EXTRAPYRAMIDAL DISORDERS Flashcards
Function of the basal ganglia?
It’s like a collection of brakes or accelerators
To fine-tune voluntary movements
It recieves impulses fron the cerebral cortex, processes them and adjusts them and then covey this infromation to the thalamus and then back to the cortex
Ultimately the fine-tuned movement instruction is sent to skeletal muscles via the spinal cord
Also involves in planning, modulation of movements, memory, eye movements, reward processing and motivation
Components of the basal ganglia?
Caudate nucleus
Putamen
Nucleus accumbens and olfactory tubercle
Globus pallidus
Subthalamic nucleus
Substantia nigra
Which part of the striatum is part of the basal ganglia?
The dorsal striatum
What are the 2 components of the striatum?
The caudate nucleus and the putamen
What forms the corpus striatum?
The striatum and the globus pallidus
Input nuclei of the basal ganglia?
The striatum and the caudate nucleus
What is the nucleus accumbens?
The most cranial aspect of the striatum where the caudate nucleus and the putamen join together
Function of striatum?
It recieve excitatory glutamatergic inputs from the cerebral cortex.
The synapsing pattern reflects topography of the cortex e.g. caudal parts of the cortex project to the caudal part of the brain the striatum
Structure of the caudate nucleus?
Consists of a head, tail and the body
Terminates by connecting with the amygdala at the tail of the caudate nucleus
Function of the caudate nucleus?
Integrates sensory information about the spatial position of the body and according to that sends infromation about necessary fine tunes of motor response to that stimuli to the thalamus
Also contributes to body & limb posture and speed &accurary of directed movements
Intrinsic nuclei of the basal ganglia?
External globus pallidus
Subthalamic nuclei
Pars compacta of the substantia nigra
Output nuclei of the basal ganglia?
Internal globus pallidus
Pars reticulata of the substantia nigra
Function of putamen?
To regulate motor functions and influence various types of learning
It uses dopamine
What are the 2 divisions of the globus pallidus?
The internal globus pallidus and the external globus pallidus
What are the 2 components of the substantia nigra?
The pars compacta and the pars reticulata
Function of the substantia nigra pars compacta?
Output to the basal ganglia circuit, supplying the striatum with dopamine through specific D1 and D2 neurones within the nigrostriatal pathways
Function of the substantia nigra pars reticulata?
Serves as input - conveys signals from the basal ganglia to the thalamus
Why does the substantia nigra have a dark appearance?
Due to the neuromelanin present in the cells in the pars compacta
Arterial supply to the basal ganglia?
Middle cerebral artery - main aretry is the lenticulostriate artery
Direct pathway of basal ganglia structure
Glutamate neurones project from the thalamus to motor regions of cerebral cortex = excitatory = stimulates movement
Neurones from the globus pallidus internal and substantia nigra pars reticulata project to the thalamus and release GABA = inhibition = suppression of movement to prevent unwanted movements from occurring
Infromation from movement is sent from cortex to striatum via the corticostriatal pathway. Glutamate nuyerones excite neurons on the striatum. Activated stiatam neurones release GABA in the globus pallidus internal and substantia nigra pars reticulata = inhibition of these regions = stops inhibition of neurones in the thalamus which are involved in movement = movement can occur!
Neurones from the substantia nigra pars compacta travel to the striatum via the nigrostriatal pathway and release dopamine in the striatum = facilitates activity in direct pathway
Indirect pathway of the basal ganglia structure
GABA neurones project from globus pallidus external to the Subthalamic nucleus = inhibition on glutamate neurones in Subthalamic nucleus
Signals from cerebral cortex causes activation of GABA neurones in the striatum which projects to the globus pallidus external and inhibits thr activity of neurones there. This prevents globus pallidus external neurones from inhibiting the neurones in the Subthalamic nucleus
Projections from the cortex activate the Subthalamic nucleus neurones and stimulate GABA neurones in the globus pallidus internal and substantia nigra pars reticulata = project to the thalamus = inhibits thalamic neurones that travel the motor regions of the cerebral cortex to stimulate movement = therefore inhibits movement
This antagonises the activity of the direct pathway and acts to keep unwanted movements from occurring
Neurones from the substantia nigra pars compacta travel to the striatum via the nigrostriatal pathway. These can modulate the activity of the indirect pathway through dopamine release in the striatum = inhibition of activity in indirect pathway = facilitation of movement
What broadly causes movement disrders?
Disturbance of the cerebellum and extrapyramidal system e.g. basal ganglia, thalamus, Subthalamic nuclei and red nucleus
Positive symptoms of movement disorders?
Chorea
Athetosis
Ballismus
Dystonia
Tremor
Rigidity
(Due to disinhibition of undamaged parts of the motor system)
Negative symptoms of movement disorders?
Hypokinesia and bradykinesia
What is a tremor?
An involuntary, regular, rhythmic, oscillatory movement produced by alternating or irregularly synchronous contractions of antagonistic muscles
Types of tremor?
Physiological
Exaggerated physiological e.g. thyrotoxicosis or anxiety
Essential tremor
Dystonic tremor
Cerebellar tremor
Parkinsonian tremor
Functional tremor
What is an essential tremor?
An autosomal dominant condition that affects both upper limbs usually
There is often a strong FHx
Features of an essential tremor?
It’s a postural tremor i.e. worse if arms are outstretched
Improved by alcohol and rest
It’s the most common cause of titubation (a head tremor)
Why does alcohol improve an essential tremor?
Alcohol enhances GABA which is inhibitors and dampens the excessive firing of neurones
Management of essential tremor?
Propranolol first line
What is titubation?
Head tremor
Type of tremor seen in parkinsonism?
Resting, pill-rolling tremor
Causes of tremor?
Parkinsonism
Essential tremor
Anxiety
Thyrotoxicosis
Hepatic encephalopathy
CO retention
Cerebellar disease
Drug withdrawal e.g. alcohol or opiates
What type of tremor does cerebellar disease cause/
An intention tremor
What is an intention tremor?
Involuntary, thyroid muscle contractions that occur during purposeful, voluntary movement e.g. reaching for something
Most commonly affects the upper limbs
What is myoclonus?
A brief, involuntary, shock-like contraction of a group of muscles; Irregular in rhythm and amplitude, asynchronous and asyemmetrical
Can cause whole body to jerk or just an area
Caused by abnormal discharges in the CNS of motor neurones or interneurones
What is chorea?
“To dance”
Brief, semi-directed, irregular movements that are not repetitive or rhythmic, but appear to flow from one muscle to the next
What is hemiballismus?
Unilateral - affects ipsilateral arm & leg
Intermittent, sudden involuntary large movements
What is athetosis?
Slow, involuntary, convoluted, writhing movements of hands and feet
Slow, sinuous movements that flow into 1 another
What is dystonia?
Sustained muscle contractions causing abnormal, often repetitive movements or postures
Movements are typically twisting, patterned or tremulous
It can be focal, segmental or generalised
Tremor is often a feature
Often worsened by voluntary movements
Where is the lesion likely in a patient with athetosis?
In the lentiform nucleus in the basal ganglia
Where is the lesion likely in a patient with chorea?
Caudate nucleus
Causes of chorea?
Inherited e.g. huntingtons, Wilson’s
Sydenhams (as a consequence of rheumatic fever)
Hormonal and endocrine - typically oestrogen-related e.g. in pregnancy or SE of contraceptive pill
Degenerative
Drugs e.g. phenytoin, neuroleptics
Structural - stroke, tumours, trauma
SLE
Polycythemia vera
Causes of athetosis?
Birth hypoxia or kernicterus
Hepatic encephalopathy
All other causes same as chorea:
Inherited e.g. huntingtons, Wilson’s
Sydenhams (as a consequence of rheumatic fever)
Hormonal and endocrine - typically oestrogen-related e.g. in pregnancy or SE of contraceptive pill
Degenerative
Drugs e.g. phenytoin, neuroleptics
Structural - stroke, tumours, trauma
SLE
Polycythemia vera
Where is the lesion likely to be in a patient who has hemiballismus?
Subthalamic nuclei
What is considered the commonest form of tremor?
Dystonic tremor
Causes of dystonia?
Genetics
Drug-induced e.g. parkinsonian medications and neuroleptics
Related to trauma
Idiopathic
What is parkinsonism?
An umbrella term for the clinical syndrome involving bradykinesia plus at least one of tremor, rigidity or postural instability
Causes of parkinsonisms?
Parkinson’s disease
Drug induced e.g. antipsychotics and metoclopramide
Degenerative: Progressive supranuclear palsy, Multiple system atrophy
Metabolic: Wilsons disease
Infection: Post-encephalitis, prion disease e.g. cruz-felt Jakob disease
Dementia pugilistica
Toxins e.g. CO, MPTP, mercury
What is dementia pugilistica?
A form of chronic traumatic encephalopathy
Caused by chronic head trauma
Commonly seen in boxing
Red flags to diagnosing parkinsonsism and a cause that is not parkinsons disease?
Recent use of dopamine blocking drugs
Lack of the typical tremor (resting pill-rolling)
Symmetrical signs (parkinsons is usually asymmetrical i.e. affects 1 side more than the other)
Early cognitive dysfunction
Early balance disturbances eg. In PSNP where people tend to fall backwards
Significant and early autonomic dysfunction e.g. MSA
Poor response to usual parkinsons medications
Dementia with Parkinson’s vs dementia with Lewy body?
The only real difference is that in Lewy body dementia, the dementia occurs first before the motor symptoms (may also have recurrent visual hallucinations & act out dreams)
In parkinsons, the motor symptoms occur first and then dementia follows
What is parkinsons disease?
A chronic, progressive neurodegenerative condition resulting from the loss of the dopamine-containing cells of the substantia nigra
The dopamine deficiency within the basal ganglia leads to a movement disorder with classical parkinsonian motor symptoms
How much dopaminergic cell activity must be lost for parkinsons disease to be clinically apparent?
At least 50%
Cause of parkinsons?
Dopamine denervation due to Lewy body deposition and cell death in the substantia nigra
A large number of extra-nigral and non-dopaminergic brain regions are also affected
Minority of people have a FHx - associated with early-onset i..e <40