Muscle Roles in Movement

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Questions and Answers

What is the primary function of agonist muscles?

To control the undesired movement

To perform the action in question (correct)

To stabilize a joint during movement

To oppose the movement created by the prime mover

How do antagonists contribute to muscle movement?

They relax and lengthen to allow movement (correct)

They contract and shorten to create movement

They work independently from the agonists

They solely provide stability to the joint

Which type of synergist specifically neutralizes undesired actions of prime movers?

Stabilizers

Neutralizers (correct)

Conjoint synergists

Fixators

What role do stabilizers or fixators play in muscle movement?

They prevent movement at the joint Signup and view all the answers

What is a characteristic function of conjoint synergists?

They act together to create a movement neither could achieve alone Signup and view all the answers

Which example illustrates the role of antagonists correctly?

Dorsiflexors during ankle plantar flexion Signup and view all the answers

In the context of muscle interaction, what do neutralizers do?

They neutralize undesired actions created by other muscles Signup and view all the answers

Which of the following statements about synergists is true?

Some synergists may cancel out the actions of others Signup and view all the answers

What is the role of fixator muscles during an action?

To stabilize one part of the body while another moves. Signup and view all the answers

What generally characterizes the contraction of stabilizer muscles?

They contract isometrically to hold the body steady. Signup and view all the answers

Which factor does NOT affect the range of muscle extensibility and contractility?

Air temperature during exercise. Signup and view all the answers

What is defined as the area of section that cuts through every muscle fiber perpendicularly?

Physiological cross section. Signup and view all the answers

What is the average recognized absolute muscle strength per cm square cross section?

3-4 kg. Signup and view all the answers

Which type of muscle fibers arrangement typically allows for more forceful contractions?

Pennate fibers. Signup and view all the answers

What characteristic is associated with longitudinal muscles?

Fibers parallel to the long axis of muscle Signup and view all the answers

What happens when the psoas major muscle contracts during a straight leg raise?

It causes anterior tilt of the pelvis. Signup and view all the answers

Which muscle group acts as fixators during heavy weight elbow flexion?

Longitudinal trunk muscles. Signup and view all the answers

Which muscle type is characterized by having a shorter range of motion but more strength?

Pennate muscle Signup and view all the answers

What effect does increasing the pennation angle have on muscle contraction strength?

Decreases strength of contraction Signup and view all the answers

What is a defining feature of a two-joint muscle?

Can experience active insufficiency Signup and view all the answers

What refers to the inability of a muscle to stretch beyond a certain limit without causing pain?

Passive insufficiency Signup and view all the answers

What does the term 'tenodesis' refer to?

Passive tension producing movement without contraction Signup and view all the answers

Which of the following muscles is an example of a bi-pennate muscle?

Rectus femoris Signup and view all the answers

What happens during maximal hip flexion with knee extension?

Passive insufficiency occurs Signup and view all the answers

Study Notes

Muscle Roles

Muscles rarely act alone; groups of muscles interact to produce desired movements.
This interaction allows a single muscle to serve multiple roles.

Agonist

These muscles are the prime movers.
They perform the main action.
Example: Iliopsoas in hip flexion

Secondary Movers

These muscles assist the agonist.
Example: Sartorius in hip flexion

Antagonist

These muscles oppose the prime mover's action.
They relax and lengthen to allow agonist movement
Located on the opposite side of the joint from the movers.
Example: Plantar flexors are antagonists to dorsiflexors during ankle dorsiflexion.

Synergists

These muscles work together with agonists.
They either contract or relax to modify agonist action.
They prevent unwanted movements.
There are different types of synergists:

Conjoint Synergists (Mutual Neutralizers)

Two muscles work together to create a movement neither could do alone.
Example: medial and lateral hamstrings during pure knee flexion

Neutralizers

They neutralize undesired actions of prime or secondary movers.
Example: Lateral rotators counteract undesired motion of adductors during hip adduction.

Stabilizers or Fixators

These muscles surround proximal joints, contracting to allow distal joints to move smoothly.
Their contractions are usually isometric.
Example: Rectus abdominis muscles stabilize proximal attachments of psoas major during straight leg raises.

Support

Muscles that hold body parts in position during an action.
They act isometrically (same length) to hold body parts in place.
Contract in agonist and antagonist simultaneously, usually in stressful situations.
Example: Longitudinal trunk muscles stabilize the elbow during flexion against resistance.

Range of Muscle Extensibility and Contractility

Length and arrangement of muscle fibers (e.g., longitudinal vs. pennate).
Number of joints the muscle crosses.
Resistance of antagonist muscles.
Load opposing the muscle.

Physiological Cross-Section of a Muscle

Area of section that cuts every muscle fiber perpendicularly.
Determines the potential force of contraction.
Absolute muscle strength: ~3-4 kg per cm² cross sectional area

Muscle Architecture and Contraction

Longitudinal Muscles

Long fibers parallel to muscle's long axis.
Create wide range of motion but with less force.
Smaller physiological cross-sectional area.
Example: Sartorius

Pennate Muscles

Short fibers arranged obliquely to muscle's long axis.
Create more force for a shorter range of motion.
Larger physiological cross-sectional area.
Example: Rectus femoris (bi-pennate)
Pennation angle increases the force, but decreases contractile strength.

Differences Between One-Joint and Two-Joint Muscles

One-Joint Muscle

Ideal for movement in a single joint.
Sufficient shortening to move the segment without maximum angular displacement.

Two-Joint Muscles

Ideal for performing movement patterns across multiple joints.
Disadvantage of active or passive insufficiency

Muscle Insufficiency

Active Insufficiency

Muscle cannot shorten further without losing tension.
Example: Maximal hip flexion with knee extension.

Passive Insufficiency

Muscle cannot stretch further without causing pain.
Example: Forced hip flexion with maximal knee extension.

Tendon Action of Two-Joint Muscles (Tenodesis)

Passive tension without active contraction.
Muscle's elongation creates movement across two or more joints.
Example: Wrist movement and finger flexion.

Case Study

A 65-year-old woman has limited elbow flexion. What are the possible causes? (This needs additional context for a full answer).

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Description

Explore the various roles of muscles in movement, including agonists, antagonists, and synergists. This quiz offers insights into how muscles interact to produce desired actions and the significance of each type in locomotion and stability.