S6) Motor Disorders Flashcards
What are the components of the motor pathway?
- Corticospinal tract
- Corticobulbar tract
- Extrapyramidal tracts
Describe the anatomical location of the cerebellum
- Located in the posterior cranial fossa
- Separated from the occipital and parietal lobes by the tentorium cerebelli
- Separated from the pons by the 4th ventricle
What is the role of the cerebellum?
It has an important role in motor control and coordination
→ work with basal ganglia to detriment correct actions and sequence
→ profuse sensory inputs from proprioceptive neurones and sensory cortices
Describe the components of the cerebellum
- Consists of:
I. Vermis which regulates trunk musculature
II. Two lateral cerebellar hemispheres which regulate distal structures i.e. limbs
- Tracts are ipsilateral in the cerebellum
Describe how the cerebellum communicates with the brainstem via the cerebellar peduncles
- Superior cerebellar peduncle attaches cerebellum to midbrain
- Middle cerebellar peduncle attaches cerebellum to pons
- Inferior cerebellar peduncle attaches cerebellum to medulla
What are the 6 different symptoms of cerebellar disease?
- Dysdiadochokinesis (can’t do rapid, alternating movements)
- Ataxia (gait abnormality)
- Nystagmus, involuntary movements of the eye)
- Itention tremor (tremor when pointing to something)
- Slurred speech
- hypotonia
What is the basal ganglia?
- The basal ganglia is the area of the brain known to be involved in motor function
- It stimulates motor activity in the cerebral cortex
Identify some important structures found in the basal ganglia
- Caudate nucleus - long term memory and learning (Alzheimer’s disease), control of voluntary movement
- Lentiform nucleus – made up of putamen, globus pallidus externa and globus pallidus interna
- Substantia nigra – made up of pars compacta and pars reticularis
- Subthalamic nucleus below the thalamus
What composes the striatum?
What composes the lentiform nucleus?
Where is the output of the basal ganglia?
The output of the basal ganglia is via the thalamus
What type of neurons are found in the striatum?
Most of the neurons in the striatum are GABAergic inhibitory
Describe the structure of the substantia nigra
Substantia nigra is made up of pigmented neurons called the pars compacta dorsally, and a ventral strip called the pars reticularis
What type of neurons are found in the pars compacta?
Dopaminergic neurons found in substantia nigra pars compacta
The circuitry of basal ganglia is arranged in direct and indirect pathways to the thalamus.
Describe the layout and components of the direct pathway
- Direct pathway is overall excitatory to thalamus and cortex without dopamine
- Addition of dopamine from SNc encourages stimulation of cortex
The circuitry of basal ganglia is arranged in direct and indirect pathways to the thalamus.
Describe the layout and components of the indirect pathway
- Indirect pathway is overall inhibitory to thalamus and cortex without dopamine
- Addition of dopamine from SNc promotes stimulation of cortex
Identify four symptoms of basal ganglia disorders
- Abnormal motor control
- Altered posture
- Altered muscle tone
- Dyskinesia
What is Parkinson’s disease?
- Parkinson’s disease is a chronic, progressive movement disorder characterised by a triad of
bradykinesia (slow movements due to reduced cortical excitation)
tremor (not sure)
rigidity (lack of coordination between muscles)
hypophonia (bradykinesia of larynx and tongue)
- It is caused by the degeneration of the substantia nigra causes deficiency of dopamine
Describe the effect of Parkinson’s on the direct pathway of the circuitry of the basal ganglia
- In Parkinson’s, there is a deficiency in dopamine
- Hence, there is less dopamine to stimulate the direct pathway leading to less inhibition of the inhibition on the thalamus
Describe the effect of Parkinson’s on the indirect pathway of the circuitry of the basal ganglia
- In Parkinson’s, there is a deficiency in dopamine
- Hence, there is less dopamine to inhibit the indirect pathway so there is more inhibition on the thalamus
Identify the three cardinal symptoms of Parkinson’s disease
- Resting tremor
- Bradykinesia
- Hypertonia (rigidity)
Identify five other associated features of Parkinson’s disease
- Hypophonia
- Reduced facial expression
- Micrographia
- Dementia
- Depression
What is Huntington’s disease?
- Huntington’s disease is an autosomal dominant, progressive neurodegenerative disorder associated with cell loss within the basal ganglia and cortex
early stage is to do with loss of inhibitory projections from striatum to GPe = hyperkinetic features
- The onset of disease is around 30-50 years
Illustrate the effect of Huntington’s on the indirect pathway of the circuitry of the basal ganglia
Identify 5 symptoms of Huntington’s disease
- Chorea → dance like movements
- Dystonia → uncomfortable contractions of agonists and antagonists
- Incoordination
- Cognitive decline
- Behavioural difficulties
What is hemiballismus?
- Hemiballismus is a rare movement disorder associated with dysfunctional contralateral subthalamic nuclei (inhibits thalamus via GPi) damage
- It results in unilateral abnormal movement and is often secondary to sub-cortical stroke
Illustrate the effect of hemiballismus on the indirect pathway of the circuitry of the basal ganglia
what does the globes pallidus consist of
internal and external segment
what two structures form the lentiform nucleus
- putamen
- globus pallidus
what structure does the basal ganglia use to communicate with the motor Cortex?
thalamus, increased thalamus activity will increase cortical activity
what is the function of the basal ganglia?
→ determines most appropriate set of movements and order of movements:
→ compromised of the indirect and direct pathway
→ Basal ganglia: appropriate movements
→ cerebellum: appropriate order
what does the direct pathway do?
→ reinforces appropriate movements → excitatory to thalamus to stimulate the cortex
- Substantia nigra releases dopamine to stimulate putamen
- double inhibition (GABA) via GPi and thalamus
- stimulates thalamus
- glutamate stimulate the cortex
what Is the role of the indirect pathway
→ edits out inappropriate movements → inhibits the motor cortex
- overal STN is stimulated
- this excites GPi (globus pallidus internal segment)
- this then inhibits the thalamus
- reduces cortex
what type of receptors are involved in the direct and indirect pathway
excitatory D1 receptors
inhibitory D2
what are the inputs and outputs of the cerebellum and how does this effect its signs of damage
inputs: ipsilateral spinal cord and contralateral sensory cortices
output: contralateral motor cortex
damage: ipsilateral signs of cerebellar damage due to decussation of corticospinal pathway
signs of cerebellar disease
