MSK: Skeletal Muscle

Question 1

Name the 3 arrangements of skeletal muscle.

Answer 1

1. Parallel
2. Pennate
3. Circular

Question 2

What are the 3 sub catalogues of parallel arranged skeletal muscle?

Answer 2

1. Strap (fibres run longitudinally)
2. Fusiform (cylindrical and wider in the centre with tapered off ends)
3. Fan shaped (fibres converge at one end)

Question 3

Describe the structure of pennate muscles.

Answer 3

They have one or more aponeuroses running through the muscle body from the tendon and the fascicles of the muscle fibres attach these to the aponeuroses at an angle.

Question 4

What are the 3 subcategories of pennate muscles?

Answer 4

1. Unipennate (fascicles are on the same side as the tendon)
2. Bipennate (fascicles on both sides of the central tendon)
3. Multipennate (central tendon branches)

Question 5

Describe circular muscles.

Answer 5

The fibres form concentric rings around a sphincter or opening.

Question 6

What are synergists?

Answer 6

Muscles that act to assist the primary mover. (Acting alone they cannot perform the movement of the agonist)

Question 7

What are neutralisers?

Answer 7

They prevent unwanted actions that the agonist (muscle) can perform.

Question 8

What are fixators? (Stabilisers)

Answer 8

They act to hold a body part (joint) immobile whilst another body part is moving.

Question 9

What does the term contraction refer to?

Answer 9

The active cycling of cross bridges between the actin thin filaments and the Myosin thick filaments.

Question 10

What is isotonic contraction?

Answer 10

Where the tension within the muscle remains constant and the length changes.

Question 11

What are the 2 subtypes of isotonic contraction?

Answer 11

1. Concentric (muscle shortens)

2. Eccentric (muscle lengthens)

Question 12

What are the 3 types of muscle contraction?

Answer 12

1. Isometric contraction (equal tension)
2. Isotonic contraction (equal length)
3. Passive stretch

Question 13

What is isometric contraction?

Answer 13

It’s the contraction that occurs when the load against the muscle equals the contractile force being generated.

Question 14

What is passive stretch?

Answer 14

When the muscle is being lengthened whilst in a passive state, I.e. Not being stimulated to contract.

Question 15

What protein is important in muscle contraction?

Answer 15

Titin

Question 16

What is the function of titin?

Answer 16

Connects the Z line to the M line in the sarcomere.

Question 17

What type of motor neurones innervate skeletal muscle?

Answer 17

Alpha motor neurones

Question 18

Where are the cell bodies of the neurones which innervate skeletal muscle found?

Answer 18

Ventral horn of the spiral chord (for the muscle of the limbs and trunk) or the motor nuclei of the brain stem (for the head and face)

Question 19

What is the structure which connects individual muscle fibres and the alpha motor neurone?

Answer 19

Neuromuscular junction

Question 20

Define a motor unit.

Answer 20

An alpha motor neurone and the group of individual muscle fibres that it innervates.

Question 21

Which will have more muscle fibres in each motor unit?

Answer 21

Powerful muscles where fine control is less important e.g. Gastrocnemius

Question 22

What are type 1 fibres also known as?

Answer 22

Slow muscle fibres

Question 23

What are type 2 muscle fibres also known as?

Answer 23

Fast muscle fibres

Question 24

What are the 2 types of fast muscle fibres present in humans?

Answer 24

1. IIA

2. IIX

Question 25

Which type of fast fibres are also known as intermediate fibres between fast and slow?

Answer 25

IIA

Question 26

Why are type 1 fibres resistant to fatigue?

Answer 26

High mitochondria content and use of oxidative metabolism to produce ATP

Question 27

Are IIA fibres classified as glycolytic or oxidative?

Answer 27

Both!

Question 28

Are IIX fibres classified as glycolytic or oxidative?

Answer 28

Glycolytic

Question 29

TRUE OR FLASE: most muscle are composed of a mixture of different types, it is the proportion of fast to slow fibres which determines the function

Answer 29

True

Question 30

What 2 factors does the contractile force produced by a muscle depend on?

Answer 30

1. Size principle | 2. Rate code

Question 31

What is he size principle?

Answer 31

Small motor neurones are recruited before large ones.

Question 32

In general, what order does the size principle determine the motor unit will follow?

Answer 32

Type I first, then type IIA, then type IIX.

Question 33

What is the rate code?

Answer 33

The frequency at which muscle fibres are stimulated by their alpha neurone.

Question 34

What is the name of the term given to the phenomenon where no further force can be produced by a muscle?

Answer 34

Tetany

Question 35

What is tone?

Answer 35

Degree of tension

Question 36

What is the term given to a lack of muscle tone?

Answer 36

Hypotonia

Question 37

Where is skeletal muscle tone controlled?

Answer 37

Locus coeruleus in the motor control centre of the brainstem

Question 38

What are dihydropyrdine receptors also known as?

Answer 38

Voltage-gated L-type Calcium channels

Question 39

What is malignant hyperthermia?

Answer 39

A condition triggered by some volatile anaesthetic agents which lead to uncontrolled increase in oxidative metabolism, and hence increase in body temperature.

Question 40

What is the most common cause of malignant hyperthermia?

Answer 40

Polymorphism in ryanodine receptor

Question 41

How much ATP is stored in muscle fibre?

Answer 41

Very little (sufficient for only a few seconds of contraction)

Question 42

Name an additional short term store of ATP within muscle fibres.

Answer 42

Creatine phosphate

Question 43

Name a disadvantage of using glycolysis under anaerobic conditions.

Answer 43

Lactate is produce from pyruvate by the action of lactate dehydrogenase.

Question 44

For prolonged activity, what does the muscle do in order to be sufficiently supplied with ATP?

Answer 44

Switches to beta oxidation of fatty acids released from triglycerides stored in a diode tissue.