Pons
Encyclopedia
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
(pons Varolii). It is superior to the medulla oblongata
, inferior
to the midbrain, and ventral to the cerebellum
. In human
s and other biped
s this means it is above the medulla, below the midbrain, and anterior to the cerebellum. This white matter
includes tracts that conduct signals from the cerebrum down to the cerebellum and medulla, and tracts that carry the sensory signals up into the thalamus
.
The pons measures about 2.5 cm in length. Most of it appears as a broad anterior bulge rostral to the medulla. Posteriorly, it consists mainly of two pairs of thick stalks called cerebellar peduncles. They connect the cerebellum to the pons and midbrain.
The pons contains nuclei that relay signals from the forebrain to the cerebellum, along with nuclei that deal primarily with sleep, respiration, swallowing, bladder control, hearing, equilibrium, taste, eye movement, facial expressions, facial sensation, and posture.
Within the pons is the pneumotaxic center
, a nucleus in the pons that regulates the change from inspiration to expiration.
The pons also contains the sleep paralysis center of the brain and also plays a role in generating dreams.
and gives rise to two structures: the pons and the cerebellum. The alar plate
produce sensory neuroblast
s, which will give rise to the solitary nucleus
and its special visceral afferent
(SVA) column, the cochlear
and vestibular nuclei
—which form the special somatic afferent
(SSA) fibers of the vestibulocochlear nerve
—, the spinal and principal trigeminal nerve nuclei
—which form the general somatic afferent column
(GSA) of the trigeminal nerve
—, and the pontine nuclei
which relays to the cerebellum
.
Basal plate
neuroblasts give rise to the abducent nucleus—which forms the general somatic efferent fibers
(GSE)—, the facial and motor trigeminal nuclei—which form the special visceral efferent
(SVE) column—, and the superior salivatory nucleus, which forms the general visceral efferent fibers
of the facial nerve
.
The functions of these four nerves include sensory roles in hearing, equilibrium, and taste, and in facial sensations such as touch and pain; as well as motor roles in eye movement, facial expressions, chewing, swallowing, urination, and the secretion of saliva and tears.
. Since lampreys possess a pons, it has been argued that it must have evolved as a region distinct from the medulla
by the time the first agnathans appeared, 505 million years ago.
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...
, named after the Latin word for "bridge" or the 16th-century Italian anatomist and surgeon Costanzo Varolio
Costanzo Varolio
Costanzo Varolio, Latinized as Constantius Varolius, was an Italian anatomist and a papal physician to Gregory XIII. He was a pupil to the anatomist Giulio Cesare Aranzio, himself a pupil of Vesalius. He received his doctorate in medicine in 1567...
(pons Varolii). It is superior 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...
, inferior
Inferior
Inferior means of lower station, rank, degree, or grade . It may also refer to:* Inferiority complex* An anatomical term of location* Inferior angle of the scapula, in the human skeleton...
to the midbrain, and ventral to 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...
. In human
Human
Humans are the only living species in the Homo genus...
s and other biped
Biped
Bipedalism is a form of terrestrial locomotion where an organism moves by means of its two rear limbs, or legs. An animal or machine that usually moves in a bipedal manner is known as a biped , meaning "two feet"...
s this means it is above the medulla, below the midbrain, and anterior to the cerebellum. This 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...
includes tracts that conduct signals from the cerebrum down to the cerebellum and medulla, and tracts that carry the sensory signals up into 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...
.
The pons measures about 2.5 cm in length. Most of it appears as a broad anterior bulge rostral to the medulla. Posteriorly, it consists mainly of two pairs of thick stalks called cerebellar peduncles. They connect the cerebellum to the pons and midbrain.
The pons contains nuclei that relay signals from the forebrain to the cerebellum, along with nuclei that deal primarily with sleep, respiration, swallowing, bladder control, hearing, equilibrium, taste, eye movement, facial expressions, facial sensation, and posture.
Within the pons is the pneumotaxic center
Pneumotaxic center
The pneumotaxic center , also known as the pontine respiratory group , is a network of neurons in the rostral dorsal lateral pons. It consists of the Kölliker-Fuse nucleus and the medial parabrachial nucleus....
, a nucleus in the pons that regulates the change from inspiration to expiration.
The pons also contains the sleep paralysis center of the brain and also plays a role in generating dreams.
Embryonic development
During embryonic development the embryonic metencephalon develops from the rhombencephalonRhombencephalon
The rhombencephalon is a developmental categorization of portions of the central nervous system in vertebrates.The rhombencephalon can be subdivided in a variable number of transversal swellings called rhombomeres...
and gives rise to two structures: the pons and the cerebellum. The alar plate
Alar plate
The alar plate is a neural structure in the embryonic nervous system, part of the dorsal side of neural tube, that involves the communication of general somatic and general visceral sensory impulses. The caudal part later becomes sensory axon part of the spinal cord.-External links:* *...
produce sensory neuroblast
Neuroblast
A neuroblast is a dividing cell that will develop into neurons or glia. The characterisation of neuroblasts and their development in Drosophila melanogaster was widely achieved by Chris Doe, Corey Goodman and Mike Bate. In humans, neuroblasts produced by stem cells in the adult subventricular zone...
s, which will give rise to the solitary nucleus
Solitary nucleus
The solitary tract and nucleus are structures in the brainstem that carry and receive visceral sensation and taste from the facial , glossopharyngeal and vagus cranial nerves.-Anatomy:...
and its special visceral afferent
Special visceral afferent
' refers to afferent nerves that develop in association with the gastrointestinal tract. They carry the special senses of smell and taste . The cranial nerves containing SVA fibers are the olfactory nerve , the facial nerve , the glossopharyngeal nerve and the vagus nerve...
(SVA) column, the cochlear
Cochlear nuclei
The cochlear nuclei are two heterogeneous collections of neurons in the mammalian brainstem that receive input from the cochlear nerve, which carry sound information from the cochleae...
and vestibular nuclei
Vestibular nuclei
The vestibular nuclei are the cranial nuclei for the vestibular nerve.In Terminologia Anatomica they are grouped in both the pons and medulla.-Subnuclei:There are 4 subnuclei; they are situated at the floor of the fourth ventricle....
—which form the special somatic afferent
Special somatic afferent
Special somatic afferent refers to afferent nerves that carry information from the special senses of vision, hearing and balance. The cranial nerves containing SSA fibers are the optic nerve and the vestibulocochlear nerve...
(SSA) fibers of the vestibulocochlear nerve
Vestibulocochlear nerve
The vestibulocochlear nerve is the eighth of twelve cranial nerves, and is responsible for transmitting sound and equilibrium information from the inner ear to the brain...
—, the spinal and principal trigeminal nerve nuclei
Trigeminal nerve nuclei
The sensory trigeminal nerve nuclei are the largest of the cranial nerve nuclei, and extend through the whole of the midbrain, pons and medulla.The nucleus is divided into three parts, from rostral to caudal :...
—which form the general somatic afferent column
General somatic afferent fibers
The general somatic afferent fibers , afferent fibers, arise from cells in the spinal ganglia and are found in all the spinal nerves, except occasionally the first cervical, and conduct impulses of pain, touch and temperature from the surface of the body through the posterior roots to the spinal...
(GSA) of the trigeminal nerve
Trigeminal nerve
The trigeminal nerve contains both sensory and motor fibres. It is responsible for sensation in the face and certain motor functions such as biting, chewing, and swallowing. Sensory information from the face and body is processed by parallel pathways in the central nervous system...
—, and the pontine nuclei
Pontine nuclei
The pontine nuclei are a part of the pons involved in motor activity. Corticopontine fibres carry information from the primary motor cortex to the ipsilateral pontine nucleus in the ventral pons, and the pontocerebellar projection then carries that information to the contralateral cerebellum via...
which relays to 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...
.
Basal plate
Basal plate (neural tube)
In the developing nervous system, the basal plate is the region of the neural tube ventral to the sulcus limitans. It extends from the rostral mesencephalon to the end of the spinal cord and contains primarily motor neurons, whereas neurons found in the alar plate are primarily associated with...
neuroblasts give rise to the abducent nucleus—which forms the general somatic efferent fibers
General somatic efferent fibers
The *spinal* somatic efferent neurons , arise from motor neuron cell bodies in the ventral horns of the gray matter within the spinal cord...
(GSE)—, the facial and motor trigeminal nuclei—which form the special visceral efferent
Special visceral efferent
Special visceral efferent refers to efferent nerves which supply muscles which derived from the branchial arches.Some sources prefer the term "branchiomotor", or "branchial efferent"....
(SVE) column—, and the superior salivatory nucleus, which forms the general visceral efferent fibers
General visceral efferent fibers
The general visceral efferent fibers , probably arise from cells in the lateral column or the base of the anterior column and emerge through the anterior roots and white rami communicantes....
of the facial nerve
Facial nerve
The facial nerve is the seventh of twelve paired cranial nerves. It emerges from the brainstem between the pons and the medulla, and controls the muscles of facial expression, and functions in the conveyance of taste sensations from the anterior two-thirds of the tongue and oral cavity...
.
Cranial nerve nuclei
A number of cranial nerve nuclei are present in the pons:- mid-pons: The chief or pontine nucleus of the trigeminal nerveTrigeminal nerveThe trigeminal nerve contains both sensory and motor fibres. It is responsible for sensation in the face and certain motor functions such as biting, chewing, and swallowing. Sensory information from the face and body is processed by parallel pathways in the central nervous system...
sensory nucleus (V) - mid-pons: the motor nucleus for the trigeminal nerve (V)
- lower down in the pons: abducens nucleusAbducens nucleusThe abducens nucleus is the originating nucleus from which the abducens nerve emerges - a cranial nerve nucleus. This nucleus is located beneath the fourth ventricle in the caudal portion of the pons, medial to the sulcus limitans....
(VI) - lower down in the pons: facial nerve nucleus (VII)
- lower down in the pons: vestibulocochlearVestibulocochlear nerveThe vestibulocochlear nerve is the eighth of twelve cranial nerves, and is responsible for transmitting sound and equilibrium information from the inner ear to the brain...
nuclei (vestibular nucleiVestibular nucleiThe vestibular nuclei are the cranial nuclei for the vestibular nerve.In Terminologia Anatomica they are grouped in both the pons and medulla.-Subnuclei:There are 4 subnuclei; they are situated at the floor of the fourth ventricle....
and cochlear nucleiCochlear nucleiThe cochlear nuclei are two heterogeneous collections of neurons in the mammalian brainstem that receive input from the cochlear nerve, which carry sound information from the cochleae...
) (VIII)
The functions of these four nerves include sensory roles in hearing, equilibrium, and taste, and in facial sensations such as touch and pain; as well as motor roles in eye movement, facial expressions, chewing, swallowing, urination, and the secretion of saliva and tears.
Related diseases
- Central pontine myelinosis, a demyelination disease that causes difficulty with sense of balance, walking, sense of touch, swallowing and speaking. In a clinical setting it is often associated with transplant. Undiagnosed it can lead to death or locked-in syndromeLocked-In syndromeLocked-in syndrome is a condition in which a patient is aware and awake but cannot move or communicate verbally due to complete paralysis of nearly all voluntary muscles in the body except for the eyes. Total locked-in syndrome is a version of locked-in syndrome where the eyes are paralyzed as...
.
Evolution
The pons first evolved as an offshoot of the medullary reticular formationReticular 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...
. Since lampreys possess a pons, it has been argued that it must have evolved as a region distinct from the 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...
by the time the first agnathans appeared, 505 million years ago.