Every neuron is made of a cell body (also called a soma), dendrites and an axon. Dendrites and axons are nerve fibres. There are about 100 billion neurons in the human brain, which comprises roughly 10% of all brain cells. The neurons are supported by glial cells and astrocytes.
Neurons are connected to one another and tissues. They do not touch and instead form tiny gaps called synapses. These gaps can be chemical synapses or electrical synapses and pass the signal from one neuron to the next.
Types of neurons
There are three classes of neurons: afferent neurons, efferent neurons, and interneurons.
- Afferent neurons carry information from tissues and organs into the central nervous system.
- Efferent neurons transport signals from the central nervous system to the effector cells.
- Interneurons connect neurons within the central nervous system.
Sensory neurons carry signals from sense organs to the spinal cord and brain.
Relay neurons carry messages from one part of the CNS.
Motor neurons carry signals from the CNS to muscles, motor neurons are connected to the relay neurons. The signal passes between the neurons via synapses. Synapses are microscopic voids between cells where chemicals are released from the axon terminal of one cell to specialized chemical receptors on the dendrite of the receiving cell.
Mature neurons never divide: that is the general rule. They do not do not undergo cell division. In most cases, neurons are generated by special types of stem cells. A type of glial cell, called astrocytes, have also been seen to turn into neurons. In humans, neurogenesis (the origin of new nerve cells) largely ceases during adulthood – but in two brain areas, the hippocampus and the olfactory bulb, there is strong evidence for substantial numbers of new neurons.
The largest part of the human brain by far is the neocortex. It has at least~1010 neurons which stay with us from cradle to grave.
Images for kids
SMI32-stained pyramidal neurons in cerebral cortex
Neuron Facts for Kids. Kiddle Encyclopedia.