C12 - Skeletal Muscle Phys

skeletal muscle is under (voluntary/involuntary) control

voluntary

what causes skeletal muscle striation?

organized arrangement of actin and myosin (striations when viewed under microscope)

point of muscle attachment closest to the spine (proximal)

origin

point of muscle attachment on the far side of the joint (distal)

insertion

tendons

connective tissue at the end of muscle where points of attachment occur

what two muscles are on either side of a joint?

flexors and extensors

muscle fibers

skeletal muscle cells

endomysium

connective tissue layer surrounding muscle fibers

fascicles

grouped muscle fibers

perimysium

connective tissue layer surrounding fascicles, contains blood vessels and nerves

epimysium

connective tissue surrounding muscle

muscle

bundle of fascicles

tendon

grouping of connective tissue layers, joins muscle to skeleton

myotendinous junction

region of tendon where muscle fiber ends transmit force of contraction to tendon to effect skeletal movement

what are muscle connective tissues made of

elastin and collagen

myofibril

filaments running along axis of skeletal muscle cells

Z lines

two dark bands marking end of sarcomere (2 um)

I band

light bands on either side of Z line, contains thin actin filaments

A band

area between two I bands, contains thick myosin filaments

H band

light area in center of sarcomere, where no thick-thin overlap is

M line

center of sarcomere, contains proteins critical for organization and alignment

T tubules

invaginations of sarcolemma passing into fibers near A bands

(T tubules / SR) are in contact with extracellular space

T tubules

terminal cisternae

portion of SR nearest T tubules, site of Ca release

SERCA

Ca pump reuptake protein

thin filament structure

two stranded helical F-actin made of G-actin molecule aggregates, length regulated by cytoskeletal protein nebulin

tropomyosin structure and function

cover myosin-binding sites, dimers consisting of T, I, C subunit complex

tropomodulin function and location

end of thin filament, sets length

what proteins anchor thin filament to Z line?

CapZ and a-actinin

what protein contribute to thick filament structure?

titin, myomesin, and C protein

in what directions is contraction force transmitted?

longitudinally via tendon (myotendinous junction)

laterally to adjacent extracellular connective tissue (costameres)

costameres

sub-membranous, Z-line associated structures that transmit force and stabolize sarcolemma

dystrophin function and associated disease

maintains sarcolemma structure via dystrophin-glycoprotein complex connection to ECM

X-linked recessive deficiency results in Duchenne’s muscular dystrophy

what are some types of muscle dystrophy and their associated defects?

limb-girdle muscular dystrophy 2B - defect in sarcolemma repair and dysferlin

limb-girdle muscular dystrophy 2 and tibial muscular dystrophy - defects in titin

limb-girdle muscular dystrophy 2A - defects in calpain 3 protease

thick filament structure organized by heavy and light chains

2 heavy chains - backbone and N-term globular head

4 light chains - connecting heavy chain regions

essential vs regulatory light chains in myosin

essential - crucial for ATPase activity

regulatory - influences myson-actin interaction when phosphorylated

a motor neuron

innervates skeletal muscle

how does brain input get to muscles?

transmission to a motor neuronal cell body in ventral horn, transmission through ventral root

motor unit

motor nerve and all muscle fibers in innervates, functional contractile unit

how is fine motor control initiated?

activation of motor units with a small number of fibers

end plate

neuromuscular junction formed by motor neuron

tetany

increasing tension by repetitive stimulation of the muscle