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The pons is part of the brainstem, and in humans and other bipeds lies inferior to the midbrain, superior to the medulla oblongata and anterior to the cerebellum. The pons is also called the pons Varolii ("bridge of Varolius"), after the Italian anatomist and surgeon Costanzo Varolio
Costanzo Varolio
(1543–75).[1] This region of the brainstem includes neural pathways and tracts that conduct signals from the brain down to the cerebellum and medulla, and tracts that carry the sensory signals up into the thalamus.[2] The pons in humans measures about 2.5 centimetres (0.98 in) 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.[2] 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.[2] 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.[2] The pons is implicated in sleep paralysis, and may also play a role in generating dreams.[citation needed]

Contents

1 Structure

1.1 Development 1.2 Nucleus

2 Function 3 Clinical significance 4 Other animals

4.1 Evolution

5 Additional images 6 References 7 External links

Structure[edit] The pons is in the brainstem situated between the midbrain and the medulla oblongata, and in front of the cerebellum. The pons can be broadly divided into two parts: the basilar part of the pons (ventral pons), and the pontine tegmentum (dorsal pons). Development[edit] During embryonic development, the metencephalon develops from the rhombencephalon and gives rise to two structures: the pons and the cerebellum.[2] The alar plate produces sensory neuroblasts, 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 abducens 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. Nucleus[edit] A number of cranial nerve nuclei are present in the pons:

mid-pons: the 'chief' or 'pontine' nucleus of the trigeminal nerve sensory nucleus (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 (vestibular nuclei and cochlear nuclei) (VIII)

Function[edit] The functions of these four cranial nerves (V-VIII) 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, and the secretion of saliva and tears.[3] Clinical significance[edit]

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

Other animals[edit] Evolution[edit] The pons first evolved as an offshoot of the medullary reticular formation.[4] 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.[5] Additional images[edit]

Location and topography of Pons
Pons
(animation)

Axial section of the pons, at its upper part

Hind- and mid-brains; posterolateral view

Median sagittal section of brain

Nuclei of the pons and brainstem

Cerebrum. Deep dissection. Inferior dissection.

References[edit]

^ Henry Gray (1862). Anatomy, descriptive and surgical. Blanchard and Lea. pp. 514–. Retrieved 10 November 2010.  ^ a b c d e Saladin Kenneth S.(2007) ^ Cite error: The named reference arjun korah.2007 was invoked but never defined (see the help page). ^ Pritchard and Alloway Medical Neuroscience ^ Butler and Hodos Comparative vertebrate neuroanatomy: evolution and adaptation

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

Pritchard, TE & Alloway, D (1999). Medical neuroscience. Hayes Barton Press. ISBN 978-1-59377-200-0.  Butler, AB & Hodos, W (2005). Comparative vertebrate neuroanatomy: evolution and adaptation. Wiley-Blackwell. ISBN 978-0-471-21005-4. 

External links[edit]

Wikimedia Commons has media related to Pons.

Diagram at UCC Stained brain slice images which include the "Pons" at the BrainMaps project

v t e

Nervous system

Central nervous system

Meninges Spinal cord Brain

Rhombencephalon

Medulla Pons Cerebellum

Midbrain Forebrain

Diencephalon

Retina Optic nerve

Cerebrum

Limbic system

Peripheral nervous system

Somatic

Sensory nerve Motor nerve Cranial nerve Spinal nerve

Autonomic

Sympathetic Parasympathetic Enteric

v t e

Anatomy of the pons

Dorsal/ (tegmentum)

Surface

Cerebellopontine angle Superior medullary velum Sulcus limitans Medial eminence Facial colliculus

White: Sensory

Trapezoid body Trigeminal lemniscus

Dorsal trigeminal tract Ventral trigeminal tract

Medial lemniscus Lateral lemniscus

Medial longitudinal fasciculus

Vestibulo-oculomotor fibers

Anterior trigeminothalamic tract Central tegmental tract

White: Motor

Inferior cerebellar peduncle

Vestibulocerebellar tract

Medial longitudinal fasciculus

Vestibulospinal tract Medial vestibulospinal tract Lateral vestibulospinal tract

Grey: Cranial nuclei

afferent:

GSA

Trigeminal

Principal Spinal

Cochlear nucleus

Dorsal Anterior

Vestibular nuclei

Superior

efferent:

SVE: Trigeminal motor nucleus Facial motor nucleus GSE: Abducens nucleus GVE: Superior salivary nucleus Inferior salivary nucleus

Other

Apneustic center Pneumotaxic center Parabrachial nuclei

Subparabrachial nucleus Medial parabrachial nucleus Lateral parabrachial nucleus

Superior olivary nucleus Locus coeruleus

Ventral/ (base)

Grey

Pontine nuclei

White: Motor/descending

Corticospinal tract Corticobulbar tract Corticopontine fibers MCP

Pontocerebellar fibers

Surface

Basilar sulcus

Other grey: Raphe/ reticular

Reticular formation

Caudal Oral Tegmental Paramedian

Raphe nuclei<

.