Neurons

The word neuron was first used in 1884 and is the base of the nerve system. Neurons are the primary cells of the nervous system. A human is born with approximately 100 billion neurons, which are mostly located in the brain. Neurons are responsible for all of our actions; the cells receive messages from different sources and then transmit them to other parts of our body. Neurons carry messages from the brain to other body parts through a form of electrical impulses.

Unlike other body tissue, neurons do not have the ability to repair themselves if damaged by an injury or disease. For example, hands are most probably touching a keyboard or mouse right now as you read this. The reason you have the sense of touch is because the neurons created for that type of information are communicating between your hands and your brain transmitting the message. It is also the way that we can feel and tell the different between hot and cold or comfort and discomfort.

Anatomy:

• Many different types of neurons exist, in size they have no symmetry, and consist of the soma, which is the mostly fat and the central part. There is also the axon, which can be larger than the soma by tens of thousands of diameters. Projecting next to the axon are the dendrites, which are about the size of a micrometer.

Nervous Impulses:

• Nervous Impulses enter the neuron through the dendrites and travel to the axon. The axon transmits the impulse to the dendrites of the following neuron, always in the same ongoing direction.

There are three classes of neurons:

• Afferent neurons convey information from tissues and organs into the central nervous system.
• Efferent neurons transmit signals from the central nervous system to the effector cells.
• Interneurons connect neurons within the central nervous system.

Connectivity:

• Neurons join to one another and to other cells through synapses, which connect the axon tip of one cell and to a dendrite of another, or less commonly to its axon or soma. Neurons of the cortex in mammals, such as the Purkinje cells, have over 1000 dendrites apiece, enabling connections to tens of thousands of other cells.

Types of Signaling:

• Neurons stimulate one another across synapses chemically by rapid secretion of neurotransmitter molecules. They are known most, however, for their ability to undergo electrical excitation and to transmit this excitation along their axons as an impulse.

Neurons of the brain:

• There are about 100 billion neurons in the human brain.