-6B applies these terms—dorsal, ventral, rostral, and caudal—to the brain, and FIGURE 2-6C applies them to the brainstem. In comparing these terms to the brain versus the brainstem, they may seem to be at odds; however, remember that the brainstem and spinal cord are oriented in a vertical direction in humans who are bipedal in comparison to a dog whose brain stem and spinal cord are oriented in a horizontal direction because they are quadrupedal.
TABLE 2-3 Summary of Directional Terms
|
Term |
Definition |
Example |
|
Superior (or cranial) |
From a high position |
The brain is superior to the heart. |
|
Inferior (or caudal) |
From a low position |
The heart is inferior to the brain. |
|
Anterior (or ventral) |
Toward the stomach |
The sternum is anterior to the heart. |
|
Posterior (or dorsal) |
Toward the back |
The spine is posterior to the stomach. |
|
Medial |
Toward the body's midline |
The heart is medial to the ribs. |
|
Lateral |
Away from the body's midline |
The ribs are lateral to the heart. |
|
Proximal |
Point nearest limb's attachment |
The shoulder is proximal to the elbow. |
|
Distal |
Point farthest from limb's attachment |
The ankle is distal to the knee. |
|
Peripheral |
Toward the outer surface |
The cell's wall is peripheral. |
|
Central |
Toward the center |
The cell's nucleus is central. |
|
Ipsilateral |
Same side |
Canadians drive ipsilateral as Americans. |
|
Contralateral |
Opposite side |
Brits drive contralateral to Americans. |
Muscle Actions
Three sets of muscle actions will be addressed here (TABLE 2-4). The first is adduct and abduct. Adduct refers to bringing structures together (e.g., the vocal cords adduct when we talk), and abduct is the opposite—moving structures apart. These actions are pictured in FIGURE 2-7 using the hands as an example. When we flare our fingers out, we are abducting or opening up the hand; when we bring the fingers together, we are adducting them. These actions are illustrated with the legs in FIGURE 2-8A and with the vocal cords in FIGURE 2-9. Some people find remembering the add in adduction helpful because it reminds them of addition in which you bring numbers together mathematically.
Second, flexion refers to bending a joint, whereas extension denotes straightening a joint (FIGURE2-8B). These terms are applied to the hand in FIGURE 2-8C and the foot in FIGURE 2-8D. In his earlier days, Arnold Schwarzenegger did a lot of flexion and extension in bodybuilding competitions.
The third and final set is supine and pronate. Supine refers to lying faceup (i.e., ventral surface up). Pronate is the opposite and refers to lying facedown (i.e., ventral surface down). Think about sleeping as an example. Some people sleep on their stomachs (pronate position), whereas others sleep on their backs (supine position). The pronate position is also the preferred position of prayer in some religions.
FIGURE 2-6 The directional terms ventral, dorsal, rostral, and caudal applied to A. a dog, B. the brain, and C. the brainstem.
|
TABLE 2-4 |
Summary of Muscle Actions |
|
|
Term |
Definition |
Example |
|
Adduct |
To bring structures together |
The vocal folds are together during phonation. |
|
Abduct |
To move structures apart |
The vocal folds are apart during breathing. |
|
Flexion |
To bend a joint |
You bend your elbow to brush your teeth. |
|
Extension |
To straighten a joint |
You straighten your elbow to reach into the refrigerator. |
|
Supine |
Lying with ventral surface up |
John sleeps in the supine position (on his back). |
|
Pronate |
Lying with ventral surface down |
Maria sleeps in the pronate position (on her stomach). |
► Organizational Approaches to the Nervous System
An Anatomical Approach
An anatomical approach involves those structures that can be seen with the human eye (i.e., gross anatomy). This approach divides the nervous system into two basic sections, the central nervous system (CNS) and the peripheral nervous system (PNS) (FIGURE2-10). At a basic level, the CNS is made up of the brain and spinal cord, and the PNS consists of the cranial and spinal nerves (FIGURE 2-11). These basic descriptions will be fleshed out in the following paragraphs.
The Central Nervous System
As mentioned previously, the CNS consists of the brain and spinal cord. Anatomically, the brain is made up of four structures: the brainstem, cerebellum, diencephalon, and cerebral hemispheres (FIGURE 2-12). The brainstem, which consists of the medulla, pons, and midbrain, is continuous with the spinal cord and lies inferiorly to the cerebral hemispheres. (See, we are already using directional terms.) It controls many basic life functions and reflexes, including heartbeat and breathing. The brainstem also has many motor and sensory pathways that run between the brain and spinal cord. The cerebellum, which lies just posterior to the pons, is involved in the coordination and precision of fine motor movement. The thalamus, subthalamus, hypothalamus, and epithalamus make up the diencephalon, a term that will come up again in discussion of the developmental approach. The thalamus acts as a relay station for sensory fibers, the subthalamus regulates and coordinates motor function, the hypothalamus regulates various body functions (e.g., body temperature), and the epithalamus regulates genital development, the sleep-wake cycle, and optic reflexes. The last part of the brain is the two cerebral hemispheres with their characteristic grooves. The cerebral hemispheres control higher cortical functions such as cognition and language, as well as planning motor function and interpreting sensory experiences.
FIGURE 2-8 A. Adduction versus abduction. B. Flexion versus extension. C. Flexion versus extension with the hand. D. Flexion versus extension with the foot.
FIGURE 2-9 A superior view of the vocal folds. A. Abduction of the vocal folds. B. Adduction of the vocal folds.
The spinal cord makes up the final part of the CNS, and it can be thought of as the information superhighway of the body. It is housed in the spinal or vertebral column, a cylinder of 32 to 34 bony segments. This number varies because the lowest parts of the vertebral column are made up of fused bones and this fusion can be different from person to person. The spinal cord is densely packed with motor and sensory fibers, and spinal nerves exit it and course to body structures, like muscles. Damage to the spinal cord can result in weakness or paralysis in different parts of the body depending on the level of damage. For example, damage to the cervical region (i.e., neck) can result in weakness or paralysis in all four limbs; damage lower in the lumbar region (i.e., lower back region) can impair only the legs.
Both the brain and spinal cord are wrapped in a three-layer membrane called the meninges. These membranes probably seem familiar because the condition meningitis, an inflammation of the meninges, is well known. The outermost meningeal layer is the dura mater, followed by the arachnoid mater and the pia mater.
The Peripheral Nervous System
The PNS is made up of 12 pairs of cranial and 31 pairs of spinal nerves. Most cranial nerves originate off the brainstem (except I and II) and transfer motor, sensory, special sensory, and parasympathetic information back and forth between the brain and structures in the head and neck (FIGURE 2-13). Motor function involves information flowing from the brain to the muscles and other structures, leading to body movement and other functions. Sensory information, like temperature and touch, flows in the opposite direction, from the body to the brain. In addition to motor and sensory experiences, we also have special sensory experiences. Special senses have specialized organs devoted to them, and include vision, hearing, taste, and smell. Parasympathetic functions involve the regulation of organs and glands. Salivary glands are important parasympathetic structures in communication because they lubricate speech structures like the oral cavity and vocal cords.
FIGURE2-12 A sagittal section of the brain showing major brain structures.
FIGURE2-13 Ventral view of the brain and brainstem showing the 12 cranial nerves.
In addition to our 12 cranial nerves, we have 31 pairs of spinal nerves that begin at the spinal cord and course out to the rest of the body (FIGURE 2-14). They are organized into different levels as follows: 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, and 1 coccygeal. They send motor information from the brain to the body’s muscles and sensory information from the body back to the brain. Reflexes are also mediated along both cranial and spinal nerves.
A Functional Approach
Using a functional approach, two major nervous system divisions are made: the sensory (or afferent) system and the motor (or efferent) system (FIGURE 2-15). The sensory system can be further broken down into the somatosensory and the visceral sensory systems. The somatosensory system involves general sense information such as touch, pain, pressure, vibration, temperature, and proprioception in the skin and muscles as well as special senses like hearing, vision, and equilibrium. The visceral sensory system entails general sensory information like stretch, pain, temperature, and irritation in the internal organs, as well as sensations like nausea and hunger. It also conveys the special senses of taste and smell.
FIGURE2-14 Spinal nerves in relation to the brain and spinal cord.
Like the sensory system, the motor system has two major divisions, the autonomic nervous system and the somatic nervous system. The autonomic nervous system involves body functions that happen automatically and without conscious control. There are three main divisions of this system—the sympathetic, parasympathetic, and enteric systems. The sympathetic nervous system (FIGURE 2-16) triggers what is known as our “fight-or-flight” response. For example, if you were out for a walk and stumbled across a rattlesnake, you would probably want to flee without thinking about it. How does the sympathetic nervous system achieve this survival response? It excites the body for action by increasing heart rate, blood pressure, and adrenaline. The parasympathetic nervous system (FIGURE 2-17) complements the sympathetic nervous system by doing the opposite. It is sometimes referred to as the “rest-and-digest” system. It calms and relaxes the body through slowing the heart and lowering blood pressure. The final part of the autonomic nervous system is the enteric nervous system, which manages the gastrointestinal system. Some neuroscientists have called this system a second brain because it can function independently of the brain. Normally it does communicate with the CNS through the sympathetic and parasympathetic nervous systems via the vagus nerve, but when connections between the vagus nerve and the CNS are severed, it continues to work (Li & Owyang, 2003).
FIGURE2-15 A functional approach.
FIGURE2-16 The sympathetic ("fight or flight”) nervous system.
FIGURE2-17 The parasympathetic ("rest and digest”) nervous system.
FIGURE2-18 A developmental approach.
In contrast to the autonomic nervous system, the somatic nervous system is a voluntary, conscious system that coordinates the body’s skeletal muscles for movement. The 12 cranial nerves and 31 spinal nerves are part of this system. In addition, interneurons, or association neurons, are also a part of this system. These small neurons typically play an inhibitory role in motor function at the local level. In other words, they influence the functioning of other neurons called motor neurons.
A Developmental Approach
The developmental approach is focused more on the CNS, specifically the organization of the brain, rather than the nervous system as a whole (FIGURE 2-18). The names involved in this approach are Greek in nature and come from embryonic development. The Greek name for the CNS is encephalon (Greek enkephalos), which literally means “within the head.” When a prefix is added, you have a reference to a certain nervous system structure.
During the fourth week of fetal development, the prosencephalon (pros- = “in the front”), mesencephalon (mes- = “in the middle”), and rhombencephalon (rhomb- = “diamond shaped”) develop out of a precursor structure, the neural tube. These three structures can also be called the forebrain, midbrain, and hindbrain, respectively. The cerebral hemispheres and the diencephalon (dia-= through; thalamic structures) will begin to develop out of the prosencephalon, or forebrain. The mesencephalon will develop into the midbrain, and the rhombencephalon will develop into the myelencephalon (medulla) and the metencephalon (pons and cerebellum). All of these structures will begin to emerge in the fifth week of development.
Usually these terms are used only in the context of neuroembryology, but diencephalon has been retained as a more general term referring to thalamic structures. Except for a discussion of neurological development, these terms (with the exception of diencephalon) will not be used in this text.
The Approach of This Text
This text mainly follows the anatomical approach for two reasons. First, it is the simplest and most concrete method of the three presented. It is a “what you see is what you get” approach. Second, the anatomical approach does not necessitate the use of as many unfamiliar Greek terms (e.g., rhombencephalon) with the exception of diencephalon. Using the anatomical approach, this text will move from bottom to top, from the spinal cord to brainstem, from the cerebellum to the diencephalon, and finally to the cerebral hemispheres.
► Conclusion
The organization of the nervous system was surveyed in this chapter, as well as various anatomical terms useful for navigating this system. Navigation around nervous system structures is aided by the concepts of anatomical position, anatomical versus clinical orientation, body sections, directional terms, and muscle actions. In the organization of the nervous system, anatomical, functional, and developmental approaches were briefly reviewed.
SUMMARY OF LEARNING OBJECTIVES
The following were the main learning objectives of this chapter. The information that should have been learned is below each learning objective.
1. The learner will be able to list and define anatomical orientation terms to navigate nervous system structures.
• Sagittal plane: a section or plane that cuts the body or a specific anatomical structure into left and right portions
• Coronal plane: a section or plane that cuts the body or a specific anatomical structure into front and back portions
• Transverse plane: a section or plane that cuts the body or a specific anatomical structure 2. into top and bottom portions
• Superior (cranial): toward the head or from a high position
• Inferior (caudal): toward the feet or from a low position
• Anterior (ventral): toward the belly
• Posterior (dorsal): toward the back
• Medial: toward the midline of the body
• Lateral: away from the midline of the body
• Proximal: the point nearest a limb’s attachment
• Distal: the point farthest from a limb’s attachment
• Peripheral: toward the outer surface
• Central: toward the center
• Ipsilateral: same sided
• Contralateral: opposite sided
• Adduct: bringing structures together
• Abduct: moving structures apart
• Flexion: bending of a joint
• Extension: straightening of a joint
• Supine: lying on the back
• Pronate: lying on the belly
The learner will list and briefly describe the three approaches to organizing the nervous system.
• Anatomical approach: Focuses on those structures that can be seen with the human eye and divides the nervous system into two basic divisions, the central nervous system (CNS) and the peripheral nervous system (PNS).
• Functional approach: Focuses on two major nervous system divisions—the sensory (or afferent) system and the motor (or efferent) system.
• Developmental approach: Focuses on neurological development of the embryo, fetus, and newborn.
KEY TERMS
Abduct
Adduct
Anatomical position
Anterior
Autonomic nervous system
Brainstem
Caudal
Central
Central nervous system (CNS)
Cerebellum
Cerebral hemispheres
Contralateral
Coronal
Decussation
Diencephalon
Distal
Dorsal
Enteric nervous system
Epithalamus
Extension
Flexion
Hypothalamus
Inferior
Ipsilateral
Lateral
Medial
Meninges
Meningitis
Mesencephalon
Metencephalon
Midsagittal
Myelencephalon
Parasagittal
Parasympathetic nervous system
Peripheral
Peripheral nervous system (PNS)
Posterior
Pronate
Prosencephalon
Proximal
Sagittal
Somatic nervous system
Spinal cord
Subthalamus
Superior
Supine
Sympathetic nervous system
Thalamus
Transverse
Ventral
Vertebral column
Visceral sensory system
DRAW IT TO KNOW IT
1. Draw a picture of a man or woman and label the following: coronal, transverse, sagittal, superior, inferior, anterior, posterior, lateral, medial, proximal, and distal.
2. Draw a simple picture of the brain (FIGURE 2-19) and label the following: coronal, transverse, sagittal, dorsal, ventral, caudal, and rostral.
FIGURE 2-19 Simple drawing of the brain.
QUESTIONS FOR DEEPER REFLECTION
1. Explain why learning anatomical orientation terms is so important to neuroanatomy.
CASE STUDY
A speech-pathology graduate student has just begun the first day of her hospital externship. While doing rounds with the lead speech-language pathologist and the neurologist, the neurologist showed an MRI of a patient demonstrating a cerebral vascular accident
SUGGESTED PROJECTS
1. Make a Jeopardy-type game with the various navigational terms presented in this chapter. Create categories (directional terms, muscle actions, etc.) and cards with descriptions like in Table 2-3. Students then pick a category, and a card with a description is read from that
2. What approach to organizing the nervous system is most appealing? Why?
(CVA) in the left frontal lobe. This student thought the neurologist had made a mistake because the area she had shown was clearly on the right side of the MRI image. Explain why there is confusion reading this MRI. category. The student responds with “What is .”
2. As a class or in groups, have students play charades with the various navigational terms presented in the chapter.
REFERENCES
Allman, W F. (1990). Apprentices of wonder: Inside the neural network revolution. New York, NY: Bantam Books.
Li, Y., & Owyang, C. (2003). Musings on the wanderer: What’s new in our understanding of vago-vagal reflexes? V. Remodeling of
vagus and enteric neural circuitry after vagal injury. American Journal of Physiology-Gastrointestinal and Liver Physiology, 285(3), G461-G469.