CONTRIBUTION OF
CEREBELLUM TO OVERALL
MOTOR CONTROL
Anatomical Functional Areas
of the Cerebellum
►
Anatomically, the cerebellum is divided into three
lobes by two transverse fissures
(1) the anterior lobe
(2) the posterior lobe, and
(3) the flocculonodular lobe(the oldest of all
portions of the cerebellum
Longitudinal Functional Divisions
► The
anterior and posterior lobes are organized
along the longitudinal axis into:
1) A central narrow band called the vermis
2) A large, laterally protruding cerebellar hemisphere
to each side of the vermis.Each of these is divided
into an intermediate zone and a lateral zone
► Vermis
is separated from the hemispheres by
shallow grooves
Topographical Representation of
the Body
In the vermis
for muscle movements of the
axial body, neck, shoulders,
and hips
In the intermediate
zone
In the lateral zone
for muscle movements in the
distal portions of the upper
and lower limbs, especially the
hands and fingers and feet and
toes
do not have any
Topographical Representation of
the Body
Afferents
In turn, they send motor
signals back to the same
respective topographical
areas
of
the
cerebral
► corresponding
topographical motor motor cortex and those of
the
red
nucleus
and
areas in the cerebral
cortex and brain stem reticular formation in the
brain stem.
►
all the respective
parts of the body
Efferents
Lateral Zone of Cerebellar
Hemisphere
The connectivity with the cerebral cortex
allows the lateral zones to play important
roles in planning and coordinating the
body’s rapid sequential muscular activities
occuring within fractions of a second
Neuronal Circuit of the Cerebellum
1) Afferent Pathways to the Cerebellum:
1) from Other Parts of the Brain
► Cerebral cortices →the corticopontocerebellar
pathway
► From brain stem → olivocerebellar tract
→ vestibulocerebellar fibers
→ reticulocerebellar fibers
2) Afferent Pathways from the Periphery
► dorsal
spinocerebellar tract
► ventral spinocerebellar tract
The cerebellum continually collects
information about the movements and
positions of all parts of the body even
though it is operating at subconscious
level.
PATHWAYS….
1) Corticopontocerebellar Pathway
Cerebral motor ,premotor and somato- sensory
cortices → by way of the pontile nuclei and
pontocerebellar tracts →mainly to the lateral
divisions of the cerebellar hemispheres on the
opposite side of the brain
2) Olivocerebellar tract
Inferior olive →to all parts of the cerebellum and
is excited in the olive by fibers from the cerebral
motor cortex, basal ganglia, widespread areas of
the reticular formation, and spinal cord
3) Vestibulocerebellar fibers
Vestibular apparatus and brain stem vestibular
nuclei →almost all terminate in the flocculonodular
lobe and fastigial nucleus of the cerebellum
4) Reticulocerebellar fibers
Different portions of the brainstem reticular
formation →terminate in the midline cerebellar
areas ,mainly the vermis
5) Dorsal spinocerebellar tract
► 2 on each side (4 in all)
► Enters
–through the inferior cerebellar peduncle
Terminates – in the vermis and intermediate zones
on the same side
► Signals
1) mainly from the muscle spindles
2) to a lesser extent from other somatic receptors
(such as Golgi tendon organs, large tactile
receptors of the skin, and joint receptors)
► All
these signals apprise the cerebellum of the
momentary status of
(1) muscle contraction
(2) degree of tension on the muscle tendons
(3) positions and rates of movement of the parts
of the body
(4) forces acting on the surfaces of the body
6) ventral spinocerebellar tract
► Enters –through the superior cerebellar peduncle
Terminates – in both sides of the cerebellum.
► Signals
Receive less information from the peripheral
receptors. Instead, are excited mainly by motor
signals arriving in the anterior horns of the spinal
cord–efference copy of the anterior horn motor
drive.
► Significance
The spinocerebellar pathways has the most rapid
conduction in any pathway in the CNS (velocities
up to 120 m/sec) – important for instantaneous
apprisal of the cerebellum of changes in peripheral
muscle actions.
VENTRAL SPINOCEREBELLAR
TRACT
DORSAL SPINOCEREBELLAR
TRACT
2) Efferents from the Cerebellum:
► Organization
► Functional
► Neuronal
of cerebellum
unit
circuits
● Inputs
● Outputs
1) Organization of cerebellum:
1) An external 3 layered cerebellar cortex
● External molecular Layer
● Purkinje Cell Layer
● Internal granular layer
2) White matter
3) Deep cerebellar nuclei (4 on each side)
● dentate n.
● globose n.
Interpositus n.
● emboliform n.
● fastigial n.
2) Functional unit:
► 30 million
► centers on a single Purkinje cell and on a
corresponding deep nuclear cell
The Purkinje cells are among the biggest neurons
in the body
● They have very extensive dendritic arbors that
extend throughout the molecular layer, and are
oriented at right angles to the parallel fibers.
● Their axons, which are the only output from the
cerebellar cortex→ deep nuclei
3) Neuronal circuits:
2 main Inputs
Climbing fibers
Mossy fibers
Origin
single (inferior
From multiple
olivary nuclei)
sources (higher brain,
brain stem and spinal
cord)
Collateral To deep cerebellar To deep cerebellar
nuclei
nuclei
Extent
External molecular Inner granule cell
layer
layer
Climbing fibers
Termination dendrites of a PC,
around which it
entwines like a
climbing plant (1
for 5-10 PC)
Mossy fibers
dendrites of GC in
complex synaptic
groupings called
glomeruli
Effect
+++ effect on
single PC
+ on many PC via
GC’s parallel fibers
(500-1000 GC for 1
PC)
AP
Complex spike
Simple spike
PARALELL FIBERS
+
+++
CLIMBING
FIBER
MOSSY FIBER
Other Inhibitory Cells in the Cerebellum
other types of neurons are basket cells and
stellate cells.
► These are inhibitory cells
► Located in the molecular layer of the cerebellar
cortex
► Stimulated by the parallel fibers
► In turn send their axons to cause lateral inhibition
of adjacent PCs → sharpening the signal
►2
Outputs
► All
input signals that enter the cerebellum
eventually end in the deep nuclei in the form of
initial excitatory signals followed a fraction of a
second later by inhibitory signals
► However,output
of the deep cerebellar nuclei to
the brainstem and thalamus is always excitatory.
Role of Cerebellum in Movement
Signal to
Movement agonist
Signal to
antagonist
at the onset
turn-on
turn-off
Near
termination
turn-off
turn-on
1) Mechanism for agonist muscle:
A complete cerebellar circuit could cause:
►
a rapid turn-on agonist muscle contraction at the
beginning of a movement, and
►
a precisely timed turn-off of the same agonist
contraction after a given time period.
►
HOW ?
1) Signals from the cerebral cortex →brain
stem and cord pathways → directly to the
agonist muscle to begin the initial
contraction.
2) At the same time, parallel signals are sent
by way of the pontile mossy fibers into the
cerebellum.
One branch of each mossy fiber goes
directly to deep cerebellar nuclei;
This instantly sends an excitatory signal
back into the cerebral corticospinal motor
system (by way of return signals through
the thalamus or brainstem) to support the
muscle contraction signal that had already
been begun by the cerebral cortex.
► As
a consequence:
The turn-on signal, after a few msec,becomes
even more powerful than it was at the start
because it becomes the sum of both the cortical
and the cerebellar signals.
Thus,cerebellum provides secondary extra
supportive signal
3) The second branch of each mossy fibers →
eventually deep →deep nuclear cells’
inhibition
► Parallel fibers are ● slow-conducting
● weak signals
► But once the PC is excited→ strong
inhibitory signal to the same deep
nuclear cell that had originally turned on
the movement → turns off the movement
after a short time
The Purkinje Cells “Learn” to Correct Motor
Errors
● Degree of control by the cerebellum(on/off)
● Timing of contractions
Progressive adaptation of sensitivity levels
of cerebellar circuits during the training
process.
Mechanism –role of climbing fibers:
1) A new movement for the first time→ FB
signals from the muscle and joint
proprioceptors → climbing fibers send
“error” signals to the cerebellum to cause
further change
2) The climbing fiber signals alter long-term
sensitivity of the PC
3) Over a period of time this change makes the
timing and other aspects of cerebellar control of
movements approach perfection.
4) When this has been achieved, the climbing fibers
no longer need to send “error” signals to the
cerebellum to cause further change
2) Mechanism for antagonist muscle:
Role of:
► The reciprocal agonist/antagonist circuits present
throughout the spinal cord
► Several
other types of inhibitory cells besides PC in
the cerebellum.
3 functional divisions
work in association with other
parts of brain for motor control
1) Vestibulocerebellum
 Flocculonodular lobe
 adjacent vermis
Lateral zone
3) Cerebrocerebellum
 Lateral zones
Intermediate zone
Vermis
2) Spinocerebellum
 Most of Vermis
 adjacent intermediate
zone on both sides
Flocculonodular lobe
1) Vestibulocerebellum
Is most primitive
► Connections
 Afferents: from vestibular nuclei and vestibular
apparatus
 Efferents: projects to the vestibular nucleus →
vestibulospinal tract and medial longitudinal fasciculus
→ motor neurons of anterior horn
► Functions:
▪ Involved in eye movements
▪ Maintains balance (especially during rapid
changes
in body positions)
►
▪ During control of equilibrium information from
both the body periphery and the vestibular
apparatus tell the brain how rapidly and in which
directions the body parts are moving.
▪ Vestibulocerebellum calculates in advance
where the different parts will be during the next
few msec.
▪ As a result provides anticipatory correction of
postural motor signals necessary for maintaining
equilibrium even during extremely rapid motion,
including rapidly changing directions of motion.
► Damage:
▪ Equilibrium is far more disturbed during
performance of rapid motions than during stasis,
especially so when these movements involve
changes in direction of movement
▪ Problems with eye movements during head
rotations
▪ Problems with limbs and body structures during
standing or walking
▪ problems maintaining balance
▪ Patients separate legs but they move their legs
irregularly and often fall
▪ Can move arms and legs accurately
2) Spinocerebellum
► Connnections
and Functions:
 Afferents receives 2 types of information when
a movement is performed:
(1) Information from the cerebral motor cortex
and from the midbrain red nucleus→ telling the
cerebellum the intended sequential plan of
movement for the next few fractions of a
second
(2) FB information from the peripheral
parts of the body (especially distal
proprio ceptors of the limbs) telling cerebellum
what actual movements result
► Efferents:
The intermediate zone of the cerebellum
compares the intended movements with the actual
movements→ interposed nucleus send
corrective output signals :
→ back to the cerebral motor cortex through relay
nuclei in the thalamus
→ to lower portion of the red nucleus that gives
rise to the rubrospinal tract.
The rubrospinal tract in turn joins the
corticospinal tract in innervating those
anterior horn motor neurons, that control
the distal parts of the limbs, particularly the
hands and fingers.
Result is smooth, coordinate movements
of the distal limbs for performing acute
purposeful patterned movements
MOTOR CORTEX
RED
NUCLEUS
SPINOCEREBELLAR
TRACT
2 important functions of cerebellum
1) Prevent Overshoot of Movements and to
“Damp” Movements.
► Almost all movements of the body are “pendular.”
For e.g…(Because of momentum,all pendular
movements have a tendency to overshoot)
► An
intact cerebellum (subconscious) stop the
movement precisely at the intended point, thereby
preventing the overshoot --basic characteristic of a
damping system.
When cerebellum has been destroyed:
► Overshooting → conscious centers of the
cerebrum attempts to bring the arm to its
intended position
►
By virtue of its momentum arm overshoots once
more in the opposite direction → again
appropriate corrective signals instituted
►
Arm oscillates back and forth past its intended
point for several cycles before it finally fixes on its
mark~ action tremor, or intention tremor.
2) Cerebellar Control of Ballistic
Movements:
► Most rapid movements of the body that it is
not possible to receive FB information
before the movements are over
► Entire movement is preplanned and set into
motion to go a specific distance and then to
stop.
► E.g typing movements of fingers
saccadic movements of the eyes
► Removal
of the cerebellum:
(1) slow to develop and lack the extra onset surge
(2) the force developed is weak
(3) slow to turn off movement → overshooting
The automatism of ballistic movementsis lost
3) Cerebrocerebellum
► Communicates
with the premotor area and
primary and association somatosensory
areas.
► Concerned
with 2 other aspects of motor control:
(1) the “planning” of sequential movements
(2) the “timing” of the sequential movements.
(1) “Planning” of sequential movements:
what will be happening during the next sequential
movement a fraction of a second /seconds later
“Plan” begins in the cerebral cortex→ transmitted
to the lateral zones
► Between cerebellum and cerebral cortex,
appropriate motor signals provide transition from
one sequence of movements to the next.
► Smooth progression from one movement to the
next in orderly succession.
►
(2) “Timing” of the sequential movements:
appropriate timing for each succeeding movement
Absence → loss of subconscious ability
1) Of predicting ahead of time how far the different
parts of the body will move in a given time
2) To determine when the next sequential movement
needs to begin.
RESULT → failure of smooth progression of
movements
3) “Timing” of events other than movements
of the body ~Extramotor Predictive Function:
► Cerebellar
participation is required for the rates of
progression of both auditory and visual
phenomena
► Effects
of removal in monkeys:
Occasionally charges the wall of a corridor and
literally bashes its brains because it is unable to
predict when it will reach the wall.
Damage:
►
►
Disrupts motor planning and prolongs reaction
times
Have to plan out every movement before doing it
Function Overview
 Maintenance
of Equilibrium
 Coordination of half-automatic movement
of walking and posture maintenace
 Adjustment of Muscle Tone
 Motor Learning – Motor Skills
 Cognitive Function ~ Most of our motor actions
occur as a consequence of thoughts generated in
the mind, using both sensory input to the brain
plus information already stored in memory
Balance
Motor Skill
Pablo Casals
Clinical Abnormalities
To cause serious and continuing
dysfunction of the cerebellum, the
cerebellar lesion usually must involve
one or more of the deep cerebellar
nuclei
1) Dysmetria:
► ataxia (uncoordinated movements)
►
Past pointing
2) Failure of Progression:
► Dysdiadochokinesia “loses” perception of the
body parts during rapid motor movements
►
Dysarthria jumbled vocalization, with some
syllables loud, some weak, some held for long
intervals, some held for short intervals
3) Intention Tremor: especially on approaching
the intended mark, first over shooting it and then
vibrating back and forth several times before
settling on the mark
► Cerebellar
Nystagmus
off-center type of fixation → rapid, tremulous
movements of the eyes rather than steady fixation
► 4)
Hypotonia: of the peripheral body
musculature on the side of the cerebellar
lesion
Posture
Gait – Ataxia
Tremor
a
d
b
c
Cerebellar
Ataxia
Ataxic gait and
position:
Left cerebellar tumor
a. Sways to the right in
standing position
b. Steady on the
right leg
c. Unsteady on the
left leg
d. ataxic gait