Basic Concepts of Anatomy - PDF

Basic concepts The cell theory, which is now obvious, in the past was not so considered. The concept of this theory is that ‘The pathology of an organ is nothing but the pathology of the cells that compose the organ’ (R. Virchow, 1858). The cell theory is strongly connected with the Reductionist ap...

Basic concepts The cell theory, which is now obvious, in the past was not so considered. The concept of this theory is that ‘The pathology of an organ is nothing but the pathology of the cells that compose the organ’ (R. Virchow, 1858). The cell theory is strongly connected with the Reductionist approach, which says that ‘… The body is nothing but a unique mosaic of trivial items’ (J. Rostand). This means that, in order to understand what is happening and how at the level of an organ, firstly it is important to understand what is happening at a smaller, single level. The comprehension of the morphology of a single cell, then of the tissue to which it belongs, then of the organ and then of the whole body is a direct clue for physiology. Morphology and physiology are strictly connected, and therefore it is so important for us to learn the subjects of this course. The microscopic anatomy is fundamental to understand the physiology of an organ, because it is at the level of the single cells that the function of an organ is contained. Anatomical position: general terms of location and direction The anatomical position of a body is an upright body, with arms, hands, palms and feet pointing forward. When a body is observed in the anatomical position, many useful terms can be identified, such as ‘anterior/posterior’, ‘cranial (towards the skull)/caudal (towards the feet)’, ‘lateral (= towards the outside) and medial (=towards the mid-sagittal plane). From the musculoskeletal point of view, there can be terms like “distal/proximal”, “tibial/fibular” etc. Cardinal planes and axes There are three important axes and three important planes. Planes: 1) The sagittal plane divides the body in a right part and a left part. 2) The coronal plane divides the body in anterior and posterior. 3) The transverse plane divides the body in a superior and an anterior portion. This plane can be moved along the body in order to identify specific portions of the body. Axes: 1) The longitudinal axis 2) The transverse axis 3) The sagittal axis The classical mid-sagittal plane passes through the sternum and divides the body in two parts that are symmetrical. Though, infinite sagittal planes can be identified, that can pass, for example, near the clavicle or the shoulder. This gives the possibility to focus on specific parts of the body. (This plane is very important for the abdominal cavity and the thorax). To study anatomy different approaches can be used. 1. The topographic approach (Regional anatomy). It is the projection of specific organs or topographic regions on the body’s surface. Using this approach in either an anterior or a posterior view the skull, the neurocranium, the neck, the thorax, the abdominal cavity and the upper/lower limb can be identified. The regions, however, are widely different between anterior and posterior. This approach is widely used by surgeons because it lets them know exactly what structures are located near an organ of interest. 2. The systemic approach is a more didactical approach, which focuses on specific organs (in different locations of the body) related in terms of functions. Both these approaches need to be kept in consideration and be combined when studying anatomy. Specific landmarks and reference lines are needed to study anatomy, especially if the first approach is used. A landmark is a particular region or point where the skeleton becomes palpable, independently of the sex or the conformation of the body considered. Landmarks are fundamental for a clinical approach. For example, in the thorax the most important landmarks are the Jugular Notch and the Sternal Angle; in the abdominal cavity there is the transpyloric plane (where the pylorus is located), the subcostal plane, supracrestal plane, intertubercular and interspinous plane, which passes through the two anterior superior iliac spines of the superior border of pubic symphysis. There are different landmarks and reference lines for the anterior part and the posterior part of the body. For example, important landmarks of the posterior part are the spinous processes of the vertebrae. In the abdominal cavity, 9 subframes can be identified thanks to the reference lines. In fact, the subframes are all located between 2 midclavicular lines, drawn from the clavicle to the anterior superior iliac spine, and the transpyloric/iliac crest plane. Under this subframes different organs can be palpated: in the gastric region the stomach, in the umbilical region the small intestine (which is actually present in all subframes) etc. So this subdivision is very important both for surface anatomy and a semeiotic approach, especially for the organs located in the anterior abdominal wall. An important point to understand is the difference between a hollow and a solid organ, which is the first characteristic to mention when describing an organ. For example, most organs in the GI tract are hollow. Hollow organs are characterised by a lumen and an organisation of different tunicae. Examples are the cardiovascular vessels and the oesophagus: the latter is an organ similar to a tube, with a star-shaped lumen and different tunicae from the inside to the outside: tunica mucosa (innermost layer), submucosa (dense connective tissue with blood vessels/nerves), muscular layer (in the GI tract circular and longitudinal), tunica adventitia (also called serosa layer when the organ is surrounded by a serosa membrane). Solid organs have a capsula of dense connective tissue, which forms invaginations inside the organ and creates different septa, which are called the stroma of the organ. The stroma is very important as it divides the functional part of the organ, which is defined as the parenchyma. Examples are the spleen and the glands. Solid organs are usually characterised by specific structures, such as the hilum. The hilum of a solid organ is the entry/exit point. It is the ‘door’ of the organ, through which it communicates with nerves and vessels. For example, through the hilum of the kidney the ureters and the renal veins exit, while the renal artery enters. When studying an organ, the following order needs to be followed: 1. If the organ is hollow or solid 2. Surface properties 3. Systematic approach 4. Microscopic approach Cardiovascular vessels Can be arteries or veins. Arteries take blood away from the heart, veins bring the blood back to the heart. The cardiovascular system is composed by these vessels, which are hollow organs. Veins can be classified into superficial and deep veins. Deep veins are bigger and accompany the arteries, while superficial veins are smaller. In the arteries system, arteries, arterioles and capillaries are present. There are many structural differences between the arteries and the veins. In the arteries:  the muscular layer is thicker than in the veins because they have to face a higher pressure.  The adventitia layer is thinner with respect to the veins  In a histological section, the artery persists circular because it has a thick muscular layer. From the heart to the periphery there are different organisations of arteries.  Elastic artery (aorta). It faces a strong pressure. Presents a tunica intima, mainly composed of endothelial cells, a very thick muscular layer of smooth muscle cells, and the adventitia layer.   Muscular artery (ex. the renal, celiac or mesenteric arteries) branches from the aorta. All the muscular arteries present a very thick adventitia layer as they all enter inside an organ.  Capillaries lose the muscular layer and the adventitia layer because their function is to exchange gasses with the cells of peripheral organs. The knowledge of the layers of the cardiovascular vessels is important in order to be able to identify pathologies. An example is the arteriosclerotic disease: in this case a fibro-fatty plaque is present, which can develop a thrombus. Fascia It is an organized connective tissue layer that completely envelops the body beneath the subcutaneous tissue underlying the skin (between skin and muscles and bone). It is a layer that can be divided in 2 structures:  The superficial fascia is located under the skin. It is mainly composed by loose connective tissue. Nerves and vessels pass through this structure.  The deep fascia is mainly composed of dense connective tissue and fat. From this structure many septa start, which divide the muscle into different functional compartments. In the skin the deep fascia corresponds to the hypodermis. Bursae Bursae are closed sacs formed of serous membranes that are present in locations subject to friction. What is important to understand is that an organ does not enter the cavity of the bursa, but it presses the bursa. The organ pressing the bursa is surrounded by its visceral layer, which adheres internally to the organ. The inner visceral layer then reflects and constitutes the outer parietal layer. Important examples of bursae are the pericardium, which surrounds the heart; the pleurae, which surround the lungs, and the peritoneum in the abdominal cavity. In particular, the interaction between the peritoneum and the organs in the abdominal cavity is crucial. Their function is to allow one structure to move freely over another. Think about the movement of the small intestine during peristalsis: the fact that the inner intestine is surrounded by the inner visceral layer of the peritoneum allows it to move in an easier way with respect to an organ which is located in the extra-peritoneum region. The same reasoning has to be done for the heart during contraction and for the lungs during expansion. The bursae are very important also because they organize the structure of an organ within a cavity. A specific fluid is present between the visceral and the parietal layer, defined as a serous fluid. The fluid is produced by a peculiar epithelium, called mesothelium, that lies in the serous membrane, composed mainly of squamous cells. The mesothelium is present at the level of the peritoneal, pericardial and pleural cavities. Cavities The cavities can be divided into:  dorsal body cavities, which divide into I. cranial cavity II. vertebral cavity  ventral body cavities, which comprehends: I. Thoracic cavity, which contains the heart and the lungs. II. Abdominal cavity, which is physically separated from the thoracic cavity by the diaphragm. It contains the digestive viscera. III. Pelvic cavity. Actually, the abdominal and the pelvic cavity are a unique cavity, as there is no physical separation between them. The three serous membranes are located in the ventral cavities. In the thoracic cavity there are the pericardium and the pleurae, while in the abdominal-pelvic cavity there is the peritoneum.  When we are shown a picture like this one, we need to be able to orientate ourselves and understand that it is a sagittal section with smaller transverse sections. The transverse planes can be moved in order to observe different regions. Here, the second transverse section shows the abdomen: the liver, the spleen, the vertebral column can all be observed. The vertebrae are important landmarks to understand which side of the section is anterior or posterior; they also allow to identify whether it is the thoracic or of the abdominal cavity: in fact, in the thorax there is a thoracic vertebra, while in the abdominal cavity there is the lumbar vertebra. These two regions can be identified also by the organs: in the thorax there are the heart and the lungs, in the abdominal cavity there are the liver (on the right) and the spleen (on the left). The inferior vena cava is on the right, the aorta on the left. The sagittal section permits to visualize the whole abdominal cavity: it is very helpful as it shows the organization of the organs as well as the organization of the peritoneum. Organization of an intraperitoneal organ An intraperitoneal organ in surrounded by the visceral layer of the bursa, but it does not enter within the cavity. At the level of the bursae some important structures are present in order to connect the organ to the anterior or posterior abdominal wall. In this picture, for example, a mesentery is shown. A mesentery is a specific structure of the serous membrane that connects the organ to the posterior abdominal wall. Through the mesentery many nerves and vessels can pass. In the peritoneum it is very important to know the differences between the mesentery and the ligaments. The mesentery connects an organ to the abdominal wall, through which nerves and vessels pass. The ligament is another important structure, but through it neither nerves nor vessels can pass. It is just a simple connection between the organ and the abdominal wall. This is an example of the pleurae of the lungs, showing the parietal and visceral pleurae.  On the left: the pericardium surrounding the heart. On the right there is a right mid-sagittal section of the pericardium (the liver can be seen). The nervous system: few concepts The nervous system is mainly divided in:  Central nervous system (CNS), composed by the brain and the spinal cord,  Peripheral nervous system (PNS), composed of 12 pairs of cranial nerves, 31 pairs of spinal nerves and autonomic nerves. Questions and further explanations: 1) Are parenchyma, septa, capsula only for solid organs or for hollow organs too? Parenchyma, septa and capsula are specific features of solid organs. Septa are invaginations of the capsula inside the organ and septa divide the functional parts of the organ itself called parenchyma. 2) What do tibial and fibular mean? In the anatomical position the heart is medial with respect to the arm. -lateral: towards the outer part -medial: towards the mid sagittal plane Considering the leg, fibular refers to the bone which is more lateral while tibial refers to the bone which is towards the mid sagittal plane. Fibular and tibial refer to the musculoskeletal system. 3) Can CT sections be taken either from the skull so looking downwards and from the inferior part so looking upwards? Looking at transverse sections it is worth to recognize if the picture is taken from the skull or from the inferior part. The diaphragm permits to evaluate this because the thoracic part of it is different from the abdominal part. In general CT sections are cranial but sometimes can be also caudal. 4) Which is the name of the liquid between the visceral layer and the parietal layer of peritoneum, pleura and pericardium? The liquid between the parietal layer and the visceral layer takes different names depending if it refers to the peritoneum, pleura or pericardium: peritoneal liquid, pleural liquid, pericardial liquid. 5) What is a landmark and a reference line? A landmark in general is a site where the skeleton becomes palpable under the skin due to the  pressure of some bones to the skin, independently from sex and body conformation. In the thorax there are many landmarks associated with bones while in the abdomen bones are mainly associated with the pelvic cavity or there are some lines connected with specific organs such as the transpyloric plane. Reference lines join two symmetric landmarks or are connected with specific organs. A reference line defines a transverse plane. 6) In the 9 sections of the trunk are numbers important or are just for legend? Dividing the trunk in 9 sections the numbers are not strictly correlated to the regions. (numbers are just for legend and not associated with a specific zone) 7) How organs are classified in the abdominal cavity? In the abdominal cavity organs can be divided following three different schemes: -anterior (stomach), medium and posterior (kidneys) organs: this subdivision refers to surface anatomy; -retroperitoneal or intraperitoneal organs; -over the transvere mesocolon or under the transverse mesocolon: this subdivision is correlated to embryo development. Integumentary system An organ is a structure that you can dissect from other structures, in fact (in Greek) anatomy means dissection. The skin is an organ because at the level of hypodermis it can be dissected. The skin contributes to about 2 kg in a 75 kg man. The integumentary system consists of skin and its derivatives called epidermal skin appendages. The skin has different layers as shown in figure 1: -Epidermis: a superficial layer composed of a stratified squamous epithelium made of keratinocytes. Different layers of cells, at different levels of differentiation, compose the epidermis. -Dermis: a deeper layer of dense irregular connective tissue. In this layer are also present vessels, nerves, lymphatic vessels, skin appendages such as follicles of hairs, sweat glands, sebaceous glands, eccrine glands, holocrine glands (glands are usually located in the dermis of in the connection between dermis and hypodermis) -Hypodermis: it is under the dermis and contains a variable amount of adipose tissue. The superficial fascia and the deep fascia are located in the FIGURE 1: COMPOSITION OF SKIN hypodermis. Under the hypodermis there are the skeletal muscles. The morphology of the skin – epidermis, dermis, hypodermis - reflects its function: it protects the body from the outside environment, contains organs and structures, has a metabolic function, regulates heat and provides sensations, since at the level of the dermis and subcutaneous tissue some sensory cells that detect pressure, heat and cold are present. The dermis is very thick because contains vessels and nerves that sustain the epidermis; in fact, the epidermis and in general all epithelium in our body is avascularised. Epidermis The invaginations of the epidermis towards the dermis that can be seen in the histological section are called papillae of the epidermis and contain stem cells that subsequently undergo a differentiation process, turning into flattened keratinocytes, which form the stratum corneum. FIGURE 2: HISTOLOGICAL SECTION OF EPIDERMIS WITH PAPILLAE ON THE LEFT; STRATUM BASALE AND STRATUM SPINOSUM ON THE RIGHT. The epidermis is composed for 85% by keratinocytes that through different levels of differentiation form the stratified squamous keratinized epithelium. Looking at the histological sections above, at the level of the papillae there is the stratum basale SB, which contains the mitotically-active stem cells that are attached by hemidesmosomes to the underlying connective tissue (CT) and by desmosomes to each other. These stem cells undergo differentiation and form the stratum spinosum (SS), stratum granulosum (SGr) and the stratum corneum SC. The stratum corneum is the outermost layer, in which the differentiated squamous cells lose the nuclei and are completely filled with keratin filaments. These cells constantly desquamate from the skin’s surface. The stratum granulosum is a distinct layer of flattened keratinocytes filled with keratohyalin granules, which contain precursors to filaggrin, which aggregates keratin filaments and lamellar bodies which contain lipids. These, when secreted, are responsible for the formation of the epidermal water barrier. To summarize, keratinocytes differentiate and change their morphology starting from the SB going up. Keratinocytes express different isoforms of keratin depending on the stratum: keratin 5 or 14 in the stratum basale, keratin 1 or 10 in the stratum spinosum, involucrin and filaggrin in the stratum granulosum, loricrin in the stratum corneum. Different gene expression allows to identify the differentiation process of keratinocytes. (loricrin, filaggrin and involucrin are not keratin but are other proteins that are produced only when the keratinocyte is in the granulosum or corneum stratum). At the end these cells desquamate from the skin surface in an independent manner. All epidermis of our body is totally replaced in 47 days (31 days turnover from stratum basale to stratum granulosum and 14 days turnover from stratum granulosum to stratum corneum). Thick skin at the level of the fingertip with a thick stratum corneum. In thick skin it’s also possible to see the stratum lucidum between the SGr and the SC. Thin skin at the level of abdomen or forearm with a thin stratum corneum. So different parts of skin have different features. In the picture on the right, the lighter oval in the middle is an arteriole of the dermis. FIGURE 3: THICK SKIN AND THIN SKIN Melanocytes are big cells that count for 5% of cells in epidermis. They reside in the stratum basale but have long processes that allow them to act also at the level of the stratum spinosum and stratum granulosum. Melanocytes produce melanin pigment in melanosomes and thanks to these processes melanosomes (black points in the histological section) can reach keratinocytes of the above strata of epidermis. Melanin pigment guarantees protection against UV light, which can cause damages to DNA. FIGURE 4: MELANOCYTES Melanocytes are associated to melanoma cancer caused by UV light exposure in patients with low levels of skin pigment melanin. This cancer is malignant and can spread everywhere in the body. Langerhans’ cells represent from 2% to 5% of the total and are antigen-presenting cells controlling the passage of pathogens to help the immune system. Merkel’s cells represent from 6% to 10% of the total and are mechanoreceptor cells associated with sensory nerves. Both cells can be either in the epidermis or sometimes in the dermis. The change in colour of the skin marks for some pathologies: in cyanosis fingertips becomes blue demonstrating hypoxia; jaundice in adults is a sign of an abnormal heme metabolism, liver dysfunction or biliary tract obstruction. Dermis The cells of the dermis are called fibroblast. The dermis is composed by two layers:  Papillary layer (PL) more superficial and composed by loose connective tissue (collagen type I and collagen type III). At the level of the papillae there are sensory nerve endings and a network of blood (arterioles and venules) and lymphatic vessels. The papillae create the so called epidermal-dermal junction.  Reticular layer (RL) deeper and composed by dense irregular connective tissue (collagen type I, elastin that creates the elastic fibres). Larger blood vessels are found here. Sensory nerve receptors The epidermis contains lots of sensory nerve endings that allow to detect sensations. Together with Merkel’s corpuscle (Merkel’s cell with a nerve ending), other mechanoreceptors are present: Pacinian corpuscles between epidermis and dermis detect pressure and vibrations, Meissner’s corpuscles at the level of papillae detect light touch, Ruffini’s corpuscles in the deep layers of the dermis detect skin stretch and torque, Krause’s end bulb serves as cold receptor. These sensory nerve endings are in the dermis: either very near to epidermis or in deep layers of dermis, as shown in figure 5. FIGURE 5: SENSORY RECEPTORS FIGURE 6: PACINIAN AND MEISSNER’S CORPUSCLES Epidermal Skin Appendages Epidermal skin appendages include hair follicles and a lot of glands such as sebaceous glands (holocrine) that produce sebum, eccrine sweat glands (also called merocrine) that produce sweat, apocrine sweat glands that produce a form of sweat with high concentration of carbohydrates-lipids-proteins, mammary glands (apocrine) in the anterior wall of the thorax. Eccrine sweat glands, even if next to them, are not related to hair follicles: they produce sweat, which is similar in composition to an ultrafiltrate of blood in the kidneys, and it’s responsible for the thermoregulation through evaporation of water. FIGURE 7: GLAND TYPE  In the inferior segment of the hair follicle, some unipotent stem cells are present. They differentiate into hair-forming matrix cells that compose the follicular bulge. These stem cells produce the medulla, cortex and cuticle of the hair shaft. In particular, the hair shaft is composed by two layers: the external root sheath is continuous with the epidermis while the internal root sheath is composed by three layers of cells that come from differentiation of stem matrix cells. Near the base of hair shafts there are sensory nerves’ endings, while at the bottom of the follicle bulge there are blood vessels that provide the proper support to the hair follicle and hair shaft. Stem cells of both the stratum basale and hair follicles are unipotent stem cells because they can originate FIGURE 8: HAIR FOLLICLE respectively only keratinocytes and matrix cells of the follicular bulge. Nails are also skin appendages. They are mainly composed by keratinized cells located on the nail bed that is composed by hard keratin, which is formed in the nail root at the proximal part of the nail. From there, cells undergo a process of differentiation and form the plate of the nail, which grows above the nail bed. As the nail plate grows, it moves over the nail bed, with the edges always covered by skin folds. FIGURE 9: A NAIL Harvey medical school: Structure of the Body Anatomy lecture: 2-23/03/2021 Professor: Mauro Vaccarezza Transcribers: Giulia Rossi, Alice Rizzo Reviewer: Martina Mazzocchi Muscolo-skeletal System Learning anatomy and the bases of biomedical science is a matter of jargon. The etymology of words in anatomy is important to easily understand and remember its materials. It’s better to start from a map, like it is needed a map to visit a huge town, it is needed a map to study the human body too. The map is also useful to communicate to colleagues things that are related to the medical job; moreover, if there is miscommunication there can be problems also for the patient. Direction and relative position These are some definitions and jargon to use. Everything in body that is medial is towards the midline of the body: the sagittal plane. For example, the heart, present on the left side of the thorax, is medial with respect to the left arm. Figure 1: Medial position The contrary of medial is lateral, meaning away from the midline of the body. The figures present in the image above are in the anatomical position, with the palms of the hands in front; from this position, everything is described in anatomy. As it can be seen, in the anatomical position the first finger in the hand is lateral in comparison to the fifth finger. Figure 2: Lateral position  Figure 3: Proximal (left) and distal (right) position Proximal and distal are two other definitions: proximal means closer to the point of origin of the body part; distal means further away from the point of origin of the body part. To give a classical example: in the upper left arm, the shoulder is proximal to the body whereas the hand is distal. Also, the elbow is proximal while the wrist distal. This is true also for the leg: the hip joint is proximal with respect to the knee joint; the knee joint is proximal with respect to the ankle joint of the foot. Figure 4: Superior (left) and inferior (right) positions Superior means towards the head (going up); inferior is below, away from the head (going down). The head is superior with respect to the heart. The bladder is inferior with respect to the stomach. Figure 5: Posterior/Dorsal (left) and Anterior/Ventral (right) positions Anterior / ventral means towards the front of the body; posterior/dorsal means towards the back of the body. The stomach is ventral or anterior in relation to the pancreas, which is a very deep organ; at the same time, the pancreas is posterior or dorsal in relation to the stomach or to the anterior abdomen wall. The kidneys are posterior or dorsal in relation to the small intestine. Superficial means towards or at the body surface, deep means away from the body surface. The cephalic vein is superficial towards the skin whereas the aorta is deep inside the body. The oesophagus can be considered another deep organ in the Figure 6: Superficial (left) and Deep (right) positions posterior mediastinum. Planes of section Figure 7: Planes of sections of the human body The planes of section are also important in the anatomic jargon: The median/sagittal plane is in the middle, it is the vertical plane that divides the specimen into equal left and right parts. The parasagittal plane divides the body into unequal left and right parts; parasagittal planes are always parallel to the median/sagittal one. Everything that is close to the median / sagittal plane is called medial; something that is far from that plane is lateral. Once more, the person present in the image above is in the anatomical position. The Coronal/frontal plane is the vertical plane dividing the specimen into front and back parts. The horizontal/transverse plane divides the specimen into upper and lower parts. Terms of movement Again, starting from the anatomical position, there can be different movements: extension (in the plane behind the body) and flexion (in the plane in front of the body). These movements can be made for instance by the whole upper arm or even by the distal part of it, as it can be seen in the image. Flexion and extension can be Figure 8: Terms of movement (1) opposite movements for the lower arm; but this derives from the process of the evolution. In the origin, the lower limb develops as the upper limb, so that the knee, at the beginning of the development is behind. Then there is a rotation and the knee ends up in its “normal” position. These movements can be made by the trunk, with the hip as a base or by the hand like in the picture. It is suggested to exercise and practise these kinds of movements in front of the mirror to get used to them and answer correctly to the related questions.  Other movements are the abduction and adduction: the first one means getting something away/far from the body (from Latin: abducere); whereas the second one means getting something closer to the body (from Latin: adducere). In the image above (in the anatomical position), the person can be seen putting the arm or the leg away from the body/up (abducting) and then making them come back close toward the middle plane of the body (adducting). The rotation can be lateral and medial and can be made by the upper and lower arm, as in the image. Figure 9: Terms of movement (2) Supination and pronation can be performed if just the distal part of the arm is turned: starting from the regular position, supination means putting the palm of the hand in front (anatomical position). Then if the distal part of the arm is turned, so that the dorsal part of the hand is going to be anterior, there is the pronation. Figure 10: Supination/Pronation and Circumduction Dorsiflexion means putting up the foot; plantarflexion means putting it down. In the eversion the foot is pushed laterally; in the Figure 11: Dorsiflexion/Plantarflexion and Eversion/Inversion inversion the foot is pushed medially. The circumduction is kind of a mixture of all the other movements. It can be performed by the leg, but also by the shoulder: the most flexible and mobile joint of the human body which allows the arm to perform a huge circumduction. When the shoulder does a circumduction, it draws a 3D figure of a cone: the shoulder or the hip (when the movement is performed by the lower limb) represent the cone vertex. Figure 12: Other terms of movement  Other kinds of movements are the lateral bending (lateral pushing, bending the trunk left and right); rotation of the head, neck and upper trunk; elevation and depression (seethe image). There is also the protraction and the retraction of the scapula on thoracic wall, that can be done also with the mandible. Figure 13: Protraction and retraction Key prefixes for the muscolo-skeletal system Osteo means related to bones: osteon (the basic unit structure of compact bone), osteoma (the tumour of the bones), osteosarcoma (a malignant tumour of bone cells). Osteo means bone from Greek. Osteocytes are the mature cells of the bone; the osteoblasts are the growing immature cells of the tissue. The osteoclasts are other special cells that are capable of digesting the bones. Chondro is related to the cartilage: the chondrocytes are the cells of the cartilage. The chondroma is a benign tumour of the cartilage; chondrosarcoma is a malignant tumour. Chondrocytes are the cells, chondroblasts are the immature cells growing in the cartilage. Peri means around, Endo inside, Intra within (intracellular fluid), Meso middle, Os bone, Epi above and Dia between. The skeletal system The main components of the skeletal system are: bones, cartilage, tendons and ligaments (in addition to muscles). The total number of bones in a human body is around 206/208; actually thereare some people that have some little bones in between the flat ones, usually called wormian bones, whose name derives from the first Danish guy that wasable to describe them: Ole Warm. These little bones are usually in addition to the ones that a normal human body has: they are an anatomical variation. Studying anatomy is studying the most common variations found in humans. Figure 14: Overview of the skeletal system Functions of the skeletal system The main functions of the skeletal system are: ▪ Support and protection like in the rib cage or the skull. ▪ Assistance with movement. ▪ Mineral homeostasis, that is very important to regulate calcium in the body, element which is involved in the excitability of membrane systems in the cells like the Muscolo-skeletal system, the heart, or the CNS (central nervous system). Calcium has to be closely monitored in the body, and bones assist that together with other organs. Bones are actually a great calcium reservoir: they keep a lot of calcium within themselves and are capable of releasing it in certain moments. Besides the other minerals, there is a system that tries to control the calcium level in the body with hormones and communicates with the bone tissue. ▪ Blood cell production is another function of the skeletal system carried out by the bone marrow, the organ that produces, inside of the human bones, of all the blood cells: white cells (leukocytes), lymphocytes (which are fighting Covid), red blood cells (erythrocytes) which transport oxygen thanks to the haemoglobin. Even the platelets are produced by the bone marrow; they are actually pieces of cell: they do not have a nucleus and have just a little bit of cytoplasm. Platelets derive from shedding of their “father” the megakaryocyte which leads to their production in the bone marrow. ▪ Another function is the triglyceride storage, because there are a lot of adipocytes (adipose tissue) inside the bones. ▪ Bones can be considered as an endocrine organ because trough osteocalcin, a hormone produced in the bones, and other molecules helps the pancreas to keep the glucose level low in the body: it is an antidiabetic hormone. Also, osteocalcin is synergic with the male testosterone in keeping testicles and the epididymis healthy and in contributing to spermatozoa production. This is a new discovery that is not contained in the books yet. Functions of the connective tissues All of the components of the skeletal system (cartilage, bones, tendons and ligaments) are under the same definition and embryological derivation of the connective tissue. The general functions of the connective tissues, not surprisingly, overlap with the main functions of the skeletal system: enclose and separate tissue; connect tissues with one another (in part bones and muscles do that too); support moving parts of the body; cushioning and insulation; transporting; protection. In the body there is a special connective tissue: the blood, that is liquid and transports things. Protection can be macroscopic, such as a cage; but more widely it can regard the protection provided by the components of the liquid part of the connective tissue such as the white blood cells which fight against external agents, invaders, tumours or viruses on a daily base. The main components of the skeletal system are cartilage, bones, tendons and ligaments. Tendons are composed by intermediate cells between muscles and cartilage: they are called tenocytes. They are characterized by a very low metabolism and a very low turnover, (like the cartilage). This means that their repair is very slow as well; therefore, if there are damages in tendons, the repair is going to be quite slow as it is for cartilage. There is a huge biomaterial research behind cartilage and tendons; unfortunately, until now no synthetic material good enough to replace cartilage and tendons has been found yet. Names of the different connective tissue cell types These suffixes are associated with the function of cells involved in the extracellular matrix. -blast create the matrix, make the tissue; -cyte maintain the matrix, they are the mature cells; -clast breakdown the matrix (in this case, there are osteoclast important in bones remodelling have a role in osteoporosis). The prefixes allow to identify the cells location e.g. “chondro” tells that the analysed cell is a cartilage cell. Therefore, the cells associated with the cartilage are: Chondroblasts, chondrocytes and chondroclasts. The cartilage matrix The cartilage matrix is a dense network of collagen fibers and elastic fibers embedded together in the matrix. Metabolically cartilage is fairly inactive, because it is avascular: cartilage doesn’t have any blood supply, if it does that means that there is some kind of disease, or the tissue is inflamed. This is a bad sign (blood is not a friend of cartilage): if there is blood in there the tissue tends to die. Therefore, if cartilage is normally avascular, it must receive nutrients and needs by diffusion from the underlying bones, which conversely to cartilage are very well vascularized. However, (only in part) this kind of nutrition can come from the synovial liquid in the joints, but only for a little amount. This means repair of cartilage damage is very slow; this makes sense, because as their nutritional support (amino acids and energy) and metabolism are slow, the repair will be as well. Cartilage growth Cartilage can grow thanks to appositional growth or interstitial growth. The first means adding layers, the second means starting from a node, from a kind of gem inside, at a given space of the body. There are three types of cartilage: hyaline; fibrocartilage; elastic. The type depends on how many minerals are present in the tissue: hyaline has more minerals and is a little bit closer to bones; the closest with respect to the other types. Hyaline cartilage It consists in specialized cells that produce matrix: chondroblasts are young cells; chondrocytes are located in spaces called lacunae; matrix, made by collagens, that are glycoproteins or proteoglycans produced from connective tissue cells (chondroblasts produce them); perichondrium, the peripheral unit; articular cartilage, sometimes its borders and boundaries make the articulations (meaning the joints) between the neighbouring bones. Figure 15: Hyaline Cartilage This image represents the hyaline cartilage, with the matrix in between the lacunae; the chondrocytes are inside of them. Chondroblasts usually are smaller and the perichondrium on the side. This hyaline cartilage is found at the ends of the articulating bones, in the nose, trachea, bronchi and costal cartilage. It is actually the start of most of the embryological skeletal in the foetal life. Bone tissue Bone tissue is quite different: there is the bone matrix, which is 35% organic (made by cells and collagens) and 65% inorganic (made by mineral: hydroxyapatite and others). The cells associated with the bone matrix are: osteoblasts, young cells that make the tissue; osteocytes mature cells that maintain the tissue and osteoclasts that remodel the tissue by destroying and digesting parts of it; they release calcium in the blood. Osteoclasts are very interesting cells, they can be derived from macrophages, they are actually specialized macrophages scavenging cells that are cleaning around. Figure 16: Bone tissue Bone matrix The bone matrix, as described above, is characterized by an organic and an inorganic part. If the minerals are removed, the bone is too bendable; if collagen is removed, the bone is too brittle. Figure 17: (b) Bone treated with a low power acid to remove minerals, (c) an example of what happens to the bone if the collagen is removed.  How does the bone matrix form? The osteoblasts create bones through the process of ossification, also called osteogenesis. Collagen is produced from the ER (endoplasmic reticulum) and the Golgi apparatus, then it is released by exocytosis. That means that as the cells and the bones keep growing, they produce this kind of extracellular matrix. The precursors of hydroxyapatite are stored in vesicles and then they are released by exocytosis: vesicles (little organelles inside the cell) slowly go towards the membrane and then release hydroxyapatites outside. Figure 18: Bone matrix formation This creates a sort of 3D network constituting the mechanical and material properties of the bone. Bone growth Bone growth can be described as either woven or a lamella (and lacunae) structure. The osteoclasts have a role in converting woven to lamella bone, they reshape bones during growth and this process is controlled by specific hormones. There are hormones that help the bone building and keep the calcium in there and there are other hormones that promote bone consumption. This balance is really important, especially later on in life, both in females and males, for the genesis of the osteoporosis. The orientation of collagen fibers is the same in the same layer, but different in different ones: this makes the bones very strong and gives different properties in their shaping. The presence of different collagens with different lamellae will lead to the formation of different shapes and stronger material. How do bones ossify, grow and make themselves? There are different ways of making the bones. Bones are different and can be classified for their different shape. There are long bones in the upper and lower limbs; short bones like the carpal (wrist) and tarsal (foot) bones; flat bones like the ribs, the sternum, the skull (making the cranial cavity) and the scapulae. Some bones are irregular, like the vertebrae and some facial bones. Figure 19: Bone types Mesoderm and mesenchymal tissue The embryonic precursor cell and tissue of bone is the mesoderm and the mesenchymal tissue, in general considered the “father” of all the connective tissues. At about 13-14 days the developing foetus forms an embryonic disc with three layers of cells: The outer layer is the Ectoderm (epidermidis of skin); the middle layer is the Mesoderm. This tissue is also called mesenchyme (the mesenchyme creates all the bones except the facial ones, and other connective tissue); the inner layer is the Endoderm (lining of the digestive system and linked tissue and glands). During foetal development, bone forms through different ossification processes, named by the type of tissue that is replaced: Intramembranous: ossification takes place in connective tissue membranes (cartilage is not really needed and is not produced in the beginning); Endochondral ossification takes place in cartilage (there is a cartilage stamp/model before the bone tissue takes its place inside it). Both these models of ossification produce woven bone that is then remodeled; after remodeling it is not possible to distinguish how the bone was formed. The endochondral process is important to fix broken bones in adults: it is the only ossification process that take place in an adult; whereas in the fetal life both the endochondral and the intramembranous ossifications are ongoing at the same time. What is the embryonic precursor of tissue and cells forming intramembranous ossification? The intramembranous ossification occurs in mesenchymal cells within connective tissue membranes that surround the developing brain. At the site of ossification (bone development), mesenchymal cells change into osteoprogenitor cells, or osteogenic stem cells. These cells are the precursors of the young cells which produce the bone: the osteoblasts. The osteoblasts form the bone matrix: the extracellular space. They produce trabeculae of woven bone and then compact bone that is later remodeled. There is no method to distinguish, after remodeling, how the bone was formed. What is the embryonic precursor of tissue and cells forming endochondral ossification? Mesenchymal stem cells aggregate and become osteochondral progenitor cells, then they become chondroblasts, which form a cartilage framework, a sort of stamp/model of cartilage. Then the blood vessels invade the cartilage model of the chondroblasts in the perichondrium; this change is not “accepted” by the cells, which then become osteoblasts, move into the calcified cartilage framework and deposit a new bone matrix. The cartilage model present at the beginning of the process, in the end, becomes the new bone mass. This one is the process of ossification happening in adults when they try to fix a fractured bone. Endochondral ossification This process happens in the bones of the base of the skull (like in the occipital, sphenoid, part of the mandible), in the epiphysis of the clavicles, and in most of the remaining bones of the skeletal system. The majority of the bones in human body is made through endochondral ossification. Cartilage formation (meaning the frame) begins at the end of the fourth week of development. Some ossification processes start at the beginning of the eighth week of embryonic development; some do not begin until 18-20 years of age. For example, the formation of the sinuses in the frontal bone starts in adolescence and ends around the 18/20 years of age. In a young individual the frontal sinuses cannot be found because they are not completely formed yet. Sinusitis, the inflammation of this region, involves the frontal bones and cannot happen early in life, but later on. Figure 20: Steps involved in the endochondral ossification of the bones. This is the main process leading to the formation of the majority of bones during foetal development and it is the only process required for repairing broken bones in adults. Figure 21: Final steps in endochondral ossification The professor describes the steps as they are written in the image; in point 3 he adds that the ossification centre forms surrounding the vessel, and as the vessel expand, the cartilage is not “happy” and becomes bone trough the matrix and the cartilage model. The epiphyseal plate in a young person is the place where the bone grows after birth, it is important for forensic medicine, because it is visible through bone x-ray. Analysing the epiphyseal plate in a bone found in the middle of nowhere is a way to find out the age of the bone and its features. This plate becomes a line in adults: this difference is visible in figure 21, between the 6th and 7th step. As the cartilage becomes bone, it is going to be fused with the rest of the bone, thanks to the action of hormones during puberty. After this process the person stops growing. Growth (as distinct from ossification) of long bones occurs in two ways The process can be: interstitial, making bones longer in length; appositional (at the surface, by putting additional layers), making bones wider and thicker. Long bones can be an example of interstitial and appositional bone growth. Distinguishing the different types of bones There are different types of bones: compact bone is present at the periphery of the bone if the bone is observed through a longitudinal or transversal cut in the middle. Spongy bone is porous and constituted by trabeculae (columns of bones). In the spongy bone spaces the bone marrow can be found. Spongy bone functions are: to bear weight and resist bending and twisting. It is found in the spine and articulating joints. On the other hand, the compact bone is external, Figure 22: View of a bone obtained after a middle longitudinal and denser, more involved in sustaining the weight and transversal cut in keeping the shape of the bone itself. Figure 23: In this image representing a compact (cancellous) bone, the lamellae are visible (on the left: magnification of lamellae). The bone looks like a tree trunk; and the concentric lamellae make the structure more resistant to bending and more capable of sustaining weight. There are a lot of blood vessels supplying the compact bone: getting in and out. The bone is metabolically active and it has to be substantially supplied also because of the bone marrow which is inside (huge difference in comparison to cartilage). The periosteum, that is in the external part, is the only part where sensitive nerve fibers can be found in the bones; if a bone is hit or broken the pain is only due to the presence of these fibers at the periosteum. Inside the bone there are no additional sensitive fibers. Basic unit and structure of a compact bone The basic unit of compact bones is the Osteon, which is made of circumferential and interstitial lamellae; a central canal in the middle, also called Haversian (at the level of the vertical arteries present in Figure 22). The vertical arteries are the middle of the osteon which is a trunk as it can be seen in the image above between the circumferential lamellae. In the image the fibers are in different directions making the tissue stronger: this property makes the bone more suitable in pushing, bending and sustaining body weight. The perforating canals are transversal features of the bone and they allow blood vessels to penetrate from the periosteum to compact bone. There are vessels even in the central canal. Nutrients and wastes travel to and from the osteocytes via: Interstitial fluid of lacunae and canaliculi; Gap junctions: from osteocyte to osteocyte. Classification of the bones based on the shape There are long, short, flat and irregular bones. Structure of flat, short and irregular bones Flat bones have no epiphysis (the two ends present in long bones, from Greek and Latin: epi means at the side/extremities of it, top and bottom), no diaphysis (the structure in the middle of the two epiphysis in long bones). Short, flat, irregular bones cannot have diaphysis and epiphysis. Flat bones are like a “sandwich” of two layers of compact bone, between which a layer of Figure 24: Flat bones spongy bone is present: inside of it, a substantial amount of bone marrow is present. In the short and irregular bones there is compact bone surrounding a spongy bone centre (such as in the vertebrae); even here the bone marrow is present in a substantial amount. They have no diaphysis and are not elongated. Some flat and irregular bones of the skull have sinuses lined by mucous membranes. This is a characteristic of special bones in the skull. Long bones Long bones are like the femur or the tibia, which looks like a flute (in Greek/Latin the tibia is a flute to play music). They are constituted by a long body, called diaphysis: a shaft made mainly by compact bone; the two ends are the epiphysis that are composed by compact bone and a substantial amount of spongy bone inside. The epiphyseal plate, as described before, is a sign that the bone is still growing (it is made by hyaline cartilage until the growth stops, if it is present the person is still young); whereas if there is the epiphyseal line the bone has stopped growing in length (adult). The medullary cavity in children contains red Figure 25: Long bones marrow, which gradually changes to yellow in limb bones and skull (except for the epiphysis of long bones). The rest of the skeleton contains red marrow. Red marrow is the more active bone marrow, which produces cells. There is a partial substitution in adults from the red marrow to the yellow one, which contains more lipids and more fat tissue (more energy). The Periosteum is the most external part and embeds the bone. The outer layer is fibrous and it’s continuous with the fibers of tendons and ligament connected to the bone itself ; the inner portion is a single layer of bone cells, including all of the precursors (osteoblasts, osteoclasts and osteochondral progenitor cells). Moreover, the periosteum is the only bone part which has sensory fibers generating nervous stimuli such as pain when hit. Sharpey’s fibers help the periosteum to stick to the bone, and also favor the attachment of tendons to the bone by creating a layer which isquite sticky and robust. Figure 26: Bone structure The Endosteum is the inside part, more cellular than the periosteum, it is related to the passage from the compact bone to the spongy one. Bone remodelling and repair Bone is not static: it is remodelling during all life, it reflects what it is done physically and not only what is eaten or the genetic factors of the individual. In bones there is the activation and migration of osteoclasts and osteoblasts: if osteoblasts are predominant, more bone is produced; if osteoclasts are predominant, more bone is remodelled/lost. This kind of balance between the two types of cells is involved in: bone growth, the change in bone shape, bone repair and calcium regulation. Relative thickness of bone changes as bones grow. Bone is constantly removed by osteoclasts (macrophage- like): they digest it and remove it. New bone is formed by osteoblasts. In compact bones, osteoclasts enter the osteon from the blood through the central canal, and internally remove lamellae (which can be replaced by osteoblasts). Osteoclasts can also externally remove bone. Mechanical stress is important for bone remodelling process. In fact, the simplest way to keep the skeletal system and the bones healthy is exercising. Physical movement doesn’t have to necessarily include jumping or running: it is enough to start walking for one hour a day or to go mildly to the fitness. Moving affects mechanical stress in a positive way; it helps bones’ remodelling and improves their health. This in addition to diet, sunlight and gravity itself, which are absolutely fundamental in keeping the bone healthy. The bones of humans are evolved according to the gravity of the Earth: if a human is in absence of gravity, such as in the space, the bones are not happy at all. It has been proven that astronauts coming back to Earth after being in space for a long time, all experience osteoporosis. This sensory-mechanic transduction and the force exerted by the muscles (on the tendons or on the bones) are very healthy as they increase osteoblast activity. Food rich in Calcium and Vitamin D can also be helpful for the bones. The bones also have Stress lines (as shown in figure 28), which reflect the lines of the trabeculae (as shown in figure 28) in between the spongy bone. Trabeculae are interconnecting rods or plates of bone, like a scaffolding, and their orientation along stress lines helps the normal physiology of the bone, and increases the bone’s strength and fitness to sustain the body’s weight. Figure 27: Trabeculae organization Figure 28: Lines of stress in bones  The Skeletal System The skeletal system is divided into axial (80 bones), and appendicular (126 bones), in total 206 bones. The axial is in the middle, and are the skull, vertebrae and ribcage. The appendicular comprehends limbs, (upper and lower) starting from the shoulder and clavicle that are part of the upper limb and from the pelvic girdle that is part of the lower limb. Bone Overview There are several terms to describe parts of a bone: Body: the main part, also called shaft or diaphysis (if talking about a long bone) Head: the enlarged end, usually the head is coincidental with the epiphysis (distal if in the lower part of the bone, proximal if in the upper part) Neck: the constriction between head and body Margin or border: the edge or boundaries Angle: bend, for example the top part of the femur Ramus: branch off body There are also smooth areas for articulation which helps the bones to join each other and to allow movement: Condyles: smooth rounded articular surfaces Facets: usually smaller flattened articular surfaces (such as in the ribs joining the vertebrae). Bones also have projections, which are several areas of the shaft of the bone that change shape to be able to attach muscles and ligaments that make force on these. They are: Processes: prominent projections Tubercle: small, rounded bump Tuberosity: knob Trochanter: tuberosity on proximal femur (there are 2, smaller and greater) Epicondyle: near or above the condyle, so close to the free articular surface. This nomenclature is just a general overview of all the bones; it will then be applied to specific bones. An example, seen in figure 29, is the right femur; the image shows: the head, the great trochanter, the intertrochanteric line, the neck (highlighted by the rounding and the arrow) and the body (the long part) which is called shaft or also diaphysis. In the posterior view it’s possible to observe a line called linea aspera (means not smooth, from Latin, unpleasant to touch). On the lower part there is the adductor tubercle; a tubercle is something that comes a little up from the surface, and in this case, it attaches the adductor muscle. Near the condyle of the joints there is the epicondyle; for example: the patellar groove for the patella. On the posteriorpart the gluteal tuberosity can be observed where the gluteus maximum attaches. Figure 29: Anterior/posterior view of femur Bones can be classified also according to their shape; in this case there are: long bones: upper and lower limbs, like femur and tibia (tibia means flute, for its shape); short: carpals and tarsals, in wrists and ankles; flat: ribs, sternum (in front of the chest), skull and scapulae; irregular: vertebrae, facial, also the sphenoid in the skull, which looks like a bird. Joints Talking about joints, there are two main ways to classify them: From structure: based on the major connective tissue type that binds the bones of the joint together; the joint can be: fibrous, cartilaginous or Figure 30: Bones' classification synovial. On the practical (clinical) point of view, the vast majority of cartilage joints are synovial joints, which are the most important (like the glenohumeral, shoulder, knee, hip, ankle, wrist), but there are also fibrous or cartilaginous joint. From function: based on the degree of motion of the joint; they can be non-moveable, slightly moveable and freely moveable. It’s not surprising that the majority of the synovial joints are freely moveable, because they are the most functional and flexible joints; this is why they’re the most important in the clinical point of view. The major function of the joints it to allow movement in different directions, and they connect bones together allowing locomotion and rotation without bone damage, avoiding friction on the bone. If somebody lacks cartilage in a joint (such as the knee without menisci), they will be able to live with that but the friction and the subsequent inflammation will be much higher and will cause pain because the periosteum will be much more stimulated, and the joints will work less. A problem arising in the future could be arthrosis, plus deformation or degeneration of the tissue will be much easier to happen. Fibrous joints are united by fibrous connective tissue, they have no joint cavities and can move a little or not at all; they are divided in: sutures, syndesmoses and gomphoses. Sutures: they are the classical joints of the skull bones with no movement (in adults); this is optimal because they form a strong cage to protect the brain inside from the outside. As it is shown in the in the image on the right, there are several coronal sutures between the frontal and parietal bone, then there are sagittal sutures in the middle (between parietal bones) that could be a landmark for the medial sagittal plane. Finally, there is the lambdoid suture between parietal and occipital bone. It’s called lambdoid as it reminds the Greek lambda letter. Figure 31: Sutures in the skull They are very strong joints, and in adults they may have no cartilage at all between them. Sutures are not the same as children/new-borns: new-borns have some space in between them formed by membranes of connective tissue, called fontanelle. In an infant, fontanelle are flat or slightly exposed up or down, and that is used to check if the overall liquid homeostasis in the baby is normal; if they tend to be too flat or too moved away it means that there’s some problem, and the baby may be dehydrated.  Syndesmosis: there are only two of them, one the counterpart of the other. One is in the upper and one in the lower limb. Bones are further apart than in sutures, they are joint by a ligament and some movement is allowed. One is the radioulnar syndesmosis (it’s a flat syndesmosis, as shown in figure 33), while the other is in the lower limb between the tibia and fibula is the tibiofibular syndesmosis. The movement that they allow are supination, pronation and a bit of rotation. Syndesmosis, which are basically interosseous membranes, are clinically important as they divide the distal leg and the distal arm in compartments; they are crucial for surgery. Gomphosis: they are the Figure 32: Syndesmosis between radius andjoints between the tooth ulna and the underlying bone. They are very specialized joints, like pegs that fit into sockets. The periodontal ligaments hold teeth in place. They can become inflamed, giving rise to gingivitis and periodontal disease. They do not allow movement; if movement occurs, it means that there is a problem. Gingivitis and periodontal diseases may increase the movement of the roots and tooth inside the alveolar bone. Figure 33: Gomphosis Cartilaginous joints: they unite two bones by the means of cartilage, and their classification is based on the type of cartilage involved, which can be hyaline or fibrocartilage. Hyaline: examples of hyaline cartilaginous joints are showed in the image; they are classical joints where there is some movement (the joints in the image have actually little or no movement) like the synchondrosis that joins the ilium, ischium and pubis forming the pelvic bone. In this joint there are 3 bones together, and the boundaries between these are made by hyaline cartilage joints. Even the joints between growing bones, as shown in the left side of Figure 34, are synchondrosis; the epiphyseal plate where the bone grows is a synchondrosis: there can be little movement of that. Some of those joints are temporary, and cartilage will be replaced by bone, others are permanent and others will develop into synovial joints allowing for some movement, like costochondral or sternocostal joints. Figure 34: Synchondrosis Figure 35: Symphisis pubis Fibrocartilage: if fibrocartilage unites two bones, a symphysis is formed, with minimal movement. An example is the joint between the manubrium and the body of the sternum. (the sternum is one, but it is actually made of three different embryological starts: the manubrium at the top, the body in the middle, and the xiphoid process below, jointed together by a symphysis). Even the intervertebral disks between neighbouring vertebrae are an example of symphysis. Also, the symphysis pubis, between the two sides of the anterior ischium is not moveable (it is palpable: a reference point in clinic). The only exception is during childbirth, when the symphysis pubis has to loosen to allow the passage of the baby. Hormones released during pregnancy make the symphysis pubis enriched in water, and thus looser, allowing more movement thus enlarging the birth canal. Synovial joints: they are the most important joints; they are moveable and called synovial because they contain a structure known as synovial bag or synovial/joint cavity. The joints of the two bones are surrounded by this cavity, which is filled with a liquid: the synovial fluid. It helps to nourish the cells of the cartilage and to sustain the weight. In this fibrous capsule tendons and ligaments can contribute to the stability of the joint as well. Synovial joints make up the vast majority of joints; they are movable and are the most important clinically, since they are the most subject to disease, breaking or pathologies. Examples of synovial joints are: the shoulder, knee, hip, and ankle joints, but the ones between phalanges in the fingers as well: they can also be small joints. In the joint there are also nerves, blood vessels (on the sides) and bursae (as shown). The organisation of the cavities can be complicated: with ligaments even inside, for example menisci for the knee. Figure 36: Synovial joint: nerves, vessels, bursae Synovial joints can be defined as a type of joint found between bones that move against each other, such as the joints of the limbs. Their main characteristic is that they are filled with synovial fluid. In Figure 37 the articular cartilage, the articular or joint capsule on the side (which can be reinforced by ligaments), and the cavity that contains the synovial fluid can be seen as well. On the left side there are bursae, and below the enthesis, which are the borders between the synovial cavity walls and the bone itself. The image shows the extensor muscle, the flexor muscle, the epiphyseal bone, the tendons and the ligaments as well. Figure 37: Synovial joint (2) There are six types of synovial joints: plane/gliding, saddle, hinge, pivot, ball and socket, and ellipsoid. (only to mention them, as they will be important in more specialized courses, pay attention to their movements). The most important are pivot, ball and socket joints (seen in hips and glenohumeral joints) and ellipsoid. Figure 38: Types of synovial joints Overview of muscles The muscle is the third type of tissue that forms the musculoskeletal system, together with bones and cartilage. There are three types of muscle: skeletal, cardiac and smooth. Smooth muscle is the muscle of the viscera, and it does not work under conscious control: it is autonomous. When a person eats, digesting muscles handle the food, moving it in an autonomous way. Cardiac muscle is a special type of involuntary muscle, and can slow down but it cannot stop; it has to work all life, which makes it more similar to skeletal muscles than smooth muscle. Skeletal muscles are voluntary muscles. Effectors are what make the action possible. Skeletal muscles are large, their function is to maintain posture, facilitate locomotion, help to adapt to circumstances in the world around and help to move jointed bones. They are found in antagonistic pairs and are joined to bones by tendons: to make movement they have to cross the joint, if they don’t there is no movement. These muscles can be classified also based on their fascicles (fibers) which are composed by units: myofibrils. They can be parallel (strap like), like the sartorius, or fusiform (spindle shaped), like the biceps femur. The main axle of the fibers can help in understanding the action the muscle will perform; the major axis of action of the sartorius is the major axis of the muscle itself (the muscle’s action is making shorter or longer the fibers). In addition, muscle classification can be made by arrangement of fascicles. They can be: pennate, like the great pectoralis, unipennate, like the extensor digitorum longus, bipennate like the rectus femoris, or multipennate like the deltoid; they are feather shaped. Other muscles are classified based on their shape: convergent or circular. Convergent like pectoralis major Figure 39: Muscles classification because the fibres go toward one point (all toward the major tubercle of humerus, where it attaches). Circular muscles are sphincters, which are round and close and open some cavities. One is the orbicularis oris, a round shaped tissue around the mouth or the orbicularis oculis (around the eyes, used to squeeze them). Movement of muscles Overall, the movement of a muscle is due to the fact that it has two points of attachment for every given bone; one is the origin, called attachment generally speaking, and it is defined as the point that remains stationary and doesn’t move during the given movement. The insertion, instead is the attachment of the muscle to the bone that moves. The belly is the fleshy part of the muscle between the tendon of origin and/or insertion which change shape (shorter, longer) depending on the movement. Sometimes, origin and insertion can change depending on the movement, even in the same muscle. In figure 40, the basis of the movement is shown. It’s done thanks to a structure inside myofibrils called sarcomere, and it’s a matter of sliding of myosin filaments on actin filaments. The heads of myosin move on the actin filaments, sliding on it, and causing contraction and shortening of fibers. Figure 40: Muscle contraction Harvey Medical School- Course: Structure of the Body, Anatomy - Lecture 3 - 24/03/2021 - prof. Vaccarezza Transcribers: Vittoria Somenzini , Carina G. Ribeiro Reviewer: Diletta Marri Intro to the back Overview of the regions of the body, Anterior view of the left and posterior view on the right The lecture is focused on the dorsal part, in particular on the appendicular skeleton (ribs and vertebrae). Vertebral column Vertebral column, lateral and posterior views The vertebral column is composed by 31/32 vertebrae in total, divided into (from cranial to caudal): 7 cervical vertebrae 12 thoracic vertebrae 5 lumbar vertebrae 5 fused vertebrae to form the sacrum 4 fused vertebrae to form the coccyx (leftover of the tail of our precursor) The main axis of the vertebral column is the sagittal axis. If the column deviates from it, either on the left or right side, a quite common pathology of the vertebral column will be visible: scoliosis.  Some of the vertebrae, such as C7, C8, T12, T7 and all the lumbar ones, are also used as repere points. The vertebral column in the adult is characterized by two posterior convexities (I, III) and two anterior concavities (II, IV). In newborns, instead, the column is almost straight, since the baby needs time to develop the ligaments, as well as the muscles, etc. The curvature occurs naturally in the first 3 years, until 5/6 years, by letting the baby move. Vertebral column, front side In the image it is possible to see what is on the same level of each vertebra: for example, T2 is at the level of the heart valves; T3 at the level of the heart, lungs and the bronchi; T7 corresponds to the pancreas, liver and the upper part of the abdomen; the brachial plexus is between C6/C7 and T2; the left kidney is at the level of T10-T12 and the right one is at the level of T11-L1 (they are at different heights because of the presence of the liver on the right, which pushes down the kidney on that side). Posterior view of the vertebral column, shows what elements are at the level of the correspondent vertebra At level of T11/T12 there are also the last two ribs, which are free. If a car crash occurs, on the right side the accident causes the breakage of T11, T12 ribs rather than damages to the kidney, whereas on the left side it is easier that the damage involves the kidney on that side. Cervical vertebra Cervical vertebra, superior and lateral view In the cervical vertebrae there are several features: Spinous process: well pronounced and long (the longest is found in C7, which is actually a repere point: touching from the back the base of the neck of a person, it is possible to feel something coming through the skin, that is the C7 spinous process) Lamina Vertebral foramen: quite well developed, half-circle shaped (it is found in this amplitude only in the cervical vertebrae) Superior articular facets Tubercles Transverse foramen: all the cervical vertebrae have them. It is the point of passage of important arteries, the vertebral arteries, that pass through both foramina, their trajectory goes from caudal to cranial, through the posterior part of the neck towards the brain. These arteries are an important part of the blood supply for the brain, which is characterized essentially by two kinds of arteries: - The carotid arteries that pass more medially and anteriorly in the neck. They derive from the brachiocephalic trunk on the right side and directly from the aorta on the left side. - The vertebral arteries, that pass more posteriorly and laterally in the neck and derive from the subclavian artery. Corpus: it is small, since it has to sustain the head only, which is not that heavy. Thoracic vertebra In the image the difference of the thoracic vertebra compared to the cervical one is clearly visible: the spinous process is still present, but it is differently shaped; the body is bigger; the vertebral foramen has a more oval shape, it is not shaped as an half-circle anymore; the costal facets for the ribs are present. Thoracic vertebra, lateral and superior views  Links and joints of the thoracic vertebrae are appreciated in this image. For example, the superior demifacet makes a complete facet for the rib with the demifacet of the following vertebra (two consecutive vertebrae therefore form a complete facet). The rib connects to the vertebrae through two kinds of joints, one being with the demifacet on the body of the vertebra, the other one with the facet for articular part of the tubercle of the rib on the transverse process of the vertebra. Thoracic vertebra, superior view Lumbar vertebra In the case of lumbar vertebra, instead: The vertebral body is very big because the weight that the lumbar vertebra has to cope with is much larger