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Other types of cell are also present in nervous tissue, and in the CNS these cells outnumber the neurons by 10:1. Schwann cells of nerve roots and nerves and the cells associated with specialized peripheral nerve-endings.
Internal hydrocephalus: Cerebrospinal fluid (CSF) fails to escape from the ventricles, which expand. T12), lumbar (L1 - L5) and sacral (S1 - S5) nerves go through foramina below the equivalently numbered vertebrae. Lumbar puncture: Cerebrospinal fluid can be sampled by a needle put into the subarachnoid space below the level of the conus medullaris. The cross sectional area of the central gray matter indicates the number of neurons: largest for segments supplying limbs. The cross sectional area of the white matter decreases caudally because there are fewer descending and ascending fibers. Motor neurons are in the ventral horn; sensory axons enter the dorsal horn and the dorsal funiculi. Section of a thoracic segment of the spinal cord showing major groups of neurons in the grey matter, and positions of tracts in white matter. Can you determine what the motor and sensory deficits are, for parts of the body below the segmental level of the lesion? The arteries at the base of the brain anastomose in the circle of Willis (circulus arteriosus, arterial circle). The central arteries are proximal branches of the three cerebral arteries and branches of the posterior communicating arteries. Middle cerebral: Most of the lateral aspect of the hemisphere - frontal, parietal and temporal lobes. The labyrinthine artery, usually a branch of the anterior inferior cerebellar, supplies the inner ear. The differences between the two main ascending somatosensory pathways are important functionally and clinically. The spinothalamic system (= anterolateral system) is for simple touch, warmth, cold and pain. Both the spinothalamic tract and the medial lemniscus terminate in the ventral posterior nucleus of the thalamus. A horizontal section through the left eye, viewed from above, showing the focusing of a real, inverted image on the retina.
Behind the lens, the eyeball is filled by the vitreous body, which is transparent and gelatinous.
The posterior chamber of the eye is between the lens and the iris; the anterior chamber is between the iris and the cornea. The ganglion cells of the retina have axons that pass through the optic nerve to the midbrain and thalamus.
November 27, 2011 By Antranik 15 Comments We have 31 pairs of spinal nerves and they are named after the section of the spine they come out of. Why do we have an 8th pair of cervical nerves if we only have 7 cervical vertebrae you ask?  Well because we start at the top of the atlas and all the nerves are in between the vertebrae so the 8th pair is in between C7 and T1.
Note the difference between roots and rami (ramus is singular).  The rootlets extend out of the spinal cord medially and combine to form roots. The dorsal rami innervate the deep muscles of the back for motor control, such as the erector spinae and also a horizontal strip of skin for sensory input.
Radial travels along radius and innervates Triceps brachii and muscles of the posterior compartment, and overlying skin. The sacral plexus lies caudal to the lumbar plexus (stems from L4 to S4) and is often referred together withthe lumbar plexus as the lumbosacral plexus.  The branches innervate buttocks, pelvis, perineum and lower limb (except for anterior and medial thigh).
Could someone please list the nerves that provide MOTOR INNERVATION to the LOWER extremities? Hello, my name is Antranik and I have a passion for all things relating to the body and mind. You will find a wide range of topics ranging from anatomy and physiology to yoga to gymnastics strength training and more (you just have to explore). I also have a YouTube channel which ties in together with this blog to serve as another outlet for creativity.
Antranik’s Rings Oriented Bodyweight Training RoutineGymnastic rings are the best way to develop strength using only your bodyweight. The ArmAid is a gnarly self-massage tool for your forearms and here is my video review of it! For general information on our other products and services or for technical support, please contact our Customer Care Department within the United States at (800) 762-2974, outside the United States at (317) 572-3993 or fax (317) 572-4002. It is always gratifying to publish the second edition of a textbook because it is an indication that our efforts were well received, that our colleagues endorsed our work, and that students have been well served by it.
Every chapter of this edition was revised to include current material and to make it even easier to read than the first edition. We continued to highlight the interrelationships between systems, structures, and the rest of the body as we describe the various regions of the brain. While we appreciate all of the assistance that we received from our editors and colleagues, the responsibility for errors, omissions, and shortcomings is ours.
The human nervous system is an extremely efficient, compact, fast, and reliable computing system, yet it weighs substantially less than most computers and performs at an incredibly greater capacity. The nervous system is subdivided, morphologically, into two compartments, the central nervous system (CNS) and the peripheral nervous system (PNS). Discussion of the topics of neuroanatomy requires that the student be familiar with some of the specialized terminology of the subject matter. Additional cells, known as neuroglia, constitute several categories of non-neuronal supporting cells. Ependymal cells form a simple cuboidal epithelium that lines the central canal of the spinal cord and the ventricles of the brain. Oligodendroglia form myelin sheaths around axons and also surround dendrites and cell bodies of neurons in the CNS.
The central nervous system is a complex, hollow tube, whose rostral end, the brain, is enlarged and folded in an elaborate manner, whereas its caudal end, the spinal cord, is a long, tubular structure (Fig. The brain is subdivided into five major regions, the largest being the telencephalon, which is composed of the cerebral hemispheres. Figure 1.2 a€? The spinal cord, its meninges, spinal nerves, and sympathetic chain ganglia. The white matter of the spinal cord is composed of ascending and descending tracts of nerve fibers that connect regions of the CNS to each other. White matter is composed of neuroglia and processes of neurons, many of whose axons are wrapped in a myelin sheath, which in a living individual has a white color.
The peripheral nervous system is composed of cranial nerves, spinal nerves, their associated ganglia, and nerve fibers and ganglia of the autonomic nervous system. There are 12 pairs of cranial nerves, identified both by name as well as by Roman numerals I through XII.
There are 31 pairs of spinal nerves (8 cervical, 12 thoracic, 5 lumbar, 5 sacral, and 1 coccygeal), attesting to the segmentation of the spinal cord (see Fig.
Each spinal nerve bifurcates to form a smaller dorsal primary ramus and a larger ventral primary ramus. The autonomic nervous system is a motor system, but unlike somatic motoneurons, it does not serve skeletal muscle cells, instead it innervates visceral muscle (cardiac muscle cells, smooth muscle cells), and secretory cells of glands (see Chapter 10, Autonomic Nervous System).


Figure 1.3 a€? Diagram demonstrating the difference between autonomic innervation (top) and somatic motor innervation (bottom).
The autonomic nervous system is responsible for the maintenance of homeostasis, and is composed of three functional components: sympathetic, parasympathetic, and enteric. Cell bodies of preganglionic sympathetic neurons are located in the lateral horn of the thoracic and upper lumbar spinal cord (T1 to L2, 3), whereas those of the preganglionic parasympathetic neurons are located in the brain (and their axons travel with CN III, VII, IX, and X) and the lateral horn of the sacral spinal cord (S2a€“S4).
The cell bodies of the sensory neurons that supply the viscera are located in the dorsal root ganglia of spinal nerves or in the sensory ganglia of cranial nerves, along with the somatic sensory neurons.
What single characteristic is the major difference between microglia and the other neuroglia of the central nervous system?
What is the major difference between a two-neuron reflex arc and a three-neuron reflex arc, aside from the simplistic fact that one has an extra neuron associated with it?
This diagram also shows structural elements that will be referred to later in this Section. A stretch reflex (tendon jerk) requires the integrity of both the motor and the proprioceptive sensory innervation of the muscle. The posterior inferior cerebellar artery supplies the lateral part of the mid- and upper medulla in addition to the cerebellum. Click the links on the right side of the table to look at the images (which are the ones shown in the lecture). The roots combine to form the spinal nerve and then they split apart again and are now called rami (ramus for singular).  The dorsal root is posterior to the ventral (front) root. Look into the next article about dermatomes for a continuation of the spinal nerve discussion and find out what area of skin is innervated by which spinal nerve. The Sciatic nerve is made up of many roots (L3-S2), but specifically it has two large branches that run together in the posterior thigh region (Tibial and Common Fibular Division). My rings program provides detailed progressions for building strength, learning dozens of fun skills, and a good mix of mobility & prehab accessory exercises that keep you feeling great! No warranty may be created or extended by sales representatives or written sales materials. This new edition of the Textbook of Neuroanatomy, as indeed was the first, was written with the student in mind in full knowledge of the trepidation with which he or she faces the prospect of learning a subject matter that appears to be daunting and intimidating. Two new chapters were added, one concerning the Brainstem (Chapter 7) and the other Spinal Reflexes (Chapter 11), in order to stress the importance of those two topics and to enhance the student's understanding of their significance in the functioning of the central nervous system. We think a broad understanding of neuroanatomy, supported with a basic understanding of its physiology, is critical so that students instead of merely memorizing structures learn the principles thus establishing the foundation for future studies in the health sciences and for the logical forces that help drive it. The first 11 chapters provide an overview of neuroanatomy that introduces terms and should be viewed as the vocabulary lessons that are necessary evils in the mastering of a new language. We would also like to thank our artist, Todd Smith, who worked closely with us to ensure a first-rate art program and Dr.
It has the capability of performing tasks that are far beyond the abilities of any computer yet devised. The CNS is composed of the brain and spinal cord whereas the PNS is composed of cranial and spinal nerve fibers and ganglia, and emanates from and is a physical extension of the CNS. One of the problems that students have in studying neuroanatomy is that there may be numerous terms applied to the same or similar structures. Although there are several types of neurons (detailed in Chapter 3) they all have similar structures and functions. Those in the central nervous system are known as ependymal cells, macroglia, and microglia. Additionally, these cells also participate in the formation of the choroid plexus, vascular tufts of tissue that manufacture cerebrospinal fluid. Schwann cells are located in the PNS and they function in forming myelin around axons of the PNS.
Note that the back of the skull as well as the spinal processes of the vertebrae have been removed and that the dura mater and the arachnoid have been opened up so that the spinal cord may be viewed in its entire length. 1.2) is concentric more or less cylindrical aggregate of nervous tissue, where a cylinder of white matter surrounds a central cylinder of gray matter.
Ventral and dorsal roots at each level of the spinal cord join one another to form the spinal nerves that leave the spinal cord at regular intervals, a condition that is indicative of its segmentation. These axons are collected into small bundles, known as fasciculi, or large bundles, called funiculi (L. It must be understood that the PNS is in physical continuity with the CNS, in fact cell bodies of many of the nerve fibers (axons) of the PNS are located in the CNS. All cranial nerves, with the exception of the vagus (CN X), serve structures in the head and neck only. Dorsal primary rami supply sensory and motor innervation to the back, whereas ventral primary rami supply the lateral and anterior portion of the trunk. Observe that two neurons are present in the autonomic supply, whereas a single motoneuron is present in the somatic motor system.
However, their peripheral processes accompany the preganglionic autonomic fibers into their respective ganglia, but do not synapse in those ganglia. The material appears overwhelming because of the many eponyms that have been retained and add to the inherent complexity of the nervous system. For no matter how well one understands the grammar of a foreign language, it is the possession of a rich vocabulary that permits one to communicate with speakers of that tongue.
Scott Thompson who wrote the clinical cases that begin and close each chapter but two; as well as Dr. The present textbook discusses not only the anatomy of the central nervous system but also its function.
Functionally, the nervous system is also subdivided into two components, the somatic nervous system, which is under the individual's conscious control, and the autonomic nervous system, which controls the myriad of activities in conjunction with the voluntary nervous system. It is important, therefore, to begin the discussion of this subject matter by listing and defining in Table 1.1 some, but not all, of the terminology the student will encounter. Most important is that neurons are specialized in that they are capable of receiving, conducting, and transmitting impulses to each other as well as to muscle cells and cells of glands. The first two are derived from cells of the neural tube, whereas microglia are macrophages whose origins are monocyte precursors of the bone marrow. Macroglia is a collective term for the protoplasmic astrocytes, fibrous astrocytes, and oligodendroglia.
The brain is housed in the cranial cavity and, at the foramen magnum, is continuous with the spinal cord, which is housed in the vertebral canal.
Frequently the medulla oblongata, mesencephalon, and the pons are collectively termed the brainstem.
The neurons of the spinal cord are arranged in such a fashion that those concerned with somatic motor function are located in the ventral horn and their axons leave via the ventral rootlets. Each dorsal root displays a swelling, a dorsal root ganglion, housing the soma of the unipolar (pseudounipolar) neurons. There are two major categories of neurons, (1) those whose axons leave the CNS and (2) those whose axons remain within the CNS. The vagus nerve innervates structures in the head and neck, but also serves many of the thoracic and abdominal viscera, for example, the heart and alimentary tract. The cell bodies of sensory neurons (unipolar neurons) are located in the dorsal root ganglia (sensory ganglia). Ventral rami that supply the thorax and abdomen usually remain as separate nerves, whereas those of the cervical and lumbosacral regions join each other to form plexuses from which individual nerve bundles arise to serve the head, neck (cervical plexus), and upper and lower extremities (cervical and lumbosacral plexuses). 1.3), in the autonomic nervous system the neuron whose cell body is located in the CNS (preganglionic or presynaptic neuron) synapses with a second neuron (postganglionic or postsynaptic neuron) located in a ganglion in the PNS.


The enteric nervous system is situated completely within the wall of the digestive tract and controls the entire process of digestion. The cell bodies of postganglionic parasympathetic neurons, however, are located in ganglia that are in the vicinity of the viscera being innervated. Moreover, these peripheral fibers continue to accompany the postganglionic autonomic fibers to the same destinations.
Happily, for the student the reports of being an overwhelming subject is an unjust reputation, for neuroanatomy is a fascinating topic, whose comprehension does not require amazing brilliance, but merely a willingness to learn new words, the aptitude for reading maps, and following pathways from one place to another.
The second part of this textbook, Chapters 12a€“25, utilizes the vocabulary of the first part to detail information concerning the various pathways and discrete systems that act in concert to perform the myriad of functions of the human nervous system. In case the reader wonders why one should study neuroanatomy, it should be recalled that it is our central nervous system more than anything else about us that makes us what we are, human beings.
The autonomic nervous system is a tripartite organization, in that it has a sympathetic, a parasympathetic, and an entreric component. Neurons have processes known as dendrites and usually that is where they receive information. Protoplasmic astrocytes support neurons in the gray matter, form a subpial barrier, and envelop capillaries of the CNS. The dorsal surface of the spinal cord is closer to the spinous processes of the vertebrae, whereas its ventral surface is closer to the bodies of the vertebrae.
The lumen of the CNS is a narrow slit, which is known as the central canal in the spinal cord.
These are accompanied by axons of the preganglionic sympathetic neurons, located in the lateral horn of the spinal cord in all the thoracic and upper two or three lumbar segments, and axons of preganglionic parasympathetic neurons located in the lateral horn of the sacral spinal cord.
Those cranial nerves that have sensory components possess sensory ganglia housing the cell bodies of unipolar neurons whose single process bifurcates into a central and a peripheral process. Again, it must be remembered that just as in the sensory ganglia of the cranial nerves there are no synapses occurring in the dorsal root ganglia. Each spinal nerve receives sensory information from the skin of the segment, or dermatome, of the body that it serves. It is the axon of the postganglionic neuron that synapses with the cardiac muscle cell, smooth muscle cell, or secretory cell of a gland.
Although the sympathetic and parasympathetic components of the autonomic nervous system do modulate its activities, the enteric nervous system can function quite well on its own if the connections of the sympathetic and parasympathetic components are cut off from it. In spite of their route, these sensory neurons are not considered to be a part of the autonomic nervous system.
Rule of thumb in anatomy or medicine for that matter: Be specific and as accurate as possible. Neither the publisher nor author shall be liable for any loss of profit or any other commercial damages, including but not limited to special, incidental, consequential, or other damages. In order to help the student more easily achieve the goal of learning neuroanatomy we made this textbook complete, concise, yet easy to read, and well-illustrated with many schematic diagrams to expound upon the concepts being discussed. Simply stated, the first initiates the a€?flight or fight or freezea€? response, the second is concerned with the body's vegetative activities, whereas the enteric nervous system is involved in regulating the process of digestion.
They also have a single process, known as an axon, and it is via that single process that they transmit information to other neurons and to effector organs.
Fibrous astrocytes are located in the white matter and appear to function in a similar fashion to protoplasmic astrocytes. Since the CNS, as well as most of the body, is bilaterally symmetrical, the sagittal (midsagittal, according to some) plane bisects it into right and left halves. However, the lumen is expanded into a system of ventricles in the brain and these ventricles are filled with cerebrospinal fluid. The dorsal horn of the spinal cord is the location where central processes of unipolar neurons of dorsal root ganglia enter the spinal cord via dorsal rootlets bringing sensory information to the CNS.
The central process of a unipolar neuron enters the brain, whereas its peripheral process goes to a sensory receptor.
The single process of each neuron bifurcates and the short central process joins other central processes to form dorsal rootlets that enter the spinal cord. The entire body is mapped into a number of dermatomes; however, there are overlaps in the innervation, so that a single dermatome is supplied by more than one spinal nerve. Thus the autonomic nervous system is said to be a two cell system, and synapses always occur within an autonomic ganglion (Fig.
Presenting the material in a relevant context will make the learning experience simpler, more enjoyable, and more memorable.
It must be understood, however, that the interplay of these three systems maintains homeostasis.
Thus dendrites conduct information toward the cell body, whereas axons conduct information away from the cell body. Astrocytes also function in scavenging ions and neurotransmitter substances from the extracellular spaces. Positioning toward the sagittal plane is considered to be the medial direction and away from the sagittal plane is the lateral direction. Twelve pairs of cranial nerves emerge from the brain to supply motor, sensory, parasympathetic innervation, and proprioceptive information for the head and neck and much of the viscera of the body. The most massive commissure of the CNS is the corpus callosum, which connects the two cerebral hemispheres of the brain. Such overlaps prevent the total anesthesia of a particular dermatome if the dorsal rootlets of the spinal nerve supplying it are damaged. The autonomic nervous system acts upon three cell types to perform its functions, namely cells of glands, smooth muscle, and cardiac muscle.
Thus, interneurons have the capability of facilitating or inhibiting a motor response to a sensory stimulus. Axons that travel up or down the CNS and cross the midline from one side to the other are said to decussate at the point of crossing over. Although this description is true for reflex arcs, it must be realized that in most instances the incoming information is transmitted to higher levels in the brain and is processed either cognitively or subconsciously, or both, rather than just relying on simple spinal reflex phenomena which do not involve the brain.
The axon of the preganglionic neuron is myelinated and is known as the preganglionic fiber. Neurons may also communicate with each other via gap junctions which are exceptionally small aqueous pores in the cell membranes of each of two adjacent cells. For example, if one pricks one's finger the reflex response is to pull the finger away from the offending stimulus; however, if a health professional sticks one's finger for a blood test, the interneuron, receiving that information from higher levels in the central nervous system, inhibits the withdrawal of the finger. These motoneurons are multipolar neurons whose cell bodies are located in the ventral horn of the spinal cord and serve skeletal muscle cells only. The axon of the postganglionic neuron is not myelinated, and is known as the postganglionic fiber.
The sensory component collects information and transmits it to the CNS (and is therefore called afferent), where the information is sorted, analyzed, and processed.
These pores are aligned with each other in such a way that they permit the movement of small secondary messenger molecules from the cytoplasm of one cell (the signaling cell) into the cytoplasm of the neighboring cell (the target cell), initiating a requisite response in the target cell.
Their axons leave via the ventral rootlets that join the dorsal rootlets to form the spinal nerve. Generally speaking, the motor component delivers the results of the analysis away from the CNS (and is therefore called efferent) to the effector organs, that is, muscles (all three types: skeletal, smooth, and cardiac) and glands, resulting in a response to the stimulus.



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