Muscle Microanatomy

Question 1

Myoblast are derived from mesenchymal cells (embryonic ct) what do they form

Answer 1

myoblast fuse to form a myotube and some myoblast become satellite cells.

Question 2

What do satellite cells do?

Answer 2

they are able to proliferate after injury

Question 3

Muscle fibers are surrounded by what?

Answer 3

endomysium

Question 4

what are fascicles surrounded by ?

Answer 4

Perimysium

Question 5

The muscle organ is surrounded by a tough fibrous ct called ?

Answer 5

epimysium

Question 6

What are the featuresof type 1 muscle fiber?

Answer 6

lots of myoglobin and mitochondria , used for extended periods of slow contraction. example : muscles on the back for posture

Question 7

features of type IIa muscle fiber?

Answer 7

intermediate fibers rich in myoglobin and glycogen .

use for extended periods of slow contractions with high peak tension , example limb muscles

Question 8

type IIb fiber?

Answer 8

large fibers rich in glycogen few mitochonria and myoglobin

use for rapid contraction, high peak tension and fatigue quickly

Question 9

How do you know there is high oxidative enzyme activity ?

Answer 9

dark staining indicates high oxidative enzyme activity

Question 10

Myofilaments are organized in contractile units called?

Answer 10

Sarcomeres

Question 11

How is the sarcomere defined?

Answer 11

from z disk to z disk

Question 12

How does the A zone look?

Answer 12

dark portion of the sarcomere represented by the location of myosin , some overlap with actin/thin filaments.

Question 13

M line?

Answer 13

standing for middle of sarcomere a region for anchor protein for myosin

Question 14

I band

Answer 14

only thin filaments no region of overlap

Question 15

what links actin to basal lamina ? what disease is associated with this?

Answer 15

dystrophin, in muscular dysttrophy this is targeted

Question 16

what attaches z lines to other z lines and sarcolemma

Answer 16

desmin

Question 17

what protein anchor thick filament to adjacent z lines

Answer 17

titin

Question 18

What happens when Ca2+ is sequestered back to the SR?

Answer 18

it stops contraction because the binding site of Troponin C on actin will be blocked so the muscle will relax

Question 19

what happens if atp is not available to bind the sarcomere

Answer 19

if no atp, then myosin stays attached because atp binding is what happens in order for myosin to be released which this leads to rigor mortis

Question 20

in a contracted sarcomere what is not visible?

Answer 20

the I band or H band.

Question 21

In skeletal muscle a triad formation is formed, what is this?

Answer 21

one t tubule and two terminal cisternae of SR at junction of a band and i band.

Question 22

What happens in the autoimmune disease Myasthenia gravis?

Answer 22

antibodies bind acetylcholine receptors in the junctional folds of the motor endplate and therefore no innervation . symptoms weak movement of muscles (hypotonia)

Question 23

how can you increase muscle mass?

Answer 23

by hypertrophy, on the contrary if you don’t work out like most of us med students we get atrophy of muscles
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Question 24

What are some characteristics of cardiac muscle?

Answer 24

fibers have 1-2 centrally located nuclei, striations are present, sarcoplasm contains elongated mitochondria, and glycogen granules.

Question 25

What are some characteristics of cardiac muscle?

Answer 25

fibers have 1-2 centrally located nuclei, striations are present, sarcoplasm contains elongated mitochondria, and glycogen granules.

adjacent cells connected by specialized juncions

Question 26

for the conducting system for cardiac muscle how does it differ from skeletal?

Answer 26

SR is similar to skeletal muscle, gap junctions, and a diad instead of the triad formation.

Also intercalated discs available

Question 27

why does cardiac tissue if it dies does not repair and become fibrous scar?

Answer 27

because in cardiac cells there is not satellite cell. if tissue die there will be scarring.

Question 28

What are some characteristics of smooth muscle tissue?

Answer 28

found in visceral (involuntary) organs and blood vessels, with a centrally located nucleus oval shape and long. No striations!!

Question 29

What are some examples of molecules that affect Smooth Muscle?

Answer 29

atrial natriuretic factor a vasodilator , oxytocin in labor