HOW DOES the BRAIN DEVELOP?
The brain and spinal cord (our “Central Nervous System”) start out as a sheet of cells called the neural plate. These cells divide and fold to form the neural folds that eventually close together to form the neural tube. The cells of the neural tube will continue to divide and turn into all of the cells that form the brain and spinal cord.
Pictures of cross sections of chick neural tubes (yellow arrows) at different stages of development. This picture was made using scanning electron microscopy.
Picture of a chick neural tube. This picture was made using scanning electron microscopy. The round structures are somites that become other structures later in development.
As the cells in the neural tube continue to divide they eventually form the brain at one end with the rest of the neural tube forming the spinal cord.
Stages of human brain development. One end of the neural tube will undergo massive numbers of cell divisions giving rise to all of the cells of the brain. The brain must fold many times so that it can fit inside of the skull. Times shown are post-conception.
The brain is made up of many different types of cells
The cells that form the circuits of our brains. Electrical impulses enter through dendrites and are transmitted down the axon.
The long branches of these cells make contact with the axons of neurons, wrap around the axons, and form a substance called myelin that increases the speed of nerve impulses.
There are more astrocytes in the brain than any other cell type. They play a role in regulating how neurons communicate with each other and also form scar tissue when the nervous system is damaged,
SYNAPSE: from the Greek “synaptein” – to fasten together
Neurons are connected to one another to form circuits via synapses. These are chemical connections where axons can connect to dendrites or to other axons (many axons, for example, can connect with branches of dendrites). Electrical signals that travel down axons cause the release of chemicals called neurotransmitters (like dopamine, epinephrine, acetylcholine) that are taken up by proteins on the surface of dendrites, signaling an electrical impulse in the next cell in the circuit. Other proteins (enzymes) in the synapse destroy excess neurotransmiiters.
MYELIN: Making nerve impulses travel faster
Myelin made by oligodendrocytes does not cover the entire axon. There are interruptions in the myelin called nodes of Ranvier. Signals jump from one node to the next, increasing the speed of electrical impulses 100 times!
A cross section of an myelinated axon viewed using an electron microscope. The arrow is pointing to a small portion of the oligodendrocyte that made the myelin. Note that the myelin wraps many times around the axon.
Three critical processes needed for brain developmental and brain maintenance throughout life can each be influenced by music:
During development and throughout life cells called neural stem cells can become new neurons (shown here in green), new oligodendrocytes or new astrocytes. Learning and memory require the formation of new neurons (neurogenesis) and new oligodendrocytes and astrocytes (gliogenesis)
After neurons are born, they need to form synapses (a process called synaptogenesis). New synapses form when we learn new things, and old synapses are strengthened when we rehearse things that we have learned.
Some axons need to be myelinated to increase the speed at which they conduct nerve impulses. This process, achieved by oligodendrocytes, is called myelination.