Anatomy and Histology

Apart from the neurons other cells are also part of the nervous tissue. They are supporting cells or neuroglia.

1. 1)  Maintain an optimal environment for neuronal functioning (keep homeostasis)

2. 2)  Limit the number and types of stimuli affecting individual neurones (myelination)

3. 3)  Are not terminally differentiated, i.e. can divide

4. 4)  Five times more neuroglia than neurones

5. 5)  Account for ca. half the nervous tissue volume

6. 6)  Found in the PNS as well as the CNS.

   • In the PNS: satellite cells and Schwann cells

   • In the CNS: oligodendrocytes, astrocytes, microglia, ependymal cells

Wikipedia: 

Glial cells, sometimes called neuroglia or simply glia, are non-neuronal cells that maintain homeostasis, form myelin, and provide support and protection for neurons in the central and peripheral nervous systems. In the central nervous system, glial cells include oligodendrocytes, astrocytes, ependymal cells and microglia, and in the peripheral nervous system glial cells include Schwann cells and satellite cells.

Oligodendrocytes
• in the CNS
• Myelination of axons: insulation of axons and more efficient propagation of electrical impulses 

cell in the CNS

Microglia cell are in the CNS

The cell is in the CNS

Als Mantelzellen, Satellitenzellen oder auch Amphizyten bzw. Amphicyten wird eine Klasse von Gliazellen des Peripheren Nervensystems bezeichnet. Sie begrenzen periphere Neurone in Ganglien, hauptsächlich in Spinalganglien. Sie ummanteln den Zellkörper der Neurone als einschichtig flache Lage und dienen deren Stoffwechsel.

Das Pendant der Mantelzellen im Zentralen Nervensystem sind die Astrozyten.

The soma (pl. somata or somas), perikaryon (pl. perikarya), cyton, or "cell body" is the bulbous end of a neuron, containing the cell nucleus.

The cerebral cortex is the brain’s outer layer of neural tissue in humans and other mammals

• Sagittally divided into left and right hemispheres by the medial longitudinal fissure

• In mammals is highly folded, increase its surface area, so that it occupies a smaller

  volume in the head

• Layered structure 

The five characteristic types of cortical neuron are shown diagrammatically in (a), the pyramidal and stellate cells being by far the most common types: 

1. Pyramidal cells

2. •Stellate (granule) cells

3. •Cells of Martinotti

4. •Fusiform cells

5. •Horizontal cells of Cajal

•Pyramidal cells have pyramid‐shaped cell bodies with the apex directed towards

the cortical surface. From the apex, a thick branching dendrite passes towards the surface where it has an array of fine dendritic branches. An axon arises from the base of the cell and passes into the white matter though, in the case of small superficial cells, the axon may synapse in the deep layers of the cortex. Short dendrites also arise from the edges of the base and ramify laterally. The size of pyramidal cells varies, with the smallest tending to sit superficially. The huge upper motor neurons of the motor cortex, known as Betz cells, are the largest pyramidal cells in the cortex. 

Stellate (granule) cells are small neurons with a short vertical axon and several short branching dendrites, giving the cell body the shape of a star, although other shapes have been described. With routine histological methods, the cells look like small granules, giving rise to their alternative name. 

Cells of Martinotti are small polygonal cells with a few short dendrites; the axon extends towards the surface and bifurcates to run horizontally, usually in the most superficial layer. 

Fusiform cells are spindle‐shaped cells oriented at right angles to the surface of the cerebral cortex. The axon arises from the side of the cell body and passes superficially. Dendrites extend from each end of the cell body, branching into deeper and more superficial layers. 

Horizontal cells of Cajal are small and spindle‐shaped but oriented parallel to the surface. They are the least common cell type and are only found in the most superficial layer, where their axons pass laterally to synapse with the dendrites of pyramidal cells. 

Schwan cells

1) Most abundant glial cells of the PNS

2) Two types: myelinating (form a sheath around the axons of motor and sensory neurons); and non myelinating.

3) Functions: conduction of impulses, nerve development and regeneration, trophic support for neurons, production of nerve ECM, modulation of neuromuscular synaptic activity, presentation of antigens to T‐ lymphocytes 

Nerves:

• Enclosed cable like bundles of axons in the PNS

• Afferent nerves: conduct signals from sensory neurons to the CNS

• Efferent nerves: conduct signals from the CNS to muscle and glands

• Mixed nerves: contain both afferent and efferent nerves

• Can be categorized in spinal nerves that innervate the most of the body and connect to the spinal cord, and cranial nerves, that innervate parts of the head and connect directly to the brain

• Between neurons there are layers of connective tissue:

  1. Epineurum – the most external layer that encapsulates the whole nerve

  2. Perineurum – membrane surrounding each nerve fascicle

  3. Endoneurum – loose collagenous tissue that packs together several fascicle 

Epineurum – the most external layer that encapsulates the whole nerve

Perineurum – membrane surrounding each nerve fascicle

Endoneurum – loose collagenous tissue that packs together several fascicle 

Ganglia, aggregations of neurone cell bodies (soma) outside the central nervous system 

The peripheral nervous system (PNS) is the part of the nervous system that consists of the nerves and ganglia outside of the brain and spinal cord. 

Das periphere Nervensystem (PNS) umfasst den Teil des Nervensystems, der außerhalb des Gehirns und Rückenmarks gelegen ist. Letztere bilden das Zentrale Nervensystem (ZNS). Im Gegensatz zu diesem ist das PNS nicht durch Knochen oder die Blut-Hirn-Schranke geschützt. Sowohl das ZNS als auch das PNS sind weiter unterteilt in das somatische Nervensystem und das autonome Nervensystem.

The somatic nervous system (SoNS or voluntary nervous system) is the part of the peripheral nervous system^[1]associated with skeletal muscle voluntary control of body movements.

Vegetatives Nervensystem

Two groupes: sympathetic and parasympathetic nervous system

The autonomic nervous system (ANS) is a division of the peripheral nervous system that influences the function of internal organs. The autonomic nervous system is a control system that acts largely unconsciously and regulates bodily functions such as the heart rate, digestion, respiratory rate, pupillary response, urination, and sexual arousal. This system is the primary mechanism in control of the fight-or-flight response and the freeze-and-dissociate response.

The sympathetic nervous system's primary process is to stimulate the body's fight-or-flight response

The parasympathetic system is responsible for stimulation of "rest-and-digest" or "feed and breed" activities that occur when the body is at rest, especially after eating, including sexual arousal, salivation, lacrimation (tears), urination, digestion and defecation.

The enteric nervous system (ENS) or intrinsic nervous system is one of the main divisions of the nervous system and consists of a mesh-like system of neurons that governs the function of the gastrointestinal system.

Gastrointestinal system: Magen-Darm-Trakt

The nervous system is the part of an animal's body that coordinates its actions and transmits signals to and from different parts of its body.

Three groups: somatic nervous system, automatic nervous system and enteric nervous system

Homeostasis or homoeostasis is the property of a system in which a variable (for example, the concentration of a substance in solution, or its temperature) is actively regulated to remain very nearly constant. This regulation occurs inside a defined environment (mostly within a living organism's body). Examples of homeostasis include the regulation of the body temperature of an animal, the pH of its extracellular fluids, or the concentrations of sodium (Na⁺) and calcium (Ca²⁺) ions or of glucose in the blood plasma, despite changes in the animal’s environment, or what it has eaten, or what it is doing (for example, resting or exercising).

Dendriten (altgr. δένδρον dendron ‚Baum‘ bzw. dendrites ‚zum Baum gehörend‘) heißen in der Biologie Zellfortsätze von Nervenzellen, die aus dem Zellkörper hervorgehen und vorwiegend der Reizaufnahme dienen

some axons are wrapped in a fatty sheath which electrically insulate, speeding signal transmission. This sheath is made by the peripheral nervous system from the swann cell  and by the central nervous system from the oligodendrocytes cells.

In the peripheral nervous system axons are enveloped by Schwann cells, which provide metabolic and structural support to the neurons.
Small diameter neurons are just englobed by the cytoplasm of Schwann cell (non‐ Myelinated)

Larger nerve fibbers are wrapped in a variable number of concentric layers of Schwan cells cytoplasmic membrane forming a myelin sheath (Myelinated)
In the CNS, the myelin sheath are produced by the oligodendrocytes.
Advantages of myelination:

• Myelination greatly increases conduction speed (as does axon diameter)
The gap between myelin sheaths are called NODES of RNAVIER. These spaces are very rich in ion channels. In the case of myelinated neurons the action potential jumps from one node of Ranvier to the next (saltatory conduction) 

1 Definition

Neurofilamente sind Intermediärfilamente der Nervenzellen. Sie stellen eine von drei Hauptklassen von Zytoskelett-Proteinen neben Aktinfilamenten und Mikrotubuli dar. 

2 Bedeutung

Neurofilamente sind der maßgeblich Struktur-bestimmenden Bestandteil der Axone von Nervenzellen. Sie sind in myelinisierten Axonen mit großem Durchmesser zahlenmäßig deutlich häufiger enthalten als Mikrotubuli, was ihre Bedeutung für die strukturelle Integrität von Axonen mit großen Kalibern unterstreicht.

Impulse directed towards the CNS ( central nerveus system)

Impulse away from the CNS (central nervous system)

Anaxonic = no discernible axon, found in CNS and special sense organs, function unknown 

Bipolar = one dendrite at opposite pole to the axon, rare, ACh as receptor neurons for senses of smell, sight and balance. 

Pseudo‐unipolar =Primary sensory neurons. Dendrite and axon arise from same stem, convey information 

Multipolar = most common. Numerous dendrites arising from one pole of the cell body, opposite to the axon. Most common in integratory and motor neurons. 

Divergent circuit: one incoming fiber triggers a response in a large number of new

neurons. These circuits amplify the signal along the path. Sensory and motor system 

Convergent circuit: several neurons trigger a response in one single neuron. This

circuit causes stimulation and inhibition. Sensory and motor pathways.