awinml/medqa-textbooks-chunked · Datasets at Hugging Face

id stringlengths 14 28	file_name stringclasses 18 values	content stringlengths 1 722k
Anatomy_Gray_200	Anatomy_Gray.txt	Testing movements at successive joints can help in localizing lesions to specific nerves or to a specific spinal cord level. For example:
Anatomy_Gray_201	Anatomy_Gray.txt	Muscles that move the shoulder joint are innervated mainly by spinal nerves from spinal cord levels C5 and C6.
Anatomy_Gray_202	Anatomy_Gray.txt	Muscles that move the elbow are innervated mainly by spinal nerves from spinal cord levels C6 and C7.
Anatomy_Gray_203	Anatomy_Gray.txt	Muscles in the hand are innervated mainly by spinal nerves from spinal cord levels C8 and T1.
Anatomy_Gray_204	Anatomy_Gray.txt	Visceral part of the nervous system
Anatomy_Gray_205	Anatomy_Gray.txt	The visceral part of the nervous system, as in the somatic part, consists of motor and sensory components:
Anatomy_Gray_206	Anatomy_Gray.txt	Sensory nerves monitor changes in the viscera.
Anatomy_Gray_207	Anatomy_Gray.txt	Motor nerves mainly innervate smooth muscle, cardiac muscle, and glands.
Anatomy_Gray_208	Anatomy_Gray.txt	The visceral motor component is commonly referred to as the autonomic division of the PNS and is subdivided into sympathetic and parasympathetic parts.
Anatomy_Gray_209	Anatomy_Gray.txt	Like the somatic part of the nervous system, the visceral part is segmentally arranged and develops in a parallel fashion (Fig. 1.39).
Anatomy_Gray_210	Anatomy_Gray.txt	Visceral sensory neurons that arise from neural crest cells send processes medially into the adjacent neural tube and laterally into regions associated with the developing body. These sensory neurons and their processes, referred to as general visceral afferent fibers (GVAs), are associated primarily with chemoreception, mechanoreception, and stretch reception.
Anatomy_Gray_211	Anatomy_Gray.txt	Visceral motor neurons that arise from cells in lateral regions of the neural tube send processes out of the anterior aspect of the tube. Unlike in the somatic part, these processes, containing general visceral efferent fibers (GVEs), synapse with other cells, usually other visceral motor neurons, that develop outside the CNS from neural crest cells that migrate away from their original positions close to the developing neural tube.
Anatomy_Gray_212	Anatomy_Gray.txt	The visceral motor neurons located in the spinal cord are referred to as preganglionic motor neurons and their axons are called preganglionic fibers; the visceral motor neurons located outside the CNS are referred to as postganglionic motor neurons and their axons are called postganglionic fibers.
Anatomy_Gray_213	Anatomy_Gray.txt	The cell bodies of the visceral motor neurons outside the CNS often associate with each other in a discrete mass called a ganglion.
Anatomy_Gray_214	Anatomy_Gray.txt	Visceral sensory and motor fibers enter and leave the CNS with their somatic equivalents (Fig. 1.40). Visceral sensory fibers enter the spinal cord together with somatic sensory fibers through posterior roots of spinal nerves. Preganglionic fibers of visceral motor neurons exit the spinal cord in the anterior roots of spinal nerves, along with fibers from somatic motor neurons.
Anatomy_Gray_215	Anatomy_Gray.txt	Postganglionic fibers traveling to visceral elements in the periphery are found in the posterior and anterior rami (branches) of spinal nerves.
Anatomy_Gray_216	Anatomy_Gray.txt	Visceral motor and sensory fibers that travel to and from viscera form named visceral branches that are separate from the somatic branches. These nerves generally form plexuses from which arise branches to the viscera.
Anatomy_Gray_217	Anatomy_Gray.txt	Visceral motor and sensory fibers do not enter and leave the CNS at all levels (Fig. 1.41):
Anatomy_Gray_218	Anatomy_Gray.txt	In the cranial region, visceral components are associated with four of the twelve cranial nerves (CN III, VII, IX, and X).
Anatomy_Gray_219	Anatomy_Gray.txt	In the spinal cord, visceral components are associated mainly with spinal cord levels T1 to L2 and S2 to S4.
Anatomy_Gray_220	Anatomy_Gray.txt	Visceral motor components associated with spinal levels T1 to L2 are termed sympathetic. Those visceral motor components in cranial and sacral regions, on either side of the sympathetic region, are termed parasympathetic:
Anatomy_Gray_221	Anatomy_Gray.txt	The sympathetic system innervates structures in peripheral regions of the body and viscera.
Anatomy_Gray_222	Anatomy_Gray.txt	The parasympathetic system is more restricted to innervation of the viscera only.
Anatomy_Gray_223	Anatomy_Gray.txt	Spinal sympathetic and spinal parasympathetic neurons share certain developmental and phenotypic features that are different from those of cranial parasympathetic neurons. Based on this, some researchers have suggested reclassifying all spinal visceral motor neurons as sympathetic (Espinosa-Medina I et al. Science 2016;354:893-897). Others are against reclassification, arguing that the results only indicate that the neurons are spinal in origin (Neuhuber W et al. Anat Rec 2017;300:1369-1370). In addition, sacral nerves do not enter the sympathetic trunk, nor do they have postganglionic fibers that travel to the periphery on spinal nerves, as do T1-L2 visceral motor fibers. We have chosen to retain the classification of S2,3,4 visceral motor neurons as parasympathetic. “Parasympathetic” simply means on either side of the “sympathetic,” which correctly describes their anatomy.
Anatomy_Gray_224	Anatomy_Gray.txt	The sympathetic part of the autonomic division of the PNS leaves thoracolumbar regions of the spinal cord with the somatic components of spinal nerves T1 to L2 (Fig. 1.42). On each side, a paravertebral sympathetic trunk extends from the base of the skull to the inferior end of the vertebral column where the two trunks converge anteriorly to the coccyx at the ganglion impar. Each trunk is attached to the anterior rami of spinal nerves and becomes the route by which sympathetics are distributed to the periphery and all viscera.
Anatomy_Gray_225	Anatomy_Gray.txt	Visceral motor preganglionic fibers leave the T1 to L2 part of the spinal cord in anterior roots. The fibers then enter the spinal nerves, pass through the anterior rami and into the sympathetic trunks. One trunk is located on each side of the vertebral column (paravertebral) and positioned anterior to the anterior rami. Along the trunk is a series of segmentally arranged ganglia formed from collections of postganglionic neuronal cell bodies where the preganglionic neurons synapse with postganglionic neurons. Anterior rami of T1 to L2 are connected to the sympathetic trunk or to a ganglion by a white ramus communicans, which carries preganglionic sympathetic fibers and appears white because the fibers it contains are myelinated.
Anatomy_Gray_226	Anatomy_Gray.txt	Preganglionic sympathetic fibers that enter a paravertebral ganglion or the sympathetic trunk through a white ramus communicans may take the following four pathways to target tissues: 1. Peripheral sympathetic innervation at the level of origin of the preganglionic fiber
Anatomy_Gray_227	Anatomy_Gray.txt	Preganglionic sympathetic fibers may synapse with postganglionic motor neurons in ganglia associated with the sympathetic trunk, after which postganglionic fibers enter the same anterior ramus and are distributed with peripheral branches of the posterior and anterior rami of that spinal nerve (Fig. 1.43). The fibers innervate structures at the periphery of the body in regions supplied by the spinal nerve. The gray ramus communicans connects the sympathetic trunk or a ganglion to the anterior ramus and contains the postganglionic sympathetic fibers. It appears gray because postganglionic fibers are nonmyelinated. The gray ramus communicans is positioned medial to the white ramus communicans.
Anatomy_Gray_228	Anatomy_Gray.txt	2. Peripheral sympathetic innervation above or below the level of origin of the preganglionic fiber
Anatomy_Gray_229	Anatomy_Gray.txt	Preganglionic sympathetic fibers may ascend or descend to other vertebral levels where they synapse in ganglia associated with spinal nerves that may or may not have visceral motor input directly from the spinal cord (i.e., those nerves other than T1 to L2) (Fig. 1.44).
Anatomy_Gray_230	Anatomy_Gray.txt	The postganglionic fibers leave the distant ganglia via gray rami communicantes and are distributed along the posterior and anterior rami of the spinal nerves.
Anatomy_Gray_231	Anatomy_Gray.txt	The ascending and descending fibers, together with all the ganglia, form the paravertebral sympathetic trunk, which extends the entire length of the vertebral column. The formation of this trunk, on each side, enables visceral motor fibers of the sympathetic part of the autonomic division of the PNS, which ultimately emerge from only a small region of the spinal cord (T1 to L2), to be distributed to peripheral regions innervated by all spinal nerves.
Anatomy_Gray_232	Anatomy_Gray.txt	White rami communicantes only occur in association with spinal nerves T1 to L2, whereas gray rami communicantes are associated with all spinal nerves.
Anatomy_Gray_233	Anatomy_Gray.txt	Fibers from spinal cord levels T1 to T5 pass predominantly superiorly, whereas fibers from T5 to L2 pass inferiorly. All sympathetics passing into the head have preganglionic fibers that emerge from spinal cord level
Anatomy_Gray_234	Anatomy_Gray.txt	T1 and ascend in the sympathetic trunks to the highest ganglion in the neck (the superior cervical ganglion), where they synapse. Postganglionic fibers then travel along blood vessels to target tissues in the head, including blood vessels, sweat glands, small smooth muscles associated with the upper eyelids, and the dilator of the pupil.
Anatomy_Gray_235	Anatomy_Gray.txt	3. Sympathetic innervation of thoracic
Anatomy_Gray_236	Anatomy_Gray.txt	Preganglionic sympathetic fibers may synapse with postganglionic motor neurons in ganglia and then leave the ganglia medially to innervate thoracic or cervical viscera (Fig. 1.45). They may ascend in the trunk before synapsing, and after synapsing the postganglionic fibers may combine with those from other levels to form named visceral nerves, such as cardiac nerves. Often, these nerves join branches from the parasympathetic system to form plexuses on or near the surface of the target organ, for example, the cardiac and pulmonary plexuses. Branches of the plexus innervate the organ. Spinal cord levels T1 to T5 mainly innervate cranial, cervical, and thoracic viscera.
Anatomy_Gray_237	Anatomy_Gray.txt	4. Sympathetic innervation of the abdomen and pelvic regions and the adrenals
Anatomy_Gray_238	Anatomy_Gray.txt	Preganglionic sympathetic fibers may pass through the sympathetic trunk and paravertebral ganglia without synapsing and, together with similar fibers from other levels, form splanchnic nerves (greater, lesser, least, lumbar, and sacral), which pass into the abdomen and pelvic regions (Fig. 1.46). The preganglionic fibers in these nerves are derived from spinal cord levels T5 to L2.
Anatomy_Gray_239	Anatomy_Gray.txt	The splanchnic nerves generally connect with sympathetic ganglia around the roots of major arteries that branch from the abdominal aorta. These ganglia are part of a large prevertebral plexus that also has input from the parasympathetic part of the autonomic division of the PNS. Postganglionic sympathetic fibers are distributed in extensions of this plexus, predominantly along arteries, to viscera in the abdomen and pelvis.
Anatomy_Gray_240	Anatomy_Gray.txt	Some of the preganglionic fibers in the prevertebral plexus do not synapse in the sympathetic ganglia of the plexus but pass through the system to the adrenal gland, where they synapse directly with cells of the adrenal medulla. These cells are homologues of sympathetic postganglionic neurons and secrete adrenaline and noradrenaline into the vascular system.
Anatomy_Gray_241	Anatomy_Gray.txt	The parasympathetic part of the autonomic division of the PNS (Fig. 1.47) leaves cranial and sacral regions of the CNS in association with: cranial nerves III, VII, IX, and X: III, VII, and IX carry parasympathetic fibers to structures within the head and neck only, whereas X (the vagus spinal nerves S2 to S4: sacral parasympathetic fibers innervate inferior abdominal viscera, pelvic viscera, and the arteries associated with erectile tissues of the perineum.
Anatomy_Gray_242	Anatomy_Gray.txt	Like the visceral motor nerves of the sympathetic part, the visceral motor nerves of the parasympathetic part generally have two neurons in the pathway. The preganglionic neurons are in the CNS, and fibers leave in the cranial nerves.
Anatomy_Gray_243	Anatomy_Gray.txt	In the sacral region, the preganglionic parasympathetic fibers form special visceral nerves (the pelvic splanchnic nerves), which originate from the anterior rami of S2 to S4 and enter pelvic extensions of the large prevertebral plexus formed around the abdominal aorta. These fibers are distributed to pelvic and abdominal viscera mainly along blood vessels. The postganglionic motor neurons are in the walls of the viscera. In organs of the gastrointestinal system, preganglionic fibers do not have a postganglionic parasympathetic motor neuron in the pathway; instead, preganglionic fibers synapse directly on neurons in the ganglia of the enteric system.
Anatomy_Gray_244	Anatomy_Gray.txt	The preganglionic parasympathetic motor fibers in CN
Anatomy_Gray_245	Anatomy_Gray.txt	III, VII, and IX separate from the nerves and connect with one of four distinct ganglia, which house postganglionic motor neurons. These four ganglia are near major branches of CN V. Postganglionic fibers leave the ganglia, join the branches of CN V, and are carried to target tissues (salivary, mucous, and lacrimal glands; constrictor muscle of the pupil; and ciliary muscle in the eye) with these branches.
Anatomy_Gray_246	Anatomy_Gray.txt	The vagus nerve [X] gives rise to visceral branches along its course. These branches contribute to plexuses associated with thoracic viscera or to the large prevertebral plexus in the abdomen and pelvis. Many of these plexuses also contain sympathetic fibers.
Anatomy_Gray_247	Anatomy_Gray.txt	When present, postganglionic parasympathetic neurons are in the walls of the target viscera.
Anatomy_Gray_248	Anatomy_Gray.txt	motor fibers.
Anatomy_Gray_249	Anatomy_Gray.txt	Visceral sensory fibers follow the course of sympathetic fibers entering the spinal cord at similar spinal cord levels. However, visceral sensory fibers may also enter the spinal cord at levels other than those associated with motor output. For example, visceral sensory fibers from the heart may enter at levels higher than spinal cord level T1. Visceral sensory fibers that accompany sympathetic fibers are mainly concerned with detecting pain.
Anatomy_Gray_250	Anatomy_Gray.txt	Visceral sensory fibers accompanying parasympathetic fibers are carried mainly in IX and X and in spinal nerves S2 to S4.
Anatomy_Gray_251	Anatomy_Gray.txt	Visceral sensory fibers in IX carry information from chemoreceptors and baroreceptors associated with the walls of major arteries in the neck, and from receptors in the pharynx.
Anatomy_Gray_252	Anatomy_Gray.txt	Visceral sensory fibers in X include those from cervical viscera, and major vessels and viscera in the thorax and abdomen.
Anatomy_Gray_253	Anatomy_Gray.txt	Visceral sensory fibers from pelvic viscera and the distal parts of the colon are carried in S2 to S4.
Anatomy_Gray_254	Anatomy_Gray.txt	Visceral sensory fibers associated with parasympathetic fibers primarily relay information to the CNS about the status of normal physiological processes and reflex activities.
Anatomy_Gray_255	Anatomy_Gray.txt	The enteric system
Anatomy_Gray_256	Anatomy_Gray.txt	The enteric nervous system consists of motor and sensory neurons and their support cells, which form two interconnected plexuses, the myenteric and submucous nerve plexuses, within the walls of the gastrointestinal tract (Fig. 1.48). Each of these plexuses is formed by: ganglia, which house the nerve cell bodies and associated cells, and bundles of nerve fibers, which pass between ganglia and from the ganglia into surrounding tissues.
Anatomy_Gray_257	Anatomy_Gray.txt	Neurons in the enteric system are derived from neural crest cells originally associated with occipitocervical and sacral regions. Interestingly, more neurons are reported to be in the enteric system than in the spinal cord itself.
Anatomy_Gray_258	Anatomy_Gray.txt	Sensory and motor neurons within the enteric system control reflex activity within and between parts of the gastrointestinal system. These reflexes regulate peristalsis, secretomotor activity, and vascular tone. These activities can occur independently of the brain and spinal cord, but can also be modified by input from preganglionic parasympathetic and postganglionic sympathetic fibers.
Anatomy_Gray_259	Anatomy_Gray.txt	Sensory information from the enteric system is carried back to the CNS by visceral sensory fibers.
Anatomy_Gray_260	Anatomy_Gray.txt	Nerve plexuses are either somatic or visceral and combine fibers from different sources or levels to form new nerves with specific targets or destinations (Fig. 1.49). Plexuses of the enteric system also generate reflex activity independent of the CNS.
Anatomy_Gray_261	Anatomy_Gray.txt	Major somatic plexuses formed from the anterior rami of spinal nerves are the cervical (C1 to C4), brachial (C5 to T1), lumbar (L1 to L4), sacral (L4 to S4), and coccygeal (S5 to Co) plexuses. Except for spinal nerve T1, the anterior rami of thoracic spinal nerves remain independent and do not participate in plexuses.
Anatomy_Gray_262	Anatomy_Gray.txt	Visceral nerve plexuses are formed in association with viscera and generally contain efferent (sympathetic and parasympathetic) and afferent components (Fig. 1.49). These plexuses include cardiac and pulmonary plexuses in the thorax and a large prevertebral plexus in the abdomen anterior to the aorta, which extends inferiorly onto the lateral walls of the pelvis. The massive prevertebral plexus supplies input to and receives output from all abdominal and pelvic viscera.
Anatomy_Gray_263	Anatomy_Gray.txt	Specific information about the organization and components of the respiratory, gastrointestinal, and urogenital systems will be discussed in each of the succeeding chapters of this text.
Anatomy_Gray_264	Anatomy_Gray.txt	Fig. 1.1 The anatomical position, planes, and terms of location and orientation.
Anatomy_Gray_265	Anatomy_Gray.txt	Feet togethertoes forwardHands by sidespalms forwardFace looking forwardInferior margin of orbit level withtop of external auditory meatusSagittal planeCoronal planeSuperiorAnteriorPosteriorMedialLateralInferiorTransverse, horizontal,or axial plane
Anatomy_Gray_266	Anatomy_Gray.txt	Fig. 1.2 Cathode ray tube for the production of X-rays.
Anatomy_Gray_267	Anatomy_Gray.txt	Fig. 1.3 Fluoroscopy unit.
Anatomy_Gray_268	Anatomy_Gray.txt	Fig. 1.4 Barium sulfate follow
Anatomy_Gray_269	Anatomy_Gray.txt	through.
Anatomy_Gray_270	Anatomy_Gray.txt	Fig. 1.5 Digital subtraction angiogram.
Anatomy_Gray_271	Anatomy_Gray.txt	Fig. 1.6 Ultrasound examination of the abdomen.
Anatomy_Gray_272	Anatomy_Gray.txt	Fig. 1.7 Computed tomography scanner.
Anatomy_Gray_273	Anatomy_Gray.txt	Fig. 1.8 Computed tomography scan of the abdomen at vertebral level L2.
Anatomy_Gray_274	Anatomy_Gray.txt	Fig. 1.9 A T2-weighted MR image in the sagittal plane of the pelvic viscera in a woman.
Anatomy_Gray_275	Anatomy_Gray.txt	Fig. 1.10 T1-weighted (A) and T2-weighted (B) MR images of the brain in the coronal plane.
Anatomy_Gray_276	Anatomy_Gray.txt	Fig. 1.11 A gamma camera.
Anatomy_Gray_277	Anatomy_Gray.txt	Fig. 1.12 The axial skeleton and the appendicular skeleton.
Anatomy_Gray_278	Anatomy_Gray.txt	Fig. 1.13 Accessory and sesamoid bones. A. Radiograph of the ankle region showing an accessory bone (os trigonum).
Anatomy_Gray_279	Anatomy_Gray.txt	B. Radiograph of the feet showing numerous sesamoid bones and an accessory bone (os naviculare).
Anatomy_Gray_280	Anatomy_Gray.txt	Fig. 1.14 A developmental series of radiographs showing the progressive ossification of carpal (wrist) bones from 3 (A) to 10 (D) years of age.
Anatomy_Gray_281	Anatomy_Gray.txt	Fig. 1.15 T1-weighted image in the coronal plane, demonstrating the relatively high signal intensity returned from the femoral heads and proximal femoral necks, consistent with yellow marrow. In this young patient, the vertebral bodies return an intermediate darker signal that represents red marrow. There is relatively little fat in these vertebrae; hence the lower signal return.
Anatomy_Gray_282	Anatomy_Gray.txt	Fig. 1.16 Radiograph, lateral view, showing fracture of the ulna at the elbow joint (A) and repair of this fracture (B) using internal fixation with a plate and multiple screws.
Anatomy_Gray_283	Anatomy_Gray.txt	Fig. 1.17 Image of the hip joints demonstrating loss of height of the right femoral head with juxta-articular bony sclerosis and subchondral cyst formation secondary to avascular necrosis. There is also significant wasting of the muscles supporting the hip, which is secondary to disuse and pain.
Anatomy_Gray_284	Anatomy_Gray.txt	Normal left hipBladderAvascular necrosisWasting of gluteal muscle
Anatomy_Gray_285	Anatomy_Gray.txt	Fig. 1.18 Joints. A. Synovial joint. B. Solid joint.
Anatomy_Gray_286	Anatomy_Gray.txt	Fig. 1.19 Synovial joints. A. Major features of a synovial joint. B. Accessory structures associated with synovial joints.
Anatomy_Gray_287	Anatomy_Gray.txt	Fig. 1.20 Various types of synovial joints. A. Condylar (wrist). B. Gliding (radio-ulnar). C. Hinge (elbow). D. Ball and socket (hip). E. Saddle (carpometacarpal of thumb). F. Pivot (atlanto-axial).
Anatomy_Gray_288	Anatomy_Gray.txt	Fig. 1.21 Solid joints.
Anatomy_Gray_289	Anatomy_Gray.txt	Fig. 1.22 This operative photograph demonstrates the focal areas of cartilage loss in the patella and femoral condyles throughout the knee joint.
Anatomy_Gray_290	Anatomy_Gray.txt	Fig. 1.23 This radiograph demonstrates the loss of joint space in the medial compartment and presence of small spiky osteophytic regions at the medial lateral aspect of the joint.
Anatomy_Gray_291	Anatomy_Gray.txt	OsteophytesLoss of joint space
Anatomy_Gray_292	Anatomy_Gray.txt	Fig. 1.24 After knee replacement. This radiograph shows the position of the prosthesis.
Anatomy_Gray_293	Anatomy_Gray.txt	Fig. 1.25 This is a radiograph, anteroposterior view, of the pelvis after a right total hip replacement. There are additional significant degenerative changes in the left hip joint, which will also need to be replaced.
Anatomy_Gray_294	Anatomy_Gray.txt	Fig. 1.26 Axial inversion recovery MR imaging series, which suppresses fat and soft tissue and leaves high signal intensity where fluid is seen. A muscle tear in the right adductor longus with edema in and around the muscle is shown.
Anatomy_Gray_295	Anatomy_Gray.txt	Fig. 1.27 Photograph demonstrating varicose veins.
Anatomy_Gray_296	Anatomy_Gray.txt	Fig. 1.28 Lymphatic vessels mainly collect fluid lost from vascular capillary beds during nutrient exchange processes and deliver it back to the venous side of the vascular system.
Anatomy_Gray_297	Anatomy_Gray.txt	Fig. 1.29 Regions associated with clusters or a particular abundance of lymph nodes.
Anatomy_Gray_298	Anatomy_Gray.txt	Cervical nodes(along courseof internaljugular vein)Axillary nodes(in axilla)Deep nodes(related to aortaand celiac trunkand superior andinferior mesentericarteries)Pericranial ring(base of head)Tracheal nodes(nodes related totrachea and bronchi)Inguinal nodes(along course ofinguinal ligament)Femoral nodes(along femoral vein)
Anatomy_Gray_299	Anatomy_Gray.txt	Fig. 1.30 Major lymphatic vessels that drain into large veins in the neck.

Anatomy_Gray_200

Anatomy_Gray.txt

Testing movements at successive joints can help in localizing lesions to specific nerves or to a specific spinal cord level. For example:

Anatomy_Gray_201

Anatomy_Gray.txt

Muscles that move the shoulder joint are innervated mainly by spinal nerves from spinal cord levels C5 and C6.

Anatomy_Gray_202

Anatomy_Gray.txt

Muscles that move the elbow are innervated mainly by spinal nerves from spinal cord levels C6 and C7.

Anatomy_Gray_203

Anatomy_Gray.txt

Muscles in the hand are innervated mainly by spinal nerves from spinal cord levels C8 and T1.

Anatomy_Gray_204

Anatomy_Gray.txt

Visceral part of the nervous system

Anatomy_Gray_205

Anatomy_Gray.txt

The visceral part of the nervous system, as in the somatic part, consists of motor and sensory components:

Anatomy_Gray_206

Anatomy_Gray.txt

Sensory nerves monitor changes in the viscera.

Anatomy_Gray_207

Anatomy_Gray.txt

Motor nerves mainly innervate smooth muscle, cardiac muscle, and glands.

Anatomy_Gray_208

Anatomy_Gray.txt

The visceral motor component is commonly referred to as the autonomic division of the PNS and is subdivided into sympathetic and parasympathetic parts.

Anatomy_Gray_209

Anatomy_Gray.txt

Like the somatic part of the nervous system, the visceral part is segmentally arranged and develops in a parallel fashion (Fig. 1.39).

Anatomy_Gray_210

Anatomy_Gray.txt

Visceral sensory neurons that arise from neural crest cells send processes medially into the adjacent neural tube and laterally into regions associated with the developing body. These sensory neurons and their processes, referred to as general visceral afferent fibers (GVAs), are associated primarily with chemoreception, mechanoreception, and stretch reception.

Anatomy_Gray_211

Anatomy_Gray.txt

Visceral motor neurons that arise from cells in lateral regions of the neural tube send processes out of the anterior aspect of the tube. Unlike in the somatic part, these processes, containing general visceral efferent fibers (GVEs), synapse with other cells, usually other visceral motor neurons, that develop outside the CNS from neural crest cells that migrate away from their original positions close to the developing neural tube.

Anatomy_Gray_212

Anatomy_Gray.txt

The visceral motor neurons located in the spinal cord are referred to as preganglionic motor neurons and their axons are called preganglionic fibers; the visceral motor neurons located outside the CNS are referred to as postganglionic motor neurons and their axons are called postganglionic fibers.

Anatomy_Gray_213

Anatomy_Gray.txt

The cell bodies of the visceral motor neurons outside the CNS often associate with each other in a discrete mass called a ganglion.

Anatomy_Gray_214

Anatomy_Gray.txt

Visceral sensory and motor fibers enter and leave the CNS with their somatic equivalents (Fig. 1.40). Visceral sensory fibers enter the spinal cord together with somatic sensory fibers through posterior roots of spinal nerves. Preganglionic fibers of visceral motor neurons exit the spinal cord in the anterior roots of spinal nerves, along with fibers from somatic motor neurons.

Anatomy_Gray_215

Anatomy_Gray.txt

Postganglionic fibers traveling to visceral elements in the periphery are found in the posterior and anterior rami (branches) of spinal nerves.

Anatomy_Gray_216

Anatomy_Gray.txt

Visceral motor and sensory fibers that travel to and from viscera form named visceral branches that are separate from the somatic branches. These nerves generally form plexuses from which arise branches to the viscera.

Anatomy_Gray_217

Anatomy_Gray.txt

Visceral motor and sensory fibers do not enter and leave the CNS at all levels (Fig. 1.41):

Anatomy_Gray_218

Anatomy_Gray.txt

In the cranial region, visceral components are associated with four of the twelve cranial nerves (CN III, VII, IX, and X).

Anatomy_Gray_219

Anatomy_Gray.txt

In the spinal cord, visceral components are associated mainly with spinal cord levels T1 to L2 and S2 to S4.

Anatomy_Gray_220

Anatomy_Gray.txt

Visceral motor components associated with spinal levels T1 to L2 are termed sympathetic. Those visceral motor components in cranial and sacral regions, on either side of the sympathetic region, are termed parasympathetic:

Anatomy_Gray_221

Anatomy_Gray.txt

The sympathetic system innervates structures in peripheral regions of the body and viscera.

Anatomy_Gray_222

Anatomy_Gray.txt

The parasympathetic system is more restricted to innervation of the viscera only.

Anatomy_Gray_223

Anatomy_Gray.txt

Spinal sympathetic and spinal parasympathetic neurons share certain developmental and phenotypic features that are different from those of cranial parasympathetic neurons. Based on this, some researchers have suggested reclassifying all spinal visceral motor neurons as sympathetic (Espinosa-Medina I et al. Science 2016;354:893-897). Others are against reclassification, arguing that the results only indicate that the neurons are spinal in origin (Neuhuber W et al. Anat Rec 2017;300:1369-1370). In addition, sacral nerves do not enter the sympathetic trunk, nor do they have postganglionic fibers that travel to the periphery on spinal nerves, as do T1-L2 visceral motor fibers. We have chosen to retain the classification of S2,3,4 visceral motor neurons as parasympathetic. “Parasympathetic” simply means on either side of the “sympathetic,” which correctly describes their anatomy.

Anatomy_Gray_224

Anatomy_Gray.txt

The sympathetic part of the autonomic division of the PNS leaves thoracolumbar regions of the spinal cord with the somatic components of spinal nerves T1 to L2 (Fig. 1.42). On each side, a paravertebral sympathetic trunk extends from the base of the skull to the inferior end of the vertebral column where the two trunks converge anteriorly to the coccyx at the ganglion impar. Each trunk is attached to the anterior rami of spinal nerves and becomes the route by which sympathetics are distributed to the periphery and all viscera.

Anatomy_Gray_225

Anatomy_Gray.txt

Visceral motor preganglionic fibers leave the T1 to L2 part of the spinal cord in anterior roots. The fibers then enter the spinal nerves, pass through the anterior rami and into the sympathetic trunks. One trunk is located on each side of the vertebral column (paravertebral) and positioned anterior to the anterior rami. Along the trunk is a series of segmentally arranged ganglia formed from collections of postganglionic neuronal cell bodies where the preganglionic neurons synapse with postganglionic neurons. Anterior rami of T1 to L2 are connected to the sympathetic trunk or to a ganglion by a white ramus communicans, which carries preganglionic sympathetic fibers and appears white because the fibers it contains are myelinated.

Anatomy_Gray_226

Anatomy_Gray.txt

Preganglionic sympathetic fibers that enter a paravertebral ganglion or the sympathetic trunk through a white ramus communicans may take the following four pathways to target tissues: 1. Peripheral sympathetic innervation at the level of origin of the preganglionic fiber

Anatomy_Gray_227

Anatomy_Gray.txt

Preganglionic sympathetic fibers may synapse with postganglionic motor neurons in ganglia associated with the sympathetic trunk, after which postganglionic fibers enter the same anterior ramus and are distributed with peripheral branches of the posterior and anterior rami of that spinal nerve (Fig. 1.43). The fibers innervate structures at the periphery of the body in regions supplied by the spinal nerve. The gray ramus communicans connects the sympathetic trunk or a ganglion to the anterior ramus and contains the postganglionic sympathetic fibers. It appears gray because postganglionic fibers are nonmyelinated. The gray ramus communicans is positioned medial to the white ramus communicans.

Anatomy_Gray_228

Anatomy_Gray.txt

2. Peripheral sympathetic innervation above or below the level of origin of the preganglionic fiber

Anatomy_Gray_229

Anatomy_Gray.txt

Preganglionic sympathetic fibers may ascend or descend to other vertebral levels where they synapse in ganglia associated with spinal nerves that may or may not have visceral motor input directly from the spinal cord (i.e., those nerves other than T1 to L2) (Fig. 1.44).

Anatomy_Gray_230

Anatomy_Gray.txt

The postganglionic fibers leave the distant ganglia via gray rami communicantes and are distributed along the posterior and anterior rami of the spinal nerves.

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The ascending and descending fibers, together with all the ganglia, form the paravertebral sympathetic trunk, which extends the entire length of the vertebral column. The formation of this trunk, on each side, enables visceral motor fibers of the sympathetic part of the autonomic division of the PNS, which ultimately emerge from only a small region of the spinal cord (T1 to L2), to be distributed to peripheral regions innervated by all spinal nerves.

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White rami communicantes only occur in association with spinal nerves T1 to L2, whereas gray rami communicantes are associated with all spinal nerves.

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Fibers from spinal cord levels T1 to T5 pass predominantly superiorly, whereas fibers from T5 to L2 pass inferiorly. All sympathetics passing into the head have preganglionic fibers that emerge from spinal cord level

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T1 and ascend in the sympathetic trunks to the highest ganglion in the neck (the superior cervical ganglion), where they synapse. Postganglionic fibers then travel along blood vessels to target tissues in the head, including blood vessels, sweat glands, small smooth muscles associated with the upper eyelids, and the dilator of the pupil.

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3. Sympathetic innervation of thoracic

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Preganglionic sympathetic fibers may synapse with postganglionic motor neurons in ganglia and then leave the ganglia medially to innervate thoracic or cervical viscera (Fig. 1.45). They may ascend in the trunk before synapsing, and after synapsing the postganglionic fibers may combine with those from other levels to form named visceral nerves, such as cardiac nerves. Often, these nerves join branches from the parasympathetic system to form plexuses on or near the surface of the target organ, for example, the cardiac and pulmonary plexuses. Branches of the plexus innervate the organ. Spinal cord levels T1 to T5 mainly innervate cranial, cervical, and thoracic viscera.

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4. Sympathetic innervation of the abdomen and pelvic regions and the adrenals

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Preganglionic sympathetic fibers may pass through the sympathetic trunk and paravertebral ganglia without synapsing and, together with similar fibers from other levels, form splanchnic nerves (greater, lesser, least, lumbar, and sacral), which pass into the abdomen and pelvic regions (Fig. 1.46). The preganglionic fibers in these nerves are derived from spinal cord levels T5 to L2.

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The splanchnic nerves generally connect with sympathetic ganglia around the roots of major arteries that branch from the abdominal aorta. These ganglia are part of a large prevertebral plexus that also has input from the parasympathetic part of the autonomic division of the PNS. Postganglionic sympathetic fibers are distributed in extensions of this plexus, predominantly along arteries, to viscera in the abdomen and pelvis.

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Some of the preganglionic fibers in the prevertebral plexus do not synapse in the sympathetic ganglia of the plexus but pass through the system to the adrenal gland, where they synapse directly with cells of the adrenal medulla. These cells are homologues of sympathetic postganglionic neurons and secrete adrenaline and noradrenaline into the vascular system.

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The parasympathetic part of the autonomic division of the PNS (Fig. 1.47) leaves cranial and sacral regions of the CNS in association with: cranial nerves III, VII, IX, and X: III, VII, and IX carry parasympathetic fibers to structures within the head and neck only, whereas X (the vagus spinal nerves S2 to S4: sacral parasympathetic fibers innervate inferior abdominal viscera, pelvic viscera, and the arteries associated with erectile tissues of the perineum.

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Like the visceral motor nerves of the sympathetic part, the visceral motor nerves of the parasympathetic part generally have two neurons in the pathway. The preganglionic neurons are in the CNS, and fibers leave in the cranial nerves.

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In the sacral region, the preganglionic parasympathetic fibers form special visceral nerves (the pelvic splanchnic nerves), which originate from the anterior rami of S2 to S4 and enter pelvic extensions of the large prevertebral plexus formed around the abdominal aorta. These fibers are distributed to pelvic and abdominal viscera mainly along blood vessels. The postganglionic motor neurons are in the walls of the viscera. In organs of the gastrointestinal system, preganglionic fibers do not have a postganglionic parasympathetic motor neuron in the pathway; instead, preganglionic fibers synapse directly on neurons in the ganglia of the enteric system.

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The preganglionic parasympathetic motor fibers in CN

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III, VII, and IX separate from the nerves and connect with one of four distinct ganglia, which house postganglionic motor neurons. These four ganglia are near major branches of CN V. Postganglionic fibers leave the ganglia, join the branches of CN V, and are carried to target tissues (salivary, mucous, and lacrimal glands; constrictor muscle of the pupil; and ciliary muscle in the eye) with these branches.

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The vagus nerve [X] gives rise to visceral branches along its course. These branches contribute to plexuses associated with thoracic viscera or to the large prevertebral plexus in the abdomen and pelvis. Many of these plexuses also contain sympathetic fibers.

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When present, postganglionic parasympathetic neurons are in the walls of the target viscera.

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motor fibers.

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Visceral sensory fibers follow the course of sympathetic fibers entering the spinal cord at similar spinal cord levels. However, visceral sensory fibers may also enter the spinal cord at levels other than those associated with motor output. For example, visceral sensory fibers from the heart may enter at levels higher than spinal cord level T1. Visceral sensory fibers that accompany sympathetic fibers are mainly concerned with detecting pain.

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Visceral sensory fibers accompanying parasympathetic fibers are carried mainly in IX and X and in spinal nerves S2 to S4.

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Visceral sensory fibers in IX carry information from chemoreceptors and baroreceptors associated with the walls of major arteries in the neck, and from receptors in the pharynx.

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Visceral sensory fibers in X include those from cervical viscera, and major vessels and viscera in the thorax and abdomen.

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Visceral sensory fibers from pelvic viscera and the distal parts of the colon are carried in S2 to S4.

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Visceral sensory fibers associated with parasympathetic fibers primarily relay information to the CNS about the status of normal physiological processes and reflex activities.

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The enteric system

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The enteric nervous system consists of motor and sensory neurons and their support cells, which form two interconnected plexuses, the myenteric and submucous nerve plexuses, within the walls of the gastrointestinal tract (Fig. 1.48). Each of these plexuses is formed by: ganglia, which house the nerve cell bodies and associated cells, and bundles of nerve fibers, which pass between ganglia and from the ganglia into surrounding tissues.

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Neurons in the enteric system are derived from neural crest cells originally associated with occipitocervical and sacral regions. Interestingly, more neurons are reported to be in the enteric system than in the spinal cord itself.

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Sensory and motor neurons within the enteric system control reflex activity within and between parts of the gastrointestinal system. These reflexes regulate peristalsis, secretomotor activity, and vascular tone. These activities can occur independently of the brain and spinal cord, but can also be modified by input from preganglionic parasympathetic and postganglionic sympathetic fibers.

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Sensory information from the enteric system is carried back to the CNS by visceral sensory fibers.

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Nerve plexuses are either somatic or visceral and combine fibers from different sources or levels to form new nerves with specific targets or destinations (Fig. 1.49). Plexuses of the enteric system also generate reflex activity independent of the CNS.

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Major somatic plexuses formed from the anterior rami of spinal nerves are the cervical (C1 to C4), brachial (C5 to T1), lumbar (L1 to L4), sacral (L4 to S4), and coccygeal (S5 to Co) plexuses. Except for spinal nerve T1, the anterior rami of thoracic spinal nerves remain independent and do not participate in plexuses.

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Visceral nerve plexuses are formed in association with viscera and generally contain efferent (sympathetic and parasympathetic) and afferent components (Fig. 1.49). These plexuses include cardiac and pulmonary plexuses in the thorax and a large prevertebral plexus in the abdomen anterior to the aorta, which extends inferiorly onto the lateral walls of the pelvis. The massive prevertebral plexus supplies input to and receives output from all abdominal and pelvic viscera.

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Specific information about the organization and components of the respiratory, gastrointestinal, and urogenital systems will be discussed in each of the succeeding chapters of this text.

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Fig. 1.1 The anatomical position, planes, and terms of location and orientation.

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Feet togethertoes forwardHands by sidespalms forwardFace looking forwardInferior margin of orbit level withtop of external auditory meatusSagittal planeCoronal planeSuperiorAnteriorPosteriorMedialLateralInferiorTransverse, horizontal,or axial plane

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Fig. 1.2 Cathode ray tube for the production of X-rays.

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Fig. 1.3 Fluoroscopy unit.

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Fig. 1.4 Barium sulfate follow

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through.

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Fig. 1.5 Digital subtraction angiogram.

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Fig. 1.6 Ultrasound examination of the abdomen.

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Fig. 1.7 Computed tomography scanner.

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Fig. 1.8 Computed tomography scan of the abdomen at vertebral level L2.

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Fig. 1.9 A T2-weighted MR image in the sagittal plane of the pelvic viscera in a woman.

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Fig. 1.10 T1-weighted (A) and T2-weighted (B) MR images of the brain in the coronal plane.

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Fig. 1.11 A gamma camera.

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Fig. 1.12 The axial skeleton and the appendicular skeleton.

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Fig. 1.13 Accessory and sesamoid bones. A. Radiograph of the ankle region showing an accessory bone (os trigonum).

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B. Radiograph of the feet showing numerous sesamoid bones and an accessory bone (os naviculare).

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Fig. 1.14 A developmental series of radiographs showing the progressive ossification of carpal (wrist) bones from 3 (A) to 10 (D) years of age.

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Fig. 1.15 T1-weighted image in the coronal plane, demonstrating the relatively high signal intensity returned from the femoral heads and proximal femoral necks, consistent with yellow marrow. In this young patient, the vertebral bodies return an intermediate darker signal that represents red marrow. There is relatively little fat in these vertebrae; hence the lower signal return.

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Fig. 1.16 Radiograph, lateral view, showing fracture of the ulna at the elbow joint (A) and repair of this fracture (B) using internal fixation with a plate and multiple screws.

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Fig. 1.17 Image of the hip joints demonstrating loss of height of the right femoral head with juxta-articular bony sclerosis and subchondral cyst formation secondary to avascular necrosis. There is also significant wasting of the muscles supporting the hip, which is secondary to disuse and pain.

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Normal left hipBladderAvascular necrosisWasting of gluteal muscle

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Fig. 1.18 Joints. A. Synovial joint. B. Solid joint.

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Fig. 1.19 Synovial joints. A. Major features of a synovial joint. B. Accessory structures associated with synovial joints.

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Fig. 1.20 Various types of synovial joints. A. Condylar (wrist). B. Gliding (radio-ulnar). C. Hinge (elbow). D. Ball and socket (hip). E. Saddle (carpometacarpal of thumb). F. Pivot (atlanto-axial).

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Fig. 1.21 Solid joints.

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Fig. 1.22 This operative photograph demonstrates the focal areas of cartilage loss in the patella and femoral condyles throughout the knee joint.

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Fig. 1.23 This radiograph demonstrates the loss of joint space in the medial compartment and presence of small spiky osteophytic regions at the medial lateral aspect of the joint.

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OsteophytesLoss of joint space

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Fig. 1.24 After knee replacement. This radiograph shows the position of the prosthesis.

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Fig. 1.25 This is a radiograph, anteroposterior view, of the pelvis after a right total hip replacement. There are additional significant degenerative changes in the left hip joint, which will also need to be replaced.

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Fig. 1.26 Axial inversion recovery MR imaging series, which suppresses fat and soft tissue and leaves high signal intensity where fluid is seen. A muscle tear in the right adductor longus with edema in and around the muscle is shown.

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Fig. 1.27 Photograph demonstrating varicose veins.

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Fig. 1.28 Lymphatic vessels mainly collect fluid lost from vascular capillary beds during nutrient exchange processes and deliver it back to the venous side of the vascular system.

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Fig. 1.29 Regions associated with clusters or a particular abundance of lymph nodes.

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Cervical nodes(along courseof internaljugular vein)Axillary nodes(in axilla)Deep nodes(related to aortaand celiac trunkand superior andinferior mesentericarteries)Pericranial ring(base of head)Tracheal nodes(nodes related totrachea and bronchi)Inguinal nodes(along course ofinguinal ligament)Femoral nodes(along femoral vein)

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Fig. 1.30 Major lymphatic vessels that drain into large veins in the neck.