Skeletal and Muscle Systems Part 3

Question 1

Sprain V Strain

Answer 1

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.

Question 2

Structure of Skeletal Muscle

Answer 2

-CONNECTIVE TISSUE COVERINGS
Fascia
epimysium
perimysium (separate fibers into fascicles)
endomysium (individual muscle fibers)
-TENDONS

Question 3

Skeletal Muscle Fibers

Answer 3

-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

Question 4

Motor Unit

Answer 4

• Motor neuron in brain or spinal cord
• Somatic Neuron (axon)
• Synapse (NMJ)
• Skeletal Muscle fibers that are innervated

Question 5

Neuromuscular Junction (NMJ):

Answer 5

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.

Question 6

Alterations in Muscles

Answer 6

General Terms

Question 7

Weakness

Answer 7

• Loss of strength in one of more muscle groups

- primary or secondary

Question 8

Cramps (Spasms):

Answer 8

-involuntary contractions
-skeletal
-idiopathic, disease motor, -metabolic, electrolytes
low glucose, K, Na, -dehydration

Question 9

Injury

Answer 9

trauma to tissue

Question 10

Twitches

Answer 10

Spontaneous discharge of motor units and single muscle fibers

Question 11

Fasiculations:

Answer 11

• spontaneous discharge of single motor unit
• dimple or twitch of skin
• rhythmic, start/stop
• Hypersensitivity to Ach?

Question 12

Fibrillations

Answer 12

• involuntary contraction single muscle fibers
• not visible
• e.g.- cardiac

Question 13

Tetany

Answer 13

• spasmodic contraction

- hypocalcemia, hypomagnesemia

Question 14

Myoclonus

Answer 14

• sudden unexpected contraction of single muscle group limbs or trunk
• e.g. night jerks, CNS disease

Question 15

Myotonia

Answer 15

-sustained involuntary contraction of a group of muscles

Question 16

Tics

Answer 16

• sudden and behavior related repetitive motions

- e.g.- tourettes syndrome

Question 17

Hypertrophy v Atrophy

Answer 17

• can you recall this from basic pathophysiology

Question 18

Atrophy

Answer 18

-non specific
-abnormally small muscle fibers
-causes:
neurogenic
disuse
glucocorticoids
Endogenous hypercortisolism (cushings disease)
myopathies

Question 19

Pathological Process of Skeletal Muscles

Answer 19

See below

Question 20

Skeletal Muscle Disorder Categories

Answer 20

1. Neurogenic changes or myofiber atrophy
2. Muscular Dystrophies
3. Congenital, toxic, or infectious myopathies
4. Neuromuscular junction

Question 21

Muscular Dystrophies

Answer 21

• 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

Question 22

• 2 common forms that a X-linked (same gene in both)

Answer 22

• Duchenne Muscular Dystrophy (DMD)
  most severe and most common
  -Becker Muscular Dystrophy

Question 23

Morphology of DMD and BMD:

Answer 23

● variation muscle fiber size
● degenerative changes- splitting or necrosis
● regenerative changes
● Increased connective tissue
● Abnormal staining for dystrophin
● fat tissue

Question 24

Pathogenesis (note the term!) of DMD and BMD:

Answer 24

● 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

Question 25

Clinical Presentation of DMD:

Answer 25

●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

Question 26

Clinical Presentation of BMD:

Answer 26

● onset later childhood or early adolescence ● slower and variable progression rate ● Normal life span possible

Question 27

Autosomal Muscular Dystrophies:

Answer 27

● 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

Question 28

Myotonic Dystrophy

Answer 28

● 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)

Question 29

Myopathy : Congenital myopathies

Answer 29

Congenital Myopathies ● Inherited mutations of ion channels (Channelopathies) ● Inborn errors of metabolism ● Mitochondrial myopathies

Question 30

Inherited mutations of ion channels (channelopathies):

Answer 30

- 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

Question 31

Inborn errors of metabolism

Answer 31

-disorders of glycogen -synthesis and degradation | disorders of lipid handling

Question 32

Mitochondrial Myopathies

Answer 32

- 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

Question 33

Toxic Myopathies

Answer 33

``` ● Intrinsic - Thyrotoxic myopathy acute or chronic proximal muscle weakness ● Extrinsic - Alcohol - Drugs (e.g. Statins) rhabdomylosis pain, myocyte swelling, necrosis, myophagocytosis, regeneration ```

Question 34

Inflammatory Myopathies:

Answer 34

- Polymyositis and Dermatomyositis - --autoimmune or viral - --rare inflammatory

Question 35

Disorders of NMJ:

Answer 35

See below

Question 36

Myasthenia Gravis

Answer 36

``` Pathogenesis -autoimmune -Antibodies to NMJ Ach receptors loss of receptors -block Ach binding ```

Question 37

Clinical features:

Answer 37

- 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

Question 38

Lambert-Eaton Myasthenic Syndrome:

Answer 38

- 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

Question 39

Describe Rhabdomyolysis: | also called myoglobinuria

Answer 39

- based on McCance pages 1547-1550