lab 7 - powerlab one

frequency

number of occurrences of a repeating event per unit time

signal conditioning

amplification and filtering of a voltage

amplitude

height of the wave from baseline to crest

waveform

shape and form of a signal

wavelength

length from the crest of one peak to the crest of the next peak

what prefixes refer to muscle?

myo, mys, amd sarco

what percentage of cell mass does skeletal muscle cells make up in the body?

40%

what are muscles made of?

individual muscle fibers (muscle cells) organized into fascicles

upper motor neuron lesions

loss of muscle movement due to damaged neurons in the brain

what separates skeletal muscle from other types of muscle energy wise?

skeletal muscle is powerful compared to others and can contract rapidly but it also tires rapidly (uses ATP)

excitability

the electric charge differential that can be changed upon stimulation to produce an intracellular muscle response

contractility and extensibility

muscles shorten when stimulated and can stretch

elasticity

recoil of muscle after stretching

where do nerves and blood vessels enter the muscle?

near the middle, then branch throughout the muscle running through the connective sheaths (epi, peri, and endomysium)

how is a bone moved?

connective tissue sheaths of muscles are continuous with each other and with tendons to transfer the force of the contracting muscle to the structure (bone) to be moved

direct attachment

fusion between tissues (periosteum or perichondrium fusion with the muscle’s epimysium

indirect attachment

more durable, smaller connections like aponeurosis or tendons

tendon

mostly collagen, rope-like extension of a muscle’s connective tissue

aponeurosis

sheet-like extension of a muscle’s connective tissue

antagonist muscle pairing

as one muscle contracts and shortens, its antagonist relaxes and elongates

sarcolemma

plasma membrane of a muscle fiber

sarcoplasm

cytoplasm of a muscle fiber

myoglobin

stored oxygen in the muscle

gylcosomes

granules of glycogen that can be broken down to supply atp from glucose to energy

myofibrils

repeating units of sarcomeres - smallest contractile units of skeletal muscle fibers

sarcomeres

smallest, contractile units of skeletal muscle fibers

thick filaments

contain the protein myosin and run the length of the A band

how long is a sarcomere?

runs z band to z band OR half I band to half I band with an A band in the middle

z-line (z-disc)

dark midline region of I band

what do myosin proteins contain?

protruding globular heads that each associate with two light chains; only where actin proteins overlap with myosin proteins

what connects the thin filaments?

the M line

what is a cross bridge?

forms when muscles contract; globular myosin heads link the thick and thin filaments together that swivel as motors to create force that shortens the sarcomere

what is a thin filament made of?

a helix of two actin subunit strands (that have active sites where myosin heads attach) plus the proteins tropomyosin and troponin

where is the H band?

part of the thick filament that is not overlapped with the thin filament (the M line and its extensions)

tropomyosin

in a relaxed muscle, it blocks actin’s myosin binding

troponin

composed of three globular peptides; one binds actin, another binds tropomysosin, the last binds calcium that is sandwiched between the other two

titin

elastic filaments that run from Z line to the end of the thick filaments to hold them in place, prevent hyperextension, and provide flexible recoil to the sarcomere as it contracts, relaxes, and stretches

sarcoplasmic reticulum

elaborate smooth endoplasmic reticulum in muscle

terminal cisterns

large perpendicular cross channels made by the sarcoplasmic reticulum at the A band I band junction; founds in pairs

what is high in abundance near the sarcoplasmic reticulum?

mitochondria and glycogen granules

what is the job of the sarcoplasmic reticulum?

controls calcium levels within the sarcoplasm and stores and releases calcium to control muscle fiber contraction

t-tubules

elongated tubular extensions of the sarcolemma dive deeply into the cell

triad

t tubule plus terminal cisterns

how do electrical signals reach the innermost portions of a fascicile?

when a nerve stimulates a muscle, the electrical signal travels down the sarcolemma, and since T tubules are just tubular extensions of the sarcolemma, the electrical signal can be carried deep into the muscle to every sarcomere

what happens once sarcomeres receive electrical signal?

the electrical signals cause a release of calcium from the terminal cisterns - causing contraction

what do integral proteins in T-tubules do?

function as voltage sensors

what do integral proteins in terminal cisterns do?

create gated channels for the release of calcium

what is a cell polarization?

resting charge where the inside of the cell is more negative relative to the outside

what are the three steps of the initiation and propagation of a muscle action potential?

1. acetylcholine binds to its receptor opening chemical ligand-gated ion channels for sodium - making the inner surface of the sarcolemma less negative (depolarization) and is called the end plate potential

2. voltage gated sodium channels on the surrounding sarcolemma respond to the change and open to allow positive sodium to enter down its electrochemical gradient. once the threshold potential is reached, further channels are opened and cause a depolarization wave termed muscle action potential

3. once voltage becomes sufficiently positive, the channels close and potassium channels open to allow the membrane to become more negative again as positive potassium exits the cell down its concentration gradient (repolarization)

depolarization

the process where a cell's internal electrical charge becomes less negative (more positive) relative to the outside, reversing its resting state

where does step one of depolarization begin?

the end plate

muscle action potential

a rapid, temporary reversal of electrical charge across a muscle cell membrane (sarcolemma), triggered by a nerve signal. It causes an influx of sodium () to depolarize the cell (making it positive), followed by potassium () efflux to repolarize it, initiating contraction

why does the change in polarity of a muscle cause it to contract?

depolarization) causes contraction by triggering an action potential that spreads along the membrane, causing calcium ions () to be released from the sarcoplasmic reticulum. This exposes actin binding sites, allowing myosin heads to bind and pull the filaments together in a sliding motion, shortening the muscle fiber

where is the traid relative to the sarcomere?

where the I band is not crossing over with the A band

what structure controls the movement of sodium and potassium in and out of the cell?

sodium potassium ATPase pump

what is the refractory period?

while repolarizing, the cell cannot be stimulated again until the membrane is sufficiently negative

how does a muscle action potential cause depolarization?

by triggering a rapid influx of sodium ions into the muscle cell, reversing the membrane polarity. This occurs when neural stimulation causes acetylcholine to open ligand-gated ion channels, allowing Na to rush in, triggering voltage-gated channels to open in a chain reaction

what’s a more fluid description of how a muscle is stimulated?

the muscle action potential travels along the sarcolemma and down the T tubules where the depolarization causes voltage-sensitive tubule proteins to undergo a change in shape which leads to opening of calcium release channels in the terminal cisterns

what happens once calcium is released into the terminal cisterns?

calcium moves into the sarcoplasm