Structure of Muscles

Question 1

What is the name of the usually fixed point where the muscle attached and is this proximal or distal?

Answer 1

The origin

It is proximal

Question 2

What is the name of the usually moveable attachment of the muscle and is this proximal or distal?

Answer 2

Insertion

It is distal

Question 3

What exists between the origin and the insertion of a muscle?

Answer 3

The muscle belly

Question 4

Skeletal Muscle fibres are mononucleated. T/F?

Answer 4

False

Question 5

What is the name for a bundle of muscle fibres bound together by collagenous supporting tissue?

Answer 5

Fassicles

Question 6

What is the name of the connective tissue which surrounds individual muscle fibres?

Answer 6

The endomysium

Question 7

What is the name of the connective tissue which surrounds each fascicle?

Answer 7

The perimyosium

Question 8

What is the name of the connective tissue which surrounds the whole muscle mast?

Answer 8

Epimysium

Question 9

What is the role of the perimysium?

Answer 9

To protect the fascicles from damage. It also contains blood vessels and nerves the nourish the muscle fibres

Question 10

Muscles which have small fascicles and a large proportion of perimysium are most likely involved in what kind of movement?

Answer 10

Fine, highly controlled movement (e.g. Movement of the fingers)

Question 11

What binds skeletal muscle directly to the skeleton?

Answer 11

Tendons

Question 12

What binds skeletal muscle indirectly to the skeleton?

Answer 12

Aponeurosis

Question 13

Where are the nuclei of muscle fibres?

Answer 13

At the periphery

Question 14

What is the name of the plasma membrane of muscle cells?

Answer 14

Sarcolemma

Question 15

What is the name of the organelle of a muscle fibre which is analogous to the endoplasmic reticulum of other cells?

Answer 15

The sarcoplasmic reticulum

Question 16

Where is calcium stored in muscle fibres?

Answer 16

The terminal cisternae of the sarcoplasmic reticulum

Question 17

Large amounts of glycogen and myoglobin exist in the sarcoplasm. What is their role in a muscle fibre?

Answer 17

Glycogen - provides energy during muscle contraction by conversion to glucose for respiration
Myoglobin - acts as an oxygen store

Question 18

Each muscle fibre is composed of bundles of…?

Answer 18

Myofibrils

Question 19

What are the two main components of the myofibril?

Answer 19

The thin filament (mostly actin)

The thick filament (mostly myosin)

Question 20

What is the structure of myosin?

Answer 20

Myosin has two large heavy chains and four small light polypeptide chains. They combine to form two globular heads (of both heavy and light chains) and a long tail of the two intertwined heavy chains. The two heads stick out to the sides to form cross-bridges

Question 21

What are the two binding sites of the myosin molecule for?

Answer 21

The ATP binding site is to bind ATP and can also act as an ATP-ase
The other binding site is to bind to the thin filament

Question 22

What is the role of tropomyosin?

Answer 22

It sits on the actin element of the thin filament and stops myosin from binding to it.

Question 23

What is to role of troponin?

Answer 23

Troponin holds tropomyosin in its blocking position on the actin element of the thin filament.

Question 24

What is the structure of tropomyosin?

Answer 24

It is a long rod-shaped molecule comprised of two intertwined polypeptides and is about seven actin monomers long

Question 25

What is the structure of troponin?

Answer 25

It is a small globular protein and has three subunits: TnI - inhibitory TnT - tropomyosin binding TnC - calcium binding

Question 26

What is the structure of actin?

Answer 26

Actin is made up of monomers (G actin) which polymerise (forming F actin) and is made up of to intertwined helical strands

Question 27

What is the role of the protein nebulin?

Answer 27

It is sheath-like and covers actin to help anchor the filaments to the Z line

Question 28

What is the role of dystophin?

Answer 28

It is a structural protein which links actin to the sarcolemma, helping to transmit tension from the filaments to the tendon of the muscle. It helps reinforce the strength of the sarcolemma

Question 29

In a microscopic view of a muscle fibre what does the A band represent?

Answer 29

The A band is a dark wide bind showing the thick filaments which reside in the middle of the sarcomere

Question 30

What is the Z line of the sarcomere?

Answer 30

One end of each thin filament is anchored to a network of interconnected proteins known as the Z line. Thin filaments from to adjacent cells are anchored to the two sides of the Z line. The Z line marks the boundary of the sarcomere.

Question 31

What is the name of the structural protein which makes up the Z line?

Answer 31

Alpha actinin

Question 32

In a microscopic view of a muscle fibre what does the I band represent?

Answer 32

The I band lies between the ends of adjacent A bands and shows the thin filaments which do not overlap with the thick filaments

Question 33

What is the M line?

Answer 33

The M line is in the middle of the sarcomere and joins to two halves of the thick filament

Question 34

What protein is the M line composed of?

Answer 34

Myomesin

Question 35

What is the name of the elastic protein which extends from the Z line to the M line and is linked to the M line proteins and the thick filaments?

Answer 35

Tintin

Question 36

In a microscopic view of a muscle fibre what does the H band represent?

Answer 36

The H band is a narrow, light band in the centre of the A band which shows the space between opposing ends of the two sets of thin filaments.

Question 37

What structure lies directly between and is intimately related to adjacent segments of the sarcoplamsic reticulum?

Answer 37

Transverse(T)-tubules

Question 38

What structure exists in the area where the A and I bands meet?

Answer 38

T-tubules

Question 39

What does a motor unit consist of?

Answer 39

A somatic motor neuron with all of the muscle fibres that it innervates

Question 40

What does motor recruitment refer to?

Answer 40

The number of motor units activated during a contraction

Question 41

The overall muscle movement produced depends on the recruitment of...?

Answer 41

Different sized motor units Different strengths of motor unit Quantity of motor units

Question 42

All the muscle fibres of one motor unit are of the same fibre type. T/F?

Answer 42

True