Muscle

Question 1

What type of PNS innervation are the 3 types of muscle cells?

Answer 1

Skeletal= somatic motor
Cardiac= involuntary automatic nervous system control
Smooth= involuntary automatic nervous system control

Question 2

1. What does skeletal muscle look like on a slide?

2. Difference between cardiac and smooth muscle on a slide?

Answer 2

1. Many muscle cells are fused together
2. Cardiac cells are separated by intercalated discs; smooth cells are separated by ECM (on slide, cardiac looks like there is more white spots - glycogen)

Question 3

Hierarchical levels of organization of skeletal muscle? (From big to small)

Answer 3

Muscle fascicles, muscle fiber, myofibril, sarcomere

Question 4

3 connective tissue layers that surround and subdivide skeletal muscle?

What do these connective layers contain?

Answer 4

Epimysium, perimysium,
Endomysium

Blood vessels and nerves supplying muscle cells

Question 5

When staining a skeletal muscle slide, which type of fiber looks darker?

Answer 5

Dark staining = slow twitch fibers

Light staining = fast twitch fibers

Question 6

Function of the sarcoplasmic reticulum?

Answer 6

Ca2+ storage site; releases Ca2+ into cytoplasm when muscle is activated

Question 7

What is a triad?

Answer 7

Cell membrane of muscle cell forms T tubules arranged in parallel with sarcoplasmic reticulum (terminal cisterna) — triads can cause the SR to release its Ca2+

Question 8

muscle contraction: Inside a myofibril, two major types of proteins are anchored at the ___

Answer 8

Z line

Question 9

Thick filaments = ?
Thin filaments are combination of 3 things = ?

Which ones are anchored to the Z line?

Answer 9

Thick = myosin
Thin= actin, tropomyosin and troponin

Thin

Question 10

What causes skeletal muscle to appear striped (striated)?

Answer 10

Sarcomere

Question 11

Sarcomere extends from the ___ (location)

What is dystrophin?

Answer 11

Z line which is linked to the sarcolemma

A protein that links the Z line to the cell membrane

Question 12

What is happening in muscle contraction?

Answer 12

Thick and thin filaments pull on each other to shorten the sarcomere and entire muscle

Question 13

Myosin has a head and tail, significance?

Answer 13

Myosin heads have binding sites for actin, ATP, and ATPase

Question 14

What does the enzyme ATPase do?

Answer 14

Releases energy by converting ATP to ADP + Pi

Question 15

Function of troponin?

Answer 15

Can bind tropomyosin and Ca2+

Question 16

Steps of the cross bridge cycle (sliding filament model)

Answer 16

~Before cycle starts, troponin blocks myosin head~
Activation of muscle cell leads SR to release Ca2+
Ca2+ binds to troponin, leading it to expose the myosin head for actin to bind to
ATP binds to myosin head, causing actin to detach
ATP gets broken down and energy is released causing conformational change in myosin head
POWER STROKE= unbinding of Pi leads to strengthened binding of actin, which pulls on the thin filament thus shortening the sarcomere

Question 17

After power stroke step, how does another contraction start or cycle stop?

Answer 17

When no ATP is present, the myosin will remain attached to then actin (so unable to start another contraction) (rigor mortis)

Question 18

So what two things are necessary for muscle contraction?

Answer 18

ATP and Ca2+ release

Question 19

Neural input steps in order to get to the start of the cross bridge cycle?

Answer 19

Nerve impulse triggers release of acetylcholine into synaptic cleft
Acetylcholine binds to ionotropic receptors (Na+ channels) allowing Na+ to enter the cell thus increasing voltage
The voltage change causes Ca2+ release from SR into cytoplasm

Question 20

What is another name for an axon terminal?

Answer 20

Bouton

Question 21

So overall, release of ___ leads to Ca2+ release

Answer 21

Acetylcholine

Question 22

Clinical correlation: Myasthenia Gravis

1. Pathophysiology?
2. How does it present?
3. Diagnostic tests? Will see improvement upon administering?

Answer 22

1. Antibodies are generated against nicotinic acetylcholine receptor
2. Muscle weakness (at first muscle strength will seem the same, but muscle will fatigue much quicker than it should)
3. Detection of nAchR antibodies; administration of acetycholinesterase inhibitor (edrophonium)

Question 23

1. Muscular Dystrophy (Duchenne and Becker Types) is caused by what?
2. More common in boys or girls? How does it present?
3. Difference in onset and progression of Duchenne vs Becker

Answer 23

1. Mutations of dystrophin gene
2. More common in boys (X linked); presents as weakness after achieving motor milestones (crawling, standing, walking, etc.)
3. Duchenne- 3-5 years old, much more rapid progression (inability to walk by 12)
   Becker- 12 year old onset, slower progression (unable to walk by 25)

Question 24

Two sensory structures of skeletal muscle and what they sense?

Answer 24

Muscle spindles- sense muscle stretch

Golgi tendon organs-sense contraction

Question 25

What type of muscle spindle senses the muscle length and speed of stretch? These provide what information to the CNS?

Answer 25

Intrafusal muscle fibers (purely sensory) Proprioception and reflexive contraction of muscle (“muscle tone”)

Question 26

How do golgi tendon organs sense muscle contraction? What information do they send to CNS?

Answer 26

By detecting tension on tendon during muscle contraction (innervate the tendons, not muscle) Proprioception and they mediate 2 reflexes (reflexive inhibition of the same muscle and activates reflexive contraction of opposing muscle)

Question 27

How does one cardiac cell commuicate with another cardiac cell?

Answer 27

Gap junctions

Question 28

Cardiac muscle release hormone like peptides (ANF, atriopeptin, and auriculin) what do they do?

Answer 28

Act at the kidney to promote Na+ and water excretion

Question 29

What are purkinje fibers?

Answer 29

Processes coming off of cardiac conducting cells

Question 30

Energy sources for cardiac muscle?

Answer 30

Primarily metabolize fatty acids but can also use glycogen

Question 31

Autonomic NS control of smooth muscle?

Answer 31

Generally, parasympathetics activate contraction; sympathetics inhibit or do not innervate the muscle

Question 32

Smooth muscle also follows the cross bridge cycle but their filaments are anchored at various points in the cell at ____ that intersect with what?

Answer 32

“Dense bodies” that intersect with intermediate filaments of the cytoskeleton

Question 33

1. What kind of innervation activates Ca2+ release in smooth muscle? 2. What complex does this calcium release activate? 3. This complex activates?

Answer 33

1. Parasympathetic 2. Calcium-calmodulin complex 3. Kinases (which allow formation of the actin-myosin cross bridges)

Question 34

Which muscle type has the slowest contraction? Length of contraction of smooth muscle? Explain?

Answer 34

Smooth (its also graded, not all or none- similar to skeletal) Smooth can also stay in contracted state for extended time ATPase can be inhibited by phosphorylation, blocking cleavage of ATP and release of energy needed to detach myosin head from actin

Question 35

1. What is a myoepithelial cell? | 2. Name 5 instances of these in the body

Answer 35

1. Tissues composed of epithelial cells that contain contractile mechanisms similar to smooth muscle cells 2. Sweat glands, salivary glands, mammary glands, seminiferous tubules of testis and iris