Cardiac Muscle Tissue - Downing

Question 1

General Features of Cardiac Muscle:

Answer 1

Striated (involuntary)
T-tubule system (at z lines, not AI junctions)
Sarcoplasmic reticulum less well developed than in skeletal muscle
Single nucleus/cell; centrally located
Intercalated disks are diagnostic features of cardiac muscle tissue

If things look messy…. its cardiac muscle!

Question 2

What is the comparison in number of mitochondria between cardiac and normal skeletal muscle?

Answer 2

Cardiac has TON of mitochondria!

Question 3

Where do you normally find intercalated discs?

Answer 3

They can be located in spots where you would normally see the Z-disc

Question 4

What parts of the intercalated discs do you see the macula adherens(desmosomes), zonula adherens, and gap junctions????

Answer 4

In the vertical portion:
Zonula adherens
Macula adherens

Horizontal portion:
gap junctions

Question 5

What is microscopic feature unique to atrial cadriac muscle cells?

Answer 5

Atrial granules

Contain atrial natriuretic peptide
Lowers blood pressure by decreasing renal tubules ability to resorb (conserve) sodium and water

Question 6

What are the modified cardiac muscle cells in the conduction system of the heart called?

Answer 6

Purkinje fibers!

Myofibrils reduced in number
Much larger
Contain more sarcoplasm
Nuclei more rounded
Large diameter
Lack T-tubules
More glycogen

Question 7

Referring to their development, why do cardiac muscles have a single nucleus rather than many like in skeletal muscle?

Answer 7

Myoblasts DO NOT fuse in cardiac muscle

Question 8

What is a diad?

Answer 8

Occurs in cardiac muscle

Made up of t-tubule and terminal portion of adjacent sarco reticulum