Lec 6

• How do muscles typically act during movement?

  Muscles act in groups, not singly.
• What is the role of agonist muscles?

  Agonists are prime movers for actions.
• What is the function of antagonist muscles?

  Antagonists oppose prime movers during contraction.
• What is an example of an agonist muscle in hip flexion?

  Illiopsoas
• What is an example of a secondary mover in hip flexion?

  Sartorius
• How do antagonists contribute to movement control?

  They relax and lengthen to allow movement.
• Where are antagonists typically located in relation to prime movers?

  On the opposite side of the joint.
• What happens to antagonists during an action?

  They lengthen as the action occurs.
• What are synergists?

  Muscles that work together to modify actions.
• What is the purpose of synergists in muscle action?

  To eliminate undesired movements.
• What are the types of synergists?

  • Conjoint
  • Neutralizers
  • Stabilizers or Fixators
• What do conjoint synergists do?

  They act together to produce a movement.
• Give an example of conjoint synergists.

  Medial and lateral hamstrings during knee flexion.
• What is the role of neutralizers?

  They cancel undesired actions of prime movers.
• What is an example of a neutralizer?

  Lateral rotators during hip adduction.
• What do stabilizers or fixators do?

  They prevent unwanted actions of muscles.
• How do stabilizers function during movement?

  They contract isometrically to stabilize joints.
• What is an example of a stabilizer muscle?

  Rectus abdominis during leg raising.
• What is the role of support muscles?

  They hold body parts in position during actions.
• How do support muscles work during an action?

  They work isometrically to hold parts in place.
• What factors affect muscle extensibility and contractility?

  Length, arrangement of fibers, and resistance.
• What is the physiological cross-section of a muscle?

  Area that cuts every muscle fiber perpendicularly.
• How does physiological cross-section relate to muscle strength?

  It determines the potential force of contraction.
• What is the recognized absolute muscle strength?

  3-4 kg per cm square cross-section.
• What characterizes longitudinal muscles?

  They have long fibers parallel to the muscle axis.
• What is an example of a longitudinal muscle?

  Sartorius muscle
• What characterizes pennate muscles?

  They have short fibers arranged obliquely.
• What is an example of a bi-pennate muscle?

  Rectus femoris
• How does the pennation angle affect muscle strength?

  Increased angle decreases contraction strength.

  
• What are the differences between one joint and two joint muscles?

  One joint muscle:

  • Moves one joint only
  • Shortens sufficiently for maximum movement

  
  

  Two joint muscle:

  • Performs patterns of movement
  • Can experience active or passive insufficiency
• What is active insufficiency?

  The muscle cannot shorten beyond a limit.
• What is passive insufficiency?

  The muscle cannot stretch beyond a limit.
• Give an example of active insufficiency.

  Maximal hip flexion with knee extension.
• Give an example of passive insufficiency.

  Pain when flexing hip with knee extended.
• What is tenodesis?

  Passive tension producing joint movement.
• How does tenodesis occur?

  Muscle elongated over multiple joints simultaneously.
• What happens to the fingers during wrist flexion?

  Digits extend without finger extensor contraction.
• What happens to the fingers during wrist extension?

  Fingers partially flex without extensor contraction.
• What could cause limited elbow flexion in a 65-year-old woman?

  Possible causes include muscle weakness or stiffness.