Pons
Boundaries
•Anterior – Basilar artery, Basilar part of occipital bone.
•Posterior – Cerebellum.
•Inferior – Medulla oblongata.
•Superior – Midbrain.
•It is about 1 inch long
•Pons means bridge , connecting the right and left Cerebellar hemispheres.
Central Cavity
•4th ventricle.
•Pons forms the upper half of floor of 4th ventricle.
EXTERNAL FEATURES (VENTRAL)
Midline shallow groove called as the basilar groove , houses the basilar artery.
•Connected to the cerebellum by middle cerebellar peduncle.
•Striated appearance due to presence of transverse fibers (corticopontocerebellar fibers)
•Sensory and motor root of trigeminal nerve.
•6th,7th,8th cranial nerve nuclei at pontomedullary junction.
•Nervus intermedius
Superior border
•superior cerebellar peduncles
•Superior cerebellar artery.
Inferior border
•Continues as the medulla oblongata.
•Anterior inferior cerebellar artery
EXTERNAL FEATURES(POSTERIOR)
•Hidden by cerebellum. Triangular in shape , connected by the middle cerebellar peduncle.
•Upper half formed by floor of 4th ventricle.
•Laterally bounded by superior cerebellar peduncles.
•Median sulcus divides it into equal halves.
•Medial eminence (eminence laterally placed to median sulcus)
•Sulcus limitans (lateral to medial eminence)
•Facial colliculus (bulging formed by fibers of facial nerve wrapped around abducent nucleus)
•Stria medullaris (pontomedullary junction)
•Substantia ferruginea
External Features (Posterior)
•Inferior end of sulcus limitans is expanded to form facial colliculus (produced by root of facial (VII) nerve winding around nucleus of abducent (VI) nerve).
•The floor of superior part of sulcus limitans is bluish gray in color and is called substantia ferruginea.
•Lateral to sulcus limitans – Area vestibuli (produced by underlying vestibular nuclei).
Structure present in pons
Internal Structure
•For purpose of description, the pons is commonly divided into:
•An anterior portion :Basal part.
•A posterior part :Tegmentum.
Transverse sections
Two levels of transverse section :
•At level of facial colliculus
•At level of trigeminal nuclei
Level of facial colliculus
BASILAR PART :
•Small masses of nerve cells called pontine nuclei.
•Bundles of corticospinal and corticonuclear fibers
•Corticopontine fibers that run to the cerebellum through middle cerebellar peduncle.
TEGMENTUM PART :
•Medial leminiscus
•Facial nucleus
•Facial colliculus
•Medial longitudinal fasiculus
•Medial vestibular nucleus
Level of trigeminal nuclei
BASILAR PART :
•Same as facial colliculus level
•Pontine nuclei
•Corticospinal , corticonuclear , corticopontine fibers.
TEGMENTUM PART :
•Motor nucleus of trigeminal nerve
•Spinal nucleus of trigeminal nerve
Nuclei of Cranial Nerves
•Abducens nucleus. (CN VI)
•Motor nucleus of facial nerve. (CN VII)
•Cranial part of nucleus of tractus solitarius (sensory nucleus of facial nerve). (CN VII)
•Superior & inferior salivatory (lacrimal) nuclei. (Parasympathetic nuclei of CN VII)
•Superior, medial, lateral vestibular nuclei. (CN VIII)
•Main sensory, motor & spinal nuclei of trigeminal nerve. (CN V)
Other Nuclei
•Pontine nuclei.
•Trapezoid nuclei (receives afferents from cochlear nuclei).
Sensory Tracts
•Spinal lemniscus (Fibers from anterior & lateral spinothalamic and spinotectal tracts).
•Medial lemniscus (Fibers from nucleus gracilis and nucleus cuneatus).
•Trigeminal lemniscus (Fibers from spinal, pontine and mesencephalic nuclei of trigeminal system).
•Anterior spinocerebellar tracts.
•Lateral lemniscus (Fibers from contralateral trapezoid nuclei).
Motor Tracts
•Corticospinal and corticonuclear tracts.
•Medial longitudinal fasciculus (interconnect the nuclei of 3rd, 4th, 6th and 8th cranial nerves).
•Rubrospinal and Tectospinal tracts.
•Transverse pontine fibers (efferent fibers from pontine nuclei).
