What are neurons
They are collection of cells in the nervous system, that are specialized in transmitting the information to other nerve cells, muscle cells, glands cells by generating and conducting the action potential
The mammalian brain contains between 100 million and 100 billion neurons, depending on the species. Each mammalian neuron consists of a cell body, dendrities, and an axon.
According to Suzana Herculano-Houzel neuroscientist : on average the human brain has 86 billion neurons.
Note : they are also supportive cells ; their job is to support neurons, they are the connective tissue cells of the nervous system (they are known as neuro glia cells)
The parts of the neuron :
Cell body (contains the nucleus and cytoplasm ; the interior of the soma)
Dendrites : they extend from the neuron cell body and receive messages from other neurons.
Axon : he extends from the cell body and often gives rise to many smaller branches before ending at nerve terminals (axon terminals)
When neurons receive or send messages, they transmit electrical impulses along their axons, which can range in length from a tiny fraction of an inch (or centimeter) to three feet (about one meter) or more to the axon terminales
At the end of the terminal button you have the synapse (Neurotransmitters).They are used to carry the signal across the synapse to other neurons. When an electrical signal reaches the terminal buttons, neurotransmitters are then released into the synaptic gap.
Many axons are covered with a layered myelin sheath, which accelerates the transmission of electrical signals along the axon (picture on the top).This sheath is made by specialized cells called glia (supportive cells)
Note : In the brain, the glia that make the sheath are called oligodendrocytes, and in the peripheral nervous system, they are known as Schwann cells.
Node of Ranvier : they are the periodic gap in the insulating sheath on the axon of certain neurons that serves to facilitate the rapid conduction of nerve impulses
How does the neurone activate ?
With the axon hillock wich is located at the end of the soma.The axon hillock controls the firing of the neuron. If the total strength of the signal exceeds the threshold limit of the axon hillock, the structure will fire a signal (known as an action potential) down the axon to the terminales
Neurons in Other Animals
- Mouse: 75 million neurons5
- Cat: 250 million neurons6
- Chimpanzee: 7 billion neurons
- Elephant: 257 billion neurons
“Any man could, if he were so inclined, be the sculptor of his own brain.” Santiago Ramon y Cajal, Advice for a Young Investigator