Stuart B. Bauer, MD

• Professor of Surgery (Urology)
• Harvard Medical School
• Senior Associate in Urology Department of Urology Boston Children? Hospital Boston, Massachusetts

The decreased motility also prolongs the transit time for the intestinal contents so that more water and nutrients are reabsorbed doctor for erectile dysfunction in dubai cheap apcalis sx on line. Intestinal Reflexes There are two reflexes observed in the intestine: intestinointestinal reflex and gastroileal reflex champix causes erectile dysfunction discount 20 mg apcalis sx with visa. Chapter 49: Small Intestinal Motility 415 Intestinointestinal Reflex When a part of the intestine is over-distended erectile dysfunction treatment by homeopathy buy discount apcalis sx on line, the rest of the intestine relaxes erectile dysfunction after 70 apcalis sx 20 mg lowest price. For example relaxation of the sphincter occurs by vagal stimulation as seen in gastroileal reflex webmd erectile dysfunction treatment purchase apcalis sx 20 mg without prescription. This decreases the intestinal motility impotence and high blood pressure order apcalis sx 20 mg otc, sometimes even resulting in paralysis of the gut. This occurs due to increased discharge of non-adrenergic fibers in the splanchnic nerves. Gastroileal Reflex When food enters the stomach (stretching of stomach), the motility of the terminal part of the ileum is enhanced. This increases entry of contents of ileum into the colon through ileocecal sphincter. Law of the Intestine When a bolus of chyme enters the intestine, the part of the intestine behind the bolus contracts and the portion of the intestine ahead of it relaxes. This is meant to propel the intestinal content in the forward direction as occurs in peristalsis. Normally, the ileocecal sphincter is tonically contracted, and therefore the sphincter remains closed most of the time and prevents small intestinal emptying. When a peristaltic wave reaches the terminal part of the ileum, the sphincter relaxes so that the ileal content enters the cecum. Intestinal Colic Severe abdominal cramps are experienced in localized obstruction of small intestine. The segment proximal to the obstruction dilates and gets filled with fluid and gas. This increases the pressure inside the lumen that causes compression of blood vessels in the intestinal wall. Abdominal cramps are also experienced in other diseases that result in distention of the intestine. The primary function of small intestine is to adequately mix the chyme with intestinal and pancreatic juice. In examinations, "Describe the mechanism and significance of intestinal motitlites" may come as a Long Question. Understand the physiology of colonic movements, colonic reflexes, and their functions. Learn the physiological basis of Hirschsprung, disease, irritable bowel syndrome, diarrhea, and constipation. Colon constitutes about 90% of large intestine and consists of ascending, transverse, descending, and sigmoid colons. Small intestine receives chyme of meals sequentially with no mixing of individual meals, whereas large intestine contains mixture of chymes of many meals of one to three days. On average the total transit time of chyme of a meal through large intestine as recorded from passage of radiopaque markers is about 30 to 48 hours. From pelvic colon to rectum, the transit is very slow, which may take 2 to 3 days. Transit time is less in high fiber diet, sometimes may even be reduced to 6 hours through the entire gut. Therefore, though colon receives about 2 liters of chyme per day from small intestine, its output is only about 200 mL. The objectives of colonic contractions are to mix the chyme and circulate it across the mucosal surface of the colon so that maximum contact occurs between the chyme and the mucosal epithelium. Longitudinal muscle layer of muscularis externa is concentrated into three bands, called as tenia coli. Colonic Movements Colonic movements include haustral contractions, propulsive movements, mass peristalsis, and colonic reflexes. Note, absence of villi, many goblet cells in the mucosal epithelium, outer longitudinal muscle layer is specialized into tenia coli. Mass Peristalsis Mass colonic peristalsis is a stronger peristaltic contraction that forcefully pushes the contents from colon into the rectum. Activation of mass peristalsis in colon finally leads to the initiation of defecation reflex. Parasympathetic innervation to cecum, ascending, transverse and most part of descending colon comes via vagus nerve, whereas innervation to the sigmoid colon, rectum, and anal canal comes via pelvic nerves that arise from the sacral spinal cord. Sympathetic fibers to large gut come via superior and inferior mesenteric plexuses, and superior and inferior hypogastric plexuses. Parasympathetic stimulation increases and sympathetic stimulation decreases colonic movements. Colonic Reflexes Colonic reflexes include colonocolonic reflex and gastrocolic reflex. Colonocolonic Reflex Colonocolonic reflex is the relaxation of the entire colon in response to distention of one part of the colon. Electrophysiology of Colonic Muscle Colon consists of both circular and longitudinal muscle. Gastrocolic Reflex Gastrocolic reflex is initiated when food accumulates in the stomach. This pushes colonic content into the rectum, which stimulates the desire for defecation. Therefore, usually after taking a large meal, the urge for defecation is enhanced. Gastrocolic reflex is proposed to be mediated by gastrin secreted from stomach in response to gastric distension, and not by neural factors. Circular Muscle There are two types of pace making (rhythm generating) cells in the colon. The one set of cells that are present near the inner border of circular muscles produce regular slow waves of high amplitude like that of gastric slow waves. The chyme that comes out from the gut is collected in a colostomy bag fastened around the colostomy opening. This procedure per se does not affect the health of the individual if water and electrolyte balance are maintained. Anal canal always remains closed by the tonic contractions of internal and external anal sphincters. The internal anal sphincter is made up of thickening of circular smooth muscle of the anal canal. Thus, external sphincter is innervated by somatic motor fibers via pudendal nerves, which brings it under voluntary control. Before initiation of the defecation reflex, colonic peristalsis pushes colonic contents into the rectum. This causes filling and distension of the rectum that initiates relaxation of internal anal sphincter and constriction of external anal sphincter. The center for defecation is present in the sacral portion of the spinal cord, which is influenced by higher centers. The efferent pathway involves cholinergic parasympathetic fibers in the pelvic nerves. Stimulus Defecation reflex is initiated when mass peristaltic movement of the descending and sigmoid colons pushes the colonic content into the rectum (filling of the rectum). As the external anal sphincter is innervated by somatic nerves, the voluntary effort is also important in initiating defecation. Receptors for defecation reflex are stretch receptors located in the wall of rectal rectum. Afferent information from the wall of rectum is conveyed to sacral segment (S3) of spinal cord via pelvic nerve. Efferent input from spinal cord to rectum and internal anal sphincter comes via pelvic nerve and to external anal sphincter via somatic nerve. Higher center, especially cortex influences spinal cord center via corticospinal pathway. Relaxation of internal anal sphincter is due to inhibitory signals that originate in myenteric plexus in response to peristaltic wave approaching anus. Thus, it has both reflexive (automatic) and voluntary Chapter 50: Motility of Large Intestine 419 Mechanism the individual sits on toilet and strains. This increases intra-abdominal pressure, which forcefully expels the rectal contents through the anal canal. This is assisted by relaxation of external anal sphincter, decreased anorectal angle and relaxation of puborectalis muscle. Evacuation of bladder is preceded by a deep breathing that pushes the diaphragm downward. Contraction of respiratory muscles increases intrathoracic and intra-abdominal pressures. When all these mechanisms elevate the intra-abdominal pressure to about 200 cm of H2O, the feces is forced out through the external anal sphincter. Features Clinically, it manifests as abdominal distention, anorexia and lassitude. Oral rehydration therapy is the immediate treatment to prevent volume and electrolyte loss. However, evacuation of bowel and bladder can be achieved by activating mass reflex in paraplegic patients. However, the physiological basis is the decreased intestinal motility that causes stasis of chyme in the large intestine, which facilitates water absorption and dehydration of intestinal contents. Bacteria and inorganic materials constitute 30% and 15% of the total solids respectively. The composition of feces is relatively not affected by diet as a large fraction of it comes from non-dietary origin. The smell of feces is due to presence of indole and skatole, the amines that are produced by colonic bacterial flora. Irritable Bowel Syndrome this condition has been known by several synonyms such as mucous colitis, spastic colon, irritable colon, and colonic neurosis. In India this is very common and many cases used to be misdiagnosed as chronic amebiasis in the past. Changes in gut motility are observed in several studies though they poorly correlate with the symptoms. In the constipated variety the frequency of high altitude peristaltic contraction is less whereas nonpropulsive segmentation contractions are more. Moreover food induced hypermotility of the colon occurring normally about one hour after the meal is reduced in many patients. In this condition, the entire neuronal plexuses in the wall of the colon are congenitally absent. The enteric neurons are usually markedly absent in the anus and distal part of the rectum. Failure of migration of neural crest from cranial to caudal region results in absence of ganglion in both myenteric and submucosal plexuses in distal part of colon and rectum. This prevents relaxation of rectal outlet and internal anal sphincter in response to rectal filling. Thus, obstruction occurs to the outflow of feces and feces accumulate behind the obstruction. Ulcerative colitis is an idiopathic form of acute and chronic ulcero-inflammatory colitis affecting chiefly the mucosa and submucosa of the rectum and descending colon, though sometimes it may involve the entire length of the large bowel. Both these disorders primarily affect the bowel but may have systemic involvement in the form of polyarthritis, uveitis, ankylosing spondylitis, skin lesions, and hepatic involvement. Both diseases can occur at any age but are more frequent in 2nd and 3rd decades of life. Clinical Features In India the female to male ratio is 1:3, though in the West, female suffer more. Symptoms are vague and these include abnormal bowel habits ranging from constipation to diarrhea (often alternating irregularly), pallet like stools, increased gastrocolic reflex, vague abdominal pain ranging from dull ache to severe colic, flatulence relieved by belching, capricious appetite and insomnia. The primary function of large intestine is to reabsorb water and electrolytes from chyme and from fecal matters. The mass peristalsis pushes feces into the rectum and initiates defecation reflex. External anal sphincter is made up of striated muscle, and therefore defecation reflex can be voluntarily controlled. Defecation reflex is a spinal reflex, which can be taught to spinal man to self-initiate the process. Colonic movements, Mass peristalsis, Colonic reflexes, Gastrocolic reflex, Defecation reflex, may come as Short Questions. Digestion is a complex process involving breaking down of foodstuffs by many enzymes into their absorbable form.

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Therefore xarelto impotence generic apcalis sx 20mg overnight delivery, to relieve untreatable chronic facial pain as occurs in trigeminal neuralgia erectile dysfunction specialist order apcalis sx 20mg on-line, surgical lesion of the caudal sub-division spinal nucleus of trigeminal nerve is performed erectile dysfunction treatment old age buy generic apcalis sx on line. The middle sub-division is the interpolar sub-division erectile dysfunction doctor mumbai order apcalis sx on line amex, which receives mechanosensitive and nociceptive erectile dysfunction and alcohol buy apcalis sx with a mastercard. The upper most is the oral sub-division that receives nociceptive inputs mainly from the oral cavity young healthy erectile dysfunction order 20mg apcalis sx fast delivery. The spinal nucleus receives mainly the nociceptive inputs via small diameter fibers. Therefore, this is considered as the spinothalamic pathway of the trigeminal system. Chapter 121: Trigeminal System 1025 Main Sensory V this nucleus is situated rostrally. It receives ipsilateral projections from the low threshold mechanoreceptors from face and teeth. Therefore, the main sensory V is considered to be the trigeminal homologue of dorsal column nuclei. The cortical representation of the face is relatively enormous, due to its high innervation density. The pain is initiated by application of an innocuous stimulus to the trigger zone, which is a very specific and restricted area on the face. The trigger zone may be located on the cheek, nose, lip, oral mucosa, teeth, or scalp. The trigger zone may not have a particular relation to the area from which the pain is perceived. Most patients develop this syndrome following compression of the trigeminal nerve roots. The root compression causes nerve irritation or degeneration that results in episodic bursts of severe pain. If adequate control is not achieved with analgesic, surgical release of trigeminal compression or lesions of trigeminal ganglion may be considered. Innervation of the face, What are the area of the face supplied by different trigeminal nerve divisions, How trigeminal system differs from other body pain pathways, What is the cause and treatment of trigeminal neuralgia. It receives ascending sensory inputs and projects them to the sensory cortical areas. Anteriorly they are separated by the third ventricle and the corpora quadrigemina is present between their posterior parts. The thalamocortical and corticothalamic fibers form the external medullary lamina that covers the lateral surface of the thalamus and passes between the reticular nucleus and the rest of the thalamus. Anatomically, a Y shaped internal medullary lamina splits thalamus into three parts. The anterior group of nuclei is enclosed by the bifurcation of the internal medullary lamina. The medial group of nuclei consists of the medial nucleus, the midline nucleus, centromedian and the intralaminar nucleus. The lateral group of nuclei is further divided into dorsal and ventral nuclear groups of nuclei. The dorsal nuclear group contains lateral posterior nucleus, lateral dorsal nucleus and pulvinar. The ventral nuclear group is comprised of ventral anterior, ventral lateral and ventral posterior nuclei, and medial and lateral geniculate bodies. The ventral posterior group, also known as ventrobasal complex, consists of ventroposterolateral and ventroposteromedian groups of nuclei (Flowchart 122. Association nuclei: this nuclear group consists of pulvinar, dorsal nuclei and lateral posterior nucleus. The ventral anterior nucleus receives inputs from basal ganglia and projects to the premotor cortex. The specific relay nuclei are known as extrinsic nuclei and rest others as intrinsic nuclei. It should be noted that all somatosensory information reaches all of these different types of thalamic nuclei. Functions of Thalamus All afferent impulses on their way to the sensory cortex terminate in the thalamus. Relay station for all somatic sensations: Thalamus conveys the sensory information to the cortex through thalamocortical projections (Table 122. Thus, it is the major relay station for sensory inputs in humans and higher order of animals, whereas in lower order of animals, it acts as the center for sensory integration. Relay of special sensations: Thalamus is the relay center for all special sensations except olfaction. The lateral and medial geniculate bodies receive the visual and auditory afferents respectively. Arousal mechanisms: Thalamocortical projects from nonspecific nuclei to cortex contributes to reticular activating system that activates arousal mechanisms and keeps the individual awake. Subcortical Perception of Sensations: Subcortical perception of pain, temperature, pressure (crude touch) occurs to some extent in thalamus. Thalamus is not only the relay station, but also the integration center for these sensations. Each pathway has a typical pattern of termination Chapter 122: Thalamus Table 122. Postero-ventral Dorsal-lateral Pulvinar Dentatothalamic tract, and pallidothalamic tract Thalamocortical tract (to motor area 4 and 6) Proprioceptive input to control of voluntary Relay of all somatosensory inputs including face. Vision Audition Memory and emotion Integration of somatic and visceral sensations, and arousal. Major Afferents Major Efferents Functions 1031 Spinothalamic fibers, trigeminothalamic To sensory cortex fiber, & medial lemniscus. Nonspecific Nuclei Anterior group Midline group Intralaminar Dorso-medial synthesis to the motor cortex (via thalamocortical fibers), which projects back to the basal ganglia. Thalamus also links cerebellum and motor cortex via dentatorubro-thalamo-cortical tract. Through this connection, thalamus influences planning and programming of movements. Role in Sleep: A circuit linking the thalamus and cortex (thalamocortical loop) is important in generating the pattern of brain activity in sleep-wake cycle. Inhibitory thalamic reticular neurons are proposed to be the part of this neuronal network that causes induction of sleep. Sensory Motor Coordination: Thalamus receives all sensory inputs from the body and closely interacts with basal ganglia, cerebellum and motor cortex. Therefore, thalamus is one of the major structures in the brain for coordination between sensory and motor functions, especially in the sensory feedback for correction and improvement in motor output. Language and Speech: Dorsal lateral nucleus of thalamus is reciprocally connected with parietal lobe of the brain, and therefore is concerned with language and speech and complex integrated functions. This results in severe impairment of the discriminative touch and pressure sensations of contralateral side, whereas diffuse touch, temperature, and pain sensations are often less impaired. Other Deficits When the thalamus is damaged, not only thalamic functions are lost, but also many cortical functions are affected, as cortex is intimately connected with thalamus. Electrical lesion of intralaminar nuclei relieves chronic suffering type of pain, though the acute perception of pain remains intact. Subthalamus contains sensory fasciculi, rostral extensions of midbrain nuclei, fiber bundle from cerebellum and globus pallidus, and subthalamic nuclei. The subthalamic nucleus (body of Luys) has reciprocal connection with the globus pallidus. Lesion of subthalamic nucleus results in hemiballismus (for detail, see Basal Ganglia). Though thalamus is major relay center of all sensations, it interacts and integrates with many brain areas and functions. The specific nuclei (ventral, lateral, anterior, posterior group) covey sensations to sensory cortex. The nonspecific nuclei (intraluminal and midline group) interact with reticular formation and cortex for arousal mechanisms. Thalamic nuclei, Connections and functions of thalamus, Functions of thalamus, thalamic syndrome, may come as Short Questions. Name the thalamic nuclei, Connections and functions of each nuclear group of thalamus, What are the specific and nonspecific nuclei of thalamus and what their functions, What is thalamic syndrome. Third order neurons of ascending sensory pathways project to the somatosensory cortex. There are other somatosensory cortical areas that are called secon dary somatosensory cortical areas. There are minimum four distinct areas in the cortex that receive somatosensory inputs. Supplementary sensory area: this is part of the posterior parietal association area located on the medial wall of the parietal lobe. Precentral gyrus (area 4): Though this is the primary motor cortex, it also receives somatosensory signals. Connections of Somatosensory Areas Somatosensory areas are interconnected to each other. That means whether they respond to cutaneous (from the skin) or deep (from muscles and joints) stimuli. Area 5 receives input only from the lateral posterior nucleus of the thalamus, which does not receive direct somatosensory inputs. In this sensory map in brain, face is represented in the lateral part, hand and upper extremity are represented in the dorsolateral part of the postcentral gyrus, and lower extremity on the medial surface of the hemisphere. The greatest area of the map is devoted for face, especially lips (area devoted for speech), and hand, especially the digits (cutaneous sensations from areas involved in skilled activities). Cortical columns that are located adjacently process different sensory modalities. For example, the column in the area 3b responds to cutaneous stimulation (that come from rapidly adapting mechanoreceptors), whereas the column in the area 3a responds to deep stimulation (mainly from slowly adapting mechanoreceptors). It also processes higher sensory orders like perception of the direction of an applied stimulus. Supplementary sensory area Effects of Lesions Cortical lesions do not completely abolish somatic sensation. Cortical sensations (tactile localization, tactile Chapter 123: Sensory Cortex 1035. With selective lesions of area 3, there is failure to learn the discriminative task even after repeated trials. Lesion of area 1 causes significant impairment of hardsoft, or smooth-rough discrimination, but no deficit in other aspects of sensory learning. Damage to postcentral gyrus also causes impairment of kinesthesia (inability to appreciate passive position and movements of different body parts). Damage to area 5 specifically affects stereognosis, with other tactile sensation remaining intact. Association Cortex Association sensory cortex is present in the parietal lobe (parietal association cortex). The major function of the parietal association cortex is to coordinate the relationship of the body to extrapersonal space. In the non-dominant hemisphere, the association cortex is involved in spatial relations, whereas in the dominant hemisphere it is concerned with language. A lesion of parietal association cortex of the nondominant hemisphere produces impairments in the ability to relate to extrapersonal space. For example, if the subject is asked to copy a geometry, the figures are distorted. The person develops constructional apraxia (defect in constructing a picture) and hemineglect syndrome (he denies existence of the opposite side of the body). The topographic organization is such that head is represented at the inferior end of the postcentral gyrus and the feet at the bottom of the sylvian fissure. The hand and face are more represented in sensory cortex, as these parts are most used by human beings. Correlate the knowledge of sensory physiology in understanding the abnormalities of sensory system. Understand the sensory deficits produced by lesion at different levels of sensory system. It also helps us learn the physiological basis of diag nosis and management of the sensory abnormalities. It is not only important to detect the nature of the deficit, but also to localize the site (the level of the sensory neuraxis) of sensory deficit. The detection and localization of lesions of the sen sory system depend on the distribution and type of sensory loss. The disease may affect the nerve, the nerve roots, the spinal cord, the brainstem, the thalamus, and the cortex. He also studied glands of internal secretion, showing indispensability of the adrenals. He is remembered for his classic description of pathways of conduction in tracts in spinal cord. Lesion of a cutaneous nerve results in sensory loss in the corresponding areas of distribution of that parti cular nerve. However, deficit is always less than the anatomic dis tribution because of overlap from the adjacent nerve. Perception of deep pressure and passive movements is usually not affected, as these modalities are medi ated by nerve fibers from subcutaneous structures and joints.

About 80% of the fibers after passing through the pyra mid erectile dysfunction venous leak treatment buy 20mg apcalis sx fast delivery, immediately decussate (cross over to the oppo site side) and descend down in the lateral funiculus of the spinal cord impotence urinary cost of apcalis sx. The lateral corticospinal fibers have monosynap tic connections with anterior horn cells erectile dysfunction university of maryland buy apcalis sx in united states online. The remaining 20% of the fibers descend down ipsilate rally (do not decussate) in the anterior funiculus of the spinal cord erectile dysfunction treatment options exercise cheap apcalis sx 20mg mastercard. The fibers cross over to the oppo site side only at the spinal cord segments through their termination on the interneurons impotence young buy apcalis sx australia. The fibers of ventral corticospinal tract do not directly terminate on the motor neurons erectile dysfunction protocol + 60 days 20mg apcalis sx with amex, rather they end on the interneurons in the same side of the spinal cord, which in turn cross over to the opposite side and terminate on the medial group of motor neurons. Few fibers from the interneurons terminate on the same side of medial group of motor neurons. These motor neurons supply the proximal limb muscles and axial muscles of the body. Functions the motor cortex is mainly involved in initiation, planning and control of movement. Corticospinal tracts transmit central command signal from motor cortex to the spinal cord interneurons and motor neurons: 1. Lateral corticospinal tract controls the skilled volun tary movements of the body. Termination Fibers of lateral corticospinal tract terminate on lateral group of motor neurons in the ventral horn of spinal cord: 1. Effects of Lesions Lesion of lateral corticospinal tract results in impairment of skilled voluntary activities like writing, painting, etc. But, as the rubrospinal tract is intact, the subject recovers after few days or weeks: 1064 Section 11: Neurophysiology 1. However, isolated lesion of lateral corticospinal tract is very uncommon in humans. In addition, diseases that affect corticospinal tract also affect the corticobulbar tracts that influence activities of extrapyramidal sys tems. Lesion of anterior corticospinal tract in animals results in inability to maintain posture while walking, climb ing, etc. But in human beings, postural deficit following lesion of anterior corticospinal tract is not prominent because of two reasons; firstly, this tract is not well developed in humans and secondly, other major pos ture regulating pathways especially the reticulospinal tract and vestibulospinal tracts are still intact. This indicates that descend ing fibers passing through pyramid are mostly the fibers of lateral corticospinal tract. The features described for pyramidal tract disease indicate the involvement of corti cobulbar fibers that influence brainstem motor nuclei in addition to the interruption of corticospinal fibers. Clinical Importance Corticospinal pathway may be interrupted anywhere along its course from cortex to spinal cord: 1. However, the lesion of corticospinal tract at the inter nal capsule (capsular lesion) is the commonest pyra midal tract lesion: - As the fibers coming from different parts of the cortex pass through a narrow tunnel in the pos terior limb of the internal capsule, disease of the internal capsule results in complete interruption of corticospinal fibers. It should be noted that, the ascending fiber systems from basal ganglia and cerebellum pass close to the internal capsule. Therefore, extrapyramidal systems are also affected in addition to involvement of corticospinal fibers. Consequently, pyramidal tract disease due to capsular lesion is often termed as complete upper motor neuron paralysis. In upper motor neuron lesions, not only the corticospi nal fibers are interrupted, but also the corticoreticular fibers are damaged. Normally, corticoreticular fibers (fibers from motor cortex to the brainstem reticular formation, especially to the pontine reticular nuclei that forms pontine reticulospinal tract) inhibit reticulospinal pathway. Therefore, interruption of corticoreticular pathway facil itates reticulospinal activity. Loss of inhibitory corticoreticular influence makes the reticulospinal tract more facilitatory, and therefore, muscle tone increases. Absence of Muscle Atrophy Muscle atrophy occurs when either the blood supply or the nerve supply to a muscle is disrupted. Clinically, pyra midal (corticospinal) tract lesion is referred to as upper motor neuron paralysis. No muscle atrophy (mild atrophy may occur in the long run due to disuse of the muscle, called disuse atrophy). Exaggeration of Deep Tendon Reflexes Usually, the upper motor neurons are inhibitory to the lower motor neurons. Especially, the increased motor neuron discharge increases the sensitivity of the muscle spindle to stretch. The afferent pathways of superficial reflexes ascend up in the ascending sensory systems. The efferent pathways are the descending motor pathways that finally terminate in skeletal muscles. Extensor Planter Response Corticospinal tract excites the flexor motor neurons and inhibits the extensor motor neurons supplying the mus cles of the digits of the limbs. Rubrospinal Tract Origin Rubrospinal tract originates from red nucleus, located in the midbrain. Course Immediately after originating from red nucleus, fibers cross over to the opposite side at the same level. After descending down through contralateral brain stem, fibers occupy the lateral column of the spinal cord. The fibers terminate on lateral group of motor neurons that innervate distal limb muscles. Vestibular nuclei are also connected reciprocally with superior colliculi, cerebellum and reticular formation. Therefore, they also control eye position during head movement and balance of the body during movement. There are two important vestibulospinal tracts: late ral vestibulospinal and medial vestibulospinal tracts. Applied Physiology In experimental animal, lesion of rubrospinal tract pro duces deficit in the distal limb muscles, especially in the flexor group of muscles. However, if the lateral corticospi nal tract is intact, the deficit persists temporarily. Course this tract descends down ipsilaterally through the brain stem and spinal cord. The fibers occupy the ventral funi culus of the spinal cord and terminate on the medial group of interneurons and motor neurons in the ventral horn of spinal cord. There are four vestibular nuclei: lateral, medial, 1066 Section 11: Neurophysiology midthoracic spinal cord segments. The input to medial vesti bular nucleus comes mainly from the semicircular canals. Reticular formation receives inputs from spinal cord, vestibular nuclei, cerebellum, hypothalamus, tectum and cortex, and projects mainly to cortex, thalamus, and spinal cord: 1. Projection of reticular nuclei to spinal cord is impor tant in control of motor activity as they profoundly affect motoneuronal excitability, especially of the motor neurons. In this regard, two reticular nuclei are important: nucleus reticularis pontis in pons and nucleus gigantocellularis in medulla. Accordingly, there are two main reticulospinal tracts: the pontine reticulospinal tract, and the medullary reti culospinal tract. Reticulospinal tracts are most impor tant medial system pathways for control of posture. Pontine Reticulospinal Tract Origin Pontine reticulospinal tract originates from nucleus reti cularis pontis oralis and nucleus reticularis pontis caudalis located in the pontine reticular formation. Functions It excites motor neurons that supply the proximal group of muscles (especially the extensor muscles of the limb). The input to lateral vestibular nucleus comes mainly from semi circular canals and otolith organs of the inner ear. Course this tract descends down ipsilaterally in the medial funic ulus of the spinal cord. The fibers terminate on the medial group of interneurons and motoneurons that innervate the proximal and axial groups of muscles of the body. In humans, brainstem lesion due to stroke or injury facilitates vesti bulospinal tract activity that manifests in the form of neck, arms and leg rigidity. Functions the function of pontine reticulospinal tract is similar to that of lateral vestibulospinal tract. It excites the motor neurons of the proximal extensor muscles that are involved in regulation of posture. Medullary Reticulospinal Tract Origin Medullary reticulospinal tract originates from nucleus gigantocellularis located in the reticular formation of the medulla. Course the tract descends down ipsilaterally in the ventral funi culus of the spinal cord to terminate on the medial group of interneurons and motoneurons that innervate the prox imal group of muscles. Tectospinal Tract Origin Tectospinal tract originates from the tectum or superior colliculus (from deep layers). Raphespinal Tract Origin this tract originates from nucleus raphe magnus in the medulla. Course Immediately after originating from superior colliculus, fibers cross-over to the opposite side below the peri aqueductal gray. The fibers then descend down in the ventral funiculus of the spinal cord to terminate on the medial group of interneurons and motor neurons. This is the smallest of all descending tracts as it extends upto the midcervical region of the spinal cord. Course the fibers descend down ipsilaterally and terminate on the interneurons in the dorsal horn (refer. Few fibers also terminate on the interneurons in the ventral horn that are excitatory to the motor neurons. They inhibit the nociceptive transmission in the spinal cord (endogenous pain inhibiting system). Through their termination on the motor neurons, they are involved in sensory-motor coordination at the level of spinal cord. There fore, tectospinal tract regulates contralateral movement of the head in response to visual stimuli. Course Fibers mainly descend down ipsilaterally in the spinal cord to terminate on the interneurons and motor neurons. The pathway is inhibitory to the nociceptive afferents, and also to the motor neurons. It alters the excitability of the motor neurons to different stimuli and brings sensory-motor coordination in the spinal cord. Individual muscles are affected depending on the mus cles supplied by that particular nerve. Loss of motor neurons disrupts the reflex arc of the stretch reflexes, as well as superficial reflexes. Usually, muscular paralysis is associated with sensory changes, because the nerve that carries the motor impulses from the spinal cord also transmits sensory information to the spinal cord. Patterns of Paralysis Paralysis or plegia means complete loss of voluntary movement, whereas paresis refers to the weakness of muscles (incomplete paralysis). Depending on the distri bution of parts of the body involved, paralysis is divided into following categories. Monoplegia Monoplegia refers to weakness or paralysis of all the muscles of one limb (leg or arm). Examples of monoplegia are crural (leg) monoplegia that occurs due to trauma, myelitis, discprolapse or tumor of thora columbar segments of the spinal cord or brachial (arm) Physiological Basis 1. As the lower motor neurons are interrupted, the innervation to the muscle is lost. Therefore, pronounced Chapter 129: Descending Pathways 1069 monoplegia that occurs due to diseases affecting cervical segments. Monoplegia may also occur due to a central cortical defect (thrombotic or embolic infarction, or a cir cumscribed tumor or abscess). Rarely the diseases of motor cortex, cauda equina, or peripheral nerves cause paraplegia. Quadriplegia Quadriplegia or tetraplegia indicates paralysis of all four extremities. It usually occurs due to transection of spinal cord in the upper cervical segments. Disease of the upper motor neurons bilaterally in the cervical cord, brainstem, or cere brum can also cause quadruplegia. Triplegia occurs most often as a transitional condition in the development of or partial recovery from tetraplegia. This is the commonest form of paralysis that involves arm, leg and sometimes the face on one side of the body. Usually it occurs due to lesion of the corticospinal pathway at the internal capsule that results in contralateral hemiplegia (as discused above). It usually occurs due to spinal cord injury or diseases that Isolated Paralysis Isolated paralysis of one or more muscle groups occurs due to disease of a particular nerve or the branch of the nerve. Lateral descending pathways control functions of distal group of muscles (skilled activities), and medial descending pathways control functions of proximal group of muscle (posture regulation). Describe the features in spinal, decerebrate, midbrain and decorticate preparations. Understand the role of various components of neuraxis in regulation of posture and movement. Spinal motor neurons are continuously influenced by the impulses arriving from various supraspinal centers via descending fibers. The command is conveyed to the spinal cord motor neurons from the cortex directly via corticospinal tract, and from basal ganglia and cortex via corticobulbar pathways and from cerebellum via its projection to the brainstem nuclei that influence the activities of extrapyramidal system. These upper motor neurons regulate movement by constantly altering the activities of the spinal motor neurons according to the need of the situation.

Fallopian Tubes Two fallopian tubes (also called oviducts) arise from both sides of upper poles of uterus impotence at 17 cheap apcalis sx american express. First Meiotic Division the first meiotic division starts in primary oocytes during fetal life erectile dysfunction after radical prostatectomy treatment options purchase apcalis sx 20 mg on-line, which occurs at about 8th week of pregnancy is arrested in prophase erectile dysfunction 20 purchase discount apcalis sx online. However erectile dysfunction treatment hong kong cheap apcalis sx 20 mg mastercard, the first meiotic division is not completed in fetal life erectile dysfunction boyfriend discount apcalis sx 20 mg with visa, not even till puberty; in fact causes of erectile dysfunction in young adults buy apcalis sx 20 mg overnight delivery, it is completed just prior to ovulation. Therefore, the life span of a primary oocyte can be up to 50 years, as ovulation can continue up to this age. The suspension of oocyte division in prophase for such a long period depends on the internal hormonal environment provided by the surrounding supporting cells. Note that the cortex contains ovarian follicle in different stages of development. The primary function of ovary is to develop ovarian follicles and release ovum at the time of ovulation, and to secrete steroid hormones that control various reproductive and metabolic functions. The oocyte degeneration however, starts from the intrauterine life so that only about 1 million primary oocytes remain at the time of birth. By the time of puberty about 200,000 and by the age of 30 only about 26,000 oocytes remain in the ovary. A major difference in male and female gametogenesis is that the process of spermatogenesis is a continuous phenomenon and the production of sperm is unlimited, whereas primary oocytes degenerate with age (Application Box 68. As new oogonia cannot be manufactured in ovary, the oocytes totally disappear at the time of menopause. The oocyte that ovulates at about 40 years of age is about 25 years older than the oocyte that ovulates at the age of 15. This one of the important factors that contribute to the anomalies in children born to older woman as the aged-eggs oocyte have degenerative changes and therefore their fertilization may result in defective embryo. Also, the process of development of each spermatocyte is completed in few days, whereas development of each oocyte that begins in intrauterine life is completed with ovulation that occurs during menstrual cycle. Thus, many sperms are produced in few days whereas single ovum is produced during each cycle, the development of which occurs at different stages of life till ovulation. The stages of development of oocytes occur in three stages: Oogonium becoming primary oocyte, primary oocyte converted to secondary oocyte, and finally secondary oocyte developing to mature ovum. Oogonia Becoming Primary Oocyte Oogonia the primordial germ cells (oogonia) migrate from the yolk sac of embryo to the genital ridge at about 6th week of gestation. The, oogonia undergo many mitotic divisions and the number of oogonia reaches to about 7 millions. Primary Oocyte Converted to Secondary Oocyte In fetus, oogonia develop into primary oocyte, which undergo first meiotic division. Thus, all eggs present at birth are primary oocytes 608 Section 7: Reproductive System. Note, first meiotic division of oocyte begins during fetal life and completes prior to ovulation, whereas second meiotic division completes at the time of fertilization. The primary oocyte that is destined for ovulation completes the first meiotic division just before the ovulation. This division results in production of two structures: one is the daughter cell, called secondary oocyte containing 23 chromosomes, and the other is the first polar body. However, the cytoplasmic division is grossly unequal in this process in which the secondary oocyte retains nearly all the cytoplasm with polar body containing very little of it. Along with development of oocyte in ovarian follicle, follicles also grow in different phases. It starts during intrauterine life and continues till ovulation that occurs during each menstrual cycle. However, only the one dominant follicle finally matures and releases ovum, whereas rest others undergo degeneration (atresia). Secondary Oocyte Forming Ovum Second Meiotic Division the second meiotic division occurs in the secondary oocyte after ovulation, and is arrested in metaphase. As a result of this meiotic division, the ovum containing 23 chromosomes and the second polar body are formed. Stage 1 (Primordial Follicular Stage) the ovarian follicle, also called Graafian follicle begins as a primordial follicle. The primordial follicle consists of a primary oocyte at the center surrounded by a layer of spindle cells (flattened pregranulosa cells) that form granulosa cells later. The oocyte enters into first meiotic division and the division is arrested in prophase. Stage 2 (Primary Follicular Stage) the primordial follicles grow into the primary follicles. During this process the flattened pregranulosa cells (spindle cells) become cuboidal granulosa cells that further proliferate to form a continuous cell layer surrounding the oocyte. A type of glassy material consisting of mucopolysaccharide is secreted from granulosa cells, which forms a thick layer between the oocyte and the granulosa cell layer, called as zona pellucida. The primordial follicle becomes primary follicle at about 28th weeks of gestation. Stage 4 (Tertiary Follicular Stage) this is the final stage of follicular development. It occurs in two sub-stages: the early tertiary stage and the Graafian follicular stage. Early Tertiary or Antral Follicular Stage In this stage, the spindle cell layer surrounding the basement membrane proliferates and differentiates into inner theca interna and outer theca externa. Theca interna cells multiply to form multiple cell layers and become steroidogenic. Theca externa cell lie in a single layer and provide mechanical support to the follicle from outside. Theca cells receive blood, lymphatic and nerve supply whereas granulosa cells remain avascular as blood vessel cannot penetrate the basement membrane. A long with the expansion of theca cell layer, a fluidfilled space is created in the midst of granulosa cells, called as antrum. Therefore, the follicle in this stage is also called early antral follicle and the stage also as early antral follicular stage. Stage 3 (Secondary Follicular Stage) the primary follicle becomes secondary follicle in this stage during which the granulosa cells divide and form several layers of cells around the oocyte. A layer of spindle cells (pre or early theca cells) is formed at the periphery of the basal lamina, which forms the theca cell layer in the next stage. Late Tertiary or Graafian Follicular Stage this is the most rapid stage of development. The size of the antrum and the amount of antral fluid are increased significantly. The mucopolysaccharide, which is present in the antral fluid, is depolymerized to increase the osmotic pressure of the fluid. It also contains plasminogen activator, mucopolysaccharide, proteins, electrolytes, glycosaminoglycans and proteoglycans. The granulosa cells in this stage are anatomically divided into three compartments: antral, cumulus and mural granulosa cells. Antral granulosa cells: Granulosa cells lining the antral cavity are called antral granulosa cells (Discus proligerous). Cumulus granulosa cells: Granulosa cells surrounding the oocyte are cumulus granulosa cells (cumulus oophoricus). Mural granulosa cells: Granulosa cells that are attached to the basement membrane are called mural granulosa cells (Membrana granulosa). The follicle is called pre-ovulatory follicle as it is ready for ovulation at this stage. The basement membrane close to the surface of the ovary undergoes proteolysis that slowly leads to rupture of the follicle resulting in release of oocyte from the follicle, the process called ovulation. If fertilization occurs, the penetration of ovum by the sperm completes the second meiotic division, which results in functional ovum (fertilized egg). If fertilization does not occur, the oocyte begins to degenerate in 24 to 48 hours. Corpus Luteum Formation Luteinization After ovulation, the ruptured follicle is quickly filled with blood, and at this time, the follicle is called corpus hemorrhagicum. However, the cells lining the follicle rapidly proliferate to replace blood with luteal cells that are rich in lipid. Now, the follicle is called corpus luteum and its appearance heralds the beginning of luteal phase of the cycle. The corpus luteum is a yellow body made up of endocrine tissue that consists of granulosa luteal cells, theca luteal cells and fibroblasts. The number of mitochondria, lipid droplets and the endoplasmic reticulum increase in the granulosa cells of corpus luteum. These morphological changes are collectively known as luteinization, which is essential for synthesis of more steroid hormones. Chapter 68: Female Reproductive System: Functional Anatomy, Oogenesis and Follicular Development 611 2. The granulosa and theca cells of matured corpus luteum are respectively called as granulosa lutein cells and theca lutein cells. Luteal granulosa cells are vascular unlike the follicular granulosa cells that are nonvascular. Vascularity of luteal cells facilitates the synthesis of steroid hormones by promoting the supply of cholesterol from plasma to these cells. It maintains the early part of pregnancy by secreting progesterone in adequate concentration till the placenta becomes functional. Due to inadequate secretion of progesterone from malfunctioning corpus luteum, pregnancy is terminated very early. Luteal insufficiency is diagnosed by demonstrating a low progesterone level in the midluteal phase in successive cycles. Regulation of Luteinization Progesterone, estrogen and androgen are formed in corpus luteum. Progesterone secretion reaches its peak in menstrual cycle at about 7 days after ovulation, which correlates with the full maturity of corpus luteum. These hormones (Progesterone, estrogen and androgen) may be playing some role in luteinization. Atresia of Follicle During the entire reproductive period of a woman, about 400 oocytes grow to culminate in ovulation. The follicles that do not become dominant undergo a process of degeneration called atresia. Luteal Regression If fertilization does not occur, corpus luteum degenerates in about 13 days after ovulation. The endocrine cells of corpus luteum become necrotic, and are invaded by leucocytes and fibroblasts. However, it is proposed to be due to the action of luteolysins that are produced locally in the ovary. The degenerated corpus luteum is replaced by avascular and nonfunctional fibrous tissue, known as corpus albicans. Regulation of Follicular Development Factors affecting development of follicles are different in different phases of follicular growth. Primordial Follicular Stage the growth of primordial follicle is not affected by gonadotropins. Primary Follicular Stage the chemical substances secreted by oocyte stimulate the transformation of pregranulosa cells to granulosa cells. The products of granulosa cells stimulate the formation of spindle (pre-theca) cells. During luteal phase, increased secretion of progesterone, estrogen and inhibin A occurs from corpus luteum. Secondary Follicular Stage At the time of puberty, secondary follicles start developing. Late Tertiary Stage Between 5th to 7th days of follicular phase, only one follicle grows sufficiently to become the dominant follicle. Breaking down of follicular wall is facilitated by the proteolytic enzyme plasmin. In females, the period of gametogenesis is restricted from puberty to menopause, which is less than for 40 years. The development of each oocyte that begins in intrauterine life is completed with ovulation that occurs during menstrual cycle. If fertilization occurs, corpus luteum provides hormonal support for implantation of fertilized egg and maintenance of early part of pregnancy. Oogenesis, Corpus luteum, Graafian follicle, Stages of follicular development, Regulation of follicular development, may be asked as Short Questions in exam. How the corpus luteum is formed, What are the functions of corpus luteum, How is the lutenization regulated, What is luteal regression, What is luteal deficiency and what are its features, What is D and C, What are the functions of ovary, What are the stages of oogenesis, How the age of oocyte contributes to the health of children, List the stages of follicular development, How the early tertiary stage is regulated, How is the late tertiary stage regulated, What are the changes that occur in primordial follicular stage, What are the changes that occur in primary follicular stage, What are the changes that occur in secondary follicular stage, What are the changes that occur in tertiary follicular stage. Describe (with the help of a schematic diagram) the uterine, ovarian, and hormonal changes in menstrual cycle. The fundamental difference in female and male reproductive functions is the cyclical release of gametes in females during their reproductive life. The structural and functional changes of female reproductive system during each cycle are synchronized with the changes in hypothalamopituitary-ovarian axis.

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