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 a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through ...

, "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 ...

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, cultu ...

s and other bipeds 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 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 (invol ...

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 cerebe ...

. 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 Vesaliu ...

(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 ano ...

and tracts that conduct signals from the

brain A brain is an organ (biology), 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 Visual perception, vision. I ...

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 direct ...

.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 (ventral pons), and the pontine tegmentum (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 ...

. Most of the pons is supplied by the pontine arteries, 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 unambiguously describe the anatomy of animals, including humans. The terms, typically derived from Latin or Greek language, Greek roots, describe something in its standard anatomical position. Th ...

and posterior inferior cerebellar arteries. 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) and midbrain ( superior cerebellar peduncle).

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 develops from the rhombencephalon 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

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 cell ...

s, 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 (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 (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 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 che ...

, and the pontine nuclei 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, c ...

(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 (GVE) of the facial nerve.

Nuclei

A number of cranial nerve nuclei 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 The trigeminal motor nucleus contains motor neurons that innervate muscles of the first branchial arch, namely the muscles of mastication, the tensor tympani, tensor veli palatini, mylohyoid muscle, mylohyoid, and anterior belly of the digastric. T ...

(V) * lower down in the pons: abducens nucleus (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 br ...

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 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, and may also play a role in generating dreams.

Clinical significance

* Central pontine myelinolysis is a demyelinating 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 or rapid correction of blood sodium. Undiagnosed, it can lead to death or locked-in syndrome.

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 formatio ...

. Pritchard and Alloway ''Medical Neuroscience'' 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, 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