Muscle

Question 1

What shape is smooth muscle?

Answer 1

Spindle-shaped (thinner at the ends and fatter in the middle)

Question 2

List the 3 skeletal muscle types.

Answer 2

Red
White
Intermediate

Question 3

Do red or white fibres have a wider diameter in skeletal muscle?

Answer 3

White fibres

Question 4

How many subunits does myoglobin have?

Answer 4

1 subunit

Question 5

What type(s) of muscle is myoglobin present in?

Answer 5

Skeletal muscle
Cardiac muscle
(Not smooth muscle)

Question 6

What enzymes are apparent in white muscle fibres? How does this compare to red muscle fibres?

Answer 6

In red muscle fibres there are high amounts oxidative enzymesof but a low amount of ATPases. The opposite is true in white muscle fibres; there are low amounts of oxidative enzymes, but high amounts of ATPases

Question 7

Describe the vascularisation, myoglobin count, mitochondria count, and rate of contraction in red muscle fibres and white muscle fibres.

Answer 7

Red muscle fibres are highly vascularised, have high amounts of myoglobin, high amounts of mitochondria, and contract at a much slower/weaker rate.
Conversely, white muscle fibres are poorly vascularised, have low amounts of myoglobin, low amounts of mitochondria, and contract at a much higher/stronger rate.

Question 8

Do white muscle fibres fatigue more slowly or quickly in comparison to red muscle fibres?

Answer 8

White muscle fibres fatigue more quickly than red muscle fibres

Question 9

What is the perimysium?

Answer 9

Connective tissue that surrounds fascicles of muscle fibres, that contain nerves and blood vessels

Question 10

Which subunit of troponin does Ca2+ bind?

Answer 10

TnC

Question 11

What is the sarcolemma?

Answer 11

The plasma membrane of a muscle cell

Question 12

What is the A band? What is the I band?

Answer 12

The A band is the area composed of the length of the myosin filament - the I band is the area where actin filament is not overlapped by any myosin filament

Question 13

When does disuse atrophy occur?

Answer 13

When a muscle is used less than previously, causing it to atrophy (decrease in size)

Question 14

What neurotransmitter is used at the neuromuscular junction? On what surface do they bind receptors?

Answer 14

Acetylcholine, on the surface of the sarcolemma

Question 15

Where abouts are nuclei positioned in cardiac muscle fibres? How does this differ in skeletal muscle fibres?

Answer 15

In cardiac muscle cells nuclei are positioned centrally - this is different to skeletal muscle cells where they are positioned peripherally

Question 16

What promotes the dissociation of O2 from haemoglobin/myoglobin?

Answer 16

Respiration produces carbonic acid (or lactic acid in anaerobic respiration) which decreases the pH of the surrounding tissue - these acidic conditions promote dissociation of O2

Question 17

What is the difference between hypertrophy and hyperplasia?

Answer 17

Hypertrophy is the enlargement of a singular cell, while hyperplasia is the multiplication of a cell

Question 18

Define myalgia, myasthenia, and myoclonus.

Answer 18

Myalgia - muscle pain
Myasthenia - muscle weakness
Myoclonus - sudden spasm of the muscle

Question 19

What is the function of ANP and BNP?

Answer 19

They are released by the heart to reduce blood volume in order to reduce high blood pressure putting considerable strain on the heart

Question 20

What is a sarcomere?

Answer 20

The basic unit of striated muscle tissue

Question 21

What is the difference between cardiac and skeletal muscle fibres?

Answer 21

Myofibrils are not present - instead, myofilaments (actin and myosin) form huge masses within the cardiac fibre - perimysium does not surround the myofilaments to form myofibrils

Question 22

What is the sarcolemma, sarcoplasm, and the sarcoplasmic reticulum?

Answer 22

The plasma membrane, the cytoplasm, and the endoplasmic reticulum found in muscle fibres

Question 23

Other than colour, how do red and white muscle fibres differ on a histology slide?

Answer 23

Red muscle fibres are narrower, while white muscle fibres are wider

Question 24

Do red fibres contract quickly or slowly? How does this mean they utilise energy?

Answer 24

Red fibres contract slowly, and as such are designed to utilise energy for longer

Question 25

Where are nuclei located in skeletal muscle?

Answer 25

At the periphery

Question 26

Which structure is composed of the myosin and actin filaments?

Answer 26

A myofibrils

Question 27

What does muscle hypertrophy describe?

Answer 27

An increase in the diameter of a muscle fibre, and increased metabolic changes in the cell, such as more mitochondria and greater blood flow

Question 28

In a muscle fibre, where do mitochondria lie?

Answer 28

Mitochondria lie in between the myofibrils

Question 29

What is a fascicle composed of?

Answer 29

A fascicle is composed of muscle fibres, which are composed of myofibrils, which are composed of myofilaments (actin and myosin)

Question 30

What can be used as a marker for cardiac ischaemia?

Answer 30

Troponin

Question 31

Where is creatine kinase seen?

Answer 31

There are elevated levels in the blood she heart muscle is damaged

Question 32

Describe the structure of myosin.

Answer 32

A myosin filament contains many myosin molecules, which have a rod-like tail from which 2 heads protrude - a myosin filament contains many myosin molecules

Question 33

What structure does an actin filament form?

Answer 33

A helix

Question 34

In which zone are the actin filaments devoid of heads?

Answer 34

H band

Question 35

What structure reinforces the actin helix? What other molecule is attached to this molecule?

Answer 35

Tropomyosin coils around the actin helix, reinforcing it - a troponin complex is attached to each tropomyosin molecule

Question 36

What happens to tropomyosin when Ca2+ levels rise within the muscle fibre?

Answer 36

Ca2+ binds the TnC component of troponin, which induces a conformational change in tropomyosin, which removes it from the myosin binding site on the actin helix - this then allows the myosin head to bind actin and cause isle contraction

Question 37

What is rigor conformation?

Answer 37

This denotes that a lack of ATP causes the myosin head to remain fixed to the actin molecule - this is seen in rigor mortis

Question 38

How does ATP act on myosin? What does hydrolysis of the ATP molecule cause?

Answer 38

It causes it to uncouple from the actin filament - hydrolysis shifts the myosin back into its original conformation where it binds the actin filament again

Question 39

How does an action potential in skeletal muscles cause Ca2+ release?

Answer 39

Acetylcholine binds nicotinic acetylcholine receptors on the sarcolemma of a muscle fibre - this instigates an action potential, via Na+ entry into the muscle fibre - this action potential travels along the sarcolemma and down T-tubules, where it changes their conformation at terminal cisternae - these then release Ca2+ from the sarcoplasmic reticulum

Question 40

What is a terminal cisternae?

Answer 40

Enlarged areas of the sarcoplasmic reticulum that surround the T-tubules - these regions secrete Ca2+ into the sarcoplasm, eliciting muscle contraction

Question 41

Where are nuclei positioned in cardiac muscle fibres? How many are there per fibre?

Answer 41

Nuclei are positioned centrally in cardiac muscle fibres, and there are usually 1-2 nuclei per muscle fibre

Question 42

What is endomysium? What is perimysium?

Answer 42

The endomysium is a layer of connective tissue that surrounds each muscle fibre/cell - the perimysium is the layer of connective tissue that surrounds each muscle fascicle (which itself is composed of several muscle fibres)

Question 43

Which muscle type are intercalated discs found? What do they replace, and what is their function?

Answer 43

Intercalated discs are found in cardiac muscle - they replace Z bands, and have gap junctions for electrical coupling, and adherens-type junctions to anchor the actin filaments

Question 44

Which muscle tissue is associated with diads? Which muscle tissue is associated with triads?

Answer 44

Cardiac muscle is associated with diads - skeletal muscle is associated with triads

Question 45

Where is ANP synthesised, stored, and released?

Answer 45

Atrial myocytes in response to distension

Question 46

How do ANP and BNP reduce blood pressure?

Answer 46

They increase the kidneys glomerular filtration rate, lowering the blood volume, and inhibit renin production from the kidney, inhibiting the cascade that would lead to angiotensin II - this causes vasodilation which contributes to the lowering of blood pressure

Question 47

Do smooth muscle fibres contain T-tubules?

Answer 47

No

Question 48

List 2 types of modified smooth muscle cells, and what their function is.

Answer 48

- myoepithelial cells - surround glands and assist contraction for secretion - myofibroblasts - prominent in wound contraction at sites of wound healing