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Flashcards in Musculoskeletal UWorld Deck (84)
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Which sarcomere bands remain the same and which change over the course of muscle contraction?

The A-band (myosin filaments) stays the same.
The H-band (area where myosin does not overlap actin) and I-band (area where actin does not overlap myosin) decrease during contraction. "An Interesting Zoo Must Have Mammals" = Actin in the I-band attaches to the Z-line. Myosin in the H-band attaches to the M-line.



Probability a diseased person will test positive

TP / (TP + FN)



Probability a non-diseased person will test negative

TN / (TN + FP)


Positive predictive value

Probability disease is present given a positive result

TP / (TP +FP)
*affected by prevalence and pre-test probability


Negative predictive value

Probability disease is absent given a negative result

TN / (TN + FN)
*affected by prevalence and pre-test probability


Positive likelihood ratio

Likelihood of having the disease given a positive result

Sensitivity / (1 - Specificity)


Negative likelihood ratio

Likelihood of not having the disease given a negative result

(1 - Specificity) / Sensitivity


A child is born with flaccid leg paralysis, dorsiflexed foot contractures and urinary incontinence. Physical exam reveals anal atresia. What condition did the mother likely have during pregnancy?

Poorly controlled maternal diabetes can result in caudal regression syndrome.


Sensorimotor innervation of the peroneal nerve

Superficial: sensation to dorsum of foot and innervation to lateral compartment (eversion)

Deep: sensation to 1st webbed space and motor to anterior compartment (dorsiflexion)


Numbness/pain on sole of foot vs medial foot.

Sole = tarsal tunnel compression of tibial nerve.
Medial foot = compression of saphenous nerve


HLA class II antigens

DR, DP and DQ


Rotator cuff muscle origins, insertions, innervation and function

Supraspinatus: originates at supraspinous fossa, inserts at greater tuberosity, innervated by suprascapular nerve, abducts arm.

Infraspinatous: originates at infraspinous fossa, inserts at greater tuberosity, innervated by suprascapular nerve, externally rotates arm.

Teres minor: originates at lateral border of scapula, inserts at greater tuberosity, innervated by axillary nerve, externally rotates arm.

Subscapularis: originates at sub scapular fossa, inserts at lesser tuberosity, innervated by upper and lower subscapular nerves, adducts and internally rotates arm.


Function of free ribosomes

Synthesis of proteins in the cytosol, nucleosol, peroxisome matrix and nuclear-encoded mitochondrial proteins.


Function of rER ribosomes

Synthesis of secretory proteins, membrane proteins and proteins within the rER, golgi and lysosomes.


How do ribosomes end up on the rER?

The 60S subunit binds translocon on the rER.


In which organelle does steroid hormone synthesis take place?



What is responsible for skin wrinkling as people age?

Reduced collagen fibril production leads to a net decrease in dermal collagen


What histones make up the nucleosome core?

H2A, H2B, H3 and H4. H1 is located outside of the core and binds to DNA of adjacent nucleosomes, resulting in more efficient DNA packing.


Epigenetic process involved in genomic imprinting

DNA methylation by DNA methyltransferases


B. anthracis toxins

Edema factor: acts as adenylate cyclase, increases cAMP, increasing edema and causing phagocyte dysfunction.

Lethal factor: zinc-dependent protease that inhibits MAP-K signaling, resulting in apoptosis

Protective antigen: gets LF and EF intracellular


B. pertussis toxins

Pertussis toxin: Gi ribosylation results in disinhibition of adenylate cyclase -> increased cAMP, edema and phagocyte dysfunction.

Adenylate cyclase toxin: functions as adenylate cyclase, increasing cAMP, edema and phagocyte dysfunction.


C. botulinum toxin

Blocks pre-synaptic release of ACh


C. difficile toxin

A: recruits and activates PMNs

B: induces actin depolymerization leading to cell death, necrosis and pseudomembrane formation.


S. dysenteriae toxin

Shiga toxin: disables 60S subunit, reducing protein synthesis and inducing cell death


S. pyogenes toxins

Pyrogenic exotoxin: superantigen, scarlet fever

Streptolysin O & S: damages erythrocyte membranes


Viral DNA/RNA recombination mechanism

Genetic exchange via crossing over on homologous regions


Viral DNA/RNA reassortment mechanism

2 segmented viruses exchange whole genome segments ("BOAR": bunyavirus, orthomyxovirus, arenavirus, reovirus"


Viral phenotypic mixing mechanism

Co-infection of a host cell and incorporation into DNA results in a capsid from one virus and genome from the other virus


Why is there reduced complement levels in patients with SLE?

Immune-complex deposition results in complement activation.


What determines to natural progression of leprosy in patients infected by M. leprae?

Tuberculoid: least severe, skin hypopigmentation, plaques and decreased sensation due to intact cell-mediated immune response (Th1)

Lepromatous: most severe, weak cell mediated response (Th2) results in disseminated disease,