Corpus: Nervous system

The nervous system is the part of the human organism that is responsible for stimulus perception, stimulus processing and reaction control. It forms the control circuit of behaviour in response to external and internal stimuli and consists morphologically of networked nerve cells, the neurons, and glial cells.

The main functions of the nervous system are to:

• Controlling the activity of the viscera and skeletal muscles
• Communication between the inside of the body and the environment, including rapid adaptation to changes in the inside and outside world
• Exercising complex higher-order functions (memory, thinking, emotions).

...according to topography[Bearbeiten]

Topographically, the nervous system can be divided into a

• central nervous system (CNS) and a
• peripheral nervous system (PNS).

The CNS consists of the brain (cerebrum) and the spinal cord (medulla spinalis) as nervous control centres for information processing (coordination, integration, association). In the PNS, the nerve fibres run in the form of bundles as nerves (nervi). A distinction is made between cranial nerves and spinal nerves according to their origin. They are used for wiring between the CNS and the peripheral organs. The PNS also contains collections of nerve cells known as ganglia.

...according to function[Bearbeiten]

According to functional aspects, a distinction is made between the

• somatic nervous system and the
• vegetative nervous system.

The somatic nervous system is also known as the animal nervous system and innervates the skeletal muscles. It also serves the conscious perception of sensory impressions.

The vegetative nervous system, also known as the autonomic nervous system, unconsciously controls the activity of organs in particular. It is further subdivided into

• sympathetic nervous system (sympathetic nervous system),
• parasympathetic nervous system (parasympathetic nervous system) and
• enteric nervous system (ENS).

The somatic and autonomic systems influence each other. In addition, both the CNS and the PNS contain autonomic and somatic parts.

The human nervous system is a very efficient control system. Although the majority of stimulus processing and control processes take place in the central nervous system, they are distributed over several decision-making levels so that simpler or time-critical functions (e.g. reflexes) do not generate unnecessary "overhead". Primitive control processes that have to take place almost continuously (e.g. intestinal peristalsis) are handled by autonomous neuronal networks close to the organ - largely independently of the CNS.

The nervous system is made up of specialised cellular functional units, the nerve cells (neurons). They have the ability to depolarise and thus to transmit electrical excitation. The human nervous system consists of around 30-40 billion of these nerve cells, which are connected by an even larger number of logical connections, the synapses. The synapses are the morphological correlate of the conduction of excitation between the cells.

From a functional point of view, the excitation conduction of nerve cells can be divided into incoming (afferents) and outgoing stimuli (efferents) with regard to the CNS, whereby each nerve cell can only fulfil one of the two functions. Depending on localisation and function, a further simplified classification of afferents is made into:

• Visceral receptors with visceral afferents (viscerosensory system): e.g. blood pressure, feeling of fullness, oxygen content of the blood
• Somatic receptors with somatoafferents (somatosensory system):
  • Exteroceptors in skin (touch), eye (sight), ear (hearing)
  • Proprioceptors in skeletal muscles, tendons and joint capsules (stretching and thus position in space)

The efferents can also be categorised accordingly:

• Somato efferents (somatomotor function): Voluntary and involuntary muscle contraction
• Visceroefferences (visceromotor function): Unconscious innervation of viscera

The nervous tissue emerges from the ectoderm. The CNS develops from the neural plate, the PNS from the neural crest.

Diseases of the nervous system are the domain of neurology and psychiatry. However, the nervous system is also involved in many diseases from other specialisms. Neurological diseases can be congenital (genetic defects) or acquired (infection, trauma, degeneration). Important acquired diseases of the nervous system include

• Poliomyelitis
• Parkinson's disease
• Stroke
• Polyneuropathy
• Brain tumours

• Image source podcast (nerve cell): © canacrtrk / Pexels
• Image source podcast (nervous system): Gatewood/Unsplash