The human nervous system

Nothing in our body is as complex as the nervous system. Here are some impressive comparisons. The total length of all nerve fibers would reach approximately to the moon and back again. The data on the total amount of all nerve cells vary considerably and range from 15 billion to 100 billion. Some experts even speak of up to a trillion nerve cells.


Overview Nervous System

Systems of the nervous system

The human nervous system is divided into the following three systems:


Central nervous system. This includes the nerves of the brain and spinal cord.


Peripheral nervous system. Includes the nerves of skin, sensory organs and muscles.


Vegetative nervous system. Includes two subsystems through which all organs are innervated.

Central Nervous System (CNS) subsystems

Illustration BrainThe CNS consists of many single regions:

  • Cerebrum
  • Interbrain
  • middle brain
  • Cerebellum
  • Lengthened spinal cord (also called the afterbrain)

Just to name a few. And our brain is an energy guzzler. Although it accounts for only 2% of our body mass, it devours about 20% of our daily energy needs!

Subsystems of the autonomic nervous system (VNS)

The vegetative nervous system is divided into the following two subsystems:


Adjustment of all organs to action / flight of the whole body.

  • heart: pulse rises
  • intestine: inhibition


Adjustment of all organs to recovery / regeneration of the whole body.

  • heart: pulse sinks
  • Gastrointestinal: excited

Here is an example of a stimulus processing of our organism and the resulting reaction using the example of a steaming pizza:

  1. Pizza baker smells pizza in the ovenA person perceives the following with the sensory organs eyes and nose (sensitive nerves): Eyes → “Pizza”, nose → “smells good”. These two sensations are reported to the responsible area of the central nervous system (CNS) via somato-sensitive nerves and processed there.
  2. At the same time the intestinal receptors report -> “stomach empty”. Via viscero-sensitive nerves this message reaches the CNS at the same time and is processed there as well.
  3. In response to these stimuli, the following occurs from the CNS:
  4. A nerve impulse from the CNS reaches the intestines, glands and muscles via visceromotor nerves: The salivary gland produces more saliva, the stomach growls and produces more gastric juice.
  5. A nerve impulse from the CNS reaches the skeletal muscles of the arm, hand and mouth via somato-motor nerves: The hand reaches for the pizza, the mouth opens to bite off a piece.
  6. Controlled by motor nerves, the pizza is eaten.


Infoleitung along the nerve cells

Schema of the state of charge of a nerve cell at rest.

  • The diffusion force at the cell membrane is greater than the force of electrical attraction ( Fdiff > Fel. Anz )
  • Since some K+ pores in the membrane are open, some K+ ions diffuse outside.
  • There are more positively charged ions outside the nerve cell.
  • There are more negatively charged ions inside the nerve cell.
  • This results in a charge difference of -70 mV.

Types of stimulation

A stimulus is a signal from the environment that triggers a reaction. There are different types of stimuli.

MechanicalPressure, vibration.
ThermalHeat, cold.
ChemicalOdor, taste, synaptic carriers, hormones, O2, CO2, ph-value.
Acousticloud bang (e.g. supersonic bang).
Opticalz. B. Photos or slides of trips etc.
ElectricalElectric shock, statically charged objects.
Noxe – Tissue Destructive (Pain)burns, abrasions, etc.

Receptor types

Stimulants are absorbed by the receptors and converted into an electrical impulse ( = excitation).

receptor typeStimulus
MechanoreceptorsTactile (pressure, tension, vibration), Acoustic, Equilibrium
ThermoreceptorsCold, heat
chemoreceptorsacid, alkaline solutions, etc.

Receptor potential

A stimulus opens Na+ pores in the membrane. Na+ a → depolarisation (= excitation) possibly re-polarisation (Fig.3). The receptor potential represents the stimulus: the stronger and longer the stimulus, the greater and longer the depolarization.




The synapse is a contact point between nerve cell → nerve cell, nerve cell → muscle cell and nerve cell → gland cell.

Transmission of excitation via a synapse

  • AP arrives at the end head of the neurite of NZ1 (= presynapse).
  • Ca++ flows through now open channels into the presynapse.
  • Vesicle release (= exocytosis) = release of the transmitter stimulated by Ca++.
  • diffusion of the TM (=transmitter) through the synaptic gap to the post-synapse.
  • reaction of the transmitters with the receptor proteins of the postsnapse ( key /lock principle).
  • opening of Na+ channels in the post-synapse membrane.
  • Receptor potential → Action potential.

End of excitation

  • transmitters cleave the enzyme (e.g. acetylcholinesterase)
  • The fragments (e.g. acetyl + choline) are reabsorbed into the presynapse.



Acetylcholine (Ach)

  • Motoneuron → Skeletal muscle cell
  • Sensitive neuron → Motoneuron and interneuron
  • Parasympathetic N. → Organ (myocardial cells are inhibited, intestinal muscle cells are excited).

Noradrenaline (NA)

Sympathetic neuron → Organ (heart muscle cells are excited, intestinal muscle cells are inhibited).

Gamma-aminobutyric acid (GaBa)

Inhibitory interneurons of the spinal cord → alpha-Motoneuron


Interneuron → alpha-Motoneuron (brain), inhibitory

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William C. Hilberg
As an author, Mr. Hilberg has published several papers on health issues that have gained international recognition. He is close to nature and loves the seclusion and activity as a freelance journalist. In his function as editor William C. Hilberg manages the entire content of PENP. Our team greatly appreciates his expertise and is proud to have him on board.