Week 4

Question 1

Muscles cannot contract on their own, they need input from the ________ to send signals to the muscle.

Answer 1

nervous system

Question 2

Where do motor units connect with muscles

Answer 2

Neurotransmitter junction

Question 3

What is the synaptic cleft

Answer 3

It is where all the neurotransmitter diffuses in order to produce a contraction

Question 4

How does an action potential travel from the CNS to the muscle fibre

Answer 4

1.CNS sends an action potential to the muscle fibre via the axon,
2. Potential arrives via the axon terminal which will depolarize the plasma membrane. This opens calcium channels, which produces calcium ions into the axon terminals.
3. This calcium binds to proteins.
4. Synaptic vesicles then release acetylcholine. This diffuses across the synaptic cleft to the motor end plate, binding to nicotinic receptors.
5. This binding of acetylcholine opens an ion channel. Na+ can pass through these channels, creating local depolarization of the motor end plate.
6. The muscle fibre action potential is then initiated.

Question 5

What is the latent period

Answer 5

After the action potential, there is a latent period before the tension in the muscle fibre begins to increase

Question 6

Relationship between muscle fibre action potential and the muscle contraction

Answer 6

Action potential creates tension in the muscle.
It is over before the signs of muscular contraction begins

Question 7

What is the contraction time

Answer 7

Time from the beginning of tension development (at the end of the latent period) to the peak tension

Question 8

How does calcium aid the sliding filament model

Answer 8

Calcium binds to troponin, which will uncover the binding sites of the actin filament and will help for actin to form a cross bridge with myosin to generate force.

Question 9

Difference between a relaxed and active muscle in the sliding filament model

Answer 9

In a relaxed muscle, there is low calcium, cross bridge cannot form as tropomyosin is covering the binding site (held back by troponin)
In an active muscle, there is high Calcium. Ca2+ binds to troponin. Tropomyosin moves away from cross bridge binding site. Actin binds to cross bridge

Question 10

Difference between a relaxed and active muscle in the sliding filament model

Answer 10

In a relaxed muscle, there is low calcium, cross bridge cannot form as tropomyosin is covering the binding site (held back by troponin)
In an active muscle, there is high Calcium. Ca2+ binds to troponin. Tropomyosin moves away from cross bridge binding site. Actin binds to cross bridge

Question 11

Summary of the sliding filament model PART 1 - Calcium, troponin, tropomyosin

Answer 11

The formation of a cross bridge is initiated when calcium ions released from the sarcoplasmic reticulum bind to troponin. This causes troponin to change shape. Tropomyosin moves away from the myosin binding site on actin allowing the myosin head to bind actin to form a cross bridge.

Question 12

Summary of sliding filament model PART 2 - myosin, ATP, hydrolysis

Answer 12

The myosin head must be activated before a cross bridge cycle can begin. This occurs when ATP binds to the myosin head and is hydrolysed to ADP and inorganic phosphate. The energy liberated from the hydrolysis of ATP activates the myosin head.

Question 13

Summary of the sliding filament model PART 3 - the contraction

Answer 13

The activated myosin head binds to actin, forming a cross bridge. Inorganic phosphate is released.
ADP is released and the myosin head pivot sliding the myofilament towards the centre of the sarcomere. When another ATP binds to the myosin head, the length between the myosin head and actin weakens, and the myosin head detaches. ATP is hydrolysed to ADP and inorganic phosphate. The energy released during hydrolysis reactivates the myosin head for cycle to start again.

Question 14

Difference between tension and load in a muscle

Answer 14

Tension is the force that a muscle exerts on the joint when it is contracting
Load is the force that is exerted on a muscle by an object

Question 15

Muscle tension must _____ the load in order for the muscle fibres to shorten, and therefore move the object that is responsible for the load.

Answer 15

Exceed

Question 16

Concentric contractions in relation to tension and load

Answer 16

Tension > load

Question 17

Eccentric contractions in relation to tension and load

Answer 17

Load > tension

Question 18

In a shortening contraction, an increasing load causes

Answer 18

The latent period to increase
The duration of the twitch to become shorter
The velocity of shortening to slow down (gradient to decrease)

Question 19

In the absence of a load, a shortening contraction reaches its ________________

Answer 19

maximum shortening velocity

Question 20

Difference between an unfused tetanus and a fused tetanus

Answer 20

Unfused = the muscle fibre has time to partially relax before the next stimulation. Oscillation
Fused = muscle fibre has no time to relax between stimulations. The development of tension is continuous.

Question 21

Tension in a slow oxidiative muscle fibre

Answer 21

Tension is low but can be maintained for a long time

Question 22

Tension in te type 2a, fast oxidative muscle fibre

Answer 22

Tension in the muscle begins high, but slows over a period

Question 23

Tension in the type 2x fast glycolytic muscle fibre

Answer 23

Fibre produces lots of tension quickly, but that quickly drops

Question 24

Techniques to determine fibre type

Answer 24

Colour of fibre – type I fibres are more red in colour due to more capillaries and mitochondria due to their oxidative capacity
Muscle biopsy – use of a needle to cut a piece of muscle – puts untder microscope and able to see the MFTs.

Question 25

Spikes and discharge frequencies

Answer 25

When you record an action potential, we call it a spike. Multiple spikes are called discharges. If the frequency of discharges increases, the force produced by a muscle increases

Question 26

Main mechanisms in which motor units can generate more force is by

Answer 26

An increase in discharge rate and also increasing motor unit recruitment

Question 27

Hypertrophy v hyperplasia

Answer 27

Hypertrophy is an increase in the size of the muscle fibres
Hyperplasia is an increase in the number of muscle fibres

Question 28

Ananbolism

Answer 28

the rate of muscle protein synthesis > muscle protein breakdown = muscle gain

Question 29

Catabolism

Answer 29

the rate of muscle protein breakdown > muscle protein synthesis = muscle loss