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;
70 Cards in this Set
- Front
- Back
|
Main function of myocytes is
|
contraction
|
|
|
Two principal myofilaments
|
THIN filaments : composed of ACTIN- A polymer of fibrousactin formed from globular actin (G-actin)
THICK filaments -composed of MYOSIN II protein |
|
|
Classification
|
Striated muscle : cells exhibit cross-striations at LM
Smooth muscle : cells lack cross-striations at LM |
|
|
The cross-striations are due to
|
the architectural organization of the actin and myosin myofilaments
|
|
|
Striated muscle is further sub classified into
|
Skeletal muscle
Visceral Striated muscle Cardiac muscle |
|
|
skeletal muscle |
– attached to bone, produces skeletal movement and maintains posture
|
|
|
visceral smooth muscle |
– morphologically indistinct from skeletal muscle, localized to tongue, pharynx, diaphragm and upper oesephagus
|
|
|
skeletal muscle |
Composed of multinucleated syncitia (muscle fibre) formed bythe fusion of multiple individual myoblast cells that vary inlength
|
|
|
Held together by connective tissue
|
Endomysium : reticular fibres surrounding each muscle fibre
Perimysium : a connective tissue layer surrounding groups of fibres to form bundles/fascicles Epimysium : dense connective tissue that surrounds collections of fascicles to form muscle |
|
|
how many types of muscle fibers are found I skeletal muscle |
3 |
|
|
Type I / slow oxidative
|
small fibres that appear red
Many mitochondria, large amounts of myoglobin and cytochromes Slow-twitch fatigue-resistant Low myosin ATP-ase activity Principal fibres in long muscles of the back – they are adapted to the long slow contraction to maintain erect posture. has the smallest diameter |
|
|
Type IIa/ fast-oxidative
|
Intermediate color in fresh tissue
High numbers of mitochondria and myoglobin They contain large amounts of glycogen and perform anaerobic glycolysis Fast-twitch fatigue resistant |
|
|
Type IIb / fast glycolytic
|
Paler
contain few mitochondria than Type I or IIa fibers Contain high amounts of glycogen and high anaerobic activity Low levels of oxidative enzymes Fast-twitch fatigue prone units that generate high tension Adapted for rapid contraction and precise fine movements has the largest diameter |
|
|
Muscle fibers are composed
|
of longitudinally -arrayed structural units called myofibrils
|
|
|
myofibrils are i turn made up of |
myofilaments |
|
|
Myofilaments are the
|
individual filamentous polymers of myosin II (thick) and actin (thin) and their associated proteins
They are the actual contractile units in skeletal muscle |
|
|
The sarcomere
|
the segment of the myofibril between two adjacent Z -lines
The sarcomere is the functional unit of the myofibril |
|
|
a band |
dark band-hold whole length of myosin |
|
|
i band |
light band-hold only actin fibers |
|
|
Z-disc
|
traverses I-band
|
|
|
M-line
|
traverses bisects the A-band
|
|
|
thin filament |
composed of f actin troponine and trophomyosin |
|
|
thick filaments |
composed of myosin II only |
|
|
Myosin
|
Thick filaments
Functions as a motor protein which can achieve motion Convert ATP to energy of motion Projections of each myosin molecule protrude outward (myosin head) |
|
|
Actin
|
Thin filaments
Actin molecules provide a site where a myosin head can attach Tropomyosin and troponin are also part of the thin filament |
|
|
actin mode of action |
In relaxed muscle Myosin is blocked from binding to actin
Strands of tropomyosin cover the myosin-binding sites Calcium ion binding to troponin moves tropomyosin away from myosinbindingsites Allows muscle contraction to begin as myosin binds to actin |
|
|
Titin
|
Stabilize the position of myosin
accounts for much of the elasticity and extensibility of myofibrils |
|
|
Dystrophin
|
Links thin filaments to the sarcolemma
|
|
|
The Sliding Filament Mechanism
|
1.Myosin heads attach to and “walk” along the thin filaments at both ends of a sarcomere 2.Progressively pulling the thin filaments toward the center of the sarcomere
3.Z discs come closer together and the sarcomere shortens 4.Leading to shortening of the entire muscle |
|
|
The contraction cycle consists of 4 steps
|
1) ATP hydrolysis
2) Formation of cross-bridge 3) Power stroke 4) Detachment of myosin from actin Continuing cycles applies the force that shortens the sarcomere |
|
|
ATP hydrolysis
|
Hydrolysis of ATP reorients and energizes the myosin head
|
|
|
Formation of cross-bridges
|
Myosin head attaches to the myosin-binding site on actin
|
|
|
Power stroke
|
During the power stroke the cross-bridge rotates, sliding the filaments
|
|
|
Detachment of myosin from actin
|
As the next ATP binds to the myosin head, the myosin head detaches from actin
The contraction cycle repeats as long as ATP is available and the Ca++ level is sufficiently high |
|
|
When a muscle fiber isstretched
|
there is less overlap between the thick and thin filaments and tension (forcefulness) is diminished
|
|
|
When a muscle fiber is shortened
|
the filaments are compressed and fewer myosin heads make contact with thin filaments and tension is diminished
|
|
|
why is ATP needed in the muscle |
Power the contraction cycle
Pump Ca++ into the SR |
|
|
what produces ATP after reserves are used up
|
the muscle fiber
|
|
|
Muscle fibers have three ways to produce ATP
|
1) From creatine phosphate
2) By anaerobic cellular respiration 3) By aerobic cellular respiration |
|
|
Creatine phosphate and ATP provide enoughenergy for contraction for about
|
15 seconds
|
|
|
Anaerobic respiration can provide enough energy forabout
|
30 to 40 seconds of muscle activity
|
|
|
Activity that lasts longer than half a minute depends on
|
aerobic respiration
|
|
|
Each molecule of glucose in aerobic respiration yields about
|
36 molecules of ATP
|
|
|
Muscle tissue has two sources of oxygen
|
1) Oxygen from hemoglobin in the blood
2) Oxygen released by myoglobin in the muscle cell |
|
|
Muscle Fatigue
|
Inability of muscle to maintain force of contraction after prolonged activity
|
|
|
Factors that contribute to muscle fatigue
|
Inadequate release of calcium ions from the SR Depletion of creatine phosphate
Insufficient oxygen Depletion of glycogen and other nutrients Buildup of lactic acid and ADP Failure of the motor neuron to release enough acetylcholine |
|
|
Oxygen debt
|
The added oxygen that is taken into the body after exercise
|
|
|
the oxygen dept is used to restore muscle cells to the resting level in three ways
|
1) to convert lactic acid into glycogen
2) to synthesize creatine phosphate and ATP 3) to replace the oxygen removed from myoglobin |
|
|
Twitch Contraction
|
The brief contraction of the muscle fibers in a motor unit in response to an action potential Twitches last from 20 to 200 m sec
|
|
|
Latent period
|
(2 msec)
A brief delay between the stimulus and muscular contraction The action potential sweeps over the sarcolemma and Ca++ is released from the SR |
|
|
Contraction period
|
(10–100 msec)
Ca++ binds to troponin Myosin-binding sites on actin are exposed Cross-bridges form |
|
|
Relaxation period
|
(10–100 msec)
Ca++ is transported into the SR Myosin-binding sites are covered by tropomyosin Myosin heads detach from actin |
|
|
Refractory period
|
When a muscle fiber contracts, it temporarily cannot respond to another action potential, this period of time is known as the refractory period
|
|
|
Skeletal muscle has a refractory period of
|
5 milliseconds
|
|
|
Cardiac muscle has a refractory period of
|
300 milliseconds
|
|
|
Types of Contractions
|
Isotonic contraction
Isometric contraction |
|
|
isotonic contraction |
The tension developed remains constant while themuscle changes its length
Used for body movements and for moving objects eg Picking a book up off a table |
|
|
isometric contraction |
The tension generated is not enough for the objectto be moved and the muscle does not change itslength
Holding a book steady using an outstretched arm |
|
|
smooth muscle |
Occurs as bundles of elongated fusiform cells that havetapered ends
Cells vary in size in different tissues Interconnected by gap junctions – to enable synchronouscontraction of bundles of smooth muscle cells Cells have characteristic nuclei in longitudinal setion – theyappear elongate and have tapering ends - match the shape ofthe cell |
|
|
Fusiform,
|
having a spindle-like shape that is wide in the middle and tapers at both ends
|
|
|
The cells of smooth muscle possess a cytoskeleton containing
|
desmin and vimentin intermediate filaments
|
|
|
what type of muscle is specialised for prolonged contraction without fatigue |
smooth muscle |
|
|
Most SM is directly innervated by
|
SNS and PNS (sympathetic,parasympathetic)
|
|
|
do sm Exhibit spontaneous contractile activity in the absence of nervestimuli |
yes |
|
|
sm Produce peristaltic movements by
|
contracting in a wave-like manner
|
|
|
where is extrusive movement produced by SM |
the urinary bladder, gallbladder or uterus
|
|
|
primarysource of innervation to smooth muscle in the gut
|
enteric division of the ANS
|
|
|
example of hormones that act as ligands on ligand-gated Ca channels toinitiate SM contraction
|
oxytosin and ADH( released from the posterior pituitary) |
|
|
what propagatecontraction through the muscle layer
|
Gap junctions between smooth muscle cells
|
|
|
can smooth muscle maintain tone in the lack of nerve stimulation |
yes |
