Muscle

Question 1

Where is skeletal muscle derived from?

Answer 1

Mesodermally derived myogenic stem cells give rise to myoblasts.

Question 2

Explain why skeletal muscle initially has centrally positioned nuclei and then where these nuclei move to.

Answer 2

Myoblasts fuse to produce a primary myotube. The nuclei are then gradually displaced to the periphery by the newly synthesised actin/myosin micro filaments.

Question 3

What is the difference between red and white skeletal muscle fibres?

Answer 3

Red muscle fibres fatigue slower and can do many repeated repetitions whilst white muscle fibres fatigue quickly but they are faster and stronger (for sprinting).

Question 4

What is a myotendious junction?

Answer 4

These is the junction between muscle and the collagen of tendons. Sarcolemma lies between the muscle fibres and the tendon collagen.

Question 5

Where would u find the perimysium? What is it’s function?

Answer 5

This is found surrounding a fasicle (bundle of muscle fibres) in a muscle. It carries nerves and blood vessels.

Question 6

What is the name of the membrane which surrounds an individual muscle fibre?

Answer 6

Endomysium.

Question 7

What two muscle types does the tongue have and what is their function?

Answer 7

Intrinsic which change the shape of the tongue and extrinsic which moves the position of the tongue within the mouth.

Question 8

What accounts for the mobility and flexibility of the tongue?

Answer 8

Multidirectional muscle fibres. Also plasticity and strength of the connective tissue assists with this.

Question 9

Describe the banding pattern in skeletal muscle.

Answer 9

MHAZI. The A line is found within the H zone of the M band, and the I band is found within the Z disc.

Question 10

What is a sacromere?

Answer 10

This is one muscle unit which is the same length as a muscle fibre.

Question 11

What is seen when skeletal muscle is cut transversely?

Answer 11

Micro fibrils can be seen as dots.

Question 12

Where in skeletal muscle are mitochondria found and how can they be seen on a stained section?

Answer 12

Mitochondria are between myofibrils and are seen as purple streaks.

Question 13

What three substances are thin filaments of muscle composed of?

Answer 13

Actin, tropomyosin and troponin.

Question 14

What is a good clinical marker for cardiac muscle damage?

Answer 14

Troponin is released from ischaemic heart muscle, small changes indicate damage to cardiac muscle but levels are not proportional to the damage.

Question 15

Describe the structure of a thick muscle filament.

Answer 15

These are made from myosin molecules. These have a long tail and 2 heads. The heads protrude from the sides. Of the bundle of myosin molecules.

Question 16

Actin molecules form a helix structure. What other molecules are involved in thin filaments?

Answer 16

Tropomyosin molecules wrap around this to stabilise the structure, and to each of these a troponin complex attaches.

Question 17

What can be said about the thick filaments in the centre of the sacromere (the M line)?

Answer 17

Here there are no myosin heads because they point outwards to where the actin molecules are present.

Question 18

What is the role of calcium in activating muscle contraction?

Answer 18

Calcium binds to the TnC of the troponin complex and this causes a conformational change and the tropomyosin molecule moves away from actins binding sites. This allows myosin to bind and contraction begins.

Question 19

What is the role of ATP in muscle contraction?

Answer 19

When ATP binds to the myosin filament this releases the actin molecule. Hydrolysis of ATP leads to movement of this head and it cocks back. It then binds to another Troponin molecule.

Question 20

What is rigor Mortis?

Answer 20

This is because there is no ATP and so the myosin head is not released from the troponin molecules and so the muscles are very stiff.

Question 21

Where are T tubules found in skeletal muscle?

Answer 21

They are found at the join between the A and the I band. It is a triad in this type of muscle.

Question 22

What are the two different types of muscle?

Answer 22

Striated and non-striated.

Question 23

What is a neuromuscular junction?

Answer 23

This is a small terminal swelling on an axon which contain vesicles of acetylcholine.

Question 24

What is the action of acetylcholine?

Answer 24

This binds to receptors on sarcolemma and initiates an action potential which propagates along the length of the muscle.

Question 25

Explain how a nerve impulse leads to muscle contraction.

Answer 25

The nerve impulse stimulates release of acetylcholine which leads to depolarisation of sarcolemma and voltage gated sodium channels open. This causes a change in voltage sensor proteins of t tubules which leads to opening of calcium channels. Calcium is released into sarcoplasm.

Question 26

Describe features of cardiac muscle that allow us to differentiate it from skeletal muscle.

Answer 26

It has centrally positioned nuclei, and it branches. It also has intercalating discs for electrical and mechanical coupling.

Question 27

What is a adherents type junction?

Answer 27

These are found in cardiac muscle and are for actin anchorage.

Question 28

Are there myofilaments in cardiac muscle?

Answer 28

No, there are only actin and myosin molecules.

Question 29

Where do T tubules lie in cardiac muscle?

Answer 29

They lie along Z bands. Here they are dials and the proximity of this to the sarcoplasmic recticulum allows calcium release for muscle contraction.

Question 30

What can be said about the contraction of cardiac cells?

Answer 30

It is spontaneous rhythmic contraction. Potentials are generated by the SAN and AVN.

Question 31

What are the distal conducting cells called in the heart and what is important about their structure?

Answer 31

They are called purkinje fibres. They have abundant glycogen, sparse myofilaments and e tensile gap junctions which all allow for rapid contraction.

Question 32

State the most common location where smooth muscle is found.

Answer 32

Contractile walls of vessels such as the gut.

Question 33

What shape are smooth muscle cells?

Answer 33

They are spindle shaped with central nuclei.

Question 34

How do contractions of smooth muscle compare to those of striated muscle?

Answer 34

They are much slower and sustained and the muscle can remain contracted for days. This means they are capable of being stretched.

Question 35

Where are myoepithelial cells found?

Answer 35

They are found around secretory units of some exocrine glands so assist in secretion through ducts. They are also present in the ocular iris and dilate the pupil.

Question 36

What is a myofibroblast cell?

Answer 36

These are found at wound healing sights and are responsible for collagen secretion but also contraction.

Question 37

How is smooth muscle in the gut innervated?

Answer 37

It is innervated by the autonomic nervous system which stimulates release of neurotransmitters.

Question 38

Explain how the contraction of smooth muscle is different to that of skeletal muscle.

Answer 38

Smooth muscle has thick and thin filaments in a diagonal arrangement, and this leads to a twisting contraction motion. Intermediate filaments are attached to dense bodies which are scattered throughout the sarcoplasm.

Question 39

How do cells in smooth muscle repair?

Answer 39

These cells retain their mitotic capability and so they form new smooth muscle.

Question 40

Explain the consequences of cardiac muscle becoming damaged.

Answer 40

Cardiac muscle is unable to regenerated and therefore once it is damaged it is not replaced. This can lead to heart failure if it no long has sufficient contraction.

Question 41

Explain how hyperplasia and hypertrophy occur in skeletal muscle.

Answer 41

Skeletal muscle does not have mitotic capability, however new cells are produced by satellite cells. This leads to hyperplasia (increase in cell number) and hypertrophy (increase in cell size).

Question 42

How often does muscle remodelling occur?

Answer 42

This is a continuous process with myosin and actin molecules being replaced once every two weeks.

Question 43

When muscle destruction is higher than replacement what is this called?

Answer 43

Atrophy.

Question 44

What is the metabolic adaption of muscles caused by increased exercise?

Answer 44

With increased exercise the SR swells and there is an increase in mitochondria abundance. This means more ATP is produced which leads to increased T tubule density and increased contractile proteins.

Question 45

What is the difference between high resistance exercise and endurance exercise on muscles?

Answer 45

High resistance exercises lead to hypertrophy whilst endurance exercises lead to an increase in endurance due to stimulated mitochondrial synthesis and vascular changes.

Question 46

What is a side effect of disuse atrophy?

Answer 46

Disuse atrophy is where there is loss of protein and therefore muscle mass due to disuse. This has an impact on thermoregulation and can lead to hypothermia in severe cases.

Question 47

What is Denervationatrophy?

Answer 47

This is where loss of motor neuron lesions leads to weakness and muscle atrophy.

Question 48

How can muscle length be changed?

Answer 48

Sustained stretching can increase the length of muscles. Immobilisation reduces muscle length.

Question 49

What is myasthenia gravis?

Answer 49

This is autoimmune destruction of the end plates Ach receptors or loss of junctional folds at the end plate.

Question 50

What are the symptoms of myasthenia gravis?

Answer 50

Someone suffering from this will find it hard to maintain muscle contraction. They may have drooping eyelids and double vision.

Question 51

What enzyme is responsible for the breakdown of ACh?

Answer 51

Acetylcholinesterase.

Question 52

What is duchennes?

Answer 52

Duchennes is a form of muscular dystrophy, as there is a lack of the molecule dystrophin.

Question 53

What is pseudo hypertrophy?

Answer 53

This is a condition which occurs as part of duchennes. The lack of dystrophin means that muscles tear themselves apart and then this leads to necrosis as calcium enters the cell. Swelling presents as pseudo hypertrophy before fat and connective tissue replaces the muscle.

Question 54

Why can contracture occur in duchennes?

Answer 54

This can occur because there is an imbalance in muscle pairs.

Question 55

What is malignant hyperthermia?

Answer 55

It is when someone is given general anaesthesia or a similar drug and this leads to an opening in the calcium channels. This leads to an increase in calcium concentration which causes muscles to contract. This use of ATP stimulates more synthesis and their causes an excessive amount of heat.