CEREBELLUM
28. 04. 2014
Kaan Yücel
M.D., Ph.D.
https://yeditepeanatomyfhs122.wordpress.com
Dr.Kaan Yücel
yeditepeanatomyfhs122.wordpress.com
Cerebellum
The cerebellum (L. “little brain”) is the largest part of the hindbrain and lies posterior to the fourth
ventricle, the pons, and the medulla oblongata. The cerebellum is situated in the posterior cranial fossa and is
covered superiorly by the tentorium cerebelli. It is made up of two lateral cerebellar hemispheres and a median
vermis (L. “worm”). The surface of the cerebellum displays slender and parallel elevations (ridges) known as
folia and depressions (grooves) known as sulci that facilitate a great increase in the surface area of the
cerebellar cortex.
Though apparently smaller than the cerebral cortex, the cerebellum contains ~2X as many neurons as
the cerebral cortex. Its function is to make our movements as fast, accurate, smooth, and consistent as possible.
Cerebellar damage does not cause paralysis but renders movements slow, inaccurate, inconsistent, and jerky.
Though the cerebellum sends very few fibers to the spinal cord it exerts a powerful influence on movements via
projections, either direct or via one relay neuron, to the structures from which all four major descending motor
tracks originate.
The cerebellum is connected to the dorsal aspect of the brainstem by three pairs of prominent fiber
bundles, the superior, middle, and inferior cerebellar peduncles. On its ventral surface, near the middle
cerebellar peduncle, a small, bulb-like region of each cerebellar hemisphere, known as the flocculus, is
connected to a region of the vermis known as the nodulus.
The effect of this fissuring is to give the cerebellum in section the appearance of a many branched tree which is
called as arbor vitae; the tree of life.
The cerebellum is somewhat ovoid in shape and constricted in its median part.
The cerebellum has traditionally been recognized as having three anterior-posterior divisions: the anterior lobe
(lobules I – V) is separated from the posterior lobe by the primary fissure, and the posterior
lobe (lobules VI – IX) is separated from the flocculonodular lobe (lobule X) by the posterolateral fissure
(posterior fissure or uvulonodular fissure). A deep horizontal fissure that is found along the margin of the
cerebellum separates the superior from the inferior surfaces.
The anterior lobe receives its input primarily from the spinal cord and is referred to as the paleocerebellum
The posterior lobe receives its input primarily from the cerebral cortex via relay neurons in the pontine nuclei
and is called the neocerebellum. The flocculonodular lobe receives most of its input from the vestibular system
and is called the vestibulocerebellum.
The cerebellum plays a very important role in the control of posture and voluntary movements. It
unconsciously influences the smooth contraction of voluntary muscles and carefully coordinates their actions,
together with the relaxation of their antagonists. Each cerebellar hemisphere controls muscular movements on
the same side of the body and that the cerebellum has no direct pathway to the lower motor neurons but exerts
its control via the cerebral cortex and the brainstem.
The cerebellum is composed of an outer covering of gray matter called the cortex and inner white
matter. Embedded in the white matter of each hemisphere are three masses of gray matter forming the
intracerebellar nuclei (deep cerebellar nuclei).
The human cerebellum contains more than 100 billion neurons, a number that represents about 80% of
the total number of neurons in the brain. Unlike the cerebral cortex, the cortex of the cerebellum has uniform
anatomical structure, suggesting that there may be a similar mode of operation for all its possible functions. The
cortex of the cerebellum is deeply folded. If one looks at the human cerebral cortex,one can see about one third
of it; two thirds is buried on the banks and depths of the fissures. For the cerebellar cortex, one would see only
about one tenth; 90% is buried within the fissures.
The output from the cortex is mainly to the intracerebellar nuclei, which are buried within the white
matter of the cerebellum. The white matter consists of fibers coming into the cerebellum and the axons of the
output neurons of the cerebellar cortex, Purkinje cells, coursing to terminate in the cerebellar nuclei.
There are four nuclei on each side. Most laterally is the dentate or lateral nucleus. Most medially is the
fastigial or medial nucleus. Between the lateral and medial nuclei are the intermediate, or interpositus nuclei,
the globose (more lateral) and emboliform (more medial).
http://www.youtube.com/yeditepeanatomy
2
Dr.Kaan Yücel
yeditepeanatomyfhs122.wordpress.com
Cerebellum
Thirty million Purkinje cells are the only neurons whose axons carry information from the cortex to the
nuclei. Purkinje cell axons run through the white matter to terminate in the cerebellar nuclei. All output from
the cerebellar cortex leaves the cortex via Purkinje cell axons. Climbing fibers terminate directly on the
dendrites of ~10 Purkinje cells. An action potential in a climbing fiber always causes an action potential in the
Purkinje cells that it contacts. Thus a mossy fiber has a small effect on many Purkinje cells, whereas climbing
fibers have a large effect on a small number of Purkinje cells.
Cerebellar Peduncles
The cerebellum is linked to other parts of the central nervous system by numerous efferent and afferent fibers
that are grouped together on each side into three large bundles, or peduncles. The superior cerebellar peduncles
connect the cerebellum to the midbrain, the middle cerebellar peduncles connect the cerebellum to the pons,
and the inferior cerebellar peduncles connect the cerebellum to the medulla oblongata.
Functions of the cerebellum
Cerebellum makes an important contribution to the control of voluntary movement and movement
coordination, as well as control of balance, gait, and posture.
Functions- 3 major functional roles
1. Coordination of Movement-the cerebellum controls the timing and pattern of muscle activation during
movement.
2. Maintenance of Equilibrium (in conjunction with the vestibular system)
3. Regulation of Muscle Tone-modulates spinal cord and brain stem mechanisms involved in postural
control.
There is also strong evidence for a cerebellar role in cognition (memory, attention, language and executive
functions), emotions, and anxiety. More @ Limbic System class!!!
http://nbio401.biostr.washington.edu/PDF/22-Cerebellar%20Anatomy.pdf
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