PSIO exam 3

functions of skeletal muscle (4)

locomotion, facial expression, posture and body position, regulation of body temperature

muscles _____ on bones

pull

origin

muscle attachment to a relatively fixed structure

insertion

muscle attachment that moves (towards the origin for the most part)

reverse muscle action

the origin moves towards the insertion

first class lever

e, f, l (jaw)

second class lever

f, l, e (ball of foot)

third class lever

f, e, l, most common (elbow)

flexion

decrease in joint angle

extension

increase in joint angle

abduction

move away from midline

adduction

move toward midline

agonist

prime mover

antagonist

opposition

synergist

assist agonist

fixator

type of synergist, stabilizes origin

covering of muscle fibers

endomysium

covering of fascicles

perimysium

covering of muscles

epimysium

hypertrophy

increase in cell size

functional unit of contraction

sarcomere

sarcolemma

plasma membrane of a muscle fiber

sarcoplasmic reticulum

stores Ca, surrounds myofibrils

z discs

anchor thin filaments

thin filament composition

actin, troponin, tropomyosin

thick filament composition

myosin

m line

anchors thick filaments

I band

thin filaments only, decreases during contraction

A band

extend the length of thick filaments, includes zone of overlap

zone of overlap

where thick and thin filaments overlap, increases during contraction

h zone

only thick filaments, decreases during contraction

actin

thin, myosin binding sites

myosin

motor protein, thick, forms crossbridges

tropomyosin

regulatory protein, covers myosin binding sites

troponin

regulatory protein that binds to calcium

rigor complex

attached myosin group after a power stroke

rigor mortis

no ATP to detach the crossbridge

excitation

electrical signal transmitted from motor neuron to skeletal muscle fiber

excitation-contraction coupling

Ca is released from SR

contraction

Ca binds to troponin and crossbridge cycling occurs

relaxation

Ca is resequestered

ACh

acetylcholine (neurotransmitter)

acetylcholine esterase

breaks down ACh

creatine phosphate

for re-synthesis of ATP, stores high energy phosphate, supports ~15 seconds of contraction

anaerobic glycolysis

occurs in cytoplasm, rapid ATP production, supports ~2 minutes of contraction

aerobic metabolism

needs oxygen, uses glycogen, fatty and amino acids, occurs in mitochondria, slow, supports 40+ minutes of contraction

fatigue

inability for a muscle to maintain force

cori cycle

recycles lactate produced from anaerobic glycolysis back to glucose

oxygen debt

reset cost of exercise

muscle twitch

contraction arising from a single electrical stimulus

latent period

<2msec, action potential sweeps over sarcolemma, Ca is released from SR and binds to troponin, myosin binding sites exposed, no tension change

period of contraction

10-100msec, crossbridges form and swivel, peak tension develops

period of relaxation

10-100msec, Ca returns to SR, binding sites are covered by tropomyosin, myosin heads detach, tension decreases

tetanus

summation of individual twitches

temporal summation

increased effort of one motor unit

motor unit

A motor neuron and all of the muscle fibers it innervates

spatial summation

recruitment of more motor units

size principle

Recruitment of motor units from small to large.

small motor units

slow oxidative (SO) fibers, high resistance to fatigue

intermediate motor units

fast oxidative-glycolytic (FOG) fibers, fatigue-resistant

large motor units

fast glycolytic (FG) fibers, fatigable

isometric contraction

tension increases, length stays constant, every contraction begins isometrically

isotonic contraction

change in length

concentric isotonic contraction

shortens, effort>load

eccentric isotonic contraction

lengthens, load>effort

length-tension relationship

tension generated is proportional to number of crossbridges formed, peak tension at intermediate sarcomere length

muscle performance

power = speed x strength

endurance

sustained activity

slow oxidative fibers

low speed (slow myosin ATPase activity), high resistance to fatigue, aerobic metabolism

fast-glycolytic fibers

high speed, low resistance to fatigue, anaerobic glycolysis

fast-oxidative glycolytic fibers

moderate speed, intermediate resistance to fatigue, relies primarily on glycolysis, higher aerobic capacity than FG fibers

myoglobin

binds and releases oxygen

muscle hypertrophy

increase in myofibril diameter, more sarcomeres working in parallel

satellite cells

increase number of myonuclei

strength training

large increase in hypertrophy and myonuclei, increase in capillary density and mitochondria

endurance training

increase in hypertrophy and myonuclei, large increase in capillary density and mitochondria

cardiac muscle

heart, contract around confined volume, increase pressure

gap junctions

allow cardiac muscle cells to communicate

desmosomes

cardiac muscle cell adhesion

visceral smooth muscle

single unit