Anatomy of Hindbrain
The hindbrain, also known as the rhombencephalon is the lower part of the brain that consists of the metencephalon which contains the cerebellum and pons and the myelencephalon which contains the medulla oblongata.Cerebellum
The cerebellum, also called the little brain, is the second largest part of the brain and the largest part of the hindbrain. It is found in the back portion of the skull, underneath the temporal and occipital lobe and behind the brainstem.Three pairs of cerebellar peduncles attach the cerebellum and brainstem.
The cerebellar cortex is made up of grey matter while the inner surface is made up of white matter. The internal surface of the cerebellum gives a tree-like appearance and is termed arbor vitae or tree of life.
The white matter of the cerebellum contains four main cerebellar nuclei that are the dentate nucleus, emboliform nucleus, globose nucleus and fastigial nucleus.
A central compressed structure called the vermis is made up of lobules that divide the cerebellum into two hemispheres, the left cerebellar hemisphere and the right cerebellar hemisphere.
The cerebellum has three anatomical lobes i.e. anterior lobe, posterior lobe and flocculonodular lobe. The anterior and posterior lobes are separated by a primary fissure while the posterolateral fissure separates the flocculonodular lobe from the posterior lobe.
Functionally, the cerebellum is divided into three main parts cerebrocerebellum, vestibulocerebellum and spinocerebellum.
Pons
The pons, also called pons verolli the part of the hindbrain. It is 2.5 cm in length and located above the medulla oblongata, below the midbrain and in front of the cerebellum. It consists of mostly grey matter and some white matter.The pons forms most of the floor of the fourth ventricle and is like a home for several cranial nerve nuclei which are the trigeminal nucleus, facial motor nucleus, abducens nucleus and vestibular nucleus. The pons also contains the locus coeruleus, the largest nor epinephrine-containing neurons in the brain and some of the raphe nuclei that produce serotonin.
The pons serves a channel for many tracts passing up and down through the brainstem like the corticospinal tract for voluntary movements, the medial lemniscus for tactile and proprioceptive sensations and the spinothalamic tract for pain and temperature sensations.
The anterior part of the pons looks like a bridge that connects the two cerebellar hemispheres. Pons is attached to the cerebellum by middle cerebellar peduncles which serves as a major pathway between the brainstem and cerebellum. The inferior cerebellar peduncles also travel to the pons to carry information to the cerebellum while superior cerebellar peduncles enter the brainstem at the level of pons and carry information from the cerebellum to the brainstem.
The pons also has two main parts i.e. ventral and dorsal parts.
Ventral or basilar part
The ventral part consists of pontine nuclei which are small masses of grey matter expended between longitudinally and transversely arranged fibers. It also contains the corticospinal fibers, cortico-nuclear fibers and transverse fibers that form middle cerebral peduncles called pontocerebellar peduncles.Trapezoid body
The ventral and dorsal parts of the pons are separated by a trapezoid body that consists of descending fibers.Dorsal or tegmental part
It is an upward continuation of the medulla that is bounded by the fourth ventral. It is related to inferior cerebral peduncles in its lower part and superior cerebral peduncles. Superiorly, the pons is continuous with the tegmentum of the midbrain.Medulla oblongata
The medulla oblongata is a part of the hindbrain that looks like a stem. It is located above the spinal cord and below the pons and connected to the cerebellum. It is 2.5cm in length.The medulla has two main surfaces i.e. the anterior surface and the posterior surface.
The anterior surface of the medulla oblongata contains five grooves which are named as follows;
- The anterior medial fissure
- Right anterolateral sulcus
- Left anterolateral sulcus
- Right posterolateral sulcus
- Left posterolateral sulcus
On the lateral side of pyramids, the medulla has olives which contain olivary nuclei and some cranial nerve nuclei.
The anterior part of the medulla also contains cranial nerve 12(hypoglossal nerve) going out from the anterolateral sulci which then goes to the tongue.
The posterolateral sulci contain cranial nerves 9(glossopharyngeal nerve), 10(vagus nerve) and 11(accessory nerve).
The posterior side of the medulla also has a midline structure called posterior median sulcus which continues down to the spinal cord. On the lateral side of the midline, the cuneate tubercle and gracile tubercle nuclei are present which contain important tracts. The important tracts of medulla oblongata are the spinocerebellar tract, lateral spinothalamic tract, tectospinal tract, medial longitudinal fasciculus tract and cranial nerve 5 tract.
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