Week 2 - Skeletal Muscle Structure, Morphology and Function

Question 1

What is the most common shape of muscle? Give an example of a muscle which takes this shape.

Answer 1

Fusiform

Biceps brachii

Question 2

List the shapes a muscle may be, and give examples of each.

Answer 2

Fusiform - biceps brachii
Circular
Convergent - pectoralis major
Parallel - sartorius
Unipennate - extensor digitorum longus
Bipennate - rectus femoris
Multipennate - deltoid

Question 3

Describe a convergent muscle

Answer 3

Wide at origin but narrow at its insertion

Question 4

Describe what a parallel muscle looks like

Answer 4

Straight up and down

Question 5

What is the difference between unipennate, bipennate and multipennate muscles?

Answer 5

Unipennate - like half a feather
Bipennate - like a feather
Multipennate - like several feathers

Question 6

What structure is every tendon continuous with?

Answer 6

The epimysium

Question 7

What is fasciculation? Give an example of when it may occur.

Answer 7

Muscle twitching

In the eyes when tired

Question 8

Which type of lever is most efficient?

Answer 8

1st class lever

Question 9

Describe a first class lever

Answer 9

Pivot in the centre, with the force underneath to one side, and the load above on the other side

Question 10

Describe a second class lever.

Answer 10

Like a wheelbarrow - force and load both on the left of the pivot.

Question 11

Describe a 3rd class lever.

Answer 11

Like a fishing rod -

Force and load both on the right of the pivot

Question 12

Briefly explain what happens in compartment syndrome.

Answer 12

Bleeding occurs within a compartment, which is bound by inextensible connective tissue. This raises the pressure inside the compartment, and as it cannot expand, leads to compression of the neurovasculature within the compartment.

Question 13

Give the 4 muscle groups in terms of function.

Answer 13

Agonists
Antagonists
Synergists
Fixators

Question 14

What is an agonist, in terms of muscles?

Answer 14

A “prime mover” - i.e. the main muscle performing a movement

Question 15

What is a synergist?

Answer 15

A muscle aiding an agonist

Question 16

What is an antagonist, with regards to muscles?

Answer 16

A muscle opposing the action of an agonist

Question 17

What do fixator muscles do?

Answer 17

Stabilise the action of prime movers (agonists)

Question 18

What are the two types of muscle contraction, and how do they differ?

Answer 18

Isotonic - tension constant, length variable

Isometric - length constant, tension variable

Question 19

What are the two types of isotonic muscle?

Answer 19

Concentric - gets shorter

Eccentric - gets longer

Question 20

What are the two major muscle fibre types?

Answer 20

Type I

Fast Twitch

Question 21

What are type I muscle fibres?

Answer 21

Slow oxidative

Question 22

How are fast twitch muscle fibres subdivided?

Answer 22

Type IIa - fast oxidative

Type IIb - fast glycolytic

Question 23

Which muscle fibre type appear red, and why?

Answer 23

Slow oxidative

Due to the very high myoglobin content

Question 24

Which are the palest muscle fibres?

Answer 24

Fast glycolytic

Question 25

Which muscle fibre types are aerobic and which are anaerobic?

Answer 25

Slow and fast oxidative are aerobic | Fast glycolytic are anaerobic

Question 26

Give 3 characteristics of both fast and slow oxidative muscle types.

Answer 26

High myoglobin (but more in slow) Many mitochondria Many capillaries

Question 27

Which muscle fibre type(s) is/are fatigue resistant?

Answer 27

Slow and fast oxidative, although slow more so.

Question 28

What functions may slow oxidative muscle fibres perform?

Answer 28

Posture | Endurance activity

Question 29

Give an example of an activity facilitated by fast oxidative muscle fibres

Answer 29

Walking

Question 30

Fast glycolytic muscle fibres rapidly fatigue. What sorts of activity do they therefore allow?

Answer 30

Short, intense activity

Question 31

What are the major functions of skeletal muscle?

Answer 31

Movement Posture Stability of Joints Heat generation (although only around 20% efficient)

Question 32

What are proprioreceptors?

Answer 32

Muscle spindles that send signals to the brain telling it how much tension is being exerted.

Question 33

What does proprioreception allow? | What might disrupt it?

Answer 33

Feedback control of movement | Alcohol

Question 34

What is a motor unit?

Answer 34

A motor neurone and the muscle fibre(s) it innervates

Question 35

What structure do motor neurones leave the brain via?

Answer 35

The ventral root

Question 36

What is "crosstalk"?

Answer 36

Communication between neurones and muscle, via signalling molecules.

Question 37

Why may atrophy of a muscle cause atrophy of the nerve that innervates it, and vice versa?

Answer 37

Lack of crosstalk due to fewer chemical signals being produced.

Question 38

What two factors mean that baseline muscle tone is always present at rest?

Answer 38

Muscle activity | Motor neurone activity

Question 39

How is muscle tone controlled?

Answer 39

Feedback via afferent fibres from the muscle to the motor control centres of the brain.

Question 40

What is hypotonia?

Answer 40

Lack of muscle tone

Question 41

What are the 3 possible causes of hypotonia?

Answer 41

1. CNS problems 2. PNS problems 3. Muscle problems - myopathies (primary muscle degeneration)

Question 42

What is an EMG and what is it used for?

Answer 42

An electromyogram | Used to measure electrical activity in the muscles; helps diagnose conditions such as MND.

Question 43

How is the force of contraction of skeletal muscle controlled?

Answer 43

Spatial summation | Temporal summation

Question 44

Explain spatial summation

Answer 44

More motor neurones are activated, and hence more muscle fibres contract, giving more forceful contraction

Question 45

Explain temporal summation, including what it can lead to.

Answer 45

Increased frequency of action potentials in the muscle fibres. In extremes, this can lead to tetany.

Question 46

What is a contracture?

Answer 46

Continuous muscle contraction without relaxation

Question 47

What are the possible sources of ATP within skeletal muscle?

Answer 47

ATP stores Creatine phosphate Glycolysis Oxidative phosphorylation

Question 48

Explain the pathophysiology behind muscle cramps.

Answer 48

Increased lactate causes the pH of the muscle to fall. This acts on nerve endings, causing pain.

Question 49

If blood flow to a muscle is interrupted, how quickly are the glycogen stores depleted?

Answer 49

Within around 1 minute