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.