Structure of Rhombencephalon. Development of Brain.

Structure of Rhombencephalon. Development of Brain.

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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 Cerebellum
Saggital 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 peduncles
The 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 fossa
It resides on the dorsal surface of the medulla oblongata
and pons
Relief 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. trigemeni
2. 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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