Cerebral motor control Flashcards
What is the definition of functional segregation?
Different areas that control particular aspects of movements
What type of tracts are the corticospinal and corticobulbar tracts?
Pyramidal tracts (major descending)
What is the corticospinal tract responsible for?
motor pathway that carries efferent information from the cerebral cortex to the spinal cord.
voluntary movements of the limbs and trunk.
Where are the first order neurones located in terms of the corticospinal tract?
Primary motor cortex
What is the function performed by the corticobulbar tract?
Provides voluntary movements of body and face
What are the four types of extrapyramidal tracts?
1) Vestibulospinal
2) Tectospinal
3) Reticulospinal
4) Rubrospinal
Where is the primary motor cortex located?
Resides within the precentral gyrus anterior to the central sulcus.
What is the function performed by the primary motor cortex?
Such a cortex is responsible for controlling fine, discrete, precise voluntary movements and transmits descending signals to execute movements.
What is the function performed by the premotor cortex?
Concerned with movement planning and regulates externally cued movements
What area is responsible for planning internally cued movements?
Supplementary motor area
What structure is included in the midbrain?
Cerebral peduncles
Where do the majority of descending motor fibres decussate?
Medulla
What tract is formed from decussated upper motor neurone fibres?
Lateral corticospinal tract
What tract is formed from the ipsilateral upper motor neurone fibres?
Anterior corticospinal tract
Which muscles are innervated by the anterior corticospinal tract?
Trunk (axial) muscles
Which muscles are innervated by the lateral corticospinal tract?
Limb muscles
Who is the primary motor cortex arranged?
Somatopically
Which brainstem cranial nuclei are responsible for innervating the extra-ocular muscles?
Oculomotor, trochlear and abducens nerve
Where do the upper motor neurones synapse within the corticobulbar tract?
Synapse within the brainstem cranial nuclei
What structures are innervated by the facial nerve?
Muscles of the face
What structure is innervated by the hypoglossal nerve?
Tongue
What structures are innervated by the trigeminal nerve?
Muscles of mastication
Where are the lower motor neurones located within the extrapyramidal tracts?
Within the brainstem nuclei
Which extrapyramidal tract is responsible for stabilising the head during body movements, and coordinates with eye movements?
Vestibulospinal tract
What is the function of the vestibulospinal tract?
Stabilises head during body movements or as head moves. Coordinate head movements with eye movements and mediates postural adjustments.
What is the function of the reticulospinal tract?
Most primitive descending tract – from medulla and pons. Changes in muscles tone associated with voluntary movement and concerned with postural stability.
What is the function of the tectospinal tract?
From superior colliculus of midbrain. Orientation of head and neck during eye movements.
Where within the midbrain are the lower motor neurones arise from for the tectospinal tract?
Superior colliculus
Where do the lower motor neurones arise from for the rubrospinal tract?
Red nucleus of the midbrain
What is the function of the rubrospinal tract?
Innervates lower motor neurones of flexors of the upper limb. The corticospinal tract dominates rubrospinal activity.
What are the negative signs for a patient with an upper motor neurone lesion?
There is a loss of voluntary motor function
Paresis (graded weakness of movements)
Paralysis (plegia): Complete loss of voluntary muscle activity
What are the four main positive signs of an upper motor neurone lesion?
Spasticity: Increased muscle tone
Hyperreflexia: Exaggerated reflexes
Clonus: Abnormal oscillatory muscle contractions
Babinski’s sign
What is apraxia?
A disorder of skilled movement, patients are not paretic however lost information regarding how to perform skilled movements
Which cerebral lobe lesions are commonly associated with apraxia?
Lesion of inferior parietal lobe. Frontal lobe (premotor cortex and supplementary motor area)
Which motor areas are affected in apraxia?
Supplementary motor area (SMA) and premotor cortex
What are the most common causes of apraxia?
Strokes and dementia
Why do positive signs occur in an upper motor lesion?
Increased abnormal motor function due to loss of inhibitory descending inputs
Where do lower motor neurones reside?
Within cranial nuclei to corticobulbar tracts or within spinal cord for innervating limb muscles
What are the 6 main signs of a lower motor neurone lesion?
1) Weakness
2) Muscle wasting (atrophy)
3) Tongue fasciculations and wasting
4) Hypotonia (reduces muscle tone)
5) Hyporeflexia (reduced reflexes)
6) Fibrillations
What are fasciculations?
Damaged motor units produce spontaneous action potentials resulting in a visible twitch.
What are fibrillations?
Spontaneous twitching of individual muscle fibres; recorded during electromyography examination
What is another term used to describe motor neurone disease?
Amyotrophic lateral sclerosis
What is motor neurone disease?
Progressive neurodegenerative disorder of the motor system (upper and lower motor neurones)
What are the upper motor neurone signs in motor neurone disease?
- Spasticity (Increased tone of limbs and tongue).
- Brisk limbs and jaw reflexes
- Babinski’s sign: Palmar extension of the toes upon stimulation is indicative of a corticospinal tract lesion, a typical response is concerned with palmar flexion.
- Loss of dexterity
- Dysarthria (Difficulty speaking)
- Dysphagia (Difficulty swallowing).
What is Babinski’s sign?
Palmar extension of the toes upon stimulation is indicative of a corticospinal tract lesion, a typical response is concerned with palmar flexion.
Muscle atrophy is an example of what type of motor neurone lesion?
Lower motor neurone
Fasciculations is an example of what type of motor neurone lesion?
Lower motor neurone
Babinski’s sign is an example of what type of motor neurone lesion?
Upper motor neurone
What are the 7 main structures of the basal ganglia?
Caudate nucleus
Putamen
External globus pallidus
thalamus
nucelus accumbens
amygdala
anterior commisure
The subthalamic nucleus is associated with which other basal ganglia structure?
Globus pallidus
Which type of neurones are affected in Parkinson’s disease?
Dopaminergic neurones
Which basal ganglia structure is predominantly affected in Parkinson’s disease?
Substania nigra
The dopaminergic neurones originating in the substantia nigra project to which structure?
Striatum
What are the 5 main clinical presentations of Parkinson’s disease?
Bradykinesia
Hypomimic face
Akinesia
Rigidity (muscle tone increases, causing resistance to externally imposed joint movements)
Tremor at rest
What is bradykinesia?
Slowness of small movements
What is a hypomimic face?
Expressionless (absence of movements that normally animate the face).
What is akinesia?
Difficulty in the initiation of movements because cannot initiate movements internally
What type of neurones are affected in Huntington’s disease?
GABAergic neurones
Which basal ganglia structures are affected in patients with Huntington’s disease?
Striatum
Caudate
Putamen
What is the inheritance pattern of Huntington’s disease?
Autosomal dominant
What type of mutation is inherited in a patient with Huntington’s disease?
CAG repeat
What are the presenting symptoms in a patient with Huntington’s disease?
Choreic movements (chorea)- rapid jerky involuntary movements of the body hands and face a
Speech impairment
Difficulty swallowing (dysphagia)
Unsteady gait
Later stages, cognitive decline and dementia
Which part of the body is affected first by choreic movements?
Hands and face affected first, then legs
Which basal ganglia structure is associated with Ballism?
Subthalamic nucleus
What is ballism?
Sudden uncontrolled flinging of the extremities, symptoms occur contralaterally
Where is the cerebellum located?
Posterior cranial fossa
Which structure separates the cerebrum from the cerebellum?
Tentorium cerebelli
What is the main function of the cerebellum?
Coordinator and predictor of movement
Which cerebellum structure is associated the regulation of gait, posture and equilibrium?
Vestibulocerebellum
A tumour to the vestibulocerebellum can cause what type of symptoms?
Symptoms of vestibular disease leading to gait ataxia and tendency to fall
What is the function of the spinocerebellum?
Coordination of speech
Adjustment of muscle tone
Coordination of limb movements
A lesion to the spinocerebellum can lead to what?
Causes abnormal gait and stance (wide-based)
Affects mainly legs
Chronic alcoholism affects which part of the cerebellum?
Spinocerebellum
Which cerebellar region is the most lateral?
Cerebrocerebellum
What is the function of the cerebrocerebellum?
Coordination of skilled movements
Cognitive function, attention,
processing of language
Emotional control
A lesion to the cerebrocerebellum affects what?
Mainly affects arms/skilled coordinated movements (tremor) and speech.
What are the main signs of cerebellar dysfunction?
Ataxia
Dysmetria
Intention tremor
Dysdiadochokinesia
Scanning speech
What is dysmetria?
Inappropriate force and distance for target directed movements
What is intention tremor?
Increasingly oscillatory trajectory of a limb in a target-directed movement
What is dysdiadochokinesia?
Inability to perform rapidly alternating movements (rapidly pronating and supinating hands and forearms)
