Muscle Teamwork

1
Muscle Teamwork

• Agonist (prime mover)
• - the muscle or group of muscles producing a
  desired effect
• Antagonist
• - the muscle or group of muscles opposing the
  action
• Synergist
• - the muscles surrounding the joint being
  moved
• Fixators
• - the muscle or group of muscles that steady
  joints closer to the body axis so that the
  desired action can occur

2
Bending or straightening of elbow requires the
coordinated interplay of the biceps and triceps
muscles
3
Contractile MachinerySarcomeres

• Contractile units
• Organized in series ( attached end to end)
• Two types of protein myofilaments
• - Actin thin filament
• - Myosin thick filament
• Each myosin is surrounded by six actin filaments
• Projecting from each myosin are tiny contractile
  myosin bridges

4
High microscope magnification of sarcomeres
within a myofibril
5
Contractile MachineryCrossbridge formation and
movement

• Cross bridge movement
• - similar to the stroking of the oars and
  movement of rowing shell
• - movement of myosin filaments in relation to
  actin filaments
• - shortening of the sarcomere
• - shortening of each sarcomere is additive

• Cross bridge formation
  
  - a signal comes from the motor nerve
  activating the fibre
  - the heads of the myosin filaments
  temporarily attach themselves to the actin
  filaments

Longitudinal section of myofibril
b) Contraction
6
Contractile MachineryOptimal Crossbridge
formation
Longitudinal section of myofibril

• Sarcomeres should be optimal distance apart
• For muscle contraction optimal distance is
  (0.0019-0.0022 mm)
• At this distance an optimal number of cross
  bridges is formed
• If the sarcomeres are stretched farther apart
  than optimal distance
• - fewer cross bridges can form ? less force
  produced
• If the sarcomeres are too close together
• - cross bridges interfere with one another
  as they form ? less force produced

c) Powerful stretching
d) Powerful contraction
7
Contractile MachineryOptimal muscle length and
optimal joint angle

• The distance between sarcomeres is dependent on
  the stretch of the muscle and the position of the
  joint
• Maximal muscle force occurs at optimal muscle
  length (lo)
• Maximal muscle force occurs at optimal joint
  angle
• Optimal joint angle occurs at optimal muscle
  length

8
Muscle tension during elbow flexion at constant
speed
9
Contractile MachineryTendons, origin, insertion

• In order for muscles to contract, they must be
  attached to the bones to create movement
• Tendons strong fibrous tissues at the ends of
  each muscle that attach muscle to bone
• Origin the end of the muscle attached to
  the bone that does not move
• Insertion the point of attachment of the
  muscle on the bone that moves