Usmle Muscle Tissue Histology

Front 1

differentiate between skeletal, cardiac, and smooth muscle on gross microscopy?

Back 1

Skeletal muscle and cardiac muscle are striated, but skeletal muscles do NOT branch, while cardiac muscle branches extensively. Both have peripheral nuclei.
Smooth muscle is not striated and has central nuclei

Front 2

which elements shorten and do not shorten during muscular contraction, and what does this represent?

Back 2

A Band: does not change, because it represents the myosin filament.
I Band: Shortens because it represents the non overlapping portion of the F-actin filament, during contraction less becomes non-overlapping as it cross-bridges with the myosin filament.
H band shortens it is the space between extendending myosin filaments

Front 3

what is the role of tropomyosin in resting muscle?

Back 3

prevents actin cross linking

Front 4

what is the interaction between Ca2+ and troponin?

Back 4

when troponin binds Ca+, tropomyosin is displaced, exposing the myosin binding site on the actin molecule.

Front 5

What does the binding of ATP t myosin crossbridge site do?

Back 5

causes loss of affinity for actin, and disociation of cx bridge.
SUbsequent hydrolysis of ATP yields actin to bind to myosin, but no cx linking.

Front 6

what is the primary innervation/conductive difference b/w skeletal and other muscle.

Back 6

in Sk musc. each fiber is innervated, and there is no interfiber conduction.
Other muscle conducts ions between muscle cells.

Front 7

what is the ionic movement responsible for the action potential depolarization/upstroke of all muscle cells?

Back 7

Na+ inflow ... the only pseduo exception is that Ca+ inflow causes depolarization of the SA node, which is truly conductive tissue not muscle tissue.

Front 8

which muscle fibers show an action potential plateau

Back 8

only cardiac muscle fibers (not SA node)

Front 9

what is are the mechanisms of excitation-contraction coupling in smooth muscle?

Back 9

An AP can open a VOLTAGE gated Ca+ channel on the sarcolemma or
Hormones/NTs can open IP3-gated Ca+ channels from SR

Front 10

What is unique about the calcium binding location in Smooth muscle?

Back 10

Ca+ binds to calmodulin, as opposed to troponin, in the smooth muscle.

Front 11

what role do T-tubules play in muscle contraction?

Back 11

when the membrane depolarizes, the T-tubules which are membrane invaginations allow rapid spread of the AP throughout the cell, and open voltage gated Ca+ channels allowing EC Ca+ into the cell triggering a much larger intracellular SR Ca+ release which causes excitation coupling.

Front 12

where does the Ca of contraction in skeletal muscles come from?

Back 12

The SR

Front 13

what are the SK muscle triads and what is their significance?

Back 13

this is the association of T-Tubules and the SR allowing membrane depolarization to trigger Ca rls from the SR

Front 14

what happens during sk muscle relaxtion, and what causes it?

Back 14

muscle relaxation is caused by a reduction in intracellular Ca caused by ATP dependant pumps on the SR which pump cytosolic Ca back into SR.

Front 15

what muscle type has intercalated discs, why, and what functional purpose do they serve??

Back 15

only cardiac muscle has IC junctions, which are a combo of gap and adherens junctions, they spread mechanical distortion and electrical signal, allowing coordinated/unified conractile movements which are unique to cardiac muscle

Front 16

what is the significance of the lack of striations in smooth muscle?

Back 16

striations are caused by sarcomeres /Z-lines, instead the actin filaments are longitidinal in orientation and adhere to cell membrane in many locations, not just the ends, called dense bodies, allowing greater contraction shortening.

Front 17

what three proteins compose a thin filament?

Back 17

actin, tropomyosin, and troponin.

Front 18

significance of vimentin?

Back 18

in all messenchymal contractile cells, in vasc smooth muscle but not gastro, used to identify sarcomas/messenchyal cell tumours