Lateral reticular formation
Encyclopedia
Moving caudally from the rostral midbrain, at the site of the rostral pons
and the midbrain, the medial RF becomes less prominent, and the lateral RF becomes more prominent.
Existing on the sides of the medial reticular formation is its lateral cousin, which is particularly pronounced in the rostral medulla
and caudal pons.
Out from this area spring the cranial nerves, including the very important vagus nerve
.
The Lateral RF is known for its ganglion
s and areas of interneurons around the cranial nerves
, which serve to mediate their characteristic reflexes and functions.
, which relays their signals to the cortex
, forming the Ascending reticular activation system or ARAS.
This is part of the ascending reticular activation system pictured above.
These axonal projections are both cholinergic
and noradrenergic, the former of which projects to the sensory nucleus of the thalamus and the reticular nucleus of the thalamus.
The reticular nucleus of the thalamus (not pictured) has nothing to do with the reticular formation; its naming was a coincidence.
This nucleus wraps around the thalamus, forming a thin net, for which it is named (reticular means netlike or an intricate network). The reticular nucleus of the thalamus, when active, inhibits the sensory nucleus with GABA
.
The sensory nucleus is positively stimulated by acetylcholine, while the reticular nucleus is inhibited by acetylcholine.
This means that when the Ascending Reticular Activation System is active, as during waking hours, the inhibitory actions of the reticular nucleus are inhibited.
The thalamus is never fully stimulated to an action potential via these projections from the ARAS, but it is sensitized by them .
During sleep, when the ARAS shuts down, the reticular nucleus is free to inhibit the sensory nucleus of the thalamus. This is how the reticular formation mediates attention and wakefulness.
This makes sense because during wakefulness, it is easy to take in sensory stimuli.
Once the ARAS system begins to shut down, the world seems duller, and it is much harder to take in information from the outside world.
The chemical equivalent of this would be if the thalamus was being partially inhibited by GABA, making it more difficult to relay information to the cortex.
Pons
The pons is a structure located on the brain stem, named after the Latin word for "bridge" or the 16th-century Italian anatomist and surgeon Costanzo Varolio . It is superior to the medulla oblongata, inferior to the midbrain, and ventral to the cerebellum. In humans and other bipeds this means it...
and the midbrain, the medial RF becomes less prominent, and the lateral RF becomes more prominent.
Existing on the sides of the medial reticular formation is its lateral cousin, which is particularly pronounced in the rostral medulla
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...
and caudal pons.
Out from this area spring the cranial nerves, including the very important vagus nerve
Vagus nerve
The vagus nerve , also called pneumogastric nerve or cranial nerve X, is the tenth of twelve paired cranial nerves...
.
The Lateral RF is known for its ganglion
Ganglion
In anatomy, a ganglion is a biological tissue mass, most commonly a mass of nerve cell bodies. Cells found in a ganglion are called ganglion cells, though this term is also sometimes used to refer specifically to retinal ganglion cells....
s and areas of interneurons around the cranial nerves
Cranial nerves
Cranial nerves are nerves that emerge directly from the brain, in contrast to spinal nerves, which emerge from segments of the spinal cord. In humans, there are traditionally twelve pairs of cranial nerves...
, which serve to mediate their characteristic reflexes and functions.
Ascending reticular activation system
The dorsolateral reticular formation shoots long ascending axons to the thalamusThalamus
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...
, which relays their signals to the 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...
, forming the Ascending reticular activation system or ARAS.
This is part of the ascending reticular activation system pictured above.
These axonal projections are both cholinergic
Cholinergic
The word choline generally refers to the various quaternary ammonium salts containing the N,N,N-trimethylethanolammonium cation. Found in most animal tissues, choline is a primary component of the neurotransmitter acetylcholine and functions with inositol as a basic constituent of lecithin...
and noradrenergic, the former of which projects to the sensory nucleus of the thalamus and the reticular nucleus of the thalamus.
The reticular nucleus of the thalamus (not pictured) has nothing to do with the reticular formation; its naming was a coincidence.
This nucleus wraps around the thalamus, forming a thin net, for which it is named (reticular means netlike or an intricate network). The reticular nucleus of the thalamus, when active, inhibits the sensory nucleus with GABA
Gabâ
Gabâ or gabaa, for the people in many parts of the Philippines), is the concept of a non-human and non-divine, imminent retribution. A sort of negative karma, it is generally seen as an evil effect on a person because of their wrongdoings or transgressions...
.
The sensory nucleus is positively stimulated by acetylcholine, while the reticular nucleus is inhibited by acetylcholine.
This means that when the Ascending Reticular Activation System is active, as during waking hours, the inhibitory actions of the reticular nucleus are inhibited.
The thalamus is never fully stimulated to an action potential via these projections from the ARAS, but it is sensitized by them .
During sleep, when the ARAS shuts down, the reticular nucleus is free to inhibit the sensory nucleus of the thalamus. This is how the reticular formation mediates attention and wakefulness.
This makes sense because during wakefulness, it is easy to take in sensory stimuli.
Once the ARAS system begins to shut down, the world seems duller, and it is much harder to take in information from the outside world.
The chemical equivalent of this would be if the thalamus was being partially inhibited by GABA, making it more difficult to relay information to the cortex.
Nuclei
- nucleus reticularis lateralis
- nucleus reticularis paramedianus
- nucleus reticularis tegmenti pontis