Are motor neurons myelinated

Alpha motor neurons:

large motor neurons in the anterior horn of the spinal cord; their axons run over the anterior roots in the spinal nerves and innervate transversely striated skeletal muscle fibers through motor endplates. You have acetylcholine as a neurotransmitter. An alpha motor neuron and all of the skeletal muscle fibers it innervates form a motor unit.

Epicritical sensations:

very differentiated perception of touch sensations via specialized receptors in the skin and joints.

Gamma motor neurons:

small motor neurons in the anterior horn of the spinal cord; their axons run over the anterior root in the spinal nerves. They innervate the skeletal muscle fibers in the muscle spindles (intrafusal muscle fibers) via motor end plates

Gray matter:

Substantia grisea, part of the spinal cord enclosed by the white matter (substantia alba), which includes the perikarya of the nerve cells and the neuropil (a network of nerve and glial cell processes with many synapses). In the cross-section of the spinal cord it has the characteristic butterfly shape.

Cornu dorsale / posterius:

Posterior horn of the spinal cord; Part of the gray matter that contains nerve cells that transmit sensory stimuli. The posterior root of the spinal cord pulls into the posterior horn, part of the fibers of the posterior root, which conduct sensitive impulses from the periphery, are synaptically switched here.

Funiculus dorsalis / posterior:

Posterior cord of the spinal cord; Part of the white matter in which nerve fibers run that carry impulses of epicritical sensitivity. The posterior cords consist of the medial gracilis fasciculus and the laterally cuneatus fasciculus. The cuneatus fasciculus carries information from the upper extremity and neck, it is only found in cross-sections through the cervical medulla.

Ependymal cells:

iso- to highly prismatic glial cells that line the inner liquor spaces. They are connected to one another by nexus and have apical microvilli and, in places, kino cilia.

Lissauer tract:

Posterolateral tract, divides the posterior cords from the lateral cords. The central processes of the pseudounipolar spinal ganglion cells, which convey pain stimuli, run in the posterolateral tract; they are synaptically switched at neurons in the dorsal horn (substantia gelatinosa).

Nociceptive Neurons:

pseudounipolar dorsal root ganglion cells that perceive and transmit pain stimuli. The receptors (nociceptors, pain receptors) are free nerve endings that arise from branching of the peripheral process of the nociceptive dorsal root ganglion cells. The pain receptors can be excited by various stimuli (thermal, mechanical or chemical). They do not adapt or only very slowly.

Nucleus intermediolateralis:

Nucleus in the lateral horn of the spinal cord; here are the central neurons of the autonomic nervous system. In the thoracic and upper lumbar cords, the intermediolateral nucleus houses the first sympathetic neuron.

Posteromarginal nucleus:

cap-shaped posterior end of the posterior horn belonging to the spongiosa zone in the cervical medulla.

Nucleus proprius:

Main core area of ​​the posterior horn, target of proprioceptive afferents from the musculoskeletal system and the skin.

Protopathic sensations:

Pain and temperature as well as rough touch and pressure sensations. They are conducted in separate ascending tracts of the anterior lateral cord: pain and temperature sensations in the lateral spinothalamic tract, rough sensations of touch and pressure in the anterior spinothalamic tract.

Reissner thread:

Secretion thread formed by ependymal cells of the subcommissural organ, which extends into the lower spinal cord in animals whose central canal is not obliterated.

Medulla spinalis:

Spinal cord; peripheral part of the CNS enclosed in the spinal canal. It extends from the origin of the first cervical nerve to the conus medullaris, which in adults is at the level of the 1st or 2nd lumbar vertebra. It ends caudally with the nerve cell-free filum terminale, which attaches to the first coccyx vertebra. In the cross-section you can see the central butterfly-shaped gray matter, which is surrounded by the white matter. The gray matter contains the perikarya of the nerve cells and the neuropil; In the white matter, myelinated nerve fibers run as ascending and descending pathways.

Spinal membranes:

three-part connective tissue covering system of the spinal cord in the spinal canal. From the outside to the inside lie: dura mater (pachymeninx, hard meninges), arachnoid and pia mater. The arachnoid and pia form the soft meninges (leptomeninx). The subarachnoid space, which is filled with cerebrospinal fluid, lies between the arachnoid and pia mater. The pia mater lies on the surface of the spinal cord, separated by a basal lamina.

Cornu laterale:

Lateral horn of the gray matter of the spinal cord; this is where the intermediolateral nucleus is located, in which the central neurons of the autonomic nervous system are located.

Lateral funiculus:

Lateral cord of the spinal cord that extends from the posterior horn to the anterior root. The anterior root delimits the lateral cord only vaguely from the anterior cord; both strands are therefore combined as a front strand.

Spinal nerves:

Spinal nerves; 31 nerves emerging segmentally and in pairs from the spinal cord. There are 8 cervical, 13 thoracic, 5 lumbar and 5 sacral and coccygeal spinal nerves. The perikaryen of the motor, efferent part are in the anterior horn of the spinal cord, those of the sensitive, afferent part in the spinal ganglia and those of the visceromotor part in the lateral horn of the spinal cord. The efferent fibers of a segment form the anterior root and unite with the sensitive posterior root to form the spinal nerve, which is divided into four branches: Ramus meningeus for the sensitive supply of the spinal cord membranes Ramus posterior (dorsalis) for the motor supply of the autochthonous back muscles and for the sensitive supply of the skin region of the Back ramus anterior (ventralis) for the motorized supply of the front and side walls of the trunk and the extremities as well as for the sensitive supply of the corresponding skin areas

Substantia gelatinosa:

Core complex located dorsally in the posterior horn, at which proprio- and exteroceptive pain afferents end and are switched to the second neuron. The axons of the second neuron form the spinothalamic tract.

Substantia intermedia:

The gray matter area between the anterior horn and the posterior horn

Substantia cancellous:

The part of the gray matter which forms the end of the posterior horn and which sits on top of the substantia gelatinosa in the shape of a cap.

Cornu ventral / anterius:

Anterior horn, part of the gray matter of the spinal cord that contains the motor anterior horn cells (motor neurons), the axons of which extend via the anterior root into the spinal nerves and innervate the striated skeletal muscles via motor endplates.

Anterior / ventral funiculus:

Front strand, usually combined with the side strand to form the front strand.

White matter:

Substantia alba; it surrounds the gray matter of the spinal cord in a jacket-like manner and contains essentially myelinated and un myelinated nerve fibers, but almost no perikarya of nerve cells. The nerve fibers are arranged in strands: anterior strand (funiculus anterolateralis); (Funiculus posterior).

Central channel:

Liquor-filled canal located in the center of the gray matter, continuation of the ventricular system (inner liquor compartment) of the brain. It often appears obliterated in specimens of the human spinal cord.

Anterior median fissure:

longitudinal notch on the front of the spinal cord.

Butterfly figure:

The shape of the gray matter that appears in the cross section of the spinal cord, it consists of the anterior horns, the posterior horns and the lateral horns. Viewed spatially, these horns represent pillars. The anterior horn (Cornu anterius) contains the motor anterior horn cells, the posterior horn (Cornu posterius) contains nerve cells that receive sensory information from the periphery, and the lateral horn (Cornu laterale) houses the pericarya of the central neurons of the vegetative Nervous system.

Motor neurons:

lie in the anterior horn of the spinal cord. They are divided into large alpha and small gamma motor neurons. The alpha motor neurons innervate striated skeletal muscle fibers via motor endplates. An alpha motor neuron forms a motor unit with all of the skeletal muscle fibers it innervates. The smaller gamma motor neurons innervate the intrafusal muscle fibers of the muscle spindles.

Spinal cord:

Spinal cord; peripheral part of the CNS enclosed in the spinal canal. It extends from the origin of the first cervical nerve to the conus medullaris, which in adults is at the level of the 1st or 2nd lumbar vertebra. It ends caudally with the nerve cell-free filum terminale, which attaches to the first coccyx vertebra. In the cross-section you can see the central butterfly-shaped gray matter, which is enclosed by the white matter. The gray matter contains the perikarya of the nerve cells and the neuropil; In the white matter, myelinated nerve fibers run as ascending and descending pathways.

Dendrites:

The tree-like branching processes of a nerve cell that serve to record signals and, in contrast to the axon, contain a rough endoplasmic reticulum and are not encased by a medullary sheath.

Glial cells:

fulfill mechanical and metabolic tasks in the nervous system. A distinction is made between -Glia of the peripheral nervous system with Schwann cells, mantle cells of the ganglia and lemnocytes of the nerve end bodies -Glia of the central nervous system with astrocytes, oligodendrocytes, ependymal cells, tanycytes, epithelium of the choroid plexus and pituitarytes of the neurohypophysis. All of the named glial cell types are derived from the ectoderm. Another type of glial cell, the microglia, is of mesenchymal origin and belongs to the macrophage cell line.

Medullary axons:

In the CNS of oligodendrocytes and in the peripheral nervous system of Schwann cells, appendages of a nerve cell are surrounded. A distinction is made between medullary and medulla-poor nerve fibers. The thickness of the axon and the medullary sheath determine the speed and type of conduction of excitation: the axons containing the medullary pass the excitation on quickly and in a saltatory (erratic) manner.

Nissl staining:

Staining method for the representation of the Nissl clods, e.g. with cresyl violet.

Nissl clods:

basophilic, ribonucleic acid-rich clods in nerve cells that ultrastructurally correspond to a collection of rough endoplasmic reticulum and polysomes. Protein synthesis takes place here.

Oligodendrocytes:

form the medullary sheath around axons in the central nervous system

Perikaryon:

Cell body of a nerve cell (neuron), also called soma (Greek: body, body). In the true sense of the word, the perikaryon is the part of the cell body that surrounds the cell nucleus and contains the cytoplasm (Greek: peri - around, around; karyos - nucleus)

Axon:

transmits the excitation of the nerve cell to downstream neurons in the form of action potentials. Each nerve cell has only one axon, in the course of which, however, collaterals can branch off. In the target region, the axon can branch out several times (telodendron) and form synapses with several downstream nerve cells.

myelinated:

medullary, encased by a medullary sheath. In the CNS the medullary sheath of the axon is formed by processes of oligodendrocytes, in the peripheral nervous system by Schwann cells. Depending on the thickness of the medullary sheath, a distinction is made between medullary and medullary nerve fibers. In the case of unmarked nerve fibers, the envelope cells form. B. the Schwann cells no medullary sheath.

Euchromatin:

summarizes the genetically active sections of the chromosomes, shows the regions of the cell nucleus that are not very stained by light microscopy. The genetic information is read off in these areas. Metabolically active cells have a large, euchromatic nucleus.

Heterochromatin:

indicates the coiled, inactive chromosome areas, is intensely stained in light microscopic specimens. Heterochromatin is particularly pronounced in the nucleus of metabolically inactive cells and is often located at the edge of the cell nucleus. Areas of DNA that do not code for proteins and always remain condensed, such as the telomeres, are called constitutive heterochromatin.

Neuropil:

surrounds the perikaryen of the nerve cells in the gray matter, appears relatively structureless under the light microscope. With the electron microscope, the neuropil turns out to be a network of appendages of nerve and glial cells, in which there are numerous synapses.

Multipolar nerve cells:

Most common nerve cell type with numerous dendrites that branch near the cell body and a long axon. Typical representatives of this cell type are the motor anterior horn cells of the spinal cord.

Astrocytes:

Glial cells with sometimes very long appendages that are closely connected to capillaries and nerve cells. On the outer surface of the CNS, the widened end feet of the processes form the superficial limit gliae membrane, and the vascular limit gliae membrane on the capillaries. A distinction is made between fibrillar and protoplasmic astrocytes. The fibrillar astrocytes have long, thin, and narrow processes; they are mostly found in the white matter of the brain and spinal cord. The protoplasmic astrocytes have shorter processes, they are mainly in the gray matter of the CNS.

Myelin sheath:

Medullary sheath; Sheath of the axon by cytoplasmic processes of oligodendrocytes (CNS) or Schwann cells (peripheral nervous system).