Diseases of the
Muscular
System
Honors Anatomy & Physiology
Susan Chabot
Cause
Disease
Name
Cramps
Homeostatic
Imbalances
Atrophy
Torticullis
Physical
Interruption
Spinal cord injury
Muscular dystrophy
Degenerative
Myasthenia gravis
Multiple sclerosis
Description
Characteristic Vocabulary
 My-/myo-/mys-
: prefix meaning of
the muscles.
 -algia : suffix meaning pain.
 -itis : suffix meaning inflammation.
 dys- : prefix meaning abnormal.
 -enia : suffix meaning “disease of”.
Category Causes
 Homeostatic
Imbalances
 Physical/Chemical Interruption
 Degenerative Diseases
Homeostatic Imbalances
 Characterized
by
 loss
of function due to electrolyte
imbalance.
 loss of impulse transmission from
nervous system.
 Can
be reversed in many situations.
 Examples: muscle cramps and
“sleeping” appendages.
Muscle Cramps
 Often
due to lack of specific
electrolytes in interstitial space.
 Not enough Na+ or Ca+ can result in
incomplete muscle contraction.
 Action potential is lost along
sarcolemma (membrane) of muscle
fiber.
Muscle Atrophy
 Muscle
wasting: muscles lose “bulk”
due to inactivity.
 Several factors can cause muscle
atrophy:
 Casting
of injured limb
 Conscious inactivity
 Anorexia/malnutrition
 Paralysis
Torticollis


AKA cervical dystonia/abnormal cervical
(neck) muscle tone.
Often occurs due to inactivity during
infancy, often with head resting to one
side more often than the other.
Physical/Chemical Interruption
of Muscle Control



Traumatic Head injury: will not allow
brain to properly transmit directions to
muscle to produce voluntary movement.
Pinching: of neuro-muscular
transmission. Usually reversible with
use of anti-inflammatory
medications or physical
therapy.
Spinal Cord injury:
next slide
Spinal Cord Injuries



Interruption of neuro-muscular
function due to damage of spinal
cord neurons.
Level of spinal cord injury
determines extent of muscle
control interruption.
Stem Cell Research: working
toward using embryonic stem cells
to replace damaged permanent
spinal cord cells.
Degenerative Diseases



Muscular Dystrophy: inherited muscledestroying diseases.
Myasthenia gravis: possible autoimmune disorder.
Multiple sclerosis: nervous system
disorder that affects muscle control.
Muscular Dystrophy
A group of inherited muscle-destroying
diseases that affect specific muscle
groups.
 Muscles enlarge due to fatty deposits,
but the muscle fibers atrophy due to
degeneration.
 Several forms are known: Most common
and serious form is Duchenne muscular
dystrophy.

Duschenne Muscular Dystrophy





Most common in males. Inherited as a sexlinked recessive disorder.
Usually diagnosed between 2 and 6 years of
age.
Normal children become clumsy and fall as their
muscles weaken.
Disease begins on extremities and progresses to
skeletal muscles necessary for breathing and
smooth muscles needed for digestion.
Known cause is a genetic defect that inhibits the
production of normal sarcolemma protein
dystrophin but cure has not yet been found.
Inheritance of DMD
XY
XX
X X*
X X*
XY
X* Y
This inheritance chart demonstrates the passage of the defective DMD gene from
mother to offspring. With a carrier mother, she has the ability to pass on the
affected gene to both male and female offspring. Because female children inherit
2 copies of the gene, one from each parent, the “good” X-gene overrides the “bad”
X-gene. Male offspring can only inherit 1 X-chromosome, therefore the “bad” copy
is expressed.
Myasthenia Gravis





Antibodies seem to attack ACh receptors, rendering
them ineffective.
Blood of affected patients contains antibodies to ACh
receptors which suggests it is an autoimmune
disorder.
Progressive muscle disease resulting from loss of
ACh function at the neuromuscular junction.
Characterized by drooping of eyelids and other facial
muscles, difficulty swallowing and talking, and
generalized muscle weakness and fatigue.
Death usually the result from loss of respiratory
function.
Multiple Sclerosis




Considered an autoimmune disorder;
antibodies present that attacks the myelin
sheath.
Classified as a disease of the nervous system,
however affects the function of muscles.
Progressive loss of myelin sheath that
insulates the dendrites and axons of motor
neurons.
As demyelination occurs, nerve transmission is
slowed or completely lost, resulting in loss of
muscle control and function.
Typical Motor Neuron
Multiple sclerosis results when the myelin
sheath surrounding the axons of a motor
neuron is stripped away.
Dendrites
Cell Body
Axon
Myelin Sheath