S6) Motor Disorders Flashcards
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
- 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
Where is the output of the basal ganglia?
The output of the basal ganglia is via the thalamus
What composes the striatum?
What composes the lentiform nucleus?
What type of neurons are found in the striatum?
Most of the neurons in the striatum are GABAergic
What are the components of the basal ganglia?
- Substantia nigra pars compacta
- Striatum
- Globus pallidus
- Lentiform nucleus
- Subthalamic nucleus
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 is the substantia nigra pars compacta (SNc)?
source of dopamine in the midbrain - vital correlation in Parkinson’s disease
What type of neurons are found in the pars compacta?
Dopaminergic neurons found in substantia nigra pars compacta
Where does the striatum receive input from?
receives input from SNc and cortex
What does the striatum consist of?
- Caudate nucleus (c-shaped nucleus lining lateral ventricle)
- Putamen
Caudate + putamen = striatum (functionally related)
The globus pallidus has two parts. What are they?
Globus pallidus internus
Globus pallidus externus
(Internal and external segment)
What makes up the lentiform nucleus anatomically?
Putamen + globus pallidus = lentiform nucleus (anatomically but not functionally related)
Where is the subthalamic nucleus?
(small area sitting beneath the thalamus)
The basal ganglia always has to communicate with the motor cortex via …
the thalamus
Increased thalamic activity means …
Increased thalamic activity causes increased cortical activity and vice versa
What is the function of the basal ganglia?
role in reinforcing appropriate movements and removing inappropriate movements.
Think about a simple behaviour like picking up a cup of tea – you need to facilitate appropriate movements (e.g. elbow flexion) and suppress inappropriate movements (e.g. elbow extension)
You do not need to memorise the basal ganglia circuitry, but you must understand it! If I ask about basal ganglia in an exam I shall provide a diagram and indicate clearly which parts you need to refer to.
Look at the diagram and explain the normal pathway/function!
In the basal ganglia, what does the direct pathways result in?
Direct pathways reinforces appropriate movements (excitatory to motor cortex)
In the basal ganglia, what does the indirect pathways result in?
Indirect pathway edits out inappropriate movements (inhibitory to motor cortex)
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
In the basal ganglia pathway, what is the dual role of dopamine and therefore its net effect?
Dopamine facilitates movement by exciting the motor cortex → excites direct pathway by stimulating excitatory D1 receptors on striatal neurones taking part in the direct pathway.
Also inhibits indirect pathway by activating inhibitory D2 receptors on striatal neurones taking part in the indirect pathway.
Net effect: overall excitation of the cortex
Describe dopamines action on the basal ganglia.
Basal ganglia regulate ipsilateral motor cortex. If SNc is affected unilaterally (Rare), where will the signs be seen and why?
There will be contralateral signs due to decussation of the corticospinal tract
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, tremor and rigidity
- It is caused by the degeneration of the substantia nigra causes deficiency of dopamine
What occurs in Parkinson’s disease?
Caused by degeneration of dopaminergic neurones in SNc
Therefore have lost the dopamine-driven facilitation of movement via both pathways
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 are the signs and symptoms seen in Parkinson’s disease?
- Tremor
- Rigidity
- Bradykinesia
- Hypophonia
- Decreased facial movement/ mask-like facies
- Micrographia
- Dementia
- Depression
Explain the below symptoms and signs seen in Parkinson’s disease:
- Tremor
- Rigidity
- Bradykinesia
- Hypophonia
- Decreased facial movement/ mask-like facies
- Micrographia
- Dementia
- Depression
- Tremor = unclear mechanism, but may be related to dysfunction of indirect pathway which would normally suppress unwanted movements
- Rigidity = unknown mechanism, may be related to lack of co-ordination between agonists and antagonists)
- Bradykinesia = best understood mechanism. Slow movements due to loss of cortical excitation
- Hypophonia = quiet speech = bradykinesia of larynx and tongue
- Decreased facial movement / mask-like facies (bradykinesia of face)
- Micrographia = small handwriting =bradykinesia in hands
- Dementia = possible progression of currently unknown causative agent (e.g. protein aggregates)
- Depression = basal ganglia also have a role in cognition and mood
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
- The onset of disease is around 30-50 years
What is Huntington’s chorea?
It an autosomal dominant progressive disorder.
Early onset around 30-50 yrs old
Early stages associated with loss of inhibitory projections from striatum to GPe .: leads to hyperkinetic features (increased movement as the brakes have been taken off the thalamus)
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
- Dystonia
- Incoordination
- Cognitive decline
- Behavioural difficulties
Explain why the below features are seen in Huntington’s chorea.
- Chorea
- Dystonia
- Loss of co-ordination
- Cognitive decline and behavioural disturbances
- Chorea = dance-like movements due to increased motor cortex activation
- Dystonia = uncomfortable contractions of agonists and antagonists simultaneously leading to odd postures caused by over activity in agonist/antagonist muscle circuits and loss of co-ordination between these
- Loss of co-ordination = similar to above presumably
- Cognitive decline and behavioural disturbances = related to role of basal ganglia in higher metal functions
What is Hemiballismus?
It is a rare disorder.
Can be caused by:
- damage to subthalamic nucleus which
- *normally inhibits the thalamus via GPi**
- can also be caused by sub-cortical stroke (lacunar infarct)
This results in unilateral explosive (‘ballistic’) movements
What is hemiballismus?
- Hemiballismus is a rare movement disorder associated with dysfunctional contralateral subthalamic nuclei 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
Summary of Huntington’s chorea, Parkinson’s disease and Hemiballismus
What are the components of the motor pathway?
- Corticospinal tract
- Corticobulbar tract
- Extrapyramidal tracts
What is the anatomy of cerebellum?
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
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
Which part of the body does the midline vermis and the 2 laterally placed hemispheres deal with?
- Vermis deals with trunk
- Hemispheres with the ipsilateral side of the body
Describe how the cerebellum communicates with the brainstem (rest of the CNS) 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
As the cerebellum sits above the 4th ventricle. Identify a clinical correlate in terms of pathology that could occur.
Cerebellar lesions (e.g. tumours) can cause hydrocephalus
What is the function of the cerebellum?
Obscure! However, has a clear role in the sequencing and co-ordination of movements
Uses sensory information to decide upon the most appropriate sequence of movements to perform an action
Describe the relationship between the cerebellum and basal ganglia.
The cerebellum works with basal ganglia which decide most appropriate movements.
Cerebellum then sequences these movements.
e.g. so, to develop the picking up a cup of tea example: basal ganglia say that elbow flexion, shoulder flexion, finger flexion and wrist flexion are most appropriate. Cerebellum then puts these in most appropriate sequence based upon current position of limb (maybe finger flexion followed by wrist extension followed by elbow then shoulder depending upon position).
What are the inputs and outputs of the cerebellum?
Cerebellum receives sensory input from ipsilateral spinal cord and contralateral sensory cortices.
Its outputs are to the contralateral motor cortex.
…hence, ipsilateral signs of cerebellar damage due to decussation of corticospinal pathway
How would a person with cerebellar lesions present with?
Vomiting
Vertigo
Difficulty walking - due to problems with coordination in lower limbs
What are the 6 different symptoms of cerebellar disease?
- Dysdiadochokinesis (can’t do rapid, alternating movements - presumably as a result of a problem with sequencing pronation-supination-pronation-supination)
- Ataxia (unsteady gait due to difficulty sequencing lower limb muscle contractions as well as loss of unconscious proprioception from lower limbs)
- Nystagmus (Flickering eye movements due to malcoordination of extraocular muscles)
- Intention tremor (A tremor that worsens as a target is approached)
- Slurred speech (Caused by malcoordination of laryngeal and tongue musculature)
- Hypotonia (Unclear mechanism)
Explain the signs of the cerebellar disease.
- Dysdiadochokinesis
- Ataxia
- Nystagmus
- Intention tremor
- Slurred speech
- Hypotonia
- Dysdiadochokinesis (can’t do rapid, alternating movements - presumably as a result of a problem with sequencing pronation-supination-pronation-supination)
- Ataxia (unsteady gait due to difficulty sequencing lower limb muscle contractions as well as loss of unconscious proprioception from lower limbs)
- Nystagmus (Flickering eye movements due to malcoordination of extraocular muscles)
- Intention tremor (A tremor that worsens as a target is approached)
- Slurred speech (Caused by malcoordination of laryngeal and tongue musculature)
- Hypotonia (Unclear mechanism)
A cerebellar lesion can result in signs on which side?
Ipsilateral if a lesion is in the hemisphere
Cerebellar lesions …
Describe the normal function of the basal ganglia and the cerebellum - the cortical loop
Which side of the body will you see signs in if there is lesion to the basal ganglia?
contralateral signs of the body
Which side of the body will you see signs in if there is lesion to the cerebellum?
Look at groupwork questions page 43-48 - will help you understand about UMN and LMN lesions!!
Concepts:
Remember LMN loss is found at the same level of wherever the spinal segment is affected.
UMN loss is found from that specific spinal segment and below
In terms of signs, LMN signs will be seen more than the UMN lesion - so altho if a spinal cord segment is completely destroyed- it will have both UMN and LMN problems but you will predominantly see LMN signs as opposed to UMN signs!!!
