Ch. 9

sarcomere

A contracting unit of muscles;extends from Z line to Z line

myofibrils

A fibril collectively arranged in longitudinal bundles in muscle cells (fibers); composed of thin filaments of actin and a regulatory protein and thick filaments of myosin.

troponin

A globular protein that associated with tropomyosin as part of the thin filament of the sarcomere. Troponin binds Ca2+, which causes the conformation change in tropomyosin required to expose the myosin-binding sites on actin and initiate muscle contraction.

tropomyosin

A helical protein that winds around actin helices in skeletal and cardiac muscle cells to form the thin filament of the sarcomere. In the absence of Ca2+, tropomyosin covers the myosin-binding sites on actin and prevents muscle contraction. When calcium is present, a conformation change in tropomyosin occurs so that the myosin-binding sites are exposed and muscle contraction can occur.

isometric contraction

A muscle contraction in which no movement occurs because of an equal force in the opposite direction; the length of the muscle remains constant under tension

what happens if acetylcholinesterase is dysfunctional

A skeletal muscle membrane maintained in a depolarized state cannot generate action potentials because the voltage-gated Na channels in the membrane become inactivated, which requires repolarization to reverse

acetylcholinesterase

An enzyme that breaks down the neurotransmitter acetylcholine; excess amount of it will cause the muscle not to contract because sufficient acetylcholine cannot reach the muscle

slow oxidative fibers

Are slow to contract, slow to fatigue; they contain myosin with low ATPase activity and many mitochondria which allow for high endurance exercises; are dark red colored muscle

unfused tetanus

At low stimulation frequencies, the tension may oscillate as the muscle fiber partially relaxes between stimuli

fast glycolytic fibers

Important for short-term intense, powerful movements. Prefer anaerobic glycolysis; white muscle color

fast oxidative glycolytic fibers

Intermediate fibers, large, fast acting, myoglobin and glycogen, rely on oxidative and glycolytic pathways, fatigue resistant, mostly in sprinters. few mitochondria

motor end plate

Muscle fiber part of the NMJ that is a region of the muscle cell membrane opposite the synaptic end bulbs; contains acetylcholine receptors

sarcoplasmic reticulum

Organelle of the muscle fiber that stores calcium in the terminal cisternae

H-zone

The region at the center of an A band of a sarcomere that is made up of myosin only. The H zone gets shorter (and may disappear) during muscle contraction.

A-band

The region of the sarcomere where myosin filaments are predominantly seen with minor overlap of the actin filaments; creates the dark color

isotonic contraction

a contraction in which the muscle changes lengths but the load is constant

tetanus

a maintained contraction in response to repetitive stimulation

motor unit

a motor neuron and all the muscle fibers it innervates

M-line

a protein in the middle of the H-zone that connects the other ends of myosin to each other.

neural control of muscle tension

affected by: frequency of action potentials in individual motor units or by recruitment of motor units

tension-frequency relationship

as action potential frequency increases, the level of tension increases by summation

calcium-atpase

atp required to pump calcium back into the cell from the cytosol back into the SR; calcium level is still elevated after the action potential because it takes longer to pump calcium back into the SR

I-band

contains only thin actin filaments that do not overlap thick filaments; is separated into Two Halves by a Z-line

troponin and calcium

in the presence of calcium, troponin will bind to calcium and reveal the binding site to myosin thus allowing cross-bridges

passive tension

increasing muscle length past optimal length will increase the passive tension of a muscle fiber due to the elongation of the tintin protein that is attached to the myosin

twitch

mechanical response of a muscle fiber to a single action potential

motor unit recruitment

motor units are recruited from smallest to largest

tintin

protein that attaches the myosin to the z-line

tetanic summation vs. twitches

tetanic summation tension is greater than twitch tension because with the frequent action potentials being transmitted, calcium concentration in the cytosol remain elevated and allow for more binding sites for myosin to bind and thus produce more cross bridges

A-band during contraction

the A-band remains unchanged because the length of the myosin does not change

H-zone during contraction

the H-zone is reduced because the myosin and actin slide past each other and overlap

I-band during contraction

the I-band reduces because the area of actin that does not contain myosin is reduced as the myosin slides towards the z-line

muscle contraction

the activation of force generating sites in the muscle fibers; does not necessarily mean that the muscle shortens

twitch duration factors

the duration of a twitch depends on calcium ATPase activity and how long it takes for the fibers to complete their cross-bridges

Z-line

the end limits of a single sarcomere; it is where the myosin and actin attach to in the sarcomere

creatine phosphate

the metabolic pathway used by fast twitch fibers; provides energy for short bursts by phosphorylating ADP

motor unit strength

the more fibers in a single motor unit the more force can be produced; the less fibers innervated by a motor unit the more finely controlled the movement will be

power stroke

the movement of the cross bridge once the adp and pi of the energized myosin head detaches

antagonist muscle

the muscle that opposes the original action of the agonist muscle

acetylcholine

the only neurotransmitter used to active muscle fibers; opens ion channels on the muscle fibers once it binds to its receptors which will then cause action potentials and ultimately muscle contraction

Muscle

the organ responsible for contraction and movement of the body; made up of many muscle fibers

muscle fibers

the same as muscle cells; many of them make up a muscle

sarcomere length during contraction

the sarcomere shortens during a contraction

active tension

the tension increases as you increase the length until you get to optimal length; past optimal length, tension will decrease

latent period

the time between stimulation and the onset of contraction

contraction time

the time from the end of the latent period until the peak tension is generated

sliding filament mechanism

thick and thin filaments do not shorten their lengths but instead slide past each other to generate force

mysoin

thick filaments in the sarcomere; they contain globular heads with binding sites to actin and ATP that are crucial for the cross bridge cycle

actin

thin filaments that is found in the sarcomere; made up of troponin and tropomyosin

tropomyosin inhibition

tropomyosin blocks the myosin binding site on the actin filament until calcium binds to troponin and changes the tropomyosin's conformation

Transvers Tubules

tubular system that interact with the terminal cisternae in producing action potentials; they are continuous to the plasma membrane and allow potentials to travel deep into the muscle fiber from the plasma membrane

fused tetanus

when stimulus frequency is so high that no muscle relaxation takes place between stimuli