Nervous System Anatomy and Function

In the following, “nervous system” describes diseases that are assigned to this category according to ICD-10 (G00-G99). The ICD-10 is used for the International Statistical Classification of Diseases and Related Health Problems and is recognized worldwide.

Nervous System

The human nervous system is divided into the central nervous system (CNS) and the peripheral nervous system (PNS). Central nervous systemThe central nervous system, the control center of the body, includes the neural pathways in the brain (cerebrum) and spinal cord (medulla spinalis). The central nervous system controls all bodily functions such as breathing, movement, digestion and reproduction. Among other things, it enables thinking, learning, and ultimately consciousness. Peripheral Nervous SystemThe peripheral nervous system includes the nerve pathways that lie outside the central nervous system in the body. The peripheral nervous system transmits information (electrical impulses) received from the sensory organs to the central nervous system via a three-dimensional network of neurons (nerve cells) and, conversely, receives information from the CNS about the control of bodily functions and movements.The fibers leading to the CNS are called afferent nerve fibers. They transmit sensory information (stimulus reception).The nerve fibers leading away from the CNS are called efferent nerve fibers. They transmit motor responses to the body periphery (stimulus response).The peripheral nervous system also includes glial cells (neuroglia; supporting tissue of the nervous system). The peripheral nervous system can be divided by function as follows:

  • Somatic (voluntary) nervous system – processes can be controlled consciously.
  • Vegetative (autonomic) nervous system – no volitional control.

Somatic (voluntary) nervous systemThis includes processes that can be consciously controlled such as movements (motor system). It also includes the conscious perception of environmental stimuli and stimuli from inside the body and their transmission to the brain (sensory system). The sensory system includes the visual system (sense of sight), auditory system (sense of hearing), vestibular system (sense of balance), olfactory system (sense of smell), gustatory system (sense of taste) and the tactile system (sense of touch). Consequently, the somatic nervous system serves to interact with the environment. Vegetative (autonomic) nervous systemThe efferent (leading away from the CNS) nerve pathways of the autonomic nervous system can be assigned to a sympathetic (sympathetic) as well as a parasympathetic (parasympathetic) area. The effects of the two systems are opposite. The parasympathetic nervous system is the relaxation nerve. Among other things, stimulation of the parasympathetic nervous system causes the following:

  • Pupils constrict (miosis).
  • Salivation is stimulated
  • Heartbeat slows down (negative chronotopy)
  • Bronchial tubes narrow (bronchoconstriction).
  • Digestion is stimulated by increasing the conveying activity (peristalsis) and release (secretion) of digestive enzymes
  • Urinary bladder empties

→ The body relaxes and can regenerate. The sympathetic nervous system, on the other hand, is the excitation or tension nerve. Among other things, irritation of the sympathetic nervous system causes the following:

  • Pupils dilate (mydriasis).
  • Salivation is inhibited (positive chronotopy).
  • Heartbeat is accelerated
  • Bronchial tubes dilate (bronchodilation)
  • Digestion is inhibited
  • Glucose is released from the liver
  • Urinary bladder fills
  • Adrenaline is released

→ The body is tense and ready to perform at its best. Furthermore, there is the enteric nervous system. This is a complex network of nerve cells that runs through approximately the entire gastrointestinal tract (digestive tract). The main components of the enteric nervous system are the Auerbach’s plexus (myenteric plexus) and the Meissner’s plexus (submucosal plexus). The enteric nervous system primarily regulates intestinal motility (ability of the intestine to move) and gastrointestinal blood flow.

Anatomy

Brain (Latin : cerebrum; Greek : encephalon)The brain is surrounded by the bones of the skull. It weighs between 1.5-2 kg. As the control center of the human body, the brain requires a lot of oxygen and glucose (sugar).The neurons in the brain, estimated to number 100 billion, are embedded in a supporting tissue of glial cells.The brain is surrounded by three skins, the meninges:

  • Pia mater – delicate meninges that lie directly on the brain.
  • Arachnoid mater – “cobweb skin“; middle, soft meninges.
  • Dura mater – hard meninges, outer boundary of the brain to the skull.

Between the arachnoid mater and the pia mater is a cerebrospinal fluid space filled with cerebrospinal fluid. A rough distinction is made between the following areas of the human brain:

  • Cerebrum (telencephalon) – has folds and furrows (resembles a walnut).
    • It is divided into two hemispheres (right and left brain) connected by the bar (corpus allosum), and different lobes of the brain (frontal lobe/lobus frontalis, parietal lobe/L. parietalis, temporal lobe/L. temporalis, occipital lobe/L. occipitalis).
    • It consists of an outer part (cortex/cerebral cortex/gray matter) and an inner part (medulla/white matter).
  • Diencephalon – located between the cerebrum and midbrain and consists of thalamus, hypothalamus, subthalamus, epithalamus.
  • Brainstem – located in the lower part of the skull; it consists of:
    • Midbrain (mesencephalon) – smallest part of the brain.
    • Bridge (pons)
    • Afterbrain or medulla oblongata (medulla oblongata) – transition between brain and spinal cord.
  • Cerebellum (cerebellum) – located above the brain stem and below the cerebrum.

Spinal cord (medulla spinalis)The spinal cord runs protected within the spinal column in the spinal canal. It is a rod-shaped collection of nerve cell bodies and fibers, which is about half a meter long in adults. It is surrounded by a fluid called liqour (neural fluid).Like the cerebrum, the spinal cord consists of gray matter and white matter. The gray matter lies inside and is enveloped by the white.Nerve fibers emerge from the sides of the spinal cord and unite to form spinal nerves. They emerge from the spinal canal through interstices in the bony spinal column. They contain both efferent and afferent nerve fibers. Neurons (nerve cells; nervus, nervi)The human nervous system contains billions of neurons (nerve cells). Neurons are composed of:

  • Soma with nucleus – body of the nerve cell.
  • Dendrites – outgrowths emanating from the soma; receives excitations from other neurons and transmits them to the soma
  • Axon hillock – this is where the axon (long nerve cell extension) originates; signals accumulate at the axon hillock and are transmitted through the axon
  • Axon – passes the stimuli from the soma to the next nerve cell; passes at the end of the nerve cell in synapses
  • Myelin sheath – surrounds the axon and insulates it; consists of Schwann cells (special form of a glial cell); there is always a Ranvier’s stoker ring between two of these cells, which means that there is no insulation at this point → the stimulus jumps from stoker ring to stoker ring (“saltatory conduction of excitation”)
  • Synaptic terminal buttons – here the electrical stimulus is diverted into a chemical reaction; the synaptic terminal buttons are in contact with other nerve cells, but also with muscle cells; there is a fine gap between two synapses; when nerve cells are activated, they release neurotransmitter into this gap, which exerts influence on the downstream cell

Ganglia (Ganglia)A ganglion (nerve node) is a collection of nerve cell bodies in the peripheral nervous system and presents as a thickening. They are usually located close to the spinal cord or brain or on or in internal organs. In the central nervous system, these collections are called nuclei.

Physiology

Brain (Latin : cerebrum; Greek : encephalon).

  • Cerebrum (Telencephalon) – The cerebrum connects all organs or organ systems and tissues. Stimuli from the environment and inside the body are received via receptors, transmitted to the brain via the afferent neural pathways, and processed in the cerebrum. A response is then sent back to the organs/organ systems and periphery via the efferent nerve pathways. Not all stimuli are directed to the cerebrum (see below under “Ganglia”).
    • Right brain: language, logic
    • Left brain: creativity, sense of direction.
    • Neocortex (part of the cerebral cortex): this is where consciousness and memory are located, as well as the ability to learn, speak, and think
    • Cerebral lobes:
      • Frontal lobe or frontal lobe (lobus frontalis): control center for situational action.
      • Parietal lobe or parietal lobe (lobus parietalis): body perception, spatial thinking.
        • Temporal lobe or temporal lobe (lobus temporalis): hearing.
        • Hippocampus: storage of facts, events in memory (medium to long term).
        • Amygdala (“almond nucleus”): emotional evaluation of information.
      • Occipital lobe or occipital lobe (lobus occipitalis): visual center.
  • Diencephalon – is called “the gateway to consciousness”.
    • Thalamus – contains sensory information from the periphery and transmits it to the brain
    • Hypothalamus – controls physical and mental processes; together with the pituitary gland, forms the link between the hormonal and nervous systems
    • Subthalamus – control of gross motor skills.
    • Epithalamus – sleep-wake rhythm
  • Brainstem – automatic and reflex processes such as heartbeat, breathing, regulation of body temperature, swallowing and coughing reflex.
  • Cerebellum – belongs to the motor system → coordinates movements, balance; language acquisition.

Spinal cordIt connects the brain with the periphery of the body. Sensory nerve pathways carry information to the brain (afferent pathways) and motor pathways (efferent pathways) carry information from the brain to executive structures such as muscles. The gray matter contains nerve cell bodies that transmit pain and touch stimuli, as well as nerve cells that serve motor functions and nerve cells of the autonomic system that controls internal organs. The white matter contains ascending and descending fiber systems.Along the entire length of the spinal cord, 31 pairs of nerve roots arise at regular intervals on both sides and unite to form the spinal nerves. The spinal nerves interface with the peripheral nervous system by merging into the peripheral nerves. Neurons (nerve cells; nervus, nervi)Neurons serve to exchange information in the organism. They transmit stimuli. GangliaGanglia function as a control center. They pass on signals. The information can be rewired from one nerve fiber to another. But processing also takes place in the ganglia, so that the signals do not have to be transmitted to the brain first, but can be processed organically.

Common diseases of the nervous system

  • Apoplexy (stroke)
  • Dementia
  • Epilepsy (seizures)
  • Cerebral hemorrhages
  • Brain tumors
  • Headaches
  • Meningitis (meningitis) – bacterial meningitis, viral meningitis.
  • Migraine
  • Parkinson’s disease
  • Multiple sclerosis (MS)
  • Polyneuropathy, diabetic polyneuropathy – disease of the nerves of the peripheral nervous system; depending on the cause, motor, sensory or autonomic nerves may be affected; sensitivity disorders.
  • Obstructive sleep apnea syndrome – characterized by the obstruction (narrowing) or complete closure of the upper airway during sleep.
  • Restless legs syndrome (RLS) – insensations mostly in the lower extremities and associated urge to move (motor restlessness).
  • Traumatic brain injury (TBI)

Parkinson’s disease is already the most common neurological disease of old age today. About 1% of the over 60-year-olds are affected. In Germany, there are circa 250,000 cases of Parkinson’s disease. Alzheimer’s disease is a primary degenerative brain disease associated with progressive dementia. The disease accounts for about three quarters of all dementia cases and is thus the most common form of dementia in old age. In Germany, there are about 50,000 new cases each year.

The most important risk factors for diseases of the nervous system

Behavioral causes

  • Diet
  • Consumption of stimulants
    • Alcohol consumption
    • Tobacco consumption
  • Drug use
  • Lack of exercise
  • Psycho-social situation
    • Anxiety
    • Stress
    • Tantrum
  • Overweight
  • Increased waist circumference (abdominal circumference; apple type).

Causes due to disease

  • Atherosclerosis (arteriosclerosis / hardening of the arteries).
  • Diabetes mellitus – diabetes mellitus type 1, diabetes mellitus type 2
  • Dyslipidemias/hyperlipoproteinemias (lipid metabolism disorders).
  • Vascular anomalies
  • Hypertension (high blood pressure)
  • Thyroid disease – hyperthyroidism (hyperthyroidism), hypothyroidism (hypothyroidism).

Medication

  • Analgesics (painkillers)
  • Antibiotics
  • Anticoagulants (anticoagulants)
  • Immunosuppressants – drugs that reduce the functions of the immune system.
  • Local anesthetics
  • Psychotropic drugs

Please note that the enumeration is only an extract of the possible risk factors. Other causes can be found under the respective disease.

The main diagnostic measures for diseases of the nervous system

  • Encephalogram (EEG; recording of the electrical activity of the brain).
  • Electroneurography (ENG; method of measuring nerve conduction velocity) of affected muscles.
  • Doppler sonography (ultrasound examination that can dynamically visualize fluid flows (especially blood flow)) of the carotids (carotid arteries)
  • Extra- and intracranial vascular imaging (catheter angiography, MR or CT angiography, cervical plus transcranial Doppler sonography to detect vascular changes )
  • X-rays of the skull
  • X-rays of the cervical spine
  • Computed tomography (CT) of the skull (cranial CT or.cCT).
  • Magnetic resonance imaging of the skull (cranial MRI, cranial MRI or cMRI).
  • CT angiography or MR angiography
  • Long-term ambulatory EEG/sleep deprivation EEG.
  • Polysomnography (sleep laboratory; measurement of various body functions during sleep that provide information about sleep quality).
  • Positron emission tomography (PET; nuclear medicine procedure that allows the creation of cross-sectional images of living organisms by visualizing the distribution patterns of weak radioactive substances).
  • Single-photon emission tomography (SPECT; functional imaging method of nuclear medicine, which allows the creation of cross-sectional images of living organisms based on the principle of scintigraphy)
  • Neurophysiological examinations – on suspicion of neuritis (inflammation of the nerves).
  • Digital subtraction angiography (DSA; procedure for isolated imaging of vessels) – in suspected aneurysms (arterial dilation) or vasculitides (diseases in which autoimmunological processes lead to inflammation of arteries, arterioles and capillaries).
  • Transcranial Doppler sonography (ultrasound examination through the intact skull for orienting control of cerebral (“affecting the brain”)

Which doctor will help you?

In the case of diseases of the nervous system should first see the family doctor. Depending on the disease or its severity, a presentation to a specialist, in this case the neurologist, will be necessary.