Skeletal and Muscle Systems Part 3 Flashcards
Sprain V Strain
A sprain is a stretch and/or tear of a ligament (a band of fibrous tissue that connects two or more bones at a joint). One or more ligaments can be injured at the same time. The severity of the injury will depend on the extent of injury (whether a tear is partial or complete) and the number of ligaments involved.
A strain is an injury to either a muscle or a tendon (fibrous cords of tissue that connect muscle to bone). Depending on the severity of the injury, a strain may be a simple overstretch of the muscle or tendon, or it can result from a partial or complete tear.
Structure of Skeletal Muscle
-CONNECTIVE TISSUE COVERINGS Fascia epimysium perimysium (separate fibers into fascicles) endomysium (individual muscle fibers) -TENDONS
Skeletal Muscle Fibers
-single cell!!!!!!
-cell membrane = sarcolemma
-cytoplasm = sarcoplasm
-myofibrils (filament proteins)
1) actin
-2 proteins associated - troponin , tropomyosin
2) myosin
3) sarcomere-repeating units of actin/myosin
-organelles
sarcoplasmic reticulum (like ER)
Ca transport to sarcomere
transverse tubules
Motor Unit
- Motor neuron in brain or spinal cord
- Somatic Neuron (axon)
- Synapse (NMJ)
- Skeletal Muscle fibers that are innervated
Neuromuscular Junction (NMJ):
Synapse of the somatic neuron (axon) to Skeletal muscle fiber
neurotransmitter –Acetylcholine (Ach)
Action potential - motor end plate potential
ACh causes the muscle fiber to conduct an impulse over the surface of the fiber that reaches deep within the fiber by means of transverse tubules.
Alterations in Muscles
General Terms
Weakness
- Loss of strength in one of more muscle groups
- primary or secondary
Cramps (Spasms):
-involuntary contractions
-skeletal
-idiopathic, disease motor, -metabolic, electrolytes
low glucose, K, Na, -dehydration
Injury
trauma to tissue
Twitches
Spontaneous discharge of motor units and single muscle fibers
Fasiculations:
- spontaneous discharge of single motor unit
- dimple or twitch of skin
- rhythmic, start/stop
- Hypersensitivity to Ach?
Fibrillations
- involuntary contraction single muscle fibers
- not visible
- e.g.- cardiac
Tetany
- spasmodic contraction
- hypocalcemia, hypomagnesemia
Myoclonus
- sudden unexpected contraction of single muscle group limbs or trunk
- e.g. night jerks, CNS disease
Myotonia
-sustained involuntary contraction of a group of muscles
Tics
- sudden and behavior related repetitive motions
- e.g.- tourettes syndrome
Hypertrophy v Atrophy
- can you recall this from basic pathophysiology
Atrophy
-non specific
-abnormally small muscle fibers
-causes:
neurogenic
disuse
glucocorticoids
Endogenous hypercortisolism (cushings disease)
myopathies
Pathological Process of Skeletal Muscles
See below
Skeletal Muscle Disorder Categories
- Neurogenic changes or myofiber atrophy
- Muscular Dystrophies
- Congenital, toxic, or infectious myopathies
- Neuromuscular junction
Muscular Dystrophies
- genetic
- progressive degeneration of muscle fibers
- progressive weakness of voluntary muscles
- progressive wasting (muscle fiber atrophy)
- Muscle fibers can be replaced by fibrofatty tissue
- ——–Key distinction between dystrophies and myopathies
- 2 common forms that a X-linked (same gene in both)
- Duchenne Muscular Dystrophy (DMD)
most severe and most common
-Becker Muscular Dystrophy
Morphology of DMD and BMD:
● variation muscle fiber size ● degenerative changes- splitting or necrosis ● regenerative changes ● Increased connective tissue ● Abnormal staining for dystrophin ● fat tissue
Pathogenesis (note the term!) of DMD and BMD:
● abnormalities of dystrophin gene on short arm X chromosome (Xp21)
● What is the role of dystrophin?
Muscles, brain, peripheral nerves
Attaches portions of sarcomere to cell membrane
Maintains structure and function
Transfer force of contraction to connective tissue
● What is the dystrophin defect?
Missing in DMD!
Diminished in BMB
Clinical Presentation of DMD:
●1 of 3500 live male births
●evident by 5 yrs
●wheelchair dependent by 10-12 yrs
●Death by early 20’s
● Initial clumsiness
● developmental motor skill delays
● Weakness in pelvic girdle then progress to shoulder girdle
● Pseudohypertropy of calf muscle (big, but weak)
● Heart (failure or arrhythmias)
● Cognitive impairment
● Death respiratory insufficiency, pulmonary infection, cardiac decompensation
Clinical Presentation of BMD:
● onset later childhood or early adolescence
● slower and variable progression rate
● Normal life span possible
Autosomal Muscular Dystrophies:
● Several types, some of which affect specific muscle groups
Limb girdle muscular dystrophies
● Muscle weakness
● Inherited on autosomal genes
● 4 types due to mutations of sarcolgycan complex of proteins
● other types due to mutations of cytoskeletal proteins
● other types due to mutations of caveolin
Myotonic Dystrophy
● Inherited autosomal
● Extra CTG trinucleotide repeats on Chromosome 19 that affects the mRNA for the dystrophila myotonia-protein kinase. This leads to increase amount of protein.
● presents late in childhood
● Gait abnormalities due to weakness in foot dorsiflexors
● progress to weakness of intrinsic muscles of hands and wrist extensors
● atrophy of facial muscles with ptosis (droopy eyelids)
Myopathy : Congenital myopathies
Congenital Myopathies
● Inherited mutations of ion channels (Channelopathies)
● Inborn errors of metabolism
● Mitochondrial myopathies
Inherited mutations of ion channels (channelopathies):
- Hyperkalemic periodic paralysis
mutation in skeletal muscle sodium channel gene
myotonia and/orrelapsing episodes of hypotonic paralysis - Malignant hyperthermia
mutation in calcium channel gene
Rare
Dramatic hypermetabolic state triggered by anesthesia
Tachycardia, tachypnea, muscle spasms, hyperpyrexia
Inborn errors of metabolism
-disorders of glycogen -synthesis and degradation
disorders of lipid handling
Mitochondrial Myopathies
- mutations in mitochondrial or nuclear DNA that code for mitochondrial constituents
- mito. ATP required for muscle contraction
- Young adulthood
- Proximal weakness
- Some neurologic symptoms, lactic acidosis, cardiomyopathy
Toxic Myopathies
● Intrinsic - Thyrotoxic myopathy acute or chronic proximal muscle weakness ● Extrinsic - Alcohol - Drugs (e.g. Statins) rhabdomylosis pain, myocyte swelling, necrosis, myophagocytosis, regeneration
Inflammatory Myopathies:
- Polymyositis and Dermatomyositis
- –autoimmune or viral
- –rare inflammatory
Disorders of NMJ:
See below
Myasthenia Gravis
Pathogenesis -autoimmune -Antibodies to NMJ Ach receptors loss of receptors -block Ach binding
Clinical features:
- females more likely
- Initial weakness extraocular muscles
- ptosis
- diplodia (double vision)-Generalized muscle weakness
- fluctuations
- variable- course of days, hours, minutes
- electrophysiologic stimulation leads to weakness
- Anticholinesterase drugs improve function
- NO Sensory and autonomic dysfunction
- Due to various treatments, 95% patients live
Lambert-Eaton Myasthenic Syndrome:
- Paraneoplastic syndrome such as with small-cell lung carcinoma
- muscle weakness
- Not improved by increasing Ach at NMJ
- DOES affect autonomic function
- electrophysiologic stimulation increases strength
- Antibodies to presynaptic calcium channels
Describe Rhabdomyolysis:
also called myoglobinuria
- based on McCance pages 1547-1550
