Motor

• Motor system


  Part of the nervous system that controls voluntary movement
• Motor system


  • Consists of the brain, spinal cord and nerves that connect these structures to the effector muscles
  • The human body has about 600 skeletal muscles, which produce movements at body joints
  • The brain gives commands to the muscles through nerves
• Motor pathway

  1. Upper motor neuron

  2. Lower motor neuron
• Cerebellum and basal ganglia

  • Involved in the motor system by coordinating complex movements such as walking or running and maintaining balance
• Lower motor neuron syndrome

  Damage or disease at the level of the alpha motor neurons in the spinal cord and brain stem
• Symptoms of lower motor neuron syndrome

  • Effects limited to small groups of muscles
  • Muscle atrophy
  • Weakness
  • Fasciculation
  • Fibrillation
  • Hypotonia
  • Hyporeflexia
• Upper motor neuron syndrome

  Damage to any part of the motor system hierarchy above the level of alpha motor neurons
• Symptoms of upper motor neuron syndrome

  • Effects extend to large groups of muscles
  • Atrophy is rare
  • Weakness (paresis)
  • Absence of fasciculations
  • Absence of fibrillations
  • Hypertonia
  • Hyperreflexia
  • Clonus
  • Initial contralateral flaccid paralysis
  • Spasticity
  • Positive Babinski sign
• Apraxia


  Impairments in motor planning and strategies, and inability to perform complex motor tasks. Constructional apraxia is a neurological condition where individuals have difficulty with tasks that require spatial organization, such as assembling blocks to match a structure. dressing apraxia (inability to dress oneself) and verbal apraxia (inability to coordinate mouth movements to produce speech).
• Paralysis


  Damage to the spinal cord results in paralysis of all parts of the body below the damaged region. it is not considered a lower motor neuron disorder. If the damage occurs at the cervical level, then all four limbs will be paralyzed (quadriplegia). If the damage occurs below the cervical enlargement, then only the legs are paralyzed (paraplegia). hemiplegia (paralysis to one side of the body) and monoplegia (paralysis of a single limb).
• Dyskinesias


  Abnormal, involuntary movements associated with basal ganglia disorders
• Types of dyskinesias


  • Resting tremors
  • Athetosis
  • Chorea
  • Ballismus
  • Tardive dyskinesia
• Akinesias


  Abnormal, involuntary postures associated with basal ganglia disorders
• Types of akinesias


  • Rigidity
  • Dystonia
  • Bradykinesia
• A number of well-known movement disorders are associated with basal ganglia dysfunction, including Parkinson's disease, huntington’s disease, and hemiballisimus.
• Rigidity


  Resistance to passive movement of the limb that does not depend on the speed of the passive movement
• Lead-pipe rigidity


  Resistance to moving the patient's limb that feels like bending a lead pipe
• Cogwheel rigidity


  Rigidity coupled with tremors, where moving the limb feels like the catching and release of gears
• Mechanism of rigidity


  May result from continuous firing of alpha motor neurons causing a continual contraction of the muscle
• Dystonia


  Involuntary adoption of abnormal postures, as agonist and antagonist muscles both contract and become so rigid that the patient cannot maintain normal posture
• Bradykinesia


  Slowness or poverty of movement
• A number of well-known movement disorders are associated with basal ganglia dysfunction
• The 3 most well-understood movement disorders are Parkinson's disease, Huntington's disease, and hemiballismus
• Parkinson's disease


  Results from the death of dopaminergic neurons in the substantia nigra pars compacta, characterized by a resting tremor and severe bradykinesia or akinesia
• The cause of Parkinson's disease is still not known, but an animal model was discovered by accident when drug addicts taking MPTP developed Parkinsonian symptoms
• How Parkinson's disease causes poverty of movement

  Loss of nigrostriatal dopaminergic pathway upsets the balance of excitation and inhibition in the basal ganglia, reducing excitation of motor cortex and interfering with the ability to generate voluntary movement commands
• Treatments for Parkinson's disease


  1. Dopa to replenish dopamine, pallidotomy, deep brain stimulation of the subthalamic nucleus
• Huntington's disease


  Genetic disorder caused by an abnormally large number of CAG repeats on chromosome 4, resulting in death of indirect pathway neurons in the striatum and characteristic choreiform movements
• There is no cure or effective treatment for Huntington's disease
• Why Huntington's disease causes dyskinesias

  Loss of indirect pathway neurons in the striatum removes inhibition of motor cortex, leading to involuntary movement commands
• Hemiballismus


  Unilateral lesion to the subthalamic nucleus, usually from a stroke, resulting in ballistic movements on the contralateral side of the body
• Unlike basal ganglia, damage to the cerebellum does not result in lack of movement or poverty of movement, but rather impairments in movement coordination
• Ataxia


  General term for impairments in movement coordination and accuracy from cerebellar damage
• Disturbances of posture or gait from cerebellar lesions

  Loss of fine-control mechanisms that translate vestibular signals into precise muscle contractions to maintain balance, resulting in abnormal gait and stances
• Decomposition of movement from cerebellar damage

  Inability to coordinate the activity and timing of multiple muscle groups, performing movements in serial rather than a fluid, coordinated fashion
• Dysdiadochokinesia


  Inability to perform rapidly alternating movements, due to lack of coordination in timing of antagonistic muscle contractions
• Scanning speech


  Staccato, disjointed speech of cerebellar patients from difficulty coordinating speech muscles
• Intention tremor


  Increasingly oscillatory trajectory of a cerebellar patient's limb in a target-directed movement
• Delay in initiating movements

  Cerebellar patients take longer to initiate movements, as they must actively plan sequences that are effortless for normal individuals
• Cerebellar patients also demonstrate subtle cognitive deficits, such as impaired ability to estimate time intervals