Skeletal Muscle

Created by danyell2489 

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Connective Tissue Layers

Sheets that hold the muscle fibers (cells) together

Epimysium

Outermost layer; surrounds the entire muscle

Perimysium

Surrounds individual bundles of muscle fibers called fasicles

Endomysium

Surrounds individual muscle fibers or cells

Cell

Thin, long cylinder that generally extends the length of the muscle

Sarcolemma

Muscle cell membrane; selective membrane transport (active & passive)

Sarcoplasm

"fluid part"- cytoplasm of the msucle cell; contains cellular proteins, myofibrils, enzymes, nuclei, organelles, glycogen, & myoglobin

Myofibrils

Numberous threadlike structures that contain the contractile proteins (myofilaments)

Sarcoplasmic Reticulum

System of interconnected tubules surrounding each myofibril like a mesh sleeve

Longitudinal Tubules

Run parallel to myofibrils & surround them

Terminal Cristernae

(lateral sacs); terminations of the longitudinal that hold calcium; major storage cite of calcium: 10,000x's [cytoplams]

Transverse Tubules

Invagination of the surface membrane "dipping" into the muscle between 2 terminal cristernae

Sarcomere

Basic functional unit of the muscle cell; individual segment-subdivision of the myofibrial

A-Band

Dark colored band due to thick protein myosin and overlap thick & thin filaments; remains the same

H-Zone

Lighter Area of A-Band with only myosin; gets shorter may disappear

M-Line

Dark line in the center of the H-Zone, hold filaments in place

I-Band

Light colored band that contains only actin, thin filament; shortens

Z-Line

Boundary of sarcomere, point of attachment of the actin filaments, covers portions of 2 sarcomeres; pulls closer togehter so sarcomere shortens

Neuromuscular Junction

Communication site between alpha motor neuron & muscle cell; at this junction, the sarcolemma forms a pocket (motor end plate)

Neuromuscular Cleft

Gap between the motor neuron & muscle cell

Actin

Thin filament; composed of tropomyosin & troponin

Myosin

Thick filament; contains enzyme ATPase

Troponin

3 subunit structure that fastens down the ends of tropomyosin holding it in place

Tropomyosin

Thread-like protein that lies in the groove of the actin spiral

Sliding Filament Theory

A muscle shortens or lengthens because the thick & thin filaments slide past each other without the filaments themselves changing length

Biochemical/Oxidative Capacity

# of mitochondria - provide more ATP; # of capillaries surrounding fiber - deliver O2 to muscle;myoglobin amount - transports O2 from capillary to mitochondria

Myosin ATPase

determines speed of ATP breakdown

Contractile

Maximal force production: force/CSA; Speed of Contraction (Vmax): rate of crossbridge cycling; Muscle fiber efficiency: less energy per unit of work

Slow Oxidative

Type I, slow-twitch

Fast Oxidative Glycolytic

Type IIa, intermediate

Fast Glycolytic

Type IIb, fast-twitch

Average Human

no apparent sex difference; (~50% SF; ~50% FF)

Distance runners

70-80% SF (SO); 20-30% FF (FG, FOG)

Track Sprinters

25-30% SF (SO); 70-75% FF (FG, FOG)

Training Adaptations

most research on humans indicates that muscle fibers CANNOT change type

Endurance Training

FOG & FG--> SO; 10 wks, 90-min per day

Resistance Training

Type FG--> Type FOG

Disuse

muscle atrophy, particularly the FG

Slow phase

25-50 years; 10% muscle mass.

Rapid phase

>50 years; 40% of muscle mass

Isometric

generation of force without change in muscle length (static)

Dynamic (isotonic)

muscle action that results in joint movement

Concentric

active muscle shortens under tension; force generated by muscle is > than the resistance.

Eccentric

active muscle lengthens under tension; force generated by muscle is < than the resistance

Twitch

force output of a muscle when given a single stimulus (~100ms); Contraction Time (CT): time from the force onset to peak force; FG Fibers; short CT; SO Fibers: long CT

Tetanus

summation (addition) of twitch responses fired rapidly

Unfused Tetanus (sawtooth):

submax stimulation causes a decline before returning again to peak force values

Fused Tetanus (smooth):

results in a max force production (2-10 x's) > than twitch force.
Contraction will continue until the stimuli are stopped or the muscle fatigues (decrease in force due to repeated stimulation).

Number & Types of Motor Units (MU) Recruited

All muscle fibers within a motor unit are the same (FG, SO); FG generate > force than SO; The more MU recruited the > the force

Initial Length of Muscle

Optimal overlap between actin & myosin for crossbridges; Generally around the muscle's resting length

Neural Stimulation of the MU

Repeated stimulation results in summation of twitches = more force output

Peak Force

decreases as the speed of the movement increases (both fibers)

Golgi Tendon Organs

relay info to CNS about muscle tension; Located in the tendon near the muscle-tendon junction, sensitive to both muscle & tendon tension (much less sensitive than muscle spindle). Large tension in muscle--> GTO stimulation-->sends impulse to CNS--> causes muscle relaxation & activates antagonists (protective mechanism)

Muscle Spindles

relay info to CNS about muscle length; Located in the muscle belly; sensitive to stretch & rate of stretch. Stretch Reflex: stretch muscle --> impulse sent to CNS --> CNS activates motor neurons of the muscle--> contraction (ex. patella tendon tap).

Chemoreceptors

relay info to CNS about muscle pH, [ions], [O2, CO2]

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