edX HKPolyUx : ANA101x – Human Anatomy Submodule 2.1 Submodule 2.1 – Body Organization and Skeletal System To study Human Anatomy, you have to first know the organization of the human body and different body systems, where important organs are located. Anatomical orientation is the foundation for learning anatomy and understanding how to look at various body parts, whereas the skeletal system provides the framework for the body. Learners who successfully complete this submodule will be able to: - Locate the body regions and cavities - Describe the systems involved in each region - Identify the major organs (tissues and cells) in each system - Define the anatomical position and planes - Classify different types of bones - Describe the bone structure - Locate the major bones of the skeleton Reading – Anatomical orientation and terminologies Anatomists and health care providers use terminology that can be bewildering to the uninitiated. However, the purpose of this language is not to confuse, but rather to increase precision and reduce medical errors. For example, is a scar “above the wrist” located on the forearm two or three inches away from the hand? Or is it at the base of the hand? Is it on the palm-side or back-side? By using precise anatomical terminology, we eliminate ambiguity. Anatomical terms are made up of roots, prefixes, and suffixes. The root of a term often refers to an organ, tissue, or condition, whereas the prefix or suffix often describes the root. For example, in the disorder hypertension, the prefix “hyper-“ means “high” or “over,” and the root word “tension” refers to pressure, so the word “hypertension” refers to abnormally high blood pressure. edX HKPolyUx : ANA101x – Human Anatomy Submodule 2.1 There are two general approaches to the study of the body’s structures: regional and systemic. Regional anatomy is the study of the interrelationships of all of the structures in a specific body region, such as the abdomen. Studying regional anatomy helps us appreciate the interrelationships of body structures, such as how muscles, nerves, blood vessels, and other structures work together serve a particular body region. In contrast, systemic anatomy is the study of the structures that make up a discrete body system – that is, a group of structures that work together to perform a unique body function. For example, a systemic anatomical study of the muscular system would consider all of the skeletal muscles of the body. Anatomical Position To further increase precision, anatomists standardize the way in which they view the body. Just like maps are normally oriented with north at the top, the standard body “map”, is oriented as the anatomical position - is that of the body standing upright, with the feet at shoulder width and parallel, toes forward. The upper limbs are held out to each side, and the palms of the hands face forward as illustrated below. Using this standard position reduces confusion. It does not matter how the body being described is oriented, the terms are used as if it is in anatomical position. For example, a scar in the “anterior (front) carpal (wrist) region” would be present on the palm side of the wrist. Directional Terms Certain directional anatomical terms appear throughout this and any other anatomy textbook (Figure 1.13). These terms are essential for describing the relative locations of different body structures. For instance, an anatomist might describe one band of tissue as “inferior to” another or a physician might describe a tumor as “superficial to” a deeper body structure. Commit these terms to memory to avoid confusion when you are studying or describing the locations of particular body parts. edX HKPolyUx : ANA101x – Human Anatomy Submodule 2.1 o Anterior (or ventral) Describes the front or direction toward the front of the body. The toes are anterior to the foot. o Posterior (or dorsal) Describes the back or direction toward the back of the body. The popliteus is posterior to the patella. o Superior (or cranial) describes a position above or higher than another part of the body proper. The orbits are superior to the oris. o Inferior (or caudal) describes a position below or lower than another part of the body proper; near or toward the tail (in humans, the coccyx, or lowest part of the spinal column). The pelvis is inferior to the abdomen. o Lateral describes the side or direction toward the side of the body. The thumb (pollex) is lateral to the digits. o Medial describes the middle or direction toward the middle of the body. The hallux is the medial toe. o Proximal describes a position in a limb that is nearer to the point of attachment or the trunk of the body. The brachium is proximal to the antebrachium. o Distal describes a position in a limb that is farther from the point of attachment or the trunk of the body. The crus is distal to the femur. o Superficial describes a position closer to the surface of the body. The skin is superficial to the bones. o Deep describes a position farther from the surface of the body. The brain is deep to the skull. Session 2.1.1 – Organization of Human Body edX HKPolyUx : ANA101x – Human Anatomy Submodule 2.1 Before you begin to study the different structures and functions of the human body, it is helpful to consider its basic architecture; that is, how its smallest parts are assembled into larger structures. It is convenient to consider the structures of the body in terms of fundamental levels of organization that increase in complexity: subatomic particles, atoms, molecules, organelles, cells, tissues, organs, organ systems, organisms and biosphere. The body is organized from the microscopic atom to the complex human organism. Tiny atoms form molecules and then in turn form larger molecules. The larger molecules are eventually organized into cells, the basic unit of life. Similar types of cells form tissues. Different types of tissues are then arranged into organs like blood vessels, heart, urinary bladder, and kidneys. Groups of organs then in turn create organ systems. Each organ system has a function, such as digestion, excretion, or reproduction. We will discuss each of these organ systems one by one in the following videos. All the organ systems work together and form the human organism. So now you can see how our human body is built from the tiny atom to the human being. The Levels of Organization: To study the chemical level of organization, scientists consider the simplest building blocks of matter: subatomic particles, atoms and molecules. All matter in the universe is composed of one or more unique pure substances called elements, familiar examples of which are hydrogen, oxygen, carbon, nitrogen, calcium, and iron. The smallest unit of any of these pure substances (elements) is an atom. Atoms are made up of subatomic particles such as the proton, electron and neutron. Two or more atoms combine to form a molecule, such as the water molecules, proteins, and sugars found in living things. Molecules are the chemical building blocks of all body structures. A cell is the smallest independently functioning unit of a living organism. Even bacteria, which are extremely small, independently-living organisms, have a cellular structure. Each edX HKPolyUx : ANA101x – Human Anatomy Submodule 2.1 bacterium is a single cell. All living structures of human anatomy contain cells, and almost all functions of human physiology are performed in cells or are initiated by cells. A human cell typically consists of flexible membranes that enclose cytoplasm, a water-based cellular fluid together with a variety of tiny functioning units called organelles. In humans, as in all organisms, cells perform all functions of life. A tissue is a group of many similar cells (though sometimes composed of a few related types) that work together to perform a specific function. An organ is an anatomically distinct structure of the body composed of two or more tissue types. Each organ performs one or more specific physiological functions. An organ system is a group of organs that work together to perform major functions or meet physiological needs of the body. Session 2.1.2 – Tissues of Human Body The body contains at least 200 distinct cell types. These cells contain essentially the same internal structures yet they vary enormously in shape and function. The different types of cells are not randomly distributed throughout the body; rather they occur in organized layers, a level of organization referred to as tissue. Although there are many types of cells in the human body, they are organized into four broad categories of tissues: epithelial, connective, muscle, and nervous. Each of these categories is characterized by specific functions that contribute to the overall health and maintenance of the body. A disruption of the structure is a sign of injury or disease. Such changes can be detected through histology, the microscopic study of tissue appearance, organization, and function. Let’s move on to the various types of tissues found in our body. Tissues are composed of different cells. And these various types of body tissues vary in shape, structure, function and distribution. Here are the 4 major tissue types in our body, namely, epithelial tissue, connective tissue, muscular tissue and nervous tissue. Epithelial tissues can be found in our skin surface as well as lining of GI tract organs and other hollow organs. They cover exposed surfaces. They line internal passageways & chambers, such as trachea, blood vessels as well as heart chambers. edX HKPolyUx : ANA101x – Human Anatomy Submodule 2.1 Some of these tissues are specialized in glandular secretions such as sweat glands, digestive juice production along our GI tract. Connective tissues vary widely in appearance and function. They occur throughout the body but never exposed to the outside environment. They provide protective structural framework for other tissue types and interconnect parts of the body. Examples include fat and other soft padding tissues, bones, ligaments and tendons. Their major functions include filling internal spaces, providing structural support and storing energy. We need muscle tissues to produce active movement. By processing active muscular contractions, skeletal muscles offer joint movement; cardiac muscles offer heart pumping; and smooth muscles offer intestinal movement, which is called peristalsis. Nervous tissues can be found in the brain, the spinal cord and nerves. By conducting and receiving electrical impulses, these tissues perform internal communication among the whole body. Four Major Types of Tissues: Epithelial tissue, also referred to as epithelium, refers to the sheets of cells that cover exterior surfaces of the body, lines internal cavities and passageways, and forms certain glands. Connective tissue, as its name implies, binds the cells and organs of the body together and functions in the protection, support, and integration of all parts of the body. Muscle tissue is excitable, responding to stimulation and contracting to provide movement, and occurs as three major types: skeletal (voluntary) muscle, smooth muscle, and cardiac muscle in the heart. Nervous tissue is also excitable, allowing the propagation of electrochemical signals in the form of nerve impulses that communicate between different regions of the body. Session 2.1.3 – Important body systems Part 1 edX HKPolyUx : ANA101x – Human Anatomy Submodule 2.1 The next level of organization is the organ, where several types of tissues come together to form a working unit. Just as knowing the structure and function of cells helps you in your study of tissues, knowledge of tissues will help you understand how organs function. In this video, let’s look into the components and structures of the following body systems: integumentary, skeletal, muscular, nervous, endocrine, cardiovascular, and lymphatic systems. The first organ system we are going to learn is the integumentary system. It refers to the skin and its accessory structures, such as hairs, nails and sweat glands. Skin is the largest and heaviest organ in our body. It makes up about 16% of body weight and covers an area of 1.5 to 2 m². The skin is composed of multiple layers of cells and tissues, which are attached to underlying structures by connective tissue. Skin protects the underlying tissues from injury. As you can see from the diagram shown here, the skin is composed of 2 main layers, the epidermis and dermis. The epidermis made of closely packed epithelial cells. Immediately below the epidermis, we have dermis which composed of different connective tissues. It houses many blood vessels, hair follicles, sweat glands and receptors as well. With these structures, we can excrete salts via perspiration, regulate body temperature as well as detect what is happening at the body surface. Directly below the dermis, we have hypodermis and it serves to connect the skin to the underlying connective tissues of the bones and muscles. Now we move on to individual organ systems and see how they work. The skeletal system consists of bones, cartilages, ligaments, joints and bone marrow. The adult skeleton is composed of 206 bones, but some of us may have more than this number. Think of those people with extra digit, also known as Polydactyly. The skeletal system provides support & protection for other tissues AND framework for skeletal muscle contraction. It also acts as storehouse for minerals such as calcium and most of our blood cells are made in the bone marrow. Typically we have about 640 skeletal muscles. They can only pull in one direction by contraction. So for this reason, they always come in pairs. When one muscle in a pair contracts, say to bend the elbow joint, its counterpart then contracts and pulls in the opposite direction to strengthen the joint out again. By performing this synchronized muscular contraction, we can do various voluntary actions ranging from walking, running to playing piano. Moreover, our muscular system also edX HKPolyUx : ANA101x – Human Anatomy Submodule 2.1 allows postural maintenance facial expressions as well as heat production so that we can maintain body temperature. The nervous system is the body’s fast-acting control system. It consists of the brain, spinal cord, nerves and sensory organs such as eyes and pain receptors located in the skin. It can be further divided into central nervous system, CNS, and peripheral nervous system, PNS. CNS is composed of the brain and the spinal cord whereas any neural tissues outside the CNS belong to PNS. As a whole, the nervous system directs immediate responses to stimuli, coordinates or moderates activities of other organ systems, provides and interprets sensory information about external conditions. Like the nervous system, the endocrine system controls body activities, but it acts much more slowly. The endocrine glands produce hormones and release them into the blood to travel to relatively distant target organs. The major endocrine glands include pituitary gland, thyroid gland, pancreas, adrenal glands, testes and ovaries. In general, body functions controlled by hormones consist of many and varied, including growth, reproduction, nutrients use by body cells. Now we move on to cardiovascular system. The primary organs involved are the heart and blood vessels. Heart has its own signal conduction system in which itself can generate its own unidirectional electrical impulse and thus result in contraction of the heart chambers for pumping blood into the major vessels. So here is the conduction system of the heart. Specialized conducting components include sinoatrial node, atrioventricular node and atrioventricular bundle and Purkinje fibers. First, the SA node initiates electrical impulses which sweeps across the atria to the AV node, and thus the atria contract. It then passes rapidly through the AV bundle, and its branches and then finally the Purkinje fibers, resulting in ventricular contraction. Using blood as the transporting fluid, the cardiovascular system carries oxygen, nutrients, hormones and other dissolved materials to and from the tissue cells where exchanges are made. The blood also distributes heat and regulates body temperature. The role of the lymphatic system complements that of the cardiovascular system. Its organs include lymphatic vessels, lymph nodes and other lymphoid organs such as the spleen and thymus. The lymphatic vessels return fluid leaked from the blood back to the bloodstreams so that blood can be kept continuously circulating through the body. The lymph nodes and other lymphoid organs defends against pathogens. edX HKPolyUx : ANA101x – Human Anatomy Submodule 2.1 Session 2.1.4 – Important Body Systems Part 2 Now, let’s look at the remaining four body systems: respiratory, digestive, urinary and reproductive systems. The work done by the respiratory system is to keep the body constantly supplied with oxygen and to remove carbon dioxide. The respiratory system can be further divided into upper and lower respiratory tract. The major passages and structures of the upper respiratory tract include the nose, nasal cavity, mouth, throat or pharynx, and voice box or larynx. The lower respiratory tract consists of airway below the larynx, which is, the trachea, bronchi and bronchioles and lung. Within the lungs, there are numerous tiny air sacs called alveoli where gas exchange occurs. Oxygen diffuses from the alveolus into the pulmonary capillary blood while carbon dioxide diffuses from the pulmonary blood into the alveolus. Other than gaseous exchange, respiratory system is also important for sound production so that we can communicate with each other. The digestive system is basically a very long tube running through the body from mouth to anus. Digestive system consists of oral cavity, esophagus, stomach, small intestine, large intestine, and accessory organs such as liver, gallbladder and pancreas. Their role is to process and digest food, absorb and conserve water, absorb nutrients and eliminate undigested food waste. Urinary system consists of kidneys, ureters, urinary bladder as well as urethra. The kidney excretes waste products such as urea from the bloodstream; it also controls water balance by regulating the volume of urine produced. The kidney also regulates blood ion concentration and pH by controlling the composition of urine produced. The urinary bladder can temporarily store urine prior to voluntary elimination. The reproductive system exists primarily to produce offspring. The testes of the male produce sperms while ovaries of female produce eggs. In male, sperm cells are produced in seminiferous tubules which are located inside the testes. These immature sperm cells then passively moved to epididymis for temporary storage and maturation. Other male reproductive organs include accessory glands like the prostate and associated duct systems. The female duct system consists of the uterine tubes, uterus and vagina. Eggs produced in ovary passively passed through the uterine tube and then reach the uterus. If fertilization occurs, the growing fetus will attach to the uterus by forming the edX HKPolyUx : ANA101x – Human Anatomy Submodule 2.1 placenta. Mammary glands are milk-producing glands found in the breasts. After the birth of a baby, they produce milk in response to hormonal stimulation. Session 2.1.5 – Location of Organs in Relation to the Body Cavities The body maintains its internal organization by means of membranes, sheaths, and other structures that separate compartments. The dorsal (posterior) cavity and the ventral (anterior) cavity are the largest body compartments. These cavities contain and protect delicate internal organs, and the ventral cavity allows for significant changes in the size and shape of the organs as they perform their functions. The lungs, heart, stomach, and intestines, for example, can expand and contract without distorting other tissues or disrupting the activity of nearby organs. Our body maintains its internal organization by having different compartmentalization. The dorsal and ventral cavities are the largest body compartments. These cavities contain and protect delicate internal organs. In the dorsal or posterior cavity, we have cranial cavity, which houses the brain, and the spinal cavity, which encloses the spinal cord. These two cavities are continuous and uninterrupted so as to protect the delicate nervous system. In the ventral or anterior cavity, we have the thoracic and the abdominopelvic cavities which separated by the diaphragm. The thoracic cavity is the more superior subdivision and it is enclosed by the rib cage. It contains vital organs such as lungs and the heart. The cavity inferior to the diaphragm is the abdominopelvic cavity, which is the largest body cavity. It is further subdivided into the superior abdominal cavity which houses the digestive organs and the inferior pelvic cavity, which houses the organs of reproduction. Have you noticed that after enjoying buffet dinner, your stomach or belly enlarges quite obviously? It is because the ventral cavity allows for significant changes in the size and shape of the organs. However, the dorsal cavity does not allow this to happen. Subdivisions of the Posterior (Dorsal) and Anterior (Ventral) Cavities: The posterior (dorsal) and anterior (ventral) cavities are each subdivided into smaller cavities. In the posterior (dorsal) cavity, the cranial cavity houses the brain, and the spinal edX HKPolyUx : ANA101x – Human Anatomy Submodule 2.1 cavity (or vertebral cavity) encloses the spinal cord. Just as the brain and spinal cord make up a continuous, uninterrupted structure, the cranial and spinal cavities that house them are also continuous. The brain and spinal cord are protected by the bones of the skull and vertebral column and by cerebrospinal fluid, a colorless fluid produced by the brain, which cushions the brain and spinal cord within the posterior (dorsal) cavity. The anterior (ventral) cavity has two main subdivisions: the thoracic cavity and the abdominopelvic cavity. The thoracic cavity is the more superior subdivision of the anterior cavity, and it is enclosed by the rib cage. The thoracic cavity contains the lungs and the heart, which is located in the mediastinum. The diaphragm forms the floor of the thoracic cavity and separates it from the more inferior abdominopelvic cavity. The abdominopelvic cavity is the largest cavity in the body. Although no membrane physically divides the abdominopelvic cavity, it can be useful to distinguish between the abdominal cavity, the division that houses the digestive organs, and the pelvic cavity, the division that houses the organs of reproduction. Abdominal Regions and Quadrants: To promote clear communication, for instance about the location of a patient’s abdominal pain or a suspicious mass, health care providers typically divide up the cavity into either nine regions or four quadrants. The more detailed regional approach subdivides the cavity with one horizontal line immediately inferior to the ribs and one immediately superior to the pelvis, and two vertical lines drawn as if dropped from the midpoint of each clavicle (collarbone). There are nine resulting regions. The simpler quadrants approach, which is more commonly used in medicine, subdivides the cavity with one horizontal and one vertical line that intersect at the patient’s umbilicus (navel). Session 2.1.6 – Body Planes and Movements As mentioned “anatomical position” serves as the basic reference for medical communication. The body planes and some terminologies of movements will be introduced in this video. To communicate in anatomy, we need some point of reference. The basic reference starts with the anatomical position. In this position the subject stands upright facing forward. The edX HKPolyUx : ANA101x – Human Anatomy Submodule 2.1 arms are at the sides with the palms directed forward. The legs spread naturally with the toes facing forward. The three major anatomical planes are the coronal plane, the sagittal plane, also called median plane and the transverse plane, also called horizontal or axial planes. The coronal plane extends vertically along the mid axillary line. It divides the body into anterior, front, and posterior, back, portions. The sagittal plane also extends vertically but along the mid sagittal line. It is perpendicular to the coronal plane and divides the body into right and left portions. The direction towards the midline is called medial. Whereas the direction away from the midline is called lateral. The transverse plane divides the body or an organ horizontally into superior, upper and inferior, lower, portions. Other terms that are used include proximal or cephalad, and distal or caudad. Now that we have learned some planes, we can carry on to learn some terms about movements. First, we focus on the arms. Abduction is the movement in the coronal plane away from the midline of the body. Adduction is the movement towards the midline. To draw circles with the arm is called circumduction. Similarly in the leg, movement in the coronal plane away from the midline of the body is called abduction. Movement in the coronal plane towards the midline of the body is called adduction. Flexion is the movement that decreases a joint angle such as drawing the forearm towards the shoulder. Extension is the movement that straightens a joint such as stretching the forearm. Supination and pronation refer to forearm movements. Supination of the forearm is a movement that turns the palm to face anteriorly. Pronation is the opposite movement, causing the palm to face posteriorly. Body Planes: A section is a two-dimensional surface of a three-dimensional structure that has been cut. Modern medical imaging devices enable clinicians to obtain “virtual sections” of living bodies. We call these scans. Body sections and scans can be correctly interpreted, however, only if the viewer understands the plane along which the section was made. A plane is an imaginary two-dimensional surface that passes through the body. There are three planes commonly referred to in anatomy and medicine, as illustrated below. o The sagittal plane is the plane that divides the body or an organ vertically into right and left sides. If this vertical plane runs directly down the middle of the body, it is called the edX HKPolyUx : ANA101x – Human Anatomy Submodule 2.1 midsagittal or median plane. If it divides the body into unequal right and left sides, it is called a parasagittal plane or less commonly a longitudinal section. o The frontal plane is the plane that divides the body or an organ into an anterior (front) portion and a posterior (rear) portion. The frontal plane is often referred to as a coronal plane. (“Corona” is Latin for “crown.”) The transverse plane is the plane that divides the body or organ horizontally into upper and lower portions. Transverse planes produce images referred to as cross sections. Session 2.1.7 – The Skeletal System Bones make good fossils. While the soft tissue of a once living organism will decay and fall away over time, bone tissue will, under the right conditions, undergo a process of mineralization, effectively turning the bone to stone. A well-preserved fossil skeleton can give us a good sense of the size and shape of an organism, just as your skeleton helps to define your size and shape. Unlike a fossil skeleton, however, your skeleton is a structure of living tissue that grows, repairs, and renews itself. The bones within it are dynamic and complex organs that serve a number of important functions, including some necessary to maintain homeostasis. The most apparent functions of the skeletal system are the gross functions—those visible by observation. Simply by looking at a person, you can see how the bones support, facilitate movement, and protect the human body. Just as the steel beams of a building provide a scaffold to support its weight, the bones and cartilage of your skeletal system compose the scaffold that supports the rest of your body. Without the skeletal system, you would be a limp mass of organs, muscle, and skin. Bones also facilitate movement by serving as points of attachment for your muscles. While some bones only serve as a support for the muscles, others also transmit the forces produced when your muscles contract. From a mechanical point of view, bones act as levers and joints serve as fulcrums. Unless a muscle spans a joint and contracts, a bone is not going to move. edX HKPolyUx : ANA101x – Human Anatomy Submodule 2.1 For information on the interaction of the skeletal and muscular systems, that is, the musculoskeletal system, seek additional content. The skeletal system consists of different types of bones located in different body parts. This video is going to introduce to you the bone classification and markings. Have you ever wondered how many bones are there in the human skeleton? At birth, there are about 270 bones, and even more bones formed during childhood. With age, however, some bones fused and ending up with an average of 206 bones in adults. Bones are classified into different groups according to their shapes and corresponding functions. The four major groups are namely: long bones, short bones, flat bones and irregular bones. Long bones serve as rigid levers that are acted upon by the skeletal muscles to produce body movements. An example here is the femur. Short bones have limited motion and merely glide across one another, enabling the ankles and wrists to flex in multiple directions. An example here is the tarsal bones in the foot. Flat bones enclose and protect soft organs and provide broad surfaces for muscle attachment. An example here is the sternum in our chest. Irregular bones include the vertebrae and some skull bones. They are irregular in shape. Externally, most of the bone is covered with a sheath called the periosteum. Underneath the periosteum is the hard compact bone. The inner layer is the relatively less dense spongy bone. The bone, even though stable in shape, is a dynamic tissue. It requires good blood supply through some nutrient arteries. Inside the spongy bone, the fine structures are arranged according to the stress lines called trabeculae. The two major bone cells are called osteoblasts which is responsible for bone building, whereas the osteoclasts are responsible for bone cutting and resorption. The skeleton is divided into two regions namely the axial and appendicular skeleton. The axial skeleton forms the central supporting axis of the body and mainly includes the skull, the vertebral column and the rib cage. The appendicular skeleton includes the bones of the upper limb and pectoral girdle, and bones of the lower limb and pelvic girdle. The skull is the most complex part of the skeleton. it is composed of 22 bones. Most of them are rigidly joined by sutures, joints that appear as seams on the cranial surface. The bones forming the cranium include the frontal bone, parietal bone, occipital bone, temporal bone, sphenoid bone and ethmoid bone. Some of the facial bones can be seen such as the nasal bone, zygomatic bone, maxillary bone and mandible. In this lateral view we can see that the edX HKPolyUx : ANA101x – Human Anatomy Submodule 2.1 frontal bone forms the forehead, the parietal bones form most of the cranial roof and part of its walls, while the occipital bones form the back of the skull. The cranium serves to protect the brain. Commonly called the backbone, the vertebral column, spine consists of a chain of 33 vertebrae with intervertebral discs of fibrocartilage between most of them. The vertebrae are divided into five groups – 7 cervical vertebrae in the neck, 12 thoracic vertebrae in the chest, 5 lumbar vertebrae in the lower back, 5 sacral vertebrae at the base of the spine, and 4 tiny coccygeal vertebrae. This is a lateral view of the vertebral column showing the spinal curvatures. The thoracic and pelvic curvatures are called primary curvatures because they are present at birth. Primary curvatures is concave anteriorly and developed during embryonic growth. The cervical and lumbar curvatures are called secondary curvatures. They are developed later when the baby lifts its head and starts walking. The thoracic cage consists of the sternum,ribs and thoracic vertebrae. The sternum, breastbone, is a bony plate anterior to the heart. It is subdivided into three regions the manubrium, body, and xiphoid process. There are 12 pairs of ribs. Ribs 1 through 7 are called true ribs; each has its own costal cartilage connecting it to the sternum. Ribs 8 through 12 are called false ribs because they lack independent cartilaginous connections to the sternum. The costal cartilages fused to form the costal margin. Ribs 11 and 12 are also called floating ribs. They are the "trouble-maker" because when they are fractured in traffic accidents, they may puncture the kidneys and liver causing severe internal bleeding. Please note that the clavicle and the scapula form the pectoral girdle and they are part of the appendicular skeleton, not the axial skeleton. A typical rib has a head that articulates with the body of its corresponding vertebra. Immediately distal to the head, the rib narrows to a neck and then widens again to form a rough area called the tubercle. Beyond the tubercle, the rib flattens and widens into a gently sloping bladelike body, also called shaft. There are 12 thoracic vertebrae T1 – T12, corresponding to the 12 pairs of ribs attached to them. The most obvious feature of a vertebra is the body. This is the weight-bearing portion. The pedicle and lamina form the vertebral arch to surround the vertebral foramen in the centre. This is the passage for the spinal cord. The transverse process and the spinous process provide points of attachment for spinal muscles and ligaments. One of the typical features for thoracic vertebrae is that the body of each thoracic vertebra has small, smooth, slightly concave spots called costal facets for attachment of the ribs. The rib articulates with the inferior costal facet of the upper vertebra and the superior costal facet of the vertebra below that. The joints between the ribs edX HKPolyUx : ANA101x – Human Anatomy Submodule 2.1 and thoracic vertebrae are called costovertebral joints. There are two costovertebral joints on each side, namely the costotransverse joint, attaching the tubercule to the transverse process, and the capitular joint joining the head of the rib to the body of the vertebra. Bone Classification: The 206 bones that compose the adult skeleton are divided into five categories based on their shapes: Long bones, short bones, flat bones, irregular bones, and sesamoid bones. Their shapes and their functions are related such that each categorical shape of bone has a distinct function were mentioned in the video above. Bone Markings: The surface features of bones vary considerably, depending on the function and location in the body. There are three general classes of bone markings: (1) articulations, (2) projections, and (3) holes. As the name implies, an articulation is where two bone surfaces come together (articulus = “joint”). These surfaces tend to conform to one another, such as one being rounded and the other cupped, to facilitate the function of the articulation. A projection is an area of a bone that projects above the surface of the bone. These are the attachment points for tendons and ligaments. In general, their size and shape is an indication of the forces exerted through the attachment to the bone. A hole is an opening or groove in the bone that allows blood vessels and nerves to enter the bone. As with the other markings, their size and shape reflect the size of the vessels and nerves that penetrate the bone at these points. The table below describes different bone markings and their examples. Session 2.1.8 – The bones of the upper and lower limbs The upper limb includes the shoulder, humerus, elbow, forearm, wrist and hand. This is the anterior view of the left shoulder. The humerus is the long bone in the upper arm. The scapula is a triangular plate of flat bone on the back. The head of humerus articulates with the glenoid fossa of the scapula to form the shoulder joint, also called glenohumeral joint. This is the lateral view of the left shoulder. We are looking directly at the glenoid fossa from the side of edX HKPolyUx : ANA101x – Human Anatomy Submodule 2.1 the body. The spine arises from the dorsal surface. The acromion is the lateral expansion that corresponds to the summit of the shoulder joint. The coracoid process is a bony projection that protrudes from the costal surface of the scapula. The head of humerus is characteristic of a rounded surface that articulates with the glenoid fossa of the scapula. The ill-defined anatomical neck corresponds to the rim of bone surrounding the base of the humeral head. The surgical neck corresponds to the common site of traumatic fractures. The lesser tubercle and the greater tubercle are two bony eminences for the insertions of the rotator cuff muscles. The intertubular groove, also called bicipital groove is the location of the bicep tendon. The distal end of the humerus is triangular in profile. The condyle of the humerus is a collective term corresponding to the trochlea, capitulum, coronoid fossa, radial fossa and the olecranon fossa. The trochlea and the capitulum are smooth articular surfaces of the elbow joint. The medial epicondyle and the lateral epicondyle are the bony eminences bilateral to the humeral condyle. The epicondyles are devoted to the muscles attachment. The elbow joint consists of a pair of articulations with contributions from the humerus, radius and ulna. Laterally, the capitulum articulates with the head of the radius. Medially, the trochlea articulates with the trochlear notch. Flexion and extension of the forearm takes place at the elbow joint. Supination and pronation of the forearm take place at the superior and inferior radio-ulnar joints. The superior radio-ulnar joint is an articulation across the head of radius and the radial notch of ulna. Please note that the radius crosses over the ulna in pronation. In this specimen, the head, neck and radial tuberosity of the radius are demonstrated. At the proximal end of the ulna is a deep, C-shaped trochlear notch that wraps around the trochlea of the humerus. The posterior side of this notch is formed by a prominent olecranon process. The anterior side is formed by a less prominent coronoid process. Does it look like a spanner? The hand has a delicate bony framework. There are eight carpal bones at the wrist, five metacarpal bones I -V at the palm and fourteen phalanges making up the bones of the thumb and four fingers. Movements of the fingers take place at the joints which are named according to the corresponding bones. The carpal bones interarticulate with one another in two rows. The proximal row includes the scaphoid, lunate, triquetral and pisiform. The distal row includes the trapezium, trapezoid, capitate, and hamate. One way to remember the order of the carpal bones is to remember the first letter of the phrase "Sam left the party to take Candy home." The pelvis girdle consists of a complete ring composed of three bones – two hip bones and the sacrum. Bilaterally, the edX HKPolyUx : ANA101x – Human Anatomy Submodule 2.1 sacrum articulates with hip bones via the sacro-iliac joints. Anteriorly, the hip bones articulate at the cartilaginous pubic symphysis to give continuity of the bony pelvis around the pelvic brim. The femur is attached to the pelvis at the hip joint. The spherical femoral head, when fitting into the cup-shaped acetabulum, allows a wide-range of movements at the hip region. The femur is the longest bone of the human body. The femoral head is an articular part of the hip joint that connects to the femoral neck. The junction between the femoral neck and the body is marked by two prominent bony projections known as the greater trochanter and the lesser trochanter. The long axis of the femoral neck usually makes an angle of approximately 120º to the long axis of the shaft of the femur. At the distal end of the femur, there are two very prominent bony parts known as the femoral condyles. The smooth areas of the medial femoral condyle and lateral femoral condyle contribute to the articular surfaces of the knee joint. The intercondylar fossa is an integral part of the knee joint that houses the cruciate ligaments. The patella attaches to the anterior patellar surface. At the knee joint, the femur articulates with the patella as well as the tibia. The thick strong tibia on the medial side bears all the weight. The slender fibula on the lateral side helps to stabilize the ankle. Much of the shaft of the tibia and the shaft of the fibula are devoted to muscles attachment. The gap between the tibia and the fibula is connected by the interosseous membrane. At the ankle region, there are two prominent bony eminences arising from the tibia and fibula known as the medial malleolus and lateral malleolus respectively. Similar to the hand, the foot is made up of several kinds of bones. Tarsal bones form the heel and ankle Metatarsal bones form the dorsum of the foot. Phalanges form the toes. There are seven tarsal bones, namely the three cuneiforms, cuboid, navicular, talus, and calcaneus. Humerus, radius and ulna are the long bones of upper limbs. Recall what we mentioned in video 2.1.7, the structure of a long bone allows for the best visualization of all of the parts of a bone. A long bone has two parts: the diaphysis and the epiphysis. The diaphysis is the tubular shaft that runs between the proximal and distal ends of the bone. The hollow region in the diaphysis is called the medullary cavity, which is filled with yellow marrow. The walls of the diaphysis are composed of dense and hard compact bone. edX HKPolyUx : ANA101x – Human Anatomy Submodule 2.1 The wider section at each end of the bone is called the epiphysis (plural = epiphyses), which is filled with spongy bone. Red marrow fills the spaces in the spongy bone. Each epiphysis meets the diaphysis at the metaphysis, the narrow area that contains the epiphyseal plate (growth plate), a layer of hyaline (transparent) cartilage in a growing bone. When the bone stops growing in early adulthood (approximately 18–21 years), the cartilage is replaced by osseous tissue and the epiphyseal plate becomes an epiphyseal line. The medullary cavity has a delicate membranous lining called the endosteum (end- = “inside”; oste- = “bone”), where bone growth, repair, and remodeling occur. The outer surface of the bone is covered with a fibrous membrane called the periosteum (peri- = “around” or “surrounding”). The periosteum contains blood vessels, nerves, and lymphatic vessels that nourish compact bone. Tendons and ligaments also attach to bones at the periosteum. The periosteum covers the entire outer surface except where the epiphyses meet other bones to form joints. In this region, the epiphyses are covered with articular cartilage, a thin layer of cartilage that reduces friction and acts as a shock absorber. 0