Muscle and blood vessels (Dr Campbell)

Question 1

What is meant by the term muscle ?

Answer 1

When referring to a tissue, the term muscle also includes connective tissue elements and services (blood vessels and nerves).

Question 2

Why does sk muscle look striated ?

Answer 2

Because its contractile proteins are highly organised into an almost crystalline array that refracts light (clearly visible at LM level).

Question 3

How large are sk myocytes ?

Answer 3

Very large:

• length = 1 mm - 30 cm
• diameter = up to 100 microns

Question 4

How are sk myocytes connected together ?

Answer 4

Mechanically connected by associated connective tissue.

Question 5

What does the SR have which is absolutely crucial for contraction ?

Answer 5

Terminal cisternae.

Question 6

What is a triad made of ?

Answer 6

Triads = 2 terminal cisternae of SR + 1 T-tubule

Question 7

How many nuclei do sk muscle cells contain ?

Answer 7

Many nuclei (result from fusion of 2 or more sk myoblasts).

Question 8

How do muscle cells meet the high NRJ demand for contraction ?

Answer 8

By having lots of mitochondria.

Question 9

What are myofibrils ?

Answer 9

Bundles which contain contractile proteins.

Question 10

What is the contractile unit of the myofibril ?

Answer 10

The sarcomere.

Question 11

What are myofibrils made of ?

Answer 11

Myofilaments:

• thin filaments = actin
• thick filaments = myosin

Question 12

What happens to the contractile proteins during contraction ?

Answer 12

Actin filaments slide over myosin filaments.

Question 13

What do the striations in sk muscle represent ?

Answer 13

Alternating dark and light bands:

• dark band = overlap of actin and myosin
• light band = actin only

Question 14

Where are actin filaments anchored ?

Answer 14

At one end of the Z-lines.

Question 15

What delimitates the sarcomere ?

Answer 15

2 adjacent Z-lines.

Question 16

What are the three general arrangements cells can form ?

Answer 16

Bundles, sheets or bands.

Question 17

What is the structure of smooth muscle cells ?
How are they coupled ?
How big are they ?
Are their the same number of organelles as sk myocytes ?

Answer 17

• spindle-shaped
• mononucleate, w/ centrally located nucleus
• ectrically coupled to one another via gap junctions
• contain little connective tissue (compared to sk muscle)
• diameter = 5 microns (2 - 10 microns)
• length 0.2 mm (10 - 600 microns)
• SR = poorly developed –> cells possess plasmalemmal structures = caveolae
• no T-tubule system.
• few mitochondria (compared to sk muscle)

Question 18

What are intercalated dics ?

Answer 18

Intercalated discs = specialized junctions made of desmosomes (mechanical coupling) and gap junctions (electrical coupling) between cardiomyocytes

Question 19

How many nuclei do cardiomyocytes posess ?

Answer 19

1-2

Question 20

How ar T-tubules arranged in cardiomyocytes ?

Answer 20

THERE ARE NO T-TUBULES IN CARDIOMYOCYTES !

Question 21

How developed is the SR in cardiomyocytes ?

Answer 21

Lack terminal cisternae.

Question 22

How many mitochondria to cardiomyocytes contain ?

Answer 22

A LARGE number (more than sk myocytes) !

Question 23

How large are cardiomyocytes ?

Answer 23

• Diameter = 10 - 20 microns

- Length = 50 - 100 microns.

Question 24

What are the contractile proteins in cardiomyocytes ?

How are these contractile proteins arranged ?

Answer 24

Contractile proteins:

• similar to those in sk muscle
• arranged in a branching myofibrillar network throughout the cytoplasm (the contractile unit of which = sarcomere)

Question 25

What is the motor endplate ?

Answer 25

Synapse of an motoneuron on the sarcolema of a sk myocyte.

Question 26

How is sk muscle controlled ?

Answer 26

CNS –> voluntary control

Question 27

How is smooth muscle controlled ?

Answer 27

Autonomic nerves.

Question 28

How is cardiac muscle controlled ?

Answer 28

• cardiac muscle cells –> can contract w/o neural stimulation –> automaticity
• timing of contraction –> controlled by specialized cardiac muscle cells w/in nodes
• Purkinje cells = specialized cardiac muscle cells that carry this control to the cardiac muscle cells of the myocardium

Question 29

What are the different types of bl vessels ?

Answer 29

Venous circuit: large vein > medium vein > venule > fenestrated capillary
Arterial system: large artery > medium artery > arteriole > continuous capillary

Question 30

What is the main role of arterioles ?

Answer 30

Arterioles = major contributors to peripheral resistance, and therefore blood pressure

Question 31

What is the role of capillaries + small venules ?

Answer 31

Exchange nutrients, gases + metabolites

Question 32

What are continuous capillaries ?

Answer 32

• most common type
• adjacent endothelial cells –> connected to each other via junctional complexes
• most impermeable type

Question 33

What are fenestrated capillaries ?

Answer 33

• endothelial cells –> have small pores = fenestrae
• adjacent cells –> connected via junctional complexes
• quite/very permeable (typically found in kidney –> Bowman’s capsules + in GI tract –> villi of small intestine)

Question 34

What are endothelial cells ?

Answer 34

• cells lining all components of the circulatory system

- simple squamous epithelium (a single layer of flattened cells)

Question 35

What are the 3 layers of blood vessels ?

Answer 35

• Tunica intima = inner-endothelial cells + connective tissue (avascular)
• Tunica media = middle layer –> smooth muscle + connective tissue (may be absent from small vessels)
• Tunica adventitia = outer layer –> connective tissue (may be absent from small vessels)

Question 36

How are the media and adventitia different in larger vessels ?

Answer 36

Media + adventitia of larger vessels –> have their own blood supply from vessels = vasa vasorum (= the vessels of the vessels)

Question 37

What are the 2 types of large arteries ?

What are their respective characteristics ?

Answer 37

Large elastic arteries (e.g. aorta):

• Intima = endothelial cells + thin layer of connective tissue (collagen and few elastic fibres)
• Media = thick spiral of smooth muscle interleaved w/ sheets of elastic fibres (+collagen fibres)
• Adventitia = thick connective tissue (collagen), vasa vasorum + nerves

Large muscular arteries (most systemic arteries):

• Intima = endothelial cells, prominent layer of CT = inner elastic lamina (IEL) (elastic fibres + some collagen fibres)
• Media: thick spiral of smooth muscle + limited CT (collagen + few elastic fibres)
• Adventitia = thick CT, external elastic lamina (EEL, elastic fibres + collagen) bl vessels + nerves.

Question 38

What are the different layers of arterioles composed of ?

Answer 38

• Intima = endothelial cells, IEL absent from small arterioles
• Media = smooth muscle (approx. 3 to 6 cells thick)
• Adventitia = merges with surrounding CT, no EEL.

Question 39

What are the different layers of capillaries composed of ?

Answer 39

Endothelial cells. No media + no adventitia.

Question 40

What are the different layers of venules and veins composed of ?

Answer 40

• Intima = endothelial cells, no IEL
• Media = smooth muscle (venules 1 - 2, veins 2+ cells thick)
• Adventitia = absent or indistinct, merging with surrounding CT
  Veins > 2 mm diameter contain valves: two leaflets of connective tissues (collagen fibres) covered with endothelial cells.

Question 41

Why do veins > 2mm thick contain valves ?

Answer 41

To prevent back-flow of blood.