Week 5 Flashcards
*Structure of cerebellum?
3 lobes (Anterior, posterior and flocculonodular)
3 functional subdivisions - vestibulo, spino, cerebrocerebellum.
3 pairs of peduncles - superior, middle, inferior
3 pairs of deep nuclei - deep, fastigial, interposed
3 cortical layers- molecular, purkinje, granule
*Functions of the cerebellum?
Coordinates movement, maintains posture and balance, and enables motor learning.
Integrates sensory and motor information for smooth execution of movements.
Location of cerebellum?
Posterior of the brainstem
Consequences of cerebellar damage?
Causes severe movement disruption
Can lead to ataxia which is the abnormal execution of multi-jointed voluntary movements, characterized by lack of coordination and is caused by strokes, MS or tumours etc.
*Gross anatomy of the cerebellum?
Cerebellar peduncles - Superior, Middle, Inferior
Cerebellar cortex -Cerebrocerebellum, Spinocerebellum, Vestibulocerebellum
Deep cerebellar nuclei -
Dentate nucleus, Interposed nucleus, Fastigial nucleus
*Cerebellar peduncles?
The cerebellum is connected to the dorsal aspect of the brainstem by 3 symmetrical
pairs of peduncles:
Superior peduncle
* No inputs
* Outputs to motor cortex (via thalamus) and
red nucleus
Middle peduncle
* Inputs from motor cortex (via pons)
* No outputs
Inferior peduncle
* Inputs from inferior olivary nucleus, spinal
cord and vestibular nuclei
* Outputs to reticular formation (brainstem),
spinal cord and vestibular nuclei
Cerebellar cortex subdivisions?
Cerebrocerebellum
Spinocerebellum
Vestibulocerebellum
Spinocerebellum?
Comprises the vermis and
intermediate cortex
Regulates body and limb movements
Somatic sensory inputs exhibit somatotopy:
Vermis: Input(s) spinal cord carrying sensory info from trunk and head
Output(s): Fastigial nucleus to medial descending
reticulospinal and vestibulospinal tracts, Motor execution
Intermediate cortex:
Input(s): Spinal cord, carrying sensory information from the limbs
Output(s): Interposed nucleus to lateral descending
corticospinal and rubrospinal tracts, Motor planning
Vestibulocerebellum?
Also known as the flocculonodular lobe -
Oldest evolutionary part of cerebellum
Only region of the cerebellar cortex to
bypass the deep cerebellar nuclei
Regulates balance and eye movements
Input(s): Vestibular nucleus, from semicircular canals
and otolith organs
Output(s): Vestibular nucleus, to axial and proximal muscles, limb extensors, and head/eye muscles
Cerebrocerebellum?
Largest, involved in motor planning.
Input(s): Pons, from motor cortex (via thalamus)
Inferior olive, from motor cortex (via red
nucleus) and spinal cord
Output(s): Dentate nucleus, to motor cortex (via
thalamus)
Deep cerebellar nuclei components?
Dentate
Interposed
Fastigial
*Dentate Deep cerebellar nuclei ?
Most lateral nucleus
Located in cerebrocerebellum
Output is to motor cortex via superior peduncle and thalamus
*Interposed Deep cerebellar nuclei ?
Located in intermediate cortex
(spinocerebellum)
Output is to red nucleus via superior peduncle
*Fastigial Deep cerebellar nuclei ?
Most medial nucleus
Located in vermis (spinocerebellum)
Output is to reticular formation and vestibular
nucleus via inferior peduncle
*Cerebellar circuitry elements?
Mossy fibres (granule layer) - Mossy fibres are the primary neurons that carry information into the cerebellum. Activate granule cells and cerebellar nuclei
Granule cells (granule layer) - attach to parallel fibres which synapse with dendrites of Purkinje cells
Climbing fibres (granule layer) - excites Purkinje cells directly (but can also inhibit via interneurons).
Originates in the inferior olive.
Believed to sense error signals to elicit learning
Purkinje cells (Purkinje cell layer) - cell body with vast dendritic tree with inhibitory function, inhibits cerebellar nuclei, modulating motor output
Parallel fibres (molecular layer)
*Overall Function of the Basal Ganglia?
The basal ganglia modulate strategic aspects of movement, including initiation, termination, and scaling of motor activity.
They influence premotor cortical activity indirectly through the cortico-basal ganglia-thalamic loop.
They have no direct connections to the spinal cord but are essential for integrating cortical input and motor planning.
*Cerebellum Connections?
Connections only to sensorimotor
areas of cerebral cortex (via
thalamus)
Receives input from brainstem and
spinal cord
Involved almost exclusively with movement
*Basal Ganglia Connections?
Widespread reciprocal connections to cerebral cortex (via thalamus)
Not just involved in movement
Behaviour and emotion
Gross anatomy of Basal Ganglia?
The basal ganglia is a
collection of 5 nuclei
- Caudate
- Putamen
- Globus pallidus
* Internal (GPi)
* External (GPe) - Subthalamic nucleus (STN)
- Substantia nigra
* Pars compacta (SNc)
* Pars reticulata (SNr)
Caudate and putamen are part of the striatum
Basal Ganglia Gross anatomy inputs/outputs?
Input(s):
Striatum (caudate and putamen)
Receives direct and indirect (via thalamus) connections from cerebral cortex
Output(s):
GPi and SNr
Provide tonic inhibitory output to thalamus
*Basal Ganglia internal connections?
Striatum projects to:
a) Globus pallidus (striato-
pallidal pathway)
b) Substantia nigra (striato-
nigral pathway)
STN forms indirect pathway
between GPe and SNr
GPi and SNr are the output
centre of the basal ganglia
and send inhibitory signals to the thalamus
Basal Ganglia feedback loop?
Basal ganglia receives excitatory input from cerebral cortex which then sends inhibitory signals to the thalamus, in turn SUPPRESSING motor cortical activity
Excessive basal ganglia input results in slow movement and reduced input results in
enhanced movement
What is the transcortical loop?
A 3 stage loop involving the cerebral cortex, basal ganglia and thalamus.
- Striatum (putamen) receives vast
array of inputs from the cerebral
cortex (motor and sensory) - Output from GPi and SNr project to
thalamus (inhibitory signal) - Inhibited thalamus projects to motor
cortex, thus suppressing movement
*Direct motor pathway?
Involves two inhibitory
synapses resulting in disinhibition, thereby
facilitating movement
*Indirect motor pathway?
Involves excitation of the
inhibition, thereby supressing movement
*Key Features of (In)Direct motor pathways?
The basal ganglia exert a tonic inhibitory output to the thalamus.
Neurotransmitters involved:
Glutamate (excitatory): Open arrows.
GABA (inhibitory): Filled arrows.
Dopamine (mixed effects): Mixed arrows
STN is a relay from the striatum (input) to the
GPi/SNr (output), forming an indirect motor
pathway
Dopamine’s Role in motor pathways?
Excites the direct pathway via D1 receptors and inhibits the indirect pathway via D2 receptors, collectively facilitating movement.
*Differences Between Basal Ganglia Diseases?
Parkinson’s Disease: Hypokinetic
Caused by the loss of dopaminergic neurons in the substantia nigra pars compacta (SNc).
Overactive indirect pathway suppresses movement.
Symptoms: Bradykinesia, rigidity, tremor, postural instability.
Huntington’s Disease: Hyperkinetic
Results from striatal atrophy, reducing activity in the indirect pathway.
Underactive indirect pathway facilitates excessive movement.
Symptoms: Uncontrolled, jerky movements (chorea).
*Cerebellum functional subdivisions?
Vestibulocerebellum: Maintains balance and eye movements.
Inputs: Vestibular system.
Outputs: Vestibular nuclei.
Spinocerebellum: Regulates posture and coordination of limb movements.
Inputs: Spinal cord (proprioceptive signals).
Outputs: Motor cortex and brainstem.
Cerebrocerebellum: Plans and fine-tunes voluntary movements.
Inputs: Cerebral cortex.
Outputs: Premotor and motor cortices.
Each subdivision integrates inputs and outputs to ensure smooth and accurate motor control.
