Flashcards in Muscle Deck (28)
List six different functions of striated muscle.
1) move bones of skeleton
2) maintain posture
4) generates heat
5) heart contractions generate blood pressure
6) store chemical energy as glycogen and fat
Describe four general functional properties of muscle tissue
1) able to exert force inwards (tension) and shorten
2) able to increase their length (extensible)
3) able to return to their original length after lengthening (elasticity)
4) conducts action potentials (excitable)
Name and describe the three kinds of muscle contractions that differ on the basis of
changes in cell length.
1) concentric (contraction while shortening)
2) eccentric (contraction while lengthening)
3) isometric (contraction while maintaining length)
Explain what it means to say that a joint operates as a third class lever and how this
is related to the function of the muscle that rotates that joint (2 marks).
-the attachment point of the tendon of the muscle is close to the angle of rotation (joint)
- the force applied by the muscle must by greater than if the muscle were attached farther from the joint BUT the speed of rotation of the joint is greater because the muscle is attached close to the joint
A neuromuscular junction is a type of ________________.
Skeletal muscle fibers are controlled by release of the neurotransmitter,
Describe the steps in excitation of a skeletal muscle (3 marks)
EXCITATION MEANS CARRYING THE ELECTRICAL SIGNALS TO THE ACTIN AND MYOSIN
- acetylcholine is released at the neuromuscular junction and binds to receptors in membrane of muscle cell, resulting in depolarization (sodium moves IN to cell)
- voltage gated sodium channels in neighbouring cell membrane open, starting an action potential
- action potential consists of depolarization (Na channels OPEN), then repolarization (Na channels CLOSED; K channels OPEN), then return to resting potential
- action potentials travel from NMF outwards towards each end of muscle cell and follow T-tubules deep into muscle cell
- proteins in T-tubule membrane (DHFRs) change shape in response to action potentials and cause oping of ryanodine receptors on sarcoplasmic reticulum
-ryanodine receptors are calcium channels that open and allow calcium to diffuse from SR to cytoplasm, starting contraction
Describe the steps in contraction of a skeletal muscle (4 marks).
-calcium released from sarcoplasmic reticulum binds to a protein (troponin) that regulates the structure of actin
-the binding of calcium to troponin causes a blocking protein (tropomyosin) to shift position and expose the sites on the thin actin filament that are capable of binding myosin to become exposed
-exposure of myosin-binding sites of actin is followed by binding of myosin head to actin
- myosin head "swivels" producing tension that may result in contraction
- myosin is released from actin
- if ATP is present it provides the energy to "swivel" the myosin head back to original position to begin another cycle of attachment and contraction
Describe the steps in relaxation of a skeletal muscle.
- calcium is pumped into the sarcoplasmic reticulum and calcium levels in the cytoplasm decline
- myosin no longer binds to actin
Explain what a muscle twitch is; name its three main stages and explain what
happens during each stage (2 marks).
a brief (about 100 ms) increase in tension of a muscle caused by a single stimulus
- latent stage (action potentials travel into cells to cause the release of calcium)
- contraction (calcium levels in cytoplasm increase causing attachment of actin to myosin)
- relaxation (calcium is pumped into sarcoplasmic reticulum, resulting in myosin no longer attaching to actin)
The tension (force generated) by a muscle varies with ________________________
- rate of arrival of action potentials along the motor nerve
- the number of fibers in the muscle that are stimulated by action potentials
Explain the process of wave summatio
if action potentials arrive at a muscle fiber so rapidly that the fiber does not have time to relax fully between two successive action potentials, then the tension generated by one action potential is added to the tension generated by the next action potential
Explain the process of physiological tetanus.
- sustained contraction of a skeletal muscle resulting from action potentials arriving so rapidly that the muscle fibers do not lose tension between action potentials
Describe how the function of a muscle varies with its length.
-there is a length of a muscle at which it produces the highest tension
- at shorter and longer lengths it generates less tension due to less overlap between actin and myosin fillaments
Explain why not all the forces produced by attachment of myosin to actin is
transferred to the Z-lines.
- a variety of proteins extend between the actin strands, through the cell membrane to the extracellular connective tissue
- these proteins (integrin and dystroglycan) are arranged at an angle to actin and myosin and transmit forces
away from the Z-lines
Explain “muscle fatigue” refers to and list 4 factors that contribute to it (3 marks).
- muscle fatigue is the reduction in force generated by a muscle that accompanies prolonged contraction
- may be caused by:
1) conversion of creatine phosphate to creatine and phosphate
2) depletion of ATP
3) depletion of calcium
4) depletion of potassium
Explain the difference between tonic and clonic contractions.
-tonic contractions are continuous
-clonic contractions involve cycles of contraction and relaxation
List 6 factors that contribute to “true cramps” of muscles (3 marks).
1) response to vigorous activity
2) injury to nerve of muscle
3) after muscle fatigue
4) posture is maintained for a long time
6) low plasma levels of sodium
7) low plasma levels of calcium
8) low plasma levels of magnesium
Define muscle contracture and explain its physiological basis
- contracture is continuous contraction of a skeletal muscle due to depletion of adenosine triphosphate (ATP)
Define rigor mortis and explain its physiological basis.
- rigor mortis is the contraction of skeletal muscles that begins several hours after death and lasts for about a day
- results from decreased ATP production and increased levels of calcium in the cytoplasm
List four characteristics that distinguish fast and slow twitch muscle fibers (4 marks).
fast twitch have
1) fast ATPase on myosin head
2) not much myoglobin (white)
3) LOW resistance to fatigue
4) GOOD anaerobic respiration; BAD aerobic respiration
slow twitch have:
1) slow ATPase on myosin head
2) quite a bit of myoglobin (red)
3) HIGH resistance to fatigue
4) BAD anaerobic respiration; GOOD aerobic respiration
List two factors that affect the percentage of fast/slow twitch fibers in a skeletal
There is enough ATP inside a typical skeletal muscle cell to last for
_____________________ (approximate time) of intense contraction.
a few seconds
Explain how skeletal muscle fibers are able to synthesize ATP by aerobic
respiration, even if oxygen is not supplied to them and why they can only carry out this action for a limited time.
myoglobin in skeletal muscle fibers stores oxygen and releases it for a short period of time if the blood stops supplying it
Describe two ways in which skeletal muscles can synthesize ATP by transferring phosphate groups from one substance to another (2 marks).
1) an enzyme that transfers the phosphate group from creatine phosphate to ADP to produce ATP and creatine is present in muscle cells
2) an enzyme that transfers a phosphate group from ADP to ADP to produce ATP and AMP is also present in muscle cells
Of the fuel burned by a skeletal muscle, approximately ______% is transferred to contraction; the remainder of the energy is used to _______________________.
25% to contraction
remainder to generate heat
Exercising muscles may reach temperatures as high as 43 oC (T/F).