Lesson 2:The Musculoskeletal System
Assignment:
 Read Chapter 3 in the textbook
 Read and Study the lesson discussion
 Complete the Lesson 2 worksheet emailed to you (Due Friday)
Musculoskeletal System Functions
The textbook does an excellent job of describing
and explaining the musculoskeletal system and its
functions. It also does justice to the anatomy and
formation of bones. Please be sure that you study
and understand the concepts addressed in Chapter
3 of the textbook.
The Merck Veterinary Manual (MVM) is considered
an excellent and concise resource for veterinary
students and practitioners alike. Its explanation of the musculoskeleton is
particularly helpful. According to the manual,
The musculoskeletal system consists of bones, cartilage, muscles, ligaments, and
tendons. Primary functions of the musculoskeletal system include support of the
body, ability for motion, and protection of the vital organs. The skeletal system
serves as the main storage system for calcium and phosphorus… . (Kahn)
Click here for classifications and images of different types of joints and their movements.
Check your understanding of the two types of skeleton by trying this activity.
Click on the following links to learn more about each topic. Once you are in the link be sure to click the 'next' or
'continue' buttons to view the complete demonstration.
Growth in long bones
Growth in flat bones
Bone remodeling
Repair after a fracture
As you learned in Lesson One, all systems of the body are interrelated, and, because
of this, disorders of one of the systems may also affect the other systems, including
the musculoskeletal system.
The MVM also indicates that
Diseases of the musculoskeletal system most often involve motion deficits or
functional disorders. The degree of impairment depends on the specific problem
and its severity. Skeletal and articular [joint] disorders are by far the most common;
however, primary muscular diseases, neurologic deficits, toxins, endocrine
aberrations, metabolic disorders, infectious diseases, blood and vascular disorders,
nutritional imbalances or deficits, and occasionally congenital defects are diagnosed
as well….
The structural and functional unit of skeletal muscle is the motor unit. It consists of
a ventral [below, under] motor neuron with its cell body in the central horn of the
spinal cord and its peripheral axon, the neuromuscular junction, and the muscle
fibers innervated by the neuron. Each of these components must be functionally
intact for the muscle to contract properly. The ventral motor neuron is the final
common pathway conducting neural impulses from the CNS [central nervous
system] to the muscle.
Disorders and diseases will be discussed further in the next section of this lesson
discussion.
Muscle Disorders
Basically, muscle disorders occur if there is a breakdown in the communication and
function of any of these parts of the motor unit.
Disorders of the muscle membrane and the actual muscle fibers are called myopathies.
These membrane disorders may be hereditary or acquired. Acquired disorders are
usually diet-related or the result of an injury. Muscular dystrophy and white muscle
disease are two common myopathies involving actual muscle fiber components.
According to the MVM,
Tendons act as bridging and attachment structures for the muscles; some bridge long
gaps between the muscle bellies and target bone and, therefore, are prone to injury
themselves, especially because they are often loaded to the extreme and are only
minimally capable of elastic elongation. A prime example is the superficial [towards the
body surface] flexor [tendon angle gets smaller] tendon of horses, which is frequently
injured by partial tearing that leads to tendinitis [inflammation of the tendon]. Another
acquired injury of tendons involves traumatic disruptions. Due to the
relatively poor blood supply of both tendons and ligaments, healing is
delayed and frequently poor. Management of injuries to ligaments and
tendons requires patience and prudent long-term rehabilitation.
Bone Diseases
Bone diseases are most often congenital or hereditary, nutritional,
or traumatic. Canine hip dysplasia is a prime example of a genetic
disorder of the bone. Bone defects due to nutrition are often caused
by imbalances or deficiencies in minerals. Trace minerals like
copper, zinc, and magnesium are of particular importance to bone
health. Calcium and phosphorous must also be present in the correct
ratio.
Excessive protein and the deficiency or excess of certain vitamins can alter the
correct nutrient ratios in developing these bones.
The MVM continues,
Traumatic causes of bone disorders
represent the vast majority of cases and
include fractures, fissures, periosteal
[outermost layer of bone] reactions as a
result of trauma …. Lack of weight-bearing,
reduced motion, instability, pain, heat, or
swelling usually accompany these disorders.
Diagnostic procedures include inspection,
manual palpation, diagnostic imaging (such
as radiography, ultrasonography, or
thermography, and increasingly
scintigraphy, computed tomography, or
MRI), and diagnostic anesthesia to
determine the specific anatomic structure or
region involved in the problem.
Joint Disorders
Joint disorders are often mechanical in nature as a secondary disorder due to ailments in
the surrounding area. Musculoskeletal disorders often affect other parts of the same system
since many of the causes are mechanical in nature. Joint damage is often "due to continuous
abnormal weight-bearing in animals with angular limb deformities or other inciting causes
of joint diseases." Bacterial and fungal infections can affect all synovial (true movable)
joints but are "clearly recognizable and require immediate and aggressive treatment"
(MVM).
"Chronic (occurring frequently) inflammation of joints and
surrounding structures is most common in [situations]
associated with locomotion … . Normal synovial fluid
lubricates the synovial tissue in a joint through boundary
lubrication…. Any joint injury alters the volume and
composition of the synovial fluid and increases … pressure
in the involved bones" (MVM). This condition occurring
over an extended period of time can cause cartilage
destruction.
The MVM indicates,
Diagnostic procedures to determine the nature, extent, and
exact location of the joint disorder include inspection,
manual palpation and manipulation, diagnostic imaging
techniques, local or intra-articular anesthesia, diagnostic
arthroscopy, and laboratory examination of synovial fluid
or biopsy of synovial membrane.
The diagnostic and therapeutic options for management of
musculoskeletal disorders have greatly expanded during
the last few years and allow a return to a useful life for
most animals if done early in the disease process.
Summary
As stated in your textbook and this discussion, bones divide into two main sections:
the axial (centerline) bones and the appendicular (limb) bones. Bones are held
together by three types of joints. These are fibrous, cartilage, and synovial. Synovial
joints are further classified by the movement they allow.
A thorough understanding of bones and joints helps veterinarians to treat diseases
and disorders of, and injuries to, this system.
Sources Cited:
Kahn, Cynthia, ed. ":Musculoskeletal System Introduction." The
Merck Veterinary Manual. Ninth Edition. New Jersey: Merck & Co.
Inc. 2006
<http://merckvetmanual.com/mvm/index.jsp?cfile=htm/bc/90100.h
tm>.

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