6.1 - Muscles (Structure)

Question 1

definition: myalgia

Answer 1

muscle pain

Question 2

definition: myalgia

Answer 2

muscle pain

Question 3

definition: myasthenia

Answer 3

weakness of the muscle

Question 4

definition: myocardium

Answer 4

muscular component of the heart

Question 5

definition: myopathy

Answer 5

any disease of the muscles

Question 6

definition: myoclonus

Answer 6

a sudden spasm of the muscles

Question 7

striated and non striated muscle

Answer 7

striated
skeletal
* myoglobin present
* voluntary control
* direct nerve-muscle communication

cardiac muscle
* myoglobin present
* involuntary control
* indirect nerve-muscle communication

non-striated muscle
smooth
* myoglobin absent
* involuntary control
* indirect nerve-muscle communication

Question 8

myoglobin

Answer 8

• only found in striated muscle
• serves as a carrier and store for oxygen in muscle cells
• red protein that is structurally similar to single subunit of haemoglobin
• myoglobin has much greater affinity for oxygen, particularly at a lower pH
• haemoglobin gives up O2 to myoglobin, especially at lower pH
• when striated muscle dies or is damaged, myoglobin is released into the bloodstream (more details on next slide)

Question 9

why would myoglobin be released into the bloodstream and what are the consequences of this

Answer 9

myoglobin released into bloodstream when…
* when striated muscle dies (muscle necrosis)
* when striated muscle is damaged (rhabdomyolysis)
* when this happens, this is called myoglobinaemia

consequences - can cause renal damage
kidneys remove myoglobin from blood into urine (myoglobinuria)… presents as tea coloured urine

Question 10

what is myoglobinuria

Answer 10

• myoglobin released into blood due to muscle dying or damaged (prev card)
• can cause kidney damage
• myoglobin removed from blood by kidneys into urine
• presents as tea-coloured urine

Question 11

definition: sarcolemma

Answer 11

outer membrane of muscle cell

Question 12

definition: sarcoplasm

Answer 12

cytoplasm of muscle cell

Question 13

definition: sarcosome

Answer 13

the mitochondrion of muscle cell

Question 14

definition: sarcomere

Answer 14

contraction unit in striated muscle

Question 15

definition: sarcoplasmic reticulum

Answer 15

aka sarcoplasmic endoplasmic reticulum
is the smooth endoplasmic reticulum of a muscle cell

Question 16

where is all calcium sequestred

Answer 16

in the tubules of the sarcoplasmic reticulum

Question 17

muscle fibre structure

Answer 17

• a striated muscle cell is called a muscle fibre
• each cell (fibre) contains many myofibrils aggregated together
• each cell is surrounded by endomysium (connective tissue)
• have many nuclei at edges
• the myofibril is made up many actin (thin) and myosin (thick) filaments
• myofibril has I bands (isotropic) which are light, A bands (anisotropic) which are dark
• also has Z lines between each sarcomere
• there are also H zones, and in the middle of this is the M line

Question 18

muscles have point of origin and insertion

Answer 18

point of origin
- muscle arises from here
- typically proximal (closer to trunk)
- doesn’t move, stays fixed when muscle contracts
- tension created here

point of insertion
- distal (further from trunk)
- does move
- movement created here

however, sometimes this isn’t the case… depending on which end is fixed, muscles can act in both directions… so some might prefer to use ‘proximal and distal attachments’

Question 19

skeletal muscle structure

Answer 19

• single muscle fibre (cell) has many myofibrils and nuclei, and is surrounded by connective tissue endomysium
• many muscle fibres aggregated together to form fasicle which is surrounded by perimysium (bit thicker as it has collagen I)
• many fasicles aggregated together to form muscle, with blood vessels and lymphatics. The muscle as a whole is surrounded by epimysium (dense connective tissue, aka fascia)
• function of muscle is to contract
• has a point of origin and insertion
• if muscle crosses a joint, movement occurs
• movement is dependent on direction of muscle fibre contraction

Question 20

what is the difference between endomysium, perimysium and epimysium

Answer 20

• Muscle fibres are wrapped in endomysium - many myofibrils and nuclei inside
• Multiple muscle fibres are collected and wrapped in perimysium (thicker due to collagen I) and become a fascicle.
• Multiple fascicles are collected along with blood vessels, and wrapped in epimysium (dense connective tissue aka fascia) becoming the muscle itself.

Question 21

different bands in the sarcomere

Answer 21

• M line is the centre of the H zone.
• H zone is the portion of the A band not to have actin present (as well as the myosin).
• A band is any portion of the sarcomere with myosin in it.
• Z line is the centre of the I band.
• I band is the portion of the sarcomere with only actin present.

distance between two Z lines = sarcomere

Question 22

rough structure of sarcomere

Answer 22

• between two Z-lines = sarcomere
• myosin filaments are thicker and have myosin heads that bind to the actin filaments
• actin filaments are thinner and have tropomyosin stabilising them
• the tropomyosin covers the myosin binding sites
• dystrophin attaches actin to sarcloemma

note: in smooth muscle does NOT contain troponin, but contains a protein in its place called calmodulin. This protein performs the same function as troponin, and is still moved out of the way by calcium, like troponin is.

Question 23

muscle contraction speeds

Answer 23

• muscle fibres can be slow, fast and intermediate
• each fasicle has at least one of each
• can see colours by histochemistry
• pale are fast fibres, as they don’t have a lot of ATP
• intermediate aka type 2A and classified as ‘fast twitch’
• fast twitch are better for short term energy, where they use energy very quickly, before intermediate take over

ie fast twitch are better for sprint, and slow twitch are better for endurance + long distance running

Question 24

type 1 vs type 2A vs type 2B muscle fibre types

Answer 24

type 1 - slow oxidative
- rich capillary supply with large vessels
- aerobic
- high myoglobin levels
- many mitochondria + cytochromes
- dark (red)
- fatigue resistance: endurance
- fatty acids as fuel
- lots of ATP/CO2

type 2A - fast oxidative glyolytic
- rich capillary supply
- aerobic
- high myoglobin levels
- intermediate mitochondria + many cytochromes
- red-pink
- moderate fatigue resistance: assist type 1 + 2B activities
- fatty acids and glycogen as fuel
- initially lots of CO2, then lots of lactate

type 2B - fast glycolytic
- poor capillary supply
- anaerobic
- low myoglobin levels
- few mitochondria + cytochromes
- white (pale)
- rapidly fatigue but quick response for strength and anaerobic activities
- glycogen as fuel
- lots of lactate, little ATP

Question 25

what does continued muscle contraction depend on

Answer 25

Ca2+ ions and amounts of ATP

Question 26

cardiac muscle structure

Answer 26

- striations - centrally positioned nuclei (one or two per cell) - intercalated discs aka gap junctions (for electrical and mechanical coupling with adjacent cells) are important for communication and define cell borders - branching - connected to many different cells at once, allows for electrical stimulation of all muscle at once

Question 27

what are intercalated discs

Answer 27

- present in cardiac muscle - characteristic when looking at microscope image - basically a specialised gap junction between neighbouring cells - allows the cells to have synchronized contractions - important for communication - defines cell borders

Question 28

what is ANP and BNP

Answer 28

* peptide hormones made by the heart * **atria natriuretic peptide (ANP)** is released by atria * **brain type natriuretic peptide (BNP)** is released by ventricles * release of peptides stimulated by atrial and ventricular distension * usually due to heart faliure * tries to reduce blood pressure by decreasing blood volume (eg by diuresis) and vasodilation ## Footnote left ventricular hypertrophy = BNP mitral valve disease = BNP congestive heart faliure = ANP

Question 29

hypertrophy and hyperplasia

Answer 29

*tissues, including muscle, which increase in size, may do so by...* - **hypertrophy** = enlargement of individual cells - **hyperplasia** = multiplication of their cells

Question 30

hypertrophy and atrophy of heart

Answer 30

**atrophy** is where heart is smaller than normal (smaller cardiomyocytes) **hypertrophy** is where heart is bigger than normal heart. Heart does this by enlargment of individual cells (hypertrophy), rather than by hyperplasia.... adult hearts cannot enlarge by hyperplasia as the ability has been lost after growing from childhood

Question 31

electrical transmission in heart

Answer 31

**done by purkinje fibres** * these are large, modified cardiac muscle cells * they have abundant glycogen * they have sparse myofibrils * they have extensive gap junction sites: need this for passing electrical signals quickly... allows for rapid conduction * the purkinje fibres conduct action potentials much more rapidly compared to cardiac muscle fibres * this rapid conduction enables the ventricles to contract in a synchronous manner

Question 32

smooth muscle cells

Answer 32

* spindle shaped (fusiform) with a single central large nucleus * not striated, no sarcomeres, no T-tubules * capable of being stretched * contraction relies on actin-myosin interactions * contraction is slower, more sustained and requires less ATP * may remain contracted for hours or days * respond to numerous stimuli (eg nerve signals, hormones, drugs and blood gases * form sheets, bundles or layers containing many cells * each cell has numerous pinocytic caveolae (small cave-like invaginations) ## Footnote fusiform = come to tapered ends

Question 32

smooth muscle cells

Answer 32

* spindle shaped (fusiform) with a single central large nucleus * not striated, no sarcomeres, no T-tubules * capable of being stretched * contraction relies on actin-myosin interactions * contraction is slower, more sustained and requires less ATP * may remain contracted for hours or days * respond to numerous stimuli (eg nerve signals, hormones, drugs and blood gases * form sheets, bundles or layers containing many cells * each cell has numerous pinocytic caveolae (small cave-like invaginations) ## Footnote fusiform = come to tapered ends

Question 33

smooth muscle distribution

Answer 33

**often form contractile walls of passageways or cavities** * role is to modify volume * eg vascular structures * eg in gut, resp tract and mucosal membranes **involuntary muscle can develop 'mind of its own'... can lead to disorders such as...** - high blood pressure eg primary hypertension - painful menstruation eg dysmenorrhea - lung disease eg asthma - abnormal gut motility eg IBS - incontenence

Question 34

mature muscle repair | skeletal vs smooth vs cardiac

Answer 34

**skeletal muscle** - skeletal muscle cells cannot divide - regenerate by mitotic activity of satellite cells (so hyperplasia follows muscle injury) - satellite cells can also fuse with existing muscle cells to increase mass (skeletal muscle hypertrophy) **cardiac muscle** - incapable of regeneration - following damage, fibroblasts invade, divide and lay down scar tissue - makes remaining muscle less flexible (nto good) **smooth muscle** - these myocytes retain their mitotic activity and can form new smooth muscle cells - particularly useful for cells like smooth muscle cells in uterus, because these need to be able to multiply during pregnancy