Muscle form and actions at joints

Question 1

What three factors determine muscle function?

Answer 1

1. Length of muscle fibres
2. Number of muscle fibres
3. Arrangement of muscle fibre

Question 2

How can the length of the muscle fibres affect muscle function?

Answer 2

The fibres can shorten due to sarcomere movement up to 50% of the resting muscle length. If the muscle is long, shortening up to 50% is a long contraction and can cause significant range of movement at that joint.

Question 3

How can number of muscle fibres affect muscle function?

Answer 3

The amount of force that can be generated at a joint (tension) is proportional to the cross sectional area (CSA). A greater number of muscle fibres means a greater CSA and therefore more force generated

Question 4

How does arrangement of muscle fibres affect muscle function?

Answer 4

Pennate muscle arrangements allows for more tension as the muscle fibres pull at an angle to the tendon and do not move the tendon as far as parallel muscles. The contraction of a pennate muscle generates more tension then parallel muscles of the same size and thus it is stronger.

Question 5

What are the types of pennate muscle attachments?

Answer 5

Unipennate - muscle come off in one direction only/ all one the same side of the tendon

Bipennate - muscles come off in two directions/ on both sides of the tendon

Multipennate - has branches of tendon within the muscle

Question 6

What are levers used for?

Answer 6

To manipulate the environment and create movements at our body where we have synovial joints

Question 7

What acts as the lever, fulcrum, pull and load in a anatomical lever?

Answer 7

Bones = lever

Joint (articulation) = fulcrum

Muscle contraction = pull (applied force that’s trying to move the load)

Load = external or internal (weight we are trying to move)

Question 8

What is the function of a primary/first lever?

Answer 8

Stabilises the joint position.
For example the joint between the skull and the first cervical vertebra. The load based on gravity is trying to pull the head down and a force is applied through neck muscles to keep eyes forward.

Question 9

What is the function of a secondary lever?

Answer 9

Effective at overcoming loads
For example plantar flexion at the ankle joint. The fulcrum is in front of the joint (at the toes) and the load comes down through gravity + weight of the body. To go up into plantar flexion, a force through muscles is needed.

Question 10

What is the function of a third/ tertiary lever?

Answer 10

Has a large range of movement and speed
For example at the elbow joint. The fulcrum is at the elbow and the force is applied by the biceps brachii to cause flexion at the elbow.

Question 11

What are the three types of muscle action?

Answer 11

Concentric, Isometric and eccentric

Question 12

What is concentric muscle action?

Answer 12

When the muscle is active and develops tension which results in active shortening of the muscle so creates a change in joint position

Question 13

What is isometric muscle action?

Answer 13

Muscle is active and develops tension but there in not change in joint position and no change in length of the muscle (fulcrum and load are fixed)
e.g. holding a book.

Question 14

What is eccentric muscle action?

Answer 14

Muscle is active and develops tension which results in change in joint position which is a muscle lengthening
e.g. controlled lowering of weight.

Question 15

Four types of muscle roles?

Answer 15

Agonist, antagonist, stabiliser and equaliser

Question 16

What is an agonist?

Answer 16

An agonist is the muscle which creates the movement in an action. Agonists act concentrically, so the muscle shortens.
e.g. biceps brachii in elbow flexion

Question 17

What is an antagonist?

Answer 17

Prevents ‘over-shooting’ of the muscle movement. Guides and stabilises the joint when performing an action. It will act eccentrically, so the muscle will lengthen
e.g. triceps brachii in elbow extension

Question 18

What is a stabiliser?

Answer 18

When a muscle is active to hold a joint STILL, it is a stabiliser
e.g. biceps brachii when holding a book in a fixed position. This action is isometric.

Question 19

What us a neutraliser?

Answer 19

Muscle eliminates an unwanted movement caused by another muscle
e.g. the biceps brachii causes supination when elbow is flexing to drink a glass of water. A ‘pronator’ muscle will neutralise this supinating effect.

Question 20

If a muscle lies anteriorly, what movement will it produce?

Answer 20

Flexion at the joint it crosses.

Question 21

If a muscle lies medially, what movement will it produce?

Answer 21

Adduction at that joint.

Question 22

If a muscle lies laterally, what movement will it produce?

Answer 22

Adduction at the joint it crosses.

Question 23

If a muscle lies posteriorly, what movement will it produce?

Answer 23

Extension at the joint it crossses

Question 24

What is the exception for the movement rules?

Answer 24

The knee joint. A joint that crosses anteriorly here will produce extension and a joint that crosses posteriorly will produce flexion.

Question 25

Where does the deltoid muscle attach?

Answer 25

Attachment to pectoral girdle on proximal attachment sight (clavicle and scapula)
Attachment to mid-shaft of humorous on distal attachment sight.
Crosses the anterior, lateral and posteriorly.

Question 26

What movements does the deltoid produce?

Answer 26

Because it crosses anterior, lateral and posterior, it produces flexion, abduction and extension at the shoulder joint.

Question 27

Where does the biceps brachii attach and what movements does this produce?

Answer 27

Crossed anteriorly over shoulder, so produces flexion.

Crossed anteriorly over elbow, so produces flexion.

Attaches to medial surface of the radius, so produces supernation.
When supinating biceps brachii contracts and functions to rotate the radius bone back over into supernation

Question 28

Where does the triceps brachii attach and what movements does it produce?

Answer 28

Long head attaches to scapula, causes weak extension of shoulder
Three heads will insert into the ulna, across the posterior aspect of the ulna joint causing extension of the elbow.

Question 29

What does the tricep brachii have no roles in?

Answer 29

pro/supination

Question 30

Where does the Liopsoas attach and what movements does it do?

Answer 30

Crosses anteriorly over the hip and when contracts produces flexion
–> Ischial tuberosity

Question 31

Where does the gluteus maximus attach and what movements does it do?

Answer 31

Attaches posteriorly over the hip so produces hip extension

Question 32

Where does the quadriceps femoris attach and what movements does it do?

Answer 32

The rectus femoris crosses both the hip and knee joint so it can produce flexion at hip (helping illosolas) and extension at the knee.

The lateralis, intermedius and medialis (vasti muscles) only cross knee joint so they only produce extension at the knee

Question 33

Where does the tibilais anterior attach and what movements do they do?

Answer 33

Attach laterally at top and attach medially at the bottom at the ankle to produce dorsiflexion and inversion
Produces movement at the foot (pulls distal bone upwards and medially so causes inversion)

Does not cross over knee so doesnt affect movement here

Question 34

Where do the Triceps surae cross and what movements do they do?

Answer 34

The gastronemius and soleus join to form the calcaneal tendon.
The more superficial (gastronemius) muscle crosses posteriorly over the knee. Helps the hamstrings to flex the knee.
Soleus does not cross knee joint, so doesn’t aid in flexion but contributes to most of the force in plantarflexion.

Question 35

What is the deltoid tuberosity?

Answer 35

The distal attachment of the deltoid is a special region called the tuberosity (roughing on the bone where a powerful muscle is attached)

Question 36

Where do the hamstrings cross and what movements do they produce?

Answer 36

Crosses posteriorly at the hip to produce extension
Crosses posteriorly at the knee to produce flexion and rotation when flexed
–> Attached to issural tuberosity