DLA 24 + lecture 34

Question 1

What are the two general classifications of muscle tissue?

Answer 1

striated and smooth

Question 2

What muscle tissues are striated?

Answer 2

skeletal, visceral, and cardiac

Question 3

What classification of muscle are voluntary?

Answer 3

skeletal and visceral

Question 4

what classification of muscle are involuntary?

Answer 4

cardiac and smooth

Question 5

Where is skeletal muscle found?

Answer 5

somatic/ body wall

Question 6

Where is visceral muscle found?

Answer 6

Soft tissue origin. Tongue, pharynx,

larynx, diaphragm and upper esophagus

Question 7

Where is cardiac tissue found?

Answer 7

heart and roots of great veins

Question 8

Where is smooth muscle found?

Answer 8

Walls of visceral organs. Stomach, gut tube etc

Question 9

describe the epimysium?

Answer 9

Dense connective tissue encasing
multiple fascicles.
• Contains major blood vessels and
nerves
• Continues with tendon to attach
muscle at the myotendinous
junction

Question 10

Describe the perimysium?

Answer 10

Groups of skeletal myocytes/fibers form a
fascicle (F)
• Each fascicle is surrounded by a layer of
connective tissue or perimysium
• Contains larger blood vessels & nerves

Question 11

Describe the endomysium?

Answer 11

Delicate layer of reticular fibers
that surrounds individual muscle
fiber (myocyte)
• Contains small blood vessels
and very fine neuronal
branches

Question 12

What does skeletal muscle look like histologically?

Answer 12

Multiple nuclei peripherally located
Long cylindrical cells
Striations

Question 13

What does cardiac muscle look like histologically?

Answer 13

Intercalated discs
Centrally located nucleus
Branched cells
Striations

Question 14

What does smooth muscle look like histologically?

Answer 14

Spindle-shaped cells

Centrally located nucleus

Question 15

What is the sliding filament hypothesis of huxley?

Answer 15

Sarcomere shortens and becomes thicker, but the
myofilaments remain the same length.

Sliding action results from repeated “make
and break” attachments between the heads
of the myosin molecules and neighboring
actin filaments

A band = constant
I and H band = both decrease in size
Z band = are drawn closer to the ends of the A bands

Question 16

What are the stages of contraction?

Answer 16

1. attachment/ reattachment
   myosin head is tightly bound to actin. No ATP
2. release
   ATP binds to the myosin head
3. bending
   ATP hydrolysis induces conformation change and movement of myosin head
4. Force generation
   I. myosin head weakly binds to actin, this leads to the release of Pi
   II. powerstroke: the myosin head produces force as it returns to its normal position
   III. As the myosin head straightens, it forces movement of the thin filament

Question 17

How is a sacromere defined?

Answer 17

The segment of the myofibril between two adjacent Z lines

the functional unit of the myofibril and the basic unit of contraction

Question 18

What are the contractile element of skeletal muscle?

Answer 18

Myosin II (thick filaments)

Actin (thin filaments)

Question 19

What are the associated proteins of the thin filaments

Answer 19

1. tropomyosin
2. tropomodulin
3. troponin complex

Question 20

What does tropomodulin do?

Answer 20

capping protein which maintains & regulates length of the actin filaments

Question 21

What makes up the troponin complex?

Answer 21

troponin C (TnC) = binds calcium

troponin T (TnT) = binds to tropomyosin and anchors troponin complex

Troponin I (TnI) = inhibits the interaction between myosin and actin

Question 22

what does myomesin and C-protein do?

Answer 22

accessory protein to myofilaments

Myosin binding protein that aligns thick filaments at M line

Question 23

What does myosin binding protein C do?

Answer 23

accessory protein to myofilaments

Associated with the M line and important for the assembly andstabilization of the thick filament

Question 24

What does titin do?

Answer 24

Spring like protein→ keeps thick filament centered between two the Z lines of the sarcomere and prevents excessive stretching

Question 25

What does nebulin do?

Answer 25

helps anchor thin filaments at Z line and regulates length of thin filaments during development

Question 26

What does A-actinin do?

Answer 26

Actin binding protein that bundles and helps stabilize thin filaments at Z line

Question 27

What does desmin do?

Answer 27

Surrounds the sarcomere at Z lines attaching them to one another and to the sarcolemma

Question 28

What does the protein dystrophin do? what happens if this protein does not work properly?

Answer 28

is a rod-shaped cytoskeletal protein which links to ECM proteins laminin & agrin found in the external lamina of the myocyte

if not working muscular dystrophy is the result

Question 29

What is myasthenia gravis?

Answer 29

an autoimmune disease which impacts the neuromuscular junction

Acetylcholine (Ach) receptor antibodies, which block and attack ACh receptors in the postsynaptic membrane

Question 30

What do fewer Ach receptors result in?

Answer 30

fluctuating weakness and fatigue of the skeletal muscles

Ocular, bulbar, limb and respiratory muscles
are affected

Question 31

What are intercalated discs in cardiac tissue?

Answer 31

they are attachment sites between adjacent cardiac myocytes

Question 32

What are the transverse components of cardiac tissue

Answer 32

1. fascia adherens- binds cardial myocytes at their ends

2. maculae adherentes (desmosomes) = bind muscle cells to each other

Question 33

What is the lateral component of cardial tissue?

Answer 33

gap junctions

Question 34

what type of fibers are found in cardial tissue?

Answer 34

purkinje fibers

Specialized to conduct impulses of the A-V bundle and allow synchronization of ventricular contraction
(few myofibrils, lots of glycogen and mito)

Question 35

What characteristics does smooth muscle have?

Answer 35

Elongated, fusiform cells with tapered
ends
generally organized into bundles or
sheets
No cross-striations thus even staining
with H&E staining

A central nucleus

Question 36

How are smooth muscle cells interconnected?

Answer 36

gap junctions

Question 37

explain smooth muscle contraction?

Answer 37

Contraction is regulated by the Ca2+-calmodulin-MLCK system

1. Increase in Ca2+ concentration
2. Ca2+ binds to calmodulin forming the Ca2+ -calmodulin complex
3. Ca2+ -calmodulin complex binds MLCK
4. MLCK phosphorylates regulatory light chain of myosin
5. Actin-binding site of myosin head is activated & attaches to actin

Question 38

How is smooth muscle contraction regulated?

Answer 38

1. mechanical - Passive stretching of vascular
   smooth muscle activates myogenic reflex
2. Electrical - neural stimulation
3. chemical - use of second messenger pathways

Question 39

what muscle types can go through hypertrophy?

Answer 39

skeletal - yes

cardiac- Hypertrophy as in hypertensive
cardiomyopathy

smooth - yes

Question 40

what muscle types can go through hyperplasia?

Answer 40

skeletal- no

cardiac- no

smooth- yes in certain conditions

Question 41

how does skeletal muscle respond to injury?

Answer 41

Satellite cells are responsible for skeletal muscle
regeneration
Regenerative capacity is limited

Question 42

How does cardiac muscle respond to injury?

Answer 42

No regenerative capacity

After the death of cardiac muscle cells, the tissue is replaced with fibrous connective tissue (A)

Cardiac function is lost at site of injury

Question 43

How does smooth muscle respond to injury?

Answer 43

vascular injuries can be repaired