Flashcards in ToB 14 Muscle Deck (155)
A disease of muscle tissue
Sudden spasm of groups of muscles
Outer membrane of a muscle cell
Cytoplasm of a muscle cell
Define sarcoplasmic reticulum:
Smooth endoplasmic reticulum of a muscle cell
What are the 3 types of muscle?
Which muscle type(s) appear striated?
Which muscle type(s) appear non-striated?
Which is the largest muscle cell type?
Skeletal muscle cells
What muscle cell type is approx. 50-100 um long, and 10-20 um in diameter?
What muscle cell type is approx. 20-200 um long, and 5-10 um in diameter?
What muscle cell type is approx. 1mm-20cm long, and 10-100 um in diameter?
Which muscle cell type has the largest diameter?
Which muscle cell type is branched?
How does being branched suit the function of cardiac muscle cells?
It allows every cell to be in contact with 4/5 other cells, allowing the rapid conduction of electrical impulse across, for rapid and precise muscle contraction.
Which muscle cell type has peripherally placed nuclei?
Which muscle cell type is multinucleated?
Which muscle cell type(s) are cylindrical?
Describe the shape of a smooth muscle cell:
Which muscle type(s) have a single central nucleus?
In what type of muscle do the cells run the whole length of the muscle?
What is the difference between the somatic nervous system and the autonomic nervous system?
The somatic system controls things which are under conscious control, the autonomic system controls things which are not under voluntary control.
Which muscle type is under somatic control?
Which muscle type(s) are under autonomic control?
Which muscle type generates slow/sustained or rhythmic contractions?
Which muscle type gives rapid, forceful contractions?
From which embryonic germ layer does muscle derive?
What is the name of the cell which can differentiate into a muscle cell?
How do skeletal muscle cells form?
Myoblasts line up forming a chain or primary myotubule. These develop gap junctions, and the central nuclei are peripherally displaced due to the production of actin and myosin.
What are the 3 types of skeletal muscle fibres?
1) Red (slow contracting)
3) White (fast fatigue)
With which stain can you see the different types of skeletal muscle fibres present?
No stain required to differentiate between the different skeletal muscle fibres.
Which skeletal muscle fibre type has the largest diameter?
White (fast fatigue) fibres
Which skeletal muscle fibre type has the smallest diameter?
Red (slow contracting) fibres
Which skeletal muscle fibre type has the richest vascularisation?
Red (slow contracting) fibres
Compare the amount of mitochondria present in the different skeletal muscle fibre types:
Red fibres have the most mitochondria present. Intermediate fibres have less, with white fibres having the least mitochondria present.
Which skeletal muscle fiber type fatigues the fastest?
Why do oxidative slow contracting skeletal muscle fibers appear red?
Because of the high proportion of myoglobin (red) in oxidative muscle fibres, compared to the white, fast fatigue fibers.
Which skeletal muscle fiber type is richest in oxidative enzymes?
Red (slow contracting)
Which skeletal muscle fiber type has the least amount of oxidative enzymes present?
White (fast fatigue)
Which skeletal muscle fiber type has the most myosin ATPase activity?
White (fast fatigue)
Why do white skeletal muscle fibers require higher myosin ATPase activity than red fibres?
White fibers give faster, stronger contractions. The strength and speed of a contraction depends on the speed that cross-bridge cycling can occur. More ATPase activity means the cycling can occur faster.
Which type of skeletal muscle fiber contains the most myoglobin?
Red oxidative fibers
Why do red fibers contain more myoglobin than white skeletal muscle fibers?
Red fibers are oxidative, so requires myoglobin, which is an oxygen-binding protein, which provides a store of oxygen within the fiber.
Name the oxygen binding protein found in high quantities in oxidative skeletal muscle fibers:
Fast glycolytic skeletal muscle fibers have a fast contraction velocity due to high activity of ?
Fast glycolytic skeletal muscle fibers produce more tension in a twitch because they have more ?
What type of skeletal muscle fiber is innervated by the smallest somatic efferent neurons?
Slow, oxidative (red)
Which size neurons are the easiest to excite?
Which skeletal muscle fibre type is recruited first when causing a muscle contraction?
Slow, oxidative (red)
Slow oxidative fibers are resistant to ?
Through recruitment, an increase in muscle force is achieved by increased activation of ?
Which type of skeletal muscle fiber has the most neuromuscular junctions present?
White (fast fatigue)
What is the function of the extraocular muscles?
Control the movement of the eye
What type of skeletal muscle fibers are found in the postural muscles of the back?
Red oxidative fibers
What type of skeletal muscles fiber are the extraocular fibers?
White fast fatigue fibers
How would the skeletal muscle fibers differ in the breast muscles of migrating birds vs domestic hen?
Migrating birds = red oxidative fibers
Domestic hen = white fast fatigue fibers
What is a fascicle?
Group of muscle fibers/cells, wrapped by perimysium
What membrane covers each muscle fiber/cell individually?
What membrane encases a fascicle?
What is the epimysium?
The membrane/sheath which encases the entire muscle (groups of muscle facicles)
What connects muscle to bone?
Are all skeletal muscles attached to bone?
No, but most are
How is the tongue so mobile?
The extrinsic muscles of the tongue have multidirectional orientation, and interdigitate with connective tissue which has high plasticity and strength.
What is carried to and from the muscle via the perimysium?
What letter is used to name the dark band of a striated muscle filament?
A (anisotropic) band
What letter is used to name the light band of a striated muscle filament?
I (isotropic) band
Name the dark band of a striated muscle filament, and what it contains:
A(nisotropic) band, containing myosin and interdigitating actin fibers
Name the light band of a striated muscle filament, and what it contains:
I(sotropic) band, containing only actin
What is a sarcomere?
A contractile unit of a myofibril in striated muscle, consisting of a dark band and the nearer half of each adjacent pale band (between 2 adjacent z lines)
What is the H zone of a striated myofibril?
The area which contains only myosin. It is a lighter band present in the center of the A band.
What disc lies in between sarcomeres?
Name the dark line in the middle of the A band:
Where are the actin filaments anchored, within a striated myofibril?
What does MHAZI mean?
M line lies within the
H band, which is within the
A band, which lies between the
Z lines, which are present in the
What happens to the length of the A, H and I bands of striated muscle with contraction?
A band stays the same, H and I band shortens as the actin interdigitates with the myosin
What types of filaments are present in a cross section of a myofilament, cut through the H band?
Myosin filaments only
What types of filaments are present in a cross section of a myofilament, cut through the A band during contraction of the muscle?
Actin and myosin filaments, interdigitating
How does the presence of different filaments in the A band change with contracted vs stretched muscle?
During contraction both actin and myosin filaments are present, as the muscle shortens so the filaments overlap.
When the muscle is stretched, z lines move apart, and there is less/no overlap of actin and myosin, so only myosin will be present in the A band.
What 3 molecules make up the troponin complex?
What molecules complex to form the thin filaments in striated muscle?
Which Troponin forms are most useful assays as a clinical marker for cardiac ischemia?
What is the assay of choice, used as a marker for cardiac ischemia?
Within what time frame must troponin levels be measured to give useful marker for cardiac ischemia?
Within what time frame is troponin released from ischaemic cardiac muscle?
Why is a troponin assay so reliable as a marker for cardiac ischemia?
- Serum troponin is very constant, so the smallest changes are indicative of cardiac ischaemia
- Ischaemic cardiac muscle will always release troponin
- Relatively long half life (stays in blood for ~20hrs)
An extremely high level of troponin in the blood is indicative of what?
Cannot be used to estimate degree of damage, as not proportional.
List the structural features of a myosin II molecule:
- 2 globular heads of heavy chain
- Neck/hinge region of heavy chain
- Tail-like structure of heavy chains coiled (alpha helix)
Which form of myosin molecules generate force in skeletal muscle contractions?
Myosin II molecules
Which component of the thin filament forms a bistranded helix?
Why can't cross-bridging occur in the center of a sarcomere?
There are no myosin heads protruding from the thick filaments in the center of the sarcomere.
Which type of filament contains ATPase activity?
Thick filament (myosin)
How many myosin binding sites does each actin molecule have?
Where does Ca2+ bind to initiate muscle contraction?
TnC of troponin complex
How does the presence of Ca2+ allow cross-bridging to occur?
- Ca2+ binds to TnC
- Conformational change
- Troponin complex is bound to Tropomyosin, and the conformation change causes Tropomyosin to move away from the myosin binding sites on actin
Which part of the thin filament blocks the myosin binding sites on actin?
The presence of which ion is required for muscle contraction?
Name the 5 states during the cross-bridge cycle:
1) Attached state
2) Released state
3) Cocked state
4) Cross-bridge state
5) Power-stroke state
What causes the cross-bridge cycle to move from the attached state to the released state?
ATP binding to the myosin head = breaks cross-bridge
What causes the cross-bridge cycle to move from the released state to the cocked state?
ATP hydrolysis (myosin head has ATPase activity)
What causes the cross-bridge cycle to move from the cocked state to the cross-bridge state?
High affinity of myosin for actin at binding site
What causes the cross-bridge cycle to move from the cross-bridge state to the power-stroke state?
Power-stroke requires the conformational change of the myosin head rotation, caused by the release of phosphate
What causes the cross-bridge cycle to move from the power-stroke state to the attached state?
Release of ADP
Why does rigor mortis occur?
Once body has died, ATP will not be synthesised anymore. Muscle requires ATP to break the cross-bridge and enter the relaxed state, so after death muscle will be contracted.
What breaks the cross-bridge between actin and myosin during muscle contraction?
ATP binding to myosin head
Approximately how far does the myosin head advance between the released state and the cocked state?
The triad of sarcoplasmic reticulum and t-tubule within skeletal muscle runs over what structural point of the myofilaments?
Where the A and I band join
What neurotransmitter is contained within the vesicles of motor neurones innervating skeletal muscle?
Define neuromuscular junction:
The synapse between a motor neurone and a skeletal muscle.
Which neurotransmitter is present in a neuromuscular junction?
What causes the initial depolarisation of the sarcolemma?
Uptake of Acetylcholine from neuromuscular junction,
causes voltage-gated Na+ channels to open, so Na+ movement into cell causes depolarisation of sarcolemma
Invaginations of the sarcolemma running deep through the skeletal muscle, allowing contraction to be initiated quickly throughout the whole myofibril.
Why can muscle not contract at low intracellular [Ca2+]?
The troponin and tropomyosin complex blocks the myosin binding site on actin during low [Ca2+].
Which 2 structures are key to the regulation of intracellular [Ca2+]?
2) Sarcoplasmic reticulum
Why do muscle cells have a sarcoplasmic reticulum?
It is a store of Ca2+, which can be released very close to the myofibrils
What type of fluid are t-tubules filled with?
Extracellular fluid, as they are invaginations of the sarcolemma
Why do t-tubules project deep into a skeletal muscle cell?
They allow the action potential to be propagated throughout the muscle cell, causing regular contractions
What causes the opening of gated Ca2+ channels in the SR of skeletal muscle?
The AP generated at the neuromuscular junction is propagated down t-tubules, causing voltage-sensor proteins in the t-tubule to undergo conformational change. These proteins are linked to the gated-Ca2+ channels of the SR, and cause them to open (after conformational change).
A triad of sarcoplasmic reticulum and t-tubules is present in what type of muscle?
A diad of sarcoplasmic reticulum and t-tubules is present in what type of muscle?
The t-tubules of cardiac muscle lie in register with what part of a myofilament?
What type of intercellular junctions are present in the cardiac intercalated discs?
Define gap junction:
Junctions between cells which allow the transfer of small molecules/ions, and electrical coupling. They directly connect the cytoplasm of the 2 cells.
Adhesion sites which provide strong intercellular adhesion, by anchoring the intermediate filaments of the cells together.
What junctions are required between cardiac myocytes to allow electrical coupling?
What junctions are required between cardiac myocytes to anchor them together?
Desmosomes or adherens junctions
Where are cardiac action potentials generated from?
Sinoatrial (SA) node
What is the name of the fibres which carry the cardiac AP from the atrioventricular node to the ventricles?
What is the name of the lining of the interior of the heart?
How are purkinje fibre cells adapted for rapid electrical conduction?
- Large cells
- Many gap junctions
- Contain abundant glycogen
Do purkinje fibre cells contain more or less myofilaments compared to cardiac myocytes?
Compare the speed of conduction between purkinje fiber cells, and cardiac muscle fibres:
Purkinje fiber cells conduct electrical impulses MUCH FASTER ~ 3-4m/s compared to 0.5m/s in cardiac muscle fibers
Where are the t-tubules located in smooth muscle cells?
Smooth muscle doesn't have t-tubules
Compare the stimuli required for contraction between skeletal and smooth muscle:
Skeletal muscle requires Acetylcholine binding at post-synaptic membrane of sarcolemma
Smooth muscle responds to: nerves/hormones/drugs etc.
Describe the shape and function of myoepithelial cells:
Stellate smooth muscle cells which form a basketwork around the secretory units of some exocrine glands, to aid secretion.
Name the 2 types of modified smooth muscle cells which can occur singly:
1) Myoepithelial cells
Where are myofibroblasts found?
At sites of wound healing
What type of modified smooth muscle cells are found at sites of wound healing?
What type of muscle cell is a myofibroblast?
Modified smooth muscle cell
What type of muscle cell is a myoepithelial cell?
Modified smooth muscle cell
What is the function of myofibroblasts?
Produce collagenous matrix and to contract, to aid wound healing
What type of muscle is present in the wall of the small intestine?
From what structure are neurotransmitters released to innervate smooth muscle?
Varicosities of nerve fibers
Why do smooth muscle cells contract in a twisting way?
The intermediate filaments (of actin and myosin) are organised diagonally so that they spiral down the smooth muscle cell. When these contract, the cell shortens and spirals.
What anchor the intermediate filaments to the sarcolemma?
What are caveoli, and where are they found?
Small invaginations of the sarcolemma, increasing the surface area of smooth muscle cells
What are muscle satellite cells?
Cells which can differentiate into skeletal muscle cells, important for growth and repair of the muscle cells.
How can skeletal muscle repair itself after injury?
Stimulate activation and proliferation of satellite cells, which can either fuse and repair the damaged myofiber, or create a new myofiber.
How can cardiac muscle repair itself after injury?
Cardiac muscle cannot repair after injury, instead fibroblasts lay down scar tissue.
What type of muscle is incapable of repair/regeneration?
What type of muscle cell can undergo mitosis?
Smooth muscle cells
What happens to cardiac muscle after injury?
Fibroblasts lay down scar tissue