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Human Anatomy Lesson 2

Robert is an anatomy professor at Benedictine University in Lisle, IL.


Lesson 2 - Medical Imaging, Systems, Bones

This is the second lesson in a semester-long Human Anatomy course. I assume since you've found this module on Hubpages that you are either one of my undergraduate students at Benedictine University or you are someone who is interested in human anatomy and wants to follow a long, detailed course to learn more about the human body. Either way, welcome! Today's lesson is a hodge-podge of topics that will provide important background information for topics that you will be studying in the rest of the course. First, I will briefly discuss medical imaging. The goal here is not to provide an exhaustive overview of the procedures used to produce medical images, but instead to briefly survey the major types of images, how they are produced, and some basic facts about how they are interpreted. Second, I will list nine body systems. Although this course takes a regional approach to human anatomy, it is important to know the basic components of key anatomical systems. As we move through the body's various regions, I will be pointing out the components of these various systems. Third, I will list the bones of the body and give you basic information about how they are connected to one another.

Learning Objectives - By the end of this module, you should be able to ...

  1. Identify the main characteristics of different medical imaging modalities
  2. Differentiate, at a very elementary level, between CT, MRI, and ultrasound, the main types of images you will be seeing in this course
  3. Understand a few basic facts about how medical images are interpreted
  4. Name and identify the key properties of nine anatomical systems
  5. Name a number of large, visible bones in the body (we will save the names for many of the bones of the wrist, ankle, and head for later)
  6. Understand how these bones articulate with each other

Medical Imaging

The modern era of medical imaging began in 1895 when Wilhelm Roentgen exposed a photographic plate under his wife's hand to the x-rays from a cathode ray tube to produce an image. The physics behind radiography have not changed in the past 120 years.

  • X-ray: A cathode ray tube produces x-rays, a type of photon, which a tech directs through a collimator (a lead-lined shutter), through an object (such as Mrs. Roentgen's hand), and onto an underlying photographic plate. The x-rays that pass through the hand are attenuated to some degree depending on the types of material that they pass through, and the corresponding image on the photographic plate ranges from white to black depending on how many of the x-rays were able to get through. Areas of the body, such as body cavities, that are relatively empty appear black; fat and other soft tissues appear gray; and bone appears white, since almost no x-rays were able to pass through that part of the body. Traditional plain radiography is a static procedure that produces a static image, but there are modifications to this technique. For one, various parts of the body can be imaged under continuous x-ray exposure to produce cine-x-ray movies. This type of procedure is common for patients experiencing problems swallowing. Contrast agents like barium sulfate are sometimes used in cine-x-ray to track the movement of fluids through the body.
  • Computed Tomography, or CT, is an x-ray technology. In this case, the patient, positioned on a gurney, is passed into a tube where x-rays pass all around the body. A complex set of algorithms is used to reconstruct images in a transverse (axial) plane. When interpreting CT scans, it is standard practice to view the scan as if you are looking at the patient from the feet up to the head, so that the patient's right side is on the left side of the image and anterior is toward the top.
  • Magnetic Resonance Imaging, or MRI, is a powerful method that is useful for imaging the brain and other soft tissue structures. MRI operates by realigning the free protons in hydrogen nuclei in the body's water. Like with CT, the patient is placed on a gurney and passed into a closed tube. Instead of an x-ray tube, though, a strong magnet is set to rotate about the body, which causes free protons to align. A pulse of radio waves is then passed through the patient so that the protons are deflected and emit radio pulses. An image is created by measuring the strength, frequency, and time it takes for the protons to realign.
  • Ultrasonography, or ultrasound, is a powerful technology commonly used to image the abdomen and developing fetus. In ultrasound, a high-frequency sound wave is generated by peizoelectric materials, which capture the sound waves that bounce off organs and other soft tissues. The sound waves are attenuated based on the tissues that they encounter on their way back to the machine. Doppler ultrasound can be used to track blood flow and velocity.

Anatomical Systems

Although in this course we are studying the human body using a regional approach, it is to our benefit at this point to briefly summarize the various anatomical systems.

  1. Skeletal - cartilage, bone, joints, ligaments
  2. Integumentary - skin, fascia
  3. Muscular - skeletal, cardiac, smooth
  4. Cardiovascular - heart and blood vessels, including arteries, veins, capillaries
  5. Lymphatic - "capillaries" and larger lymphatic vessels, including lymph nodes, trunks, and ducts
  6. Nervous - brain and spinal cord (CNS), cranial and spinal nerves, visceral nerves and plexuses (PNS)
  7. Respiratory - lungs, supporting structures
  8. Gastrointestinal - stomach, intestines, colon, rectum, accessory structures such as the pancreas and liver
  9. Urogenital - bladder, sex organs, glands and other supporting structures

The Skeleton

There are 206 bones in the human body (if you count pairs of bones). Many of these bones are small bones in the wrist, ankle, and head that we will cover later in the course. That leaves us with the larger and more visible bones to learn now. This part of the lesson is really the "knee-bone-is-connected-to-the-shin-bone" part of human anatomy. We will discuss how all of the bones of the body fit together to make an integrated organism.

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Bones of the Head

Starting at the top, the head is made up of two main parts: the cranium, which includes the braincase, face, and upper jaw; and the mandible, or lower jaw. Together, the mandible and cranium make up the skull. In a mature adult, many of the individual bones of the cranium are fused together, so that the skull can really be considered to consist of these two "bones" attached to one another at the temperomandibular joint (TMJ). However, the cranium is really made up of 22 separate bones. We will cover the individual bones of the cranium in lesson #14.

Schematic of the axial and appendicular skeleton

Schematic of the axial and appendicular skeleton

Bones of the Postcranium

Moving inferiorly, the cranium articulates with the atlas of the vertebral column. The vertebral column can be split into several regions, including the cervical, thoracic, and lumbar regions, and the sacrum and coccyx. The vertebral column surrounds and protects the spinal cord. We will cover the vertebral column in lesson #3 and the spinal cord in lesson #4, so I will not go into more detail here. The hyoid is a "U"-shaped bone that is "floating," in the sense that it is not directly connected to any other bone in the body. It is slung from the mandible and several other bones via a series of muscles, tendons, and ligaments. Many of the muscles of the tongue and pharynx attach to the hyoid bone. Twelve pairs of ribs are attached to the thoracic vertebrae, and 10 of these run in an anteroinferior direction to attach to the sternum, or "breastbone," or to cartilage that attaches to the sternum. The other two ribs are "floating," since they don't attach to the sternum, either directly or indirectly. Together, the bones of the head, the hyoid, vertebral column (including the sacrum and coccyx), and ribs make up the axial skeleton.

The other bones of the body make up the appendicular skeleton. These are the limb bones and the bones that attach the limb bones to the axial skeleton. The clavicles are "S"-shaped bones on either side of the thorax that articulate medially with the sternum and laterally with the scapula, which is a triangular-shaped bone that glides across the posterior and superior aspects of the rib cage. The humerus is the bone of the arm, and participates in the shoulder joint at its proximal end and the elbow joint at its distal end. The clavicle, scapula, and humerus make up the pectoral (shoulder) girdle. At its distal end, the humerus articulates with the radius and ulna at the elbow joint. The radius is the lateral bone in the forearm, on the thumb side, and the ulna is the medial bone of the forearm on the pinkie side. At their distal ends, the radius and ulna articulate with the bones of the wrist, called carpals; the carpals articulate with metacarpals (which are in the palm of the hand); and the metacarpals articulate with phalanges. There are three phalanges (proximal, middle, and distal) in each finger but only two (proximal, distal) in the thumb. The digits are numbered from one to five, and by convention, Roman numerals are used. Therefore, we can now replace our casual terminology with specific anatomical terms: digit I for thumb, digit II for index finger, digit III for middle finger, digit IV for ring finger, and digit V for pinkie. The same holds true for the toes: digit I is the big toe and digit V is the little toe.

Let's move on to the lower limb. At the inferior end of the vertebral column, the sacrum articulates with the two pelvic bones, which articulate with one another anteriorly in the midline at the pubic symphysis, a symphyseal joint. The bone of the thigh, the femur, fits into a socket in the pelvis called the acetabulum. The femur participates in the hip joint at it proximal end and the knee joint at its distal end. The femur articulates with the tibia at the knee joint. There is an additional free-floating bone in the knee joint called the patella which works to increase the mechanical advantage of the quadriceps muscles. The tibia is the medial bone of the leg, and the fibula is the long, spindly lateral bone. Both articulate with the bones of the ankle joint but only the tibia articulates directly with the femur at the knee joint. The talus and calcaneus are the two really large bones of the ankle and heel. The talus participates in the ankle joint and the calcaneus is the heel bone. They articulate with the tarsal bones, which articulate with the metatarsals and then with phalanges. Like in the hand, there are 3 phalanges in each of the toes but only two in the big toe.

Preview of Upcoming Lessons

At this point in the course, we have covered basic anatomical terminology and some introductory materials about medical imaging, anatomical systems, and the human skeleton. In the next lesson, we will apply this information to our first anatomical region, the back. We will start with the bones, ligaments, and joints of the vertebral column in lesson #3, then move to the spinal cord and somatic nervous system in lesson #4, the autonomic nervous system in lesson #5, and the muscles of the back in lesson #6.

  • Human Anatomy Lesson 3
    This lesson covers the vertebrae, joints, and ligaments that make up the spine and back.
  • Human Anatomy Lesson 4
    This lesson covers the anatomy of the spinal cord, spinal nerves, and somatic nervous system.
  • Human Anatomy Lesson 5
    This lesson covers the autonomic nervous system, focusing on how sympathetic nerve fibers get to different parts of the body.
  • Human Anatomy Lesson 6
    This lesson covers the muscles and movements of the back.

Be sure to leave any comments that will help me improve this lesson.

This content is for informational purposes only and does not substitute for formal and individualized diagnosis, prognosis, treatment, prescription, and/or dietary advice from a licensed medical professional. Do not stop or alter your current course of treatment. If pregnant or nursing, consult with a qualified provider on an individual basis. Seek immediate help if you are experiencing a medical emergency.

© 2014 Robert McCarthy

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