Blood supplyBlood supply The medulla is supplied The medulla is supplied

by blood vessels from by blood vessels from the posterior the posterior circulation . The ventral circulation . The ventral aspect is supplied by aspect is supplied by the vertebral and the vertebral and basilar basilar arteries ,laterally and arteries ,laterally and dorsally by posterior dorsally by posterior inferior cerebellar art.inferior cerebellar art.

The anterior spinal The anterior spinal branch from the branch from the vertebral art.gives vertebral art.gives pentrating branches pentrating branches which supply area near which supply area near midline.”pyramid,medimidline.”pyramid,medial lemniscus and al lemniscus and hypoglossal nucleus. hypoglossal nucleus.

Blood supply Blood supply of medullaof medulla

Damage to one or more of these vessels may produce specific lesions as occurred when damage to posterior inferior cerebellar artery when there will be loss of nucleus ambiguus nucleus which paralyses the vocal folds and palatal and pharyngeal muscles on that side giving dysphonia and dysphagia.loss of uncrossed spinal tract of trigeminal and the crossed spinal lemniscus results in loss of pain and temperature sensation

Tracts of brain Tracts of brain stemstem

Most of tracts ascending or descending Most of tracts ascending or descending are passing through the brain stem .and are passing through the brain stem .and some of them begin in the brain stem.some of them begin in the brain stem.

Corticonuclear and corticospinal are Corticonuclear and corticospinal are concerned with voluntary concerned with voluntary movement .while the reticulospinal and movement .while the reticulospinal and vestibulospinal tracts are concerned with vestibulospinal tracts are concerned with posture and coordination of movement .posture and coordination of movement .

Main ascending tracts are the medial Main ascending tracts are the medial lemniscus which begins in the medulla lemniscus which begins in the medulla and the spinal lemniscus and and the spinal lemniscus and spinoreticulothalamic tracts begin in the spinoreticulothalamic tracts begin in the spinal cord and brain stem spinal cord and brain stem

Descending tractsDescending tracts Corticospinal tract is the main Corticospinal tract is the main

descending motor tract it arises in the descending motor tract it arises in the motor cortex .they lie in the anterior motor cortex .they lie in the anterior 2/3 of the posterior limb of the internal 2/3 of the posterior limb of the internal capsule continuing down to the capsule continuing down to the brainstem .the fibers of the tract brainstem .the fibers of the tract occupy the central and lateral parts of occupy the central and lateral parts of the crus of the midbrain peduncle.the crus of the midbrain peduncle.

In the pons the fibers broken up into In the pons the fibers broken up into the bundles among the pontine nuclei. the bundles among the pontine nuclei. Passing on to medulla the bundles Passing on to medulla the bundles collect into a single large mass forming collect into a single large mass forming the bulging pyramid of medulla.the bulging pyramid of medulla.

In the lower part of medulla about 75-In the lower part of medulla about 75-90% of the fibers cross to the opposite 90% of the fibers cross to the opposite side in the pyramidal decussation to side in the pyramidal decussation to form the lateral corticospinal tract .form the lateral corticospinal tract .

Descending tractsDescending tracts

Corticopontine fibers arises in the cortex in different areas. Then pass through all parts Corticopontine fibers arises in the cortex in different areas. Then pass through all parts of the internal capsule to crus of the midbrain peduncle.of the internal capsule to crus of the midbrain peduncle.

Frontopontine fibers occupy the medial 1/6 of the crus and all end by synapsing with Frontopontine fibers occupy the medial 1/6 of the crus and all end by synapsing with cells in pontine nuclei.then axons decussate to form the pontocerebellar fibers of the cells in pontine nuclei.then axons decussate to form the pontocerebellar fibers of the middle cerebellar peduncle .this is one of the communicating pathways between middle cerebellar peduncle .this is one of the communicating pathways between cerebral cortex and cerebellum. cerebral cortex and cerebellum.

From the superior cerebellar peduncle the fibers pass to the midbrain and decussate at From the superior cerebellar peduncle the fibers pass to the midbrain and decussate at the level of inferior colliculi on their way to red nucleus at superior colliculus the level of inferior colliculi on their way to red nucleus at superior colliculus level ,whose efferent fibers form the rubrospinal tract which immediately decussate. level ,whose efferent fibers form the rubrospinal tract which immediately decussate.

Descending tractsDescending tracts

Medial longitudinal bundle lies Medial longitudinal bundle lies immediately ventral to grey matter immediately ventral to grey matter round the aqueduct ,and remains round the aqueduct ,and remains adjacent to the midline at lower adjacent to the midline at lower levels.it extends from upper border levels.it extends from upper border of midbrain to the upper cervical of midbrain to the upper cervical spinal cord.spinal cord.

It links between vestibular nuclei It links between vestibular nuclei with with occulomotor,trochlear ,abducent ,socculomotor,trochlear ,abducent ,spinal accessory and reticular pinal accessory and reticular nuclei.to help coordinate conjugate nuclei.to help coordinate conjugate eye movements and audiovisual eye movements and audiovisual reflexes involving head and neck.reflexes involving head and neck.

Lateral and medial Lateral and medial reticulospinal tracts reticulospinal tracts and the vestibulospinal and the vestibulospinal tracts they are tracts they are extrapyramidal tracts extrapyramidal tracts that originate in the that originate in the brain stem and largely brain stem and largely mixed with mixed with corticospinal tract and corticospinal tract and end in the anterior end in the anterior horn cell.horn cell.

Hypothalamospinal Hypothalamospinal fibers from fibers from hypothalamus run in hypothalamus run in the region of spinal the region of spinal lemniscus to lemniscus to sympathetic and sympathetic and parasympathetic parasympathetic neurons in the neurons in the thoracolumbar and thoracolumbar and sacral lateral horns.sacral lateral horns.

Ascending tractsAscending tracts Medial lemniscus which is the main Medial lemniscus which is the main

ascending pathway concerned with ascending pathway concerned with the touch and its associated the touch and its associated sensation .sensation .

Spinal lemniscus : it is the upward Spinal lemniscus : it is the upward continuation of the lateral continuation of the lateral spinothalamic tract most of its fibers spinothalamic tract most of its fibers end in the reticular formation and end in the reticular formation and become smaller.become smaller.

Lateral lemniscus started from the Lateral lemniscus started from the upgoing fibers of trapezoid upgoing fibers of trapezoid body ,which is a mass of body ,which is a mass of transversely decussating fibers from transversely decussating fibers from cochlear nuclei at the cochlear nuclei at the pontomedullary junction.some of pontomedullary junction.some of fibers terminate in the inferior fibers terminate in the inferior colliculus for auditory reflexes.colliculus for auditory reflexes.

Anterior and Posterior Anterior and Posterior spinocerebellar tracts spinocerebellar tracts

Cerebrospinal FluidCerebrospinal Fluid CSF is largely produced by the CSF is largely produced by the

choroid plexuses of the choroid plexuses of the third,lateral and fourth third,lateral and fourth ventricles ..other sources of CSF ventricles ..other sources of CSF from brain capillaries .from brain capillaries .

Total volume of CSF is about 130-Total volume of CSF is about 130-150cc ,total daily production is 150cc ,total daily production is about 500 ml ,but there is about 500 ml ,but there is constant circulation and resorption constant circulation and resorption which take place mainly through which take place mainly through the arachnoid granulations.the arachnoid granulations.

It forms the waterbath in which the It forms the waterbath in which the brain can float which can brain can float which can effectively reduce the 1500 g effectively reduce the 1500 g weight of the brain to 50 g .weight of the brain to 50 g .

It is also a pathway to remove the It is also a pathway to remove the brain metabolitesbrain metabolites