Transcript cerebellum and basal ganglia

What does the learning:
I) Spinal cord and brainstem
II) Forebrain
Spinal cord and brainstem
Spinal cord organization:
• four major divisions
– Cervical (8)
– Thoracic (12)
– Lumbar (5)
– Sacral (5)
• Each spinal segment
controls a set of muscles
Spinal cord organization
White matters
(nerve fibres)
lateral
dorsal
Sensory
inflow
Dorsal
horn
medial
Ventral
horn
Grey matters
(cell bodies)
ventral
Motor
commands
Spinal cord organization
Dorsal root
Sensory
neuron
Interneuron
Motor
neuron
Ventral root
Spinal cord organization
Some interneurons project
within their own spinal
segments, while others
relay information to other
spinal segments and/or the
brain.
Proprioceptive pathways to the brain
• Dorsal column-medial
lemniscal pathway 
major pathway by
which proprioceptive
and touch information
ascend to the
cerebral cortex
• Spinocerebellar tract
 ascend to the
cerebellum
Brainstem organization
• like the spinal cord, the brainstem contain motor
neurons who axons make up the cranial nerves
that innervate the muscles of the tongue, face
and eyes etc.
• some neurons in the
brainstem also project to
interneurons and motor
neurons in the spinal cord
Medial brain stem pathways
Basic postural
control
Tectum
Tectospinal tract
Vestibular nucleus
Vestibulospinal tract
Influence axial &
proximal
muscles
Reticulospinal tract
Medial brain stem pathways
Basic postural control
Phylogenetically oldest descending motor pathway
Individual axons project widely, coordinating
different regions of spinal cord
In ventromedial cord, contact interneurons, long
propriospinal cells, & some MNs
Influence axial & proximal muscles
Reticulospinal adjustments
• maintaining balance during limb movements
• voluntary movements of our arm can have
postural consequences, ex. lifting an object
• to counter this, leg muscles need to increase
their activity just before you pick up the object
Reticulospinal adjustments
Cordo & Nashner, 1982
- found activity of the
legs precedes the
activity of the biceps
- depends on the
context (sitting vs
standing)
Reticulospinal adjustments
Lateral brain stem pathways
Goal-directed limb
movements, e.g.
reaching,
manipulation
Main path is
rubrospinal
From red
nucleus
Crosses
midline in brain
stem
Influence distal
muscles
Red nucleus
• receives input from the deep cerebellar nuclei, as
well as the motor cortex
• sends majority of its neurons down the spinal cord
(rubrospinal tract) and to the cerebellum through
the inferior olive nucleus (source for climbing
fibres)
Cerebellum
• contains ~70% of all
the brain's neurons;
contributes to timing,
coordination, and the
learning of motor
skills.
• only approx. 10% of
the volume
• complete removal produces no muscle weakness
or loss of perception
Cerebellum: divisions
Anterior
Lobe
Anterior
Lobe
vermis
Posterior
Lobe
Posterior
Lobe
nodulus
flocculus
Front View
Side View
• cerebellar cortex (gray matter), white matter
• 2 hemispheres, vermis – ridge in centre
• 3 lobes – anterior, posterior, flocculonodular
Lateral zone:
participates more
directly in reaching
and pointing
 I/O cerebral
cortex (via pons)
nodulus
flocculus
Lateral zone
Vermis & intermediate zone:
mainly controls posture
 I/O spinal cord
Vermis
Intermediate zone
Cerebellum: divisions
Intrinsic architecture
Main inputs:
- Mossy fibres
(via parallel
fibres from
Granule cells)
- Climbing fibres
Granule
cell
fibre
Mossy
INPUT
Climbing
fibres
Purkinje
cell
Mossy
fibres
Main output:
- Purkinje cells
Parallel fibre
Inferior
olive
Climbing fibre
Deep nuclei
OUTPUT
Cerebellum: inputs
Climbing fibres (CF) arise from neurons in the
inferior olive and terminate of Purkinje cells and
the cells in the deep cerebellar nuclei
Inputs from CF cause complex spikes – supposed
to signal motor errors (teaching signal) or loss of
coordination
Cerebellum: inputs
Mossy fibres also terminate on the deep cerebellar nuclei as well as granule cells (whose axons
make the parallel fibres)
Parallel fibres supply a huge & continuous supply
of sensory information to the Purkinje cells which
cause simple spikes.
Cerebellum: outputs
Purkinje cells inhibits neurons in the deep
cerebellar nuclei.
These deep nuclei send
excitatory outputs to a
variety of structures,
e.g. thalamus, reticulospinal system, ION,
spinal cord, superior
colliculus.
Dentate nuclei
Interpositus nuclei
Fastigial
nuclei
Cerebellum
What does the learning:
I) Spinal cord and brainstem
II) Forebrain
Forebrain
Forebrain comprises the diencephalon & telencephalon
Basal ganglia plays an enigmatic, role in motor
control and learning, including reaching & pointing
Thalamus acts as a key node in recurrent, loops
which integrate the cerebral cortex & subcortical
motor-control systems.
The motor cortex and the posterior parietal cortex
make important contributions to reaching and
pointing.
Anatomy review: Basal ganglia
Basal ganglia consists of a group of subcortical
nuclei: caudate, putamen, globus pallidus.
Anatomy review: Basal ganglia
Clinically includes
subthalamic nucleus
& substantia nigra
These
structures
are highly
interconnected
anatomically.
Anatomy review: Basal ganglia
Input:
striatum
{
Output: globus pallidus & substantia nigra
Basal ganglia
Major inputs to the striatum come from the
cerebral cortex & the thalamus
Globus pallidus sends GABAergic, inhibitory
projections to the brainstem and thalamus.
Subthalamic nucleus plays an important role in
control of the basal ganglia’s output.
Circuitry of the basal ganglia
Cerebral cortex
Motor areas
Caudate/Putamen
Globus
pallidus
(external)
Subthalamic
nucleus
Spinal
cord
Excitatory
glutamate
Thalamus
dopamine
Substantia
nigra pars
compacta
Inhibitory
GABA
Globus
pallidus
(internal)
Substantia
nigra pars
reticulata
Circuitry of basal ganglia
The cerebral cortex (and thalamus) projects to the
striatum: excitatory.
Striatum also receives dopaminergic projections
from the SN pars compacta (SNc).
The striatum inhibits the globus pallidus (GP) and
substantia nigra pars reticulata (SN pr).
STN sends excitatory projections to the GPi, GPe &
SN pr.
GPi or SN pr inhibits (GABAergic) the thalamus.
Thalamus projects to the cortex: excitatory.
Circuitry of basal ganglia
Direct path: striatum GPi (internal) thalamus
cortex
Indirect path: striatum GPe (external) STN
GPi thalamus cortex
Cerebral cortex
Motor areas
Caudate/Putamen
Globus
pallidus
(external)
Subthalamic
nucleus
Spinal
cord
Excitatory
glutamate
Thalamus
dopamine
Substantia
nigra pars
compacta
Inhibitory
GABA
Globus
pallidus
(internal)
Substantia
nigra pars
reticulata
Circuitry of basal ganglia
Direct path:
-Leads to less inhibition of the thalamus, i.e.
striatum inhibits GPi which in turn inhibits its normal
(inhibitory) action on the thalamus, thus leading to
greater excitation from the thalamus to the cortex.
-Allows for sustain actions or initiation of action
Indirect path:
-Excites the GPi thereby increasing its inhibition of
the thalamus
-Suppresses unwanted movements.
Parkinson disease: Basal ganglia circuitry
Abnormal functioning
Cerebral cortex
Motor areas
Caudate/Putamen
Globus
pallidus
(external)
Subthalamic
nucleus
Excitatory
glutamate
Inhibitory
GABA
Thalamus
dopamine
Substantia
nigra pars
compacta
Globus
pallidus
(internal)
Substantia
nigra pars
reticulata
Circuitry of the basal ganglia
Cerebral cortex
Motor areas
Caudate/Putamen
Globus
pallidus
(external)
Subthalamic
nucleus
Spinal
cord
Excitatory
glutamate
Thalamus
dopamine
Substantia
nigra pars
compacta
Inhibitory
GABA
Globus
pallidus
(internal)
Substantia
nigra pars
reticulata
Context switching & Basal ganglia
- activity of the legs precede the activity of the
biceps  depends on the context (sitting vs
standing)
- but patients who had
Parkinson’s disease –
couldn’t use their body’s
state for predicting the
consequences to
minimize them
Thalamus
• Dorsal thalamus sends its largest outputs to the
cerebral cortex and basal ganglia
• Ventral thalamus has a diverse pattern of
connections, including direct projections to the
spinal cord
• Thalamus: relay station for all sensory
information; maintains two loops (recurrent
modules) between 1) the cerebellum and the
cerebral cortex & 2) the basal ganglia and the
cerebral cortex, on the other hand.
Thalamus loops
Cerebellar
cortex
STN
gran
GPe
Deep Cb
Nuclei
Thalamus
Cortex
GPi
Pons
Thalamus
Striatum
Cortex
Thalamus
SMA
VApc
GPi
VLo
M1
VLc
X
VPlo
Cb
Cortical organization
• Cerebrum
1) Allocortex – includes hippocampus &
piriform
2) Neocortex – cerebral cortex
Cortical organization
• Neocortex has 6 layers of neurons (sheets of
cells parallel to the surface of the cortex)
Cortical organization
Cortical organization
Lateral corticospinal tracts
Largest descending tract, ~750,000
fibres from each hemisphere
Originates from primary motor,
premotor, & somatosensory cortex.
Descends through brain in internal
capsule; strokes here causes
contralateral weakness
Crosses at pyramidal decussation
In lateral ventral horn, contacts Ins
and MNs of distal muscles.
Ventral corticospinal tracts
~ 250,000 fibres from each hemisphere
Originates from premotor and primary
motor cortex
Remains uncrossed until spinal cord
Bilaterally activates MNs of axial
muscles
Primary & Non-primary motor cortex
M1
SMA
Premotor
area (PMA)
SMA
PMA
M1
PPC