#neural development

«Poison owner” by @geneartor

06.20.2020 // Figures from yesterday’s study time lapse. Moving onto stem cell biology today. (ig: guavadays)

[♫ Who’s There - Nujabes]

Handedness Arises From Genes in the Spinal Cords of Embryos

Our nervous systems have left-right differences that are important for correct functioning. Handedness is probably the best known asymmetry arising from the development of the nervous system. This is observed very early on: embryos of eight weeks already tend to move their right arms more often than their left arms. At this ‘age’ signals are not sent from the brain to the arms yet, but only from the spinal cord. A few weeks later, left-right differences also become visible in the shape and size of the premature brain.

TA team of scientists from the Netherlands, the UK and China searched for genes that contribute to left-right differences in the nervous system, in the period between four and eight weeks after fertilization. The genetic analysis showed that the left and right sides of the spinal cord develop at different paces.

The left side of the spinal cord matures slightly faster than the right side. Sets of key genes that control growth and maturity were found to reach a more advanced profile of activity on the left side than the right. In the hindbrain, an area which is the predecessor for some adult parts of the brain, this was the other way around.

“This seems logical, since many nerve fibers cross over from one side to the other at the boundary between the hindbrain and spinal cord,” says Carolien de Kovel, lead author of the study and researcher at the Max Plank Institute for Psycholinguistics (MPI). “How exactly this left-right genetic difference in the spinal cord leads to right-handedness is, however, not yet clear.”

“Left-right asymmetry of maturation rates in human embryonic neural development” by Carolien G.F. de Kovel, Steven Lisgo, Guy Karlebach, Jia Ju, Gang Cheng, Simon E. Fisher, and Clyde Francks in Biological Psychiatry. Published online February 1 2017 doi:10.1016/j.biopsych.2017.01.016

Some definitions:

Embryo - the term for what has developed from an egg and sperm up until week 10

Fetus - starting in week 11 up until birth

Baby - offspring after it has been born

Some developmental steps:

At 8 weeks, the embryo has some nerve cells, which are branching out and forming primitive neural pathways.

Almost all organs are completely formed by week 12, except for the brain and spinal cord, which continue to form and develop throughout pregnancy.

Statements on fetal pain:

“In reviewing the neuroanatomical and physiological evidence in the fetus, it was apparent that connections from the periphery to the cortex are not intact before 24 weeks of gestation and, as most neuroscientists believe that the cortex is necessary for pain perception, it can be concluded that the fetus cannot experience pain in any sense prior to this gestation.”  - Royal College of Obstetricians and Gynecologists

“Pain perception requiresconscious recognition or awareness of a noxious stimulus. Neither withdrawal reflexes norhormonal stress responses to invasive procedures prove the existence of fetal pain, becausethey can be elicited by nonpainful stimuli and occur without conscious cortical processing….The review concluded that fetal perception of pain is unlikelybefore the third trimester.” - American College of Obstetricians and Gynecologists

“Evidence regarding the capacity for fetal pain is limited but indicates that fetal perception of pain is unlikely before the third trimester.” - Journal of the American Medical Association

Embryos do not feel pain, they barely have a neural system to transmit pain stimuli.  Fetuses likely don’t feel pain until at least the third trimester, somewhere around 28-30 weeks gestation.  And even then, there’s a lot to be discussed about whether or not that means pain the way the we experience pain.  “[W]hile nociception is neural activity, pain is an unpleasant feeling. It follows that while pain requires some level of consciousness, nociception does not.”  [source]  Does having the ability to transmit the signal mean the fetus is experiencing an ‘unpleasant feeling’?