Skeletal/smooth muscle phys

Question 1

differentiate myofibril, myofiber, myofilament

Answer 1

myofiber= biggest, same as the muscle cell/fiber

myofibril= unit w/i myofiber made up of actin and myosin myofilaments

Question 2

sarcomere

Answer 2

functional unit of the myofiber, demarcated by Z line- contains overlapping thick and thin myofilaments

Question 3

myofiber triad

Answer 3

T tubule w/ SR terminal cisternae on either side, for Ca++ release

Question 4

NMJ

Answer 4

synapse b/w somatic motor neuron and skeletal muscle fiber

Question 5

motor unit

Answer 5

all muscle fibers innervated by one motor neuron (each fiber innervated by only one neuron, one neuron can innervate multiple fibers)

Question 6

motor endplate

Answer 6

post synaptic region of skeletal muscle cell

Question 7

endplate response to ACh from somatic motor neuron

Answer 7

nicotinic ACh receptors open to Na and K, graded EPP produced and initiates AP w/ voltage gated Na channels in sarcolemma

Question 8

location of ACh receptors on endplate

Answer 8

top of junctional folds

Question 9

location of voltage gated Na channels on endplate

Answer 9

bottom of junctional folds and on longitudinal sarcolemmal surface

Question 10

muscle triad response to muscle AP at end plate

Answer 10

depolarization down into T-tubules, opens DHP/L-type Ca++ channels which mechanically opens ryanodine receptors on SR, Ca++ moves into cytosol from SR and binds troponin

Question 11

how is Ca++ release from SR different in skeletal muscle?

Answer 11

single AP enough to bind all troponin, maximize cross bridging

SR directly linked to T tubules

Question 12

SERCA

Answer 12

SR Ca++ ATPase- lowers cytosolic Ca++ by bringing it into SR, facillitates relaxation

Question 13

major histological differences w/ smooth

Answer 13

spindle shaped, myofilaments arranged diagonally (reason for no striations), no Z bands, contraction causes ballooning outward (for shrinking a lumen)

Question 14

vascular smooth muscle regulation

Answer 14

does not fire APs, under involuntary control (hormones, NTs)

Question 15

mutiunit smooth muscle

Answer 15

not much electrical coupling b/w cells, fine motor control w/ independent contraction (eg iris)

Question 16

single unit smooth muscle

Answer 16

extensive electrical coupling, coordinated contraction as in visceral organ lining

Question 17

walk thru steps of smooth muscle contraction beginning w/ Ca++ release from SR

Answer 17

• Ca++ binds calmodulin
• Ca-Calmodulin activates Myosin light chain kinase
• MLCK phosphorylates MLC= contraction

Question 18

role of MLC phosphatase

Answer 18

dephosphorylates MLC, causing relaxation of smooth muscle

active constitutively

Question 19

characteristics of smooth muscle contraction compared w/ skeletal

Answer 19

slow and energy effecient compared to skeletal muscle, can be graded contraction dependent on Ca++

Question 20

synthesis of NO

Answer 20

NO synthase w/ NADPH and L-Arginine, occurs in endothelial cells

Question 21

fn of NO

Answer 21

potent vasodilator: stimulates cGMP production in smooth muscle which activatetes Protein kinase G– more reuptake of cytosolic Ca++ and opening of K+ channels

less Ca++ and MLCK activity= relaxtion