Muscles

Question 1

What is a motor unit?

Answer 1

A group of muscle fibres innervated by a single neuron

Question 2

Where do T tubules invaginate the sarcoplasm?

Answer 2

At the junction of the I and A bands

Question 3

What is a triad?

Answer 3

A T tubule flanked by two terminal cisternae of the SR

Question 4

What hydrolyses ATP in the actin/myosin structure?

Answer 4

The globular myosin head which is as ATPase

Question 5

What are you seeing when striations appear?

Answer 5

The organisation of thick and thin filaments

Question 6

What becomes narrower when the sarcomer contracts?

Answer 6

The H and I bands

Question 7

Where is the A band

Answer 7

Extends length of thick filaments

Question 8

Where is I band

Answer 8

Extends from the ends of each group of thick filaments between two sarcomeres. Includes the Z disc in the middle

Question 9

Where is the H band

Answer 9

Extends the distance between the thin filaments in the middle of the sarcomere.

Question 10

What promotes the myosin head to hydrolyse ATP?

Answer 10

Actin binding

Question 11

Steps of cross bridge cycle

Answer 11

1) Cross bridge formation. Ca2+ release exposes actin binding sites on actin filaments. ATP hydolyses on the myosin heads and they become ‘cocked’ and bind to actin binding sites. Inorganic phosphate is released and the bond between actin and myosin becomes stronger
2) The power stroke. With the release of ADP the myosin head move sliding the thin filament towards the M line
3) Cross bridge detachment. Another ATP binds to myosin head releasing the bond between actin and myosin
4) reactivation of the myosin head. ATP is hydrolysed activating the myosin head.

Question 12

What level is Ca2+ when muscle is relaxed and contracted?

Answer 12

Relaxed

Question 13

What process removes Ca2+ from the cytoplasm?

Answer 13

Active transport. Ca2+ channels close (voltage gated), pumps return Ca2+ to stores (SR) and extracellular space

Question 14

What is the optimal length of a sarcomere for contraction?

Answer 14

Between 2.0 and 2.2 micrometers

Question 15

What is resting membrane potential of the muscle cell?

Answer 15

-90mV

Question 16

Describe Ca2+ transient, stimulus, change in levels, return of Ca2+ to SR

Answer 16

AP in t-tubules causes SR to open Ca2+ channels.
Ca2+ levels change from 10-7 to 10-5
Ca2+ is then actively transported back to the SR via a Ca-ATPase pump.

Question 17

What is the muscle contraction called that is a result of one AP?

Answer 17

A twitch

Question 18

Three methods of ATP production for muscle energy

Answer 18

1) The enzyme creatinine phosphokinase transfers the phosphate group from Creatinine phosphate to ADP
2) Anaerobic- glucose is glycolysised to form pyretic acid which produced 2 ATP snd also lactic acid. Fast action but can’t be prolonged due to build up of metabolic products that inhibit cell reactions
3) Aerobic metabolism. Slow and steady oxidative form of ATP production via cellular respiration and the citric acid cycle.

Question 19

Control of muscle tension can occur with two mechanism…?

Answer 19

Increase the frequency of the AP

Recruit additional motor units

Question 20

Describe temporal summation

Answer 20

AP is shorter than Ca release, so there is still residual Ca if another AP occurs in quick succesion. If frequency of AP is continued the muscle reaches a higher steady state called a tetanus contraction.

Question 21

Three muscle fibre types

Answer 21

Type 1, slow oxidative. Type 2B, fast glycolytic. Type 2A (fast oxidative)

Question 22

Describe Type 1 muscle fibres

Answer 22

Slow ATPase rate
Have a low maximum force production
Oxidative in metabolism
Large amounts of myoglobin and mitochondria giving them red appearance
High oxygen demand offset by small diameter allowing rapid O2 diffusion

Question 23

Describe type 2B muscle fibres

Answer 23

Glycolytic in metabolism
high ATPase rate
low amounts of myoglobin and mitochondria
white in colour
Large diameter
Fatigue rapidly but generate large forces for short periods of time.

Question 24

Type 2A muscle fibres

Answer 24

Not found in humans
Glycolytic and oxidative
Large quantity of myoglobin and mitochondria
High ATP ase rate

Question 25

How many types of muscle fibre can one nerve cell innervate?

Answer 25

One… So the motor unit is given the same classification as that type

Question 26

Describe skeletal muscle fibre recruitment

Answer 26

Many more type 1 muscle fibres so these are recruited first in greater numbers, type 2b fibres and the last to be recruited.

Question 27

Main types of fibres in cardiac muscle

Answer 27

Oxidative

Question 28

Where do the t tubules invaginate the cardiac muscle fibres?

Answer 28

At the Z disc

Question 29

Difference between skeletal SR and cardiac SR

Answer 29

Cardiac SR less developed

Question 30

Describe the initiation of contraction in cardiac muscle

Answer 30

It is myogenic, in that it initiates in the muscle fibre. Contraction is initiated in the senatorial node where it spreads via specialised conduction fibres know as purkinje fibres.

Question 31

Describe action potential in cardiac muscle fibres

Answer 31

10Depolarisation due to large Na+ influx

2) Plateau due to slow release Ca2+ channels opening and influx of Ca2+
3) Repolarisation due to Ca2+ channels inactivating and K+ channels opening, K+ efflux

Question 32

What controls the regulation of the heart rate?

Answer 32

Symapthethic and parasympathetic stimulation.
Sympathethic increases (noradrenaline)
Parasympathetic decreases (vagus nerve)

Question 33

What controls the force of the heart contraction?

Answer 33

Increasing the rate of firing
Increase the diameter of the ventricle (stretch)
Use neurotransmitters to alter rate and calcium handling

Question 34

How long is an action potential in skeletal muscle

Answer 34

1-2mSec

Question 35

how long is a muscle twitch in skeletal muscle

Answer 35

20-200msec