1.16 Muscle tissues

Question 1

Briefly describe what are muscle tissues and how movements are initiated.

Answer 1

• 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).

Question 2

What are the different names for muscle cells?

Answer 2

Muscle cells = Muscle Fibres = Myofibres = Myocytes

Question 3

Muscle classification

Answer 3

1. 3 types: smooth, skeletal, cardiac
2. microscopic apearance (internal structural appearance)
   > striated= stripy (skeletal and cardiac
   > smooth
3. 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)

Question 4

Where do we find the different muscles types in the human body?

Answer 4

1. 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…
2. Cardiac Muscle-
   wall of the heart
3. Smooth Muscle- blood vessels, any viscera (internal organs) with a lumen; e.g. much of the gastrointestinal, urinary, respiratory, reproductive tracts.

Question 5

What are the three types of muscles?

Answer 5

skeletal, cardiac and smooth.

Question 6

what do muscle tissues compose of?

Answer 6

elongated cells called myofibres (myo=muscle, fibre= long thin things)

Question 7

What is depolarisation? (hint: happens in muscle tissues)

Answer 7

shift in electric charge distribution, resulting in less negative charge inside the cell compared to the outside

Question 8

Describe the relationship between connective tissues and muscle tissues.

Answer 8

• 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).

Question 9

Structure of skeletal muscle cells

Answer 9

• regular organisation of contractile proteis and cytoskeleton
• whole muscle cell shrinks in size when contracts
• They can be very long cells (up to 30cm).

Question 10

Describe the parts of a skeletal muscle cell (its organisation) and how CT plays a major role in it.

Answer 10

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

Question 11

Describe myofibrils and where they are found.

Answer 11

• 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

Question 12

What’s special about the nuclei of skeletal myocytes?

Answer 12

• 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

Question 13

What allows skeletal muscles to have voluntary movements?

Answer 13

It is innervated by the somatic nervous system

Question 14

muscle tissue diagram fill in

Answer 14

photos

Question 15

Explain the organisation of skeletal muscles.

Answer 15

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.

Question 16

what classification of tissue is the tendon?

Answer 16

Dense regular connective tissue

Question 17

Describe the striations of a skeletal muscle cell.

Answer 17

– repeating series of dark A bands and light I bands

Question 18

Explain the structure of cardiac muscle tissues.

Answer 18

• 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)

Question 19

Describe organelles: function in cardiac muscle tissues.

Answer 19

• 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

Question 20

Describe the cell junctions in a cardiac muscle tissue.

Answer 20

• 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

Question 21

Why do heart transplant patients sometimes feel that they have a fast heart rate?

Answer 21

Because the autonomic pacemaker cells aren’t connected yet (takes time for nerve to grow back (isn’t connected yet to slow it down

Question 22

Describe the cell branching of cardiac muscle tissues.

Answer 22

• 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

Question 23

What muscle tissues do striated muscle cells include?

Answer 23

includes both skeletal and cardiac

Question 24

Describe, in depth, the different parts of the myofibril structure.

Answer 24

• 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

Question 25

Describe the structure of thick filaments. (what they are composed of, structure,

Answer 25

• 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

Question 26

Describe the structure of thin filaments. (what they are composed of, structure, what it does)

Answer 26

• 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

Question 27

Explain what sarcoplasmic reticulum is.

Answer 27

• 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)

Question 28

Explain the process of muscle contraction (what happens physically)

Answer 28

• 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.

Question 29

Compare striated muscle fibres in skeletal and cardiac muscle cells.

Answer 29

• 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

Question 30

What is a coronary artery disease and why is it significant?

Answer 30

• 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

Question 31

Striated muscle cells: myofibril diagram fill in

Answer 31

photos

Question 32

What structure/ feature allows striated muscle cells to generate force?

Answer 32

because their cytoskeletons have highly organised myofilaments of actin and myosin.

Question 33

Draw a thick filament

Answer 33

photos

Question 34

Draw a thin filament

Answer 34

photos

Question 35

Compare thin filament structure in contracted and non-contracted states.

Answer 35

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

Question 36

What are the other organelles associated with striated muscle cells other than myofibrils?

Answer 36

Sarcoplasmic reticulum and T-tubules

Question 37

Explain what T-tubules are- full name, what it is, what it does- how it processes a contraction

Answer 37

• 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

Question 38

Sarcoplasmic reticulum and T-Tubules diagram fill in

Answer 38

photos

Question 39

What are triads? Where can they be found

Answer 39

Skeletal muscle cells have “triads” – one central T
tubule flanked by two cisternae(membranes) of sarcoplasmic
reticulum

Question 40

Describe the structure of smooth muscles.

Answer 40

• 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

Question 41

Explain how actin is placed in smooth muscle cells and how contraction occurs. Give an example of how this can be useful.

Answer 41

• 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

Question 42

How is smooth muscles different from striated muscles?

Answer 42

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

Question 43

Where is smooth muscle found?

Answer 43

found in hollow viscera (e.g.,
stomach, bladder, uterus, ductus
deferens, etc.. ) and blood vessels