By J. Alima. Florida Memorial College.

Classification Based on their anatomical location purchase careprost 3 ml mastercard medications in mexico, anorectal abscesses are classified into four main varieties: Perianal(subcutaneous) abscess:- This is the commonest type and can affect people of all age groups discount careprost 3 ml amex medicine holder. Ischiorectal abscess:- Is also common and is located in the ischiorectal fossa Sub mucous abscess:- This an abscess located under the mucous membrane 167 Pelvirectal abscess:- This is an abscess located above levator ani and follows spread from pelvic abscess Clinical features: Patient complaints include pain (usually severe), fever, constitutional symptoms such as sweating and anorexia, features of proctitis and constipation Physical findings (rectal examination) include - A lump visible and palpable at the anal margin/anal canal or ischiorectal fossa which is tender brownish induration palpable on the affected side - Rectal tenderness, rectal tender mass Management of anorectal abscess: The abscess needs drainage as soon as it is diagnosed followed by irrigation, packing with saline soaked gauze and Sitz bath twice daily till wound healing. They are needed when there are systemic manifestations and in immunocompromised patients. Causes (risk factors) - It results from: • Usually an untreated or inadequately treated anorectal abscess (see also causes and risk factors for anorectal abscesses) • Granulomatous infections and inflammatory bowel diseases • May give rise to multiple external openings and include e. Tuberculous proctitis Crohn’s disease Classification: It can be grouped into two according to the level of the internal opening: - Low level: with an internal opening below the anorectal ring - High level: with an internal opening at or above the anorectal ring. Clinical features - Seropurulent discharge with perianal irritation - An external opening (frequently single) seen as a small elevated opening on the skin around the anus with a granulation - An internal opening may be felt as a nodule on digital rectal examination (almost always single) irrespective of the number of external openings) - Sings of underlying/associated diseases Management - Emergency treatment for abscesses - Treatment of underlying cause - Surgery for fistula in ano - Preceded by • Preoperative bowel cleansing (enema) • Examination under anesthesia Low level fistula • Laying open the entire fistulous tract, fistulotomy. It is located commonly in the posterior midline, occasionally along the anterior midline and rarely at multiple sites. Classification: Anal fissure can be classified as acute or chronic based on its pathologic features. Clinical features: A patient with anal fissure presents with: - Pain is the commonest feature - Characteristic sharp, severe pain starting during defecation and lasting an hour or more and ceases suddenly to reappear during the next bowel motion. It includes: - A high fiber diet and high fluid intake with a mild laxative, such as liquid paraffin, to encourage passing of soft, bulky stools - Administration of a local anesthetic ointment or suppository Surgical Measures: Surgical measures are needed when the above measures fail, in chronic fissures with fibrosis, a skin tag or a mucous polyp or recurrent anal fissures. Procedures include: • Lateral anal sphincterotomy • fissurectomy and • sphincterotomy This procedure can be used for cases with a chronic fissure. It needs an experienced operator to reduce complications, which include hematoma formation, incontinence and mucosal prolapse. After care: This consists of bowel care, daily bath and softening the stool till wound healing. They develop within areas of enlarged anal lining (anal cushions’) as they slide downwards during straining. Since the internal and external (subcutaneous perianal) venous plexus communicate (Porto-systemic anastomosis) engorgement of the internal plexus is likely to lead to involvement of the latter. With the patient in the lithotomy position, internal hemorrhoids are frequently arranged in three groups at 3, 7 and 11 o’clock positions. This arrangement corresponds to the distribution of the superior hemorrhoidal vessels (2 on the right, one on the left) but there can be smaller hemorrhoids in between the three groups. Hemorrhoids are graded based on the degree of prolapse and reducibility in to: ⇒ First degree hemorrhoids: those confined to the anal canal (do not prolapse out side the anal canal) ⇒ Second degree hemorrhoids: prolapse on defecation but reduce spontaneously or are replaced manually and stay reduced. These give rise to a feeling of heaviness in the rectum - A mucoid discharge frequently accompanies prolapsed hemorrhoids and is due to mucus secretion from the engorged mucus membrane. Unrelieved strangulation/thrombosis may lead to ulceration of the exposed mucus membrane. Management: Any underlying or associated more important condition or disease should be excluded or treated accordingly before commencing specific treatment for hemorrhoids. Hemorrhoids can be managed with: ƒ Conservative measures which include: - High fiber-diet for a regular soft and bulky motion - Hydrophilic creams or suppositories - Local application of analgesic ointment /suppository. This is recommended and usually effective for many patients with early hemorrhoids particularly those secondary to other conditions and likely to regress with removal of the underlying conditions (e. It appears as an inflamed tense tender and easily visible on inspection of the anal verge. Continuous pain, on the other hand, signifies infection, inflammation or ischemia. Signs: Acute abdomen may present with one or combination of the following clinical signs • Abdominal distention, visible peristalsis • Direct and rebound tenderness, guarding • Anemia, hypotension • Toxic with Hippocratic faces • Absence of bowel sound ( peritonitis) • Special tests (for signs) are possible e.

In develop- The deep veins of the calf are the venae comitantes of the anterior and ing countries infection with Filaria bancrofti is a significant cause of posterior tibial arteries which go on to become the popliteal and lymphoedema that can progress to massive proportions requiring limb femoral veins discount 3ml careprost visa 5 asa medications. The veins and lymphatics of the lower limb 97 44 The nerves of the lower limb I Anterior superior iliac spine Inguinal ligament Lateral cutaneous External oblique aponeurosis nerve of thigh Femoral nerve Femoral artery Iliacus Femoral vein Femoral canal Psoas tendon Lacunar ligament Pubic tubercle Lateral cutaneous nerve of thigh Pectineus Iliacus Inguinal ligament Femoral nerve Pubic tubercle Nerve to sartorius To pectineus Tensor fasciae latae Pectineus To vastus lateralis Adductor longus Psoas Femoral vein To vastus intermedius Great saphenous vein and rectus femoris Femoral artery Sartorius Saphenous nerve Intermediate To vastus medialis cutaneous nerve Medial cutaneous of thigh nerve of thigh (Skin of front of thigh) (Skin of medial thigh) Rectus femoris Gracilis Obturator externus Pectineus Posterior division Adductor Adductor brevis longus Anterior division Gracilis Deep fascia (Skin of medial leg Branch to and foot) Fig buy careprost 3ml with mastercard treatment notes. The latter supply • Course: the majority of the branches of the plexus pass through the sartorius and pectineus. The latter nerve is the only branch to extend • Intra-abdominal branchesathese are described in Chapter 21. Obese patients sometimes describe paraesthesiae over the • Origins: the anterior divisions of the anterior primary rami of lateral thigh. At this point it lies on iliacus, which it supplies, and is situ- • Anterior divisionagives rise to an articular branch to the hip joint ated immediately lateral to the femoral sheath. It branches within the as well as muscular branches to adductor longus, brevis and gra- femoral triangle only a short distance (5 cm) beyond the inguinal liga- cilis. The nerves unite, and are joined by the lumbosacral trunk (L4,5), artery from the lateral to medial side. The nerve • The superior gluteal nerve (L4,5,S1)aarises from the roots of the crosses the posterior tibial artery from medial to lateral in the mid-calf sciatic nerve and passes through the greater sciatic foramen above and, together with the artery, passes behind the medial malleolus and the upper border of piriformis. In the gluteal region it runs below then under the flexor retinaculum where it divides into its terminal the middle gluteal line between gluteus medius and minimis (both branches, the medial and lateral plantar nerves. In the gluteal region it penetrates and supplies gluteus • Sural nerveaarises in the popliteal fossa and is joined by the sural maximus. It pierces the • The posterior cutaneous nerve of the thigh (S1, 2, 3)apasses deep fascia in the calf and descends subcutaneously with the small through the greater sciatic foramen below piriformis. It passes behind the lateral malleolus and under the supply the skin of the scrotum, buttock and back of the thigh up to flexor retinaculum to divide into its cutaneous terminal branches the knee. It sends four motor branches and a cutaneous supply to the region by passing out of the greater sciatic foramen below pirifor- medial 3 /12 digits. It runs forwards in the pudendal plantar artery to the base of the 5th metatarsal where it divides into (Alcock’s) canal and gives off its inferior rectal branch in the superficial and deep branches. It continues its course to the perineum and the lateral 1 /12 digits and the remaining muscles of the sole. In the gluteal • Branches: region it passes over the superior gemellus, obturator internus and in- • Genicular branches to the knee joint. In addition it supplies the skin over the lateral lower two-thirds • Muscular branchesato the hamstrings and the ischial part of of the leg and the whole of the dorsum of the foot except for the adductor magnus. The central and inferior parts of the acetabulum (a) Iliofemoral ligament (Bigelow’s ligament)ais inverted, Yshaped are devoid of articulating surface. It arises from the anterior inferior iliac spine and notch from which the ligamentum teres passes to the fovea on the inserts at either end of the trochanteric line. The capsule (c) Ischiofemoral ligamentafibres arise from the ischium and some attaches to the femur anteriorly at the trochanteric line and to the bases encircle laterally to attach to the base of the greater trochanter. Posteriorly the capsule attaches to the femur at a The majority of the fibres, however, spiral and blend with the higher levelaapproximately 1 cm above the trochanteric crest. This is an outpouching of synovial 2 Vessels in the ligamentum teres which enter the head through membrane through a defect in the anterior capsular wall under the small foramina in the fovea. The hip joint and gluteal region 103 Gluteus medius Gluteus medius Gluteus minimus Gluteus maximus Superior gluteal artery and nerve Inferior gluteal nerve Piriformis Obturator internus and gemelli Femoral insertion Inferior gluteal artery of gluteus maximus Quadratus femoris Posterior cutaneous nerve of thigh Internal pudendal nerve and artery Sciatic nerve Vastus lateralis Biceps femoris Adductor magnus Semimembranosus Opening in adductor magnus Semitendinosus Biceps (short head) Biceps (long head) Sciatic nerve Semimembranosus tendon Gastrocnemius Fig. Pertrochanteric Extracapsular The smaller diagram shows how the sacrotuberous and sacrospinous ligaments resist rotation of the sacrum Fig. Fractures near the head can cause avascular necrosis because of the disruption of the arterial supply to the head The fractured neck of femur (Fig. This occurs as the adductors, hamstrings and rectus femoris pull • Nerves: of the gluteal region include the: sciatic nerve (L4,5,S1–3), upwards on the distal fragment whilst piriformis, the gemelli, obtur- posterior cutaneous nerve of the thigh, superior (L4,5,S1,2) and in- ators, gluteus maximus and gravity produce lateral rotation.

The pulmonic (semilunar) valve is located between the right ventricle and the pulmonary artery that leads to the lungs discount 3ml careprost with visa medicine lodge treaty. As soon as the right ventricle has finished emptying itself cheap careprost 3ml online symptoms 1974, the valve closes in order to prevent blood on its way to the lungs from returning to the ventricle. Following contraction of the left ventricle, the aortic valve closes to prevent the flow of blood back from the aorta to the ventricle. Blood Supply to the Myocardium Although blood flows through the heart chambers, only the endocardium comes into contact with it. Therefore, the myocardium must have its own blood vessels to provide oxygen and nourishment and to remove waste products. The arteries 262 Human Anatomy and Physiology that supply blood to the muscle of the heart are called the right and left coronary arteries (Figure 9-5). These arteries, which are the first branches of the aorta, arise just above the aortic semilunar valve (see Figure 9-4). After passing through capillaries in the myocardium, blood drains into the cardiac veins and finally into the coronary (venous) sinus for return to the right atrium. Valves of the heart, seen from above, in the closed position (From Memmler and Wood: The Human Body in Health and Disease, ed 6, Philadelphia, 1987, J. The blood is squeezed through the chambers by a contraction of heart muscle beginning in the thin-walled upper chambers, the atria, followed by a contraction of the thick muscle of the lower chambers, the ventricles. This 263 Human Anatomy and Physiology active phase is called systole, and in each case it is followed by a resting period known as diastole. The contraction of the walls of the atria is completed at the time the contraction of the ventricles begins. Thus, the resting phase (diastole) begins in the atria at the same time as the contraction (systole) begins in the ventricles. After the ventricles have emptied, both chambers are relaxed for a short period of time as they fill with blood. The fibers are interwoven so the stimulation that causes the contraction of one fiber results in the contraction of the whole group. As more blood enters the heart, as occurs during exercise, the muscle contracts, with greater strength so push the larger volume of blood out into the blood vessels. It is determined by the volume of blood ejected from the ventricle with each beat−the stroke 265 Human Anatomy and Physiology volume−and the number of beats of the heart per minute−the heart rate. The Conduction System of the Heart The cardiac cycle is regulated by specialized areas in the heart wall that forms the conduction system of the heart. Two of these areas are tissue mass called nodes; the third is a group of fibers called the atrioventricular bundle. The sinoatrial node, which is located I the upper wall of the right atrium an initiates the heart beat, is called the pacemaker. The second node, located in the ineratrial septum at the bottom of the right atrium, is called the atrioventricular node. The atrioventricular bundle, also known as the bundle of His, is located at the top of the interventricular septum; it has branches that extend to all parts of the ventricle walls. Fibers travel first down both sides of the interventricular septum in groups called the right and left bundle branches. Smaller Purkinje fibers then travel in a branching network throughout the myocardium of the ventricles (Figure 9- 6). The relatively slower conduction through this node allows time for the atria to contract and complete the filling of the ventricles.

As soon as these mutations interfere with antibody binding purchase careprost 3 ml otc medications xerostomia, the slightly altered virus variant has a selective advantage over its peers and quickly spreads in a previously protected human population order 3 ml careprost with amex 68w medications, causing a new wave of infections. The H-N-type is maintained: for example, isolate A/Syndey/1977/H3N2 drifts to reinvent itself as A/Moscow/1999/H3N2. At the first influenza infection, a child produces antibodies against all antigenic domains of this specific virus subtype. In the event of later infections, efficient antibody responses are only induced against domains that were already part of the first virus. The probable reason is that memory cells stemming from the first encounter with influenza are activated so quickly that the immune system is not able –or does not need to— activate new naive cells. In addition, influenza A viruses are not restricted to humans, but also infect pigs and fowl (chickens, ducks, swans, etc. Some subtypes of influenza A virus circulate mainly in humans, but many others are best adapted to fowl. The danger is a coinfection, be it in a human or a bird, with two influenza virus subtypes that leads to an exchange of genetic material. If that happens, a novel, human-adapted subtype may emerge against which nobody has any useful antibodies, leading to one of the dreaded pandemics. Such a pandemic during the period 1918-1920 took the lives of approximately 30 million people (out of a world population of 1. During the last ten years, the biggest perceived threat was the fowl-adapted influenza A subtype H5N1. First in Hong Kong in 1997, and several times later on in other places, it infected singular human individuals. A H5N1 epidemic in birds spread and reached western Europe in 2005, exposing more and more humans to the virus. Infected individuals contracted H5N1 from massive contact with infected fowl, and in all but a handful of cases did not transmit the virus to other humans. However, the latest pandemic was unexpectedly caused by a different virus which started to spread from Mexico in 2009. Here, the antigen shift mechanism had reassorted genome segments of swine-adapted influenza virus strains with human-adapted segments. The virus was of the H1N1-Type, yet the specific variants of H1 and N1 differed from those which had been around previously. In these young adults, the 1918 H1N1 caused an especially strong inflammatory response; lung alveoli quickly filled with exsudate, causing respiratory failure). Herpes simplex virus first replicates in the epithelial cells of the oral cavity, then infects the afferent neurons of the trigeminal nerve. Cytotoxic T cells quickly eliminate infected epithelial cells in a painful immune reaction, but some viruses go into hiding in the cell bodies of neurons in the trigeminal ganglion. In response to certain changes in exterior conditions, like exposure to sunlight, other infections or hormonal changes, the virus is reactivated by insufficiently understood mechanisms and reinfects the oral epithelium in the form of cold sores. Analogously, another virus from the herpes group, the varicella virus, sometimes causes herpes zoster after years of latency in spinal ganglia. This might be a useful evolutionary compromise, as the effects of an immune attack against neuronal cells might be even less desirable. Intracellularly propagating Listeria, for example, is able to commandeer a host "rocket propulsion system" of polymerizing actin to "shoot" itself into neighboring cells, thereby completely avoiding the threat of antibodies. Antibodies are formed, but the bacteria do not provide their targets at the required density to be attacked efficiently.

But once you have understood the basic word roots order careprost 3 ml free shipping medicine pills, combining word forms 3 ml careprost with amex treatment of lyme disease, prefixes and suffix you will find that anatomical terminologies are not as difficult as you first imagined. Anatomical positions are universally accepted as the starting points for positional references to the body. In anatomical position the subject is standing erect and facing the observer, the feet are together, and the arms are hanging at the sides with the palms facing forward. Relative means the location of one part of the body is always described in relation to another part of the body. Body parts Regions The body can generally be described to have areas of: Axial body part: - It is the part of the body near the axis of the body. It is customary to subdivide the abdominal area into nine regions or more easily in to four quadrants. The two main body cavities are the larger ventral (anterior) and the smaller, dorsal (posterior) body cavity. It consists of the right and left pleural cavities and mediastinum (the portion of tissues and organs that separates the left and right lung). It is divided into superior abdominal and inferior pelvic cavity by imaginary line passing at upper pelvis. The anatomical term opposite to lateral is: - a) Proximal b) Distal c) Medial d) Superficial e) Caudal. This phenomenon is called: a) Anatomical integrity b) Physiological stablity c) Homeostasis d) Hemostasis e) Body stasis 3. A plane that divided the body into anterior and posterior parts is: - a) Medial plane b) Coronal or frontal plane c) Sagital plane d) Transverse plane e) Oblique plane 5. Cytology: - It is a branch of science concerned with a study of cells Cell Theory explains about a) All living organisms are composed of cell and cell products. To know more about cell, we can divide the cell in to four principal parts: - Plasma (cell) membrane: it is the outer lining, limiting membrane separating the cell internal parts from extra cellular materials & external environment. Cytoplasm: cytoplasm is the substance that surrounds organelles and is located between the nucleus and plasma membrane 17 Human Anatomy and Physiology Organelles: these are permanent structures with characteristic morphology that are highly specialized in specific cellular activity. Extra cellular materials are also referred to as the matrix, which are substances external to the cell surface. The quality selective permeability Movement across-cell membrane Movements a cross membrane takes place in two ways. Simple diffusion, the random movements of molecules from area of high concentration to the area of low concentration. Facilitated diffusion, larger molecules, which are not soluble in lipid need protein channel to pass through the plasma membrane. Osmosis, a special type of diffusion referring to the passage of water through a selectively permeable membrane from an area of high water concentration to lower water concentration. Filtration, small molecules pass through selectively permeable membrane in response to force of pressure. Active movements across membranes Substances move through a selectively permeable membrane from areas of low concentration on side of a membrane to an area of higher concentration on the other side. But if equilibrium reached and still more molecules are needed, they must be pumped 20 Human Anatomy and Physiology through the membrane against concentration gradient. It includes: Pinocytoss – cell drinking Receptor – mediated Endocytosis- Endocytosis with the help of receptor. It is thick semi transparent, elastic fluid containing suspended particles and a series of minute tubules and filaments that form cytoskeleton. The inorganic components exist as solutions 21 Human Anatomy and Physiology because they are soluble in water. In the nucleus a jelly like fluid that fill the nucleus is karylymph (neucleoplasm), which contain the genetic material called chromosome.

Regions of the body are identified using terms such as “occipital” that are more precise than common words and phrases such as “the back of the head discount 3 ml careprost free shipping medications used to treat schizophrenia. Images of the body’s interior commonly align along one of three planes: the sagittal discount careprost 3ml visa treatment quadricep strain, frontal, or transverse. The body’s organs are organized in one of two main cavities—dorsal (also referred to posterior) and ventral (also referred to anterior)—which are further sub-divided according to the structures present in each area. Serous membranes cover the lungs (pleural serosa), heart (pericardial serosa), and some abdominopelvic organs (peritoneal serosa). A scientist wants to study how the body uses foods and studying all of the structures of the ankle and foot? Which of the following is an example of a normal changes physiologic process that uses a positive feedback loop? The person is standing facing the observer, with upper limbs extended out at a ninety-degree angle 13. Cancer cells can be characterized as “generic” cells that from the torso and lower limbs in a wide stance perform no specialized body function. Humans have the most urgent need for a continuous long, thin, right and left sides along the ________. Which of the following imaging techniques would be best to use to study the uptake of nutrients by rapidly a. Identify the four components of a negative feedback characteristics of the human heart come more easily: an loop and explain what would happen if secretion of a body alien who lands on Earth, abducts a human, and dissects his chemical controlled by a negative feedback system became heart, or an anatomy and physiology student performing a too great. Explain why the smell of smoke when you are sitting produce sequential images of the body in the sagittal plane? If a bullet were to penetrate a lung, which three anterior thoracic body cavities would it enter, and which layer of the 33. Introduction Chapter Objectives After studying this chapter, you will be able to: • Describe the fundamental composition of matter • Identify the three subatomic particles • Identify the four most abundant elements in the body • Explain the relationship between an atom’s number of electrons and its relative stability • Distinguish between ionic bonds, covalent bonds, and hydrogen bonds • Explain how energy is invested, stored, and released via chemical reactions, particularly those reactions that are critical to life • Explain the importance of the inorganic compounds that contribute to life, such as water, salts, acids, and 42 Chapter 2 | The Chemical Level of Organization bases • Compare and contrast the four important classes of organic (carbon-based) compounds—proteins, carbohydrates, lipids and nucleic acids—according to their composition and functional importance to human life The smallest, most fundamental material components of the human body are basic chemical elements. In fact, chemicals called nucleotide bases are the foundation of the genetic code with the instructions on how to build and maintain the human body from conception through old age. Human chemistry includes organic molecules (carbon-based) and biochemicals (those produced by the body). All of the elements that contribute to chemical reactions, to the transformation of energy, and to electrical activity and muscle contraction—elements that include phosphorus, carbon, sodium, and calcium, to name a few—originated in stars. These elements, in turn, can form both the inorganic and organic chemical compounds important to life, including, for example, water, glucose, and proteins. This chapter begins by examining elements and how the structures of atoms, the basic units of matter, determine the characteristics of elements by the number of protons, neutrons, and electrons in the atoms. An object’s mass is the amount of matter contained in the object, and the object’s mass is the same whether that object is on Earth or in the zero-gravity environment of outer space. Where gravity strongly pulls on an object’s mass its weight is greater than it is where gravity is less strong. An object of a certain mass weighs less on the moon, for example, than it does on Earth because the gravity of the moon is less than that of Earth. Elements and Compounds All matter in the natural world is composed of one or more of the 92 fundamental substances called elements. An element is a pure substance that is distinguished from all other matter by the fact that it cannot be created or broken down by ordinary chemical means. While your body can assemble many of the chemical compounds needed for life from their constituent elements, it cannot make elements.

Neuroblastoma Velo-cardio-facial syndrome careprost 3 ml line medications breastfeeding, Hypoplasia of thymus and parathyroids buy careprost 3 ml line symptoms you may be pregnant, third and fourth pharyngeal pouch syndrome. Abnormalities: cardiovascular, thymic and parathyroid, craniofacial anomalies, renal anomalies, hypocalcemia and immunodeficiency. Clinically this is detected by one or more tests (barium enema and x ray, manometry or biopsy) and can currently only be treated by surgery. A temoporary ostomy (Colostomy or Ileostomy) with a stoma is carried out prior to a more permanent pull-through surgery. Melanoma In Australia each year 8,800 people are diagnosed with melanoma, and almost 1000 people die (Data, Cancer Council Australia). Two different findings on the reprogramming of melanoma cells, which have a neural crest origin, when transplanted between species into embryos. Multiple café-au-lait spots (flat skin patches darker than the surrounding area) appear in early childhood which increase in both size and number with age. In the iris of the eye, Lisch nodules (benign growths) also appear (French, café-au-lait = coffee with milk) Atlas of Genetics and Cytogenetics in Oncology- Neurofibroma (http://atlasgeneticsoncology. Segmental restriction of neural crest cells and motor neurons by the ephrin proteins of the sclerotome (http://www. Diagram of an E10 embryo showing the origins of neural crest cells that colonize the developing gastrointestinal tract (http://www. In the body, this is mainly about mesoderm differentiation beginning with an embryonic connective tissue structure, the mesenchyme. In the head, this is a mixture of mesoderm and neural crest differentiation, from mesenchyme and ectomesenchyme respectively. Francis-West - Chapter 11 Limb Dev (bone not well covered in this textbook) Before we Are Born (5th ed. Scleretome has 2 components upper loose (pathway for artery and nerve) and lower compact Vertebra (http://embryology. Adult vertebral column 33 total - 7 cervical, 12 thoracic, 5 lumbar, 5 sacral, and 5 coccygeal Intervertebral Disc Structure - annulus and nucleus pulposus dense region of sclerotome. Chondroblasts in existing cartilage divide and form small groups of cells (isogenous groups) which produce matrix to become separated from each other by a thin partition of matrix. Mesenchymal cells surrounding the cartilage in the deep part of the perichondrium (or the chondrogenic layer) differentiate into chondroblasts. These sutures gradually fuse at different times postnatally, firstly the metopic suture in infancy and the others much later. Osteogenesis Formation of mature osteoblasts - the mesenchymal stem cells initially form preosteoblasts that then differentiate. These cells differentiate first into mitotically active cells, myoblasts, which contain a few myofilaments. Myoblasts undergo frequent divisions and coalesce with the formation of a multinucleated, syncytial muscle fibre or myotube. In the course of the synthesis of the myofilaments/myofibrils, the nuclei are gradually displaced to the periphery of the cell. Skeletal Muscle Stages Myoblast - individual progenitor cells Myotube - multinucleated, but undifferentiated contractile apparatus (sarcomere) Myofibre (myofiber, muscle cell) - multinucleated and differentiated sarcomeres primary myofibres - first-formed myofibres, act as a structural framework upon which myoblasts proliferate, fuse in linear sequence secondary myofibers - second later population of myofibres that form surrounding the primary fibres. The electrical properties of the motor neuron will regulate the contractile properties of all associated myofibres. Each somite pair level gives rise to a group of skeletal muscles supplied by a specific segmental spinal nerve. The muscle arises from a specific somite and the spinal nerve arises from a specific level of the spinal cord (identified by vertebral column).