Cytology Week 12 Flashcards
What is muscle tissue specialised for
- contractility
- enabling movement with organ systems
- Blood flow
What is muscle contraction driven by ?
- Actin microfilaments and associated proteins
What are muscle cells derived from
Mesoderm
What does muscle cell differentiation involve
- cell lengthening
- The synthesis of myofibrillar proteins
Name the 3 types of muscle tissue
- Skeletal muscle
- Cardiac muscle
- Smooth muscle
What does skeletal muscle contain ?
Explain the skeletal muscle contractions
- Long multitnucleated cells with cross striations
- Contractions are quick, forceful and under voluntary control
What is the Sarcoplasm?
Muscle cell cytoplasm
What is Sarcoplasmic Reticulum
Smooth ER of muscle cells
What is sarcolemma
Muscle cell membrane and its external lamina
What is Hypertropy
Increase in cell volume due to new myofibrils
What is Hyperplasia
Increase in cell production
What does Cardiac muscle contain
- Elongated,often branched cells with cross striations
- Cells are connected by intercalated discs
Explain Cardiac muscle contractions
- They are involuntary, vigorous,rhythmic
What is smooth muscle cmoposed of
- Fusiform(spindle shaped ) cells without striations
Explain smooth muscle contractions
- Slow and involuntary
What is muscle contraction caused by
- The sliding interaction of myosin(thick) and actin(thin) filaments
Explain the structure of skeletal muscles
- Composed of muscle fibers, long cylindrical cells that are multinucleated
How are straited muscle fibers formed
- During embryonic development, mesenchymal myoblasts fues to form myotubes, which differentiate into striated muscle fibers
Where is Nucei located in skeletal muscle
- Peripherally, under the sarcolemma
What are muscle satellite cells
- A reserve progenitor cell poulation
Name the layers of connective tissue in which skeletal muscle is supported and organized by
-Epimysium
-Perimysium
-Endomysium
What is the functional role of connective tissue
- They Transmit the mechanical forces generated by muscle contraction
Explain structure and function of Epimysium
- Dense irregular connective tissue
- Surronds the entire muscle and carries larger nerves
Explain the structure and function of Perimysium
- Thin connective tissue surrounds muscle fiber bundles
Explain the structure and function of Endomysium
- Delicate recticular fibers and fibroblasts
-Surround individual muscle fibers , providing a rich capillary network for oxygen supply
What are myofibrils
Cylindrical bundles running parallel to the muscle fiber axis
What do sacromeres contain
- Thick mysoin and thin actin filaments
What is thick mysoin filaments composed of and their function
- Composed of myosin molecules with heavy chains forming rodlike tails and heads that bind actin and ATP.
-Myosin heads facilitate actin binding and energy release for contraction.
What does thin actin filamentsa contain
- Contain myosin binding sites
-Associated with tropomysoin and troponin
Waht is the brief function of tropmyosin
Stabilises actin
Describe the structure of the protein Troponin
-It has a complex of 3 subunits
-TnT: Attaches to tropomyosin.
TnC: Binds calcium.
TnI: Regulates actin-myosin binding.
Explain what is the I band and A band
I Bands: Lighter regions containing only thin filaments.
A Bands: Dark regions with overlapping thick and thin filaments
Explain what the H zone and M line is( and what it contains)
H Zone: Center of the A band with only thick filaments.
M Line: Bisects the H zone and contains proteins like myomesin and creatine kinase to stabilize thick filaments and regenerate ATP
What are the 2 functions of the sarcoplasmic reticulum
- Surrounds myofibrils + functions in calcium sequestration
- Releases calacium from cisternae via voltage gated calcium channels triggered by membrane depolarization
What are transveres tubules
-Tubular infoldings of the sarcolemma that penetrate deep into the sarcoplasm
What are the 2 functions of transvere tubules
- Encircle each myofibril at the A and I band boundaries of the sarcomere
- It ensures simultaneous calcium release across the muscle fiber
Desribe the structure of the Triad
- Composed of one T tubule and 2 adjacent terminal cisternae of the sarcoplasmic reticulum
What is the sliding Filament Model
- That muscle contraction occurs when thin actin and thick mysoin filaments slide pass each other
- The filaments dont change length and the sacromere shortens
Explain the initiation of muscle contraction
- A neural signal reaches the neuromuscular junction and travels along the T tubules to the sarcoplasmic reticulum , triggering the release of calcium ions
Explain the Troponin and Tropmyosin complex when the muscle is in resting
The complex blocks myosin-binding sites on actin
What happens when the release of calcium is triggered by the neural signal
The Released calcium binds to troponin , causing a shape change that moves tropmyosin and exposes the myosin binding sites on actin.
How is a cross bridge formed
When the myosin heads bind to actin, forming cross bridges
What is required for the attach pivot death cycle
- ATP
- Calcium
Explain the process of Relxation in Muscle contraction
-Neural impulses stop , leading to reduced free calcium levels
- Tropomysoin re blocks myosin binding site on actin
What does the myelinated motor nerve branch into
-Branches into unmyelinated twigs within the perimysium and endomysium
What are the components of a Neuromuscular junction
-Axon terminal
-Synaotic cleft
- Post synaptic sarcolemma
What does the Axon terminal contain
Mitochondria and synaptic vessels with acetylcholine
What is the synaptic cleft
- Gap between the Axon terminal and muscle fiber
Explain the process of muscle contraction
- Nerve action potential triggers the release of acetylcholine into the synaptic cleft
- Acetylcholine binds to receptors , opening cation channels and depolarising the sarcolemma.
-An action potential then propagates along the sarcolemma and T tubules - Then Depolarisation at triads trigger caloric release from the sarcoplasmic reticulum, initiating the contraction cycle
Explain the precision of small muscles
They have precise control
Explain the precision of Large muscles
They have coarser movements
What is the All or None response in muscles
Where individual fiberw contract fully or not at all .
What is Rigor Mortis
- When in the absence of ATP, actin-myosin cross bridges stabilize, causing muscle rigidity
What does a motor unit consist of
- A motor untit consits of one motor neuron and all the muscle fibers it innervates
Where are Golgi Tendons found
Found at the myotendinous junctions
What is the structure of Golgi Tendon organs
- They are small,encapsulated structures, with sensory axons embedded among collagen bundles
What is the function of Golgi Tendons
- Detct changes in tension within tendons caused by muscle contraction
What is the function of proprioceptors
- They provide the CNS with information about the musculoskeletal system , aiding in posture and movement regulation
Where are muscle spindles found?
-They are found amongs muscle fascicles
What is the Function of muscle spindles
- Relay information to the spinal cord through sensory nerve axons
What is Duchenne Muscualr Dystrophy caused by
- Cuased by mutation in the dystophin gene, leading to defective cytoskeletion-ECM linkages
What is Myasthenia Gravis
- An autoimmune disorder where circulating antibodies target proteins in the acetycholine receptors
Different types of fibers can be identified on the basis of their….
- Rate of ocntraction(fast or slow fibers)
2.ATP synthesis pathway (oxidative phosphorylation or glycolysis).
Name the types of Skeletal Muscle fibers
- Slow Oxidative fibers
-Fast glycolytic fibers
-Fast oxidative-Glycotic Fibers
Explain slow oxidative fibers
-What they are adapted for
-What they contain
- Explain their endurance and fatigue
- Adapted for slow contractions
-Rich in mitochondria, capillaries, and myoglobin, making them dark/red in color.
-High endurance, fatigue resistant
Explain Fast Glycolytic Fibers
-What it is specialised for
-What it contains
-Its endurance/fatigue
-Specialized for rapid, short-term contractions.
-Few mitochondria and capillaries; rely on anaerobic glycolysis, leading to white color.
- Fatigue quickly due to lactic build up
Explain compact ( cortical )bones + location
- They are dense and located near the surface of the bones
Explain where Cancellous (Trabecular Bone) are located
- Deeper within the interconnecting cavities
