Neural pathway
Encyclopedia
A neural pathway, neural tract, or neural face, connects one part of the nervous system
with another and usually consists of bundles of elongated, myelin
-insulated neuron
s, known collectively as white matter
. Neural pathways serve to connect relatively distant areas of the brain
or nervous system, compared to the local communication of grey matter
.
, and were named by the great anatomists of the Renaissance
using cadaver material. Examples of these include the great commissures of the brain such as the corpus callosum
(Latin
, "hard body"; not to be confused with the Latin word "colossus" - the "huge" statue), anterior commissure, and posterior commissure. Further examples of this (by no means a complete list) include the pyramidal tract
, crus cerebri
(Latin
, "leg of the brain"), and cerebellar peduncles (Latin
, "little foot of the cerebellum
"). Note that these names describe the appearance of a structure but give one no information on its function or location.
Later, as neuroanatomical
knowledge became more sophisticated, the trend was toward naming pathways by their origin and termination. For example, the nigrostriatal pathway
, which is degenerated in Parkinson's disease
, runs from the substantia nigra
(Latin
, "black substance") to the corpus striatum
(Latin
, "striped body"). This naming can extend to include any number of structures in a pathway, such that the cerebellorubrothalamocortical pathway originates in the cerebellum
, synapse
s in the red nucleus
("ruber" in Latin), on to the thalamus
, and finally terminating in the cerebral cortex
.
Sometimes, these two naming conventions coexist. For example, the name "pyramidal tract
" has been mainly supplanted by lateral corticospinal tract
in most texts. Note that the "old" name was primarily descriptive, evoking the pyramids
of antiquity, from the appearance of this neural pathway in the medulla oblongata
. The "new" name is based primarily on its origin (in the primary motor cortex
, Brodmann area
4) and termination (onto the alpha motor neurons of the spinal cord
).
s receive information either at their dendrite
s or cell bodies. The axon
of a nerve cell is, in general, responsible for transmitting information over a relatively long distance. Therefore, most neural pathways are made up of axon
s. If the axon
s have myelin
sheaths, then the pathway appears bright white because myelin
is primarily lipid
. If most or all of the axons lack myelin
sheaths (i.e., are unmyelinated), then the pathway will appear a darker beige color, which is generally called gray (American English
, or grey in British English
).
Some neurons are responsible for conveying information over long distances. For example, motor neurons, which travel from the spinal cord to the muscle, can have axons up to a meter in length in humans; the longest axon in the human body is almost two meters long in tall individuals and runs from the great toe
to the medulla oblongata
of the brainstem. These are archetypical examples of neural pathways.
Dopamine pathways:
Nervous system
The nervous system is an organ system containing a network of specialized cells called neurons that coordinate the actions of an animal and transmit signals between different parts of its body. In most animals the nervous system consists of two parts, central and peripheral. The central nervous...
with another and usually consists of bundles of elongated, myelin
Myelin
Myelin is a dielectric material that forms a layer, the myelin sheath, usually around only the axon of a neuron. It is essential for the proper functioning of the nervous system. Myelin is an outgrowth of a type of glial cell. The production of the myelin sheath is called myelination...
-insulated neuron
Neuron
A neuron is an electrically excitable cell that processes and transmits information by electrical and chemical signaling. Chemical signaling occurs via synapses, specialized connections with other cells. Neurons connect to each other to form networks. Neurons are the core components of the nervous...
s, known collectively as white matter
White matter
White matter is one of the two components of the central nervous system and consists mostly of myelinated axons. White matter tissue of the freshly cut brain appears pinkish white to the naked eye because myelin is composed largely of lipid tissue veined with capillaries. Its white color is due to...
. Neural pathways serve to connect relatively distant areas of the brain
Brain
The brain is the center of the nervous system in all vertebrate and most invertebrate animals—only a few primitive invertebrates such as sponges, jellyfish, sea squirts and starfishes do not have one. It is located in the head, usually close to primary sensory apparatus such as vision, hearing,...
or nervous system, compared to the local communication of grey matter
Grey matter
Grey matter is a major component of the central nervous system, consisting of neuronal cell bodies, neuropil , glial cells and capillaries. Grey matter contains neural cell bodies, in contrast to white matter, which does not and mostly contains myelinated axon tracts...
.
Naming of neural pathways
The first named pathways are evident to the naked eye even in a poorly-preserved brainBrain
The brain is the center of the nervous system in all vertebrate and most invertebrate animals—only a few primitive invertebrates such as sponges, jellyfish, sea squirts and starfishes do not have one. It is located in the head, usually close to primary sensory apparatus such as vision, hearing,...
, and were named by the great anatomists of the Renaissance
Renaissance
The Renaissance was a cultural movement that spanned roughly the 14th to the 17th century, beginning in Italy in the Late Middle Ages and later spreading to the rest of Europe. The term is also used more loosely to refer to the historical era, but since the changes of the Renaissance were not...
using cadaver material. Examples of these include the great commissures of the brain such as the corpus callosum
Corpus callosum
The corpus callosum , also known as the colossal commissure, is a wide, flat bundle of neural fibers beneath the cortex in the eutherian brain at the longitudinal fissure. It connects the left and right cerebral hemispheres and facilitates interhemispheric communication...
(Latin
Latin
Latin is an Italic language originally spoken in Latium and Ancient Rome. It, along with most European languages, is a descendant of the ancient Proto-Indo-European language. Although it is considered a dead language, a number of scholars and members of the Christian clergy speak it fluently, and...
, "hard body"; not to be confused with the Latin word "colossus" - the "huge" statue), anterior commissure, and posterior commissure. Further examples of this (by no means a complete list) include the pyramidal tract
Corticospinal tract
The corticospinal or pyramidal tract is a collection of axons that travel between the cerebral cortex of the brain and the spinal cord....
, crus cerebri
Cerebral peduncle
Mainly, the three common areas that give rise to the cerebral peduncles are the cortex, the spinal cord and the cerebellum. The cerebral peduncle, by most classifications, is everything in the mesencephalon except the tectum. The region includes the midbrain tegmentum, crus cerebri and pretectum...
(Latin
Latin
Latin is an Italic language originally spoken in Latium and Ancient Rome. It, along with most European languages, is a descendant of the ancient Proto-Indo-European language. Although it is considered a dead language, a number of scholars and members of the Christian clergy speak it fluently, and...
, "leg of the brain"), and cerebellar peduncles (Latin
Latin
Latin is an Italic language originally spoken in Latium and Ancient Rome. It, along with most European languages, is a descendant of the ancient Proto-Indo-European language. Although it is considered a dead language, a number of scholars and members of the Christian clergy speak it fluently, and...
, "little foot of the cerebellum
Cerebellum
The cerebellum is a region of the brain that plays an important role in motor control. It may also be involved in some cognitive functions such as attention and language, and in regulating fear and pleasure responses, but its movement-related functions are the most solidly established...
"). Note that these names describe the appearance of a structure but give one no information on its function or location.
Later, as neuroanatomical
Neuroanatomy
Neuroanatomy is the study of the anatomy and organization of the nervous system. In contrast to animals with radial symmetry, whose nervous system consists of a distributed network of cells, animals with bilateral symmetry have segregated, defined nervous systems, and thus we can begin to speak of...
knowledge became more sophisticated, the trend was toward naming pathways by their origin and termination. For example, the nigrostriatal pathway
Nigrostriatal pathway
The nigrostriatal pathway is a neural pathway that connects the substantia nigra with the striatum. It is one of the four major dopamine pathways in the brain, and is particularly involved in the production of movement, as part of a system called the basal ganglia motor loop.Loss of dopamine...
, which is degenerated in Parkinson's disease
Parkinson's disease
Parkinson's disease is a degenerative disorder of the central nervous system...
, runs from the substantia nigra
Substantia nigra
The substantia nigra is a brain structure located in the mesencephalon that plays an important role in reward, addiction, and movement. Substantia nigra is Latin for "black substance", as parts of the substantia nigra appear darker than neighboring areas due to high levels of melanin in...
(Latin
Latin
Latin is an Italic language originally spoken in Latium and Ancient Rome. It, along with most European languages, is a descendant of the ancient Proto-Indo-European language. Although it is considered a dead language, a number of scholars and members of the Christian clergy speak it fluently, and...
, "black substance") to the corpus striatum
Striatum
The striatum, also known as the neostriatum or striate nucleus, is a subcortical part of the forebrain. It is the major input station of the basal ganglia system. The striatum, in turn, gets input from the cerebral cortex...
(Latin
Latin
Latin is an Italic language originally spoken in Latium and Ancient Rome. It, along with most European languages, is a descendant of the ancient Proto-Indo-European language. Although it is considered a dead language, a number of scholars and members of the Christian clergy speak it fluently, and...
, "striped body"). This naming can extend to include any number of structures in a pathway, such that the cerebellorubrothalamocortical pathway originates in the cerebellum
Cerebellum
The cerebellum is a region of the brain that plays an important role in motor control. It may also be involved in some cognitive functions such as attention and language, and in regulating fear and pleasure responses, but its movement-related functions are the most solidly established...
, synapse
Synapse
In the nervous system, a synapse is a structure that permits a neuron to pass an electrical or chemical signal to another cell...
s in the red nucleus
Red nucleus
The red nucleus is a structure in the rostral midbrain involved in motor coordination. It comprises a caudal magnocellular and a rostral parvocellular part.-Function:...
("ruber" in Latin), on to the thalamus
Thalamus
The thalamus is a midline paired symmetrical structure within the brains of vertebrates, including humans. It is situated between the cerebral cortex and midbrain, both in terms of location and neurological connections...
, and finally terminating in the cerebral cortex
Cerebral cortex
The cerebral cortex is a sheet of neural tissue that is outermost to the cerebrum of the mammalian brain. It plays a key role in memory, attention, perceptual awareness, thought, language, and consciousness. It is constituted of up to six horizontal layers, each of which has a different...
.
Sometimes, these two naming conventions coexist. For example, the name "pyramidal tract
Corticospinal tract
The corticospinal or pyramidal tract is a collection of axons that travel between the cerebral cortex of the brain and the spinal cord....
" has been mainly supplanted by lateral corticospinal tract
Corticospinal tract
The corticospinal or pyramidal tract is a collection of axons that travel between the cerebral cortex of the brain and the spinal cord....
in most texts. Note that the "old" name was primarily descriptive, evoking the pyramids
Great Pyramid of Giza
The Great Pyramid of Giza is the oldest and largest of the three pyramids in the Giza Necropolis bordering what is now El Giza, Egypt. It is the oldest of the Seven Wonders of the Ancient World, and the only one to remain largely intact...
of antiquity, from the appearance of this neural pathway in the medulla oblongata
Medulla oblongata
The medulla oblongata is the lower half of the brainstem. In discussions of neurology and similar contexts where no ambiguity will result, it is often referred to as simply the medulla...
. The "new" name is based primarily on its origin (in the primary motor cortex
Cerebral cortex
The cerebral cortex is a sheet of neural tissue that is outermost to the cerebrum of the mammalian brain. It plays a key role in memory, attention, perceptual awareness, thought, language, and consciousness. It is constituted of up to six horizontal layers, each of which has a different...
, Brodmann area
Brodmann area
A Brodmann area is a region of the cerebral cortex defined based on its cytoarchitectonics, or structure and organization of cells.-History:...
4) and termination (onto the alpha motor neurons of the spinal cord
Spinal cord
The spinal cord is a long, thin, tubular bundle of nervous tissue and support cells that extends from the brain . The brain and spinal cord together make up the central nervous system...
).
Functional aspects
In general, neuronNeuron
A neuron is an electrically excitable cell that processes and transmits information by electrical and chemical signaling. Chemical signaling occurs via synapses, specialized connections with other cells. Neurons connect to each other to form networks. Neurons are the core components of the nervous...
s receive information either at their dendrite
Dendrite
Dendrites are the branched projections of a neuron that act to conduct the electrochemical stimulation received from other neural cells to the cell body, or soma, of the neuron from which the dendrites project...
s or cell bodies. The axon
Axon
An axon is a long, slender projection of a nerve cell, or neuron, that conducts electrical impulses away from the neuron's cell body or soma....
of a nerve cell is, in general, responsible for transmitting information over a relatively long distance. Therefore, most neural pathways are made up of axon
Axon
An axon is a long, slender projection of a nerve cell, or neuron, that conducts electrical impulses away from the neuron's cell body or soma....
s. If the axon
Axon
An axon is a long, slender projection of a nerve cell, or neuron, that conducts electrical impulses away from the neuron's cell body or soma....
s have myelin
Myelin
Myelin is a dielectric material that forms a layer, the myelin sheath, usually around only the axon of a neuron. It is essential for the proper functioning of the nervous system. Myelin is an outgrowth of a type of glial cell. The production of the myelin sheath is called myelination...
sheaths, then the pathway appears bright white because myelin
Myelin
Myelin is a dielectric material that forms a layer, the myelin sheath, usually around only the axon of a neuron. It is essential for the proper functioning of the nervous system. Myelin is an outgrowth of a type of glial cell. The production of the myelin sheath is called myelination...
is primarily lipid
Lipid
Lipids constitute a broad group of naturally occurring molecules that include fats, waxes, sterols, fat-soluble vitamins , monoglycerides, diglycerides, triglycerides, phospholipids, and others...
. If most or all of the axons lack myelin
Myelin
Myelin is a dielectric material that forms a layer, the myelin sheath, usually around only the axon of a neuron. It is essential for the proper functioning of the nervous system. Myelin is an outgrowth of a type of glial cell. The production of the myelin sheath is called myelination...
sheaths (i.e., are unmyelinated), then the pathway will appear a darker beige color, which is generally called gray (American English
American English
American English is a set of dialects of the English language used mostly in the United States. Approximately two-thirds of the world's native speakers of English live in the United States....
, or grey in British English
British English
British English, or English , is the broad term used to distinguish the forms of the English language used in the United Kingdom from forms used elsewhere...
).
Some neurons are responsible for conveying information over long distances. For example, motor neurons, which travel from the spinal cord to the muscle, can have axons up to a meter in length in humans; the longest axon in the human body is almost two meters long in tall individuals and runs from the great toe
Toe
Toes are the digits of the foot of a tetrapod. Animal species such as cats that walk on their toes are described as being digitigrade. Humans, and other animals that walk on the soles of their feet, are described as being plantigrade; unguligrade animals are those that walk on hooves at the tips of...
to the medulla oblongata
Medulla oblongata
The medulla oblongata is the lower half of the brainstem. In discussions of neurology and similar contexts where no ambiguity will result, it is often referred to as simply the medulla...
of the brainstem. These are archetypical examples of neural pathways.
Major neural pathways
- arcuate fasciculusArcuate fasciculusThe arcuate fasciculus is the neural pathway connecting the posterior part of the temporoparietal junction with the frontal cortex in the brain and is now considered as part of the superior longitudinal fasciculus..-Neuroanatomy:...
- cerebral peduncleCerebral peduncleMainly, the three common areas that give rise to the cerebral peduncles are the cortex, the spinal cord and the cerebellum. The cerebral peduncle, by most classifications, is everything in the mesencephalon except the tectum. The region includes the midbrain tegmentum, crus cerebri and pretectum...
- corpus callosumCorpus callosumThe corpus callosum , also known as the colossal commissure, is a wide, flat bundle of neural fibers beneath the cortex in the eutherian brain at the longitudinal fissure. It connects the left and right cerebral hemispheres and facilitates interhemispheric communication...
- pyramidal or corticospinal tractCorticospinal tractThe corticospinal or pyramidal tract is a collection of axons that travel between the cerebral cortex of the brain and the spinal cord....
Dopamine pathways:
- mesocortical pathwayMesocortical pathwayThe mesocortical pathway is a neural pathway that connects the ventral tegmentum to the cerebral cortex, particularly the frontal lobes. It is one of the four major dopamine pathways in the brain...
- mesolimbic pathwayMesolimbic pathwayThe mesolimbic pathway is one of the dopaminergic pathways in the brain. The pathway begins in the ventral tegmental area of the midbrain and connects to the limbic system via the nucleus accumbens, the amygdala, and the hippocampus as well as to the medial prefrontal cortex...
. - nigrostriatal pathwayNigrostriatal pathwayThe nigrostriatal pathway is a neural pathway that connects the substantia nigra with the striatum. It is one of the four major dopamine pathways in the brain, and is particularly involved in the production of movement, as part of a system called the basal ganglia motor loop.Loss of dopamine...
- tuberoinfundibular pathwayTuberoinfundibular pathwayThe tuberoinfundibular pathway refers to a population of dopamine neurons in the arcuate nucleus of the mediobasal hypothalamus that project to the median eminence . It is one of the four major dopamine pathways in the brain...