chapter 9 part C

Smooth muscle has less elaborate what?

SR, and no T tubules

what is less developed than in skeletal muscle?

SR

SR does store intracellular Ca2+, but what?

most calcium used for contraction has extracellular origins

Sarcolemma contains pouchlike infoldings called

caveolae

Caveolae contain numerous Ca2+ channels that open to allow what?

rapid influx of extracellular Ca2+

Smooth muscle fibers are usually electrically connected via what?

gap junctions

gap junctions

microscopic tubes that connect one cytoplasm to another

smooth muscles

Thick filaments are fewer and have myosin heads along entire length

there is no what in smooth muscle?

No troponin complex

Calcium binds to a protein called?

calmodulin

Thick and thin filaments arranged diagonally

Myofilaments are spirally arranged, causing smooth muscle to contract in corkscrew manner

Intermediate filament–dense body network

Contain lattice-like arrangement of non contractile intermediate filaments that
resist tension

the first way smooth muscle is similar to skeletal muscle contraction is

Actin and myosin interact by sliding filament mechanism

the second way smooth muscle is similar to skeletal muscle contraction is

Final trigger is increased intracellular Ca2+ level

the third way smooth muscle is similar to skeletal muscle contraction is

ATP energizes sliding process

the fourth way smooth muscle is similar to skeletal muscle contraction is

Contraction stops when Ca2+ is no longer available

calcium does not bind to troponin in smooth muscle but binds to

calmodulin

Activated calmodulin then activates

myosin kinase (myosin light chain kinase)

Activated myosin kinase phosphorylates activates what?

myosin head

Relaxation requires

Ca2+ detachment from calmodulin, Active transport of Ca2+ into SR and extracellularly, Dephosphorylation of myosin to inactive myosin

Regulation of contraction

Controlled by nerves, hormones, or local chemical changes

Neural regulation

Neurotransmitter binding causes either graded (local) potential or action
potential

Smooth muscle varies in different organs by

Fiber arrangement and organization, Innervation, Responsiveness to various stimuli

All smooth muscle is categorized as either

Unitary and Multiunit

sarcopenia

loss of muscle mass

step 1 of smooth muscle contraction

calcium ions enter the cytosol from the ECF via voltage- gated or non voltage gated Ca2+ channels or from the scant SR

step 2 of smooth muscle contraction

Ca2+ binds to and activates calmodulin

step 3 of smooth muscle contraction

activated calmodulin activates the myosin light chain kinase enzymes

step 4 of smooth muscle contraction

the activated kinase enzymes catalyze transfer of phosphate to myosin activating the myosin ATPases

step 5 of smooth muscle contraction

activated myosin forms cross bridges with actin of the thin filaments. shortening begins