Muscle Flashcards
What is skeletal muscle?
Muscle that is under voluntary control via motor neurones of the somatic nervous system, attached to the skeleton.
What is cardiac muscle?
Red skeletal muscle that is not attached to the skeleton and is not voluntarily controlled
What are the three types of muscle?
Skeletal muscle, cardiac muscle and smooth muscle
What is another name for a muscle cell?
A muscle fiber
What are muscle fibres packed with?
Myofibrils
What are myofibrils packed with?
Myofilaments
What are the two types of filament?
Thick myosin filaments and thin actin filaments
What are cross bridges between myofilaments?
Myosin heads binding to exposed actin sites
How does myosin compose the thick filament?
The tails make the backbone of the filament and the heads stick out in all directions
What is the thin filament made of?
Double helix of globular actin covered in tropomyosin and troponin
What is the A band of a sarcomere?
The length of the myosin filaments.
What is a sarcomere?
One section of muscle fiber, with actin filaments on either side and myosin filaments in the middle
What is the Z line?
The end or beginning of a sarcomere. The area from which the actin is anchored
What is the M line?
The place from which the myosin filaments are anchored
What is the I band?
The area on either side of the A band where only actin is seen
What is the H zone?
The area where only myosin is seen
How does the position of the filaments determine the banding pattern under an electron microscope?
Different shades where only actin or myosin are, and where both overlap.
What changes visually when a sarcomere contracts?
The I band and H zone get smaller as there is more overlap.
Explain the process leading up to muscular contraction
- Action potential arrives at neuromuscular junction
- Causes release of acetylcholine
- Initiates an action potential in the sarcolemma
- Action potentials occur down the T tubules
- Causes sarcoplasmic reticulum to release calcium stores and voltage gated calcium channels to open
- Calcium ions diffuse into the cell and bind to troponin, changing its tertiary structure and pulling the attached tropomyosin away from the actin binding sites
What two things does the length of a muscle contraction depend on?
Presence of ATP and Calcium
Explain muscular contraction
- ATP binds to Myosin head, causing it to extend into a cocked position
- Myosin head acts as ATPase and breaks ATP down into ADP and Pi causing the head to attach to the actin filament
- Release of ADP and Pi causes myosin head to relax and ‘power stroke’ back, pulling the actin filament in
- New ATP molecule binds to myosin head, causing it to detach and return to its original cocked position
How is the effect of muscular contraction reversed?
Contraction of the antagonist muscle
What are the three ways energy is provided for muscle contraction?
Aerobic respiration, Anaerobic Respiration and the Phoshopcreatine System
What are the types of muscle fibers?
Type I Slow twitch
Type IIa Fast Twitch
Type IIb Variable
What are the features of slow twitch muscle fibers?
- Adapted for aerobic respiration
- Can contract for long periods of time
- Speed of contraction limited by rate of oxygen supply
- No lactate produced so does not fatigue
- Contains many mitochondria and myoglobin so cells are red
What are the features of fast twitch muscle?
- Adapted for anaerobic respiration
- Can only contract for a short period
- Fast contraction speed, not limited by oxygen supply
- Lactate production leads to low pH and fatigue
- Contains a lot of glycogen but not many myoglobin or mitochondria
What is the role of phosphocreatine (PC) in providing energy during muscle contraction?
provides phosphate to make ATP
