7.2 Characteristics Of Skeletal Muscle Flashcards by Salve Billena

___ with its associated connective tissue, constitutes approximately 40% of body weight

Skeletal muscle

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Causes strations

thick and thin microfilaments

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Ability of the muscles to shorten with force

Contractility

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Capacity of skeletal muscle to respond the a stimulus

Excitability

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Means that skeletal muscles can be stretched to their normal resting length and beyond to a limited degree

Extensibility

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Ability of skeletal muscles to recoil to their original resting length after they have been stretched

Elasticity

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Connective tissue sheath surrounding the skeletal msucle

Epimysium

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Epimysium is also called ___

Muscular fascia

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Numerous visible bundles composing the muscle

Muscle fasciculi

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Muscle fasciculi are surrounded by loose connective tissue called ____

Perimysium

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Several muscles cells composing a fasciculus

Muscle fibers

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Loose connective tissue surrounding a muscle fiber

Endomysium

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A single cylindrical fiber, with several nuclei located at its periphery

Muscle fiber

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Largest human muscles are up to___

30cm long and 0.15mm in diameter

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Cell membrane of the muscle fiber

Sarcolemma

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Tubelike invaginations along the surface of the sarcolemma which occur at regular intervals along the muscle fiber and extend inward into it.

transverse tubules or T tubules

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A highly organized smooth endoplasmic reticulum

Sarcoplasmic reticulum

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Connects the sarcolemma to the sarcoplasmic reticulum

T tubules

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Has a relatively high concentration of Ca2+

Sarcoplasmic reticulum

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Cytoplasm inside each muscle fiber

Sarcoplasm

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Threadlike structures that extend from one end of the muscle to the other

Myofibrils

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Major protein fibers making up the myofibrils

Actin myofilaments and myosin myofilaments

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Actin and myosil myofilaments re arranged into highly ordered, repeating units called ____ which are joined end to end to form the myofibrils

Sarcomeres

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Actin myofilaments are also called

thin filaments

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3 components making up actin myofilaments

actin, troponin, tropomyosin

Resemble two minute strands of pearls twisted together, have attachement sites for the myosin myofilaments

Actin myofilaments

____ molecules are attached at specific intervals along the actin myofilaments which have binding sites for Ca2+

Troponin

______ filaments are located along the groove between the twisted strands of actin myofilament subunits

Tropomyosin

Myosin myofilaments are also called

thick myofilaments

These resemble bundles of minute golf clubs

Myosin myofilaments

3 important properties of myosin heads

1. The heads can bind to attachment sites on the actin myofilaments 2. they can bend and straighten during contraction 3. they can break down ATP, releasing energy

Basic structural and functional unit of skeletal muscle

Sarcomere

Smallest portion of skeletal muscle capable of contracting

Sarcomere

A network of protein fibers forming an attachment site for actin myofilaments

Z disk "Zwischensheibe"

Consists of only actin myofilaments, spans each Z disk and ends at the myosin myofilaments

I band "Isotropic"

A darker, central region in each sarcomere

A band "Anisotropic"

Second light zone in the center of each sarcomere which consists of only myosin myofilaments

H zone

The dark staining band where myosin myofilaments are anchored in the center of the sarcomere

M line "Mittelscheibe"

Inside of cell membranes is negatively charged compared to outside of the cell membrane

Polarized

Charge difference that occurs because there is an uneven distribution of ions across the cell memberance

Resting membrane potential

3 reasons for the developing of resting membrane potential

1. The concentration of K+ inside the cell membrane is higher than the outside of the cell membrane 2. The concentration of Na+ outside the cell membrane is higher that the inside of the cell membrane 3. The cell membrane is more permeable to K+ than to Na+

Inside of the cell membrane if positively charged

Depolarization

The change back to the resting membrane potential

Repolarization

The rapid depolarization and repolarization of the cell membrane

Action potential

Are specialized nerve cells that stimulate muscles to contract

Motor neurons

They generate action potentials that travel to skeletal muscle fibers

Motor neurons

Each branch of the axon of a motor neuron forms a junction with a muscle fiber called ____

Neuromuscular junction

Refers to the cell-to-cell junction between a nerve cell and either another nerve cell or an effector cell, such as in a muscle or a gland

Synapse

A single motor neuron and all the skeletal muscle fibers it innervates constitutes a ____

motor unit

An enlarged axon terminal

Presynaptic terminal

The apace between the presynaptic terminal and the muscle fiber membrane

synaptic cleft

Components of a Triad

2 terminal cisternae and a T tubule

Acts as a conduit that enables action potential to reach sarcoplasmic reticulum

Triad

Muscle fiber membrane

Postsynaptic cleft

Small vesicles in each presynaptic terminal

Synaptic vesicles

Functions as a neurotransmitter, a molecule released by a presynaptic nerve cell that stimulates or inhibits a postsynaptic cell

Acetylcholine

Enzyme that rapidly breaks down the acetylcholine released into the synaptic cleft between the neuron and the muscle fiber

Acetylcholinesterase

The sliding of actin myofilaments past myosin myofilaments during contraction

Sliding filament model of muscle contraction

Is formed between the actin and myosin myofilaments when the exposed attachments sites on the sites of the actin myofilament bind to the heads of the myosin myofilaments

Cross-bridges

States that the threshold stimulus can cause a muscle to contract to the fullest or none at all

Lucas Law or All or None Law

Condition when a person dies and no ATP is available to release cross-bridges causing the muscles to stiffen

Rigor mortis

Is the contraction of a muscle fiber in response to a timulus

muscle twitch

A cycle of rapid contraction and relaxation occuring in a muscle fiber following the occurence/application of a neural stimulus to the muscle in vivo or application of electrical stimulus during experimentation/experimental setting

Twitch

The time between the application of a stimulus and the beginning of contraction

lag phase or latent phase

Is the time during which the muscle contracts

Contraction phase

The time during which the muscle relaxes

Relaxation phase

The force of contaction of individual muscle is increased by rapidly stimulating them

Summation

A sustained contraction that occurs when the frequency of stimulation is so rapid that no relaxation occurs

Tetanus

When the number of muscle fibers contracting is increased by increasing the number of motor units stimulated, and the muscle contracts with more force

Recruitment

Requires O2 and breaks down glucose to produce 38 ATP, CO2, and H2O

Aerobic respiration

Does not require O2, and results from the breakdown of glucose to yield 2 ATP and lactic acid

Anaerobic respiration

Provides a means for storing energy that can be used rapidly to hep maintain an adequate amount of ATP in a contracting muscle fiber

Creatine phosphate

A state of reduced work capacity

Fatigue

Results when muscle fibers use ATP faster than they produce it and when the effectiveness of CA2+ to stimulate actin and myosin is reduced

Muscular fatigue

Occurs when there is too little ATP to bind to myosin myofilaments

Physiological contracture

Common type of fatigue that involves the central nervous syatem rather than the muscles themselves

Psychological fatigue

The length of the muscle does not change, but the amount of tension increases

Isometric Contractions

The amount of tension produced by the muscle is constant during the contraction, but the length of the muscle decreases

Isotonic Contractions

Isotonic contractions in which muscle tension increases as the muscle shortens

Concentric contractions

Isotonic contractions in which tension is maintained in a muscle, but the opposing resistance causes the muscle to lenghten

Eccentric contractions

The constant tension produced by body muscles over long periods of time

Muscle tone

Twitch fibers that contain type I myosin as the predominant or even exclusive type

Slow-twitch fibers

Twitch fibers that contain either type IIa or type IIb myosin myofilaments

Fast-twitch fibers

Enlargening of muscle fibers

Hypertrophy

Undifferentiated cells just below the endomysium

Satellite cells