The pons (from

Latin Latin ( or ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken by the Latins (Italic tribe), Latins in Latium (now known as Lazio), the lower Tiber area aroun ...

, "bridge") is part of the

brainstem The brainstem (or brain stem) is the posterior stalk-like part of the brain that connects the cerebrum with the spinal cord. In the human brain the brainstem is composed of the midbrain, the pons, and the medulla oblongata. The midbrain is conti ...

that in

human Humans (''Homo sapiens'') or modern humans are the most common and widespread species of primate, and the last surviving species of the genus ''Homo''. They are Hominidae, great apes characterized by their Prehistory of nakedness and clothing ...

s and other

mammals A mammal () is a vertebrate animal of the class Mammalia (). Mammals are characterised by the presence of milk-producing mammary glands for feeding their young, a broad neocortex region of the brain, fur or hair, and three middle e ...

, lies inferior to the

midbrain The midbrain or mesencephalon is the uppermost portion of the brainstem connecting the diencephalon and cerebrum with the pons. It consists of the cerebral peduncles, tegmentum, and tectum. It is functionally associated with vision, hearing, mo ...

, superior to the

medulla oblongata The medulla oblongata or simply medulla is a long stem-like structure which makes up the lower part of the brainstem. It is anterior and partially inferior to the cerebellum. It is a cone-shaped neuronal mass responsible for autonomic (involun ...

and anterior to the

cerebellum The cerebellum (: cerebella or cerebellums; Latin for 'little brain') is a major feature of the hindbrain of all vertebrates. Although usually smaller than the cerebrum, in some animals such as the mormyrid fishes it may be as large as it or eve ...

. The pons is also called the pons Varolii ("bridge of Varolius"), after the Italian anatomist and surgeon Costanzo Varolio (1543–75). This region of the brainstem includes neural pathways and

tracts Tract may refer to: Geography and real estate * Housing tract, an area of land that is subdivided into smaller individual lots * Land lot or tract, a section of land * Census tract, a geographic region defined for the purpose of taking a census ...

that conduct signals from the

brain The brain is an organ (biology), organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It consists of nervous tissue and is typically located in the head (cephalization), usually near organs for ...

down to the cerebellum and medulla, and tracts that carry the sensory signals up into the

thalamus The thalamus (: thalami; from Greek language, Greek Wikt:θάλαμος, θάλαμος, "chamber") is a large mass of gray matter on the lateral wall of the third ventricle forming the wikt:dorsal, dorsal part of the diencephalon (a division of ...

Structure

The pons in humans measures about in length. It is the part of the brainstem situated between the midbrain and the medulla oblongata. The horizontal ''medullopontine sulcus'' demarcates the boundary between the pons and medulla oblongata on the ventral aspect of the brainstem, and the roots of cranial nerves VI/VII/VIII emerge from the brainstem along this groove. The junction of pons, medulla oblongata, and cerebellum forms the cerebellopontine angle. The ''superior pontine sulcus'' separates the pons from the midbrain. Posteriorly, the pons curves on either side into a

middle cerebellar peduncle The middle cerebellar peduncle (or brachium pontis) is one of three paired cerebellar peduncles connecting the brainstem to the cerebellum. The connection is from the pons. It connects the pons to the cerebellum, with fibres originating from the ...

. A

cross-section Cross section may refer to: * Cross section (geometry) ** Cross-sectional views in architecture and engineering 3D * Cross section (geology) * Cross section (electronics) * Radar cross section, measure of detectability * Cross section (physics) ...

of the pons divides it into a ventral and a dorsal area. The ventral pons is known as the basilar part, and the dorsal pons is known as the

pontine tegmentum The pontine tegmentum, or dorsal pons, is the dorsal part of the pons located within the brainstem. The ventral part or ventral pons is known as the basilar part of the pons, or basilar pons. Along with the dorsal surface of the medulla oblonga ...

. The ventral aspect of the pons faces the clivus, with the

pontine cistern The prepontine cistern, or pontine cistern is one of the subarachnoid cisterns situated ventral to the pons. It contains the basilar artery. Each lateral aperture opens into the pontine cistern just posterior to the cranial nerve VIII. Anatom ...

intervening between the two structures. The ventral surface of the pons features a midline

basilar sulcus The basilar sulcus (groove for basilar artery) is a groove in the pons, part of the brainstem. The basilar sulcus is vertical directed and lies in the midline of the pons on its anterior (front) surface. The basilar artery The basilar artery ( ...

along which the

basilar artery The basilar artery (U.K.: ; U.S.: ) is one of the arteries that supplies the brain with oxygen-rich blood. The two vertebral arteries and the basilar artery are known as the vertebral basilar system, which supplies blood to the posterior part o ...

may or may not course. There is a bulge to either side of the basilar sulcus, created by the

pontine nuclei The pontine nuclei (or griseum pontis) are all the neurons of the ventral pons. Corticopontine fibres project from the primary motor cortex to the ipsilateral pontine nucleus; pontocerebellar fibers then relay the information to the contralater ...

that are interweaved amid the descending fibres within the substance of the pons. The

superior cerebellar artery The superior cerebellar artery (SCA) is an artery of the head. It arises near the end of the basilar artery. It is a branch of the basilar artery. It supplies parts of the cerebellum, the midbrain, and other nearby structures. It is the cause of t ...

winds around the upper margin of the pons.

Vasculature

Most of the pons is supplied by the

pontine arteries The pontine arteries are a number of small arteries which come off at right angles from either side of the basilar artery and supply the pons and adjacent parts of the brain. The pontine arteries include the paramedian arteries, the short circumfe ...

, which arise from the basilar artery. A smaller portion of the pons is supplied by the

anterior Standard anatomical terms of location are used to describe unambiguously the anatomy of humans and other animals. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position pro ...

and posterior inferior cerebellar arteries.

Development

During

embryonic development In developmental biology, animal embryonic development, also known as animal embryogenesis, is the developmental stage of an animal embryo. Embryonic development starts with the fertilization of an egg cell (ovum) by a sperm, sperm cell (spermat ...

, the

metencephalon The metencephalon is the embryonic part of the hindbrain that differentiates into the pons and the cerebellum. It contains a portion of the fourth ventricle and the trigeminal nerve (CN V), abducens nerve (CN VI), facial nerve (CN VII), an ...

develops from the

rhombencephalon The hindbrain, rhombencephalon (shaped like a rhombus) is a developmental categorization of portions of the central nervous system in vertebrates. It includes the medulla, pons, and cerebellum. Together they support vital bodily processes. Met ...

and gives rise to two structures: the pons and the cerebellum. The

alar plate The alar plate (or alar lamina) is a neural structure in the embryonic nervous system, part of the dorsal side of the neural tube, that involves the communication of general somatic and general visceral sensory impulses. The caudal part later ...

produces sensory

neuroblast In vertebrates, a neuroblast or primitive nerve cell is a postmitotic cell that does not divide further, and which will develop into a neuron after a migration phase. In invertebrates such as ''Drosophila,'' neuroblasts are neural progenitor cells ...

s, which will give rise to the

solitary nucleus The solitary nucleus (SN) (nucleus of the solitary tract, nucleus solitarius, or nucleus tractus solitarii) is a series of neurons whose cell bodies form a roughly vertical column of grey matter in the medulla oblongata of the brainstem. Their a ...

and its special visceral afferent (SVA) column; the cochlear and

vestibular nuclei The vestibular nuclei (VN) are the cranial nuclei for the vestibular nerve located in the brainstem. In Terminologia Anatomica, they are grouped in both the pons and the medulla in the brainstem The brainstem (or brain stem) is the poste ...

, which form the

special somatic afferent Special somatic afferent fibers (SSA) are the afferent nerve fibers that carry information from the special senses of vision, hearing and balance. The cranial nerves containing SSA fibers are the optic nerve (CN II) and the vestibulocochlear nerve ...

(SSA) fibers of the

vestibulocochlear nerve The vestibulocochlear nerve or auditory vestibular nerve, also known as the eighth cranial nerve, cranial nerve VIII, or simply CN VIII, is a cranial nerve that transmits sound and equilibrium (balance) information from the inner ear to the br ...

, the spinal and principal

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, and into the upper cervical spinal cord. The nucleus is divided into three parts, from rostral to ...

, which form the general somatic afferent column (GSA) of the

trigeminal nerve In neuroanatomy, the trigeminal nerve (literal translation, lit. ''triplet'' nerve), also known as the fifth cranial nerve, cranial nerve V, or simply CN V, is a cranial nerve responsible for Sense, sensation in the face and motor functions ...

, and the

which relays to the

. Basal plate neuroblasts give rise to the abducens nucleus, which forms the

general somatic efferent fibers The general (spinal) somatic efferent neurons (GSE, somatomotor, or somatic motor fibers) arise from motor neuron cell bodies in the ventral horns of the gray matter within the spinal cord. They exit the spinal cord through the ventral roots, carry ...

(GSE); the facial and motor trigeminal nuclei, which form the

special visceral efferent Special visceral efferent fibers (SVE) are the efferent nerve fibers that provide motor innervation to the muscles of the pharyngeal arches in humans, and the branchial arches in fish. Some sources prefer the term "branchiomotor" or "branchial ef ...

(SVE) column, and the

superior salivatory nucleus The salivatory nuclei are two general visceral efferent fiber, general visceral efferent Nucleus (anatomy), nuclei located in the caudal pons, dorsal and lateral to the facial nucleus. Their neurons give rise to preganglionic nerve fibers, pregan ...

, which forms the

general visceral efferent fibers General visceral efferent fibers (GVE), visceral efferents or autonomic efferents are the efferent nerve fibers of the autonomic nervous system (also known as the ''visceral efferent nervous system'') that provide motor innervation to smooth musc ...

(GVE) of the

facial nerve The facial nerve, also known as the seventh cranial nerve, cranial nerve VII, or simply CN VII, is a cranial nerve that emerges from the pons of the brainstem, controls the muscles of facial expression, and functions in the conveyance of ta ...

Nuclei

A number of

cranial nerve nuclei A cranial nerve nucleus is a collection of neuron cell bodies (gray matter) in the brain stem that is associated with one or more of the cranial nerves. Axons carrying information to and from the cranial nerves form a synapse first at these nucl ...

are present in the pons: * mid-pons: the principal sensory nucleus of the trigeminal nerve (V) * mid-pons: the motor nucleus for the trigeminal nerve (V) * lower down in the pons: abducens nucleus (VI) * lower down in the pons: facial nerve nucleus (VII) * lower down in the pons: vestibulocochlear nuclei (

and

cochlear nuclei The cochlear nucleus (CN) or cochlear nuclear complex comprises two cranial nerve nuclei in the human brainstem, the ventral cochlear nucleus (VCN) and the dorsal cochlear nucleus (DCN). The ventral cochlear nucleus is unlayered whereas the d ...

) (VIII)

Function

Functions of these four cranial nerves (V-VIII) include regulation of respiration, control of involuntary actions, 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, and the secretion of saliva and tears. 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 consisting of the subparabrachial and the medial parabrachial nuclei. This center regulates the change from inhalation to exhalation. The pons is implicated in

sleep paralysis Sleep paralysis is a state, during waking up or falling asleep, in which a person is conscious but in a complete state of full-body paralysis. During an episode, the person may hallucinate (hear, feel, or see things that are not there), wh ...

, and may also play a role in generating dreams.

Clinical significance

* Central pontine myelinolysis is a

demyelinating disease A demyelinating disease refers to any disease affecting the nervous system where the myelin sheath surrounding neurons is damaged. This damage disrupts the transmission of signals through the affected nerves, resulting in a decrease in their con ...

that causes difficulty with sense of balance, walking, sense of touch, swallowing and speaking. In a clinical setting, it is often associated with transplant or rapid correction of blood sodium. Undiagnosed, it can lead to death or

locked-in syndrome Locked-in syndrome (LIS), also known as pseudocoma, is a condition in which a patient is aware but cannot move or communicate verbally due to complete paralysis of nearly all voluntary muscles in their body except for vertical eye movements and ...

Other animals

Evolution

The pons first evolved as an offshoot of the medullary

reticular formation The reticular formation is a set of interconnected nuclei in the brainstem that spans from the lower end of the medulla oblongata to the upper end of the midbrain. The neurons of the reticular formation make up a complex set of neural networks ...

. Pritchard and Alloway ''Medical Neuroscience'' Since

lamprey Lampreys (sometimes inaccurately called lamprey eels) are a group of Agnatha, jawless fish comprising the order (biology), order Petromyzontiformes , sole order in the Class (biology), class Petromyzontida. The adult lamprey is characterize ...

s 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, 525 million years ago. Butler and Hodos ''Comparative vertebrate neuroanatomy: evolution and adaptation''

Additional images

File:Pons.gif, Location and topography of pons (animation) File:Gray701.png, Axial section of the pons, at its upper part File:Gray719.png, Hind- and mid-brains; posterolateral view File:Gray720.png, Median sagittal section of brain File:Brain stem sagittal section.svg, Nuclei of the pons and brainstem File:Slide2cuc.JPG, Cerebrum. Deep dissection. Inferior dissection.

References

* *

External links

Diagram at UCC
* {{Authority control Neurology Brain Brainstem