HIstology Lecture 1 -- Muscles Flashcards
Origin of muscle fibers
mesodermal
How does differentiation occur for muscle fibers
Mainly by a process of cell lengthening and synthesis of myofibrillar proteins
3 types of muscle fibres
Smooth
Skeletal
Cardiac
Which types of muscle fibres have myofribrils that can be seen in cross section?
Skeletal
Cardiac
Which types of muscle fibres have centrally located nuclei
Smooth
Cardiac
Which types of muscle fibres have peripherally loctaed nuclei
Skeletal
Which types of muscle fibres have striations?
Skeletal
Cardiac
What is the most abundant type of muscle in the body
Skeletal striated muscle
3 coats of connective tissue that organize muscle
Epimysium
Perimysium
Endomysium
Define epimysium
Dense connective tissue surrounding the entire muscle
Define perimysium
Connective tissue surrounding each bundle of fibres or fascicles
Define endomysium
Thin layer of connective tissue surrounding each muscle fibre
What does the endomysium contain
Basal lamina
Associated reticular fibrils (collagen type III)
Elastic fibres
Capillaries supplying blood to muscle fibres
Which types of muscle fibres are involuntary?
Smooth
Cardiac
Range of muscle fibre length
1 - 40 mm
Range of muscle fibre diameter
10 - 100 micrometers
Cell membrane of muscle fibres
Sarcolemma
Cytoplasm of muscle fibres
Sarcoplasm
Define satellite cells
Stem cells that sit between the basal lamina and the sarcolemma. Have separate cell membrane separating them from the sarcolemma
Role of satellite cells
When needed, extra nuclei can be recruited by mitotic division = one nucleus goes into sarcoplasm and other nucleus remains in satellite cell
Major organelles in striated muscle fibres
Myofibrils
Mitochondria
Smooth endoplasmic reticulum (sarcoplasmic reticulum)
Describe the contraction of smooth muscles
Slow and involuntary (i.e. wall of digestive system, blood vessels, uterus)
Describe the contraction of striated skeletal muscle
Quick, forceful, usually voluntary
Describe the contraction of striated cardiac muscle
Voluntary, vigorous, rhythmic
In what types of muscle can hypertrophy occur?
Skeletal
Cardiac
In what types of muscle can hyperplasia occur&
Smooth muscle
Function of connective tissue in skeletal muscle
Mechanical transducer to the forces generated by the contracting muscle cells
Approximate number of myofibrils in one muscle fibre
1500
Diameter of myofibrils
1 - 2 micrometers
Approximate number of thin filaments in one myofibril
3000
Approximate number of thick filaments in one myofibril
1500
Define the sarcomere
The smallest repetitive subunit of the contractile appartus extending from Z line to Z line
Approximate size of one sarcomere
2 - 3 micrometers
whats does the M line contain?
Creatine kinase
Creatine kinase purpose
Catalyze this reaction:
phosphocreatine + ADP –> ATP + creatine
What does the Z line contain?
alpha actininin
Purpose of alpha actinin
Anchor actin filamtents
What are thin filaments comprised of
Polymerized F-actin (from free G-actin)
Tropomyosin and troponin
What are thick filaments comprised of
Myosin
Titin
White distinguishes red, white and intermediate muscle fibres?
The amount of oxygen binding protein myoglobin and mitochondrial content
Define red fibres
Slow-twitch motor units resistant to fatigue
Location of red muscle fibres
Postural muscles of limbs and back
Define white muscle fibres
Fast twitch motor units that fatigue rapidly but give strong contractions
Examples of white muscle fibres
Leg and arm muscles or breast muscles in chickens
Compare red and white muscle fibres
Red is smaller than white and contains more myoglobin and mitochondria
Define T-tubules (transverse tubules)
Invaginations of the sarcolemma
What surrounds individual myofibrils?
Hollow tubules collectively referred to as the sarco-tubular apparatus
Define sarcoplasmic reticulum
A network of canals running in parallel with the sarcomere filaments, transverse to the T-tubules
What does one section of a sarcoplasmic reticulum span? What is its boundary?
The legnth of one sarcomere, bounded by (but not continuous with) a T-tubule
WHere are terminal cisternae found?
Where the sarcoplasmic reticulum abuts the transverse tubules
Define a triad
A T-tubule with its two adjoining terminal cisternae
What causes the characteristic cross-striations in skeletal muscle?
Differences in refractive indices associated with different components of the sarcomere units on each myofibril and their register from myofbril to myofibril
Which bands of the sarcomere change shape during muscle contractions?
H pseudoband, I band
What is each myosin molecule composed of
A dimer composed of two tightly intertwined heavy polypeptide chains consisting on L-meromyosin (LMM)
What is at the end of each myosin chain?
Globular head attached by a short elastic stalk, both made of H-meromyosin (HMM)
Which subtype of HMM forms the globular head? The neck?
S-1 = head S-2 = short neck
What are the myosin globular heads associated with?
A pair of “light” polypeptide chains (L1 and L2)
What do the myosin heads contain?
Specific binding sites for actin
ATP receptor site
Catalytic sit capable of hydrolyzing ATP
Function of titin
Anchor the ends of thick filaments to the Z lines
2 regulatory proteins associated with actin
Tropomyosin and troponin
Ratio of actin to tropomyosin and troponin in skeletal muscle
7:1:1
3 proteins that comprise troponin
TN-I
TN-T
TN-C
TN-T purpose
High affinity for tropomyosin
TN-I purpose
High affinity for actin
TN-C purpose
Calcium acceptor proteins that simultaneously binds to TN-T or TN-I
Role of troponin in absence of free calcium
Inhibitory role by keeping the actin-tropomyosin filaments in a configuration that masks specific myosin binding sites on the actin molecule (cross-bridge formation)
Define Nebulin
A giant protein molecule, two of which wrap around actin filaments in skeletal muscle, that is a part of the muscle cell’s cytoskeleton
Nebulin function
Regulate the assembly of the actin filament
Stabilize the length of the actin filament
Help anchor actin filament to the Z-line
Neurotransmitter found in the pre-synaptic vesicle of the neuromuscular junction
Acetylcholine
Effect of acetylcholine on the sarcolemma
Cause a local increase in the permeability of the sarcolemma = depolarization of the membrane
3 layers of the wall of the heart
Epicardium
Myocardium
Endocardium
2 layers of the pericardium
Fibrous pericardium
Inner serious pericardium
2 layers of the serious pericardium
Parietal lamina
Visceral lamina
Define the fibrous pericardium
An external layer offibrous connective tissue
Constituents of the endocardium
Smooth thin membrane consisting of:
Endothelium
Connective and smooth muscle tissue
Location of striated involuntary cardiac muscle fibres
Walls of the heart and the base of the pulmonary veins
How are individual cardiac cells attached to each other
Junctional complexes called intercalated discs
2 parts of the intercalated disc
Transverse
Lateral
Define the transverse part of the intercalated disc
The physical connection part consisting of:
Desmosomes
Adherens jjunctions (fascia adherens)
Define the lateral part of the intercalated disk
Communicating part consisting of a gap junction
Function of the gap junction
Provide a means of passing ionic signals from one cell to another = heart has a synchronous beat
What regulates the synchronization of the heart
Modified cardiac myocytes called Purkinje fibres
What do the secretory granules of the cardiac muscle fibres of the atria contain?
Atrial natriuretic factor
Brain natriurietic factor
Function of the natriurietic factors found in the cardiac muscle fibres of the atria
Diuretics that inhibit renin secretion in the kidney
Relax vascular smooth muscle
Also, brain natriuretic factor increases in CHF
Describe the nucleus of smooth muscle fibres
Centrally placed, elongated, sausage-shaped
Seen as a corkscrew shape when contracted
What surrounds each smooth muscle fibre?
Basal lamina (except at gap junctions)
What surrounds the basal lamina of smooth muscles?
Reticular fibres
Elastic fibrils
Equivalent of T-tubules in smooth muscle fibres
Caveolae
Where do the components of the reticular fibres and elastic fibrils of smooth muscle fibres come from?
Components are secreted by the smooth muscle cells (collagen type III and IV)
Where are the longest smooth muscle fibres
Gravid uterus
The 3 types of filaments found in the smooth muscle sarcoplasm
Thin filaments
Intermediate filaments
Thick filaments
Components of smooth muscle thin filaments
Actin
Tropomyosin
Where do smooth muscle thin filaments arise from?
Dense patches or dense bodies that are either membrane associated or free in the sarcoplasm
What do the smooth muscle dense bodies contain?
Alpha actinin
Describe smooth muscle intermediate filaments
Attached to dense patches
10 nm in diameter, extend between dense patches
Component of all smooth muscle intermediate filaments
Desmin
Component of vascular smooth muscle intermediate filaments
Vimentin
How are the thick filaments arranged in smooth muscle?
Lie parallel to thin filaments
What are smooth muscle thick filaments made of?
Myosin II
List the 5 steps of muscle contraction (post-membrane depolarization)
1) Ca influx from ER
2) Bind TnC
3) Myosin binds actin –> cleave ATP
4) Myosin head slides thin over thick filament
5) Ca removed by ER (let go)
What mutation causes muscular dystrophy?
Mutations in the laminin gene
Define myasthenia gravis
Autoimmune disease due to the presence of auto-antibodies against the acetylcholine receptor
What is one connexon comprised of?
6 connexins (connexin 48)
What is the consequence of connexin 48 mutations?
Lethal (kill fetus)
Describe the inactive state of myosin filaments in smooth muscle
Non-phosphorylated light chains cause binding of head to tail = looped filament
What is the reaction to activate myosin filaments?
Calcium-mediate myosin light chain kinase causing ATP -> ADP
What connective tissue layers does smooth muscle contain?
Endomysium only
