Muscles Flashcards
(35 cards)
What is a motor unit?
A group of muscle fibres innervated by a single neuron
Where do T tubules invaginate the sarcoplasm?
At the junction of the I and A bands
What is a triad?
A T tubule flanked by two terminal cisternae of the SR
What hydrolyses ATP in the actin/myosin structure?
The globular myosin head which is as ATPase
What are you seeing when striations appear?
The organisation of thick and thin filaments
What becomes narrower when the sarcomer contracts?
The H and I bands
Where is the A band
Extends length of thick filaments
Where is I band
Extends from the ends of each group of thick filaments between two sarcomeres. Includes the Z disc in the middle
Where is the H band
Extends the distance between the thin filaments in the middle of the sarcomere.
What promotes the myosin head to hydrolyse ATP?
Actin binding
Steps of cross bridge cycle
1) Cross bridge formation. Ca2+ release exposes actin binding sites on actin filaments. ATP hydolyses on the myosin heads and they become ‘cocked’ and bind to actin binding sites. Inorganic phosphate is released and the bond between actin and myosin becomes stronger
2) The power stroke. With the release of ADP the myosin head move sliding the thin filament towards the M line
3) Cross bridge detachment. Another ATP binds to myosin head releasing the bond between actin and myosin
4) reactivation of the myosin head. ATP is hydrolysed activating the myosin head.
What level is Ca2+ when muscle is relaxed and contracted?
Relaxed
What process removes Ca2+ from the cytoplasm?
Active transport. Ca2+ channels close (voltage gated), pumps return Ca2+ to stores (SR) and extracellular space
What is the optimal length of a sarcomere for contraction?
Between 2.0 and 2.2 micrometers
What is resting membrane potential of the muscle cell?
-90mV
Describe Ca2+ transient, stimulus, change in levels, return of Ca2+ to SR
AP in t-tubules causes SR to open Ca2+ channels.
Ca2+ levels change from 10-7 to 10-5
Ca2+ is then actively transported back to the SR via a Ca-ATPase pump.
What is the muscle contraction called that is a result of one AP?
A twitch
Three methods of ATP production for muscle energy
1) The enzyme creatinine phosphokinase transfers the phosphate group from Creatinine phosphate to ADP
2) Anaerobic- glucose is glycolysised to form pyretic acid which produced 2 ATP snd also lactic acid. Fast action but can’t be prolonged due to build up of metabolic products that inhibit cell reactions
3) Aerobic metabolism. Slow and steady oxidative form of ATP production via cellular respiration and the citric acid cycle.
Control of muscle tension can occur with two mechanism…?
Increase the frequency of the AP
Recruit additional motor units
Describe temporal summation
AP is shorter than Ca release, so there is still residual Ca if another AP occurs in quick succesion. If frequency of AP is continued the muscle reaches a higher steady state called a tetanus contraction.
Three muscle fibre types
Type 1, slow oxidative. Type 2B, fast glycolytic. Type 2A (fast oxidative)
Describe Type 1 muscle fibres
Slow ATPase rate
Have a low maximum force production
Oxidative in metabolism
Large amounts of myoglobin and mitochondria giving them red appearance
High oxygen demand offset by small diameter allowing rapid O2 diffusion
Describe type 2B muscle fibres
Glycolytic in metabolism
high ATPase rate
low amounts of myoglobin and mitochondria
white in colour
Large diameter
Fatigue rapidly but generate large forces for short periods of time.
Type 2A muscle fibres
Not found in humans
Glycolytic and oxidative
Large quantity of myoglobin and mitochondria
High ATP ase rate
