Anatomy Exam 3

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53 Terms

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skeletal muscle function

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

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muscle tissue properties

excitability/irritability/conductivity, contractibility, extensibility, elasticity

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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

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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

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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

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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

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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

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myofilaments

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

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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

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perimysium

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

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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

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fascia

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

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tendon/aponeurosis

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

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sarcolemma

plasma membrane of a muscle fiber

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sarcoplasm

cytoplasm of a muscle fiber

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t tubules

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

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sacroplasmic reticulum

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

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thick filaments

composed mainly of myosin

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thin filaments

composed mainly of actin

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actin

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

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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

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tropomyosin

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

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troponin

calcium binding protein

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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

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I bands

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

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H zone

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

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M line

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

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sliding filament theory

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

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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

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acetylcholine (ACh)

A neurotransmitter released by neurons

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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

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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

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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

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repolarization

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

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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

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muscle tone

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

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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

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aerobic respiration

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

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myokinase

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

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creatine kinase

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

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motor unit

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

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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

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latent period

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

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contraction period

second phase of twitch contraction; muscle generates tension and shortens

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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

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recruitment

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

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isometric contractions

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

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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

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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

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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

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intermediate twitch fibers

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

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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

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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