Histology

Question 1

Subdivisions of muscle

Answer 1

Muscle >muscle fibers(cell) >myofibrils >sarcomeres

Question 2

Embryological layer origin of muscle tissue

Answer 2

Mesodermal.

Question 3

Describe muscle fibers of skeletal striated muscle

Answer 3

Multinucleated cells
Nuclei in the perphery
Banding pattern.
Striated.

Question 4

Describe muscle fibers of cardiac muscle

Answer 4

1 nucleus in the center
Largest amount of capillaries per sq meter.
Contains intercalated disks.
Striated

Question 5

Describe muscle fibers of smooth muscle

Answer 5

A lot of actin.
No myofibrils: only myofilaments (actin)
Centrally located nuclei
Cells uniformely shaped. Myofibrils not seen in cross section.

Question 6

Type of contraction in each muscle

Answer 6

Skeletal: quick, forceful, voluntary
Cardiac: involuntary, rigorous, rhythmic
Smooth: slow, involuntary

Question 7

Which types of muscles undergo hypertrophy vs hyperplasia?

Answer 7

Hypertrophy: striated skeletal and cardiac

Hyperplasia: smooth muscle (eg. endometrium)

Question 8

Most abundant type of muscle

Answer 8

Skeletal striated muscle.

Question 9

Distinguish between endomysium, perimysium and epimysium in the skeletal striated muscle.

Answer 9

Epimysium: periphery of muscle
Perimysium: separate bundles of muscle fibers (septa). Contain gap junction.
Endomysium: separation of individual muscle fibres.

Question 10

What is a junctional complex in the striated skeletal muscle?

Answer 10

Skeletal muscle has fingerlike projections at its end containing actin inserting into connective tissue. This is also called musculotendinous junction.

Question 11

Name for a bundle of muscle fibers

Answer 11

Fascicle

Question 12

Describe the sarcomere of the striated muscle cell

Answer 12

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.

Question 13

3 subunits of troponin binding to actin

Answer 13

TnI: inhibition of the actin-myosin interaction
TnC: binding of Ca2+
TnT: anchoring to tropomyosin

Question 14

Mechanism of striated skeletal muscle contraction

Answer 14

The AP is transmitted to the cell via the T Tubule (triad). AP causes the depolarization of the SR, which now releases Ca2+.

1. Ca2+ influx from the SR.
2. Ca2+ binds to TnC of troponin
3. Myosin can now bind to actin because the tropomyosin moves away upon Ca2+ binding.
4. Myosin head bending causes sliding of the thin filament over the gthick filament.
5. Ca2+ is removed by the SR through the ATPase calcium pump.

Question 15

What happens to different bands of the sarcomere when there is contraction?

Answer 15

1. H band becomes shorter because thin filaments are displaced towards the center.
2. Sarcomere becomes shorter.
3. I band becomes shorter.

Thick and thin filaments do not change in length

Question 16

Name 3 other less important proteins that bind to skeletal muscle fibers

Answer 16

Tropomodulin, titin (supports myosin), nebulin (stabilizes actin)

Question 17

What enzyme does the M line contain?

Answer 17

Creatine kinase

Question 18

Where does the AP travel inside the skeletal muscle fiber? Where is this structure lcoated?

Answer 18

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.

Question 19

What structure allows calcium to be pumped back into the SR for muscle relaxation?

Answer 19

Calcium ATPase. Located at the membrane of the SR.

Question 20

ID A, I and Z bands on this image

Answer 20

Question 21

True or False: the perimysium surrounds the fascicle.

Answer 21

True. Fascile = bundle of muscle cells.
Then, inside, the endomysium surrounds individual muscle cells, which in turn contain myofibrils.

Question 22

What is the terminal bouton?

Answer 22

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.

Question 23

Describe the neuromuscular junction to transmit AP

Answer 23

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.

Question 24

What is myasthenia gravis?

Answer 24

An autoimmune disease due to presence of auto-Abs against acetylcholine receptor. No muscle contraction.

Question 25

3 walls of the heart

Answer 25

Epicardium (periphery, visceral serous pericardium) Myocardium (flesh, main part) Endocardium

Question 26

2 layers of the pericardium, and subdivision of the serous layer.

Answer 26

External layer: fibrous pericardium Internal layer: serous pericardium Internal serous pericardium: parietal serous pericardium (in contact with fibrous) and visceral serous, AKA epicardium.

Question 27

Are intercalated disks features of only cardiac muscles?

Answer 27

Yes. They contain gap junctions and are very important for the AP propagation through the heart. Intercalated disks separate two adjacent cardiac myocytes.

Question 28

3 zones making up the intercalated disk

Answer 28

1. Zonula adherens (transverse) 2. Macula adherens (transverse) 3. Gap junction (lateral)

Question 29

What are gap junctions made up of?

Answer 29

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.

Question 30

Where are triads and diads located on cardiac muscle cells?

Answer 30

At the Z line (opposed to skeletal muscle cells, where they were located at the A-I junction)

Question 31

Are there gap junctions in smooth muscle?

Answer 31

Yes.

Question 32

Appearance of contracted smooth muscle

Answer 32

Skewed appearance.

Question 33

Process of contraction in smooth muscle

Answer 33

1. Ca2+ influx 2. 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.

Question 34

What are dense bodies in smooth muscle cells?

Answer 34

Located on plasma membrane, rich in alpha-actinin and dystrophin. "Z line". This is from where the actin filaments emerge.

Question 35

3 muscle disorders and what causes them

Answer 35

1. Ehlers-Danlos syndrome. Mutation in smooth muscle fibers. Affects CT. 2. Myasthenia gravis. Abs destroy ACh-receptpros so no more APs and muscle excitability. 3. Muscular dystrophy. Mutation in dystrophin and laminin genes.

Question 36

What is a vasa vasorum?

Answer 36

A vessel within the vessel

Question 37

What is IELM in a vessel?

Answer 37

internal elastic limited membrane. Present in the muscular artery, like a sleeve, sometimes fenestrated.

Question 38

3 main histological layers of blood vessels

Answer 38

Intima (Endothelium, Sub-endothelial layer) Media (elastic membranes and/or smooth muscle cells) Adventitia (CT, vasa vasorum)

Question 39

Condition for a vessel to be considered an artery in histology vs condition to be considered arteriole

Answer 39

If there are > 4 layers of smooth muscle cells in the media. < 2 : arteriole.

Question 40

What causes varicose veins?

Answer 40

Dysfunction of the valves in the veins. Due to high blood pressure in superficial veins.

Question 41

Is there IELM in the media of veins? What about adventitia and vasa vasorum?

Answer 41

No IELM. There can be vasa vasorum in large veins. Adventitia is very prominent.

Question 42

How are smooth muscle cells organized despite their intrinsic disorganization?

Answer 42

Thanks to lamellae: smooth muscle cells are short and their extremities attach to adjacent lamellae. These contribute to solidity and resilience of the wall.

Question 43

How much times greater than the volume of the aorta is the volume of the capillaries?

Answer 43

800x greater

Question 44

Classification of capillaries according to permeability

Answer 44

1. Permeable: fenestrated or sinusoids. 2. Impermeable/continuous

Question 45

Is there a BM in lymphatic vessels?

Answer 45

No

Question 46

What causes vasoconstriction and what causes vasodilation in smooth muscle cells?

Answer 46

Vasoconstriction: endothelin binding to receptor causing Ca2+ increase. Vasodilation: NO, promoting conversion from GTP to cGMP leading to vasodilation.

Question 47

How is fibrin formed?

Answer 47

Thrombin acts on fibrinogen to convert it to fibrin.

Question 48

Metabolic functions of the endothelium (2)

Answer 48

1. Conversion of Angiotensin I to II 2. Inactivation of Bradykinin and of serotonin, prostalgandins, NE, etc