Download The Cerebellum

Some Terminologies
• White matter : myelinated fibre tracts
• Gray matter : areas of neuronal cell bodies
• Tracts : collections of axons subserving similar
function or location in CNS
• Nerves : peripheral axons
• Nucleus : collection of neurons subserving similar
function in CNS – e.g., caudate nucleus, red nuclei
• Brainstem: Midbrain (Mesencephalon) + Pons +
Medulla Oblongata
• Folia : Leaves
• Vermis: Worm
Brain components
Table 5.3 (1)
Page 144
Cerebral cortex
Cerebral cortex
Basal nuclei
(lateral to thalamus)
Basal nuclei
Thalamus
(medial)
Thalamus
Diencephalon
Hypothalamus
Hypothalamus
Cerebellum
Cerebellum
Midbrain
(Mesencephalon)
Brain stem
Brain stem
(midbrain, pons,
and medulla)
Pons
Medulla
oblongata
Spinal cord
The Cerebellum
•
•
•
•
Located dorsal to the pons and medulla
Makes up 11% of the brain’s mass
Cerebellar activity occurs subconsciously
Provides precise timing and appropriate
patterns of skeletal muscle contraction
Programming ballistic movements
• Acts as comparator for movements
Comparing intended and actual movement
• Correction of ongoing movements
Internal & external feedback
Deviations from intended movement
• Motor learning
Shift from conscious ---> unconscious
Anatomy of the Cerebellum
2 symmetrical hemispheres connected medially by the Vermis
Folia: Transversely oriented gyri
3 lobes in each hemisphere: Anterior, Posterior, Flocculonodular (FN)
Neural arrangement: Gray matter (Cortex), White matter (Internal),
Scattered cerebellar nuclei: dentate, globose, emboliform, fastigial
Arbor vitae (tree of life): distinctive treelike pattern of the white matter
Folium
Cerebellum
Primary fissure
Anterior Lobe
Regulation of
muscle tone,
coordination of
skilled voluntary
movement
Posterior
Lobe
Planning and
initiation of
voluntary activity
Flocculo-Nodular
Lobe (FN lobe)
Maintenance of
balance, control
of eye movements
Vestibulocerebellum
Spinocerebellum
Folia
Cerebrocerebelum
Cerebellum
Intermediate part
Lateral part
Cerebellum: the Structure
Inputs to the cerebellar cortex: Climbing fibers & Mossy fibers
Climbing fibers: originate in the inferior olive of the medulla
Mossy fibers: originate in all the cerebellar afferent tracts apart from inferior olive
Purkinje cells: The final output of the cerebellar cortex
3 Layered
Cerebellar
Cortex
Cerebellum: 3 layered cortex
Climbing fibers: excite the Purkinje cells
Mossy fibers: excite the granule cells
Granule cells: make excitatory contact with the Purkinje cells
Purkinje cells: Tonic inhibition on the activity of the neurons of the cerebellar nuclei
=> All excitatory inputs will be converted to the inhibition
=> Removing the excitatory influence of the cerebellar inputs (erasing)
Cerebellar Peduncles
Three paired fiber tracts connect the cerebellum to the brainstem:
♦ Superior peduncles connect the cerebellum to the midbrain;
♦ Middle peduncles connect the cerebellum to the pons and to the axis of
the brainstem;
♦ Inferior peduncles connect the cerebellum to the medulla.
Cerebellar
Peduncles
Cerebellar Peduncles
Superior peduncles (to the midbrain):
Fibers originate from neurons in the deep cerebellar nuclei &
communicates with the motor cortex via the midbrain and
the diencephalon (thalamus)
Middle peduncles (to the pons):
Cerebellum receives information advising it of voluntary
motor activities initiated by motor cortex
Inferior peduncles (to the medulla):
Afferents conveying sensory information from muscle
proprioceptors throughout the body & from the vestibular
nuclei of the brainstem (Spinal cord)
Cerebellar Input
Inputs to cerebellum from spinocerebellar tracts have a
somatotopic organization.
2 maps of body
Primary fissure
Signals from the motor cortex, which is also arranged somatotopically,
project to corresponding points in the sensory maps of the cerebellum.
Cerebellar Inputs
Vermis


Receives input from spinal cord regarding somatosensory and
kinesthetic information (intrinsic knowledge of the position of the limbs)
Damage leads to difficulty with postural adjustments (cerebellar ataxia)
Intermediate Zone


Receives input from the red nucleus and somatosensory information
from the spinal cord
Damage results in rigidity & difficulty in moving limbs
Lateral Zone



Receives input from the motor and association cortices through the pons
Projects to the dentate nucleus, which projects back to primary and
premotor cortex
Damage leads to 4 types of deficits:
- Ballistic movements (cerebellar ataxia)
- Coordination of multi-joint movement (lack of coordination: asynergia)
- Muscle learning (loss of muscle tone: hypotonia)
- Movement timing
Outputs of the Cerebellum
Cerebellar nuclei: dentate, globose, emboliform, fastigial
Dentate nuclei: project contralaterally through
the superior cerebellar peduncle to
neurons in the contralateral thalamus &
from thalamus to motor cortex
Func.: influence planning and initiation of
voluntary movement
Emboliform & Globose nuclei: project mainly
to the contralateral red nuclei & a small
group is projected to the motor cortex
Red Nuclei  Rubrospinal Tract
control of proximal limb muscles
Fastigial nuclei: project to the vestibular nuclei
& to the pontine and medullary reticular
formation
Vestibulospinal & Reticulospinal tracts
Inputs and outputs of the Cerebellum
Clinical Findings and Localization of Cerebellar Lesions
Ataxia refers to disordered contractions of agonist and antagonist
muscles and lack of coordination between movements at
different joints typically seen in patients with cerebellar lesions.
Normal movements require coordination of agonist and antagonist
muscles at different joints in order for movement to have smooth
trajectory.
In ataxia movements have irregular, wavering
course consisting of continuous
overshooting, overcorrecting and
then overshooting
again around the intended trajectory.
Dysmetria = abnormal undershoot or overshoot
during movements toward a target
(finger-nose-finger test).
Cerebellum and Motor Learning
• Deficits in learning complex motor tasks
after cerebellar lesions
• fMRI studies : cerebellum active during
learning of novel movements
• Postulated that cerebellar nuclei store
certain motor memories
• May be involved in cognitive functions
Cerebellum: Control of Voluntary Movement
Cerebellum has no direct connection to the spinal motoneurons (indirect effect).
Information sources: lesions & damages &
experimental stimulation of cerebellar nuclei
Primary function:
1. To supplement & correlate the activities of other motor areas
2. Control of posture
3. Correction of rapid movements initiated by cerebral cortex
4. Motor learning
Frequency of nerve impulses in the climbing fibers almost doubles when a monkey learns a new task
Movement Control:
a. Inputs from motor cortex inform the cerebellum of an intended
movement before it is initiated
b. Sensory information is then received via the
spinocerebellar tract
c. An error signal is generated and is fed back to the cortex
Cerebellar Processing
• Cerebellum receives impulses of the intent
to initiate voluntary muscle contraction
• Proprioceptors and visual signals “inform”
the cerebellum of the body’s condition
• Cerebellar cortex calculates the best way
to perform a movement
• A “blueprint” of coordinated movement is
sent to the cerebral motor cortex
Cerebellar Cognitive Function
• Plays a role in language and problem solving
• Recognizes and predicts sequences of events
Table 5.3 (1)
Page 144
Diencephalon
Thalamus
(medial)
Hypothalamus
• Central core of the forebrain
• Consists of three paired structures –
thalamus, hypothalamus, and epithalamus
• Encloses the third ventricle
Diencephalon
Table 5.3 (1)
Page 144
Thalamus
Thalamus
(medial)
Hypothalamus
Paired, egg-shaped masses that form the
superolateral walls of the third ventricle
Contains four groups of nuclei :
anterior, ventral, dorsal, and posterior
Nuclei project and receive fibers from the
cerebral cortex
Thalamus
Thalamic Function
• Afferent impulses from all senses
converge and synapse in the thalamus
• Impulses of similar function are sorted out,
edited, and relayed as a group
• All inputs ascending to the cerebral cortex
pass through the thalamus
• Plays a key role in mediating sensation,
motor activities, cortical arousal, learning,
and memory
Hypothalamic Nuclei
Table 5.3 (1)
Page 144
Thalamus
(medial)
Hypothalamus
Hypothalamic Function
• Regulates blood pressure, rate and force of
heartbeat, digestive tract motility, rate and depth
of breathing, and many other visceral activities
• Is involved with perception of pleasure, fear, and
rage
• Controls mechanisms needed to maintain
normal body temperature
• Regulates feelings of hunger and satiety
• Regulates sleep and the sleep cycle
• Endocrine Functions of the Hypothalamus
The Cerebral Cortex
Central sulcus
Frontal
lobe
Parietal
lobe
Parietooccipital
notch
Occipital
lobe
Lateral
fissure
Temporal
lobe
Preoccipital
notch
The cerebral cortex
• Cerebral Cortex : outer layer of gray matter
• It covers an inner core of white matter
• The gross structure has gyri and sulci
Different Lobes:
 Frontal : voluntary motor activity, speaking ability, and
elaboration of thought; stimulation of different areas of its
primary motor cortex moves different body regions, again
primarily on the opposite side of the body.
 Parietal : somatosensory processing; each region of its cortex
receives somaesthetic and proprioceptive input from a specific
body area, primarily from the opposite body side.
 Temporal : receives sound sensation
 Occipital : initial processing of visual input
Supplementary motor area
(programming of complex movement)
Primary motor cortex
(Voluntary movement)
Premotor cortex
Central
sulcus
(coordination of complex
movements)
Prefrontal association
cortex
Somatosensory cortex
(Somesthetic sensation and
proprioception)
Posterior parietal cortex
(integration of somatosensory and
visual input)
Parietal lobe
(planning for voluntary activity;
decision making;
personality traits)
Wernicke’s area
(speech
understanding)
Frontal lobe
Parietal-temporal-occipital
association cortex
Broca’s area
(speech formation)
(integraton of all sensory inputimp in language)
Primary auditory cortex
Occipital lobe
Limbic association cortex
(motivation, emotion, memory)
Temporal lobe
Primary visual cortex
Parietal Lobe - Somatosensory cortex
•
•
•
Somesthetic sensation - sensations from the surface of the body - touch, pain,
pressure, heat and cold
This info is projected to the somatosensory cortex - site for initial cortical
processing and perception of somesthetic and proprioceptive input
Body regions are topographically mapped - sensory homunculus
•
Sensory cortex - receives information from the opposite side of the body
(e.g., damage on right side results in sensory loss on left side)
•
Simple awareness of touch, pressure, temp or pain is first detected by the
thalamus, but cortex is required for perception - intensity and spatial
discrimination
This info is then projected (via fibre tracts) to association cortices for analysis
and integration of sensory information - eg., perception of texture, firmness,
temp, shape, position, location of an object you are holding)
•
Regions of the
cortex involved
in motor control
Frontal lobe - Motor cortex
• Primary motor cortex - voluntary control for muscle movement
• Motor cortex on each side controls muscles on the opposite side of
the body
• Tracts originating in the cortex cross (at level of pyramids) before
continuing down spinal cord to terminate on a-motor neurons that
directly innervate skeletal muscle
• Body regions are represented topographically - motor homunculus
• Extent of representation in the motor cortex is proportional to the
precision and complexity of motor skills required
Other cerebral brain regions
important for motor control
 Primary motor cortex does not initiate voluntary movement
 Premotor cortex (M1)
anterior to the primary motor cortex
acts in response to external cues
must be informed of body’s position in relation to target
 Supplementary motor area (SMA)
responds to internal cues
plays a preparatory role in programming complex
sequences of movement
 Posterior parietal cortex
It is posterior to the primary somatosensory cortex
informs premotor cortex of position
Temporal lobe
• Contains auditory centres that receive sensory fibres
from the cochlea of each ear
• Also involved in the interpretation and association of
auditory and visual information
• Temporal lobe contains the hippocampus and the
amygdala
• Involves in memory
Cortical Association areas
• Prefrontal association cortex
Functions: planning for voluntary activity, decision-making, creativity,
and developing personality traits.
– Site of operation of working memory - temporary storage and actively
manipulation of information used in reasoning and planning
• parietal-temporal-occipital association cortex
Integrates somatic, auditory, and visual sensations from three lobes
• limbic association cortex
Being involved with motivation, emotion, and memory
The cerebral hemispheres
lateralization/dominance
• Each cerebral hemisphere receives information from both sides
of the body
• The left cerebral hemisphere excels in performing logical,
analytical, sequential, and verbal tasks
Better at describing facial appearances
• The right cerebral hemisphere excels in spatial perception and
artistic and musical talents
Better at recognizing faces
The limbic system
• Refers to several forebrain structures that function together
– Cingulate gyrus
– Hippocampus
– Amygdala
– Septal nuclei
• Closed circuit of information flow between the limbic system and the
thalamus and hypothalamus
• Limbic system and hypothalamus - cooperate in the neural basis of
emotional states
Limbic System
Figure 12.18
Limbic system
 Plays a key role in emotion and works with the higher
cerebral cortex to control behavioral patterns.
 Aggression --> lesions of amygdala produce docility, while
stimulation results in rage and aggression
 Fear --> stimulation of amygdala and hypothalamus can
produce fear, while ablation results in an absence of fear
 Goal-directed behaviour - reward and punishment
system- stimulation of certain areas function as a reward,
while stimulation of other areas results in a punishment
shock