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

skeletal muscle cells

make up about 40% of the cell mass of the body

skeletal muscles so the majority of

the work for locomotion and support of the animal skeleton

each muscle is made up of individual ____ organized in fascicles.

muscle fibers (muscle cells)

to produce mechanical energy in directed movements,

muscles to the chemical energy stored in ATP

skeletal muscle structure- connective tissue sheaths of skeletal muscle: epimysium, perimysium, and endomysium

disease of muscle are rare and mostly inherited but,

trauma to muscle is very common

upper motor neuron lesions

loss of muscle function as a consequence of strokes damaging neutons in the brain

skeletal muscle is ____

consciously controlled and therefore voluntary, can rapidly contract but tires rapidly.

excitability

all muscle cell membranes have an electric charge differential which can be changed upon stimulation (such as through neurotransmitter binding) to ultimately produce an intracellular muscle response

contractility

all muscle cells shorten when stimulated

extensibility

all muscle cells can also be stretched, sometimes more than their resting length

elasticity

all muscle cells, after being stretched, can recoil to the resting cell length

an entire skeletal muscle, such s the gastrocnemius is an ___

organ and is made up of more than just muscle fibers- it has nerves, blood vessels, and connective tissue. Nerves and blood vessels enter the muscle near its center and then branch throughout the muscle running through the connective tissue sheaths (epi-, peri-, & endomysium)

tendons

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

muscle attachments can be

direct or indirect

direct attachment

the periosteum or perichondrium is fused with the muscle's epimysium

indirect attachments

more durable, smaller, and are more common. example: tendon or aponeurosis

tendons are mostly

collagen and are rope-like extensions of a muscle's connective tissue

aponeurosis are

similar sheet-like extension instead of rope like

antagonistically

as one muscle contracts and shortens, its antagonist relaxes and elongates (two or more muscles usually work like this)

skeletal muscle fibers are

very large multinucleated cells

sarcolemma

plasma membrane of a muscle fiber

sarcoplasm

the cytoplasm

myoglobin

muscle cells contains lots of it, are granules of glycogen that can be broken down to supply ATP from glucose for energy

most of the intracellular volume of skeletal muscle cells is taken up by organelles called ____. they are repeating units of sarcomeres.

myofibrils

sarcomeres

smallest "atomic" contractile units of skeletal muscle fibers

skeletal muscle is striated because the dark ____ and light _____ within the sarcomeres are perfectly lines beside one another.

A bands; I bands

each A band has a middle region that is slightly light called the

H zone (or H band)

biceps brachii/triceps brachii-an example of two muscles working antagonistically

microscopic anatomy of a skeletal muscle fiber

myofilaments' alignment

the I and has a dark midline region termed the

Z line (or Z disc)

sarcomere runs from

Z line to Z line OR from each half I band to half I band with an A band in the middle

thick filaments

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

myosin proteins contain

protruding globular heads

each globular head associates

with two light chains

The M line connects thick filaments which

only have myosin heads in areas where actin proteins of the thin filament and myosin heads of the thick filament overlap

when a muscle contracts, the globular myosin heads link the thick and thin filaments together making ____, and swivel as motors to create force that shortens the sarcomere

cross bridges

each thick filament can contain

over 300 myosin molecules

the thin filament consists of a helix of two actin subunit strands plus the proteins ____ and ____

tropomyosin; troponin

each actin subunit (tropomyosin and troponin) is

a globular actin and contains active sites where myosin heads attach

in a relaxed muscle fiber, tropomyosin ___

blocks actin's myosin-binding

troponin is composed of

three globular polypeptides each of which have different function, one polypeptide binds actin, another binds tropomyosin, calcium ions bind to the third which is sandwiched between the other two troponin polypeptides

elastic filaments, made of the protein ____ , run from the Z line to the thick filaments to hold them in place and provide flexible recoil to the sarcomere as it contracts, relaxes, and stretches.

titin

when titin reaches its normal extension, ____

it stiffens and resists further over-stretching of the muscle

cross bridge formation

cross bridge cycle

sarcoplasmic reticulum

in muscle, endoplasmic reticulum becomes very elaborate

each myofibril is surrounded by

interconnecting sarcoplasmic reticulum

at the A band I band junction, the sarcoplasmic reticulum forms large perpendicular cross channels called ______ which are always found in pairs

terminal cisterns

mitochondria and glycogen granules are highly abundant near the

sarcoplasmic reticulum

sarcoplasmic reticulum controls

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

at the A band and I band junction, elongated tubular extensions of the sarcolemma dice deeply into the cell and are ___

T tubules

triad

the T tubule plus terminal cisterns on either side

when a nerve stimulates a muscle, ____

an electrical signal travels down the sarcolemma and be carried deep into the muscle to every sarcomere.

the elctrical signal causes

the release of calcium from the terminal cisterns which leads to contraction

both the T tubules and terminal cisterns of teh sarcoplasmic reticulum have

integral membrane proteins that protrude into the space between these structures

these integral proteins if the T tubules function as

voltage sensors while the integral proteins of the terminal cisterns create gated channels for the release of calcium

all plasma membranes of all human cells, including the sarcolemma of muscle fibers, carry a resting charge or ____ wehre the inside of the cell is more negative relative to the outside

polarization

the initiation and propagation of a muscle action potential involves three steps

1. acetylcholine binds to its receptor opening chemical ligand-gated ion channels for sodium. these events transciently make the inner surface of the sarcolemma less neagtive, termed depolarization. this begins at the end plate and is thus termed the end plate potential.
2. voltage-gated sodium channels on the surrounding sarcolemma respond to the change in charge and open allowing positive sodium to enter down its electrochemical gradient. once a threshold potential is achieved, the voltagr change in the membrane becomes sufficient to open further voltage-gated sodium chanels and spread the signal in the form of a depolarization wave along the sarcolemma termed a muscle action potential.
3. once the voltage become sufficiently positive, the voltage-gated potassium channels open. the membrane then becomes more negative or repolarizes as positive potassium exits the cell down its concentration gradient. once the membrane becomes sufficiently negative again, this change in charge closes the voltage-gated potassium channels.

relationship of triads to myofilaments within myofibrils of skeletal muscle

skeletal muscle action potential example. voltage changes over time at a given point inside an axon during the course of an action potential. 1- Resting state. no ions move through coltage0gates channels. 2- depolarization cause by Na+ flowing into the cell. 3-repolarization caused by K+ flowing out of the cell. 4- hyperpolarization caused by K+ continuing to leave the cell

the gradient differences for sodium and potassium are restored by ____ which moves sdium out and potassium in

sodium potassium ATPase pump

refractory period

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

consequential contraction

may last for more than 100 times the duration of the electrical signal

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

depolarization

excitation-contraction coupling: events of contraction of the muscle description -->

ca+ moves into sarcoplasm, removes inhibitory action of tropomyosin as it bind to troponin, changing shape for tropomyosin to move away and expose binding site for myosin on actin thin filaments. myosin binds and cross bridge cycling starts.

repolarizes

voltage sensitive tubule proteins regain their resting configuration, closing the ca+ release channels of terminal cisterns.

muscle relaxation

ca+ pumps back into SR by ATP dependent ca+ punmps in the terminal cistern membrane. once ca+ levels drop, inhibitory effect of tropomyosin is restores so actin and myosin no longer cross bridge

tropomyosin

physically blocks the myosin binding active sites on actin when intracellular ca+ is low

when it is high, it binds to troponin

power stroke

occurs as phosphate and ADP are released from the myosin head allowing the myosin to swivel or stroke from its high energy configuration to a low energy state. this pulls actin filament toward M line. ATP binds to myosin head = myosin head to detach. nerve impulses arrive at muscle in rapid succession, ca+ increase, another contraction before muscle relaxes

cross bridge cycling

occurs many times during a single contraction

muscle tension

defined as the force exerted by a contracting muscle on an object

load

defined as the opposing force applied on the muscle by the mass of the object being moved

each individual muscle fiber is innervated by a branch of a

motor axon

neuronal action potential activates

all of the muscle fibers innervated by the motor neuron and its axonal branches

motor unit

motor neuron, together with all of the individual muscle fibers that it innervates

vary greatly in size, from small motor unit to large motor unit

the small the motor unit, ____

the finner the control of movement in that muscle

small units controls

movements of the fingers and eyes

large motor units controls

large limb muscles

regardless of size, specific motor units contains

only one neuron

activation process involves

initiation of an action potential along the axon of the neuron