Histology Flashcards
Subdivisions of muscle
Muscle >muscle fibers(cell) >myofibrils >sarcomeres
Embryological layer origin of muscle tissue
Mesodermal.
Describe muscle fibers of skeletal striated muscle
Multinucleated cells
Nuclei in the perphery
Banding pattern.
Striated.
Describe muscle fibers of cardiac muscle
1 nucleus in the center
Largest amount of capillaries per sq meter.
Contains intercalated disks.
Striated
Describe muscle fibers of smooth muscle
A lot of actin.
No myofibrils: only myofilaments (actin)
Centrally located nuclei
Cells uniformely shaped. Myofibrils not seen in cross section.
Type of contraction in each muscle
Skeletal: quick, forceful, voluntary
Cardiac: involuntary, rigorous, rhythmic
Smooth: slow, involuntary
Which types of muscles undergo hypertrophy vs hyperplasia?
Hypertrophy: striated skeletal and cardiac
Hyperplasia: smooth muscle (eg. endometrium)
Most abundant type of muscle
Skeletal striated muscle.
Distinguish between endomysium, perimysium and epimysium in the skeletal striated muscle.
Epimysium: periphery of muscle
Perimysium: separate bundles of muscle fibers (septa). Contain gap junction.
Endomysium: separation of individual muscle fibres.
What is a junctional complex in the striated skeletal muscle?
Skeletal muscle has fingerlike projections at its end containing actin inserting into connective tissue. This is also called musculotendinous junction.
Name for a bundle of muscle fibers
Fascicle
Describe the sarcomere of the striated muscle cell
The Z lines delimit the sarcomere (contains alpha-actinin to bind to actin molecules)
- Thin actin filaments of from Z line and penetrate into A band, but not until middle.
- Thin myosin filaments start in the middle (H band) and extend towards the Z line.
A band: thick and thin filaments. In the middle: H band is only myosin, since actin does not reach the middle. M line is in the middle of the H band and is where myosin originates (contains creatine kinase).
I band: only actin filaments, contains Z line from which actin protrudes.
3 subunits of troponin binding to actin
TnI: inhibition of the actin-myosin interaction
TnC: binding of Ca2+
TnT: anchoring to tropomyosin
Mechanism of striated skeletal muscle contraction
The AP is transmitted to the cell via the T Tubule (triad). AP causes the depolarization of the SR, which now releases Ca2+.
- Ca2+ influx from the SR.
- Ca2+ binds to TnC of troponin
- Myosin can now bind to actin because the tropomyosin moves away upon Ca2+ binding.
- Myosin head bending causes sliding of the thin filament over the gthick filament.
- Ca2+ is removed by the SR through the ATPase calcium pump.
What happens to different bands of the sarcomere when there is contraction?
- H band becomes shorter because thin filaments are displaced towards the center.
- Sarcomere becomes shorter.
- I band becomes shorter.
Thick and thin filaments do not change in length
Name 3 other less important proteins that bind to skeletal muscle fibers
Tropomodulin, titin (supports myosin), nebulin (stabilizes actin)
What enzyme does the M line contain?
Creatine kinase
Where does the AP travel inside the skeletal muscle fiber? Where is this structure lcoated?
Inside the t-tubule, which is an invagination of the sarcolemma.
T tubule is located between 2 adjacent cisternae. Located at the A-I junction.
AKA triads.
What structure allows calcium to be pumped back into the SR for muscle relaxation?
Calcium ATPase. Located at the membrane of the SR.
ID A, I and Z bands on this image
True or False: the perimysium surrounds the fascicle.
True. Fascile = bundle of muscle cells.
Then, inside, the endomysium surrounds individual muscle cells, which in turn contain myofibrils.
What is the terminal bouton?
AKA neuromuscular junction or motor end plate.
This is where the myelinated motor nerves branch out within the perimysium and endomysium, and lose their myelin sheath. 1 Nerve can innervate several muscle cells.
Describe the neuromuscular junction to transmit AP
The basement membrane of the muscle cell is continuous with the BM of the axon.
The post-synaptic membrane is folded and very irregular.
Axon releases ACh onto ACh Receptors. Na+ flows into the cell and K+ flows out, creating depolarization. There are T tubules that are continuous with the sarcolemma and go deep into sarcoplasm.
What is myasthenia gravis?
An autoimmune disease due to presence of auto-Abs against acetylcholine receptor. No muscle contraction.
3 walls of the heart
Epicardium (periphery, visceral serous pericardium)
Myocardium (flesh, main part)
Endocardium
2 layers of the pericardium, and subdivision of the serous layer.
External layer: fibrous pericardium
Internal layer: serous pericardium
Internal serous pericardium: parietal serous pericardium (in contact with fibrous) and visceral serous, AKA epicardium.
Are intercalated disks features of only cardiac muscles?
Yes. They contain gap junctions and are very important for the AP propagation through the heart.
Intercalated disks separate two adjacent cardiac myocytes.
3 zones making up the intercalated disk
- Zonula adherens (transverse)
- Macula adherens (transverse)
- Gap junction (lateral)
What are gap junctions made up of?
Coupled connexons.
Each connexon is made up of 6 connexins, which together create a half-channel. The half-channel is connected to that of the next cell, which creates a gate through which Ca2+ can flow.
Where are triads and diads located on cardiac muscle cells?
At the Z line (opposed to skeletal muscle cells, where they were located at the A-I junction)
Are there gap junctions in smooth muscle?
Yes.
Appearance of contracted smooth muscle
Skewed appearance.
Process of contraction in smooth muscle
- Ca2+ influx
- Ca2+ activates myosin light chain kinase such that the heavy chains can now bind actin.
Myosin phosphatase is what causes relaxation upon decreased Ca2+ levels.
What are dense bodies in smooth muscle cells?
Located on plasma membrane, rich in alpha-actinin and dystrophin. “Z line”. This is from where the actin filaments emerge.
3 muscle disorders and what causes them
- Ehlers-Danlos syndrome. Mutation in smooth muscle fibers. Affects CT.
- Myasthenia gravis. Abs destroy ACh-receptpros so no more APs and muscle excitability.
- Muscular dystrophy. Mutation in dystrophin and laminin genes.
What is a vasa vasorum?
A vessel within the vessel
What is IELM in a vessel?
internal elastic limited membrane.
Present in the muscular artery, like a sleeve, sometimes fenestrated.
3 main histological layers of blood vessels
Intima (Endothelium, Sub-endothelial layer)
Media (elastic membranes and/or smooth muscle cells)
Adventitia (CT, vasa vasorum)
Condition for a vessel to be considered an artery in histology vs condition to be considered arteriole
If there are >4 layers of smooth muscle cells in the media.
< 2 : arteriole.
What causes varicose veins?
Dysfunction of the valves in the veins. Due to high blood pressure in superficial veins.
Is there IELM in the media of veins? What about adventitia and vasa vasorum?
No IELM.
There can be vasa vasorum in large veins.
Adventitia is very prominent.
How are smooth muscle cells organized despite their intrinsic disorganization?
Thanks to lamellae: smooth muscle cells are short and their extremities attach to adjacent lamellae. These contribute to solidity and resilience of the wall.
How much times greater than the volume of the aorta is the volume of the capillaries?
800x greater
Classification of capillaries according to permeability
- Permeable: fenestrated or sinusoids.
- Impermeable/continuous
Is there a BM in lymphatic vessels?
No
What causes vasoconstriction and what causes vasodilation in smooth muscle cells?
Vasoconstriction: endothelin binding to receptor causing Ca2+ increase.
Vasodilation: NO, promoting conversion from GTP to cGMP leading to vasodilation.
How is fibrin formed?
Thrombin acts on fibrinogen to convert it to fibrin.
Metabolic functions of the endothelium (2)
- Conversion of Angiotensin I to II
- Inactivation of Bradykinin and of serotonin, prostalgandins, NE, etc
