Motor Pathways Flashcards
What is meant by the term motor-system heirachy?
Explain the principle
- Several systems with different tasks are involved in a movement
- The tasks in each system are differently complex going from high complexity = high heirachy (Motor cortex) to low complexity = low heirachy (e.g. corticospinal tract)
Where is the primary motor cortex located?
It is located just anteriorly to the central sulcus
What is the function of the primary motor cortex?
It controls + initiates voluntary fine, discrete and precise movements
–> Sends out signals to decending tracts to execute movements
Explain the somatotopic organisation in the primary motor cortex
It looks like a homunculus upside down: feet + legs are more medially, face is more laterally
Explain the route of the Lateral corticospinal tract
- Neurons emerge from primary motor cortex
- Run down brain in internal capsule
- Decussate in the Medulla
- Run down in contralateral corticospinal tract
- Leave the corticospinal tract at level of inntervation + enter the anterior horn
- Synapse in the anterior horn onto lower motor neuron
Explain the route of hte anterior corticospinal tract
- Originate in primary motor cortex
- Run dowin in internal capsule
- enter the medulla on ipsilateral side
- Enter the anterior corticospinal tract at ipsilateral side
- Leave the anterior cortiocospinal tract and Decussate at level of insertion
- Synapse in the Anterior Horn onto 2nd order neurons
What is the function of the corticospinal tracts?
They convey voluntary movement to the
- Anterior corticospinal tract
- Axial muscles (neck movement and thoracic muscles, intercostal muscles)
- Lateral corticospinal tract
- the rest of the body
What is a corticobulbar pathway?
Pathways for motor neurons of cranial nerves
Explain the Corticobulbar tract
- Emerge from head reagion in primary motor cortex
- Travel in internal capsule
- Synapse in nucleus of cranial nerve in brainstem
- Emerge as cranial nerves
Where is the premotor cortex located?
Anterolaterally to the primary motor cortex
What is the function of the premotor cortex?
Planning of movement, requires:
- Knowledge + understanding the intra-personal space (where musces/body parts are in relation to one another)
- Knowlledge of extrapersonal space –> Where the body is in relation to the environment
Where is the Supplementory Motor area located?
Anteromedially to the primary motor cortex
What is the function of the supplementary motor cortex?
- Planning of complex movements and + sequencing movements
- Regulation of internal movements (e.g. speech)
–> area that is active when thinking about a movement
What is the Association cortex?
Which parts are involved in it and what is their function?
Area of the brain that do play a role in movement but not directly involved in output etc
-
Posterior parietal cortex
- Motor learning + planning–> movements are accurately targeted in external space
- Prefrontal cortex
- Selection of appropriate movements
- adds personality to movements –> when having touched a hot plate before you are not likely to do it again
What is a lowe motor neuron?
Motor neuron after synapse
In spinal chord, Brain stem
What is an upper motor neuron?
Motor neuron before synapsing
In corticospinal/corticobulbar tracts
What does pyramidal in relation to motor pathways mean?
Referes to the Lateral corticospinal tract
What does Extrapyramidal in relation to motor function mean?
Basal ganglia, cerebellum
Paresis
Graded wekness of muscle
Paralysis /Plegia
complete loss of muscle activity
Spacticity
increased muscle tone
Hyper-reflexia
exaggerated reflexes
Clonus
abnormal oscillatory muscle contraction
What is…?
Graded wekness of muscle
Paresis
What is…?
complete loss of muscle activity
Paralysis /Plegia
What is…?
increased muscle tone
Spacticity
What is…?
exaggerated reflexes
Hyper-reflexia
What is…?
abnormal oscillatory muscle contraction
Clonus
Which signy would you expect to see on someone with a upper motor neuron lesion?
Loss of function (negative signs):
- Paresis: graded weakness of movements
- Paralysis (plegia): complete loss of muscle activity
Increased abnormal motor function (positive signs) due to loss of inhibitory descending inputs:
- Spasticity: increased muscle tone
- Hyper-reflexia: exaggerated reflexes
- Clonus: abnormal oscillatory muscle contraction
Babinski’s sign
What is the Babinski’s sign?
Abnormal extension of the big toe and flexion of the other toes in response to an external stimulus
Can be sign of Upper Motor neuron lesion
What is Appraxia?
Disorder of skilled movement
- No Paresis but forgot/don’t know how to perform movements (e.g. getting dressed)
When apprexia is present, where is a lesion normally present?
What are the most commonest causes?
In the inferior parietal lobe or in the frontal lobe (Premotor cortex, supplementary motor area)
–> Most common cause: dementia + stroke
What are the symptoms for a lower motor neuron lesion?
- •Weakness
- •Hypotonia (reduced muscle tone)
- •Hyporeflexia (reduced reflexes)
- •Muscle atrophy
- •Fasciculations: damaged motor units produce spontaneous action potentials, resulting in a visible twitch
- •Fibrillations: spontaneous twitching of individual muscle fibres; recorded during needle electromyography examination
What is Motorneuron disease?
Progressive neurodegenerative disorder of the motor system –> Upper and lower motor neurons
- Spectrum of disorders with many causes + genetic loci
- Most prominent: Amyotrophic Lateral Sclerosis (ALS)
Tendency to pregression from distal to proximal
What are the symptoms of Motor neuron diseases
Spectum of diseases with Combined upper + lower motor neuron symptoms
Upper motor neuron signs
- Increased muscle tone (spasticity of limbs and tongue)
- hyper-reflexia of limbs and jaw reflexes
- Babinski’s sign
- Loss of dexterity (fine movent)
- Dysarthria (disorders of speech)
- Dysphagia
Lower motor neuron signs
- Weakness
- Muscle wasting
- Tongue fasciculations and wasting
- Nasal speech
- Dysphagia
Which structures are part of the basal ganglia?
- Caudate nucleus
- Lentiform nucleus (putamen + external globus pallidus)
- Subthalamic nucleus
- Substantia nigra
- Ventral pallidum, claustrum, nucleus accumbens, nucleus basalis of Meynert
What is the patophysiology of Parkinson’s disease?
Nerodegeneration of dopaminergic neurons originating in the substantia niagra and projecting into the striatum
What are the symptoms of Parkinsons disease?
First symptoms: Motor symptoms
- Bradykinesia
- slowness of (small) movements (doing up buttons, handling a knife)
- Hypomimic face
- expressionless, mask-like (absence of movements that normally animate the face)
- Akinesia
- difficulty in the initiation of movements
- Rigidity
- muscle tone increase, causing resistance to externally imposed joint movements
- Tremor at rest
- 4-7 Hz, starts in one hand (“pill-rolling tremor”); with time spreads to other parts of the body
Explain the patophysiology of Huntingons Disease
•Degeneration of GABAergic neurons in the striatum, (= caudate and putamen)
–> genetic autosomal dominant disease
What are the major symptoms of Huntingtons disease?
Choreic movements (Chorea)
- rapid jerky involuntary movements of the body; hands and face affected first; then legs and rest of body
Speech impairment
Difficulty swallowing
Unsteady gait
Later stages, cognitive decline and dementia
Explain the route of information in the cerebellum
2 Main input ways
- Inferior olive projects to pukinje cells via climbind fibres
- Input to granule cells via mossy fibres –> then go onwards via parrallel fibres
1 output way
- Via the purkinje cells in the deep nuclei
Explain the layered structure of the Cerebellum
It has three layers
- Molecular layer (very few cells)
- Prirform layer (Purkinje cells –> mainly processing cells, recieve a lot of input)
- Granular layer (small neurons included in processing of information)
What are Choreic movements (Chorea)?
rapid jerky involuntary movements of the body; hands and face affected first; then legs and rest of body
–> typically observed in Huntintons
What is Akinesia?
difficulty in the initiation of movements because cannot initiate movements internally
What is Rigidity?
muscle tone increase, causing resistance to externally imposed joint movements
Where is the vestibulocerebellum located?
What is its function?
Regulation of gait, posture and equilibrium
Coordination of head movements with eye movements
Vestibulocerebellum
Where is the spinocerebellum?
What is its function?
- Coordination of speech
- Adjustment of muscle tone
- Coordination of limb movements
Gets input from spinal chord
•Cerebrocerebellum
•Spinocerebellum
What is the cerebrocerebellum?
What is its function?
Coordination of skilled movements
Cognitive function, attention,
processing of language
Emotional control
What are the main symptoms of cerebellar dysfunction?
Deficits apparent only upon movement
Ataxia
- General impairments in movement coordination and accuracy. Disturbances of posture or gait: wide-based, staggering (“drunken”) gait
Dysmetria
- Inappropriate force and distance for target-directed movements (knocking over a cup rather than grabbing it)
Intention tremor
- Increasingly oscillatory trajectory of a limb in a target-directed movement (nose-finger tracking)
Dysdiadochokinesia
- Inability to perform rapidly alternating movements, (rapidly pronating and supinating hands and forearms)
Scanning speech
- Staccato, due to impaired coordination of speech muscles
Where would you suspece someone to have a lesio when presenting with the following symptoms?
•Damage (tumour) causes syndrome similar to vestibular disease leading to gait ataxia and tendency to fall (even when patient sitting and eyes open)
Vestibulocerebellar Syndrome
–> Vestibulocerebellum
Where would you suspect someone to have a lesion when presenting with following symptoms
•Damage (degeneration and atrophy associated with chronic alcoholism) affects mainly legs, causes abnormal gait and stance (wide-based)
Spinocerebellar syndrome
Where would you suspece someone to have a lesio when presenting with the following symptoms?
•Damage affects mainly arms/skilled coordinated movements (tremor) and speech
Cerebrocerebellar or Lateral Cerebellar Syndrome
What is the striatum?
Part of the basal ganglia consisting of
- caudate and
- putamen
What is the lentiform nucleus?
It is part of the basal ganglia and conists of the
- Putamen (more laterally) and
- external globus Pallidus
Explain the signal circuit of the Basal ganglia
- The cerebral cortex sends information to the the Striatum
- There it can go 2 routes
- Direct (– > Globus pallidus internal and Substantia niagra) –> Exitory
- Indirect (–> Globus Pallidus External –> Subthalamic Nuclei —> Globus Pallidus internal) –> Inhibitory
- The two pathways are modulated by the nigro-striatal pathway
- Go to Thalamus
- Back to the cortex to the supplementary Motor Area (SMA)
What is the role of the infeiror cerebellar peduncle?
input from spinal cord to spino-cerebellar tracts
What is the role of the middle cerebellar peduncles?
Connect the cerebellum to pons
What is the role of the superior cerebellar peduncles?
main output pathway going up the basal ganglia and thalamus
