The cerebellum, or 'little brain', plays a crucial role in motor control, coordination, and timing of movements, with functional divisions including the cerebrocerebellum, spinocerebellum, and vestibulocerebellum. It consists of three anatomical lobes, interconnected nuclei, and various afferent and efferent pathways and is supplied by three paired arteries. Dysfunction in the cerebellum can lead to symptoms such as ataxia, dysdiadochokinesia, and intention tremor.

1. Cerebellum & Brainstem
Card-6
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2. Cerebellum: Introduction
Description:
The cerebellum, which stands for “little brain”, is a structure of the central nervous system. It has an important role in
motor control of the ipsilateral side of the body . In particular, it is active in the coordination, precision and timing of
movements, as well as in motor learning.
Embryological formation:
The hindbrain subsequently divides into the metencephalon (superior) and the myelencephalon (inferior). The
cerebellum develops from the metencephalon division.
Anatomical position
 The cerebellum is located at the back of the brain, immediately inferior to the occipital and temporal lobes, and within
the posterior cranial fossa. It is separated from these lobes by the tentorium cerebelli, a tough layer of dura mater.
 It lies at the same level of and posterior to the pons, from which it is separated by the fourth ventricle.

3. Cerebellum: External Features

4. Cerebellum: Anatomical Divisions
• There are 3 anatomical lobes divided by 2 fissures – the primary fissure and posterolateral fissure can
be distinguished in the cerebellum. These are
1) Anterior lobe: extends from the level of the cerebellar peduncles anteriorly and includes the anterior
2/3s of the superior vermis, along with the anterior third of each hemisphere. This lobe terminates at
the primary fissure.
2) Posterior lobe: lying posteriorly and laterally and continuing along the inferior surface to the
posterolateral fissure.
3) Flocculonodular lobe: flattened lobe that lies between the posterolateral fissure (inferiorly) and the
inferior medullary velum and the cerebellar peduncles (superiorly).

5. Cerebellum: Functional Divisions
The cerebellum can also be divided by function. There are 3 functional areas of
the cerebellum
Cerebrocerebellum / Pontocerebellum/ Neocerebellum – the largest division,
formed by the lateral hemispheres.It receives inputs from the cerebral
cortex and pontine nuclei, and sends outputs to the thalamus and red
nucleus.
Functions :
1) It is involved in planning movements and motor learning.
2) Regulates coordination of muscle activation and is important in
visually guided movements.
Spinocerebellum/ Paleocerebellum – comprised of the vermis and intermediate
zone of the cerebellar hemispheres.
Functions :
1) It is involved in regulating body movements by allowing for
error correction.
2) Receives proprioceptive information from spinal nerves
Vestibulocerebellum/ Archicerebellum – the functional equivalent to the
flocculonodular lobe. It receives inputs from the vestibular system, and
sends outputs back to the vestibular nuclei.
Functions :
1) Involved in controlling balance and ocular reflexes, mainly fixation on
a target.

6. Functions of the Functional Divisions

7. Cerebellum: Lobules
• The vermal lobules are assigned Roman
Numerals I – X. They can be better
appreciated when the cerebellum is
divided along the midline of the vermis.
The lobules can be better remembered
with the aid of the following mnemonic:
“Loving Caring Children Donate Food To
Poor Unfed Needy”.
• L – Lingula (I)
• C – Central lobule (II & III)
• C – Culmen (IV & V)
• D – Declive (VI)
• F – Folium (VII A)
• T – Tuber (VII B)
• P – Pyramid (VIII)
• U – Uvula (IX)
• N – Nodule (X)

8. Cerebellum: Nuclei
There are 2 major parts to the
cerebellum, the cerebellar deep
nuclei and the cerebellar cortex. Output
from the cerebellum originates solely
in the deep nuclei, where almost all of
the neurons of the cerebellum reside.
The 4 cerebellar deep nuclei include:
1) Dentate nuclei
2) Emboliform
3) Globose
4) Fastigial
(Don’t Eat Greasy Food)
3 distinct fiber bundles carry all signals
into and out of the cerebellum, these
include the
• superior cerebellar peduncles.
• middle cerebellar peduncles.
• inferior cerebellar peduncles.

9. Cerebellum: Pathways
The figure demonstrates the afferent
nerve (blue) and efferent nerve (red)
of the cerebellum
Tracts passing through superior
cerebellar peduncles:
• Cerebellothalamic tract
• Cerebellorubral tract
• Ventral Spinocerebellar tract
Tracts passing through middle
cerebellar peduncles:
• Corticopontocerebellar tract
Tracts passing through inferior
cerebellar peduncles:
• Cerebellovestibular tract
• Cerebelloreticular tract
• Vestibulocerebellar tract
• Reticulocerebellar tract
• Olivocerebellar tract
• Dorsal Spinocerebellar tract

10. Cerebellum: Histology
• Molecular layer
Superficially located stellate cells and basket cells are found
in this layer. The stellate cells usually bear short dendrites in
which make contact with small number of Purkinje cell
dendrites. In comparison, basket cells have extensive
dendritic processes that can make contact with much larger
number of Purkinje cells. Both cells receive excitatory input
from the parallel fibers and in turn exhibit inhibitory influence
on the Purkinje cells
• Purkinje cell layer
The middle layer (Purkinje cell layer) consists of a single layer
of large pear-shaped Purkinje cells. Their cell bodies are
largest in the cerebellum. The dendrites of these cells reside
in the molecular layer, while their axons project deep through
the granular layer and synapse into the deep nuclei of
cerebellum.
• Granular layer
The inner granular layer contains many, tightly packed
granule cells and Golgi type II cells. Granule cells,, usually
represent the extensions of the mossy fibers. Their axons
extend into the outer molecular layer where they branch in T
shape forming parallel fibers and synapse with the dendrites
of Purkinje, basket and stellate cells.

11. Cerebellum: Circuitry
• The cerebellum as a whole has afferent connections (input)
and efferent connections (output). Within the cerebellar cortex, ongoing
circuits driven by cerebellar input define cerebellar output.
• Cerebellar afferents (input):
Afferent axons to the cerebellum are excitatory. They send collateral
branches to cerebellar nuclei before terminating in cerebellar cortex. The
afferents generally excite neurons in cerebellar nuclei and, via cortical
circuits, selectively excite Purkinje neurons in cerebellar cortex. Cerebellar
afferents include:
– mossy fibers: from vestibular nuclei & vestibular nerves multiple
spinocerebellar tracts motor-related cerebral cortex, via pontine nuclei
– climbing fibers: from the contralateral olivary nucleus
• Cerebellar cortex circuitry:
Mossy fibers excite granule cells, whose axons enter the molecular layer
and bifurcate into parallel fibers that run longitudinally in a folium. The
parallel fibers excite bands of Purkinje cells , basket cells and stellate cells
the basket cells and stellate cells inhibit (Feed forward inhibition)Purkinje
cells along the edges of the excited band. Climbing fibers excite individual
Purkinje cells to fire action potentials repetitively.
Axons of selectively excited Purkinje cells inhibit selected neurons
within cerebellar nuclei (or within vestibular nuclei in the case of the
flocculonodular lobe).
• Cerebellar efferents (output):
Cerebellar output consists of axons from neurons within cerebellar
nuclei (or cerebellar cortex of the flocculonodular lobe). The axons synapse
on neurons in brainstem motor centers or in thalamic nuclei that project to
motor-related cerebral cortex.

12. Cerebellar control

13. Cerebellum: Vasculature
 Arterial supply
The cerebellum receives its blood supply from
three paired arteries:
– Superior cerebellar artery (SCA)
– Anterior inferior cerebellar artery (AICA)
– Posterior inferior cerebellar artery (PICA)
The SCA and AICA are branches of the basilar
artery, which wraps around the anterior aspect
of the pons before reaching the cerebellum.
The PICA is a branch of the vertebral artery.
 Venous drainage
Venous drainage of the cerebellum is by the
– superior cerebellar veins
– inferior cerebellar veins.
They drain into the superior petrosal,
transverse and straight dural venous sinuses.

14. Cerebellum Dysfunction
Dysfunction of the cerebellum can produce a wide range of symptoms and signs. The clinical picture is
dependent on the functional area of the cerebellum that is affected.
The symptoms can be remembered using the acronym ‘3DAPANISH’:
• 3D- Dysdiadochokinesia, Dysmetria, Dizziness
– Dysdiadochokinesia - inability to engage in rapid alternating movements
– Dysmetria - inability to judge distances when moving, leading to either overshooting or undershooting the amount of
movement required
– Dizziness - when someone experiences a distinct sense that things are moving even when they are not
• A- Ataxia
– Ataxia is the uncontrolled voluntary movement caused by errors in the rate, force, range and the direction of movement
• P- Pendular Knee Jerks
– Pendular knee jerks occur due to loss of cerebellar influences on stretch reflexes
• A- Absence of Rebound phenomenon
– Rebound phenomenon is a reflex that occurs when one attempts to move a limb against resistance that is suddenly
removed.
– Normally :When the resistance is removed, the limb will usually move a short distance due to the braking motion of
antagonistic muscles.
– Absence of the reflex: The patient with cerebellar dysfunction can’t brake the movement of the limb so it flies in the
original direction.
• N- Nystagmus (coarse)
– Saccadic movement of the eye when patient tries to fixate eyes on one side of the head
• I- Intention tremor
– Tremors that occur while performing voluntary motor movements
• S- Scanning speech/ dysarthria
– Ataxia of laryngeal muscles causes speech to sound gibberish
• H- Hypotonia
– Decrease in muscle tone due to loss of cerebellar influence

15. Cerebellum Dysfunction: Signs

16. Cerebellum: Functional tests

17. Brainstem: Parts
The brainstem can be divided into 3
parts:
• Midbrain
– The midbrain (also known as the
mesencephalon) is the most
superior of the 3 regions of the
brainstem. It acts as a conduit
between the forebrain above and the
pons and cerebellum below.
• Pons
– The pons is the largest part of the
brainstem, located above
the medulla and below the midbrain.
• Medulla Oblongota
– The medulla oblongata (medulla) is
the most inferior of the three and is
continuous above with the pons and
below with the spinal cord.

18. Midbrain: External Anatomy
The midbrain is the smallest of the three regions of the brainstem, measuring around 2cm in length. As it ascends,
the midbrain travels through the opening in the tentorium cerebelli.
It can be divided into two main parts:
1) Tectum – located posterior to the cerebral aqueduct
2) Paired cerebral peduncles – located anteriorly and laterally.
– Internally, the cerebral peduncles are further separated by the substania nigra into the crus cerebri (anterior) and
the tegmentum (posterior).
Tectum
The tectum houses four rounded prominences named colliculi (collectively the corpora quadrigemina) which sit
directly inferior to the pineal gland. The colliculi are separated by the cruciform sulcus; there are
a) 2 superior colliculi: centers for visual reflexes
b) 2 inferior colliculi: lower auditory centers
Extending laterally from each colliculi are the quadrigeminal brachium:
• Superior quadrigeminal brachium forms a pathway between the superior colliculus and the retina of the eye.
• Inferior quadrigeminal brachium conveys fibres from the lateral lemniscus and inferior colliculus to the medial
geniculate body.
Inferior to the colliculi, the Trochlear nerve (CN IV) emerges before sweeping across to the anterior surface.

19. Midbrain: External Anatomy
• Cerebral Peduncles
• The paired cerebral peduncles
extend from the cerebral
hemispheres to converge as they
meet the pons. They are separated
anteriorly in the midline by
the interpeduncular fossa, the
floor of which is termed the
posterior perforated substance (as
many perforating blood vessels
can be identified).
• The oculomotor nerve (CNIII) is
seen exiting from between the
peduncles while the optic
tract runs around the superior
border of the midbrain.

20. Midbrain: Internal Anatomy
Grey matter:
 oculomotor nucleus- somatic motor of CN III
 Edinger Westphal nucleus- Parasympathetic
nucleus of CN III
 Mesencephalic nucleus of CN V
 Pretectal nucleus- involved in visual reflexes
 Periaqueductal Grey mattter : Control centre
for descending pain modulation (inhibits pain
sensation).
 Red Nucleus: Red/ pink in colour due to the
presence of iron. It is only found at the level
of the superior colliculus and is involved in
motor co-odination via the rubrospinal tracts.
 Substantia Nigra: A large motor nucleus
situated between the tegmentum, and the
crus cerebri. It is composed of medium-size
multipolar neurons that possess
neuromelanin. The substantia nigra is
concerned with muscle tone and addiction.
White Matter:
 Cerebral Peduncle : contains important
descending tracts to contralateral side.
 Medial Leminiscus : Relays vibration and
proprioreciption from contralateral side.

21. Midbrain: Internal Anatomy
Grey matter
• nucleus of trochlear nerve,
• mesencephalic nucleus of trigeminal nerve.
• Periaqueductal Grey mattter
• nucleus of inferior colliculus
• Substantia nigra.
• The reticular formation
White matter
The anteriolateral surface of the midbrain
houses the paired crus cerebri. 4 fibre tracts
run within the crus:
– Frontopontine fibres – located most
medially.
– Corticospinal fibres – motor fibres from the
primary motor cortex.
– Corticobulbar tracts – motor fibres from the
primary motor cortex.
– Temporopontine fibres – located
posterolaterally.
• decussation of the superior cerebellar
peduncles

22. Midbrain: Vasculature & Functions
• The midbrain receives vascular supply
from the basilar artery and its
branches. The major vessels are:
• Posterior cerebral artery and its
peduncular branch
• Superior cerebellar artery
• Posterior choroidal artery
• Interpeduncular branches of the
basilar artery.
Functions:
 Co-ordinate eye movements
 Participates in visual and auditory
reflexes
 Consciousness and arousal

23. Pons
Description: The pons is the largest part of the
brainstem, located above the medulla and
below the midbrain. It is a group of nerves that
function as a connection between
the cerebrum and cerebellum (pons is Latin for
bridge).
Embryonic origins: The pons develops from
the embryonic metencephalon (part of the
hindbrain, developed from the
rhombencephalon), alongside the cerebellum.
Anatomical relations:
• The pons is a horseshoe-shaped collection of
nerve fibres located in the anterior part of
the posterior cranial fossa.
• Its anatomical relations are as follows:
• Posteriorly – the cerebellum, separated by the
fourth ventricle.
• Inferiorly – the medulla oblongata.
• Superiorly – the midbrain lies immediately
above the pons.

24. Pons : External Anatomy
Ventral Surface
• Ventral Surface of the pons is marked by a bulging
formed by the transverse pontocerebellar fibres. These
fibres wrap around the otherwise vertically oriented
brainstem. It measures around 2.5 cm in adults.
• The basilar groove demarcates the midline of the ventral
surface and is where the basilar artery is located.
• The pontomedullary junction is an important anatomical
landmark defined by the angle between the lower
border of the pons and the superior border of the
medulla.
Several cranial nerves originate from the ventral surface
of the pons:
• Cranial nerve V: trigeminal– originates from the lateral
aspect of mid pons
• Cranial nerve VI: abducens – originates from the
pontomedullary junction, close to the midline
• Cranial nerve VII: facial – originates from the
cerebellopontine angle, the more lateral aspect of the
pontomedullary junction.
• Cranial nerve VIII:vestibulocochlear – originates laterally
to the facial nerve.

25. Pons : External Anatomy
Posterior Surface
The pons is intimately related to the cerebellum and is
connected to it by the middle cerebellar peduncles.
Removal of the cerebellum will reveal the
underlying fourth ventricle.
The floor of the fourth ventricle is composed of the
dorsal surface of the pons and the medulla. There are
some important anatomical landmarks here:
• The medial eminence marks the midline of the floor.
• The facial colliculus is a bulging formed by the fibres of
the facial nerve looping around the abducens nucleus.
• The stria medullaris of the fourth ventricle is a bundle
of nerve fibres crossing transversely from the lateral
aspect into the midline. They mark the posterior border
between the pons and the medulla.
The angle formed at the junction of the pons, medulla,
and cerebellum is another anatomical landmark and is
named cerebellopontine angle. Here, the
cerebellar flocculus, the ventricular choroid plexus and
the emerging CNs VII and VIII surround the lateral
apertures of the fourth ventricle (the foramen of
Luschka).

26. Pons : Internal Anatomy
The pons is comprised of 2 major components – the ventral pons and the tegmentum.
 Ventral pons contains the pontine nuclei, which are responsible for coordinating movement. Fibres from the pontine nuclei cross the
midline and form the middle cerebellar peduncles on their way to the cerebellum.
 Tegmentum forms part of the reticular formation – a set of nuclei found throughout the brainstem that are responsible for arousal
and attentiveness. Damage to this part of the pons may result in anosognosia for hemiplegia, where patients are unaware of their
paralysis.
The rest of the pons is made up of tracts passing through the pons including:
 Descending corticospinal tracts – responsible for voluntary motor control of the body.
 Descending corticobulbar tracts – responsible for voluntary motor control of face, head and neck.
 Ascending medial leminiscus tracts – responsible for fine touch, vibration and proprioception.
 Ascending spinothalmic tracts – responsible for pain and temperature sensation

27. Pons : Internal Anatomy

28. Pons : Cranial Nerve Nuclei
 Principal trigeminal sensory nucleus and the trigeminal motor nucleus are located
in the midpons – at the level where the fibres originate from the lateral aspect of
the pons.
 Abducens nucleus controls the abducens nerve, which innervates the ipsilateral
lateral rectus muscle. It is located in the caudal pons, on the medial aspect of its
dorsal surface.
 Facial nucleus is located more anteriorly and laterally at the same level of the
abducens nucleus.
 Cochlear and Vestibular nuclei sit dorsolaterally from the inferior pons to the
superior medulla.

29. Pons : Vasculature & Functions
Vasculature:
Arterial supply
The blood supply of the pons is formed by branches
of the vertebrobasilar system:
• Most of the pons is supplied by the pontine arteries,
branches of the basilar artery
• A smaller part of its blood supply comes from
– the anterior inferior cerebellar artery (AICA) and
– the superior cerebellar artery (SCA).
Venous drainage
• consists of the anterior pontomesencephalic vein,
which drains
– superiorly into the basal vein, that in turn drains into
the cerebral veins.
– Inferiorly, the pons drains into the inferior petrosal
sinus, which drains into the internal jugular veins.
Function of the pons:
• to house the pontine nuclei
• To facilitate cortico-ponto-cerebellar comunication.
• Enables communication between the left and right
hemispheres of the cerebellum.

30. Medulla oblongata
Description: The medulla oblongata is the direct upward continuation of
the spinal cord, extending from foramen magnum to the lower border
of the pons. It forms the lowest part of the brainstem.
Measurements : Medulla oblongata measures about 3 cm in length, 2 cm in
breadth (at the widest part) and 1.25 cm in thickness).
Importance:
• The medulla contains vital centres which are essential for life. These
are:
– (a) cardiac centre,
– (b) vasomotor centre
– (c) respiratory centre.
• Medulla provides attachment to last 4 cranial nerves.
Divisions : It is divided into two parts based on whether or not the fossa is
present at a level:
• There is an upper, rostral or open part where the dorsal surface of
the medulla is formed by the rhomboid fossa.
• There is a lower, caudal or closed part where the fourth ventricle has
narrowed at the obex in the caudal medulla and surrounds part of the
central canal.
Embryological origins : The medulla develops from the myelencephalon,
which is a secondary brain vesicle that arises from the
rhombencephalon (the hindbrain).

31. Medulla oblongata: External Anatomy
Anterior Surface
There are several structures visible on the anterior
surface of the medulla – namely the 3 fissures/sulci,
the pyramids, the olives, and 5 cranial nerves.
• Anterior median fissure is in the midline of the
medulla and is continuous along the length of the
spinal cord. However, it is interrupted temporarily by
the decussation of the pyramids (see below). As we
move away from the midline, two sulci are visible –
the ventrolateral sulcus and the posterolateral
sulcus.
• Pyramids- are paired swellings found between the
anterior median fissure and the ventrolateral sulcus.
• Olives- are another pair of swellings located laterally
to the pyramids – between the ventrolateral and
posterolateral sulci.
• 5 cranial nerves: Arising from the junction between
the pons and medulla is the abducens nerve (CN VI).
Extending out of the ventrolateral sulcus is the
hypoglossal nerve (CN XII). In the posteriolateral
sulcus, three more cranial nerves join the medulla
(CN IX, CN X, and CN XI).

32. Medulla oblongata: External Anatomy
Posterior surface
The posterior surface of the medulla can be divided into
an upper open area and a lower closed area.
 Features of the closed part:
3 longitudinal elevations. From medial to lateral these
are:
1) fasciculus gracilis,
2) fasciculus cuneatus,
3) inferior cerebellar peduncle.
– The upper ends of the fasciculus gracilis and
fasciculus cuneatus expand to form the gracile
and cuneate tubercles respectively due to
underlying nuclei of the same name.
• Another elevation present lateral to cuneate tubercle,
the tuber cinereum is produced by the spinal nucleus of
trigeminal nerve
 Features of the open part
The open part of the medulla forms the lower part of
the floor of fourth ventricle, which presents number of
features like,
• median sulcus,
• hypoglossal triangles- location of the nucleus of CN XII
• vagal triangles- location of CN X nucleus
• vestibular areas,
• area postrema,
• Stria medullaris,

33. Medulla oblongata: Internal Anatomy
The internal structures of the medulla must be viewed
in cross section to understand the layout. 3 levels of
the medulla are typically discussed (inferior –
superior):
1) Level of decussation of the pyramids
2) Level of decussation of the medial lemnisci
3) Level of the olives
Level of the Decussation of the Pyramids
• This is the major decussation point of
the descending motor fibres. Roughly 75% of motor
fibres housed within the pyramids cross diagonally
and posteriorly, and continue down the spinal
column as the lateral corticospinal tracts.
• The posterior white matter contains the fasiculus
gracilis and the more lateral fasiculus cuneatus.
Corresponding portions of gray matter extend to
these regions and are the nucleus gracilis and
nucleus cuneatus respectively.
• Unchanged from the spinal cord, the spinocerebellar
tracts (posterior and anterior) are located laterally,
with the lateral spinothalamic tract situated between
them. The large trigeminal nucleus and tracts can be
found posterior to these tracts. This is a continuation
of the substantia gelatinosa of the spinal cord.

34. Medulla oblongata: Internal Anatomy
Level of Decussation of the Medial Lemniscus
• This level marks the sensory decussation
occurs of the medial lemniscus. Internal
arcuate fibres run from the nucleus
gracilis and nucleus cuneatus around and
anterior to the central gray matter to form
the medial lemniscus.
• Lateral to the medial lemniscus, the
trigeminal nucleus and spinal tract can
once again be seen, as can
the spinocerebellar tracts and the lateral
spinothalamic tract. Similarly, the
posterior structures are much the same at
this level.
• Centrally, the hypoglossal nucleus and
medial longitudinal fasciculus are seen.
Moving laterally, the nucleus ambiguous
can be seen. Between this structure and
the pyramids is the inferior olivary
nucleus.

35. Medulla oblongata: Internal Anatomy
Level of the Olives
• The central canal has now expanded into the 4th ventricle
and as such makes this region the open medulla.
• The large inferior olivary nucleus is responsible for the
external expansion of the olives. The related medial and
dorsal accessory olivary nuclei can be seen medial and
posterior to this structure respectively.
• The large inferior cerebellar peduncles come into view and
are surrounded by multiple nuclei. The two vestibular
nuclei (medial and inferior) are both found towards the
midline while the two cochlear nuclei are found somewhat
above and below the peduncles. Now a much smaller
structure, the trigeminal tract and nucleus is seen adjacent to
the peduncle.
• The nucleus ambiguous remains as it was previously, while
the hypoglossal nucleus has migrated with the central canal
posteriorly, joined by the medial longitudinal fasciulus. An
additional cranial nucleus comes into view lateral to the
hypoglossal – the dorsal vagal nucleus. Moving further
lateral, the nucleus of tractus solitarius comes into view.
• Centrally, the medial lemniscus hugs the midline posterior to
the pyramids, as does the tectospinal tract.
• Between the peduncle and the olivary nuclei resides the
lateral spinothalamic tract and the more lateral anterior
spinocerebellar tract.

36. Medulla oblongata: Vasculature
Vasculature
• The vessels that supply the medulla include: the
– anterior spinal
– posterior spinal
– posterior inferior cerebellar
– anterior inferior cerebellar
– vertebral arteries.
• Throughout the medulla, the anterior spinal artery supplies
a region beginning at the central canal (or anterior border of
the fourth ventricle), and fans out to encompass the
pyramids.
• Below the level of the olives the posterior half of the
medulla is supplied by the posterior spinal artery. No other
regions are supplied by this vessel. The remaining portions
are supplied by the posterior inferior cerebellar and
vertebral arteries.
• In cross section through the olives both the posterior
inferior cerebellar and vertebral arteries take on greater
territories posterolaterally and anterolaterally respectively.
They continue to do so as the medulla ascends.
• At the highest point in the medulla, the anterior inferior
cerebellar artery supplies the outermost portions of the
posterior region.

37. Reticular Formation
The reticular formation is a vast network of neurons that are involved in
maintaining consciousness and initiating arousal. This neuronal tract
extends from the spinal cord to the diencephalon and occupies
different parts of the brainstem throughout.
The nuclei of the reticular formation are situated deep within the
brainstem along its vertical axis. On each half of the brainstem, there is
a
 lateral group of nuclei.
 medial group of nuclei.
 median group of nuclei.
Functions:
Given the vast number of connections of the reticular formation to all
parts of the nervous system it serves many functions. A few of the more
important functions are considered here.
1. Control of skeletal muscle.
2. Control of facial expression muscles.
3. Control of somatic and visceral sensations.
4. Control of the Autonomic nervous system
5. Control of the endocrine system.
6. Influence on biologic clocks.
7. Reticular activating system.