Chapter 10: Muscular Tissue

cross-bridge

what the myosin head is referred to when it attaches to actin during the contraction cycle

caveolae

Although there are no transverse tubules in smooth muscle tissue, there are small pouch-like invaginations of the plasma membrane called ________ that contain extracellular Ca2+ used for muscular contraction.

Properties of Muscular Tissue

-Electrical excitability -Contractility -Extensibility -Elasticity

Muscular Tissue functions

-Movement -Stabilizing positions -Storing and mobilizing substances -Generating heat

Fascia

-dense sheet of irregular connective tissue that lines the body wall and limbs -supports and surrounds muscles and other organs of the body - holds muscles with similar functions together -allows free movement of muscles; carries nerves, blood vessels, and lymphatic vessels -fills spaces between muscles.

adipose tissue of the subcutaneous layer

-stores most of the body's triglycerides -serves as an insulating layer that reduces heat loss -protects muscles from physical trauma

main types of skeletal muscle fibers

1. slow oxidative fibers 2. fast oxidative-glycolytic fibers 3. fast glycolytic fibers

cramp

A painful spasmodic contraction. Caused by inadequate blood flow to muscles, overuse of a muscle, dehydration, injury, holding a position for prolonged periods, and low blood levels of electrolytes, such as potassium.

ligand-gated ion channels

ACh receptors are

Heat stroke

A dangerous condition in which the body loses its ability to cool itself through perspiration

how extra oxygen is used to restore metabolic conditions to the resting level:

1. convert lactic acid back into glycogen stores in the liver 2. resynthesize creatine phosphate and ATP in muscle fibers 3. replace the oxygen removed from myoglobin.

how muscle fibers produce ATP:

1. from creatine phosphate 2. by anaerobic glycolysis 3. by aerobic respiration

sources of oxygen in muscular tissue

1. oxygen that diffuses into muscle fibers from the blood 2. oxygen released by myoglobin within muscle fibers.

ATP hydrolysis

ATP is converted to ADP & phosphate energized myosin heads (removal of phosphate) need energy

Extensibility

Ability to be stretched (ex. smooth wall of stomach stretching as receiving food and cardiac muscle of heart stretch as it fills with blood)

Contractility

Ability to shorten forcibly when stimulated

Activation of ACh receptors

Binding of two molecules of ACh to the receptor opens an ion channel in it. Once open, Na+ ca flow across the membrane.

Botox

Blocks nerve signals temporarily

synaptic cleft

At most synapses a small gap, called the ______________, separates the two cells.

axon terminal

At the NMJ, the end of the motor neuron, called the _____________, divides into a cluster of synaptic end bulbs

lactic acid

Cardiac muscle fibers can also use ___________ produced by skeletal muscle fibers to make ATP, a benefit during exercise.

spastic paralysis

Certain disorders of the nervous system and electrolyte disturbances may result in _________________, partial paralysis in which the muscles exhibit spasticity

neurotransmitter

Chemical messengers that cross the synaptic gaps between neurons

Atrophy

Decrease in muscle size

mesoderm

Except for muscles such as those of the iris of the eyes and the arrector pili muscles attached to hairs, all muscles of the body are derived from ________. arranged in dense columns on either side of the developing nervous system as it develops.

acetylcholine (ACh)

Inside each synaptic vesicle are thousands of molecules of ___________________, the neurotransmitter released at the NMJ

delayed onset muscle soreness (DOMS)

From 12 to 48 hours after a period of strenuous exercise, skeletal muscles often become sore. ____________________________________ is accompanied by stiffness, tenderness, and swelling.

Cardiac muscle

Location: heart Function: pump blood Appearance: one nucleus, striated, intercalated discs Control: involuntary

Skeletal muscle

Location: skeletal Function: move bones Appearance: multi-nucleated and striated Control: voluntary

Smooth muscle (Visceral)

Location: various hollow internal organs (ex. GI tract, blood vessels, airways) Function: various functions (ex. peristalsis) Appearance: one nucleus and no striations Control: involuntary

myomesin

Molecules of the protein ________ form the M line. (M line proteins bind to titin and connect adjacent thick filaments to one another). holds the thick filaments in alignment at the M line.

2,3

If another nerve impulse releases more acetylcholine, steps _ and _ repeat.

aerobic respiration

If sufficient oxygen is present, the pyruvic acid formed by glycolysis enters the mitochondria, where it undergoes __________________, a series of oxygen-requiring reactions (the Krebs cycle and the electron transport chain) that produce ATP, carbon dioxide, water, and heat

Myalgia

Pain in or associated with muscles

neuromuscular junction (NMJ)

Muscle action potentials arise at the ____________________________, the synapse between a somatic motor neuron and a skeletal muscle fiber

Myomalacia

Pathological softening of muscle tissue

Myocytes

Muscle fibers; elongated

concentric isotonic contraction

If the tension generated in a(n) _______________________________ is great enough to overcome the resistance of the object to be moved, the muscle shortens and pulls on another structure, such as a tendon, to produce movement and to reduce the angle at a joint.

Myotonia

Increased muscular excitability and contractility, with decreased power of relaxation

Myositis

Inflammation of muscle fibers (cells)

Volkmann's contracture

Permanent shortening of a muscle due to replacement of destroyed muscle fibers by fibrous connective tissue, which lacks extensibility. Typically occurs in forearm muscles.

myosin-binding site

On each actin molecule is a __________________, where a myosin head can attach.

zone of overlap

Toward each end of the A band where the thick and thin filaments lie side by side

Myoma

Tumor composed of muscle tissue

tetrads

Voltage-gated Ca2+ channels arranged in clusters of four

Thermogenisis

Production of heat

smooth

______ muscle can both shorten and stretch to a greater extent than the other muscle types

cardiac

_______ (skeletal or cardiac) muscle tissue contraction lasts longer due to prolonged delivery of Ca2+ into the sarcoplasm

release

_______ of Ca2+ from the terminal cisterns of the sarcoplasmic reticulum triggers muscle contraction.

mitochondria

_____________ lie in rows throughout the muscle fiber, close to the contractile muscle proteins that use ATP during contraction so that ATP can be produced quickly as needed

Three types of muscular tissue

Skeletal, cardiac, and smooth

Glycogen

Storage form of glucose, can be used for synthesis of ATP

Myology

Study of muscles

Connective tissue

Surrounds and protects muscle tissue

synaptic vesicles

Suspended in the cytosol within each synaptic end bulb are hundreds of membrane-enclosed sacs called _________________.

shaft of the thick filament

Tails of neighboring myosin molecules lie parallel to one another

Elasticity

The ability to be stretched or compressed and then return to original size

Electrical excitability

The ability to respond to a stimulus and convert it into an action potential

A band

The darker middle part of the sarcomere, extends the entire length of the thick filaments

Termination of ACh activity

The effect of ACh binding lasts only briefly because ACh is rapidly broken down by an enzyme called acetylcholinesterase (AChE).

Attachment of myosin to actin

The energized myosin head attaches to the myosin-binding site on actin and releases the previously hydrolyzed phosphate group.

Production of muscle action potential

The inflow of Na+ (down its electrochemical gradient) makes the inside of the muscle fiber more positively charged. This change in the membrane potential triggers a muscle action potential. Each nerve impulse normally elicits one muscle action potential. The muscle action potential then propagates along the sarcolemma into the system of T tubules. This causes the sarcoplasmic reticulum to release its stored Ca2+ into the sarcoplasm, and the muscle fiber subsequently contracts.

energized

The myosin head is said to be _________ when it contains stored energy.

motor end plate

The region of the sarcolemma opposite the synaptic end bulbs, called the _______________, is the muscular part of the NMJ.

excitation-contraction coupling

The sequence of events that links excitation (a muscle action potential) to contraction and occurs at the triads of the skeletal muscle fiber

eccentric isotonic contraction

When the length of a muscle increases during a contraction, the contraction is a(n) ______________________________. tension exerted by the myosin cross-bridges resists movement of a load and slows the lengthening process.

flaccid

When the motor neurons serving a skeletal muscle are damaged or cut, the muscle becomes _______, a state of limpness in which muscle tone is lost.

acetylcholine receptors

Within each motor end plate are 30-40 million _______________________, integral transmembrane proteins to which ACh specifically binds.

stress-relaxation response

allows smooth muscle to undergo great changes in length while retaining the ability to contract effectively (ex. the walls of blood vessels and hollow organs such as the stomach, intestines, and urinary bladder can stretch, the pressure on the contents within them changes very little. After the organ empties, the smooth muscle in the wall rebounds, and the wall retains its firmness)

Striations

alternating A bands and I bands

Myasthenia gravis

an autoimmune disease that causes chronic, progressive damage of the neuromuscular junction produces antibodies that bind to and block some AChreceptors, thereby decreasing the number of functional ACh receptors at the motor end plates of skeletal muscles.

fasciculation

an involuntary, brief twitch of an entire motor unit that is visible under the skin; it occurs irregularly and is not associated with movement of the affected muscle. (seen in multiple sclerosis or in amyotrophic lateral sclerosis)

anabolic steroids

artificial forms of the hormone testosterone that promote muscle growth and strength

sarcomeres

basic functional units of a myofibril

calsequestrin

calcium binding protein in the sarcoplasmic reticulum

muscular dystrophy

a group of inherited muscle-destroying diseases that cause progressive degeneration of skeletal muscle fibers.

Nebulin

a long, nonelastic protein wrapped around the entire length of each thin filament. It helps anchor the thin filaments to the Z discs and regulates the length of thin filaments during development.

refractory period

a muscle fiber receives enough stimulation to contract, it temporarily loses its excitability and cannot respond for a time.

tremor

a rhythmic, involuntary, purposeless contraction that produces a quivering or shaking movement.

wave summation

a second stimulus occurs after the refractory period of the first stimulus is over, but before the skeletal muscle fiber has relaxed, the second contraction will be stronger than the first.

Interval training

a workout regimen that incorporates both types of training (ex. alternating sprints with jogging)

thin filaments

actin; troponin and tropomyesin

aerobic

cardiac muscle depends largely on _______ respiration to generate ATP

curare

causes muscle paralysis by binding to and blocking ACh receptors. Ion channels do not open. Often used during surgery to relax skeletal muscles.

H zone

center of each A band, contains thick but not thin filaments

flaccid paralysis

characterized by loss of muscle tone, loss or reduction of tendon reflexes, and atrophy (wasting away) and degeneration of muscles.

Fibromyalgia

chronic, painful, nonarticular rheumatic disorder that affects the fibrous connective tissue components of muscles, tendons, and ligaments.

types of isotonic contractions

concentric and eccentric

aponeurosis

connective tissue elements extending as a broad, flat sheet (ex. epicranial ___________ on top of the skull between the frontal and occipital bellies of the occipitofrontalis muscle)

motor unit

consists of a somatic motor neuron plus all of the skeletal muscle fibers it stimulates

multi-unit smooth muscle tissue

consists of individual fibers, each with its own motor neuron terminals and with few gap junctions between neighboring fibers stimulation causes contraction of that fiber only found in the walls of large arteries, in airways to the lungs, in the arrector pili muscles that attach to hair follicles, in the muscles of the iris that adjust pupil diameter, and in the ciliary body that adjusts focus of the lens in the eye.

Ca2+ release channels

present in the terminal cisternal membrane of the SR blocked by a cluster of voltage-gated Ca2+ channels in a relaxed muscle, preventing Ca2+ from leaving the SR 1) skeletal muscle fiber is excited and an action potential travels along the T tubule 2) Ca2+ channels detect the change in voltage and undergo a conformational change 3) Ca2+ release channels open 4) large amounts of Ca2+ flow out of the SR into the sarcoplasm around the thick and thin filaments. 5) the Ca2+ concentration in the sarcoplasm rises tenfold or more 6) the released calcium ions combine with troponin

neuromuscular disease

problems with somatic motor neurons, neuromuscular junctions, AND muscle fibers.

motor unit recruitment

process in which the number of active motor units increases

Botulinum toxin

produced by the bacterium clostridium botulinum, blocks release of ACh

intermediate filaments

protein fibers that provide stability of shape; smooth muscle fibers contain these

Dystrophin

protein that links thin filaments of sarcomere to integral membrane proteins in sarcolemma, which are attached in turn to proteins in connective tissue matrix that surrounds muscle fibers; help reinforce sarcolemma and transmit tension generated by sarcomeres to tendons.

Motor proteins

pull various cellular structures to achieve movement by converting the chemical energy in ATP to the mechanical energy of motion, that is, the production of force.

nutrients needed for aerobic respiration to supply enough ATP for muscles (with oxygen)

pyruvic, fatty acids, and amino acids

myogram

recording of a muscle contraction

myoglobin

red-colored protein in sarcoplasm that binds oxygen molecules that diffuse into muscle fibers from interstitial fluid and releases oxygen when it is needed by the mitochondria for ATP production

oxygen debt

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

Hypotonia

refers to decreased or lost muscle tone

synapse

region where communication occurs between a somatic motor neuron and a muscle fiber.

Tendon formed by all three connective tissue layers

ropelike; may extend beyond the muscle fibers to attach a muscle to the periosteum of a bone. (ex. calcaneal (Achilles) tendon of the gastrocnemius (calf) muscle, attaches the muscle to the calcaneus (heel bone))

contraction period

second phase (10-100 msec); Ca2+ binds to troponin, myosin-binding sites on actin are exposed, and cross-bridges form. Peak tension develops in the muscle fiber.

Z discs

separate one sarcomere from the next

myopathy

signifies a disease or disorder of the skeletal muscle tissue itself

anticholinesterase agents

slowing the enzymatic activity of acetylcholinesterase, thus slowing removal of ACh from the synaptic cleft. can strengthen weak muscle contractions.

filaments/myofilaments

smaller protein structures within myofibrils

tic

spasmodic twitching made involuntarily by muscles that are ordinarily under voluntary control. (ex. twitching of the eyelid and facial muscles)

sarcoplasm

cytoplasm of a muscle fiber containing a substantial amount of glycogen

red muscle fibers

dark red with high myoglobin (also contain more mitochondria and are supplied by more blood capillaries)

rigor mortis

stiffening of the body after death

somatic motor neurons

stimulate skeletal muscle to contract; has a threadlike axon that extends from the brain or spinal cord to a group of skeletal muscle fibers.

anaerobic training

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

junctional folds

deep grooves within acetylcholine receptors in the motor end plate that provide a large surface area for ACh.

latent period

delay between stimulus and contraction (2msec); muscle action potential sweeps over the sarcolemma and calcium ions are released from the sarcoplasmic reticulum.

Perimysium

dense irregular connective tissue coat, surrounds groups of muscle fibers, separating them into fascicles

terminal cisterns

dilated end sacs of the sarcoplasmic reticulum butt against the T tubule from both sides

myosin heads

each has two binding sites: an actin-binding site and an ATP-binding site.

recovery oxygen uptake

elevated oxygen use after exercise: elevated body temperature increases the rate of chemical reactions throughout the body. Faster reactions use ATP more rapidly, and more oxygen is needed to produce the ATP. the heart and the muscles used in breathing are still working harder than they were at rest, and thus they consume more ATP. tissue repair processes are occurring at an increased pace.

Anaerobic Glycolysis

entire process by which the breakdown of glucose gives rise to lactic acid when oxygen is absent or at a low concentration (2 minutes)

Layers of connective tissue extend from the fascia to protect and strengthen skeletal muscle

epimysium, perimysium, endosmysium

aerobic training

exercise that increases the body's capacity to use oxygen

Strength training

exercising with progressively heavier resistance for the purpose of strengthening the musculoskeletal system increase bone strength by increasing the deposition of bone minerals

sliding filament mechanism

explains how the entire muscle contracts but muscle fiber length remains constant

sarcoplasmic reticulum (SR)

fluid-filled system of membranous sacs encircling each myofibrils; similar to smooth endoplasmic reticulums

visceral (single-unit) smooth muscle tissue

found in the skin and in tubular arrangements that form part of the walls of small arteries and veins and of hollow organs (ex. stomach, intestines, uterus, and urinary bladder) autorhythmic fibers connect to one another by gap junctions contract in unison, as a single unit.

ATP-binding site

functions as an ATPase—an enzyme that hydrolyzes ATP to generate energy for muscle contraction

myoblasts

fusion of several small mesodermal cells called __________, how skeletal muscle fibers arises during embryonic development

troponin

holds tropomyosin strands in place and when calcium ions (Ca2+) bind to it, it undergoes a conformational change moving tropomyosin away from myosin-binding sites on actin, and muscle contraction subsequently begins as myosin binds to actin.

calmodulin

in smooth muscle cells a regulatory protein called __________ binds to Ca2+ in the sarcoplasm. (Recall that troponin takes this role in striated muscle fibers)

muscle fatigue

inability of a muscle to maintain force of contraction after prolonged activity

creatine phosphate

supplies energy for the synthesis of excess ATP

twitch contraction

the brief contraction of all muscle fibers in a motor unit in response to a single action potential in its motor neuron

exercise-induced muscle damage

include torn sarcolemmas in some muscle fibers, damaged myofibrils, and disrupted Z discs. indicated by increases in blood levels of proteins, such as myoglobin and the enzyme creatine kinase In response, muscle fibers undergo repair: new regions of sarcolemma and more muscle proteins (including those of the myofibrils) are synthesized in the sarcoplasm of the muscle fibers.

hyperplasia

increase in number of fibers

Rigidity

increased muscle tone in which reflexes are not affected, as occurs in tetanus

length-tension relationship

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

cardiac muscle tissue

involuntary muscle tissue that makes up the heart

smooth muscle tissue

involuntary; visceral and multi-unit

intercalated discs

irregular transverse thickenings of the sarcolemma that connect the ends of cardiac muscle fibers to one another contain desmosomes: holds fibers together and gap junctions: allow muscle action potentials to spread from one fiber to another has an endomysium and perimysium, but lacks an epimysium mitochondria is plentiful and larger (than skeletal)

Spasticity

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

Fast oxidative-glycolytic (FOG) fibers

largest fibers contain many myoglobin and blood capillaries; dark red appearance generate ATP by aerobic respiration, which gives them a moderately high resistance to fatigue generate ATP by anaerobic glycolysis because intracellular glycogen level is high ATPase in their myosin heads hydrolyzes faster contribute to walking and sprinting

I band

lighter, less dense area that contains the rest of the thin filaments but no thick filaments, a Z disc passes through its center.

Voltage-gated Ca2+ channels

located in the T tubule membrane; serve as voltage sensors that trigger the opening of the Ca2+ release channels

acetylcholinesterase (AChE)

located on the extracellular side of the motor end plate membrane. It breaks down ACh into acetyl and choline, products that cannot activate the ACh receptor.

Fast glycolytic (FG) fibers

low myoglobin content, few blood capillaries, and few mitochondria; white large amounts of glycogen and generate ATP by glycolysis adapted for intense anaerobic movements of short duration, (ex. weight lifting) but fatigues quickly. muscle enlargement due to hypertrophy of these fibers

Actin

main component of the thin filament is the protein _____

Myosin

main component of thick filaments and functions as a motor protein in all three types of muscle tissue

central fatigue

mental fatigue from feelings of tiredness and desire to stop

M line

middle of the sarcomere

tendon

muscle to bone

thick filaments

myosin

contractile proteins

myosin and actin: generate force during contraction

Detachment of myosin from actin

myosin heads rebind to ATP and the crossbridges detach from actin

Release of acetylcholine

nerve impulse at the synaptic end bulbs stimulates voltage-gated channels to open. Because calcium ions are more concentrated in the extracellular fluid, Ca2+ flows inward through the open channels. The entering Ca2+ in turn stimulates the synaptic vesicles to undergo exocytosis. During exocytosis, the synaptic vesicles fuse with the motor neuron's plasma membrane, liberating ACh into the synaptic cleft. The ACh then diffuses across the synaptic cleft between the motor neuron and the motor end plate.

action potentials (impulses)

nerve impulses

pericytes

new smooth muscle fibers can arise from cells called _________, stem cells found in association with blood capillaries and small veins.

glycolysis

occurs in the cytosol and quickly breaks down each glucose molecule into two molecules of pyruvic acid; does not require oxygen

Epimysium

outer layer, encircling the entire muscle consisting of dense irregular connective tissue

white muscle fibers

pale with low myoglobin

function of thin and thick filaments

part of contractile process

Endomysium

penetrates the interior of each fascicle and separates individual muscle fibers, mostly reticular fibers

sarcolemma

plasma membrane of a muscle cell

capillaries in muscular tissue

plentiful, bring in oxygen and nutrients and remove heat and waste products of muscle metabolism

myosin tail

points toward the M line in the center of the sarcomere

isotonic contraction

the tension (force of contraction) developed in the muscle remains almost constant while the muscle changes its length. used for body movements and for moving objects.

relaxation period

third phase (10-100 msec); Ca2+ is actively transported back into the SR, myosin-binding sites are covered by tropomyosin, myosin heads detach from actin, and tension in the muscle fiber decreases.

regulatory proteins

tropomyosin and troponin: help switch contraction process on and off

transverse (T) tubules

tubules that extend across the sarcoplasm and allow electrical impulses to travel deep into the cell

composition of filaments in regions of filament overlap

two thin filaments for every thick filament

Ca2+-ATPase pumps

use ATP to constantly transport Ca2+ from the sarcoplasm into the SR

triad

a transverse tubule and the two terminal cisterns on either side of it form a _____

Subcutaneous layer (Hypodermis)

-Separates muscle from skin -areolar connective tissue and adipose tissue -pathway for nerves, blood vessels, and lymphatic vessels

titin

-connects a Z disc to the M line of the sarcomere, helps stabilize the position of the thick filament. -the part that extends from the Z disc is elastic, can stretch to at least 4x its resting length spring back unharmed -accounts for much of the elasticity and extensibility of myofibrils -helps the sarcomere return to its resting length after a muscle has contracted or been stretched, helps prevent overextension of sarcomeres, and maintains the central location of the A bands.

A nerve impulse (nerve action potential) elicits a muscle action potential in the following way:

1. Release of acetylcholine 2. Activation of ACh receptors 3. Production of muscle action potential 4. Termination of ACh activity

myosin light chain kinase

After binding to Ca2+, calmodulin activates an enzyme called _________________________. It uses ATP to add a phosphate group to a portion of the myosin head. Once the phosphate group is attached, the myosin head can bind to actin, and contraction can occur (slow)

voltage-gated Ca2+ channels and Ca2+ release channels

At a given triad, the T tubule and terminal cisterns are mechanically linked together by two groups of integral membrane proteins:

Fasicles

Bundles of muscle fibers

higher

In a relaxed muscle fiber, the concentration of Ca2+ is 10,000 times ______ in the SR than in the sarcoplasm

stores

In a relaxed muscle fiber, the sarcoplasmic reticulum ______ calcium ions (Ca2+).

tropomyosin

In relaxed muscle, myosin is blocked from binding to actin because strands of ___________ cover the myosin-binding sites on actin.

dense bodies

In smooth muscle fibers, the thin filaments attach to structures called ____________, which are functionally similar to Z discs in striated muscle fibers.

Hypertrophy

Increase in muscle fiber size

alpha actinin

The dense material of the Z discs contains molecules of _________, which bind to actin molecules of the thin filament and to titin

Power stroke

What is the term for the flex of the myosin cross bridge to slide actin?

fused (complete) tetanus

a skeletal muscle fiber is stimulated at a higher rate of 80-100x/sec and doesn't relax. The result is ________________________, a sustained contraction in which individual twitches cannot be detected

unfused (incomplete) tetanus

a skeletal muscle fiber is stimulated at a rate of 20-30x/sec, it partially relaxes between stimuli. The result is a sustained but wavering contraction called _____________________________

muscle tone

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

Creatine

a small, amino acid-like molecule that is synthesized in the liver, kidneys, and pancreas and then transported to muscle fibers. (15 seconds)

fibrillation

a spontaneous contraction of a single muscle fiber that is not visible under the skin but can be recorded by electromyography. May signal destruction of motor neurons.

smooth muscle tone

a state of continued partial contraction

spasm

a sudden involuntary contraction of a single muscle in a large group of muscles

Slow oxidative (SO) fibers

appear dark red because of large amounts of myoglobin and many blood capillaries have many large mitochondria, generates ATP mainly by aerobic respiration ATPase in the myosin heads hydrolyzes ATP relatively slowly contraction cycle proceeds slowly resistant to fatigue and capable of prolonged contractions adapted for maintaining posture and for aerobic, endurance-type activities such as running a marathon. increases with aging

Myofibrils

contractile organelles of skeletal muscle, what makes it look striated

3 proteins in myofibrils

contractile, regulatory, structural

isometric contraction

contraction without movement; increase tension, no motion; eg. bar hang

autorhythmicity

heart's ability to control its own contractions

frequency of stimulation

the number of impulses per second

synaptic end bulbs

the neural part of the NMJ

contraction cycle

the repeating sequence of events that causes the thin filaments to slide past the thick filaments: 1. ATP hydrolysis 2. Attachment of myosin to actin 3. Power stroke 4. Detachment of myosin from actin

Contraction of smooth muscle fibers

the sliding filament mechanism involving thick and thin filaments generates tension that is transmitted to intermediate filaments. dense bodies attached to the sarcolemma are pulled, causing a lengthwise shortening of the muscle fiber. The fiber twists in a helix as it contracts, and rotates in the opposite direction as it relaxes.

structural proteins

titin, α-actinin, myomesin, nebulin, and dystrophin: alignment, stability, elasticity, and extensibility of myofibrils.