Chapter 11: Muscle

thin filaments

8 nm in diameter

recovery oxygen uptake

A better term than oxygen debt for the elevated use of oxygen after exercise

F actin

A fibrous protein made of a long chain of G actin molecules twisted into a helix

Steps of Contraction Cycle

ATP hydrolysis, attachment of myosin to actin, power stroke, detachment of myosin from actin

Examples of contractile proteins

Actin and Myosin

Resting membrane potential of skeletal muscle fiber

-90 mV

Calsequestrin

-bind to Ca2+, allowing even more Ca2+ to be sequestered (stored) within the SR

Power Stroke

As the myosin head changes to its new position, it pulls the thin filament past the thick filament towards the center f he sarcomere

contraction period

Ca2+ binds to troponin Myosin-binding sites on actin are exposed. Cross-bridges form

Release of ____ from the ___ of the sarcoplasmic reticulum triggers muscle contraction

Ca2+ from the terminal cisternae

Relaxation Period

Ca2+ gets actively transported back into the sarcoplasmic reticulum, myosin-binding sites are covered by tropomyosin, myosin heads detach from actin, and tension in the muscle fiber decreases

Sarcomeres

Compartments thick and thin filaments in a myofibril are arranged in

Myofibrils are built from three kinds of proteins:

Contractile proteins, regulatory proteins, and structural proteins.

Excitation-contraction (EC) coupling

The sequence of events that links the muscle action potential to muscle contraction

Neuromuscular Junction

The synapse between a somatic motor neuron and a skeletal muscle fiber

Examples of structural proteins

Titin, a-actinin, myomesin

ATP Hydrolysis

When a myosin head that includes ATPase hydrolyzes ATP into ADP and a phosphate group

Store-operated channels

When the intracellular reserves of Ca2+ in the SR are depleted, a signal from the SR to the sarcolemma opens these

Sliding Filament Mechanism

When the muscle shortens during contraction because the thick and thin filaments slide past one another

Each tintin molecule connects

Z discs to the M line of the sarcomere

Each myosin head has...

a binding site for an ATP molecule and for an actin molecule, and the ability to swivel when powered by ATP.

latent period

a brief delay that occurs between application of the stimulus and the beginning of contraction

Tendon

a cord of connective tissue that attaches the muscle to a bone

electromyography

a diagnostic test that measures the electrical activity (muscle action potentials) in resting and contacting muscles

Sarcoplasmic reticulum

a fluid-filled system of membranous sacs that encircle each myofibril

functional syncytium

a mass of interconnected muscle fibers that act as a single coordinated unit

Troponin

a protein that consists of three globular subunits: one that binds to tropomyosin, one that binds to actin, and one that has binding sites for calcium ions (Ca2+).

Calmoudin

a regulatory protein in the sarcoplasm that is similar in structure to troponin

lever

a rigid structure that can move around a fixed point

Tropomyosin

a rod-shaped protein that join together and wrap around the F-actin double helix

aerobic respiration

a series of oxygen-requiring reactions that produce ATP, carbon dioxide, and heat

motor unit

a single motor neuron and all the muscle fibers it innervates

Creatine

a small amino acid like molecule that is synthesized in the liver, kidneys, and pancreas and then transported to muscle fibers

Muscle Tone

a small amount of tautness or tension in the muscle due to weak, involuntary contraction of its motor units

fused (complete) tetanus

a smooth, sustained contraction in which individual twitches cannot be detected and maximum tension is reached.

smooth muscle tone

a state of continued partial contraction caused by prolonged presence of Ca2+ in the sarcoplasm

Interval training

a workout regimen that incorporates both anaerobic and aerobic training

Extensibility

ability of the muscle to stretch without being damaged

Flexion

action of bending a limb at the joint

Extension

action of straightening out a limb at a joint

Krebs cycle and electron transport chain is included in

aerobic respiration

The muscular system

all of the skeletal muscles in the body

Stress-relaxation response

allows smooth muscle to undergo great changes in length while retaining the ability to contract effectively

Muscle action potentials travel

along the sarcolemma and through the t tubules

Striations

alternating light and dark bands that are visible under a light microscope

asynchronous recruitment

alternation of contracting and relaxing motor units, which delays muscle fatigue

Muscular Hypertrophy

an increase in the diameter of muscle fibers due to increased myofibrils and other organelles.

hyperplasia

an increase in the number of fibers

I band

area that contains the rest of the thin filaments but no thick filaments; on either side of the A band

Hair moving muscles

arrector pili

Disuse Atrophy

atrophy that occurs because muscles are not being used.

Single-unit smooth muscle as a functional syncytium consists of two types of cells:

autorhythmic fibers and contractile fibers

autorhythmicity

built in rhythm

Autorhythmicity

built in rhythm of the heart

Fascicles

bundles of muscle fibers separated by connective tissue.

Flaccid paralysis

characterized by loss of muscle tone, loss or reduction of tendon reflexes, and atrophy and degeneration of muscles

Smooth muscle receptors are not

confined to the motor end plate, but are on the entire surface of the cell

Multi-unit smooth muscle

consists of fibers that act independently of each other as multiple units

Ca2+-ATPase Pumps

constantly transport Ca2+ from the sarcoplasm into the SR

Glycogen

contained in the sarcoplasm; a large polysaccharide that serves as a storage form of glucose.

Postural muscles contract _____ when you are awake

continuously

Fast glycolytic fibers

contract quickly, have fast myosin ATPase, and are easily fatigued

slow oxidative fibers

contract slowly, have slow acting myosin ATPases, and are fatigue resistant, smallest

myofibrils

contractile elements of the skeletal muscle fiber that extend throughout the sarcoplasm.

Graded contractions

contractions that vary in strength depending on how much force is needed by the muscle to support a particular object

Structural Proteins

contribute to the alignment, stability, elasticity, and extensibility of myofibrils

Creatine + ATP =

creatine phosphate + ADP

Slow-wave potentials

cycles of alternating depolarization and repolarization that do not necessarily reach threshold

hypotonia

decreased or lost muscle tone

Myosin light-chain kinase (MLCK)

enzyme that phosphorylates light protein chains of myosin in smooth muscle

aerobic training

exercise such as walking or jogging, which increase the supply of oxygen rich blood available to skeletal muscles

Single-unit smooth muscle

fibers contract together as a single unit

muscles produce

force and stabilizing joints

Tension

force of contraction

Myoglobin

found in the sarcoplasm; red-colored, oxygen-binding protein that is only found in muscle.

Visceral Smooth muscle

found in the walls of viscera (internal organs) such as the stomach

Skeletal muscle fibers have three ways to produce ATP

from creatine phosphate, anaerobic glycolysis, and aerobic respiration

Myosin

functions as a motor protein in all three types of muscle tissue

Contractile proteins

generate force during contraction

glycogen can be broken down into...

glucose molecules that can be used to synthesize ATP.

Regulatory proteins

help switch the contraction process on and off

Sustained contractions of your neck muscle...

holds your head upright

hyperplasia can occur in

in limited types of smooth muscle

series elastic elements

in series with the contractile elements of a muscle and transfers the tension generated by sliding filaments to bone

Muscle fatigue

inability of muscle to maintain force of contraction after prolonged activity

spasticity

increased muscle tone (stiffness) associated with an increase in tendon reflexes and pathological reflexes

Rigidity

increased muscle tone in which reflexes are not affected

motor unit recruitment

increasing the number of active motor units

length-tension relationship

indicates how the forcefulness of muscle contraction depends on the length of the sarcomeres within a muscle before contraction begins

G actin

individual molecules of actin

load-velocity relationship

inverse relationship between the load and the velocity of shortening

Cardiac muscle is...

involuntary and striated

Smooth muscle is usually..

involuntary, some have autorhythmicity

Structural proteins

keep the thick and thin filaments in proper alignment and link the myofibrils to the sarcolemma and extracellular matrix. gives the myofibril its elasticity

bones are

levers

Dihydropyridine receptor

located in the t-tubule membrane

Smooth Muscle

located in the walls of hollow internal structures

Actin

main component of the thin filament

Smooth muscle

mainly found in the walls of hallow organs and tubes, where it contracts to move substances through the interior spaces of these structures.

Activity can be consciously controlled by...

motor neurons that are part of the somatic nervous system

Mature skeletal muscle has..

multiple nuclei

Muscle fibers

muscle cells arranged parallel to one another.

cardiac muscle

muscle only contained in the heart

Skeletal muscle

muscle that is attached to bones and moves parts of the skeleton

Extensors

muscles that promote extension

Flexors

muscles that promote flexion of a limb

Satellite cells

myoblasts that persist in mature skeletal muscle

In a relaxed muscle,

myosin is blocked from binding to actin because the strands of of tropomyosin cover the binding sites on actin

cardiac muscle

only found in the heart

Receptor-activated channels

opened by some neurotransmitters and hormones in the sarcolemma of smooth muscle fiber, allows Ca2+ into the sarcoplasm

load/resistance

opposes movement

cardiac muscle has a high demand for

oxygen

autorhythmic cells

pacemaker cells

Spastic paralysis

partial paralysis in which the muscles exhibit spasticity

refractory period

period of lost excitability after stimulus is applied in all muscle and nerve cells

Sarcolemma

plasma membrane of a muscle fiber

Light chains

portion of myosin molecule, contains four chains

Heavy chains

portion of myosin molecule, contains two chains wrapped around each other

Ca2+ release channels

present in the terminal cisternal membrane of the SR

Muscle functions

producing body movements, stabilizing body positions, storing and moving substances within the body, Generating heat

Antagonistic muscles

promote opposite actions at the same joint, one muscle contracts while the other relaxes

Excitatory

promote the contraction of smooth muscle

inhibitory

promotes relaxation of smooth muscles

Electrical Excitability

properties of both neurons and muscle cells; ability to respond to certain stimuli by producing action potentials.

Glycolysis

quickly breaks down each glucose molecule into two molecules of pyruvic acid

fast glycolytic fibers are used for

rapid, intense movements such as weight lifting

Myogram

record of a muscle contraction

Motor end plate

region of muscle fiber membrane opposite the synaptic end bulb

L-type voltage gated Ca2+ channels

remain open for a relatively long period of time in response to activation

Sphincters

ringlike bands of smooth muscle which prevent outflow of the contents of a hollow organ.

Slow oxidative fibers are used when

running marathons and maintaining posture

Z discs

separate one sarcomere from the next

Stabilizing Body Positions

skeletal muscle contractions stabilize joints and help maintain body positions, such as standing or sitting

Caveolae

small pouch-like invaginations of the plasma membrane that release extracellular Ca2+

Pacemaker potential

spontaneous depolarization that always reaches threshold and therefore triggers the production of an action potential

anaerobic training

stimulate synthesis of muscle proteins and result, over time, in increased muscle size (muscle hypertrophy). Sprinting

Wave summation

stimuli arriving at different times cause larger contractions

Storage and moving substances within the body

storage is accomplished by sustained contractions of sphincters

Smooth muscle lacks..

striations

filaments

structures within myofibrils that have either a thick or thin diameter

M line

supporting proteins that hold the thick filaments together in the H zone

unfused (incomplete) tetanus

sustained, but wavering contraction with partial relaxation between stimuli

Varicosities

swollen regions on the axons of autonomic motor neurons branching into smooth muscle

Sphincters allow for

temporary storage of food in the stomach or urine in the urinary bladder, cardiac muscle contractions

Isotonic contraction

tension developed by the muscle that remains constant while the muscle changes its length

maintenance of heart rate is done by

the ANS

Contractility

the ability of muscle to contract forcefully when adequately stimulated.

oxygen debt

the added oxygen, over and above the resting oxygen consumption, that is taken into the body after exercise

Origin

the attachment of a muscle's tendon to the more stationary bone

insertion

the attachment of the muscle's other tendon to the more movable bone

twitch

the brief contraction of a group of muscle fibers within a muscle in response to a single action potential

Satellite cells retain..

the capacity to fuse with one another or with damaged muscle fibers to regenerate functional muscle fibers.

H zone

the center of each A band contains thick filaments but no thin filaments

Sarcoplasm

the cytoplasm of a muscle fiber

A band

the dark middle part of the sarcomere which extend the entire length of the thick filaments

hypertrophy

the enlargement of existing cells

anaerobic glycolysis

the entire process by which the breakdown of glucose gives rise to lactic acid when oxygen is absent or at a low concentration

Acetylcholinesterase (AChE)

the enzyme that breaks down acetylcholine in the synaptic cleft

What occurs during the latent period?

the events of excitation-contraction coupling

The myosin heads contain

the light chains

Dense bodies

the structure that allows smooth muscle to generate intracellular contractile tension, similar to z discs

The neuromuscular junction has three components

the synaptic end bulbs of a terminal branch of the somatic motor neuron, a synaptic cleft, and the motor end plate

action

the type of movement that occurs when a muscle contracts

Examples of Structural Proteins

tintin, myomesin,

Triad

transverse tubule and the two terminal cisternae on either side of it.

When Ca2+ binds to troponin,

troponin undergoes a change in shape that releases

Transverse (T) tubules

tunnel in from the surface toward the center of each muscle fiber

lactic acid

under anaerobic conditions, the pyruvic acid generated from glycolysis is converted into this

Myoblasts

undifferentiated cells that fuse to form muscle fibers during emrbyonic development

Skeletal muscle works in a...

voluntary manner

Fast oxidative glycolytic fibers are used for

walking snd sprinting

Muscular Atrophy

wasting away of muscle due to progressive loss of myofibrils.

Crossbridge

when a myosin head attaches to actin during the contraction cycle

mechanical disadvantage

when a relatively large effort is required to move a small load

Mechanical advantage

when a relatively small effort is required to move a large load over a small distance.

Mechanically-gated channels

when a smooth muscle fiber is stretched, these open, allowing extracellular Ca2+ to move into the sarcoplasm

latch state

when myosin heads in smooth muscle attach to actin for a longer portion of the crossbridge cycle

Flaccid

when the motor neurons serving a skeletal muscle are damaged or cut

denervation atrophy

when the nerve supply to a muscle is disrupted or cut

Concentric Isotonic Contraction

when the tension generated is great enough to exceed the load and the muscle shortens, pulling another structure to produce movement

Isometric Contraction

when the tension generated is not enough to exceed the load, and the muscle length does not change

Terminal Cisternae

Dilated end sacs of the sarcoplasmic reticulum

Four functions of muscle that enable it to function and contribute to homeostasis:

Electrical excitability, contractility, extensibility, elasticity

myosin phosphatase

Enzyme that dephosphorylates light protein chains of myosin

Voltage Gated Channels

In smooth muscle, these open in a graded potential in response to strength of depolarization

hypertonia

Increased muscle tone that is expressed as spasticity or rigidity

fast oxidative glycolytic fibers

Intermediate in diameter, moderate resistance to fatigue, faster speed of contraction

Ca 2+ release channels

Open with muscle action and allow Ca2+ to flow out of the SR into the sarcoplasm

IP3-gated channels

Opened by a second messenger pathway activated by Ca2+, releases Ca2+ ions from the SR into the sarcoplasm

Producing Body Movements

Relies on integrated functioning of skeletal muscle, bones, and joints. Ex: walking, running, localized movements

contractile fibers

Specialized fibers for contraction that make up the great mass of the heart.

End plate potential

The depolarization of the motor end plate on a muscle cell.

thick filaments

16 nm in diameter

Generating Heat

As muscle contracts, it produces hear in a process known as thermogenesis

Plateau phase

L-type voltage gated Ca2+ channels remain open and voltage-gated K+ channels partially open

Ca2+ induced Ca2+ release (CICR)

The process by which extracellular Ca2+ triggers the release of additional Ca2+ from the SR

Examples of Regulatory Proteins

Tropomyosin and troponin