Use LEFT and RIGHT arrow keys to navigate between flashcards;
Use UP and DOWN arrow keys to flip the card;
H to show hint;
A reads text to speech;
98 Cards in this Set
- Front
- Back
A band
|
Where the thick filaments are located at the center of a sacromere; The dark bands; The length of the A band is equal to the typical length of a thick filament; includes 3 subdivisions: M line, H band, Zone of overlap; triad found on the edge of the A band in the zone of overlap
|
|
M line
|
Dark-staining proteins that help stabilize the position of the thick filaments in the A band; connects central portion of each thick filament to its neighbors
|
|
H band
|
Lighter region on either side of the M line when the sarcomere is at rest; contains thick filaments and no thin filaments.
|
|
Zone of overlap
|
region in which each thin filament is surrounded by 3 thick filaments, and each thick filament is surrounded by six thin filaments; triad found at the edge of zone of overlap and releases calcium ions into the zone of overlap to begin muscle contraction
|
|
Sarcomere
|
functional units of myofilaments; approx. 10,000 in a myofibril from end to end; smallest functional unit of the muscle fiber; interactions between thick and thin filaments are responsible for muscle contraction; has dark bands (A band) and light bands (I band)
|
|
I band
|
contains thin flaments, is made of actin, is the light colored band in the sarcomere; extends from A band of 1 sarcomere to A band of another; Z line is located in the middle of the I band
|
|
Z line
|
is the boundary between sarcomeres; made of proteins called actinins which interconnect the thin filaments of adjacent sarcomeres; from z lines thin filaments extend toward M lline into zone of overlap; strands of titin extend from the tips of thick filaments and attach to the Z line; intermediate filaments surround the Z line and connnect adjacent myofibrils to each other and to the sarcolemma membrane; this is what gives the skeletal muscle fiber a banded, striated look
|
|
Titin
|
extend from the tips of thick filaments and attach to the Z line; helps keep thick and thin filament in proper alignment and aid in restoring resting sarcomere length; also helps muscle fiber resist extreme stretching
|
|
Sarcoplasmic reticulum (SR)
|
related to the smooth endoplasmic reticulum of other cells; forms a tubular network around each myofibril, fitting over like a lacey shirtsleeve; thickens and enlarges on each side of a T tubule (called terminal cisternae); called a triad in conjunction with the T tubule
|
|
Triad
|
2 terminal cisternae surrounding a T tubule; membranes bound tightly, but fluids totally seperate and different; found on the edge of the A band at the zone of overlap; calcium released from cisternae enter the zone of overlap to begin muscle contraction
|
|
Terminal cisternae
|
thicker, bounded SR found on each side of a T tubule; Calcium ions are actively transported into the terminal cisternae from the sarcoplasm; 1000 times as many free calcium ions in TC; TC also contain calsequestrin, which binds calcium ions; total free and bound calcium in SR is 40,000 times that of sarcolasm surrounding; this is where a muscle contraction begins
|
|
Sarcolemma
|
plasma membrane of a muscle fiber; has transmembrane potential due to unequal distribution of positive and negative charges across the membrane; sudden change in this potential is the beginning of muscle contraction
|
|
Sarcoplasm
|
cytoplasm of muscle fiber; generally low concentration of calcium ions
|
|
T tubules
|
narrow tubes that are a continuation of the sarcolemma that extend into the cell at right angles to the cell surface; have same general properties of sarcolemma and contain extracellular fluid; action potentials travel across the sarcolemma and down the T tubules to trigger muscle fiber contractions simultaneously throught the fiber; encircle myofibrils
|
|
Myofibril
|
cyclindrical structures about 1-2 micrometers in diameter that stretch the length of a muscle fiber; hundreds found in one skeletal muscle fiber; made of myofilaments
|
|
Myofilaments
|
bundles of protein filaments that make up myofibrils; 2 types: thin filaments (made mostlly of actin and thick filaments made of myosin; also contain titn
|
|
Major Functions of skeletal muscles
|
1. Produce skeletal movement
2. Maintain posture and body position 3. Support soft tissues\ 4. Guard entrances and exits 5. Maintain Body Temperature 6. Store nutrient reserves |
|
Example of skeletal muscle producing skelatal movement
|
breathing, swimming, moving arm
|
|
Example of skeletal muscle maintaining posture and body position
|
holding head still; balancing body over feet during walking
|
|
Example of skeletal muscle supporting soft tissues
|
abdominal wall and floor of pelvic cavity consists of layers of skeletal muscle and supports the weight of internal organs and shield them from injury
|
|
Example of skeletal muscle guarding entrances and exits
|
skeletal muscles encircle digestive and urinary tracts and provides voluntary control over swallowing, defecation, and urination
|
|
Example of skeletal muscle maintaining body temperature
|
muscle contraction requires energy, some of which is converted to heat which keeps body temp in normal range; running heats us up
|
|
Example of skeletal muscle storing nutrient reseves
|
when body contains inadequate proteins or calories, contractile proteins in SM can be broken down into AAs and used to make glucose or broken down to provide energy
|
|
Skeletal Muscles
|
organs composed primarily of skeletal muscle tissue but also contain connective tissues, nerves, and blood vessels
|
|
CT found in a skeletal muscle
|
1. epimysium
2. perimysium 3. endomysium |
|
Epimysium
|
dense irregular layer of collagen fibers that surround a skeletal muscle; seperates muscle from surrounding tissues and organs and is connected to the deep fascia
|
|
Perimysium
|
dense irregular CT; divide skeletal muscle into a series of compartments containing a bundle of fibers called fasciles; possess collagen and elastic fibers, as well as blood vessels and nerves
|
|
Endomysium
|
surrounds individual skeletal muscle cells (fibers) and loosely interconnects adjacent muscle fibers; elastic CT and areolar CT; contains capillary networks, myosatellite cells, and nerve fibers that control the muscle
|
|
Myosatellite cells
|
embryonic stem cells found in the endomysium that function in the repair of damaged muscle cells
|
|
Tendon or Aponeurosis
|
a bundle or broad sheet of the collagen fibers from epimysium, perimysium, and endomysium found at the ends of a muscle; usually attach muscles to bone, extending into the matrix of the bone
|
|
4 proteins found in thin filaments
|
F-actin, nebulin, tropomyosin, and troponin
|
|
F-actin
|
1 of 4 proteins found in SM thin filaments; "Filamentous actin"; a twisted strand of 2 rows of 300-400 G-actin (globular molecules); G-actin molecules have active sites where myosin bind
|
|
Nebulin
|
long strand that extends along F-actin in cleft between rows of G-actin; holds F-actin strands together
|
|
Tropomyosin
|
cover active sites on G-actin, preventing actin, myosin interaction; a molecule is double stranded that covers 7 active sites and binds to 1 molecule of troponin midway
|
|
Troponin
|
made of 3 globular subunits -
1. binds to tropomyosin 2. binds to 1 unit G-actin to hold position 3. has receptor that binds 2 calcium ions (starting point of muscle contraction) |
|
Thick filament structure
|
300 myosin molecules made of paired myosin subunits twisted; titin core
1. tail: bound to other myosin molecules 2. head: projects toward thin filament and is known as cross bridge when interactin gwith thin filament |
|
F-actin
|
1 of 4 proteins found in SM thin filaments; "Filamentous actin"; a twisted strand of 2 rows of 300-400 G-actin (globular molecules); G-actin molecules have active sites where myosin bind
|
|
Nebulin
|
long strand that extends along F-actin in cleft between rows of G-actin; holds F-actin strands together
|
|
Tropomyosin
|
cover active sites on G-actin, preventing actin, myosin interaction; a molecule is double stranded that covers 7 active sites and binds to 1 molecule of troponin midway
|
|
Troponin
|
made of 3 globular subunits -
1. binds to tropomyosin 2. binds to 1 unit G-actin to hold position 3. has receptor that binds 2 calcium ions (starting point of muscle contraction) |
|
Thick filament structure
|
300 myosin molecules made of paired myosin subunits twisted
1. tail: bound to other myosin molecules 2. head: projects toward thin filament and is known as cross bridge when interactin gwith thin filament |
|
Sliding Filament Theory
|
Explanation for muscle contraction that states thin filaments are sliding toward the center of each sarcomere and because myofibrils are attached to sarcolemma, muscle contracts
|
|
During skeletal muscle contraction
|
1.H bands and I bands shrink
2.zones of overlap enlarge 3.Z lines move closer together 4.width of A band remains constant |
|
Muscle cell tension
|
Muscle cells can only pull an object, never push (no compression)
|
|
Muscle contraction detail
|
1.skeletal muscles are under control of neural cells; a neuron activates a muscle fiber through stimulation of its sarcolemma (called excitation-contraction coupling)
2.calcium is released from the terminal cisternae of the SR 3.calcium ions trigger interactions between thick and thin filaments, resulting in contraction and use of ATP 4.filament interaction produces active tension |
|
Neuromuscular junction/Myoneural junction
|
Connection between the nervous system and skeletal muscle fiber
|
|
Synaptic terminal
|
End of a fine branch of an axon which has branched in the perimysium and stops about half way down the length of a fiber; cytoplasm of synapse terminal contains mitochondria and vesicles filled with molecules of ACh
|
|
Acetylcholine (ACh)
|
A neurotransmitter that alters the permeability of the sarcolemma and trigger the contraction of muscle fibers
|
|
Neurotransmitter
|
A chemical released by a neuron to change the permeability or other properties of another plasma membrane
|
|
Synaptic Cleft
|
Narrow space that seperates the synaptic terminal from the sarcolemma motor end plate; contains acetylcholinesterase (AChE)
|
|
Motor end plate
|
Part of sarcolemma that contains the Ach receptors; contains lots of folds to increase surface area and # of receptors; contains acetylcholinesterase (AChE)
|
|
Acetylcholinesterase (AChE)
|
Enzyme that breaks down ACh
|
|
Steps of neural stimulation
|
1.arrival of action potential
2.release of ACh 3.ACh binding at motor end plate 4.appearance of action potential in sarcolemma 5.return to initial state |
|
Action Potential
|
Electrical impulse from a sudden change in the transmembrane potential that travels along the length of an axon
|
|
Step 1 of neural stimulus of muscle fiber
|
Arrival of action potential at the synaptic terminal
|
|
Step 2 of neural stimulus of muscle fiber
|
Action potential changes membrane permeability of synaptic terminal and ACh is exported via exocytosis into the synaptic cleft
|
|
Step 3 of neural stimulus of muscle fiber
|
ACh diffuse across synaptic cleft and bind to receptors on the motor end plate (sarcolemma); this changes the permeability of the membrane to sodium ions, which rush into the sarcoplasm; process continues until AChE binds to ACh in synaptic cleft and ACh unbinds from the receptors at the motor end plate, returning the membrane permeability to normal
|
|
Step 4 of neural stimulus of muscle fiber
|
Action potential is created in the sarcolemma by the inrush of sodium
|
|
Step 5 of neural stimulus of muscle fiber
|
ACh has been broken down by AChE and some products will be used by neuron to make more ACh
|
|
Excitation-contraction coupling
|
Link between action potential in sarcolemma and start of muscle contraction; action potential triggers triads to release stored calcium ions from SR to sarcomere surroundings; calcium binds with troponin, weakening the bond with actin and turning the strand to remove tropomyosin from covering the active sites on actin
|
|
SM Contraction Cycle
|
1. Exposure of active sites
2. Formation of cross-bridges 3. Pivoting of myosin heads 4. Detachment of cross-bridges 5. Reactivation of myosin |
|
Step 1 of SM contraction cycle
|
calcium binds with troponin, weakening the bond with actin and turning the strand to remove tropomyosin from covering the active sites on actin and allowing interaction with myosin heads
|
|
Step 2 of SM contraction cycle
|
Myosin heads bind to active sites on actin, forming cross-bridges
|
|
Step 3 of SM contraction cycle
|
The cocked myosin head releases ADP & P as it pivots toward the M line (usually facing away); called the power stroke.
|
|
Step 4 of SM contraction cycle
|
ATP binds to myosin head and cross-bridge between myosin and actin is broken
|
|
Step 5 of SM contraction cycle
|
ATP in the myosin head is broken into ADP + P and that energy used to recock the myosin head
|
|
Myosatellite Cells
|
Stem cells that function in endomysium as part of muscle development and repair; proliferate, differentiate, and fuse into multinucleate muscle cells
|
|
Isotropic
|
Light in color; I band
|
|
Dystrophin
|
A thin filament; links actin to sarcolemma and transmit force to sarcolemma and ultimately to the tendons
|
|
Characteristics of a resting SM fiber
|
1. [Ca2+] in cytoplasm is relatively low vs. SR
2. [Ca2+] in sarcoplasmic reticulum (SR) is relatively high (40,000X higher than cytoplasm) a. Ca2+ is continually pumped into SR b. Calsequestrin binds Ca2+ within SR 3. Myosin heads are already “cocked” with ATP 4. Myosin-binding sites on actin are blocked by troponin-tropomyosin complex |
|
Muscle relaxation
|
Motor neuron quits firing Æ no new ACh release
• Acetylcholinesterase (AChE) in synapse is continually breaking down ACh Result: • No new action potential on muscle cell ¸No new Ca2+ release from SR ¸Ca2+ continuously pumped into SR ¸[Ca2+] in cytoplasm drops • T-T complex covers up myosin-binding sites ¸No interaction between actin and myosin ¸Muscle relaxes passively |
|
Rigor Mortis = Stiffness of Death
|
• Myosin heads already “cocked” with ATP
• Ca2+ leaks out of SR (ATP required to pump it back in) • Intracellular [Ca2+] rises • T-T complex binds Ca2+ and uncovers myosinbinding sites • Contraction occurs • ATP stores depleted over time • No ATP available to release myosin from actin and recock heads • Rigor mortis |
|
Inhibitory effects of drugs/toxins on contraction
|
• Block ACh release - Botulinus toxin
• Block binding of ACh to receptor - Atropine (belladonna), curare |
|
Exhibitory effects of drugs/toxins on contraction
|
• Block acetylcholinesterase - Neostigmine,
DFP (nerve gas) • Increase ACh release - some spider venoms • Mimic ACh - Nicotine |
|
SM fiber tension all-or-none principle
|
All sarcomeres in a SM fiber contract together in response to a given dose of calcium ions
|
|
Facors in SM fiber tnesion production
|
1. fiber length at time of stimulation, which affects overlap of actin and myosin
2. frequency of stimulation, which affects duration of calcium ion concentration 3. fiber diameter, which affects the amount of actin and myosin available |
|
Ideal range of sarcomere length
|
75 - 130% of optimal length
|
|
Twitch
|
a single stimulus-contraction-relaxation sequence in a muscle fiber; 3 phases: latent period, contraction phase, relaxation phase
|
|
Latent period of a twitch
|
stimulation, action potential sweep, release of Ca ions from SR; no tension
|
|
Contraction period of a twitch
|
tension rises as myosin and actin interact
|
|
Relaxation period of a twitch
|
calcium ion concentration decreases, active sites being covered, cross bridges declining, and tension returns to normal
|
|
Treppe
|
"warm up effect"; gradual increase in strength of contraction with same stimulus over time; due to increased calcium available and warmed up fiber (enzymes more efficient at higher temperatures); not common
|
|
Wave summation
|
when a stimulus to the SM fiber occurs before the relaxation phase ends; can reach 4 times that of treppe
|
|
Incomplete tetanus
|
muscle never completely relaxing, happens during summation
|
|
Complete tentanus
|
the relaxation phase in muscle contraction disappears completely; continuous contraction
|
|
Motor unit
|
all the muscle fibers controlled by a single motor neuron; smaller size = finer control of movement
|
|
Recruitment
|
the smooth and steady increase of muscular tension by increasing the number of active motor units
|
|
Factors affecting tension production in a whole muscle
|
1. internal and external tension
2. recruitment 3. muscle size (# of muscle fibers |
|
Internal tension
|
tension generated inside a contracting muscle (myosin pulling on actin)
|
|
External tension
|
tension generated in extracellular fibers; endo, peri, epimysium form tendons that stretch
|
|
Series elastic component
|
difference in tension between internal and external from simple twitch
|
|
Muscle tone
|
some motor units active at any one time, change throughout the day; stabilizes bones and joints, maintains body position/posture, allows more rapid activation of whole muscle, contributes to body heat
|
|
Isotonic contraction
|
"same tension", muscle shortens; muscle starts shortening at point it reaches amount of tension required to move 2 kg of weight
|
|
Isometric contraction
|
"same length", muscle never shortens because there is not enough tension to lift the weight
|
|
Creatine
|
small molecule assembled by muscle cells from AA
|
|
Creatine phosphate
|
CP; the storage of the phosphate broken off of ATP, used in the recreation of ATP during muscle contraction
|
|
Energy-production systems in muscle
|
1. phosphogen system (ATP & CP reserves)
2. glycolysis 3. aerobic system |
|
Phosphogen system
|
found only in muscle cells; involves creatine phosphate (CP) and ATP; fast, short-term method of ATP generation; involves 1 enzyme (creatine phosphokinase)`
|