Motor Disorders Flashcards
Through what structures does the cerebellum communicate with the brain
- Communicates with the brainstem and cortex
- Communicates with the brainstem via the cerebellar peduncles
- Superior cerebellar peduncles attaches cerebellum to midbrain
- Middle cerebellar peduncle attaches cerebellum to pons
- Inferior cerebellar peduncle attaches cerebellum to medulla
- Communicates with the cortex via the thalamus
Describe the structure of the cerebellum and the role of each
- Consists of the vermis and two lateral hemispheres
- Vermis regulates trunk musculature
- Lateral cerebellar hemispheres regulate distal structures (limbs)
- Tracts are ipsilateral in the cerebellum
Describe how lesions of the vermis and cerebellar hemispheres cause different symptoms
- Lesions in the midline (vermis) can cause truncal ataxia and abnormal gait
- Extensions of midline lesions can also cause compression of the fourth ventricle and lead to hydrocephalus
- Cerebellar hemispheres lesions cause ipsilateral symptoms in the limbs
State the significance of the fourth ventricle to the cerebellum
- Fourth ventricle located between cerebellum and pons
- Extensions of midline lesions can also cause compression of the fourth ventricle and lead to hydrocephalus
Describe the symptoms of cerebellar disease
- DANISH
- Dysdiadochokinesis - repetitive movement problem
- Ataxia - lack of voluntary coordination of muscle movements, eg. Abnormal gait, balance problem
- Nystagmus - quick lateral movement of eyes, uncoordinated eye movement
- Intention tremor
- Slurred speech
- Hypotonia - floppy movement of limbs
Describe the structure that make up the basal ganglia
- Caudate nucleus - C-shaped nucleus which wraps around lentiform nucleus
- Lentiform nucleus consists of the putamen + globus pallidus externa + globus pallidus interna
- Striatum consists of the putamen + caudate nucleus
- Substantia nigra made up of pigmented neurones called the pars compacta dorsally, and a ventral strip called the pars reticularis
- Dopaminergic neurones found in substantia nigra pars compacta
Describe the direct pathway of the basal ganglia
- Substantia nigra sends excitatory dopaminergic connections to the putamen, stimulating it and inhibiting globus pallidus interna
- Normally globuls pallidus interna inhibits thalamus activity, thus inhibition of it increases thalamus activity
- Direct pathway is overall excitatory to thalamus and cortex without dopamine
- Dopamine acts as an ‘on’ switch to increase stimulation of cortex
Describe the indirect pathway of the basal ganglia
- Substantia nigra sends inhibitory dopaminergic connections to the putamen, which leads to decreased inhibition of globus pallidus externa
- Enhanced globus pallidus externa stimulation increases inhibitory input to subthalamic nucleus
- Thus decreased stimulation of subthalamic nucleus decreases stimulation of globus pallidus interna, which decreases inhibition to thalamus
- Indirect pathway is overall inhibitory to thalamus and cortex without dopamine
- Dopamine acts as an ‘off’ switch, turning off the inhibition and thus promoting stimulation of cortex
What is the overall net effect of dopamine on the basal ganglia
The overall net effect of dopamine in the direct and indirect pathways is motor cortex stimulation via the thalamus
State the symptoms of basal ganglia disorders
- Abnormal motor control
- Altered posture
- Affects muscle tone
- Dyskinesia - abnormal movement
- Contralateral symptoms
Describe Parkinson’s disease and its pathophysiology
- Chronic, progressive movement disorder characterised by a triad of bradykinesia, tremor, and rigidity
- Degeneration of substantia nigra pars compacta causes deficiency of dopamine
- Direct pathway - has overall stimulatory effect on thalamus without dopamine
- Pathway stimulation will decrease in Parkinson’s - bradykinesia
- Indirect pathway - has overall inhibitory effect on thalamus without dopamine
- No stimulations from the indirect pathway - bradykinesia
- Direct pathway - has overall stimulatory effect on thalamus without dopamine
Describe the symptoms of Parkinson’s disease
- Parkinson’s disease symptoms are unilateral
- Cardinal symptoms
- Bradykinesia - slow movement
- Tremor - resting tremor (disappears on movement)
- Rigidity - increased muscle tone
- Other associated features
- Hypophonia - quieter phonation/tone
- Reduced facial expression
- Micrographia - handwriting small overtime
- Dementia
- Depression
Describe the mechanism behind Huntington’s disease
- Autosomal dominant, progressive neurodegenerative disorder
- Onset of disease around 30-50 years
- Associated with cell loss with the striatum (putamen + caudate nucleus)
- Decreased inhibition to GPe due to less cells in putamen
- Causes increased stimulation from the thalamus causing increased cortex stimulation
Describe the symptoms of Huntington’s disease
- Chorea - involuntary jerk movements
- Dystonia - sustained or repetitive movements causing twisting of trunk/limbs
- Incoordination
- Cognitive decline
- Behavioural difficulties
Describe the different symptoms at each stage of Huntington’s
- Early stage - chorea within the limbs, severe behavioural symptoms (depression, irritability)
- Middle stage - severe chorea, cognitive problems, behavioural symptoms
- Late stage - trouble walking, chorea stopped, cognitive symptoms