10 Motor Disorders Flashcards
overview of the motor system
- frontal cortex and premotor areas: action planning and initiation
- motor cortex: voluntary motor execution
- basal ganglia: action learning and kinematic control
- cerebellum & thalamus: sensory error adaptation
- brainstem: autonomic motor control and routing
- spinal cord: integration and maintenance of voluntary and autonomic motor control
- skeletal muscles: force generation and motor execution
corticospinal tract / pyramidal system
- upper motor neurons originate in motor cortex
- descend through internal capsule
- pass through midbrain and pons
- decussate (cross over) at the medullary pyramids
- travel down the spinal cord
- synapse with lower motor neurons in spinal cord segments
- cervical segment: controls arms and hands
- thoracic segment: controls trunk
- lumbosacral segment: controls leg and feet
causes and results of damage to motor neurons
upper motor neurons:
- pathological signs: spastic paralysis, hyperreflexia, presence of pathological reflexes (e.g. Babinski sign), clonus, increased muscle tone
- causes: stroke, multiple sclerosis, cerebral palsy
lower motor neurons:
pathological signs: flaccid paralysis, muscle atrophy, fasciculations, decreased muscle tone and reflexes
- causes: polio, peripheral nerve injury, amyotrophic lateral sclerosis (initial stage)
Facial palsy / Bell’s palsy
viral inflammation of cranial nerve VII (= LMN)
- sudden, temporary weakness or paralysis of muscle tone on one side of the face
- cause: multifactorial, herpes simplex virus
- symptoms: dropping of eyelid and corner of mouth, loss of facial expression, decreased tear and saliva production
- recovery often spontaneous
- treatment: corticosteroids reducing inflammation
Amyotrophic lateral sclerosis (ALS)
combined upper and lower motor neuron degeneration
- average onset age: 55 (40-70), men slightly more often affected
- loss of motor neurons in cortex, brainstem and spinal cord
- symptoms: fasciculations, cramps, limb weakness, slurred speech, difficulty swallowing
- progression: begins focally and then spreads, death after 3-5 years due to respiratory failure
hemiplegia
- upper motor syndrome
- weakness or paralysis of one entire side of the body
stroke
- strokes causing motor symptoms are typically ischemic or hemorrhagic
- interruption of blood flow leads to neuronal death in areas like motor cortex, basal ganglia or internal capsule
- sudden onset of hemiparesis or hemiplegia often accompanied by facial muscle weakness
- long-term effects: spasticity, muscle stiffness, contractures
- motor recovery can occur, especially within 6 months
- rehabilitation focuses on regaining motor skills, functional independence
spinal cord injury
- combined upper and lower motor neuron disruption
- completed (no sensory or motor function preserved in sacral segments S4-S5) vs. incomplete (partial preservation of sensory or motor functions below the level of injury)
- common effects: paralysis (quadriplegia/tetraplegia or paraplegia), loss of sensation, dysregulation of autonomic functions)
subcortical and extrapyramidal motor systems - purpose
- facilitate and modulate voluntary motor functions and automated movements
- ensure precision, coordination, and timing of muscle activity
subcortical and extrapyramidal motor systems - structures
- Basal Ganglia: involved in movement selection, initiation, kinematics and motor learning
- Thalamus: Integration of motor information from Cerebellum, basal ganglia and sensory systems before it reaches the cortex
- Cerebellum: Error correction in motor movements, timing, precision, and coordination.
- Brainstem: Contains motor nuclei and integrates autonomic and spinal motor signals for automatic function (e.g. breathing and walking)
extrapyramidal tracts
Modulators and teachers for motor control
- Rubrospinal Tract: Originates from the red nucleus, primarily facilitates flexor muscles and inhibits extensor muscles
- Tectospinal Tract: Mediates reflex postural movements of the head in response to visual stimuli
- Vestibulospinal Tracts (Lateral and Medial): Regulate head balance, body posture, and muscle tone in response to vestibular input
- Reticulospinal Tracts (Medial and Lateral): influence voluntary and reflex control of the muscles, particularly those responsible for maintaining posture and balance
Cerebellum as a comparator
sensory monitoring and motor adaptation
- Cerebellum compares intended movement with actual performance
- Adjusts motor output to improve accuracy and coordination.
- Corticospinal Tracts: Carry motor commands from cortex to muscles
- Spinocerebellar Tract: Sends sensory feedback to cerebellum
- Inferior Olive: Sends a copy of motor commands to cerebellum for comparison with actual performance
- Error Correction: Cerebellum adjusts ongoing movement to reduce discrepancies
- Cerebellar damage results in uncoordinated and erratic movement (ataxia).
- cerebellum likely has generalizable computational function across domains
Huntington’s disease
hyperkinetic movement disorder with striatal degeneration (basal ganglia)
- genetic neurodegenerative disorder
- neuronal degeneration, particularly in the striatum and cerebral cortex
- motor symptoms: choreiform movements (involuntary, jerky movements that are hallmark features), dystonia (sustained muscle contractions causing twisting and repetitive movements), Bradykinesia and rigidity in later stages
- cognitive symptoms: gradual decline in executive function, memory, and processing speed, difficulty in multitasking, planning, and decision-making
- psychiatric manifestations: depression, irritability, apathy, and anxiety, in later stages, symptoms may include psychosis and severe behavioral changes
dystonia
involuntary muscle contractions
- sustained or intermittent muscle contractions causing abnormal, often repetitive, movements or postures
- abnormal activity in the basal ganglia-thalamo-cortical circuits, cerebellum, and sensory motor pathways
- can be task-specific, such as in writer’s cramp, or present in a more generalized form.
Parkinsonism
syndrome with stereotypical hallmarks
- motor symptoms: Bradykinesia, resting tremor, muscle rigidity, and postural instability
- non-motor symptoms: cognitive impairment, mood disorders, autonomic dysfunction, sleep disturbances, and sensory symptoms
- pathophysiology: loss of dopaminergic neurons in the substantia nigra pars compacta and the presence of Lewy bodies are characteristic in idiopathic Parkinson’s disease.
- circuit effects: Disruption of basal ganglia circuits leads to an imbalance in direct and indirect pathways, affecting movement regulation
