6.1 - Muscles (Structure) Flashcards
definition: myalgia
muscle pain
definition: myalgia
muscle pain
definition: myasthenia
weakness of the muscle
definition: myocardium
muscular component of the heart
definition: myopathy
any disease of the muscles
definition: myoclonus
a sudden spasm of the muscles
striated and non striated muscle
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
myoglobin
- 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)
why would myoglobin be released into the bloodstream and what are the consequences of this
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
what is myoglobinuria
- 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
definition: sarcolemma
outer membrane of muscle cell
definition: sarcoplasm
cytoplasm of muscle cell
definition: sarcosome
the mitochondrion of muscle cell
definition: sarcomere
contraction unit in striated muscle
definition: sarcoplasmic reticulum
aka sarcoplasmic endoplasmic reticulum
is the smooth endoplasmic reticulum of a muscle cell
where is all calcium sequestred
in the tubules of the sarcoplasmic reticulum
muscle fibre structure
- 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
muscles have point of origin and insertion
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’
skeletal muscle structure
- 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
what is the difference between endomysium, perimysium and epimysium
- 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.
different bands in the sarcomere
- 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
rough structure of sarcomere
- 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.
muscle contraction speeds
- 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
type 1 vs type 2A vs type 2B muscle fibre types
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
what does continued muscle contraction depend on
Ca2+ ions and amounts of ATP
cardiac muscle structure
- 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
what are intercalated discs
- 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
what is ANP and BNP
- 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
left ventricular hypertrophy = BNP
mitral valve disease = BNP
congestive heart faliure = ANP
hypertrophy and hyperplasia
tissues, including muscle, which increase in size, may do so by…
- hypertrophy = enlargement of individual cells
- hyperplasia = multiplication of their cells
hypertrophy and atrophy of heart
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
electrical transmission in heart
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
smooth muscle cells
- 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)
fusiform = come to tapered ends
smooth muscle cells
- 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)
fusiform = come to tapered ends
smooth muscle distribution
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
mature muscle repair
skeletal vs smooth vs cardiac
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
