21. Motor Systems Flashcards
What is the collective term given to the basal ganglia and cerebellum?
Extrapyramidal system
Broadly speaking, what is the role of the extra-pyramidal system?
- It checks that the movement selected by the motor cortex is correct
- They are responsible for the involuntary and automatic control of all musculature:
- Muscle tone
- Balance
- Posture
- Locomotion
- They are responsible for the involuntary and automatic control of all musculature:
- Both parts of the extrapyramidal system has functions aside from modulating motor control
Where is the basal ganglion located?
White matter in the middle of the brain
What are the different parts of the basal ganglia?
-
Striatum
- Caudate nucleus
- Putamen
-
Globus Pallidus
- External segment (GPext)
- Internal segment (GPint)
-
Substantia nigra
- Pars compacta (SNc)
- Pars reticulata (SNr)
- Subthalamic nucleus
What is the function of the basal ganglia?
- It is involved in planning and coordinating movement
- It elaborates associated movements
- e.g. swinging arms when walking
- Contribute to the smoothness of complex action Involved in moderating and coordinating movements
Describe the structure of the direct pathway in the basal ganglia.
Fibres initially come from the motor cortex to the striatum (caudate and putamen)
- Direct Pathway: putamen –> internal segment (GPi) + pars reticulata (SNr)
Describe the structure of the indirect pathway in the basal ganglia.
- Fibres initially come from the motor cortex to the striatum (caudate and putamen)
- Putamen –> globus pallidus external segment –> subthalamic nucleus –> globus pallidus internal segment
What is the difference in the function of the direct and indirect pathways?
- Direct Pathway = excitatory on the motor cortex
- Indirect Pathway = inhibitory on the motor cortex
What extra component modulates the function of the direct and indirect pathways?
Nigro-striatal pathway
Where do the projections go after leaving the basal ganglion structures?
- They go to the thalamus
- From the thalamus they go to the cortex
-
Primary motor area (BA4) and supplementary motor area (BA6)
- two regions involved in movement preparation and planning
-
Primary motor area (BA4) and supplementary motor area (BA6)
Describe how the basal ganglia are involved in choosing correct motor programmes to carry out particular functions
- The basal ganglia and cortex form a processing loop
- The basal ganglia enable proper motor programmes (stored in the cortex) via the direct pathway (excitatory)
- The basal ganglia inhibit the competing motor programmes via the indirect pathway
- In summary, the basal ganglia and its direct and indirect pathways make sure that appropriate motor commands get transmitted down the hierarchy.
Connections with which parts of the brain allow the basal ganglia to have a role in enabling various cognitive, executive and emotional programmes?
- Prefrontal cortex
- Limbic system
What causes Parkinson’s disease?
- Parkinson’s disease is the neuronal degeneration of dopaminergic neurones in the pars compacta (SNc)
- It is caused by the progressive depletion of dopaminergic neurones
- NOTE: symptoms only appear when 80% of the dopamine cells in the substantia nigra have died
What are the consequences of Parkinson’s with regards to the circuitry of the basal ganglia?
- The loss of nigro-striatal dopaminergic axons in the caudate and putamen mean that the connection between the striatum and pars compacta (SNc) is lost.
- Striatum = caudate nucleus and putamen
- This means that the direct pathway is reduced and so the excitation of the motor cortex is reduced
- The lack of excitatory input interferes with the ability of the motor cortex to generate commands for voluntary movement, resulting in poverty of movement.
State the main signs of Parkinson’s disease.
-
Bradykinesia
- slow movement
-
Akinesia
- difficulty in the initiation of movements
-
Hypomimic face
- expressionless face
- Tremor
-
Rigidity
- increase in muscle tone
Describe the Parkinsonian gait.
- Walking slowly
- Small steps
- Shuffling feet
- Reduced arm swing
- Stooped posture with head and body bent forwards and downwards
What is Huntington’s disease caused by?
- Abnormality on chromosome 4 (autosomal dominant)
- Caused by the degeneration of GABAergic neurones in the striatum
- Firstly the caudate and then the putamen
What are the consequences of Huntington’s disease with regards to the circuitry of the basal ganglia?
- The inhibitory effect of the indirect pathway no longer keeps the direct pathway under control so the cortex will be hyperexcitable
- Patients will continuously have abnormal movements because the cortex is continuously sending involuntary commands for movements
What are the main signs of Huntington’s disease and how does the disease progress?
- Chorea = brief, semi-directed, irregular movements that are not repetitive or rhythmic, but appear to flow from one muscle to the next
- Choreic movements
- Rapid, jerky, involuntary movements of the body
- Hands and face are affected first
- Chorea gradually increases over time until the patients are totally incapacitated by it
- Later on the patients will develop cognitive decline and dementi
State the 3 lobes of the cerebellum.
Anterior Posterior Flocculonodular
The cerebellum is divided sagitally into 3 zones. What are these zones?
Vermis (midline) Intermediate hemisphere (closest to vermis) Lateral hemisphere
State the 3 layers of the cerebellar cortex.
Granule cell layer Purkinje cells Molecular layer
Name the 3 deep nuclei that are involved in the connections of thecerebellum with other parts of the body. Include their function.
Fastigial = involved in control of balance and connected with vestibular nuclei Interposed + Dentate = both involved in voluntary movement and are connected to the thalamus and the red nucleus
What are the 3 sources of input into the cerebellum and what do they connect with?
Mossy Fibres – from the cortex and pons (corticopontine fibres) Mossy Fibres – from the spinocerebellar tract Climbing Fibres – from the inferior olive
Functionally, the cerebellum can be divided in three. What are these three divisions?
Vestibulocerbellum Spinocerebellum Cerebrocerebellum
What is the role of the vestibulocerebellum?
Vestibulocerbellum is the flocculonodular lobe It is connected to vestibular nuclei Involved in balance, posture and regulation of gait It is also involved in coordination of head movements with eye movements
Which parts of the cerebellum are part of the spinocerebellum?
Vermis and intermediate hemisphere
From where does the spinocerebellum receive inputs?
Afferents from axial portions of the body, visual, auditory and trigeminal inputs –> vermis Afferents from limbs –> intermediate hemisphere
What are the roles of the spinocerebellum?
Coordination of speech Adjustment of muscle tone Coordination of limb movement
Which part of the cerebellum is part of the cerebrocerebellum?
Lateral hemisphere
From where does the cerebrocerebellum receive inputs and what are its main functions?
It receives projections from the cortex Main functions are: Coordination of skilled movements Cognitive function Attention Processing of language Emotional control
In summary, what are the four main functions of the cerebellum?
Maintenance of balance and posture Coordination of voluntary movements Motor learning Cognitive functions
State three syndromes caused by dysfunction of different parts of the cerebellum.
Vestibulocerebellar syndrome/Flocculonodular lobe syndrome Spinocerebellar syndrome Cerberocerebellar syndrome
What are the symptoms of vestibulocerebellar syndrome?
This syndrome is similar to vestibular disease Patients tend to lose their balance with gait ataxia and a tendency to fall.
What behavioural habit is spinocerebellar syndrome associated with?
Chronic alcoholism
Describe the symptoms of spinocerebellar syndrome.
Mainly affects the legs It causes abnormal gait and a wide-based stance
Describe the symptoms of cerebrocerebellar syndrome.
Damage mainly affects the arms It affects coordinated movements Speech becomes very hesitant and slow (staccato)
What are the main signs of cerebellar disorders?
Ataxia– general impairments in movement coordination and accuracy Dysmetria– inappropriate force and distance for target-directed movements Intention tremor– increasingly oscillatory trajectory of a limb in a target directed movement (nose-finger tracking) Dysdiadochokinesia– inability to perform rapid alternating movements Scanning speech– staccato, due to impaired coordination of speech muscles
State a hereditary and acquired cause of the symptoms listed above.
Hereditary – Friedreich’s Ataxia Acquired – Multiple Sclerosis
What is volition?
Motor systems produce movements that are adaptive and accomplish a certain goal
Describe the hierarchical organisation of motor control.
Association Cortex Motor Cortex Brainstem Spinal Cord
What are postural adjustments and unconscious processing?
Postural Adjustments – the motor system has to compensate for changes in the body’s centre of mass during movements Unconscious Processing – many of the postural adjustments occur without our awareness
What are the three parts of the motor cortex?
Primary Motor Cortex Premotor Cortex Supplementary Motor Area
What is volition?
Motor systems produce movements that are adaptive and accomplish a certain goal
Describe the hierarchical organisation of motor control.
Association Cortex Motor Cortex Brainstem Spinal Cord
What are postural adjustments and unconscious processing?
Postural Adjustments – the motor system has to compensate for changes in the body’s centre of mass during movements Unconscious Processing – many of the postural adjustments occur without our awareness
What are the three parts of the motor cortex?
Primary Motor Cortex Premotor Cortex Supplementary Motor Area
What makes up the association cortex?
Frontal Cortex Parietal Cortex NOTE: this is not exactly part of the motor pathway but it influences the planning and execution of movements
What are the two parts of the pyramidal (descending) system?
Corticospinal Tract – starts in the cortex and exits and innervates the muscles in the arms and legs Corticobulbar Tract – starts in the cortex then exits and innervates the muscles in the face
Describe the side loops of this descending pathway and their role.
The descending pathway also has two side loops that go to the cerebellum and basal ganglia The cerebellum and basal ganglia check the motor information before ittravels to the muscles and has its effect
Which lobe are the three parts of the motor cortex found in? Describe their arrangement.
Frontal (anterior to the central sulcus) The primary motor cortex is on the precentral gyrus The premotor cortex and the supplementary motor area are anterior to the primary motor area
What is another name given to the three parts of the motor cortex?
Primary Motor Cortex = Broadmann’s Area 4 Premotor + Supplementary Motor Area = Broadmann’s Area 6
What are the most important cells in the primary motor cortex?
Betz Cells (pyramidal cells)
Where are these cells located within the grey matter and which tracts originate from here?
They are found in the 5th layer of grey matter The corticospinal tracts originate from here
Describe what happens to the upper motor neurones that come from the primary motor cortex.
They travel through the brainstem to the pyramidal decussation in themedulla where 90% of the axons cross the midline. These axons continue down the spinal cord and synapse with a lower motor neurone and exit into a peripheral nerve to the reach the skeletal muscle. The pathway of the corticobulbar tract is somewhat similar – upper motor neurones go down into the brainstem and synapse with a lower motor neurone and they exit to the muscles of the face
What are the two types of descending pathway?
Lateral and Medial
Which tracts fall into each of these types?
Lateral Lateral corticospinal tract Rubrospinal tract Medial Anterior corticospinal tract Reticulospinal tract Vestibulospinal tract Tectospinal tract
What is the function of each of these types of pathway?
Lateral Control of proximal and distal musculature Voluntary movements or arms and legs Medial Control of axial muscles Balance and posture
Describe the structure and function of the lateral corticospinal tract.
The lateral corticospinal tract originates in the primary motor cortex from the Betz cells. Their axons pass down through the brainstem and decussate at the pyramidal decussation in the medulla. It then passes down the spinal cord and synapses with a lower motor neurone. It goes onto control mainly the distal musculature. NOTE: 90% of axons from the primary motor cortex decussate at the medulla (these are the lateral corticospinal tract axons). The 10% that don’t decussate form the anterior corticospinal tract.
Where does the rubrospinal tract originate?
Red nucleus of the midbrain
What is the function of the rubrospinal tract?
It is an alternative pathway that allows voluntary motor commands to be sent down the spinal cord meaning that the body can compensate for a lesion in the primary motor cortex. It also has a role in movement velocity.
Describe the structure and function of the vestibulospinal tract.
The lateral vestibulospinal tract originates at the lateral vestibular nucleus. The medial vestibulospinal tract originates at the medial vestibular nucleus. They mediate postural adjustments and head and eye movements
Describe the structure and function of the reticulospinal tract.
It originates in the reticular formation in the brainstem then goes down the spinal cord to innervate muscle. It is involved in complex actions: Orienting Stretching Maintaining a complex posture
Describe the structure and function of the tectospinal tract.
It originates in the superior colliculus (brainstem) Its function is not known but is most likely involved in reflexive turning of the head to orient to visual stimuli.
Describe the structure and function of the anterior corticospinal tract.
The anterior corticospinal tract is made up of the upper motor neurone axons coming from the primary motor cortex that do not decussate at the pyramidal decussation. These fibres cross the midline at the level of the spinal cord It controls proximal musculature.
What diagram depicts the somatotopic organisation of the primary motor cortex?
Penfield’s Motor Homunculus
How can the cortical representation of a muscle in the motor cortex change?
The more we use a muscle, the bigger the representation of that muscle in the cortex.
What is the function of the premotor cortex?
Plans movements and assembles movements into coordinated actions NOTE: premotor cortex is anterior to the primary motor cortex
What is the function of the supplementary motor area?
Planning complex internally driven voluntary movements e.g. speech It also becomes active when you are thinking about movement before movement (e.g. rehearsing a dance)
What are the two parts of the association cortex that are involved in motor control? State their functions.
Posterior Parietal Cortex – ensures movements are targeted accurately to objects in external space Prefrontal Cortex – involved in the selection of appropriate movements for a particular course of action
Describe the features of upper motor neurone lesions.
Initially you get loss of function of the motor neurones leading to: Paresis = graded weakness of movement Paralysis = complete loss of muscle activity After a few weeks, the loss of descending inhibitory pathways leads to increased abnormal motor activity such as: Spasticity (increased muscle tone) Hyperreflexia (exaggerated reflexes) Clonus (abnormal oscillatory muscle contraction) Babinski’s Sign NO muscle atrophy
What is Babinski’s Sign?
You stroke the plantar surface of the foot and in a normal subject you will see flexion of the toes (they curl downwards) In the case of upper motor neurone lesions, the patient will show an EXTENSOR PLANTAR RESPONSE where their toes fan out and their big toe lifts up.
Why is muscle atrophy not seen in upper motor neurone lesions?
The lower motor neurones are still in tact and they have a role inproviding nutrients to the muscle. There will still be partial atrophy due to muscle disuse.
Define apraxia.
A disorder of skilled movement not caused by weakness, abnormal tone or posture or movement disorders (tremors or chorea). It is caused by the loss of information on how to perform skilled tasks rather than loss of motor command to the muscles.
Lesions in which part of the brain tend to cause apraxia?
Inferior parietal lobe Frontal lobe (premotor cortex and supplementary motor area)
What are the two most common causes of apraxia?
Stroke and Dementia
Describe the features of lower motor neurone lesions.
It is generally the opposite of upper motor neurone lesions. Hypotonia Hyporeflexia Weakness Muscle Atrophy– the metabolic trophic support to the muscles is lost FASCICULATIONS– damages motor units produce spontaneous action potentials, resulting in a visible twitch Fibrillations – twitch of individual muscle fibres (aren’t visible to the naked eye but are picked up on EMG)
What is motor neurone disease?
A progressive neurodegenerative disorder of the motor system – it is a spectrum of disorders. MND can affect upper motor neurones, lower motor neurones or both
What is the term given for upper AND lower motor neurone disease?
Amyotrophic Lateral Sclerosis (ALS)
Describe how the symptoms of ALS change as the disease progresses.
Some patients may present with only upper motor lesion symptoms or only lower motor lesion symptoms but as the disorder progresses, both upper and lower motor neurone signs will be coexistent.
List some signs of ALS.
Increased muscle tone (spasticity in the limbs and tongue) Brisk limb and jaw reflexes (hyperreflexia) BABINSKI’s SIGN Loss of dexterity Dyarthria – difficulty speaking Dysphagia – difficulty swallowing
Which lower motor neurone controls the tongue?
Hypoglossal Nerve (CN XII)
What might you see in the tongue of an MND patient?
Fasciculations and spasticity
What makes up the association cortex?
Frontal Cortex Parietal Cortex NOTE: this is not exactly part of the motor pathway but it influences the planning and execution of movements
What might you see in the tongue of an MND patient?
Fasciculations and spasticity
Which lower motor neurone controls the tongue?
Hypoglossal Nerve (CN XII)
List some signs of ALS.
Increased muscle tone (spasticity in the limbs and tongue) Brisk limb and jaw reflexes (hyperreflexia) BABINSKI’s SIGN Loss of dexterity Dyarthria – difficulty speaking Dysphagia – difficulty swallowing
Describe how the symptoms of ALS change as the disease progresses.
Some patients may present with only upper motor lesion symptoms or only lower motor lesion symptoms but as the disorder progresses, both upper and lower motor neurone signs will be coexistent.
What is the term given for upper AND lower motor neurone disease?
Amyotrophic Lateral Sclerosis (ALS)
What is motor neurone disease?
A progressive neurodegenerative disorder of the motor system – it is a spectrum of disorders. MND can affect upper motor neurones, lower motor neurones or both
Describe the features of lower motor neurone lesions.
It is generally the opposite of upper motor neurone lesions. Hypotonia Hyporeflexia Weakness Muscle Atrophy– the metabolic trophic support to the muscles is lost FASCICULATIONS– damages motor units produce spontaneous action potentials, resulting in a visible twitch Fibrillations – twitch of individual muscle fibres (aren’t visible to the naked eye but are picked up on EMG)
What are the two most common causes of apraxia?
Stroke and Dementia
Lesions in which part of the brain tend to cause apraxia?
Inferior parietal lobe Frontal lobe (premotor cortex and supplementary motor area)
Define apraxia.
A disorder of skilled movement not caused by weakness, abnormal tone or posture or movement disorders (tremors or chorea). It is caused by the loss of information on how to perform skilled tasks rather than loss of motor command to the muscles.
Why is muscle atrophy not seen in upper motor neurone lesions?
The lower motor neurones are still in tact and they have a role inproviding nutrients to the muscle. There will still be partial atrophy due to muscle disuse.
What is Babinski’s Sign?
You stroke the plantar surface of the foot and in a normal subject you will see flexion of the toes (they curl downwards) In the case of upper motor neurone lesions, the patient will show an EXTENSOR PLANTAR RESPONSE where their toes fan out and their big toe lifts up.
Describe the features of upper motor neurone lesions.
Initially you get loss of function of the motor neurones leading to: Paresis = graded weakness of movement Paralysis = complete loss of muscle activity After a few weeks, the loss of descending inhibitory pathways leads to increased abnormal motor activity such as: Spasticity (increased muscle tone) Hyperreflexia (exaggerated reflexes) Clonus (abnormal oscillatory muscle contraction) Babinski’s Sign NO muscle atrophy
What are the two parts of the association cortex that are involved in motor control? State their functions.
Posterior Parietal Cortex – ensures movements are targeted accurately to objects in external space Prefrontal Cortex – involved in the selection of appropriate movements for a particular course of action
What is the function of the supplementary motor area?
Planning complex internally driven voluntary movements e.g. speech It also becomes active when you are thinking about movement before movement (e.g. rehearsing a dance)
What is the function of the premotor cortex?
Plans movements and assembles movements into coordinated actions NOTE: premotor cortex is anterior to the primary motor cortex
How can the cortical representation of a muscle in the motor cortex change?
The more we use a muscle, the bigger the representation of that muscle in the cortex.
What diagram depicts the somatotopic organisation of the primary motor cortex?
Penfield’s Motor Homunculus
Describe the structure and function of the anterior corticospinal tract.
The anterior corticospinal tract is made up of the upper motor neurone axons coming from the primary motor cortex that do not decussate at the pyramidal decussation. These fibres cross the midline at the level of the spinal cord It controls proximal musculature.
Describe the structure and function of the tectospinal tract.
It originates in the superior colliculus (brainstem) Its function is not known but is most likely involved in reflexive turning of the head to orient to visual stimuli.
Describe the structure and function of the reticulospinal tract.
It originates in the reticular formation in the brainstem then goes down the spinal cord to innervate muscle. It is involved in complex actions: Orienting Stretching Maintaining a complex posture
Describe the structure and function of the vestibulospinal tract.
The lateral vestibulospinal tract originates at the lateral vestibular nucleus. The medial vestibulospinal tract originates at the medial vestibular nucleus. They mediate postural adjustments and head and eye movements
What is the function of the rubrospinal tract?
It is an alternative pathway that allows voluntary motor commands to be sent down the spinal cord meaning that the body can compensate for a lesion in the primary motor cortex. It also has a role in movement velocity.
Where does the rubrospinal tract originate?
Red nucleus of the midbrain
Describe the structure and function of the lateral corticospinal tract.
The lateral corticospinal tract originates in the primary motor cortex from the Betz cells. Their axons pass down through the brainstem and decussate at the pyramidal decussation in the medulla. It then passes down the spinal cord and synapses with a lower motor neurone. It goes onto control mainly the distal musculature. NOTE: 90% of axons from the primary motor cortex decussate at the medulla (these are the lateral corticospinal tract axons). The 10% that don’t decussate form the anterior corticospinal tract.
What is the function of each of these types of pathway?
Lateral Control of proximal and distal musculature Voluntary movements or arms and legs Medial Control of axial muscles Balance and posture
Which tracts fall into each of these types?
Lateral Lateral corticospinal tract Rubrospinal tract Medial Anterior corticospinal tract Reticulospinal tract Vestibulospinal tract Tectospinal tract
What are the two types of descending pathway?
Lateral and Medial