Muscle physiology and histology

Question 1

What are the four levels found in a muscle?

Answer 1

Whole muscle
Fascicle 
Muscle fibre 
Myofibril
Sarcomere

Question 2

What types of cells are found in the whole muscle?

Answer 2

Muscle fibres
Connective tissue
Blood vessels and lymph

Question 3

What is a muscle fibre?

Answer 3

One muscle cell

Question 4

Name three unique features of a muscle fibre.

Answer 4

Multinucleate
Contain myofibrils
Very long.

Question 5

How big are muscle fibres?

Answer 5

10-100microM in diameter

1000-2000microM in length

Question 6

What are myofibrils?

Answer 6

Collections of sarcomeres packaged together.

Question 7

What is a sarcomere?

Answer 7

Basic functional unit of the muscle that allows for contraction.

Question 8

What two proteins make up a sarcomere?

Answer 8

Myosin (heavy chain)

Actin (light chain)

Question 9

What are the five regions of a sarcomere called and what do they represent?

Answer 9

A Band- From one end of myosin to the other
I Band- Area w/ no myosin
H Zone- Area w/ no actin
Z Line- Area linking actin
M Line- Area linking myosin

Question 10

What are the five stages of a muscle contraction?

Answer 10

Resting
Binding- requires Ca2+
Bending- ADP+Pi dissociate 
Detachment- Fresh ATP binds
Energised- with ATP bound ready for next stroke

Question 11

How does Ca2+ allow binding?

Answer 11

Binds to troponin to move it out the way allowing myosin to bind to tropomyosin on actin.

Question 12

What is a muscle fascicle?

Answer 12

A collection of muscle fibres in found in the whole muscle.

Question 13

What is the connective tissue round the whole muscle called?

Answer 13

Epimysium

Question 14

What is the connective tissue around the fascicle called?

Answer 14

Perimysium

Question 15

What is the connective tissue around a single muscle fibre called?

Answer 15

Endomysium

Question 16

What are the three types of muscle fibres?

Answer 16

Type I
Type IIa
Type IIb

Question 17

Describe Type I muscle fibres.

Answer 17

Aerobic red fibres with lots of mitochondria and myoglobin. Slow contracting but resistant to fatigue.

Question 18

Describe Type IIa fibres.

Answer 18

Intermediate fibres. Relatively fast contracting but relatively fatigue resistant.

Question 19

Describe Type IIb fibres.

Answer 19

Anaerobic white fibres with little mitochondria and myoglobin. Fast contracting but fatigue easily.

Question 20

How many nerves synapse onto a singe muscle fibre?

Answer 20

One

Question 21

What is a neuromuscular unit?

Answer 21

An alpha motor neuron and all the muscle fibres it innervates.

Question 22

What is the neurotransmitter in somatic motor neurons?

Answer 22

ACh

Question 23

What ions does nAChR let through?

Answer 23

Na in and K out

Question 24

What is an EPP?

Answer 24

The sum of all the mepp caused by each quanta of ACh binding.

Question 25

How many ACh molecules does it take to open a nAChR?

Answer 25

Two

Question 26

Describe the presynaptic events that lead to ACh release.

Answer 26

An AP travels down the nerve fibre to the bouton where it activates VGCC allowing Ca in which allows for binding of ACh vesicles.

Question 27

Describe how ACh is recycled.

Answer 27

ACh is broken down by AChesterase to choline and acetate. Choline is reuptaken into the presynaptic cell where it is combined with acetyleCoA to form ACh.

Question 28

How does the EPP propagate a contraction?

Answer 28

It allows opening of VCSC to propagate the depol across the cell. This travels down the T-tubules to allow Ca2+ release from the SR.

Question 29

What two factors does the generation of muscle tension rely on?

Answer 29

Number of fibres recruited | Tension developed per muscle fibre.

Question 30

What three things determine the tension developed per muscle fibre?

Answer 30

Frequency of stimulation Thickness of fibre Length of starting contraction

Question 31

Is the length of contraction in skeletal muscle long or short?

Answer 31

Long

Question 32

What is summation of contraction?

Answer 32

When another AP arrives before the muscle has finished contracting and relaxing it can cause it to contract further thus generating extra force.

Question 33

What is tetanising a muscle?

Answer 33

When it is fully contracted and can contract no further.

Question 34

What is the maximal tetanic contraction?

Answer 34

The maximum length change for each muscle. This is described as 100% of its length. If it is shorter than this you won't get full length contraction and longer won't get full power.

Question 35

What are isotonic contractions?

Answer 35

Contractions used for body movement.

Question 36

What are isometric contractions?

Answer 36

Contractions used to fix an object in space.

Question 37

What are the origins of the two potential motor inputs to a muscle?

Answer 37

UMN and LMN from brain giving conscious control | Reflex arc of somatic sensory, interneuron and somatic motor.

Question 38

Describe the stretch reflex arc.

Answer 38

Resists passive change to the muscle length to maintain optimal muscle length. Important for walking. Muscle stretch activates stretch receptors thus causing reflex muscle contraction.

Question 39

What senses muscle stretch?

Answer 39

Muscle spindles/intrafusal fibres. Annulospiral fibres in them do the sensing.

Question 40

What are extrafusal fibres?

Answer 40

Normal muscle fibres

Question 41

Where are muscle spindles usually found?

Answer 41

In the middle of the muscle.

Question 42

How do they detect stretch?

Answer 42

Increase stretch causes increase discharge.

Question 43

What neurons synapse onto muscle spindles?

Answer 43

Gamma MN to adjust level of tension.

Question 44

What do ligaments do?

Answer 44

Attach bone to bone.

Question 45

What do tendons do?

Answer 45

Attach muscle to bone.

Question 46

Describe tendons.

Answer 46

Parallel collagen fibres Type 1 Collagen 99% Type 2 Collagen 1%

Question 47

Describe ligaments

Answer 47

Nearly parallel collagen fibres Type 1 Collagen 90% Type 2 Collagen 10%

Question 48

What are the four stages of tendons entering bone?

Answer 48

Parallel collagen fibres Unmineralised fibrocartilage Mineralised fibrocartilage Cortical bone

Question 49

What are the five morphologies of skeletal muscle and give examples of them.

Answer 49

``` Flat- External obliques Fusiform- Biceps brachii Circular- Orbicularis oculi Pennate- Deltoid Quadrate- Rectus abdominis. ```