Muscle Tissue. Flashcards
What are the three classes of muscle tissue?
Skeletal, Smooth, and Cardiac.
What muscle groups are striated?
Cardiac and skeletal.
What muscle groups are multi-nucleated?
Skeletal, cardiac as well but only 1-2.
Somitic muscles AKA:
Brachiomeric muscles or Pharyngeal arch muscles.
What is the function of brachiomeric and pharyngeal arch muscles used for in fish Vs tetrapods?
Fish: pumping water across the gills
Tetrapods: Swallowing.
Somatic muscles:
Muscles of the outer body such as biceps brachii.
These muscles arise from myotomes- segments of the mesoderm.
What is a group of muscle that is innervated by a single spinal nerve called?
A myotome. These arise from the paraxial mesoderm.
Pharyngeal arch muscles/Brachiomeric muscles/ Somitic muscles:
Muscles of the pharyngeal arches and their derivatives. (Think head and some inner neck muscles.)
Striated branching muscle?
Cardiac found in the heart.
Non-striated uni-nuclear muscle tissue?
Smooth muscle tissue, found mostly in the hollow organs.
What is the cellular component of muscle tissue called?
Myofiber.
What gives the appearance of striations in muscle?
The arrangement of contractile protein filaments within the cell.
What is the dense connective tissue which encompasses an entire muscle organ?
Epimysium
What kind of connective tissue is the epimysium?
Dense regular connective tissue (Collagen and fibroblasts.)
What muscle covering is continuous with the tendon in muscles.
The epimysium.
What is a bundle of myofibers called?
Fascicles.
Connective tissue covering a fascicle within a muscle?
What kind of connective tissue?
Perimysium: a dense regular connective tissue. (collagen and fibroblasts.)
What membrane surrounds individual myofibers? (muscle cells.)
What kind of connective tissue is it usually?
Endomysium
Loose connective tissue with reticular fibers.
What surrounds myofibers and is just deep of the endomysium?
External lamina.
What do skeletal myofibers rise from?
Myoblasts. (Round, non-contractile cells with a single central nucleus.) Then become myotubes (some contractile behavior post innervation.) Then –Myofiber.
What gives rise to myoblasts?
Mesenchymal cells.
What are four things mesenchymal cells can give rise to?
- Connective tissues (fibroblasts.)
- Skeletal muscle (myoblasts.)
- Blood and lymph systems
- Skin
What gives rise to mesenchymal cells?
Mesoderm.
Where does trunk musculature originate from?
Myotomal Mesoderm.
Where does limb musculature arise from?
Somatic musculature.
Where do muscles of the face, mastication, larynx and pharynx arise from?
Somitic/ pharyngeal arches/ brachiomeric musculature.
How are mature myofibrils formed?
Mesenchymal cells –> Myoblasts which then fuse together into multinucleate myotubes which then become mature myofibrils (cells.)
About how many nuclei per myofiber (skeletal)?
50-100.
What is the muscle cell membrane also known as?
Sarcolemma.
What are the two contractile proteins of muscle myofiber?
Actin- Microfilament. (Thin filament.)
Myosin- Microtubule. (Thick filament.)
What Muscular tissue is uninucleated?
Smooth.
At what developmental point do the myotubes begin to display contractile behavior.
This occurs when the tissue begins to become innervated.
Why are skeletal muscle cells multinucleate?
Due to the myoblasts fusing together to form mature myofibers (muscle cells.)
What two muscle types are visceral muscle?
Cardiac and smooth.
Muscle Cell AKA:
Myofiber.
Organization of muscle histology largest to smallest? (3)
- Muscle Organ
- Fascicle
- Myofiber (Muscle Cell.)
Organization of connective tissue layers from smallest to largest (3)?
Endomysium- Surrounds myofiber (Cell).
Perimysium- Surrounds Fascicle.
Epimysium- Surrounds Muscle organ.
Immature Myofiber?
Myotube, becomes contractile once Innervated.
Starts to produce contractile proteins.
Where do the nuclei of myofibers lie?
Immediately deep to the sarcolemma (Muscle Cell membrane.)
Actin and Myosin are organized into parallel bundles called what?
Myofibrils.
What surrounds each myofibril?
Sarcoplasmic reticulum “Sleeve”.
- Supplies Calcium for contraction.
Where is mitochondria located within a myofiber?
Mitochondria is located between the myofibrils made of contractile protein bundles (Actin & Myosin.)
What makes up a sarcomere?
A central array of Myosin (Thick- Microtubule.) that has Actin (Thin- Microfilament.) on each side.
What is a myofibril made of?
It is a bundle of the protein filaments which contain the contractile elements of the muscle.
Myosin: Microtubule/ Thick Filament.
Actin: Microfilament/ Thin Filament.
What is each myofibril associated with?
What does it supply?
A Sleeve of Sarcoplasmic reticulum- This supplies Calcium for contraction.
What causes the striated pattern within skeletal muscle?
The arrangement of actin and myosin within the sarcomere.
A-bands are described as:
I bands are described as:
A= Anisotropic (Refractive Properties differ with direction/ Not same (AN-ISO).)
-A band includes both actin and myosin (Not Shiny.).
I= Isotropic (Refractive properties the same (ISO) no matter direction)
-I band is only Actin. Actin is shiny in polarized light.
At each end of the sarcomere the actin filaments tie in together forming which structure?
The Z-Disc.
What two intermediate filaments assist with keeping myosin and actin filament parallel within a sarcomere?
Desmin and Vimentin.
What slides towards to the A-Band during muscle contraction?
The Actin (Thin) Filaments. They will now have more overlap with the myosin filaments- shortening the sarcomere and when many do this lead to muscle contraction.
Which zone is within the A band and only exists when the muscle is at rest?
The H-Zone. This is an Actin-Free Zone.
When the sarcomeres are contracted all of the myosin filaments are overlapped with actin filaments so there is no H-zone during contraction.
What exists in the center of the H-zone?
The M-line - Where components of cytoskeleton align to stabilize the myosin filaments.
Portion of the sarcomere where the Myosin and Actin are overlapping?
A-I Junction. (Becomes larger during contraction due to actin (Thin) filaments being moved to have more interlay with the myosin (Thick) filaments.
How does troponin affect muscle contraction?
Troponin sterically masks the binding sites on actin, when calcium is released, it will favorably bind to troponin allowing the myosin extensions/ cross-bridges to bind to the actin and pull it into the A-band towards the M-line. The cross-bridges are composed of HMM (Heavy Meromyosin.)
What are the Myosin Cross-bridges composed of? Which of these makes up the main active site?
Heavy and light Meromyosin Chains.
Heavy Meromyosin Makes up Sub unit 1 which is the main active site.
How is ATP & ATPase used in muscle contraction at the level of the Myosin cross-bridges?
Mostly just for future knowledge.
The myosin cross bridge head without bound ATP is in its Rigor state (Strongly bound to actin filament.) ATP (from mitochondria- we are within the cell.) Will bind to Subunit 1 (head) and reduces its affinity for actin, and causes a conformational change in the lever/ arm of the myosin to be further along the actin, unbound.
ATPase hydrolyses ATP into ADP + Pi (phosphate.) This changes affinity for actin and the head will bind weakly to the actin, this causes a conformational change which will then release Pi then ADP bringing the head back into its original rigor strongly bound state. This pulls the actin filament towards the M-line in a “Power Stroke.”
KNOW THERE IS MYOSIN ATP.
What is the Composition of the actin filament?
(Know the filament within.)
Double Helix Globular Actin monomers arranged around a tropomyosin filament.
What organelle regulates the calcium concentration within a myofiber?
How?
The Sarcoplasmic Reticulum (Comparable to a smooth ER)
Active Transport to move Calcium within and Calcium (Voltage) Gated ion channels out.
What are the two spaces calcium can inhabit within a myofiber regulated by the sarcoplasmic Reticulum located on the myofibrils.
- Sarcoplasmic Reticulum Compartments. (Stored in)
- Cytosolic/ Sarcoplasmic Compartment.
What is it called when the electrical charge across a cell membrane changes making the cell less relatively charged than its environment?
Depolarization.
What causes calcium ion gated channels to open?
Depolarization of the sarcolemma which travels through the T-tubules (invaginations) to the sarcoplasmic reticulum.
What does T-tubule stand for?
Transverse Tubule.
What are the invaginations of the sarcolemma? What is their purpose?
The T-tubules: They function to carry a depolarization event from the nerve to the calcium ion gated channels part of the sarcoplasmic reticulum.
How does the sarcoplasmic reticulum regulate calcium concentrations within a myofiber?
The sarcoplasmic reticulum is constantly retrieving calcium from the cytosolic space using active transport (against gradient), when the T-tubules carry a depolarization event it triggers the calcium gated ions channels to release the calcium (Leads to contraction.) Once Calcium is released it will then continue to be collected back into the sarcoplasmic reticulum allowing for relaxation.
Left off Pg 10 at The skeletal muscle triad.
