Voyage of Life: Week 9
Brain activity and spontaneous movements
- Post-conception week 7
- Days 42-48
- Gestational Week 9
The embryo’s heart has formed all four chambers.1
The embryo’s heart rate peaks in week 9 around 170 beats per minute, making the heartbeat almost twice as fast as mom’s.2
Pockets of cells that resemble taste buds appear on the tongue.3
Knees and elbows appear.
Toes start to form, and the tissue between the fingers becomes thin.4
This week, the cortex, or the thinking and sensing part of the brain, doubles in size.5 The inner ear starts forming. Sounds turn into brain signals in the cochlea, a snail shaped tube in the inner ear. The tube that becomes the cochlea grows in a spiral fashion so that two weeks later it has completed 2 ½ turns. The outer ear also starts forming.
Brain cells, called neurons, have already connected to one another. Networks of neurons produce immature patterns of brain activity, or “brain waves,” that have been recorded during surgeries on ectopic pregnancies when the embryo was 8 ½ weeks gestation.6 The preborn baby starts spontaneously moving his arms, hands, and legs.7 Ultrasound recordings also show that the embryo can hiccup.8
Cartilage starts to harden and become bone in week 9. The first bones to form in the embryo are the collar bone and the jaws.9 Knees and elbows start developing.
The first several weeks of eye development are like watching an orchestra warm up. Different cells and tissues develop simultaneously and quickly as they prepare to work together to create a functional eye. The eye begins to develop 17 days after conception.10 Out of the ectoderm and mesoderm, the cornea and lens form. Simultaneously, the back of the eye grows like a cord out from the young brain. By eight weeks, the lens can be easily seen, as can the iris and the critical neural connection between the eye and the back of the brain. This week, muscles that move the eyes around continue growing and the eyelids begin forming.11