The pons (from

Latin Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through the power of the ...

, "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 cont ...

that in

human Humans (''Homo sapiens'') are the most abundant and widespread species of primate, characterized by bipedalism and exceptional cognitive skills due to a large and complex brain. This has enabled the development of advanced tools, culture, ...

s and other

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' (from Latin ''bis'' 'double' ...

s lies inferior to the

midbrain The midbrain or mesencephalon is the forward-most portion of the brainstem and is associated with vision, hearing, motor control, sleep and wakefulness, arousal (alertness), and temperature regulation. The name comes from the Greek ''mesos'', " ...

, superior to the medulla oblongata and anterior to the

cerebellum The cerebellum (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 or even larger. In humans, the cerebel ...

. The pons is also called the pons Varolii ("bridge of Varolius"), after the Italian anatomist and surgeon

Costanzo Varolio Costanzo Varolio, Latinized as Constantius Varolius (1543–1575), was an Italian anatomist and a papal physician to Gregory XIII. Varolio was born in Bologna. He was a pupil of the anatomist Giulio Cesare Aranzio, himself a pupil of Vesali ...

(1543–75). This region of the brainstem includes

neural pathways In neuroanatomy, a neural pathway is the connection formed by axons that project from neurons to make synapses onto neurons in another location, to enable neurotransmission (the sending of a signal from one region of the nervous system to an ...

and tracts that conduct signals from the

brain A brain is an organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It is located in the head, usually close to the sensory organs for senses such as vision. It is the most complex organ in a v ...

down to the

and medulla, and tracts that carry the sensory signals up into the

thalamus The thalamus (from Greek θάλαμος, "chamber") is a large mass of gray matter located in the dorsal part of the diencephalon (a division of the forebrain). Nerve fibers project out of the thalamus to the cerebral cortex in all directions, ...

.Saladin Kenneth S.(2007) Anatomy & physiology the unity of form and function. Dubuque, IA: McGraw-Hill

Structure

The pons is in the brainstem situated between the midbrain and the medulla oblongata, and in front of the cerebellum. A separating groove between the pons and the medulla is the inferior pontine sulcus. The superior pontine sulcus separates the pons from the midbrain. The pons can be broadly divided into two parts: the

basilar part of the pons The basilar part of pons, also known as basis pontis, is the ventral part of the pons; the dorsal part is known as the pontine tegmentum. The basilar pons makes up two thirds of the pons within the brainstem. It has a ridged appearance with a shal ...

(ventral pons), and the

pontine tegmentum Pontine may refer to: * Having to do with the pons, a structure located in the brain stem (from ''pons'', "bridge") * Pontine Marshes, a region of Italy near Rome * Pontine Islands The Pontine Islands (, also ; it, Isole Ponziane ) are an ar ...

(dorsal pons). Running down the midline of the ventral surface is the

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 ( ...

, a groove for the

basilar artery The basilar artery () 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 of the circle of W ...

. 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 paramedian arte ...

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

posterior inferior cerebellar arteries The posterior inferior cerebellar artery (PICA) is the largest branch of the vertebral artery. It is one of the three main artery, arteries that supply blood to the cerebellum, a part of the brain. Blockage of the posterior inferior cerebellar arte ...

. The pons in humans measures about in length. Most of it appears as a broad anterior bulge above the medulla. Posteriorly, it consists mainly of two pairs of thick stalks called

cerebellar peduncle Cerebellar peduncles connect the cerebellum to the brain stem. There are six cerebellar peduncles in total, three on each side: * Superior cerebellar peduncle is a paired structure of white matter that connects the cerebellum to the mid-brain ...

s. They connect the cerebellum to the pons (

middle cerebellar peduncle The middle cerebellar peduncle (brachium pontis) is a paired structure of the brain. It connects the pons to the cerebellum, with fibres originating from the pontine nucleus and travelling to the opposite hemisphere of the cerebellar cortex. It i ...

) and midbrain (

superior cerebellar peduncle In the human brain, the superior cerebellar peduncle (brachium conjunctivum) is a paired structure of white matter that connects the cerebellum to the midbrain. It consists mainly of efferent fibers, the cerebellothalamic tract that runs from a cer ...

Development

During

embryonic development An embryo is an initial stage of development of a multicellular organism. In organisms that reproduce sexually, embryonic development is the part of the life cycle that begins just after fertilization of the female egg cell by the male sperm ...

, 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), and a port ...

develops from the

rhombencephalon The hindbrain or rhombencephalon or lower brain 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. Metencephal ...

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

alar plate Daminozide—also known as aminozide, Alar, Kylar, SADH, B-995, B-nine, and DMASA,—is a plant growth regulator, a chemical sprayed on fruit to regulate growth, make harvest easier, and keep apples from falling off the trees before they ripen s ...

produces sensory neuroblasts, which will give rise to the

solitary nucleus In the human brainstem, the solitary nucleus, also called nucleus of the solitary tract, nucleus solitarius, and nucleus tractus solitarii, (SN or NTS) is a series of purely sensory nuclei (clusters of nerve cell bodies) forming a vertical column ...

and its

special visceral afferent A Special visceral afferent fibers (SVA) is a afferent fiber that develop in association with the gastrointestinal tract. They carry the special senses of smell (olfaction) and taste (gustation). The cranial nerves containing SVA fibers are the olfa ...

(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. Structure Path The fibers of the vestibular n ...

, 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 (II) and the vestibulocochlear nerve (VI ...

(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 bra ...

, 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 high cervical spinal cord. The nucleus is divided into three parts, from rostral to caud ...

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

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

, and the

pontine nuclei Pontine may refer to: * Having to do with the pons, a structure located in the brain stem (from ''pons'', "bridge") * Pontine Marshes, a region of Italy near Rome * Pontine Islands The Pontine Islands (, also ; it, Isole Ponziane ) are an ar ...

which relays to the

. Basal plate neuroblasts give rise to the

abducens nucleus The abducens nucleus is the originating nucleus from which the abducens nerve (VI) 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. The abd ...

, 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, car ...

(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 eff ...

(SVE) column, and the

superior salivatory nucleus The salivatory nuclei are the superior salivatory nucleus, and the inferior salivatory nucleus that innervate the salivary glands. They are located in the pontine tegmentum in the brainstem. They both are examples of cranial nerve nuclei. The s ...

, which forms the

general visceral efferent fibers General visceral efferent fibers (GVE) or 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 mu ...

(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 tas ...

Nuclei

A number of

cranial nerve nuclei A cranial nerve nucleus is a collection of neurons (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 nuclei. Lesions ...

are present in the pons: * mid-pons: the 'chief' or 'pontine' nucleus of the

sensory nucleus (V) * mid-pons: the motor nucleus for the trigeminal nerve (V) * lower down in the pons:

(VI) * lower down in the pons: facial nerve nucleus (VII) * lower down in the pons:

vestibulocochlear 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 b ...

nuclei (

and

cochlear nuclei The cochlear nuclear (CN) 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 dorsal cochlear nucleus ...

) (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 The respiratory center is located in the medulla oblongata and pons, in the brainstem. The respiratory center is made up of three major respiratory groups of neurons, two in the medulla and one in the pons. In the medulla they are the dorsal res ...

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 one is conscious but is completely paralyzed. During an episode, one may hallucinate (hear, feel, or see things that are not there), which often results in fear. Episod ...

, and may also play a role in generating dreams.

Clinical significance

Central pontine myelinolysis Central pontine myelinolysis is a neurological condition involving severe damage to the myelin sheath of nerve cells in the ''pons'' (an area of the brainstem). It is predominately iatrogenic (treatment-induced), and is characterized by acute par ...

is a

demyelinating disease A demyelinating disease is any disease of the nervous system in which the myelin sheath of neurons is damaged. This damage impairs the conduction of signals in the affected nerves. In turn, the reduction in conduction ability causes deficiency i ...

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 the body except for vertical eye movements and bli ...

Other animals

Evolution

The pons first evolved as an offshoot of the medullary

reticular formation The reticular formation is a set of interconnected nuclei that are located throughout the brainstem. It is not anatomically well defined, because it includes neurons located in different parts of the brain. The neurons of the reticular formation ...

. Pritchard and Alloway ''Medical Neuroscience'' Since

lamprey Lampreys (sometimes inaccurately called lamprey eels) are an ancient extant lineage of jawless fish of the order Petromyzontiformes , placed in the superclass Cyclostomata. The adult lamprey may be characterized by a toothed, funnel-like s ...

s possess a pons, it has been argued that it must have evolved as a region distinct from the

medulla Medulla or Medullary may refer to: Science * Medulla oblongata, a part of the brain stem * Renal medulla, a part of the kidney * Adrenal medulla, a part of the adrenal gland * Medulla of ovary, a stroma in the center of the ovary * Medulla of t ...

by the time the first

agnathans Agnatha (, Ancient Greek 'without jaws') is an infraphylum of jawless fish in the phylum Chordata, subphylum Vertebrata, consisting of both present (cyclostomes) and extinct (conodonts and ostracoderms) species. Among recent animals, cyclosto ...

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