Week 6 Reading

Question 1

What is muscle spasticity

Answer 1

a condition where muscles become stiff, tight, and difficult to control due to continuous, involuntary muscle contractions.

Question 2

What does muscle spasticity lead to?

Answer 2

leads to muscle contractures that limit range of motion and cause increased muscle stiffness

Question 3

what is titin

Answer 3

a major load bearing protein within muscle fibers

Question 4

why do children with spastic cerebral palsy develop hamstring contractures

Answer 4

due to a stiffer extracellular matrix (ECM) and longer sarcomeres in their muscles

Question 5

What did the study find?

Answer 5

while individual muscle fibers and the titin protein (which helps muscles stretch) were unchanged, the ECM was stiffer due to increased collagen.

Question 6

what does cerebral palsy result from?

Answer 6

an upper motoneuron lesion in the developing brain

Question 7

What did the combination of increased tissue stiffness and increased sarcomere length lead to?

Answer 7

leads to higher muscle tension and contractures

Question 8

What did they find was the cause of contracture formation?

Answer 8

Stiffening of the ECM with increased collagen and an increase of in vivo sarcomere length - leading to higher passive strength

Question 9

what is spastic

Answer 9

a velocity dependent resistance to stretch due to reduced inhibition of the stretch reflexes

Question 10

what do children with CP experience?

Answer 10

contractures that limit their range of motion, decrease mobility, and cause pain

Question 11

what is contracture?

Answer 11

a muscle adaptation where the muscle increases passive stiffness where the range of motion around a joint is limited without active force production of the muscle

• meaning: the muscle becomes stiffer and less flexible without the muscle actively contracting (even if ur not trying to use it)

Question 12

What did this study compare? to find what?

Answer 12

hamstring muscles from children with CP to those from non-CP children undergoing surgery, aiming to identify what causes increased muscle stiffness in CP.

Question 13

potential explanation for why spasticity results in contractures:

Answer 13

spastic muscles from children with CP are weaker than those of developing control children bc of a combination of decreased neuronal drive, decreased muscle size, and decreased specific tension

Question 14

how does caffeine increase tension of isolated muscles?

Answer 14

Caffeine induces calcium release from the sarcoplasmic reticulum and potassium depolarizes the muscle as methods to activate the crossbridge cycle that produces muscle active tension

(cross bridge cycle is where the fibers generate contractions)

Question 15

whats different about contractures from our normal contractions?

Answer 15

our muscles normally contract all the time, but in a controlled and voluntary way.

In contractures, the stiffness is passive—the muscle remains tight even without active contraction, meaning the restriction in movement is due to structural changes in the muscle, rather than the usual processes of voluntary movement.

Question 16

what do they think contracture results from?

Answer 16

shortened muscles - they did multiple ultrasounds to measure fasciae length and only confirmed reduced CP muscle volume.

Question 17

what is a major drawback of ultrasound studies?

Answer 17

there is no normalization of fascicle length to sarcomere length

Question 18

What did direct measurement of intraoperative sarcomere length reveal

Answer 18

They revealed that sarcomere lengths are indeed longer in CP muscle, suggesting increased passive stiffness.

When sarcomeres are too long, the muscle becomes less able to stretch and contract effectively, leading to stiffness and reduced range of motion (contracture).

(bc their length determines how much a muscle can stretch and contract effectively AND SO in children with CP, muscles do not grow normally due to impaired neural control. Instead of having more short sarcomeres in series (which would allow for flexibility), the existing sarcomeres stretch longer to compensate for the muscle’s restricted length which is associated with increased passive stiffness.

Question 19

explain the theory for increased passive stiffness that involves the alteration of the tissue itself

Answer 19

Studies found that individual muscle fibers from contractured muscles were stiffer than normal ones, suggesting that something inside the muscle cell was altered. They hypothesized that titan was the cause. After looking at bundles of muscle fibers, they found these were actually more flexible than normal which meant the stiffness wasn’t due to titin.

Question 20

Researchers hypothesize that the stiffness might be due to changes at multiple levels including:

Answer 20

• protein (titin)
• cellular (fibre)
• tissue (fibre bundle)
• architecture (sarcomere length)

Question 21

What were custom muscle biopsy clamps used for?

Answer 21

to determine in vivo sarcomere length in children with cerebral palsy (CP) undergoing hamstring lengthening surgery.

Question 22

What steps were taken to prepare the gracilis and semitendinosus muscles for sarcomere length measurement?

Answer 22

After a skin incision, the muscles were identified, a small segment was isolated atraumatically, and the custom clamp was applied without tension on the muscle.

Question 23

How was the muscle biopsy preserved after being resected?

Answer 23

The muscle section within the jaws of the clamp was immediately placed in Formalin to fix the biopsy specimen in its in vivo configuration.

Question 24

For muscle mechanical testing - they stretched the muscle fibers, measured the mechanical properties, and recorded stress relaxation during the stretches
1. what was measured during each stretch?
2. how much were the fibers stretched

Answer 24

1. stress relaxation
2. 100% strain

Question 25

How did researchers quantify titin isoforms? What were titin standards obtained from?

Answer 25

They looked at the molecular mass of titin in muscle samples using SDS-VAGE. Obtained from human cadaver soles and rat cardiac muscle.

Question 27

How did researchers quantify MyCh isoform distribution in muscle samples? How did they read the results? (MyCH = Myosin Heavy Chain isoforms, refer to different forms of the myosin protein found in muscle fibers)

Answer 27

They used BCA protein assay to measure protein concentration, then resuspended the protein in a sample buffer. The gels were run at a constant current and voltage, followed by silver staining to visualize MyHC bands. Progression of the band was compared and identified based on its relative molecular weight to that of a human protein standard prepared from a normal semitendinosus biopsy that showed all three human MHC bands (IIa, IIx and I) ^ that means: the researchers compared the bands they obtained from their protein samples to a "standard" protein sample. The standard was created from a normal human semitendinosus biopsy (a muscle from the back of the thigh), which showed the three main MyHC isoforms (Type I, IIa, and IIx). These isoforms have different molecular weights, so by comparing the molecular weights of the bands in the test samples to the known weights of the standard proteins, they could identify which MyHC isoform was present in the sample.