Musculoskeletal development

Question 1

Describe the appearance of skeletal muscle

Answer 1

• striated, voluntary movement, multinucleated

Question 2

What is the functional unit of muscle

Answer 2

the sarcomere

Question 3

When does mesenchyme differentiate

Answer 3

3- weeks from conception

Question 4

Describe the formation of the mesoderm & the destiny of each

Answer 4

• intra-embryonic mesenchyme differentiates into three loose aggregate pairs of mesenchyme
• paraxial mesoderm: Dermatome (dermis), myotome (muscle), sclerotome (connective tissue)
• Intermediate mesoderm: Urogenital system
• Lateral mesoderm: Body cavities and parts of body wall

Question 5

describe the development of the somites

Answer 5

• the paraxial mesoderm develops into paired cuboidal bodies (somites) - these become the sclerotome, mytome and myotome
• Somites appear as bumps on the dorsal surface of the embryo cranially to caudally
• by 3 weeks there are 4-12 somites present; between days 20-30 most appear (37); this is deemed the somite period of development
• somites can be used to age the embryo

Question 6

What is the law of original innervation

Answer 6

• myoblasts form concurrently with spinal nerves and migrate out from the notochord together
• results in the formation of 31 spinal nerves with associated connective tissue, skin and muscle

Question 7

what is a dermatome

Answer 7

an area of skin receiving mesenchyme from a specific somite that is supplied by a single spinal nerve and its ganglion

Question 8

what is a myotome

Answer 8

a muscle group supplied by a nerve

Question 9

at how many weeks of gestation do muscles deposit in segmental fashion? Form muscle groups?

Answer 9

• 6 weeks: segmental

- 8 weeks: Muscle groups

Question 10

describe the formation of a single muscle fibre from the mesenchyme

Answer 10

• mesenchyme > myoblasts > syncytial myotube > myotubule > _________> Muscle fibre

Question 11

Define mesoderm

Answer 11

• pluripotent connective tissue

Question 12

differentiate presumptive myoblast and myoblast

Answer 12

• P.M: undergoing mitosis, mononucleated cell incapable of fusion, or contractile protein synthesis
• M: Mononucleated cell not undergoing mitosis. Capable of fusion and synthesizing myofibrillar proteins

Question 13

define myotubule

Answer 13

• multinucleated cell formed from fusion of myoblasts. May contain sarcomeres. Nuclei located at centre

Question 14

define muscle fibre

Answer 14

• matured multinucleated muscle cell with myofibrils

Question 15

How does muscle grow prenatally and postnatally

Answer 15

• Prenatal: The number of muscle fibres increases (# doubles btwn 32 weeks gestation and 4 months) i.e hyperplasia
• Postnatal: Girth and length row i.e hypertrophy
• Length increases by: Increasing # of sarcomeres (most important), increase in length of sarcomere.
• Increase length at musclutendinous junctions in response to functional length

Question 16

Differentiate muscle composition of a fetus; term baby and adult

Answer 16

• fetus: Fibres are small in # and widely separated by extracellular matrix
• Term: Fibres are small, increased #, more closely packed
• Adult: Large diameter, little space btwn them
• As we age: Decrease Na/Cl (extracellular), increase in K+/Phosphorus (IC) and decreased % water

Question 17

How can we estimate muscle mass through development (list)

Answer 17

• Creatinine clearance
• K40 Estimate of fat free mass
• Skin fold adjusted girth

Question 18

Describe the method of creatinine clearance

Answer 18

Collect urine, amount of creatinine excreted links to muscle mass - 1 g creatinine = 20 kg muscle mass sensitive to diet and exercise

Question 19

Describe the method of K40 estimate of fat free mass

Answer 19

• assume a constant proportion of potassium in fat free mass
• utilize gamma ray spectroscopy to measure K40 emmissions
• expensive, large error in individual estimates*

Question 20

Describe the use of skinfold adjusted girths

Answer 20

• Indicator of muscularity

- Ga = G - (3.14 x S)

Question 21

Describe the variations in muscularity btwn boys and girls

Answer 21

• Similar up until puberty; testosterone levels spike in boys
• %muscle mass decreases in girls due to a gain in secondary sexual adipose tissue

Question 22

Describe variations in strength between boys and girls

Answer 22

• No difference when expressed per unit of cross sectional area of muscle
• Disproportionate strength increase in boys; more in upper extremities
• No significant difference in lower extremity strength after adjusting for height

Question 23

When does peak strength velocity occur relative to peak height velocity? Why? Does this occur first in boys or girls?

Answer 23

• Approximately 1.5 years after PHV
• Because the muscle length has to catch up to the bone length first, then the diameter can grow leading to an increase in strength
• Occurs first in boys

Question 24

When is peak muscle maturity reached

Answer 24

• not until late 20’s

Question 25

Describe the proper way to weight train in children and the benefits involved

Answer 25

• Train with individual monitoring
• Lots of effort and little benefit in terms of building muscle mass prior to puberty; however training has long lasting effects such as coordination and better recruitment

Question 26

Describe type I and type IIa/b fibres and their proportions in childhood compared to adulthood

Answer 26

• Type I: Red slow twitch
• Type IIa/b: White fast twitch
• High proportion of type I and undifferentiated type IIc during early/mid-childhood
• More Genetic influence of fibre type than environmental