Neuro ana doc D

• 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
• Upper motor neuron


  Nerve in the central nervous system from which the command originates
• Motor pathway


  Upper motor neuron travels to brainstem or spinal cord, synapses with lower motor neuron, lower motor neuron axon travels to target tissue
• 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


  Characteristic set of symptoms resulting from damage to alpha motor neurons
• Symptoms of lower motor neuron syndrome

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


  Set of symptoms resulting from 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
  • Babinski sign
• Apraxia


  Impairment in motor planning and strategies, inability to perform complex motor tasks
• Paralysis


  Resulting from spinal cord damage, not considered a lower motor neuron disorder as alpha motor neurons are not directly damaged
• Types of paralysis


  • Quadriplegia (all four limbs)
  • Paraplegia (only legs)
  • Hemiplegia (one side of body)
  • Monoplegia (single limb)
• Extrapyramidal disorders


  Motor deficits resulting from basal ganglia damage, divided into dyskinesias (abnormal involuntary movements) and akinesias (abnormal involuntary postures)
• Dyskinesias


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


  • Rigidity
  • Dystonia
  • Bradykinesia
• Parkinson's disease


  Results from death of dopaminergic neurons in substantia nigra pars compacta, characterized by resting tremor and severe bradykinesia/akinesia
• Rigidity


  A resistance to passive movement of the limb that does not depend on the speed of the passive movement. In some patients, this resistance is so great that it is referred to as lead-pipe rigidity, because moving the patient's limb feels like bending a lead pipe. In some patients, this rigidity is coupled with tremors and is called cogwheel rigidity, as moving the limb feels to the clinician like the catching and release of gears. The mechanism is not entirely understood, but may result from continuous firing of alpha motor neurons causing a continual contraction of the muscle.
• Dystonia


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


  A slowness, or poverty, of movement.
• A number of well-known movement disorders are associated with basal ganglia dysfunction
• The three most well-understood movement disorders associated with basal ganglia dysfunction 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. It is characterized by a resting tremor, but the most debilitating symptom is severe bradykinesia or akinesia. In advanced cases, patients have difficulty initiating movements, although involuntary, reflexive movements can be normal. It is as if the loss of the substantia nigra neurons has put a brake on the output of motor cortex, inhibiting voluntary motor commands from descending to the brain stem and spinal cord.
• The cause of Parkinson's disease is still not known, but much has been learned in the past 15 years from the development of an animal model of Parkinson's disease. This model was discovered by accident when a number of young patients presented with symptoms remarkably similar to Parkinson's disease. These patients were drug addicts who had been taking an artificially manufactured drug called MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyradine). This drug destroyed the dopaminergic neurons in the substantia nigra, leading to a Parkinsonian disorder.
• There is no cure for Parkinson's disease, but a number of effective treatments exist
• 1. Dopa


  A chemical precursor to dopamine that was used to replenish the supply of dopamine in Parkinson's disease patients, resulting in profound improvements in symptoms. However, the improvement is temporary and symptoms typically return after a number of years.
• Pallidotomy


  Surgical intervention involving making lesions to the globus pallidus internal segment, which has shown effectiveness in some Parkinson's disease patients.
• Deep brain stimulation of the subthalamic nucleus


  A new therapy for Parkinson's disease where an electrical stimulator is implanted in the subthalamic nucleus. When the electrical current is turned on, the patient's symptoms disappear immediately. The reason this procedure works is not fully understood, but one thought is that the stimulation might actually overload the subthalamic nucleus, thereby inhibiting it and disinhibiting the thalamus.
• Huntington's disease


  A genetic disorder caused by an abnormally large number of repeats of the nucleotide sequence CAG on chromosome 4. It is an autosomal dominant mutation, such that the offspring of a patient with Huntington's disease has a 50% chance of inheriting the mutation. The affected gene codes for a protein known as huntingtin, the function of which is not known. The effect of the mutated version of the gene is to kill the indirect pathway neurons in the striatum, particularly those of the caudate nucleus.
• Huntington's chorea


  Huntington's disease is also known as Huntington's chorea because it is characterized by a continuous, choreiform movements of the body (especially the limbs and face). In addition, the disease in advanced stages is associated with dementia.
• Hemiballismus


  Results from a unilateral lesion to the subthalamic nucleus, usually caused by a stroke. This lesion results in ballismus on the contralateral side of the body, while the ipsilateral side is normal. The involuntary, ballistic movements result from the loss of the excitatory subthalamic nucleus projection to the globus pallidus. Because the globus pallidus internal segment normally inhibits the thalamus when excited, the loss of the subthalamic component lessens the inhibition of the thalamus, making it more likely to send spurious excitation to the motor cortex.
• Unlike the basal ganglia, damage to the cerebellum does not result in lack of movement or poverty of movement. Instead, cerebellar dysfunction is characterized by a lack of movement coordination. Also unlike basal ganglia (and motor cortex), damage to the cerebellum causes impairments on the ipsilateral side of the body.
• Ataxia


  A general term used to describe the general impairments in movement coordination and accuracy that accompany cerebellar damage. There are two major forms: disturbances of posture or gait result from lesions to the vestibulocerebellum, and decomposition of movement results from the loss of the cerebellum's ability to coordinate the activity and timing of many muscle groups to produce smooth, fluid movements.
• Dysmetria


  Refers to the inappropriate force and distance that characterizes target-directed movements of cerebellar patients. For example, in attempting to grab a cup, they may move their hand outward with too much force or may move it too far, with the result of knocking over the cup instead of grabbing it.
• Dysdiadochokinesia


  Refers to the inability of cerebellar patients to perform rapidly alternating movements, such as rapidly pronating and supinating the hands and forearms. This diagnostic sign results from the lack of the cerebellum's ability to coordinate the timing of muscle groups, alternately contracting and inhibiting antagonistic muscles, to produce the rhythmic movements.
• Scanning speech


  Refers to the often staccato nature of speech of cerebellar patients. The production of speech is a motor act, as muscles of the jaw, tongue, and larynx need to work in unison to produce words and sounds. Cerebellar patients have difficulty in coordinating these muscle groups appropriately, and therefore their speech tends to be slow and disjointed.
• Hypotonia


  A symptom of cerebellar damage characterized by a decreased, pendulous myotatic reflex, as the decreased muscle resistance tends to cause the limb to swing back and forth after the initial reflex contraction.
• Intention tremor


  Refers to the increasingly oscillatory trajectory of a cerebellar patient's limb in a target-directed movement. For example, the hand will start out on a straight path toward the target, but as it gets closer, the hand begins to move back and forth, and the patient must slow down the movement and very carefully approach the target. This tremor contrasts with the resting tremor of Parkinson's disease, which disappears when the movement is made.
• Nystagmus


  An oscillatory movement of the eyes, resulting from damage to the vestibulocerebellum. Recall that one function of the cerebellum is to fine-tune the gain of the vestibuloocular response. Damage to the cerebellum can disrupt this circuitry, resulting in a continuing oscillation of the eyes.
• Delay in initiating movements


  Cerebellar patients take longer to initiate movements, often because they must actively plan sequences of movements that are performed effortlessly by normal individuals.
• In addition to movement disorders, cerebellar patients also demonstrate subtle cognitive deficits, such as an impaired ability to estimate time intervals.