chap 22 - skeletal muscle Flashcards
structure and function
uses 10% of the body’s oxygen at rest, and up to 80% with exercise
- the major insulin-dependent tissue
must be innervated by motor neuron to maintain integrity and function
- muscle fiber types
- type 1 and type 2
type I
slow twitch, sustained actions of movement
- utilizes oxidative phosphorylation
type II
fast twitch, white, more explosive motions
- utilizes glycolysis
most frequent and serious problems
Weakness with or without muscle atrophy
Muscle strain - in the muscle while a sprain is in the ligament or tendon
Muscular dystrophies
Muscle weakness due to disease, traumatic nerve injury, neoplasms, stroke
muscle strain
Myotrauma = injury to muscle or tendon
- Stretching
- Tearing
Symptoms
- Pain
- Redness and or bruising
- Limited mobility
- Muscle weakness
Skeletal muscle has capacity for repair through satellite cells
Depending on location and extent, may take up to 8-10 weeks to heal
symptoms, signs, and tests
Weakness is a common symptoms, regardless of whether the disease is myopathic or neurogenic
- The pattern of weakness offers indications as to the type of disease present
Myalgia = muscle pain
Muscle tests
- Muscle biopsy
- Electromyography
- Laboratory tests
- Creatine kinase - muscle enzyme - if there is damage there will be leakage of this enzyme into the blood (think of cardiac enzymes that are released during a heart attack, high levels found in blood stream)
Increased quantities in serum indicate muscle disorder
classifications of muscle disorders
myopathic and nuerogenic
signs and symptoms of myopathic muscle disorder
proximal wekaness, possible pain
signs and symptoms of neurogenic muscle disorders
distal weakness, often in nerve distributions, possible sensory loss
electromyography in myopathic muscle disorders
asynchronous spontaneous activity
electromyography in neurogenic muscle disorders
synchronous activity of small amplitude
serum enzyme (creatine kinase) in myopathic disorders
often markedly elevated
serum enzyme (creatine kinase) in neurogenic disorders
normal or slightly elevated
biopsy in myopathic muscle disorders
variable size of fibers; degenerative fibers; possible fibrosis; possible inflammation
biopsy of neurogenic muscle disorders
atrophic fibers in small groups
myopathy
Neuromuscular diseases in which the muscle fibers do not function for any one of many reasons
Resulting in muscular weakness
Classification:
- acquired, hereditary/genetic, inflammatory
acquired myopathy
infections, inflammation, endocrine/metabolic, alcohol
herditary/genetic myopathy
mutations or deletions of genes coding for parts of a muscle (proteins, mitochondrial enzymes, sarcoplasmic reticulum)
genetic/developmental diseases
Muscular dystrophies
Myopathy
Group of disorders that cause degeneration of skeletal muscle fibers
Replacement of fat and fibrous tissues
The muscular dystrophies cause progressive, symmetric weakness, and wasting of skeletal muscle groups
Typically in proximal muscle groups of extremities and shoulders
Also heart
duchenne muscular dystrophy
Most common muscular dystrophy - and most severe
- 1 in 3500 live male births
X-linked recessive inheritance
- Single gene defect on short arm of the x chromosome - mom is the carrier
Gene encodes for dystrophin
- Mediates anchorage of actin cytoskeleton of the skeletal muscle fiber to the basement membrane
- Protect muscle fibers from injury as muscle contracts/relaxes
Affected muscle cells begin to die because of damage to the membrane
Normal at birth
Manifestations appear by 3 years of age
- Slow motor development
- Progressive weakness
- Muscle wasting
- Sitting and standing are delayed
- The child is clumsy, falls frequently, and has difficulty climbing stairs
Enlarged calves (psuedo-hypertrophy)
Loss of ambulation between 8 and 12 years
Life span 12-20 years
- Usually die in late teens from respiratory insufficiency or pneumonia - due to impact on the diaphragm
inflammatory degenerative diseases
Largest group of acquired and potentially treatable causes of skeletal muscle weakness
Myogenic causes
Infectious disease (bacteria, viral, parasitic)
Immune disease
Metabolic
Other causes (radiation, ischemia)
Some treatment options
chronic inflammatory myopathy
Autoimmune disease disorders
Symptoms
Progressive muscle weakness
Elevated CK levels
Systemic inflammation
CRP
Types
Polymyositis
Muscle only, lymphocyte infiltration
Dermatomyositis
Characteristic rash of eyelids, face, and upper chest
metabolic myopathy
Metabolic disease causing muscle weakness
McArdle’s disease
- Type of glycogen storage disease
- Defect of myophosphorylase
- Autosomal recessive
Onset childhood and adolescence
Symptoms
- Exercise intolerance
- Painful muscle cramps
Myoglobinuria-preceded by: (myoglobin is a muscle protein that carries oxygen) increase in myoglobin in the urine, damage of the muscle would lead to myoglobin in the blood and then into the urine
rhabdomyolysis
“Dissolution of skeletal muscle”
Damage skeletal muscle cells will leak myoglobin into the plasma
Myoglobin in plasma filtered at the glomerulus and cause an orange and brown color
- Nephrotoxicity
- Tubular obstruction
Myoglobinuria must be distinguished from hematuria (the urine contains no RBC in myoglobinuria- but it might look like blood) and hemoglobinuria
Pathophysiology
- The damage muscle cells release large amounts of K+ into the extracellular fluid causing hyperkalemia
- Acute renal failure
- Severe muscle damage is frequently accompanied by a reduction in blood volume
- Third spacing
- Fluid sequestration in damaged tissue
- Dehydration
- Decreased blood flow to kidneys
disorders of neuromuscular transmission
neurogenic disorders
ex: myasthenia gravis
myasthenia gravis
Failure of neuromuscular transmission
Etiology: blockage and destruction of acetylcholine receptors by autoantibody
Organ-specific autoimmune disease
MG is characterized by muscle weakness that is typically aggravated by repeated contraction
Autoimmune disease in which antibodies are made against acetylcholine
- Antagonist to receptor
- Also leads to damage by immune system
May affect any skeletal muscle
Muscle with the smallest motor units are affected first
- Ocular muscles
Sometimes progress to facial muscles, limb, respiratory
- Facial expression
- Swallowing
- Drooling
- Speech impairment
- Generalized weakness
diagnostic testing of MG
Tensilon test (edrophonium challenge) = will increase muscle strength
EMG - decrease in amplitude of muscle action potentials when muscle is subjected to repeated voluntary contraction
Serum assay for anti-Ach receptor antibody
MG treatment
Immunosuppressives, cholinesterase inhibitors
Thymectomy
prognosis = normal life expectnacy
rhabdomyoma
very rare, benign tumor of striated muscle
rhabdomyosarcoma
Rare malignant tumor of striated muscle
Occurs anywhere
- More common in head, neck, and genitourinary tract
More common in children
- Most common soft tissue sarcoma in children
- May occur superficial or deep
failure of muscle
paralysis
- may be focal or widespread
types: flaccid and spastic
-Limb involvement
Quadriplegia (tetraplegia) above 1st thoracic
Paraplegia = below 1st thoracic
Hemiplegia - one side - paralysis
Hemiparesis - weakness on the left or ride side
flaccid paralysis
reduced muscle tone, typically lower motor neuron
spastic paralysis
hypertonia, nerves hyperirritable, uncoordinated movement
