Things can be very complicated when thinking about the nervous system in detail. There are a lot of parts and processes that are not discussed as it is such a complicated system. However, some individuals want to know more about the nervous system's structure when considering information about their disease or injury or hearing about a breakthrough or treatment.
The nervous system consists of two parts. The central nervous system (CNS consists of the brain and spinal cord). The brain receives and sends messages. The spinal cord carries the messages to and from the body. The peripheral nervous system (PNS) consists of all the nerves in the body outside of the brain and spinal cord. Both the CNS and PNS work together to manage and control everything that goes on inside the body, as well as responses to the outside world.
Units of the nervous system are neurons. Neurons are one nerve consisting of three parts. The cell body is full of cytoplasm, which consists of water, salts, and organic molecules. The cell nucleus (which controls cell actions) and mitochondria (the cell’s power source) are also here. From the cell, body is a long arm called an axon, which is a branch between the cell body and the dendrites. Axons are coated with myelin to keep the transmission flowing efficiently. The dendrites transmit electrochemical signals from other nerve cells to the neuron cell body control center and carry the neuron response to other nerve cells.
There are cells in the body whose job is to support nerve cells. The role of supporting cells is to provide protection and metabolic (energy) support.
Supporting cells of the Central Nervous System (CNS) include:
Oligodendrocytes: form the myelin protection in the CNS. When there is damage to oligodendrocytes, messages do not flow smoothly to the cell body and can even prevent messages from being transmitted or received.
Astrocytes: are the links between the nerves and blood vessels. They transport oxygen to the nerve and carbon dioxide away from the nerve, as well as bring nutrients to the cell for metabolism. They balance calcium and potassium in the intracellular fluid. Damage to astrocytes can lead to cell death. These cells are located in CNS gray matter. Astrocyte cells are loaded with fibers that will form a scar in the CNS if it is damaged. This particular scar is called gliosis.
Microglial cells: clean debris after CNS cell damage, infection, or cell death. They are specialized macrophage cells (cells that tidy up the area).
Ependymal cells: form from the lining of the fetal brain CNS development called the neural tube cavity. Eventually, some of these cells will join with parts of the vascular system to form the choroid plexus, which is responsible for the production of cerebral spinal fluid. Damage to these cells can upset the balance of cerebral spinal fluid, brain metabolism, and waste removal from the CNS.
Nerve cells: small cells compared to many of the other body cells. In the CNS, nerve cells are the primary cells. In the PNS, other body cells can crowd nerve cells which are comparatively small in size and number.
Supporting cells of the Peripheral Nervous System (PNS):
Satellite cells: secrete a basement membrane that protects nerve cells from the much larger cells in the body outside of the CNS. Injury or damage to satellite cells can leave the PNS nerves vulnerable to injury and poor function.
Schwann cells: form the myelin protection in the PNS. Nerves in the PNS (not in the CNS) have a protective membrane of basement cells and connective tissue called the endoneurium. This endoneurium is only in the PNS, which allows quicker regeneration of a PNS nerve if it is damaged. The endoneurium sheath connects with blood vessels to create clusters of nerves called fascicles, further protecting and supporting the (PNS) nerves. Several sets of fascicles may be in one endoneurium sheath.
Cells in the CNS and PNS:
Glial cells provide support to nerve cells, including insulation, communication, and nutrient support. They also remove waste.
How the Nervous System cells work:
Action potentials are what are commonly called nerve impulses or the transmission of messages. This is how messages are chemically conducted through nerve cells as well as muscle cells. The electrolytes sodium and potassium each contain their own charge. Cell membranes have separate ‘channels’ or ‘gates’ with specific charges to let sodium or potassium in and out of cells depending on cell needs. When in resting membrane potential, the cell is not transmitting messages. During depolarization, the inside of the cell is negatively charged, which allows sodium into the cell. Repolarization stops sodium entry and allows potassium to enter to bring the cell back to its resting state. If your electrolytes are out of balance in your body or this process is not working because of damage to a nerve, body function is affected.
Synaptic transmissions are electrical (messages travel both ways through the nerve) and chemical (messages travel one way through the nerve) sent by nerves through the dendrites. Those messages are then carried through the axon to the cell body. Most synaptic transmissions are chemical. Messenger molecules are chemical messengers.