chap 22 - skeletal muscle

Question 1

structure and function

Answer 1

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

Question 2

type I

Answer 2

slow twitch, sustained actions of movement
- utilizes oxidative phosphorylation

Question 3

type II

Answer 3

fast twitch, white, more explosive motions
- utilizes glycolysis

Question 4

most frequent and serious problems

Answer 4

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

Question 5

muscle strain

Answer 5

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

Question 6

symptoms, signs, and tests

Answer 6

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

Question 7

classifications of muscle disorders

Answer 7

myopathic and nuerogenic

Question 8

signs and symptoms of myopathic muscle disorder

Answer 8

proximal wekaness, possible pain

Question 9

signs and symptoms of neurogenic muscle disorders

Answer 9

distal weakness, often in nerve distributions, possible sensory loss

Question 10

electromyography in myopathic muscle disorders

Answer 10

asynchronous spontaneous activity

Question 11

electromyography in neurogenic muscle disorders

Answer 11

synchronous activity of small amplitude

Question 12

serum enzyme (creatine kinase) in myopathic disorders

Answer 12

often markedly elevated

Question 13

serum enzyme (creatine kinase) in neurogenic disorders

Answer 13

normal or slightly elevated

Question 14

biopsy in myopathic muscle disorders

Answer 14

variable size of fibers; degenerative fibers; possible fibrosis; possible inflammation

Question 15

biopsy of neurogenic muscle disorders

Answer 15

atrophic fibers in small groups

Question 16

myopathy

Answer 16

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

Question 17

acquired myopathy

Answer 17

infections, inflammation, endocrine/metabolic, alcohol

Question 18

herditary/genetic myopathy

Answer 18

mutations or deletions of genes coding for parts of a muscle (proteins, mitochondrial enzymes, sarcoplasmic reticulum)

Question 19

genetic/developmental diseases

Answer 19

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

Question 20

duchenne muscular dystrophy

Answer 20

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

Question 21

inflammatory degenerative diseases

Answer 21

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

Question 22

chronic inflammatory myopathy

Answer 22

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

Question 23

metabolic myopathy

Answer 23

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

Question 24

rhabdomyolysis

Answer 24

“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

Question 25

disorders of neuromuscular transmission

Answer 25

neurogenic disorders
ex: myasthenia gravis

Question 26

myasthenia gravis

Answer 26

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

Question 27

diagnostic testing of MG

Answer 27

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

Question 28

MG treatment

Answer 28

Immunosuppressives, cholinesterase inhibitors
Thymectomy
prognosis = normal life expectnacy

Question 29

rhabdomyoma

Answer 29

very rare, benign tumor of striated muscle

Question 30

rhabdomyosarcoma

Answer 30

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

Question 31

failure of muscle

Answer 31

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

Question 32

flaccid paralysis

Answer 32

reduced muscle tone, typically lower motor neuron

Question 33

spastic paralysis

Answer 33

hypertonia, nerves hyperirritable, uncoordinated movement