Muscle Tissues

What's inside a whole muscle?

smallest to largest:
myosin
sarcomere
myofibril
muscle fiber
fascicle

myosin

The contractile protein that makes up the thick filaments of muscle fibers

sarcomere

contractile unit of a muscle fiber; contains actin & myosin

myofibril

any of the elongated contractile threads found in striated muscle cells.

muscle fiber

a single muscle cell

fascicle

bundle of muscle fibers

How does actin and myosin cause muscle contraction?

myosin heads grab onto actin at binding sites and pulls to shorten muscle

What are the steps of cross-bridge cycling?

1. myosin head binds to actin
2. inorganic phosphate (Pi) is released, leading to the power stroke (sliding of thin filaments along thick filaments)
3. ADP is released from myosin and a new ATP binds
4. Binding of ATP releases myosin head from actin
5. Myosin ATPase hydrolyzes ATP to ADP+Pi, which resets the myosin head to its starting position
6. If calcium remains bound to troponin, then cross-bridge cycling will continue

How does the release of calcium cause muscles to contract?

Ca is released onto sarcomere when the muscle needs to contract. calcium binds to Traponin causing it to change shape. this moves Tripomysoin out of the way exposing binding sites

When a nerve signal reaches a muscle fiber, what happens?

t-tubules transmit nervous signal deep into the muscle fiber to release calcium inside so cross-bridge cycling can occur

How does a muscle's length affect its strength?

muscles generate the greatest force when at their resting (ideal) length, and the least amount of force when shortened or stretched relative to the resting length.

How does the frequency of stimulation affect the force of a muscle?

higher frequency= higher force

What is tetanus?

a smooth, sustained contraction of maximal strength

What is the latent period and why does it exist?

Short duration of time where nothing happens before a muscle contracts. Necessary for signal to travel to muscle and steps occur to contract muscle.

What are motor units, and how do we control how strongly one of our muscles contracts?

The combination of an individual motor neuron and all of the muscle fibers that it innervates

more motor units= stronger force

red muscle fibers

lots of capillaries
lots of blood
increased myoglobin
aerobic respiration
thin
weak
slow fatigue

white muscle fibers

few capillaries
little blood
anaerobic respiration (glycolysis)
thicker
stronger
fast fatigue

What are the 5 steps occur at the neuromuscular junction for muscle contraction to occur?

1. a nerve signal reaches neuromuscular junction
2. neurotransmitters bind to the sarcolemma
3. a signal travels down the t tubules
4. calcium is released from the sarcoplasmic reticulum
5. cross-bridge cycling occurs

This blocks the binding sites on actin

tropomyosin

This is the neurotransmitter released at the neuromuscular junction

acetylcholine

Calcium binds to this protein when released onto the sarcomeres

troponin

The thick protein of the sarcomere that "pulls"

myosin

The thin protein of the sarcomere, called the thin filament

actin

These tiny tubes carry a signal deep into a muscle fiber

t tubules