Skeletal Muscle

Question 1

What are the 3 types of muscle and where are they found?

Answer 1

Skeletal- voluntary,
Smooth- involuntary bladder
Cardiac- heart

Question 2

What is all chemical energy/ATP converted into?

Answer 2

Mechanical energy

Question 3

Define muscle fasciculus

Answer 3

a bundle of muscle fibres

Question 4

Define muscle fibre/myocyte

Answer 4

cylindrical,

multinucleated cells composed of many myofibrils

Question 5

Define Myofibril

Answer 5

the basic rod-like unit of a muscle cell

Question 6

Define myofilament

Answer 6

the myofibril’s thick, thin and

elastic filaments.

Question 7

Define myosin filament

Answer 7

the thick filaments

Question 8

Define F-actin filament

Answer 8

the thin filaments

Question 9

Define titin filaments

Answer 9

the elastic filaments that run
through the core of each thick filament and
anchor it to the Z-line

Question 10

What are these parts mean in a muscle

Td
M
SR
T tubule

Answer 10

Td – tubular triads containing a flattened tubule of the T system (T) and a pair of terminal cisternae (TC).

M – mitochondria mostly localised in the I bands close to the parts of the actin and myosin filaments that interact during contraction.

SR – sarcoplasmic reticulum

T tubule – transverse tubule

Question 11

What are these parts in a muscle?

I band
A band
H zone
M- line

Answer 11

Light band = I band
Dark band= A band

M-line is in between Hzone
H zone is distance between actin filaments

Question 12

Where does Z-line bisect?

Answer 12

Bisects the I bands

Question 13

Define sarcomere

Answer 13

basic unit of striated muscle tissue. The repeating unit between the 2 Z-lines

Question 14

Describe the filament theory.

Answer 14

Describes the mechanism of muscle contraction

The thick and thin filaments slide over one another

Hence neither of the thick or thin filaments shorten

During contraction the H-zone becomes narrower

The elastic titin filaments keeps the thick filament in a central position

Question 15

How is myosin arranged in thick filament?

Answer 15

2 Bulbous head with cross bridges and a long tail

Question 16

How is the actin arranged in thin filaments ?

Answer 16

Bound with troponin and tropomyosin with Ca2+ binding sites

Question 17

What is the role of tropomyosin?

Answer 17

A protein that binds to and stabilizes actin filaments in cells
In skeletal and cardiac muscle cells, tropomyosin is released after interacting with troponin and calcium,
facilitating the binding of actin to myosin that causes muscle contraction

Question 18

Describe the steps that causes the actin active sites on the troponin

Answer 18

AP down sarcolemma to T tubule to Sarcoplasmic reticulum. This activates voltage-sensitive receptors which triggers Ca2+ released from the terminal cisternae of SR amongst the myofilaments.
Ca2+ binds to troponin which undergoes a conformational change, exposing the actin active sites and removing blocking tropomyosin.

Question 19

Describe the cross bridge cycle

Answer 19

Myosin and actin unbind.
Myosin heads cock then rebind to actin,Pi is released.
Power stroke occurs when Actin gets pulled toward middle of sarcomere, ADP released
New ATP binds to myosin head.
Repeat

Question 20

Describe the process of muscle contraction in 7 steps

Answer 20

A nervous impulse arrives at the neuromuscular junction, which causes a release of a chemical called acetylcholine (ACh).

The presence of ACh causes the depolarisation of the motor end plate which travels throughout the muscle by the transverse tubules, causing calcium ions (Ca2+ ) to be released from the sarcoplasmic reticulum.

In the presence of high concentrations of Ca2+, the Ca2+ binds to troponin, changing its shape and so moving tropomyosin, revealing the myosin binding site of actin.

The myosin filaments can now attach to the actin, forming a cross-bridge.

Inorganic phosphate is released increasing the affinity of the myosin head group for actin

ADP released enables the myosin to pull the actin filaments inwards and so shortening the muscle. This occurs along the entire length of every myofibril in the muscle cell.

The myosin detaches from the actin and the cross-bridge is broken when an ATP molecule binds to the myosin head.

Question 21

What happens in the muscle after the impulse has stopped?

Answer 21

the Ca2+ is pumped back to the sarcoplasmic reticulum and the actin returns to its resting position causing the muscle to lengthen and relax

Question 22

What are 3 components that make up the strength of skeletal muscle contractions?

Answer 22

Twitch
Summation
Tetanus

Question 23

Define twitch

Answer 23

single contraction and relaxation cycle produced by an action potential within the muscle fibre itself.

Question 24

Define summation

Answer 24

if another action potential is applied before complete relaxation of the twitch, then the next twitch will sum onto the previous twitch.

Question 25

Define tetanus

Answer 25

when the frequency of muscle action potentials increases such that the muscle contraction reaches its peak force and plateaus. At this level, then the contraction is a tetanus.

Question 26

What does the magnitude of the tension determined by?

Answer 26

Frequency of the stimulation and the

initial resting length of muscle fibres

Question 27

What is a motor unit?
What does the unit consist of?
How neuromuscular junction per muscle fibre?
What is the principle?

Answer 27

Unit= neuron and all muscle fibre attached
one neuromuscular junction per muscle fibre
All or none principle

Question 28

Small motor units means what?

Answer 28

Muscles control fine movement

Question 29

Large motor unit means what?

Answer 29

Large weight bearing muscles

Question 30

What is the size principle?

Answer 30

Greater force means more motor units and larger fibres