L09: Cerebellum & Basal Ganglia Flashcards
What makes up the basal ganglia?
Striatum (putamen, caudate nucleus & nucleus accumbens sometimes)
Globus pallidus (interna + externa)
Subthalamic nucleus
Substantia nigra (reticulata + pars compacta)
What is the function of th basal ganglia?
Regulates cortical activity by intergrating sensory + motor info for smooth, coordinated movement.
INITIATES MOVEMENT
Where does basal ganglia recieve input from?
Sensroy & motor areas, pre frontal cortex + parts of brain involving emotion (hippocampus, amygdala etc.)
Where does basal gangla output go to?
Thalamus - then relayed back to cortex (esp area 6)
What is ‘normal’ basal ganglia outflow?
Inhibitory to the thalamus, via GABA - done by Snr & GPi
What are the different pathways within the basal ganglia ?
Direct: facilitates intended action
Indirect: supresses competing actions
Balance between both influences thalamus
What is the role of the substantia nigra?
Contains dopaminergic neurones involved in rewarding behaviour. Pars compacta modulates direct & indirect pathways
Describe the direct pathway within BG
- cortex stimulates striatum
- striatum inhibits SNr + GPi via GABA
- causes DISINHIBITION of thalamus (hence activation)
- thalamic feedback to cortex promotes movement
How does dopamine influence the direct pathway?
Dopamine excites GABAnergic neurones (via D1 receptors) in striatum –> increased inhibition of SNr + GPi hence greater thalamic activity
Describe the indirect pathway within BG
- cortex stimulates striatum
- Striatum inhibits GPe via GABA (GPe usually inhibits STN)
- inhibiton of GPe hence –> activation of STN
- STN allowed to stimulate SNr + GPe
- SNr + GPe can therefore INHIBIT thalamus to supress movement
Action of dopamine on the indirect pathway?
Acts of D2 receptors within striatum to inhibit GABAnergic neurones
Hence reduces inhibtion of GPe
Reversal of indirect pathway hence facilitates movements
What causes motor dysfunction?
Imbalance between direct & indirect pathways
Examples of hypokinetic + hyperkinetic disorders?
Hypo: Parkinsons
Hyoer: Hemibalism, huntingtons, tardive dyskinesia
What are the functional components of the cerebellum?
Spino, vestibulo + cerebro-cerebellum
Describe the actions of the spino-cerebellum
Spino-cerebellum: sensory input from spinal cord, output to RF + red nucleus –> motor cortex to control posture (axial muscles)
Describe the actions of the vestibulo-cerebellum
vestibular nuclei project to flocculonodular lobe which relays back to vestibular nuclei to control balance + eye movement, input from vestibular ear
Describe the actions of the cerebro-cerebellum
inputs from proprioceptors used to judge quality of movement compared to intented movement, output back to M1 via dentate nucleus + venterolateral thalamus for error correction
What is the functions of the cerebellum?
Controls muscle tone, sensorimotor coordination, motor learning + involved with posture + balance
Controls unconscious motor movements
Comparator between intended + actual movement
What is the result of damage to the spino-cerebellum?
hypotonia, ataxia, intention tremor (can’t stop + change direction)
What is the result of damage to the vestibulo-cerebellum?
slow saccades (movement of eyes between 2 points), nystagmus (rapid involuntary movements of eyes), ataxia
What are the functional layers of cerebellum?
molecular layer, purkinje cell, granule cell layer, white matter
Which way to impulses travek within cerebellum?
From deep cerebellar nuclei up to purkinje cells
Function of the cerebellar peduncles?
Superior: connects cerebellum to midbrain = provides feedback to cerebrum
Middle: conveys impulses FROM cerebrum –> cerebellum
Inferior: connects cerebellum to medulla + spinal cord (inputs from vestibulo & proprioception, output motor fibres)
