Human Anatomy Learning Modules: These learning modules include:
Back & Vetebral Column // Thorax // Abdomen // Pelvis & Perineum // Lower Extremity // Upper Extremity // Head & Neck
This site not only includes helpful skeletal images, but also practice questions for each of the covered regions.
BioDigital Systems: Availble for free (individual) or for a fee (groups/businesses), this interactive system will first require you to sign in via your Facebook or Google account to gain access. Once inside the system, you can zoom and rotate your virtual skeleton. Eleven systems in total are able to view and examine. Note: this site allows you to repeatedly quiz yourself on all eleven systems that are covered within the site.
Anatomy Drill & Practice: This site covers the human body, the chemical, cellular, and tissue levels of organization, the integumentary system, skeletal system, muscular system, nervous system, cardiovascular system, respiratory system, digestive system, excretory system, and reproductive system.
This site not only includes images of and information on the above listed systems, but it also includes interactive drills and practice questions for students. NOTE: Flash required for the quizzes/practice questions.
The AK Lectures are a series of lectures from a (external) educational platform designed to "promote collaboration between our users and help spread knowledge to every part of the world."
These lectures vary in length, and will open in a new window when you click on the provided link.
Introduction to the Human Skeletal System: The human skeletal system consists of an endoskeleton that is composed of two types of connective tissue - bone and cartilage. Cartilage is a much more flexible connective tissue and is found in areas that require that extra bit of flexibility, such as in the outer ear, the nose, the trachea, the joints, among other places. Bone is a much more rigid type of connective tissue and is responsible for giving us support and protection. The skeletal system is broken down into two divisions, the axial skeleton which consists of the skull, the spinal cord and the ribcage and the appendicular skeleton, which consists of the bones in the lower and upper limbs as well as the pectoral and pelvic girdles. The skeletal systems is involved in protection, support, movement, storage and mineral homeostasis as well as in blood cell production.
Compact Bone Structure and Osteon System: Bone consists of cells along with the extracellular matrix produced by some of those cells. This extracellular matrix is composed of both organic and inorganic matter. The organic component is predominantly collagen (which gives the bone tensile strength) while the inorganic component is made up of hydroxyapatite crystals (made of calcium, phosphate and hydroxide ions). These hydroxyapatite provides the bone with compressive strength. There are three major types of cells in bone. Osteoblasts are the cells that build bone by creating the extracellular matrix. They are capable of absorbing minerals such as calcium from the blood and depositing it into the matrix. They can also create collagen fibers and secrete them into the matrix. Once osteoblasts trap themselves inside the matrix, they can differentiate into osteocytes. Osteocytes are the second type of cell found in the in bone and these cells are responsible for exchanging nutrients and waste products with the blood. The final type of cell that you should be aware of are osteoclasts. These are the cells that can resorb bone. They break down the matrix of the bone and release the products to the bloodstream. The basic functional unit of bone is called the osteon. The osteon is a cylindrically-shaped unit that consists of concentric rings called lamellae. Along these lamellae are spaces called lacunae, which contain cells called osteocytes. At the center of the osteon is a central canal we call the Haversian canal that contains the blood and lymph vessels as well as the nerve cells. The Haversian canal of one osteon is connected to the Haversian canal of another by Volkamann's canal.
Structure of Long Bones: Long bones are longer than they are wide. They can be divided into three regions - epiphysis, metaphysis and the diaphysis. The epiphysis contains the spongy bone (also called cancellous), which in turn contains the red bone marrow that is responsible for synthesizing blood cells. Covering the top portion of the epiphysis is usually the articular cartilage, made of hyaline cartilage. This serves to reduce friction between bones and absorbs some of the shock during movement. The metaphysis contains the epiphyseal plate, which is responsible for elongating and lengthening the bone during the growth of the human via a process called endochondrial ossification. The diaphysis is the long, curved shaft that contains a central region called the medullary cavity (marrow cavity). It also contains compact bone that is very strong and dense and consists of units called osteons. The compact bone contains the yellow bone marrow that is responsible for storing adipose tissue. The outer layer covering the bone is called the periosteum. This layer does not only serve a protective function and as a point of attachment for muscles, but it also contains certain cells that can differentiate into osteoblasts, the cells involved in bone healing and growth.
Bone Metabolism: Bone is living tissue and it consists of specialized cells that are responsible in the bone metabolism process (also known as bone remodeling). Bone remodeling refers to the continual break down and rebuilding process that takes place in the bone throughout the lifetime of the organism. Osteoblasts are those cells that are capable of absorbing calcium and phosphate from the blood and depositing it in the extracellular matrix in the form of hydroxyapatite. They can also secrete collagen, the main component of organic matter in the matrix. The osteoclasts are those cells that resorb the matrix of the bone. That is, they break it down into its components and release some of it (i.e calcium) into the blood stream.
Cartilage and Joints: Cartilage is a type of strong connective tissue that is much more flexible than bone. Cartilage consists of cells as well as the extracellular matrix secreted by those cells. The cells of cartilage are called chondrocytes and the matrix is called the chondrin. The chondrin consists of three types of substances - collagen fibers, elastin fibers and proteoglycans. There are three types of cartilage and they differ from one another based on the concentration of the above mentioned substances in the extracellular matrix. Hyaline cartilage is the most common type of cartilage. It is transparent and consists mainly of collagen fibers. It is found around bones and joints and functions to reduce friction and absorb the shock during bone movement. Elastic cartilage is the second type of cartilage and this contains a relatively high concentration of elastin fibers. This makes the cartilage very flexible and it is no surprise that is is found in regions that require a high degree of flexibility, such as our outer ear and the epiglottis. The fibrocartilage is the third type of cartilage that consists of both types of collage fibers (type I and type II) and which is found in places like the intervertebral disc. Joints are a second type of connective tissue that either contain or found close to cartilage. Joints either function in improving movement or they function to actually hold bone together. There are three types of joints - fibrous joints (also called fixed or immovable joints), synovial joints and cartilaginous joints. Fibrous joints function to hold bones together tightly and produce little or no movement, synovial joints allow a wide range of movement while cartilaginous joints create a tiny bit of movement.
Agonist-Antagonist Muscle Pairs: The muscular and skeletal system work together to coordinate the voluntary movement of our body, which is ultimately controlled by the nervous system. Skeletal muscle attaches to our bones not directly but rather via fibrous structures called tendons, which consist predominately of collagen fibers. Tendons should not be confused with ligaments, which connect bone to other bone. The biceps-triceps system consists of these two muscles as well as a collection of bones (humerus, radius, ulna and others) that are responsible for the voluntary movement of our arms. In most of these systems, there is a large bone that does not actually move and this is called the immovable bone while the bones that do move are called the movable bones. In the case of the biceps-triceps system, the humerus does not move while the radius and ulna do move. The point where the muscle-tendon attach to the immovable bone is called the origin and this is the proximal end of the muscle. On the other hand, the point where the muscle-tendon attached to the movable bone is called the insertion and this is the distal end of the muscle. The biceps-triceps system works antagonistically. This means that when one of the muscle contracts, the other muscle elongates (stretches out) and vice versa. The muscle that contracts is called the agonist while the muscle that lengthens is called the antagonist. When we flex our biceps and move the radius and ulna bones towards our body, the biceps acts as the agonist while the triceps acts as the antagonist. On the other hand, if we reverse this motion and move the bones away from the body, the biceps will be the antagonist while the triceps will be the agonist. A muscle that flexes and contracts to decrease the angle in the joint is called the flexer while a muscle that increases the angle when it contracts is called an extensor.
Long Bones, Short Bones, Flat Bones, Irregular Bones, & Sesamoid Bones: There are five different types of bone in the human skeletal system. Long bones are longer than they are wide. A typical long bone is divided into the epiphysis (contains the spongy bone and red bone marrow), metaphysis (contains the epiphyseal plate) and the diaphysis (contains the compact bone and yellow bone marrow). The long bone is very strong and has a high tensile and compressive strength, which makes it suitable for support and and movement. In fact the majority of the weight of the body is sustained using long bones. Some examples of long bones include the radius, ulna and humerus of the arm, the clavicle found in the shoulder as well as the femur, tibia and fibula found in the legs. Short bones are in the shape of a cube and are used for support and stability. The carpals of the wrist and the tarsals of the ankle are examples of short bones. Flat bones are relatively thin and have a high surface area. They are used to protect our internal organs as well as act as attachment sites for muscle. Some examples of flat bones include the cervical, scapula, sternum and the ribs. Irregular bones have a shape that does not fit the three mentioned above. The shape of these bones is unique to their function and purpose. For instance, the maxilla and mandible are irregular bones (jaw bones) that are used for chewing. The last type of bone is called the sesamoid bone. Seasmoid bones grow on tendons and have the shape of a sesame seed. They arise due to a high degree of physical friction and tension. All humans have only one sesamoid bone (the patella) but other seasmoid bones can arise during the lifetime of the organism.