Question

b. How many neurons are there 3 months after conception? c. At what age do sulci (valleys) and gyri (hills) beginto form? d. How many neuros are present around the time of birth? e. How many neurons are formed after birth? f. Indicate whetherthe following statement is true orfalse: Neurogenesis does notoccur in adulthood.

Answer 1

Ans B: Production of neurons begins around day 42 after conception and then neurons grow at the rate of 250,000 neurons per minute. Hence three months is 91 days, production of neurons starts at 42 day, therefore number of neurons formed in(91-42=49 days) is:

1 day = 1440 minutes

49 days = 70560 minutes

1 minutes = 250000 neurons

Therefore, 70560 minutes = 70560 × 250000 neurons

= 17640000000 neurons or 17.64 billions or approximately 18 billions neurons at 3 months of conception.

Ans C: Primary cortical gyri forms first during the 10th week of pregnancy followed by secondary and tertiary gyri as the fetal development progresses. Most cortical gyri and sulci begins to take shape between 24 weeks to 38 weeks of pregnancy and continue to enlarge and mature after birth.

Ans D. At the time of birth there are more than 100 billion neurons.

Ans E: The number of neurons after birth remains same i.e more than100 billion neurons but after birth axons, dendrons and synapses increases which leads to increase in Brain size.

Ans F: The statement, Neurogenesis does not occur in adulthood is FALSE. Neurogenesis in adulthood occurs in Hippocampus and Olfactory bulb of brain.