Anatomy Exam 3

skeletal muscle function

skeletal muscle function

movement, maintain posture/stabilize joints, storage and movement of substances, generate heat, support soft tissue

muscle tissue properties

excitability/irritability/conductivity, contractibility, extensibility, elasticity

muscle

a contractible organ, usually attached to bones by tendons; composed of bundles of tightly packed, long, parallel cells; supplied with nerves and blood vessels and enclosed in a fibrous epimysium that separates it from neighboring ones

fascicle

a bundle of muscle fibers within a muscle; supplied by nerves and blood vessels and enclosed in a fibrous perimysium that separates it from neighboring ones

muscle fiber

a single muscle cell; slender, elongated, threadlike, enclosed in a specialized plasma membrane; contains densely packed bundles of contractile protein myofilaments, multiple nuclei immediately beneath the membrane, and an extensive network of specialized smooth endoplasmic reticulum; enclosed in a thin fibrous sleeve

myofibril

a bundle of protein myofilaments within a muscle fiber; collectively fill most of the cytoplasm; surrounded by a sacroplasmic reticulum and mitochondria; has banded appearance due to orderly overlap of protein myofilaments

sacromere

a segment of myofibril from one z disc to the next in the fibers striation pattern; hundreds of these compose a myofibril; functional contractile unit of the muscle fiber

myofilaments

fibrous protein strands that carry out the contraction process; includes thick and thin ones that slide over each other to shorten each sacromere

epimysium

fibrous sheath that surrounds the entire muscle; grades into the fascia on its outer surface; issues projections between fascicles to form the perimysium on its inner surface

perimysium

thicker connective sheath that wraps muscle fibers together in bundles (-fascicles)

endomysium

thin sleeve of loose connective tissue that surrounds each muscle fiber; creates room for blood capillaries and nerve fibers to reach every muscle fiber, ensuring that no muscle cell is without stimulation and nourishment; provides the extracellular chemical environment for the muscle fiber and its associated nerve ending

fascia

sheet of connective tissue that separates neighboring muscles or muscle groups from each other and from the subcutaneous tissue

tendon/aponeurosis

collagenous band or cord associated with a muscle, usually attaching it to a bone and transferring muscular tension to it

sarcolemma

plasma membrane of a muscle fiber

sarcoplasm

cytoplasm of a muscle fiber

t tubules

tubular infoldings in the sarcolemma that penetrate through the cell and emerge on the other side

sacroplasmic reticulum

the smooth endoplasmic reticulum of a muscle cell; serves as a calcium reservoir

thick filaments

composed mainly of myosin

thin filaments

composed mainly of actin

actin

protein with an active site that can bind to the head of a myosin molecule

myosin

a motor protein that constitutes the thick filaments of muscle; has globular, mobile heads of ATPase that bind to actin molecules; serves as contractile functions in other cell types

tropomyosin

blocks the active sites of actin to prevent myosin from binding when the muscle fiber is relaxed

troponin

calcium binding protein

A band

dArk bands in striated muscle; consists of thick filaments lying side by side; contains a region where thin filaments alternate with thick filaments, and a region that is just thick filaments

I bands

lIght bands in striated muscle; consist of thin filaments and elastic filaments alternating

H zone

region of the A band where thin filaments don’t reach

M line

the middle of the H zone where thick filaments are linked to each other

sliding filament theory

mechanism of contraction; thin filaments slide over thick filaments, causing each sarcomere to shorten

neuromuscular junction

motor end plate; a synapse between a nerve fiber; the point where a nerve fiber meets any target cell; the point of communication between the central nervous system and the muscular system

acetylcholine (ACh)

A neurotransmitter released by neurons

action potential

a rapid voltage change in which a plasma membrane briefly reverses electrical polarity; has a self-propagating effect that produces a traveling wave of excitation in nerve and muscle cells; produced by ion movements across the plasma membrane of excitable tissues

exicitation-contraction coupling

events that link action potentials on the sarcolemma to activation of the myofilaments, and therefore preparing them to contract; electrical impulse from the neuron —> chemical signal between the neuron and muscle fiber —> electrical signal at the muscle

depolarization

a shift in the electrical potential across a plasma membrane to a value less negative than the resting membrane potential; Na+ flowing into the cell

repolarization

reattainment of the resting membrane potential after a nerve or muscle cell has depolarized it; K+ flowing out of the cell

length-tension relationship

the idea that the tension generated by a muscle and the force of its contraction depend on how stretched or contracted it was at the outset

muscle tone

a state of continual, partial contraction of resting skeletal or smooth muscle

anaerobic respiration

enables a cell to produce ATP without the need for oxygen, but the ATP yield is very limited and the process generates a toxic by-product (lactic acid); short term energy

aerobic respiration

produces large amounts of ATP and requires a constant supply of oxygen; long term energy

myokinase

transfers Pi from one ADP to another, converting the latter to ATP that myosin can use; immediate energy

creatine kinase

obtains Pi from a phosphate storage molecule and donates it to ADP to make ATP; immediate energy

motor unit

one motor neuron and all the skeletal muscle fibers innervated by it; when stimulated, cause contraction over a wide area

twitch contraction

the contraction that results when all the fibers in a motor unit contract in response to a single action potential in a motor neuron; three phases

latent period

first phase of twitch contraction; the time required for excitation, excitation-contraction coupling, and tensing of the elastic components within the muscle

contraction period

second phase of twitch contraction; muscle generates tension and shortens

relaxation period

final stage of twitch contraction; the time it takes for a muscle to return to its normal length and low tension state after contracting

recruitment

multiple motor unit summation; the process of increasing muscle force by activating more motor units within a muscle

isometric contractions

contraction without a change in length; occurs at the beginning of any muscle contraction, but is prolonged in lifting weights

isotonic contractions

contraction without a change in tension but a change in length; begins when internal tension builds to the point that it overcomes the resistance and the muscle can then shorten, move, and maintain the tension

fast twitch muscle fibers

fast glycolytic; well adapted for quick responses; quickness comes from extensive SR with fast release and reabsorption of calcium, and a form of myosin with very quick ATP hydrolysis and cross-bridge cycling

slow twitch muscle fibers

slow oxidative; well adapted for endurance and fatigue resistance; slowness comes from a SR that is relatively slow to release and reabsorb calcium, and a form of myosin ATPase that is relatively slow in its ATP hydrolysis and cross-bridge cycling

intermediate twitch fibers

fast oxidative glycolytic; combine fast twitch responses with aerobic fatigue resistant metabolism

smooth muscle

thick, thin, and intermediats filaments with no sarcomeres or striations; thin filaments are attached to dense bodies; Ca2+ enters from ECF and SR, and binds to calmodulin; involuntary

skeletal muscle

thick and thin filaments organized into sarcomeres; thin filaments are attached to z discs; Ca2+ enters from the SR, and binds to troponin; voluntary