NSCS 730

1. NSCS 730 Subconscious Motor Control Dr. Mark Kindy 503 - STB; 792-0559; kindyms@musc.edu 621 - Subconscious motor

2. Descending regulation of motor activity • All descending activity converges on a-motor neuron pools • Simplest control is by reflex connections • Voluntary motor control is by direct cortical pathways • Subconscious motor control is carried out by several pathways with connections in brainstem • All descending pathways use reflex interneurons Subconscious motor Voluntary motor Reflex connections 621 - Voluntary motor

3. Pathways arising in brainstem influence muscle tone and posture operate at subconscious level Pathways: (more medial projections than corticospinal) Reticulospinal Vestibulospinal Cerebellum influences tone & posture indirectly through these other systems Descending systems to regulate posture & tone 621 - Subconscious motor

4. All motor neuron lesions include paralysis Lower motor neuron lesions: injury to segmental (a) motor neurons Dysfunction may involve single muscle Muscle atrophy, wasting Tone and reflexes absent, flaccidity Fasciculation of muscle cells Upper motor neuron lesions: injury to higher order neurons or descending tracts Usually all muscles of a part of the homunculus Spasticity: especially in extensors (antigravity muscles) Lack atrophy & fasciculation Spasticity: increased tone and stretch reflexes Resistance to passive movement Clasp-knife, clonus Babinski’s sign Upper vs Lower Motor neuron lesions Upper Lower 621 - Subconscious motor

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7. Reticulospinal tracts (from brainstem reticular formation) important for regulating tone Strong influence on g-motor neurons Two systems have opposite effects which are normally in balance Medial reticular formation inhibits extensors Receives strong excitation from motor cortex lateral reticular formation facilitates extensors Lesions of corticospinal tracts leaves reticular influences unbalanced Extensor fascilitation, spasticity Reticular formation of brainstem affects tone 621 - Subconscious motor

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9. Spasticity Results from abnormally high g-motor input Resistance to passive movement, increased tone Especially for extensors Velocity dependent: rapid stretch - more resistance Hyperactive stretch reflexes Clasp-knife , clonus Altered plantar reflex: Normal adult toes ventroflex After upper MN injury toes dorsiflex and fan Babinski’s sign Spasticity - hypertonia, hyperreflexia 621 - Subconscious motor

10. Vestibular portions of inner ear: 3 semicircular canals Respond to angular acceleration Utricle & Saccule Respond to linear acceleration & gravity Membrane-lined fluid filled cavities in temporal bone Receptors are hair cells Depolarize when stereocilia are bent Specializations allow head movement to stimulate them Vestibular system 621 - Subconscious motor

11. Respond to angular acceleration 3 on each side Filled with fluid Perpendicular to each other Pairs of canals in same plane Semicircular canals 621 - Subconscious motor

12. Mechanism of stimulation: Hair cells located in ampulla - Gelatinous Cupula covers stereocilia During rotation of head in the plane of a canal: Fluid moves around canal Tilts the cupula; Stereocilia bent Afferents excited on one side & inhibited on the other Semicircular canals 621 - Subconscious motor

13. Vestibular portions of inner ear: 3 semicircular canals Respond to angular acceleration Utricle & Saccule Respond to linear acceleration & gravity Membrane-lined fluid filled cavities in temporal bone Receptors are hair cells Depolarize when stereocilia are bent Specializations allow head movement to stimulate them Vestibular system 621 - Subconscious motor

14. Respond to linear acceleration & gravity One of each on each side Utricle - macular surface horizontal Saccule - macular surface vertical Mechanism of stimulation: hair cells in macular surface Stereocilia covered by gelatinous matrix Otoliths embedded in gelatin Otoliths more dense than water Linear acceleration or gravity forces otoliths to move gelatin and bend stereocilia Utrical signals horizontal forces Saccule signals vertical forces Utricle and Saccule 621 - Subconscious motor

15. Vestibular portions of inner ear: 3 semicircular canals Respond to angular acceleration Utricle & Saccule Respond to linear acceleration & gravity Membrane-lined fluid filled cavities in temporal bone Receptors are hair cells Depolarize when stereocilia are bent Specializations allow head movement to stimulate them Vestibular system 621 - Subconscious motor

16. Afferent fibers relay through 4 vestibular nuclei 2 vestibulospinal tracts Lateral: receives much input from utricle and saccule Changes muscle tone in response to gravity Medial: receives much input from semicircular canals Causes movement of head and shoulders to coordinate head and eye movements Other vestibular pathways ascend to oculomotor nuclei- CN-III, IV, VI Cause eye movement in response to head rotation: Nystagmus Strong input to cerebellum Central vestibular connections 621 - Subconscious motor

17. Subject seated on stool and rotated to left Initial response (hard to visualize) Slow tracking eye movements to right Fast eye movements back to left Nystagmus: alternate slow and fast eye movement Response to stopping turning (post-rotatory) Head stops but fluid continues moving left Eyes track slowly left, quick movement to right Nystagmus normal for head rotation and repetitive moving object (optokinetic) Nystagmus without movement = sign of lesion Vestibulo-occular control Post-rotatory nystagmus 621 - Subconscious motor

18. attached to brainstem Elaborate cortex & deep nuclei Cerebellum Deep nuclei Cortex Compares sensory inputs with motor programs to correct and fine-tune movements 621 - Subconscious motor

19. Sensory inputs: Somatic - tactile, proprioceptors Vestibular Visual, auditory Motor input: From motor and premotor cortex Signals about the intended movement All inputs converge on cerebellar cortex Complex cortical processing All output is from purkinje cell axons to deep nuclei Deep nuclei compare cerebellar inputs with cortical output pattern, and relay error signals back to cerebral motor centers Cerebellar Input / Output 621 - Subconscious motor

20. No direct connections to a-motor neurons Output from cerebellum returns to motor areas of cortex to fine-tune motor programs Cerebellar Outputs thalamus Red nucleus 621 - Subconscious motor

21. Compares sensory inputs with motor programs to correct and fine-tune movements Signs of Cerebellar damage: Ataxia, unsteady gait and stance Intention tremor Dysmetria Asynergy Reduced muscle tone Function of cerebellum 621 - Subconscious motor

22. Large nuclei of forebrain below cerebral cortex Striatum Caudate nucleus putamen Globus pallidus Substantia nigra (dopamine cells) Receive wide cortical inputs Send output up to premotor areas to help organize stereotypic motor sequences Basal ganglia 621 - Subconscious motor

23. Dysfunctions: Excess movements Resting tremor Choreoform Athetoid ballistic Bradykinesia Absent or difficult initiation Rigidity Leadpipe or cogwheel Examples: Parkinson’s disease Loss of dopamine-containing cells of substantia nigra Resting tremor, leadpipe rigidity, bradykinesis Huntington’s disease X-linked genetic Degeneration of gaba-ergic & cholinergic cells of striatum Choreoform movements Mental deterioration Basal ganglia diseases 621 - Subconscious motor

24. Cerebral palsy • About 10 percent of children with cerebral palsy have athetoid cerebral palsy. Athetoid cerebral palsy is caused by damage to the cerebellum or basal ganglia. These areas of the brain are responsible for processing the signals that enable smooth, coordinated movements as well as maintaining body posture. Damage to these areas may cause a child to develop involuntary, purposeless movements, especially in the face, arms, and trunk. These involuntary movements often interfere with speaking, feeding, reaching, grasping, and other skills requiring coordinated movements. For example, involuntary grimacing and tongue thrusting may lead to swallowing problems, drooling and slurred speech. The movements often increase during periods of emotional stress and disappear during sleep. In addition, children with athetoid cerebral palsy often have low muscle tone and have problems maintaining posture for sitting and walking. 621 - Subconscious motor