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The Department of Human anatomy

Structure of rhombencephalon.

Development of brain. Reticular formation.

Distribution of nuclei of cranial nerves in

rhomboid -shaped fossa.

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The central nervous system forms from the embryonic neural tube that developes from ectoderm.

The neural plate gives rise to neural groove, that later form the neural tube.

Development of brain

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At the end of the 4-th week the cranial (superior) part of the neural tube expands and develops into three dilations called primary vesicles:

Prosencephalon Mesencephalon Rhombencephalon

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In the beginning of the 2-d month the brain appears to comprise 5 secondary vesicles:

Prosencephalon (forebrain) Telencephalon: hemispheres Diencephalon: epithalamus, thalamus,

hypothalamus Mesencephalon (midbrain)

Mesencephalon: cerebral peduncles, tectal plate Rhombencephalon (hindbrain)

Metencephalon: pons, cerebellum Myelencephalon: medulla oblongata

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The rhombencephalon comprises the

myelencephalon (the medulla oblongata) and the metencephalon (the pons and the cerebellum)

Contains the cavity called the fourth ventricle with the floor represented with the rhomboid fossa

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The Brain Stem – The Medulla Oblongata

The medulla oblongata (bulbus) is the lower half of the brainstem. The medulla contains the cardiac, respiratory, vomiting and vasomotor centers and deals with autonomic, involuntary functions, such as breathing, heart rate and blood pressure. It contains the nuclei of IX, X, XI and XII cranial nerves.

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The medulla oblongata has ventral, dorsal and lateral surfaces.

Ventral surface The anterior median fissure The pyramids ( between the

anterior median fissure and the anterolateral sulcus).

The decussation of the pyramids (in the lower part of the medulla, the motor fibers cross each other).

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The lateral surface Olivary body (olive)

(found laterally from each pyramid).

The antero- and posterolateral sulcuses.

The inferior cerebellar peduncle

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The dorsal surface The posterior median sulcus The fasciculus gracilis and the fasciculus cuneatus

( that lying laterally). These fasciculi end in rounded elevations known as

the gracile and the cuneate tubercles. They are caused by masses of gray matter known as the nucleus gracilis and the nucleus cuneatus.

Just above the tubercles, the posterior aspect of the medulla is occupied by a triangular fossa, which forms the lower part of the floor of the fourth ventricle.

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Internal structure The cuneate and gracile nuclei that accept the

cuneate and gracile fasciculi (it transmit the impulses of proprioceptive and tactile sensivity). The axons of nuclei form the medial lemniscus.

The pyramidal tract comprises the corticonuclear and the corticospinal fibers.

The inferior olivary nucleus (communicates with the cerebellum and spinal cord)- control body equilibrium.

The reticular formation. The nuclei of cranial nerves (IX-XII)

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Functions The medulla oblongata controls autonomic

 functions, and connects the higher levels of the brain to the spinal cord. It is also responsible for regulating several basic functions of the autonomic nervous system which include:

Respiration – chemoreceptors Cardiac center – sympathetic, parasympathetic

system Vasomotor center – baroreceptors Reflex centers of vomiting, coughing, sneezing,

and swallowing Destruction of the medulla causes instant death.

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The Brain Stem – The Pons (pons Varolii) The pons is about 2.5 cm in length.

Most of it appears as a broad anterior bulge rostral to the medulla. Posteriorly, it consists mainly of two pairs of thick stalks called cerebellar peduncles. They connect the cerebellum to the pons and midbrain.

Contains the nuclei of cranial nerves V, VI, VII and VIII.

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The Pons External

features The bulbopontine

sulcus The basilar sulcus The medullary stria

of fourth ventricle The middle

cerebellar peduncle

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Internal structure of pons The trapezoid body delimits two parts of pons: The basilar part The pontine nuclei The pontocerebellar fibers The corticopontine fibers The pyramidal fibers The tegmentum The nuclei of cranial nerves (V-VIII) The superior olivary nucleus (belongs to the auditory

nuclei group) Medial lemniscus Rubrospinal and tectospinal tracts

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The functions of Pons The pons contains nuclei that relay

signals from the forebrain to the cerebellum, along with nuclei that deal primarily with sleep, respiration, swallowing, bladder control, hearing, equilibrium, taste, eye movement, facial expressions, facial sensation, and posture.

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The Cerebellum In Latin, the word

cerebellum means little brain.

Located dorsal to the pons and medulla

Is comprised of white matter and a thin, outer layer of gray matter.

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The Cerebellum Consists of two cerebellar

hemispheres and the vermis

Surface feature various cerebellar fissures delimit lobes, lobules and folia

The Cerebellum subdivided into:

Anterior lobe Posterior lobe Flocculonodular lobe

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From the evolutional point the cerebellum has: The oldest part – archicerebellum (floculus

and nodule are associated with the vestibular nuclei and are involved into body equilibrium control).

The ancient part – paleocerebellum (anterior lobe) which control muscle tone, coordinates the movement related to weight and inertia.

The newest part - neocerebellum (posterior lobe) which control voluntary and automated movements.

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The CerebellumSaggital section reveals

treelike arragment that call the arbor vitae

The nuclei of cerebellum: The dentate (6) The emboliform (5) The globose (4) The fastigial (3)

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The cerebellar pedunclesThe inferior cerebellar peduncles: The posterior spinocerebellar tract The olivocerebellar tract The external arcuate fibers The vestibulocerebellar fibers The cerebellovestibular fibers

The middle cerebellar peduncles: The pontocerebellar fibers

The superior cerebellar peduncles: The cerebellorubral fibers The cerebellothalamic fibers The anterior spinocerebellar fibers

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Functions of Cerebellum :

The cerebellum is involved in several functions of the body including:

Fine Movement Coordination Balance and Equilibrium Muscle Tone It may also be involved in some cognitive functions such as 

attention and language, and in regulating fear and pleasure responses

The cerebellum does not initiate movement, but it contributes to coordination, precision, and accurate timing. It receives input from sensory systems and from other parts of the brain and spinal cord, and integrates these inputs to fine tune motor activity.

Because of this fine-tuning function, damage to the cerebellum does not cause paralysis, but instead produces disorders in fine movement, equilibrium, posture, and motor learning.

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Rhomboid fossaIt resides on the dorsal surface of the medulla

oblongata and ponsRelief of the rhomboid fossa: Median sulcus Medial eminence Sulcus limitans Medullary stria Superior and inferior

foveas Facial colliculus Vestibular area Locus caeruleus Hypoglossal and vagal

trigones

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The nuclei of cranial nerves

1. nucleus mesencephalicus n. trigemeni2. nucleus pontinus n. trigemeni.3. nucleus spinalis n. trigemeni.4. nucleus cochlearis anterior.5. nucleus cochlearis posterior.6. nucleus vestibularis superior.7.nucleus vestibularis lateralis.8. nucleus vestibularis inferior.9. nucleus vestibularis medialis.10.nucleus solitarius (for VII, IX, X cranial nerves).11. nucleus n. hypoglossi.12. nucleus dorsalis n. vagi.13. nucleus n. accessorii.14. nucleus ambiguus (for IX, X, XI cranial nerves).15. nucleus salivatorius inferior (for IX cranial nerve).16. nucleus salivatorius superior (for VII cranial nerve).17. nucleus n. facialis.18. nucleus n. abducentis.19. nucleus motorius n. trigemeni.

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Reticular formation The reticular formation is

a part of the brain that is involved in actions such as awaking/sleeping cycle, and filtering incoming stimuli to discriminate irrelevant background stimuli. It is essential for governing some of the basic functions of higher organisms, and is one of the phylogenetically oldest portions of the brain.

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The reticular formation consists of more than 100 small neural networks, with varied functions including the following:

1.Somatic motor control  2. Cardiovascular control 3. Pain modulation 4. Sleep and consciousness 5. Habituation

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Thank you for attention!