ANAT Week 2.docx

Week 2 **Module: Epithelium (Part 1 of 3)** **Learning Outcomes** --------------------- By the end of this module, you should be able to: **LO1**: Name the primary germ layers that epithelial tissue is derived from **LO2**: Describe the characteristics and functions of the epithelium **LO3**:...

Week 2 **Module: Epithelium (Part 1 of 3)** **Learning Outcomes** --------------------- By the end of this module, you should be able to: **LO1**: Name the primary germ layers that epithelial tissue is derived from **LO2**: Describe the characteristics and functions of the epithelium **LO3**: Describe how epithelium is classified **LO4**: Describe the structure, function and location of the different types of epithelium **LO5**: Briefly describe the classification and function of the glands **Origin** ---------- ***LO1: Name the primary germ layers that epithelial tissue is derived from*** Recall from the Cells and Basic Tissues module that epithelial tissue, or epithelium, is one of the four basic tissue types in the body. Recall from the Embryology module that all tissues in the body are derived from the three primary germ layers of the embryo. Epithelial tissue is derived from all three primary germ layers, depending on the type and location of the epithelial tissue. **Characteristics and Functions** --------------------------------- ***LO2: Describe the characteristics and functions of epithelium*** Epithelium lines all body cavities, covers all body surfaces and constitutes the glands of the body. It has several characteristics including cellularity, polarity, attachment to a basement membrane, avascularity, innervation and high regeneration capacity. It also has several functions including physical protection, selective permeability, secretion and sensation. Click on the hotspots below to learn more about these characteristics and functions. **Classification** ------------------ ***LO3: Describe how epithelium is classified*** Now that we have looked at the characteristics and functions of epithelium, we are going to look at how it is classified. Epithelium can be classified in two ways -- based on the number of cell layers and based on the shape of the cells. ### **Based on the Number of Cell Layers** Based on the number of cell layers, epithelium can be classified as either simple or stratified. Click on each of the flip cards below to learn more about these two classifications. **Simple Epithelium** Simple epithelium is composed of a single layer of cells, where all cells are in direct contact with the basement membrane. **Stratified Epithelium** **Stratified epithelium is composed of two or more layers of cells, where only the deepest layer of cells, called the basal layer, is in direct contact with the basement membrane.** **There is another type of epithelium called pseudostratified epithelium, which appears stratified due to the epithelial cell nuclei being at different levels, but all cells are in direct contact with the basement membrane. For this reason, pseudostratified epithelium is classified as a type of simple epithelium.** ### **Based on the Shape of the Cells** **Based on the shape of the cells, epithelium can be classified as either squamous, cuboidal or columnar. Click on each of the flip cards below to learn more about these three classifications.** **Squamous Epithelium** **Squamous epithelium is composed of flat, irregularly shaped cells with a flattened, centrally located nucleus.** **Cuboidal Epithelium** **Cuboidal epithelium is composed of cells that are as tall as they are wide, making them resemble a cube. The cells have a round, centrally located nucleus.** **Columnar Epithelium** **Columnar epithelium is composed of cells that are taller than they are wide, making them resemble columns. The cells have an oval-shaped, basally located nucleus.** **There is another type of epithelium called transitional epithelium, where the cells are capable of changing shape depending on the degree of stretch of the epithelium. This type of epithelium has multiple layers of cells and for this reason, it is classified as a type of stratified epithelium.** **Types** --------- ***LO4: Describe the structure, function and location of the different types of epithelium*** **Now that we have looked at how epithelium is classified, we are going to look at the different types of epithelium that arise from these classifications. There are four types of simple epithelium and four types of stratified epithelium.** ### **Simple Epithelium** **The four types of simple epithelium are simple squamous epithelium, simple cuboidal epithelium, simple columnar epithelium and pseudostratified columnar epithelium. Click on each of the flip cards below to learn more about these four types.** **Simple Squamous Epithelium** **Simple squamous epithelium is composed of a single layer of squamous cells. Its main functions are diffusion and filtration, as it allows for the rapid movement of substances across its surface. It is found lining the alveoli of the lungs where gas exchange occurs and lining blood vessels where the movement of substances in and out of the blood occurs. The simple squamous epithelium lining blood vessels, as well as as lymphatic vessels and the internal surfaces of the heart chambers, is referred to as endothelium ('endo' = within). Simple squamous epithelium is also found in the membranes lining internal body cavities, where the cells secrete a lubricating fluid. This epithelium is referred to as mesothelium, as it originates from the mesoderm primary germ layer.** **Simple Cuboidal Epithelium** **Simple cuboidal epithelium is composed of a single layer of cuboidal cells. Its main functions are absorption and secretion. It is found lining the kidney tubules where substances are either reabsorbed into the blood or secreted into the tubular fluid, and lining the ducts of glands which produce secretions.** **Simple Columnar Epithelium** **Simple columnar epithelium is composed of a single layer of columnar cells. It has two forms -- ciliated, where the cells have cilia on their apical surfaces, and non-ciliated, where the cells lack cilia on their apical surfaces. The cells of the non-ciliated form often have microvilli on their apical surfaces. Specialised mucous-secreting cells called goblet cells are often found throughout simple columnar epithelium. The main functions of simple columnar epithelium are absorption and secretion. It is found lining most of the gastrointestinal tract, the uterine tubes in the female reproductive tract and the bronchioles in the respiratory tract.** **Pseudostratified Columnar Epithelium** **Pseudostratified columnar epithelium is composed of a single layer of columnar cells, but the varying levels of the nuclei make the epithelium appear stratified. It has two forms -- ciliated, where the cells have cilia on their apical surfaces, and non-ciliated, where the cells lack cilia on their apical surfaces. Specialised mucous-secreting cells called goblet cells are found throughout the ciliated form. The main function of pseudostratified columnar epithelium is protection and the ciliated form also has a secretory function due to the presence of goblet cells. The ciliated form is much more common and is found lining most of the respiratory tract. The non-ciliated form is rare and is found lining parts of the male urinary and reproductive tracts** ### **Stratified Epithelium** **The four types of stratified epithelium are stratified squamous epithelium, stratified cuboidal epithelium, stratified columnar epithelium and transitional epithelium. They are named according to the shape of the cells in the apical layer, which is the layer closest to the surface of the epithelium. Click on each of the flip cards below to learn more about these four types.** **Stratified Squamous Epithelium** **Stratified squamous epithelium is composed of multiple layers of cells, with the apical cells being squamous and the basal cells being more cuboidal or polyhedral. It has two forms -- keratinised, where the apical cells are dead, lack nuclei and other organelles and are filled with a protein called keratin, and non-keratinised, where all the cells are all living, contain nuclei and other organelles and lack keratin (this is the form that is shown on the image). The main function of stratified squamous epithelium is protection, as it prevents the underlying tissue from damage caused by abrasion. The basal cells undergo division to produce new cells that migrate towards the surface of the epithelium to replace the cells that have been damaged or lost. The keratinised form of stratified squamous epithelium is found in the epidermis of the skin and the non-keratinised form is found lining the oral cavity, part of the pharynx, the oesophagus, the anal canal and the vagina.** **Stratified Cuboidal Epithelium:Stratified cuboidal epithelium is typically composed of only a few layers of cells, with the apical cells being cuboidal. Its main functions are protection and secretion. It is primarily found lining the ducts of sweat and salivary glands.** Stratified Columnar Epithelium :Stratified columnar epithelium is typically composed of only a few layers of cells, with the apical cells being columnar. Its main functions are protection and secretion. It is rare and is primarily found lining the large ducts of some glands **Transitional Epithelium : Transitional epithelium is composed of multiple layers of cells that are capable of changing shape depending on the degree of stretch of the epithelium. When the epithelium is relaxed, the basal cells resemble cuboidal cells and the apical cells are large and rounded. When the epithelium is stretched, the apical cells resemble squamous cells. Transitional epithelium is specialised for distension and is found lining most of the urinary tract.** ### **Summary** The tree diagram below summarises the classifications of the different types of epithelium that we have just looked at. The table below summarises the functions of the different types of epithelium that we have just looked at in relation to their classifications. Glands LO5: Briefly describe the classification and function of glands Now that we have looked at the different types of epithelium, we are going to look briefly at glands, which are formed by invaginations of epithelial tissue into the underlying connective tissue. Glands can either be individual cells such as goblet cells or multicellular organs such as sweat and salivary glands. The epithelial cells that constitute glands are specialised for producing secretions such as mucous, enzymes and hormones. Glands can be classified as either exocrine or endocrine, depending on how they release their secretions. Exocrine glands maintain their connection to the epithelial surface via ducts which carry their secretions to the surface. The ducts are the conducting portions of the glands and their secretory portions which produce the secretions are called acini (singular = acinus). Sweat and salivary glands are examples of exocrine glands. Endocrine glands lack ducts and release their secretions, which are hormones, directly into the bloodstream. We will look at endocrine glands in more detail in another module on the endocrine system. **Module: Connective Tissue Proper (Part 2 of 3)** ================================================== **Learning Outcomes** --------------------- By the end of this module, you should be able to: **LO1**: Name the primary germ layer that connective tissue is derived from **LO2**: Describe the basic components and functions of connective tissue **LO3**: Name the five types of connective tissue proper or specialised connective tissue **LO4**: Describe the cell and protein fibre types in connective tissue proper **LO5**: Describe the structure of the different types of loose and dense connective tissue **Connective Tissue Origin** ---------------------------- ***LO1: Name the primary germ layer that connective tissue is derived from*** Recall from the Cells and Basic Tissues module that connective tissue is one of the four basic tissue types in the body. Recall from the Embryology module that all tissues in the body are derived from the three primary germ layers of the embryo, with connective tissue being derived from the mesoderm. Embryonic connective tissue is called mesenchyme and ultimately gives rise to all types of connective tissue. **Connective Tissue Components and Functions** ---------------------------------------------- ***LO2: Describe the basic components and functions of connective tissue*** Connective tissue is the most diverse, abundant and widely distributed of the four basic tissues in the body, as it supports, protects and binds other tissues together. Despite being highly diverse, all connective tissue has three basic components, which are cells, protein fibres and ground substance. Collectively, the protein fibres and ground substance make up the extracellular matrix, which is the primary component of connective tissue. Connective tissue also has several functions including physical protection, support, binding, storage, transport and immune protection. Click on the hotspots below to learn more about these basic components and functions. **Connective Tissue Types** --------------------------- ***LO3: Name the five types of connective tissue and classify them as either connective tissue proper or specialised connective tissue*** Now that we have looked at the basic components and functions of connective tissue, we are going to look at its types. There are five types of connective tissue, which are loose connective tissue, dense connective tissue, bone, cartilage and blood. Loose and dense connective tissue are classified as connective tissue proper, while bone, cartilage and blood are classified as specialised connective tissue. Connective tissue proper will be the focus in this module. We will look at bone and cartilage in another module and we will not look at blood in detail. **Connective Tissue Proper** ---------------------------- ***LO4: Describe the cell and protein fibre types in connective tissue proper*** Now that we have introduced the five types of connective tissue, we are going to focus on connective tissue proper. Connective tissue proper is characterised by having a mixture of different connective tissue cell types and protein fibres within a viscous ground substance. The amount and type of cells, protein fibres and ground substance will determine the properties of the connective tissue. The cells in connective tissue proper can be classified as either resident or wandering cells. The resident cells are fixed within the connective tissue and are responsible for supporting and maintaining the extracellular matrix. The main types of resident cells are fibroblasts and adipocytes. The wandering cells can move throughout the connective tissue and are involved in immune protection and tissue repair. As such, wandering cells are primarily types of leukocytes, or white blood cells, that have left the bloodstream and entered the surrounding connective tissue. The main types of wandering cells are mast cells, plasma cells, macrophages and other leukocytes. As mentioned previously, there are three types of protein fibres in connective tissue, which are collagen fibres, elastic fibres and reticular fibres. Click on the hotspots on the tree diagram below to learn more about each type of connective tissue cell and protein fibre. Now that we have looked at connective tissue proper more generally, we are going to look at its two main types and each of their subtypes. The two main types of connective tissue proper are loose connective tissue and dense connective tissue. This classification is based on the amount and type of cells, protein fibres and ground substance. **Loose Connective Tissue** --------------------------- ***LO5: Describe the structure, function and location of the different types of loose and dense connective tissue*** We are going to start by looking at loose connective tissue. Loose connective tissue has a relatively lower proportion of cells and protein fibres and a relatively higher proportion of ground substance than dense connective tissue. The protein fibres are loosely arranged within the ground substance rather than being tightly packed together. Loose connective tissue forms the "packing material" of the body, as it fills the space around organs, blood vessels, nerves and other structures. There are three types of loose connective tissue, which are areolar connective tissue, adipose connective tissue and reticular connective tissue. Click on each of the flip cards below to learn more about these three types. **Areolar Connective Tissue : This is the most abundant type of loose connective tissue in the body. It contains all connective tissue cell and protein fibre types and these are loosely arranged within the viscous ground substance, which constitutes most of the volume of areolar connective tissue. The main function of areolar connective tissue is to support, protect and bind other tissues and structures in the body. It is found in the dermis layer of the skin, in the subcutaneous layer underneath the skin and surrounding organs, blood vessels, nerves and other structures.** **Adipose Connective Tissue :This is primarily composed of adipocytes, or fat cells, which are tightly packed within the viscous ground substance. Its main functions are to store energy, provide cushioning and shock absorption for organs and act as an insulator to minimise heat loss. It is found in the subcutaneous layer underneath the skin and surrounding organs such as the kidneys.** **Reticular Connective Tissue : This is composed of a network of reticular fibres as well as scattered fibroblasts and leukocytes within the viscous ground substance. Due to the mesh-like arrangement of reticular fibres, the main function of reticular connective tissue is to form the framework of organs, which is called stroma. It is found forming the stroma of the liver, spleen, thymus and lymph nodes.** **Dense Connective Tissue** --------------------------- ***LO5: Describe the structure, function and location of the different types of loose and dense connective tissue*** **Now we are going to look at dense connective tissue. Dense connective tissue has a relatively higher proportion of cells and protein fibres and a relatively lower proportion of ground substance than loose connective tissue. It is primarily composed of protein fibres and these are tightly packed within the ground substance rather than being loosely arranged. The predominant protein fibre type in dense connective tissue is collagen fibres. There are three types of dense connective tissue, which are dense regular connective tissue, dense irregular connective tissue and elastic connective tissue.** **Click on each of the flip cards below to learn more about these three types.** **Dense Regular Connective Tissue : This is composed of tightly packed collagen fibres arranged in parallel bundles, with fibroblasts arranged in rows in between these bundles. The bundles of collagen fibres are aligned in the direction in which forces are applied to the tissue, making it capable of resisting stress in one direction. The main function of dense regular connective tissue is to bind other structures together. It is found in ligaments, which connect bone to bone, and tendons, which connect muscle to bone.** **Dense Irregular Connective Tissue : This is composed of tightly packed collagen fibres arranged in bundles that are aligned in different directions, with fibroblasts scattered in the spaces between these bundles. The random alignment of the collagen bundles makes dense irregular connective tissue capable of resisting stress in multiple directions. Its main function is therefore to protect other tissues and organs from forces applied to them in multiple directions. It is found in the dermis layer of the skin, in the periosteum and perichondrium, which are the connective tissue coverings of bone and cartilage, respectively ('peri' = around, 'osteum' = bone, 'chondrium' = cartilage), and in the capsules of organs such as the liver, kidneys and spleen.** **Elastic Connective Tissue: This is primarily composed of elastic fibres, with fibroblasts scattered in the spaces between the fibres. Due to the abundance of elastic fibres, the main function of elastic connective tissue is to allow structures to stretch and then recoil back to their original shape. It is found in the walls of elastic arteries and parts of the respiratory tract such as the trachea and bronchi, as well as in the vocal cords and some ligaments.** **Module: Skin (Part 3 of 3)** ============================== **Learning Outcomes** --------------------- **Now that we have looked at epithelium and connective tissue proper in Parts 1 and 2 of this 3 module series, we are going to bring these two tissues together and look at skin.** **By the end of this module, you should be able to:** **LO1: Describe the basic structure of a body membrane and the specific structures of serous and mucous membranes** **LO2: Name the primary germ layers that the skin is derived from** **LO3: Describe the functions of skin** **LO4: Describe the structure of the epidermis and dermis** **Body Membranes** ------------------ ***LO1: Describe the basic structure of a body membrane and the spcific structures of serous and mucous membranes*** **Before we focus on the skin specifically, we are going to look at the concept of body membranes. The internal cavities and passageways of the body are lined by membranes and these membranes are composed of epithelium with underlying connective tissue. These include serous membranes, mucous membranes and skin, which can be considered the cutaneous membrane of the body (*\'cutaneous\'* = skin). We are going to look briefly at serous and mucous membranes before looking more closely at skin. We will look more closely at specific serous and mucous membranes in the body as we come across them in later modules on different body systems.** **Click on each of the flip cards below to learn more about serous and mucous membranes.** **Serous Membrane : A serous membrane, also called a serosa, lines internal body cavities including the thoracic and abdominopelvic cavities and reflects onto the surface of some of the organs in those cavities. It is composed of a layer of simple squamous epithelium, called mesothelium due to its origin from the mesoderm (recall from the Embryology module that serous membranes are derived from the mesoderm), and an underlying layer of areolar connective tissue. A serous membrane can be divided into two parts -- an outer parietal layer which lines the internal surface of the body cavity, and an inner visceral layer which lines the external surface of some of the organs in the cavity (*\'viscera\'* = organs). In between these two layers is a potential space containing a thin film of fluid called serous fluid that is produced by the serous membrane to reduce friction.** **Mucous Membrane : A mucous membrane, also called a mucosa, lines all internal body passageways that open to the external environment. These include the respiratory, digestive, urinary and reproductive tracts. A mucous membrane is composed of an epithelial layer and an underlying layer of areolar connective tissue called the lamina propria. They often contain mucous-producing cells or glands that produce mucous to lubricate and protect the mucous membrane.** **Origin** ---------- ***LO2: Name the primary germ layers that the skin is derived from*** **Now that we have introduced the concept of body membranes, we are going to focus on the skin. Recall from the Embryology module that all tissues in the body are derived from the three primary germ layers of the embryo. The primary germ layers that the skin is derived from are the ectoderm and mesoderm, with the epidermis being derived from the ectoderm and the dermis being derived from the mesoderm. We will look more closely at these two main layers of the skin later in this module.** **Functions** ------------- ***LO3: Describe the functions of skin*** **The skin is the largest organ in the body. It is also referred to as the integument and forms the integumentary system of the body. It has many functions, including protection, water regulation, temperature regulation, metabolic regulation, immune defence, sensory reception and secretion.** **Click on the hotspots below to learn more about these functions.** **Structure** ------------- ***LO4: Describe the structure of the epidermis and dermis*** **Now that we have looked at the functions of the skin, we are going to look at its structure. The skin consists of two main layers, which are the epidermis and the dermis. The epidermis is the more superficial layer and is composed of stratified squamous keratinised epithelium. Its external location explains its origin from the ectoderm, as this is the most external primary germ layer of the embryo. Skin is classified as thick or thin depending on the relative thickness of the epidermis. The dermis is the deeper layer and is composed of connective tissue, which explains its origin from the mesoderm, as all connective tissue is derived from the mesoderm. This overall structure is why the skin can be considered a body membrane. Deep to the dermis is layer called the subcutaneous layer ('sub' = underneath, 'cutaneous'= skin) or hypodermis ('hypo' = below), which is composed of areolar and adipose connective tissue. It is not part of the skin, but helps to anchor the skin to the underlying tissue and contains blood vessels to help supply the skin.** **Now that we have introduced the overall structure of the skin, we are going to look at its two main layers individually.** ### **Epidermis** **The epidermis is composed of stratified squamous keratinised epithelium and consists of several layers, or strata -- from deep to superficial, these are the stratum basale, stratum spinosum, stratum granulosum, stratum lucidum and stratum corneum. The stratum lucidum is only present in thick skin, which is found in locations such as the palms of the hands and the soles of the feet. The most abundant cell type in the epidermis are keratinocytes, which are found in every layer. They produce the protein keratin, which gives skin its strength and water resistance. There are also other cell types in the epidermis, including melanocytes, tactile or Merkel cells and epidermal dendritic or Langerhans cells. We will look at these cells as we come across them in the different layers of the epidermis.** **Click on the hotspots on the image below to learn more about these layers.** ### **Dermis** **The dermis is composed of two types of connective tissue, which are areolar and dense irregular connective tissue. This connective tissue primarily contains fibroblasts and collagen fibres, but there are also elastic and reticular fibres present. The dermis contains blood vessels to supply the epidermis, as the epidermis is avascular and relies on diffusion of nutrients from the dermis. It also contains structures such as sweat glands, sebaceous or oil glands and hair follicles, which are collectively referred to as epidermal appendages as they are derived from the epidermis. The dermis consists of two main layers, which are the more superficial papillary layer and the deeper reticular layer.** **Click on the hotspots on the image below to learn more about these layers.** **Module: Skeletal System 1 - Introduction** ============================================ **Learning Outcomes** --------------------- **By the end of this module, you should be able to:** **LO1: Describe the main functions of the skeletal system** **LO2: Classify bones on the basis of shape** **LO3: Identify and name principle bony markings** **LO4: Describe how the skeleton is classified into axial and appendicular divisions** **What is the Skeletal System made of?** ---------------------------------------- **The skeletal system is the framework that provides structure to the rest of the body and facilitates movement. When we speak about the skeleton, we mostly think about bones. However, the skeletal system also includes cartilages and ligaments.** - - **In this module, however, we will focus specifically on the bony skeleton only.** **Skeletal System Functions** ----------------------------- **The word 'skeleton' comes from Greek word meaning 'dried-up body' or 'mummy'. Bones make up most of the skeleton. In the adult human skeleton, there are approximately 206 bones and 32 teeth. There are 22 bones in the skull alone! It does take time to learn the bones and it is important that you practice writing and pronouncing their names.** **The skeletal system has several functions, including:** - - - - - - **Click on the hotspots below to learn more about these functions.** **Bone Types** -------------- **Bones come in many sizes and shapes. They can be classified by their shape as flat, short (including sesamoid), long, and irregular. Let's look at these in more detail.** **Classification of Bones based on thier Shape** ------------------------------------------------ **Click on the hotspots on the image below to learn more about the classification of bones based on their shape.** **Bones bear surface markings that adapt bones for their functions, such as providing attachment sites for muscles, allowing nerves and vessels to pass or accommodating bony shapes for participation in joints. These bony features have some common names. Let's look at these in more detail.** **Bone Markings** ----------------- ### **Projections that are sites of muscle and ligament attachment** **Bone markings are projections, depressions, and openings found on the surface of bones that function as sites of muscle, ligament, and tendon attachment, as joint surfaces, and as openings for the passage of blood vessels and nerves. Here you can see the projections that function as sites of muscle and ligament attachment.** **Click on the hotspots on the image below to learn more about these projections.** ### **Projections that help to form joints** **Here you can see the projections that help to form joints.** **Click on the hotspots on the image below to learn more about these projections.** ### **Depressions and openings** **Here you can see the depressions and openings.** **Click on the hotspots on the image below to learn more about them.** **Now we can discuss the subdivisions of the skeleton.** **Parts of the Skeleton** ------------------------- **The complete skeleton consists of two parts: the axial skeleton and the appendicular skeleton.** - - **We will explore the axial and the appendicular skeletons in detail in the next two modules.** **Module: Skeletal System 2 - Axial Skeleton** ============================================== **Learning Outcomes** --------------------- By the end of this module, you should be able to: **LO1**: Describe the bones of the axial skeleton: skull, vertebral column and thoracic skeleton **The Axial Skeleton** ---------------------- The axial skeleton consists of the bones of the head and trunk of the body. It is composed of three main parts: the skull (including the ossicles of the middle ear and a bone associated with the skull called the hyoid bone), the vertebral column and the thoracic skeleton. Let\'s examine these three parts in more detail, starting with the skull. **The Skull** ------------- The first part of the axial skeleton is the skull. The skull is composed of 22 bones that can be divided into two main categories: the bones forming the cranium that houses and protects the brain and the bones of the facial skeleton. Click on the hotspots on the image below to learn more about these two main categories. **Sutures of the Skull** ------------------------ Except for the temporomandibular joint which unites the temporal bone and mandible, all joints of the skull are immovable and are called sutures. - - - **Cavities of the Skull** ------------------------- The skull contains several prominent cavities. The largest cavity is the cranial cavity that encloses the brain. Several smaller cavities include: - - - - **Anterior View of the Skull** ------------------------------ This anterior view of the skull shows several major bones. Click on the hotspots on the image below to learn more about some of the major features of the skull that can be seen from this view. **Lateral View of the Skull** ----------------------------- This is a lateral view of the skull. Click on the hotspots on the image below to learn more about some of the major features of the skull that can be seen from this view. **Cranial Base and Foramina** ----------------------------- Looking at an internal view of the cranial base, three cranial fossae can be seen: anterior, middle and posterior. A part of the sphenoid bone, called the lesser wing, separates the anterior and middle cranial fossae. A large bony ridge that is a part of the temporal bone, called the petrous part, separates the middle and posterior cranial fossae. Within each of these cranial fossae, there are several important foramina that transmit the cranial nerves which originate off the brain, as well as other structures such as blood vessels. Most of the anterior cranial fossa is formed by a part of the frontal bone called the orbital plate and this surrounds a part of the ethmoid bone called the cribriform (or perforated) plate. This plate forms the bony roof of the nasal cavity. It contains multiple openings called olfactory foramina that provide a passage for the olfactory nerves, which are responsible for the sense of smell. The middle cranial fossa contains several important paired openings: - - - - The posterior cranial fossa contains the following openings: - - - - Click on the hotspots on the image below to learn more about these foramina. **Cranial Nerves** ------------------ Many skull foramina are used by the cranial nerves to pass in and out of the skull and reach the structures they innervate. At this stage, we are not going to discuss the cranial nerves. However, it is helpful to understand the pattern in which the cranial nerves pass through these foramina, as this will assist you later in your anatomy studies. There are 12 cranial nerves and they are numbered from 1 to 12 using Roman numerals: CN I, CN II, CN III etc until CN XII. They pass through the skull foramina in this order from anterior to posterior. **Hyoid Bone** -------------- The hyoid bone is a bone of the axial skeleton found in the neck that does not articulate directly with any other bone. It is supported by ligaments and serves as an attachment site for muscles of the tongue and neck. **The Vertebral Column** ------------------------ The second part of the axial skeleton is the vertebral column. The adult vertebral column is typically composed of 26 bones, including 24 movable vertebrae and the fused vertebrae that form the sacrum and the coccyx. The vertebral column is divided into 5 regions. Click on the hotspots on the image below to learn more about these 5 regions. **Curvatures of the Vertebral Column** -------------------------------------- **The vertebral column is not straight**. If viewed from the lateral side, **four curvatures** can be identified: two bulging anteriorly and two bulging posteriorly. **The thoracic and sacral curvatures are convex posteriorly**. These curvatures are called primary curvatures as they are present at birth. They are also called kyphoses (singular = kyphosis). **The cervical and lumbar curvatures are concave posteriorly.** These curvatures are called secondary curvatures as they are formed after birth due to weight-bearing. The cervical curvature forms when a baby starts to lift its head, and the lumbar curvature forms when a toddler starts to walk. They are also called lordoses (singular = lordosis). In some cases, there can be distortions of these normal curvatures of the vertebral column. Distortions of the vertebral column **Features of a Typical Vertebra** ---------------------------------- Here you can see a typical thoracic vertebra as an example to learn about the main features of a typical vertebra. A typical vertebra consists of a body anteriorly and a vertebral arch posteriorly, separated by a vertebral foramen. The vertebral arch includes the pedicles, laminae and 7 processes: one spinous, two transverse, two superior articular and two inferior articular processes. The articular process have articular facets on them to allow for articulation of adjacent vertebrae. The articular processes of adjacent vertebrae are united by synovial joints, while the vertebral bodies of adjacent vertebrae are united by the intervertebral discs. Next, we are going to examine common features that are characteristic for vertebrae belonging to different regions of the vertebral column. **Types of Vertebrae** ---------------------- Vertebrae from different regions of the vertebral column have characteristic features. Click on the hotpots on the image below to learm more about these. **Atlas and Axis** ------------------ The C1 and C2 vertebrae are considered atypical due to their specific features. The first cervical vertebra, **C1**, is called the **atlas** and is ring-shaped. It has no body, but rather two lateral masses united by anterior and posterior arches. The lateral masses have two articular facets (superior and inferior) for articulation with the occipital condyles of the skull above and the C2 vertebra below. The second cervical vertebra, **C2**, is called the **axis** due to the presence of the odontoid process or dens that, when articulated with the anterior arch of C1, acts as an axis for rotatory movements of the head. ### **The Atlanto-Axial Joint** Here you can see the articulated C1 and C2 vertebrae at the joint called the atlanto-axial joint. The anterior arch of C1 articulates with the dens of C2. The inferior articular facets of C1 articulate with the superior articular facets of C2. This creates an arrangement that facilitates the pivoting movements of C1 on top of C2. **The Thoracic Skeleton** ------------------------- The third and final part of the axial skeleton is the thoracic skeleton. The bones of the thoracic skeleton include 12 pairs of ribs, the sternum and the thoracic vertebrae. Click on the hotspots on the image below to learn more about these bones. Now, let's look at the gross anatomy of a typical rib. **Typical Rib** --------------- A typical rib consists of a head with two facets, a neck, a tubercle and a shaft. The facets on the head of the rib articulate with the facets on the lateral sides of the thoracic vertebral bodies, while the facet on the tubercle of the rib articulates with the facet on the transverse process of the numerically corresponding thoracic vertebra. There is a costal cartilage on the anterior end of each rib for articulation with the sternum (either directly or indirectly), excluding ribs 11 and 12, as these do not articulate with the sternum. The internal surface of the rib features the costal groove that contains the intercostal neurovascular bundle, which is a bundle of blood vessels and nerves travelling between the ribs. **Summary** ----------- In summary, in this module we have reviewed the three main parts of the axial skeleton, which are the skull (and the associated hyoid bone), the vertebral column and the thoracic skeleton. Attached to the axial skeleton is the appendicular skeleton, which is the topic for the next module. **Skeletal System 2 Module Crossword** ====================================== **Module: Skeletal System 3 - Appendicular Skeleton** ===================================================== **Learning Outcomes** --------------------- By the end of this module you should be able to: **LO1**: Describe the bones of the appendicular skeleton **LO2**: Define the shoulder girdle and pelvic girdle **LO3**: Identify the regions and corresponding bones of the upper and lower limbs **Introduction** ---------------- The skeleton can be divided into two parts: - - Let's look at the appendicular skeleton in more detail. The appendicular skeleton includes the bones of the shoulder girdle, the upper limbs, the pelvic girdle, and the lower limbs. Although the bones of upper and lower limbs differ in their functions and mobility, they have the same fundamental organisation: each limb is composed of a girdle and a free portion, which in turn has three regions united by movable joints. Let's focus on the upper limb to start with. ### **Upper Limb Skeleton** The upper limb consists of two main parts: the **shoulder girdle** and the **free upper limb** itself. The shoulder girdle is the set of bones that connects the free portion of the upper limb to the axial skeleton. It consists of two bones, which are the clavicle and the scapula. The free upper limb consists of the three regions: - - - Let\'s focus on the shoulder girdle first. **Shoulder Girdle** ------------------- The paired shoulder or pectoral girdles and their associated muscles form the shoulders. The shoulder girdle consists of the clavicle anteriorly and scapula posteriorly. Let\'s have a look at how these bones articulate with each other and in turn, with the free upper limb. The medial end of the clavicle articulates with the sternum. This is the only point of articulation between the upper limb and the axial skeleton. The lateral end of the clavicle articulates with the scapula. The scapula, in turn, articulates with the humerus at the shoulder joint. There is no anatomical joint between the thoracic cage and the scapula. Instead, the scapula is held in place by muscles. Therefore, the shoulder girdle bones form a chain with several segments and articulations prior to the shoulder joint. This significantly increases the mobility of the upper limb. Since only the clavicle attaches to the axial skeleton, the scapula can move quite freely along the thoracic cage, allowing the free upper limb to move with it. Many muscles attach to the bones of the shoulder girdle and allow for the high mobility of this region. ### **Clavicle** Now that we have looked at the shoulder girdle as a whole, let\'s look at each of the bones it consists of in more detail, starting with the clavicle. The clavicle or 'collarbone' can be easily palpated. You can feel its rounded medial or sternal end that articulates with the manubrium of the sternum and its flattened lateral or acromial end that articulates with the acromion of the scapula. If you run your fingers along the clavicle, you will feel that the medial 2/3rd of the clavicle is convex anteriorly and the lateral 1/3rd is concave anteriorly. The superior surface of the clavicle is smooth while the inferior surface is rough due to the attachment of ligaments and muscles. ### **Scapula** Now let\'s look at the scapula, which is the other bone in the shoulder girdle. The scapula is a thin, flat bone aligned against the posterior aspect of the thoracic cage and held in place by many muscles. Like a triangle, the scapula has 3 angles: superior, inferior and lateral. The lateral angle has a feature called the glenoid fossa, which is a shallow depression for articulation with the humerus at the shoulder joint. The word glenoid is translated from Greek as the socket of a joint. Also like a triangle, the scapula has three borders: superior, lateral and medial. On the anterior surface, the scapula has a large depression called the subscapular fossa where a muscle called subscapularis originates from. This muscle belongs to a group of muscles called the rotator cuff. Projecting anteriorly from the lateral part of the superior border of the scapula is the coracoid process. Coracoid means \"like a crow\'s beak". This process is an attachment point for several muscles and ligaments. On the posterior aspect of the scapula, a prominent spine can be identified and this can be palpated. The spine extends laterally as the acromion. Acromion means the apex of the shoulder and this feature can be palpated. The acromion articulates with the lateral or acromial end of the clavicle. The spine separates the posterior surface of the scapula into two fossae: the supraspinous fossa and the infraspinous fossa. Two muscles called supraspinatus and infraspinatus originate from these fossae, respectively. These muscles also belong to the rotator cuff group. **Free Upper Limb** ------------------- Now that we have looked at the shoulder girdle, let\'s look at the **free upper limb**, starting with the first region which is the **arm**. It includes only bone, which is the **humerus**. Let\'s look at it in more detail. ### **Humerus** The humerus has a round **head** at the proximal end and an **anatomical neck** immediately below it. The head of the humerus articulates with the glenoid fossa of the scapula to form the shoulder joint. The proximal end of the humerus also features the **greater and lesser tubercles** that serve as attachment sites for the rotator cuff muscles, some of which were mentioned when we looked at the scapula (subscapularis, supraspinatus and infraspinatus). The **surgical neck** of the humerus is located below the tubercles and separates them from the shaft. This is referred to as the surgical neck due to its clinical significance. On the lateral aspect of the proximal shaft, note the **deltoid tuberosity** for the attachment of the deltoid muscle. At the distal end, two **epicondyles** (lateral and medial) can be identified, which serve as attachment sites for many forearm muscles. The medial epicondyle is particularly palpable on the medial aspect of the elbow. The humerus forms the elbow joint at its distal end with the two bones of the forearm, which are the radius and ulna. The two articular features of the humerus participating in the elbow joint are the capitulum and the trochlea, which can both be seen on the anterior aspect of the distal end. The **capitulum** articulates with the head of the *radius*. Above the capitulum is a depression called the **radial fossa**, which accommodates the radial head when the elbow is in the flexed position. The **trochlea** articulates with a feature of the *ulna* called the trochlear notch. Above the trochlea is another depression called the **coronoid fossa**, which accommodates a feature of the ulna called the coronoid process when the elbow is in the flexed position. There is a third depression at the distal end of the humerus called the **olecranon fossa**, which is on the posterior aspect and accommodates a feature of the ulna called the olecranon process when the elbow is in the extended position. ### **Radius and Ulna** Now let\'s move further down the free upper limb to the second region which is the **forearm** and look at its two bones, which are the radius and the ulna. The **radius** is the **lateral bone** of the forearm. It has a **head** at the proximal end and a **neck** immediately below it. The head of the radius articulates with the capitulum of the humerus at the elbow joint and sits in the radial fossa of the humerus when the elbow is flexed. On the anterior surface of the radius is a feature called the **radial tuberosity**, which serves as the attachment site for the tendon of the *biceps brachii muscle*. The shaft of the radius gradually widens towards the distal end, which forms the articulation at the wrist joint. The **ulna** is the **medial bone** of the forearm. The posterior aspect of its proximal end features the **olecranon process**, which translates from Greek as \"the head of the elbow'. When the elbow is fully flexed, the olecranon forms the most prominent point on the posterior aspect of the elbow and can easily be palpated. When the elbow is extended, it sits in the olecranon fossa of the humerus. The anterior surface of the proximal end features the **trochlear notch**, which articulates with the trochlea of the humerus at the elbow joint. Note the sharp **coronoid process** of the ulna that sits in the coronoid fossa of the humerus when the elbow is flexed. Below the coronoid process is a feature called the **ulnar tuberosity**, which serves as the attachment site for the brachialis muscle. Unlike the humerus and the radius which both have a head at their proximal end, the **head** of the ulna is located at its **distal end**. On this image, the radius and ulna are articulated. To enable this, the **radial head** articulates with a feature at the proximal end of the **ulna** called the **radial notch**, while the **ulnar head** articulates with a feature at the distal end of the **radius** called the **ulnar notch**. Click on the hotspot on the image below to see how the humerus, radius and ulna articulate at the elbow joint. ### **Hand** Now let\'s look at the third region of the free upper limb which is the hand. The bones of the **hand** include 8 carpals, 5 metacarpals and 5 digits (each of which consists of phalanges). The 8 **carpal bones** are arranged in two rows: proximal and distal. The proximal row of carpals articulates with the radius at the wrist joint, while the distal row articulates with the metacarpals. The **metacarpal bones** form the palm and dorsum of the hand and are numbered 1 to 5 from lateral to medial. At their distal ends, they articulate with the bones of the digits. The **digits** are also numbered 1 to 5 from lateral to medial, therefore starting at the thumb, or \'pollex\'. Each digit consists of three **phalanges**: proximal, middle, distal; *except* for the thumb, which has only two phalanges: proximal and distal. **Quiz - Upper Limb Skeleton** ------------------------------ To consolidate your understanding of the upper limb skeleton, have a go at labelling the major regions and bones of the upper limb on the image below. **Lower Limb Skeleton** ----------------------- Now let\'s move on to the second part of the appendicular skeleton, which is the **lower limb**. Although the bones of upper and lower limbs differ in their functions and mobility, they have the same fundamental organisation. The **two main parts** of the lower limb are the **girdle** **(called the pelvic girdle)** and the **free lower limb**. Similar to the shoulder girdle, which connects the free upper limb to the axial skeleton, the **pelvic girdle** connects the free lower limb to the axial skeleton. However, the pelvic girdle differs from the shoulder girdle as it consists of one big irregular bone (**the** **hip bone**) in contrast to the two small bones of the shoulder girdle (the clavicle and scapula). Similar to the free upper limb, the free lower limb also consists of **three regions**: - - - Let\'s focus on the pelvic girdle first. **Pelvic Girdle** ----------------- The pelvic girdle connects the free portion of the limb to the axial skeleton. Therefore, strictly speaking, the pelvic girdle refers to the two hip bones (also called the coxal bones or os coxae). The two hip bones articulate with each other anteriorly at the pubic symphysis, and with the sacrum posteriorly, forming a continuous bony ring. This makes the pelvic girdle significantly stronger and more stable than the shoulder girdle. The emphasis of the pelvic girdle is on stability, while that of the shoulder girdle is mobility. In contrast to the pelvic girdle, the bony pelvis includes four bones: the two hip bones, the sacrum and the coccyx. Please note that some textbooks consider the bony pelvis to be synonymous with the pelvic girdle. Now let\'s have a look at the hip bone in more detail. ### **Hip Bone** The hip bone is large and irregularly shaped. It is formed by the fusion of the three bones: the ilium, the ischium and the pubis. During childhood, these are three separate bones united by cartilage at the acetabulum, which is a deep depression for the articulation of the femur to form the hip joint. In adults, the ilium, ischium and pubis are fused. Let's have a look at each of these three bones in more detail, starting with the ilium. ### **Ilium** The ilium forms the superior region of the hip bone. It consists of the body and the ala (wing), which has a prominent ridge called the iliac crest that is palpable when you place your hands on your hips. The iliac crest ends anteriorly as the anterior superior iliac spine and posteriorly as the posterior superior iliac spine. The anterior iliac spine can be palpated on the anterior aspect of the hips. Below each of the superior iliac spines, there are corresponding inferior iliac spines: the anterior inferior and posterior inferior iliac spines. The lateral surface of the ilium is called the gluteal surface, as it serves as the origin point of the gluteal muscles. The medial surface is called the iliac fossa, as it is where a muscle called iliacus originates from. The medial surface of the ilium has a large articular surface for the sacroiliac joint, which is the immovable articulation between the hip bone and the sacrum. ### **Ischium** The second part of the hip bone is the ischium, which forms the posteroinferior region of the hip bone. It is shaped like an arch with the body superiorly and a thin inferior ramus that is continuous with the inferior ramus of the third part of the hip bone, the pubis. Located posterior to the acetabulum is a triangular feature called the ischial spine, which separates two notches: the greater (or superior) sciatic notch above and the lesser (or inferior) sciatic notch below. Inferior to the lesser sciatic notch is a prominent feature called the ischial tuberosity, which serves as the common origin point of the hamstring muscles. This is the bony point that you sit on. ### **Pubis** The third part of the hip bone is the pubis, which forms the anterior region of the hip bone. It has a body anteriorly that is continuous with two rami: the superior ramus and the inferior ramus. The pubic tubercle, which is a small round prominence on the superior aspect of the body of the pubis, is palpable. This is an attachment point for a ligament called the inguinal ligament that runs in the groin region. A large hole called the obturator foramen is located between the pubis and the ischium. The word 'obturator' means 'closed gap' and this foramen is enclosed by a fibrous membrane called the obturator membrane. **Free Lower Limb** ------------------- Now that we have looked at the pelvic girdle, let\'s look at the **free lower limb**, starting with the first region which is the **thigh**. It includes only bone, which is the **femur**. Let\'s look at it in more detail. ### **Femur** The femur has a round **head** at the proximal end and a **neck** below it. The neck is positioned at an angle to the shaft of the femur. Due to this angulation and the significant weight-bearing force it is placed under, the neck is the weakest part of the femur and frequently fractures in a broken hip. On the posterior aspect of the proximal femoral shaft, there are two large, rough projections called the **greater and lesser trochanters.** These are also visible from an anterior view, but to a lesser extent. Laterally on the posterior aspect of the proximal shaft, there is a feature called the **gluteal tuberosity** for attachment of one of the gluteal muscles. Running down the length of the posterior aspect of the shaft is a prominent ridge called **linea aspera**, which is also for muscle attachment. ### **Tibia and Fibula** Now let\'s move further down the free lower limb to the second region which is the leg and look at its two bones, which are the tibia and the fibula. The **tibia** is the **medial and weight-bearing bone** of the leg. It features two large **condyles (medial and lateral)** at its proximal end, which have two flat articular surfaces superiorly to articulate with the corresponding femoral condyles at the knee joint. Separating the two articular surfaces is an elevation called the **intercondylar eminence** that serves for the attachment of ligaments in the knee joint. Anteriorly, the proximal end of the tibia has a feature called the **tibial tuberosity** for the attachment of the patellar ligament. The shaft of the tibia has a sharp anterior border that is palpable together with the medial surface of the tibia, as these features are located subcutaneously, or underneath the skin. The posterior aspect of the tibia has a prominent line called the **soleal line**, which is the origin point of a muscle called soleus. Distally, the tibia widens and has a feature on its medial aspect called the **medial malleolus**. This can be easily palpated, as it forms the medial bulge at the ankle. Both the proximal and distal ends of the tibia feature surfaces for the articulation with the fibula. The **fibula** is the **lateral** **bone** of the leg. It is important to note that unlike the tibia, it **does not participate in the knee joint**. At the proximal end, the fibula has a **head** that articulates with the lateral tibial condyle. At the distal end, it has a feature called the **lateral malleolus** that can be easily palpated, as it forms the lateral bulge at the ankle. The distal ends of the tibia and fibula form the so-called 'malleolar mortise', which articulates with one of the tarsal bones called the talus to form the ankle joint. Click on the hotspot on the image below to see how the tibia articulates with the femur at the knee joint, noting that the fibula does not participate. ### **Foot** Now let\'s look at the third region of the free lower limb which is the foot. The foot has two important functions: it bears the body weight and it acts as a lever to propel the body forward during walking or running. Like in the hand, the bones of the foot can be divided into three regions: 7 tarsals, 5 metatarsals and 5 digits (each of which consists of phalanges). The tarsus forms the posterior aspect of the foot and consists of **7 tarsal bones**. The two main weight-bearing bones are the **talus**, which articulates with the malleolar mortise at the ankle joint, and the **calcaneus**, which forms the heel of the foot. Anteriorly, the tarsals articulate with the **metatarsals**. Like the metacarpals in the hand, the metatarsals in the foot are numbered 1 to 5, but this time from medial to lateral. Also like the hand, the metatarsals articulate with the bones of the digits at their distal ends. Like in the hand, the digits of the foot are numbered 1 to 5, but this time from medial to lateral, therefore starting with the great toe, or 'hallux\'. Each digit consists of three **phalanges**: proximal, middle and distal; except for the great toe, which has only two phalanges: proximal and distal. This is the same as the digits of the hand. To support the body weight, the foot is structured so that it is arched upward. There are two longitudinal foot arches and one transverse foot arch. These arches are supported by interlocking bones, strong ligaments and muscle tendons. As a result, the foot arches \'give\' when weight is applied to the foot, then spring back when the weight is removed, thus supporting the body weight and locomotion. Click on the hotspot on the image below to see the foot arches. **Summary** ----------- In summary, in this module we have examined the bones forming the appendicular skeleton. These include the bones of the free upper and lower limbs and their girdles. The main function of the upper limb is mobility to allow for the positioning of the hand in the best way to support its manipulation. On the other hand, the main functions of the lower limb include not only mobility to allow for locomotion, but also weight bearing. **SGTA 1: Epithelium - Class Notes** ==================================== **SGTA 1: Epithelium - Histology Slide Collection** ===================================================