Motor: basal ganglia Flashcards
What is the difference between the basal ganglia and the cerebellum?
The basal ganglia inhibits the motor cortex’s connections to voluntary muscles via the thalamus.
The cerebellum, stimulates the action of the motor cortex.
What structures does the basal ganglia consist of?
Caudate nucleus Putamen Substantia nigra pars compacta and pars reticulata Subthalamic nucleus Globus pallidus interna and externa
What are the functions of the basal ganglia?
Planning and programming movement
Elaborating associated movement
Coordinating and modifying movements
Performing movements in order
Describe the connections to and from the basal ganglia i.e. direct and indirect pathway
Info from primary motor/premotor/supplementary motor cortex is sent to neurones in the striatum (caudate and putamen).
Direct pathway: putamen -> globus pallidus interna + substantia nigra.
Indirect pathway: putamen -> globus pallidus externa -> subthalamic nucleus -> globus pallidus interna
Both then project to the thalamus and back to SMA and PMA for programming of movement
Intrinsic connections from SNc to caudate and putamen nuclei
What is the difference in effect of the direct and indirect pathway of the basal ganglia?
Direct pathway EXCITES motor cortex. The substantial nigra feeds back to the striatum and excites dopaminergic neurones. The thalamus excites the cortex.
Indirect pathway INHIBITS motor cortex
Which are the inhibitory and excitatory neurotransmitters of the basal ganglia?
Inhibitory: GABAnergic
Excitatory: Dopaminergic, glutamate
Which other cortices apart from motor is the basal ganglia involved with i.e. a sub-cortical loop?
Prefrontal association cortex
Limbic cortex
What is the histological presentation of PD?
Loss of dopaminergic nigrostriatal pathway -> Inclusion (Lewy) bodies and aggregates of proteins in neurones
Describe the nigrostriatal pathway in PD?
Degeneration of dopaminergic neurones in SNc.
Increased activity of GPi neurones from increased activity of STN.
Less feedback to striatum causes disruption of excitation and inhibition.
More inhibitory signals to VA and VL thalamic nuclei form GPi/SNr causing reduced output from the motor cortex.
List the signs of PD
Bradykinesia Hypomimic face Akinesia Stooped posture 'Pill rolling tremor': at rest Parkinsonian gait Rigidity
What is the cause of Huntington’s disease?
Autosomal dominant genetic condition
Mutation on chromosome 4 of huntingtin gene
What is the pathology of Huntington’s?
Loss of GABAnergic neurones in the striatum
Decreased inhibition of STN
Less inhibition of GPi/SNr complex (inhibitory to motor cortex)
Excessive excitatory input
Hyperkinetic disease
What is choreic movement?
Rapid jerky involuntary movements starting in the hands and face; Speech impairment Difficulty swallowing Impaired gait Dementia and cognitive decline
What are the different divisions of the cerebellum horizontally and sagittally?
Horizontal divisions; anterior, posterior, flocculonodular
Sagittal; vermis, intermediate hemisphere, lateral hemisphere
Which side of the body does the cerebellum control?
Connects to the ipsilateral side of the body and therefore contralateral cerebral hemisphere
What is the floccunodoluar lobe often referred to as and what does it do and its stimuli?
Vestibulocerebellum
Regulation of gait, posture (spatial orientation) and balance
Coordination of head movements to eye movements.
Receives input from vestibular nuclei and semicircular canals.
Visual input from superior colliculi and visual cortex.
What is the spinocerebellum?
Consists of the vermis and intermediate hemisphere
Axial portions of the body, trigeminal , auditory and visual input project to the vemis.
Distal body and limb movements project to the intermediate hemisphere (dorsal column proprioception and spinocerebllar tract).
Coordination of speech
Adjusts muscle tone
Limb movements
What is the cerebrocerebellum?
Consists of the lateral hemisphere
Involved in skilled movements, attention, processing of language
Emotional control
What are the three layers of the cerebellar cortex?
Molecular layer (outer layer containing axons of granule cells and dendrites of purkinje cells)
Purkinje cells
Granule cells
What are the fibre types found in the cerebellar cortex?
Mossy fibres; enter at granular cell layer, synapse with purkinje cells
Climbing fibres; enter at purkinje cell layer (from inferior olivary nucleus). Compare inputs and project to the deep cerebellar nuclei -> thalamus, postural and vestibular cortex
What are the three deep nuclei in the cerebellar cortex and where do they project to?
Fastigial nucleus; vestibular and reticular nuclei for balance
Interposed and dentate nucleus; thalamus and red nucleus to control voluntary movements
What are the three sources of input into the cerebellum?
Mossy fibres from spinocerebellar pathways
Mossy fibres from pons bringing info from cerebral cortex
Climbing fibres from inferior olive
What is ataxia?
Poor coordination, brain is unable to coordinate posture, strength and direction of limb movements
What is Romberg’s sign?
Romberg positive: imbalance when eyes are closed
[Cerebellar lesions will result in negative romberg sign]
