Musculoskeletal System: Form and Action at Joints

Question 1

How does skeletal muscle cause movement at joints?

Answer 1

Attaches to bone (lever), Muscle structure (length, number of fibres, arrangement of fibres), Type of contraction (roles/action), Where it crosses a joint (location).

Question 2

Anatomical Levers: what are the components?

Answer 2

Bone = Lever
Joint = pivot/fulcrum
Muscle contraction = applied force/pull
Weight of what is being moved = Load (external or internal)
Lever arrangement determines the function.

Question 3

Describe a first class lever

Answer 3

Stabilises joint position. Fulcrum between force and load.
Eg. see-saw

Question 4

Describe a second class lever

Answer 4

Effective at overcoming heavy loads. Load between fulcrum and force.
Eg. wheelbarrow

Question 5

Describe a third class lever

Answer 5

Large range of movement/speed. Force between fulcrum and load.
Eg. Fishing rod

Question 6

Muscle form determines function. What does muscle form depend on?

Answer 6

Length of muscle fibres, Number of muscle fibres, Arrangement of muscle fibres

Question 7

How does the length of muscles affect their movement?

Answer 7

Fibres can shorten up to 50% of their resting length.
If large ROM is required = long muscle fibres

Question 8

How does number of muscle fibres affect their movement?

Answer 8

Tension is directly proportional to the cross sectional area (CSA). A greater number of fibres results in greater CSA and greater tension.

Question 9

How does arrangement of muscle fibres affect their movement?

Answer 9

Parallel: Fibres arranged vertically between muscle tendons/attachments. Results in smaller CSA and greater shortening
Pannate: Fibres arranged obliquely between muscle tendons/attachments. Results in greater CSA and lesser shortening.

Question 10

What are the three types of muscle action?

Answer 10

Concentric, Isometric, Eccentric

Question 11

What is the concentric type of muscle movement?

Answer 11

Muscle is active, develops tension. Tension is greater than load. Muscle shortens, change in joint position.

Question 12

What is the eccentric type of muscle movement?

Answer 12

Muscle is active, develops tension. Tension is lesser than load. Muscle elongates: pull in other direction by gravity or another muscle. Change in joint position.

Question 13

What is the isometric type of muscle movement?

Answer 13

Muscle is active, develops tension. Tension does not outweigh load. No change is length of muscle, no change in joint position.

Question 14

List the types of muscle roles and their functions

Answer 14

Agonist (creates movement by acting concentrically)
Antagonist (opposes/controls movement by acting eccentrically)
Stabiliser (holds joint still)
Neutraliser (stops unwanted movement caused by another muscle)

Question 15

Pronator muscles in the forearm act as neutralisers to prevent supination, but still allow ___?

Answer 15

Flexion

Question 16

What do we need to know in terms of the 16 muscles we have to learn?

Answer 16

Name of muscle
Location
Concentric action at the joint

Question 17

If it crosses anteriorly at the joint it will do ____

Answer 17

Flexion

Question 18

If it crosses laterally at the joint it will do ____

Answer 18

Abduction

Question 19

If it crosses posteriorly at the joint it will do ____

Answer 19

Extension

Question 20

If it crosses medially at the joint it will do ____

Answer 20

Adduction

Question 21

The rules for concentric actions of muscles applies for all joints except for the knee. What is the rule for the knee?

Answer 21

Anterior muscles of the knee extend, posterior muscles of the knee flex