1.16 Muscle tissues Flashcards
Briefly describe what are muscle tissues and how movements are initiated.
- One of the four adult tissue types.
- All composed of elongated cells called myofibres or muscle fibres (muscle cells).
- In all types of muscle, energy from hydrolysis of ATP is transferred into mechanical energy that results in movement.
- Stimulated to contract(shortening and lengthening) by the nervous system involving depolarisation of the muscle cell’s plasma membrane (“excitable cells” – like nerve cells).
What are the different names for muscle cells?
Muscle cells = Muscle Fibres = Myofibres = Myocytes
Muscle classification
- 3 types: smooth, skeletal, cardiac
- microscopic apearance (internal structural appearance)
> striated= stripy (skeletal and cardiac
> smooth - innervation= nerve supply
-> voluntary: conscious control, e.g. skeletal muscles
-> involuntary: don’t have conscious control over (smooth and cardiac muscles, e.g. respiration, digestion)
Where do we find the different muscles types in the human body?
- Skeletal muscle–
any muscle which gives us conscious control over movement; e.g. muscles of locomotion(move arm and leg), breathing, talking, swallowing(diaphragm, intercosal muscles), control of urination and defecation, etc… - Cardiac Muscle-
wall of the heart - Smooth Muscle- blood vessels, any viscera (internal organs) with a lumen; e.g. much of the gastrointestinal, urinary, respiratory, reproductive tracts.
What are the three types of muscles?
skeletal, cardiac and smooth.
what do muscle tissues compose of?
elongated cells called myofibres (myo=muscle, fibre= long thin things)
What is depolarisation? (hint: happens in muscle tissues)
shift in electric charge distribution, resulting in less negative charge inside the cell compared to the outside
Describe the relationship between connective tissues and muscle tissues.
- Connective tissue is an essential part of muscle tissue.
- While the muscle cells generate force, that force needs CT to transmit it:
~ To bones to move joints (skeletal muscle)
~ To other muscle cells and CT to act together as one tissue
(cardiac and smooth muscle)
*pull on bones or other cells for contraction and lengthening(need to be able to connect to those stuff) - It is also through the CT that muscle tissue gets its vascular
(blood) supply and innervation (nerves).
Structure of skeletal muscle cells
- regular organisation of contractile proteis and cytoskeleton
- whole muscle cell shrinks in size when contracts
- They can be very long cells (up to 30cm).
Describe the parts of a skeletal muscle cell (its organisation) and how CT plays a major role in it.
Connective tissue is an essential part of skeletal muscle:
* Epimysium (dense irregular CT) surrounds the whole muscle proper (all the fascicles; e.g. biceps brachii)
* Perimysium (dense irregular CT) surrounds a group of muscle cells (called a “fascicle”)
* Endomysium (loose CT)
surrounds each individual muscle cell
Describe myofibrils and where they are found.
- The mature skeletal muscle cell contains densely packed, rod
-like elements which comprise ~80% of the cell volume = myofibrils - Myofibrils are made up of contractile proteins: actin and myosin, myosin interacts with actin to bring about contraction
- Myofibrils contain the functional unit within striated muscle = sarcomere
- Sarcomeres contain myofilaments– thick and thin filaments whose regular arrangement produce the striations: repeating series of dark A bands and light I bands
What’s special about the nuclei of skeletal myocytes?
- They are multinucleated (= many nuclei; several cells have fused to form very large cells).
- The nuclei are positioned on the periphery of the cells unlike cardiac and smooth muscles
What allows skeletal muscles to have voluntary movements?
It is innervated by the somatic nervous system
muscle tissue diagram fill in
photos
Explain the organisation of skeletal muscles.
Muscles, wrapped up by epimysium, are made up of many fascicles, wrapped up by perimysium, which are a bundle of muscle cells, wrapped up by endomysium, which are made up of myofibrils.
what classification of tissue is the tendon?
Dense regular connective tissue
Describe the striations of a skeletal muscle cell.
– repeating series of dark A bands and light I bands
Explain the structure of cardiac muscle tissues.
- Individual cells with one (sometimes two: bi-nucleate) centrally placed nucleus
- Cells branch so they contact several other cells
- Striated (organised myofilaments in myofibrils like skeletal muscle)
Cell junctions contain adhering and communicating junctions
(intercalated discs) – not found in skeletal muscle
Innervated by the autonomic nervous system (+ self contracting
pacemaker cells)
Describe organelles: function in cardiac muscle tissues.
- around 50% of cytoplasm is made up of mitochondria
- many mitochondria to power (lots of atp) to continue contraction
- good blood supply required- lots of capillaries (highly vascular)
- bound by endomysium above myofibrils
- endomysium surrounds each cardiac muscle cell
- has loose CT
- myofibrils with striations
Describe the cell junctions in a cardiac muscle tissue.
- Cell junctions contain adhering and communicating junctions
(intercalated discs) – not found in skeletal muscle or smooth muscle - adhering junctions prevents separation of cells, gap junctions allow ion communication (only need innervation of a few for them to flow through cytoplasm of cells
Why do heart transplant patients sometimes feel that they have a fast heart rate?
Because the autonomic pacemaker cells aren’t connected yet (takes time for nerve to grow back (isn’t connected yet to slow it down
Describe the cell branching of cardiac muscle tissues.
- has unique cell branching: has branching points and junction points to enable synchronized contraction and efficient pumping of blood throughout the body
- Cells branch so they contact several other cells
What muscle tissues do striated muscle cells include?
includes both skeletal and cardiac
Describe, in depth, the different parts of the myofibril structure.
- i band= only thin filaments
- go from z line towards the m line (thick)
- A sarcomere runs from Z disc to a Z disc- everything in between is the sarcomere-> this is the muscle’s contractile unit. * A Z disc bisects an I band – a pale region containing only thin filaments (with no overlap with thick filaments)
- In the middle of the sarcomere is the M-line – thick filaments are attached here
- The A band represents the region of the sarcomere where thick filaments exist
- In the middle of the A band is the H-zone – this is a region of thick filaments with no overlap with thin filaments
Describe the structure of thick filaments. (what they are composed of, structure,
- Composed of myosin
- Tails contain two interwoven chains
- Heads contain two smaller chains that act as cross bridges
during contraction-> contain binding sites for actin in round regions (thin filament) - contain binding sites for ATP
Describe the structure of thin filaments. (what they are composed of, structure, what it does)
- Twisted double strand of fibrous protein-> actin
- Smaller amounts of two regulatory proteins— tropomyosin and troponin— are also part of the thin filament.
- Tropomyosin and troponin are a regulatory complex that is bound to actin (particularly the myosin-binding sites)
- Actin contains active binding sites for myosin head attachment
during contraction-> namely cross-bridge cycling
Explain what sarcoplasmic reticulum is.
- sarco= muscle (individual cells prefix
- smooth ER of striated muscle cells
- Network of specialized smooth endoplasmic reticulum surrounding each myofibril
- Function in regulation of Ca2+ levels
- stores and releases Ca2+ (*IN CELLS ITS FUNCTION IS STORING CA)
Explain the process of muscle contraction (what happens physically)
- myosin pulls like rope- pulling thin filaments over the top of the thick filaments(sliding filament theory)
- thin pulled towards m line, h zone begins to shrink (originally thick filaments with no overlap)
- two z discs move together as more crossover occur, resulting in a shorter h zone
- i band also decrease in size as there’s less region with thin filament on its own, a band remains the same
- myosin heads attach to and ‘walk’ along the thin filaments at both ends of a sarcomere, progressively pulling the thin filaments towards the M line.
- the thin filaments then slide inward and meet at the centre of a sarcomere. They may even move so far inward that their ends overlap
- As the thin filaments slide inward, the I band and H zone narrow and eventually disappear altogether when the muscle is maximally contracted.
- However, the width of the A band and the individual lengths of the thick and thin filaments remain unchanged.
- Since the thin filaments on each side of the sarcomere are attached to Z discs, when the thin filaments slide inward, the Z discs come closer together, and the sarcomere shortens.
- Shortening of the sarcomeres causes shortening of the whole muscle fibre, which in turn leads to shortening of the entire muscle.
Compare striated muscle fibres in skeletal and cardiac muscle cells.
- Skeletal muscle cells have abundant sarcoplasmic reticulum (SR)- resulting in greater calcium storage; in comparison, cardiac muscle has much less SR
- this means cardiac muscles have to rely more heavily on extracellular calcium
- Both have T-tubules – they are associated with SR cisternae: Skeletal – two SR cisternae + one T-tubule (triad)
Cardiac – one SR cistern + one Ttubule (diad) - Cardiac muscles have a more extensive blood supply – coronary vessels
What is a coronary artery disease and why is it significant?
- perfusion cannot occur normally
- thickening of the wall of blood vessel (forms lumen)
- when exercise, heart increases function but not enough blood can be passed
- causes pain in heart- angina
- may eventually lead to completely blockage= myocardial infarction, or lack of blood supply at some parts of heart-> ischemia of heart muscle, muscle can die
Striated muscle cells: myofibril diagram fill in
photos
What structure/ feature allows striated muscle cells to generate force?
because their cytoskeletons have highly organised myofilaments of actin and myosin.
Draw a thick filament
photos
Draw a thin filament
photos
Compare thin filament structure in contracted and non-contracted states.
non-contracted state:
- tropomyosin covers the binding sites on the actin, where the troponin then binds to the tropomyosin, troponin sits there waiting for Ca to come along
During contraction:
- Ca floods cell from the internal store
- Ca binds to troponin, causes conformation change, pulls on tropomyosin, moves away from the binding site.
- Binding site on actin is then exposed, myosin can now bind, and contraction begins
What are the other organelles associated with striated muscle cells other than myofibrils?
Sarcoplasmic reticulum and T-tubules
Explain what T-tubules are- full name, what it is, what it does- how it processes a contraction
- Full name: Transverse Tubules (T Tubules)
- Invaginations(action of being folded to form a pouch) of the cell membrane (sarcolemma- *plasmalemma= cell membrane
) - action potential(impulse) needs to be brought inside the cell, therefore have T=Tubules invade inside the cell, closely associated with sarcopasmic reticulum
- it has lots of voltage-gated ion channels
- brings action potential in, change in voltage opens ion channels on the sarcoplasmic reticulum, allowing calcium to flood the system(triggers release of storage, calcium then binds to troponin, moves tropomyosin out of the way, now binds with actin for contraction
Sarcoplasmic reticulum and T-Tubules diagram fill in
photos
What are triads? Where can they be found
Skeletal muscle cells have “triads” – one central T
tubule flanked by two cisternae(membranes) of sarcoplasmic
reticulum
Describe the structure of smooth muscles.
- As a tissue, it consists of many individual, small myofibres with one centrally placed nucleus
- Cells are fusiform in shape= chunky in middle, taper off at either end
- each smooth muscle cell is surrounded by an endomysium
- No striations (no organised arrangments of myofilaments)
- form tissue with gap junctions and LCM and ECM around them
- no adhering junctions like cardiac tissues
- Cell junctions contain communicating junctions (gap junctions) that allows ionic transfer to adjacent cells so that they can contract as a tissue (syncytium)
- syncidium= whole group working tgt (innovate a few, when traction occur, calcium ions flood through and cause all to contract
Explain how actin is placed in smooth muscle cells and how contraction occurs. Give an example of how this can be useful.
- not in nice striation of myofilaments
- it is anchored to dense bodies (electron dense cumulations of protein-= equivalent of z lines)
- actin anchored to dense bodies on cell membrane and within the cytoplasm, myosin lies closely to actin and slides over it during contraction, this pulls on the membrane’s dense bodies and shortens the cell
- whole tissue reduces in size because it was connected with gap junctions and LCM
- allow food to pass through, e.g. in gastrointestinal tract
How is smooth muscles different from striated muscles?
Thin, short cells compared with skeletal and cardiac muscle
cells
- only one nucleus, centrally located
* Very little sarcoplasmic reticulum
* No sarcomeres, myofibrils, or T tubules
- For striated muscle cells, t-tubules are there because the cells are large and we need to bring that action potential inside the cell
- because they are small and have gap junctions, therefore we don’t need t tubules
- have actin but just not in organised myofilaments
Where is smooth muscle found?
found in hollow viscera (e.g.,
stomach, bladder, uterus, ductus
deferens, etc.. ) and blood vessels
