Skeletal Muscle Physiology Q1

skeletal muscle functions

body movement, posture, protection and support, regulate elimination, produce heat

skeletal muscle characteristics

excitability (response to stimuli), conductivity (propagate electrical signal during action potential), contractility (contract and move), extensibility (stretch muscle), elasticity (return to original length)

why is skeletal muscle an organ?

it contains muscle fiber, connective tissue, blood vessels, and nerves

bundles of muscle tissue

muscle fibers → fascicle → muscle tissue

epimysium

connective tissue ensheathing the entire muscle

perimysium

connective tissue surrounding each fascicle

endomysium

thin connective tissue investing each muscle cell (in fascicle)

aponeurosis

thin, flattened sheet of dense regular connective tissue that attaches muscles to other muscles, cartilage, or bones

blood vessels and nerves in skeletal muscle

voluntary movement, vascularized, innervated by motor neurons

neuromuscular junction

gap between fiber and neuron, specific location where muscle fiber is innervated, has the synaptic knob, motor end plate, and synaptic cleft

myofibrils

compose the muscle fiber, composed of myofilaments bundles enclosed by sarcoplasmic reticulum

myofilaments

actin (thin, 2 regulatory proteins are tropomyosin and troponin) and myosin (2 strands and a globular head that contains actin bonding site and site for changing ATP → ADP + P)

sarcolemma (plasma membrane)

connected to sarcoplasmic reticulum by T-tubules which contain voltage regulated Na+ and K+ channels)

sarcomere

microscopic repeating units of myofilaments within myofibrils, there are Z discs at both ends of the sarcomere, anchor actin filaments)

I bands

extend in both directions from Z discs, contain only actin filaments, lighter band

A band

central region sarcomere that contains entire myosin filament, overlaps with actin, does not change in length during contraction, darker band

H zone

most central portion A band, only thick filaments here

M line

myosin attaches here

motor unit

a single motor neuron and muscle fibers it controls, inverse relationship between the size of a motor unit and control