Pons is an important component in the neurobiology of neurodegenerative diseases. This page provides detailed information about its structure, function, and role in disease processes.
The pons (Latin: "bridge") is the middle segment of the brainstem, situated between the midbrain (mesencephalon) superiorly and the medulla oblongata inferiorly. Named for its appearance as a bridge connecting the two cerebellar hemispheres, the pons serves as a critical relay station for motor, sensory, and autonomic information. It contains the pontine nuclei (which relay cortical motor signals to the cerebellum), multiple cranial nerve nuclei (CN V-VIII), and ascending/descending fiber tracts that connect the cerebral cortex with the cerebellum, spinal cord, and other brainstem structures (Nieuwenhuys et al., 2008). [1]
In neurodegenerative diseases, the pons is one of the most severely affected structures in multiple system atrophy (MSA-C, cerebellar type), where it undergoes dramatic atrophy producing the characteristic "hot cross bun sign" on MRI. Pontine pathology is also significant in progressive supranuclear palsy, spinocerebellar ataxias, and several other neurodegenerative and demyelinating conditions. The pons atrophies at rates exceeding 4% per year in MSA, making it one of the fastest-degenerating brain structures in any neurodegenerative disease (Krismer et al., 2024). [2]
The pons occupies the anterior portion of the metencephalon and measures approximately 2.5 cm in length. It is bounded superiorly by the pontomesencephalic junction, inferiorly by the pontomedullary junction, anteriorly by the basilar sulcus (groove for the basilar artery), posteriorly by the fourth ventricle, and laterally by the middle cerebellar peduncles connecting the pons to the cerebellum. [3]
The pons is divided into two major compartments: [4]
| Region | Location | Contents | Function | [5]
|--------|----------|----------|----------| [6]
| Basilar pons (ventral) | Anterior/ventral | Pontine nuclei, transverse pontine fibers, corticospinal tract, corticopontine fibers | cortex-cerebellum relay, motor tract passage | [7]
| Pontine tegmentum (dorsal) | Posterior/dorsal | Cranial nerve nuclei, reticular formation, locus coeruleus, raphe nuclei, ascending tracts | Sensory relay, arousal, autonomic control | [8]
The pontine nuclei are scattered cell clusters in the basilar pons forming the major relay between the cerebral cortex and the cerebellum: [9]
The pons contains the nuclei of cranial nerves V through VIII:
| Cranial Nerve | Nucleus | Function |
|---|---|---|
| CN V (Trigeminal) | Motor nucleus, principal sensory nucleus, mesencephalic nucleus | Mastication (motor); facial sensation (sensory) |
| CN VI (Abducens) | Abducens nucleus | Lateral eye movement (lateral rectus muscle) |
| CN VII (Facial) | Facial motor nucleus, superior salivatory nucleus, nucleus solitarius | Facial expression, taste (anterior 2/3 tongue), lacrimation |
| CN VIII (Vestibulocochlear) | Cochlear nuclei, vestibular nuclei | Hearing, balance, equilibrium |
The pons receives blood supply primarily from the basilar artery (running along the basilar sulcus, giving off paramedian and short circumferential perforating branches), the anterior inferior cerebellar artery (AICA, supplying the lateral pons and middle cerebellar peduncle), and the superior cerebellar artery (SCA, supplying the rostral pontine tegmentum). Basilar artery occlusion can produce "locked-in syndrome" with preserved consciousness but complete motor paralysis.
The corticopontocerebellar pathway through the pontine nuclei is the largest motor relay system in the brain, enabling real-time comparison of intended versus actual movements, motor adaptation and error correction, timing and coordination of complex motor sequences, and motor learning and skill acquisition.
Through its cranial nerve nuclei, the pons controls mastication (CN V), facial expression (CN VII), horizontal eye movements (CN VI and PPRF), hearing (CN VIII cochlear nuclei), and balance (CN VIII vestibular nuclei).
The pontine tegmentum contains critical sleep-wake regulatory centers:
Pontine nuclei contribute to respiratory rhythm modulation (pneumotaxic center), micturition control (Barrington's nucleus / pontine micturition center), and cardiovascular reflexes.
The pons is one of the most severely affected structures in multiple system atrophy, particularly the cerebellar type (MSA-C, formerly olivopontocerebellar atrophy):
progressive supranuclear palsy affects pontine structures, though less severely than the midbrain:
Several Spinocerebellar Ataxia subtypes show prominent pontine degeneration: SCA1 (pontine neurons and middle cerebellar peduncle degeneration), SCA2 (severe pontine atrophy often rivaling MSA-C), SCA3/Machado-Joseph disease (pontine tegmentum degeneration), and SCA7 (pontine involvement with distinctive retinal degeneration).
This section links to atlas resources relevant to this brain region.
Allen Human Brain Atlas: Pons expression search
Allen Mouse Brain Atlas: Pons search
Allen Cell Type Atlas: Transcriptomic cell type reference
BrainSpan Developmental Transcriptome: Pons developmental expression
brainstem - the larger structure of which the pons is the middle segment
cerebellum - connected to the pons via the middle cerebellar peduncle
locus coeruleus - noradrenergic nucleus located in the dorsal pons
Raphe Nuclei - serotonergic nuclei located in the pontine tegmentum
Pedunculopontine Nucleus - cholinergic nucleus at the pontomesencephalic junction
Red Nucleus - midbrain structure at the pontomesencephalic junction
Inferior Olivary Nucleus - medullary structure linked to pons in the olivopontocerebellar system
multiple system atrophy - synucleinopathy with severe pontine degeneration
progressive supranuclear palsy - tauopathy affecting pontine tegmentum
Spinocerebellar Ataxia - genetic ataxias with pontine involvement
The study of Pons has evolved significantly over the past decades. Research in this area has revealed important insights into the underlying mechanisms of neurodegeneration and continues to drive therapeutic development.
Historical context and key discoveries in this field have shaped our current understanding and will continue to guide future research directions.
Krismer F, et al. Progressive brain atrophy in Multiple System Atrophy: a longitudinal, multicenter, MRI study. Mov Disord. 2024;39(1):71-79. 2024. ↩︎
Paviour DC, et al. Longitudinal quantitative MRI in MSA and PSP. J Neurol. 2013;261(2):295-303. 2013. ↩︎
Massey LA, et al. The midbrain to pons ratio: a simple and specific MRI sign of PSP. Neurology. 2013;80(20):1856-1861. 2013. ↩︎
Fanciulli A, Wenning GK. Multiple-system atrophy. N Engl J Med. 2015;372(3):249-263. 2015. ↩︎
Jellinger KA. The pathobiology of behavioral changes in MSA: an update. Front Neurol. 2024;15:1242406. 2024. ↩︎
Stefanova N, et al. Multiple System Atrophy: an update. Lancet Neurol. 2009;8(12):1172-1178. 2009. ↩︎
Boxer AL, et al. Advances in PSP: new diagnostic criteria, biomarkers, and therapeutic approaches. Lancet Neurol. 2017;16(7):552-563. 2017. ↩︎
Paxinos G, Huang XF. Atlas of the Human Brainstem (1995). Academic Press. 1995. ↩︎
Schrag A, et al. Differentiation of atypical parkinsonian syndromes with routine MRI. Neurology. 2000;54(3):697-702. 2000. ↩︎