Brain Development - Embryo 54 Day Old Central Nervous System
Image Caption : Embryo 54 Day Old Central Nervous System : Computer Generated Image from Micro-MRI, actual size of embryo = 26.0 mm - This image provides a dorsal view of the embryo during its eighth week of development. The age is calculated from the day of fertilization. The image has been manipulated so that the skin appears translucent. The primary focus of this image is the central nervous system. The two main organs that comprise this system are the brain and spinal cord which are highlighted in orange. The three main components of the brain can be observed. The largest portion in the front of the head is called the forebrain, the narrow middle segment is called the midbrain, and the hindbrain is the portion that connects the midbrain with the spinal cord. The nerve endings surrounding the spinal cord are indicated in white.
The Growing Brain
Inside the Brain: Neurons & Neural Circuits
Neurons are the basic working unit of the brain and nervous system. These cells are highly specialized for the function of conducting messages.
A neuron has three basic parts:
- Cell bodywhich includes the nucleus, cytoplasm, and cell organelles. The nucleus contains DNA and information that the cell needs for growth, metabolism, and repair. Cytoplasm is the substance that fills a cell, including all the chemicals and parts needed for the cell to work properly including small structures called cell organelles.
- Dendritesbranch off from the cell body and act as a neuron's point of contact for receiving chemical and electrical signals called impulses from neighboring neurons.
- Axonwhich sends impulses and extends from cell bodies to meet and deliver impulses to another nerve cell. Axons can range in length from a fraction of an inch to several feet.
Each neuron is enclosed by a cell membrane, which separates the inside contents of the cell from its surrounding environment and controls what enters and leaves the cell, and responds to signals from the environment; this all helps the cell maintain its balance with the environment.
Synapses are tiny gaps between neurons, where messages move from one neuron to another as chemical or electrical signals.
The brain begins as a small group of cells in the outer layer of a developing embryo. As the cells grow and differentiate, neurons travel from a central "birthplace" to their final destination. Chemical signals from other cells guide neurons in forming various brain structures. Neighboring neurons make connections with each other and with distant nerve cells (via axons) to form brain circuits. These circuits control specific body functions such as sleep and speech.
The brain continues maturing well into a person's early 20s. Knowing how the brain is wired and how the normal brain's structure develops and matures helps scientists understand what goes wrong in mental illnesses.
Scientists have already begun to chart how the brain develops over time in healthy people and are working to compare that with brain development in people mental disorders. Genes and environmental cues both help to direct this growth.
The National Institute of Mental Health (NIMH) is part of the National Institutes of Health (NIH)
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