Muscle Flashcards
List six different functions of striated muscle.
1) move bones of skeleton
2) maintain posture
3) breathing
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 ________________.
synapse
Skeletal muscle fibers are controlled by release of the neurotransmitter,
___________________.
acetylcholine
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 \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ and \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_
- 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
