Dorsal longitudinal fasciculus
Encyclopedia
The dorsal longitudinal fasciculus (DLF) (not to be confused with the medial longitudinal fasciculus
, nor the superior longitudinal fasciculus
) is a white matter
fiber tract located within the brain stem
, specifically in the dorsal brainstem tegmentum. The DLF travels through the periaqueductal gray
matter. The tract is composed of a diffuse brainstem pathway located in the periventricular gray matter comprising ascending visceral sensory axons and descending hypothalamic axons.
As with all white matter tracts, the DLF consists of myelin
ated axon
s carrying information between neuron
s. The DLF, carries both ascending and descending fibers, and conveys visceral motor and sensory signals.
of the reticular formation
. These fibers synapse
onto the hypothalamus
and carry visceral
information to the brain
.
Brainstem afferents in DLF include fibers coming from the parabrachial nucleus
, which conveys taste & general visceral sensation to the hypothalamus from the nucleus of the tractus solitarius in the medulla. Afferents distribute to the posterior nucleus and periventricular nuclei of the hypothalamus.
. These fibers then descend through the brain stem periaqueductal gray matter along the base of the fourth ventricle
. These fibers continue on into the spinal cord
where they synapse with preganglionic autonomic
neurons.
Hypothalamic efferents in DLF arise from the paraventricular nucleus
, supraoptic nucleus
and periventricular nucleus
, and send information to multiple areas, including:
Note that at least some of the output from the hypothalamus lies outside of the DLF, within a set of Descending Hypothalamic Fibers running next to the spinothalamic tract
; lesions of this area canonically lead to ipsilateral Horner's syndrome
.
Medial longitudinal fasciculus
The medial longitudinal fasciculus is a pair of crossed fiber tracts , one on each side of the brainstem. These bundles of axons are situated near the midline of the brainstem and are composed of both ascending and descending fibers that arise from a number of sources and terminate in different...
, nor the superior longitudinal fasciculus
Superior longitudinal fasciculus
The superior longitudinal fasciculus is a pair of long bi-directional bundles of neurons connecting the front and the back of the cerebrum. Each association fiber bundle is lateral to the centrum ovale of a cerebral hemisphere and connects the frontal, occipital, parietal, and temporal lobes...
) is a 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...
fiber tract located within the brain stem
Brain stem
In vertebrate anatomy the brainstem is the posterior part of the brain, adjoining and structurally continuous with the spinal cord. The brain stem provides the main motor and sensory innervation to the face and neck via the cranial nerves...
, specifically in the dorsal brainstem tegmentum. The DLF travels through the periaqueductal gray
Periaqueductal gray
Periaqueductal gray is the gray matter located around the cerebral aqueduct within the tegmentum of the midbrain. It plays a role in the descending modulation of pain and in defensive behaviour...
matter. The tract is composed of a diffuse brainstem pathway located in the periventricular gray matter comprising ascending visceral sensory axons and descending hypothalamic axons.
As with all white matter tracts, the DLF consists of 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...
ated 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 carrying information between 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. The DLF, carries both ascending and descending fibers, and conveys visceral motor and sensory signals.
Ascending fibers
The DLF ascending tract has its origins in nucleiNucleus (neuroanatomy)
In neuroanatomy, a nucleus is a brain structure consisting of a relatively compact cluster of neurons. It is one of the two most common forms of nerve cell organization, the other being layered structures such as the cerebral cortex or cerebellar cortex. In anatomical sections, a nucleus shows up...
of the reticular formation
Reticular formation
The reticular formation is a part of the brain that is involved in actions such as awaking/sleeping cycle, and filtering incoming stimuli to discriminate irrelevant background stimuli...
. These fibers 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...
onto the hypothalamus
Hypothalamus
The Hypothalamus is a portion of the brain that contains a number of small nuclei with a variety of functions...
and carry visceral
Viscus
In anatomy, a viscus is an internal organ, and viscera is the plural form. The viscera, when removed from a butchered animal, are known collectively as offal...
information to 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,...
.
Brainstem afferents in DLF include fibers coming from the parabrachial nucleus
Parabrachial nucleus
The parabrachial nucleus is a region in the pons human brain that is related to the ascending reticular activating system . It can be subdivided into the lateral parabrachial nucleus and the medial parabrachial nucleus...
, which conveys taste & general visceral sensation to the hypothalamus from the nucleus of the tractus solitarius in the medulla. Afferents distribute to the posterior nucleus and periventricular nuclei of the hypothalamus.
Descending fibers
The descending portion of the DLF originates in the hypothalamusHypothalamus
The Hypothalamus is a portion of the brain that contains a number of small nuclei with a variety of functions...
. These fibers then descend through the brain stem periaqueductal gray matter along the base of the fourth ventricle
Fourth ventricle
The fourth ventricle is one of the four connected fluid-filled cavities within the human brain. These cavities, known collectively as the ventricular system, consist of the left and right lateral ventricles, the third ventricle, and the fourth ventricle...
. These fibers continue on into 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...
where they synapse with preganglionic autonomic
Autonomic ganglion
Autonomic ganglia are clusters of neuronal cell bodies and their dendrites and are essentially a junction between autonomic nerves originating from the central nervous system and autonomic nerves innervating their target organs in the periphery....
neurons.
Hypothalamic efferents in DLF arise from the paraventricular nucleus
Paraventricular nucleus
The paraventricular nucleus is a neuronal nucleus in the hypothalamus. It contains multiple subpopulations of neurons that are activated by a variety of stressful and/or physiological changes. Many PVN neurons project directly to the posterior pituitary where they release oxytocin or vasopressin...
, supraoptic nucleus
Supraoptic nucleus
The supraoptic nucleus is a nucleus of magnocellular neurosecretory cells in the hypothalamus of the mammalian brain. The nucleus is situated at the base of the brain, adjacent to the optic chiasm...
and periventricular nucleus
Periventricular nucleus
The Periventricular nucleus is a thin sheet of small neurons located in the wall of the third ventricle, a composite structure of the hypothalamus. Functions in analgesia....
, and send information to multiple areas, including:
- 1) midbrain central gray for pain modulation,
- 2) the medullary autonomic centers for heart rate, blood pressure, and respiration,
- 3) the ventral tegmental area,
- 4) brainstem parasympathetic nuclei (dorsal motor nucleus of the Vagus and salivatory nuclei for the eyes),
- 5) thoraco-lumbar preganglionic sympathetic neurons, and
- 6) lumbo-sacral preganglionic parasympathetic neurons.
Note that at least some of the output from the hypothalamus lies outside of the DLF, within a set of Descending Hypothalamic Fibers running next to the spinothalamic tract
Spinothalamic tract
The spinothalamic tract is a sensory pathway originating in the spinal cord. It transmits information to the thalamus about pain, temperature, itch and crude touch...
; lesions of this area canonically lead to ipsilateral Horner's syndrome
Horner's syndrome
Horner's syndrome is the combination of drooping of the eyelid and constriction of the pupil , sometimes accompanied by decreased sweating of the face on the same side; redness of the conjunctiva of the eye is often also present...
.
External links
- NIF Search - Dorsal longitudinal fasciculus via the Neuroscience Information FrameworkNeuroscience Information FrameworkThe Neuroscience Information Framework is a repository of global neuroscience web resources, including experimental, clinical, and translational neuroscience databases, knowledge bases, atlases, and genetic/genomic resources.-Description:...