BIOL121: 06/02-03/26 (Mendel)

skeletal muscle

muscle fibers = myocytes, own nerve ending

ARTERY = nutrients, oxygen

VEINS = wastes, CO2

NERVE = nerve impulse; control

multiple nuclei = fusion of myoblasts

striated, voluntary control, powerful

cardiac muscle

only in heart

striated, branched cells, involuntary control

autonomous = regulated by nervous system

smooth muscle

visceral = in walls hollow organs

not striated, involuntary control, autonomous, uninucleated

muscle functions

EXCITABILITY = ability to receive and respond to stimuli

CONTRACTILITY = ability to shorten when stimulated

EXTENSIBILITY = ability to stretch

ELASTICITY = ability to recoil to restring length after stretched

movement of bones or fluids

maintain posture and body position, stabilizing joints

heat generation, protect organs, regulate digestion, dilate/constrict pupils, arrector pili muscle

connective tissue sheaths - skeletal muscle

prevent bulging and bursting under high stress

EPIMYSIUM = dense regular connective tissue surrounding entire muscle (outside)

PERIMYSIUM = fibrous connective tissue surrounding fascicle (groups of muscle fibers)

ENDOMYSIUM = fine areolar connective tissue surrounding each muscle fiber (every cell wrapped)

skeletal muscle attachments

ORIGIN = attachment point (nomove as much)

INSERTION = attachment point on moveable bone (move toward origin)

DIRECTLY = epimysium of muscle fused to periosteum of bone or perichondrium of cartilage

INDIRECTLY = connective tissue wrappings extend beyond muscle as a ropelike tendon

myocytes

SARCOLEMMA = membrane outside cell

SARCOPLASM = cytoplasm

SARCOPLASMIC RETICULUM = ER (Ca2+ storage)

MYOFIBRILS = rods of protein bundles; contracting units

T-TUBULE invagination of sarcolemma; surrounds myofibrils, how electrical signals go to muscle

myofibrils

densely packed, rodlike elements

80% of muscle cell volume

striations, sarcomeres (z-disc to z-disc), myofilaments

A-band

one end of myosin to other

dark regions

MYOSIN DOES NOT MOVE DURING CONTRACTION

I-Band

area with lack of myosin

lighter region

disappear during contraction

H-zone

light region in middle of A-band

M-line

line of protein down center of H-zone

hold myosin bundles together

Z-disc

zig-zag line through center of I-band

Z-disc to Z-disc is a sarcomere

myofilament

ACTIN = thin filaments, extend across I-band and part of A=band, anchored to Z-disc

MYOSIN = thick filament, extend length of A-band, connected at M-line

myosin composition

MYOSIN TAIL = bundled together to form filament

GLOBULAR HEAD = forms cross bridges with actin, ATP and Actin binding sites

actin composition

G ACTIN SUBUNITS = myosin binding site, link to form F ACTIN twisting to form thin finament

TROPOMYOSIN = covers up active sites for myosin (noodle looking)

TROPONIN = holds tropomyosin to actin, Ca2+ bind to pull away and expose binding site for myosin

sarcoplasmic reticulum

network of smooth ER surrounding each myofibril

TERMINAL CISTERNAE = at ends, stores/released Ca2+ when electric received down T-tubule to open door → muscle contraction

triad

T-tubule, terminal cisternae of SR (2)

AP moves into T-tubule

AP causes voltage-sensitive protein to change shape

mechanically-gated Ca2+ channels open

Ca2+ moves out of SR and into cytoplasm (sarcomere)

contraction

generation of force

not always shortening of fiber

shortening occurs when tension generated by cross bridges on thin filaments exceeds forces opposing shortening

sliding filament model of contraction

RELAXED STATE = thin and thick filament overlap slightly

CONTRACTION = myosin heads bind to actin, detach, bind again to propel thin filaments toward M-line

motor units

axon branches divide into axon terminals

GROSS MOVEMENT = more muscle cells/neuron, more muscle controlled by single neuron

FINE MOVEMENT = less muscle cells/neurons, less muscle controlled by single neuron

neuromuscular junction

where an axon branch innervates ONE muscle fiber

• nerve comes down and touches muscle

composed of many axon terminals, motor end plate

motor end plate

area of sarcolemma where axon terminals form an NMJ

JUCTIONAL FOLDS = folded depression in sarcolemma, increases surface area, ACh receptors

ONE NMJ per muscle fiber, ONE nerve ending per muscle fiber

requirements for skeletal muscle contraction

ACTIVATION = neural stimulation at neuromuscular junction (electrical stimulated to release ACh)

EXCITATION-CONTRACTION COUPLING = generate and propagate AP along sarcolemma, short rise in intracellular Ca2+ levels (t-tubule open Ca2+ door)

rigor mortis

myosin crossbridge requires ATP to detach

ATP absent, cause muscles to lock up

myosin head breaks down eventually due to decomposition

cross bridge cycle

CROSS BRIDGE FORMATION = myosin bind actin (need ATP and Ca2+)

POWER STROKE = myosin head pulls actin toward M-line, ATP released

CROSS BRIDGE DETACHMENT = myosin detaches (need ATP)

COCKING OF MYOSIN HEAD

muscle mechanics

same for muscles and muscle fibers

TENSION = force exerted by contracting muscle on an object

LOAD - force exerted by an object (weight) on a muscle

isometric contraction

muscle generates force while length remain constant

muscle tension increases but does not exceed load

isotonic concentration

muscle shortens because muscle tension exceeds load  ECENTRIC = muscle lengthens, on the way down (builds more muscle) (tension < load)

CONCENTRIC = muscle shortens, on the way up (tension > load)

muscle twitch

motor unit response to single AP (nerve impulse)

MYOGRAM = muscle contraction graph

TRACING = line recording of muscle activity on myogram

phases of muscle twitch

LATENT = events of excitation-contraction coupling, no muscle tension

CONTRACTION = cross bridge formation, tension increases

RELAXATION = Ca2+ reentry into SR, tension declines to zero, muscle contracts (ATP, Ca2+) faster than relax

COMPLETE TETANI = muscle contraction not relaxing, complete fusing of muscle, anything over max stimulus is damaging muscle

graded muscle responses

variations in strength of muscle contraction

FREQUENCY OF STIMULATION = smooth, contractions, rapidly stimulate a specific number of muscle cells

STRENGTH OF STIMUALTION = controls strength of contraction, stimulates increasing number of muscle fibers

GMR stimulus frequency

UNFUSED/INCOMPLETE = stimulus at lower frequency, interrupted relaxation, wavy myogram

FUSED/COMPLETE = stimulus at higher frequency, no relaxation, straight line at peak tension in myogram

GMR levels of stimuli

SUBTHRESHOLD = does not produce any detectable tension or contraction

THRESHOLD = lowest stimulus producing any detectable tension or contraction

MAXIMAL = lowest stimulus producing maximal peak tension

GMR Recruitment

more motor units are activated as the strength of the stimulus increases above threshold

AP strength increase to muscle = more motor units