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Yuniarti

Anatomy DepartmentFaculty of Medicine

UNISBA

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Brainstem is the part of the brain between the spinal cord andthe diencephalon

It consist of three structurally and functionally connected regions :

1. Medulla oblongata2. Pons3. Midbrain

occupies theposterior

cranial fossaof the skull

It is stalklikein shape

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serves as a conduit for the ascendingtracts and descending tracts connectingthe spinal cord to the different parts of

the higher centers

it contains important reflex centersassociated with the control of respirationand the cardiovascular system and with

the control of consciousness

contains the important nuclei of cranialnerves III through XII.

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The midbrain extendsFrom the pons to theDiencephalon

Is about 2,5 cm long

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The cerebral aqueduct passes through the midbrain

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The anterior part of the midbrain contains a pair of tractcalled cerebral peduncles

Cerebral peduncle contain:

- axon of corticospinal, corticopontine, corticobulbar motor neurons whichconduct nerve impulses from the cerebrum to the spinal cord, medullaand pons.

- axon s of sensory neurons that extend from the medulla to the thalamus

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The midbrain comprises two lateral halves, called the cerebral peduncles;each of these is divided into :-an anterior part, the crus cerebri-a posterior part, the tegmentum

by a pigmented band of gray matter, the substantia nigra

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The posterior part of the midbrain, called the tectum Contains four rounded elevations :- Two superior elevations superior colliculi (visual)

- Two inferior elevations inferior colliculi (auditory)

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Nuclei of the midbrain :1. Substansia nigra

- Darkly pigmented nuclei- Help control subsconcious muscle activity- Pigmented gray matter

2. Red nuclei- Look reddish- Function with the cerebellum to

coordinate muscular movement

3. Nuclei associated withcranial nerve III & IV

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The pons lies directly suerior to the medulla and anterior to the cerebellum Is about 2,5 cm long Links cerebellum with mesencephalon, diencephalon, cerebrum, and spinal cord

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The anterior surface is convex from side to side and shows many transversefibers that converge on each side to form the middle cerebellar peduncle There is a shallow groove in the midline, the basilar groove, which lodges thebasilar artery.

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On the anterolateral surface of the pons, the trigeminal nerve emerges oneach side.

In the groove between the pons and the medulla oblongata, there emerge,from medial to lateral, the abducent, facial, and vestibulocochlear nerves

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Cerebellar peduncles connect cerebellum to brainstem-Superior cerebellar peduncles to midbrain-Middle cerebellar peduncles to pons (largest)-Inferior cerebellar peduncles to medulla

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Nuclei of the pons :

1. Pontine nucleiare the sites at which signals for voluntary movements that originate inthe cerebral cortex are relayed into the cerebellum

2. Peumotaxic area & Apneustic areatogether with the medullary rhythmicity area help control breathing

3. Nuclei associated with cranial nerve V(trigeminal),VI(abdusent), VII(facial), VIII (vestibulocochlear)

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Medulla is a continuation of the spinal cord, it forms the inferior partof brain stem

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On the anterior surface of the medulla is the anterior median fissure. On each side of the median fissure, there is a swelling called the pyramid. The pyramids are composed of bundles of nerve fibers, called corticospinal fibers The pyramids taper inferiorly, and it is here that the majority of the descending fibers cross over to theopposite side, forming the decussation of the pyramids

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Posterolateral to the pyramids are the olives, which are oval elevations produced by

the underlying inferior olivary nuclei.

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In the groove between the pyramid and the olive emerge the rootlets of the hypoglossal nerve . In thegroove between the olive and the inferior cerebellar peduncle emerge the roots of theglossopharyngeal and vagus nerves and the cranial roots of the accessory nerve

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As in the spinal cord, the medulla oblongata consists of white matter and gray matter

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Posterior view of medulla oblongata

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Nuclei of medulla :

1. The cardiovascular centerregulate the rate and force of the heartbeat and the diameter of blood vessels

2. The medullary rhythmicity arearespiratory center

3. Inferior olivaryrelay impulses from proprioceptors (monitoring joint &muscle positions)to the cerebellum

4. Gracile & cuneatesensations of touch, conscious proprioception, pressure and vibration

5. Nuclei that receive sensory input from or provide motor output tocranial nerve IX (glossopharyngeal), X (vagus), XI (accesorry) &XII (hypoglossal)

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6. Solitary nucleus - receivesvisceral sensory information

7 Olivary nuclei lateral to pyramids

Receive s e n s o r y info fromproprioceptors (position) inskeletal muscles & joints &act as a relay point to thecerebellum

8. Non-vital reflex centersVomiting, hiccough,

swallowing, coughing,sneezing

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The reticular formation extendsthrough the central core of the medullaoblongata, pons, and midbrain

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The network may be dividedinto three longitudinal columns:

RapheMedial nuclear (large cell) groupLateral nuclear (small cell) group

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Afferent Projections of reticular system

From the spinal cord spinoreticular tracts, the spinothalamic tracts, andthe medial lemniscus.

From the cranial nerve nuclei ascending afferent tracts, which includethe vestibular, acoustic, and visual pathways

From the cerebellum the cerebelloreticular pathway. From the subthalamic, hypothalamic, and thalamic nuclei From the corpus striatum From the limbic system From the primary motor cortex of the frontal lobe From the somesthetic cortex of the parietal lobe.

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Efferent projection of reticular system

Multiple efferent pathways extend down to the brainstem and spinal cordthrough the reticulobulbar and reticulospinal tracts to neurons in the motor nucleiof the cranial nerves and the anterior horn cells of the spinal cord.

Cortico-spinal tract : This pathway originates in motor areas of the cerebralcortex. The cortico-spinal tract, from cortex to spinal cord

Cortico-bulbar fibers : This is a descriptive term that is poorly defined andincludes all fibers that go to the brainstem, both cranial nerve nuclei and otherbrainstem nuclei.

Rubro-spinal tract : The red nucleus of the midbrain gives rise to the rubro-spinal tract.

Lateral vestibulo-spinal tract : The lateral vestibular nucleus of the pons givesrise to the lateral vestibulo-spinal tract

Medial longitudinal fasciculus (MLF) : This is a complex pathway of thebrainstem andupper spinal cord that serves to coordinate various

eye and neck reflexes.

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Functions of the Reticular Formation

Control of skeletal muscle

Control of somatic and visceral sensations.

Control of the autonomic nervous system

Control of the endocrine nervous system.

Influence on the biologic clocks.

The ascending reticular activating systemMultiple ascending pathways carrying sensory information to highercenters are channeled through the reticular formation, which, in turn,projects this information to different parts of the cerebral cortex, causing asleeping person to awakenstate of consciousness is dependent on the continuous projection ofsensory information to the cortex

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