The Motor System. Chapter 8. Overview. The motor system is divided into 4 components: Direct activation pathway Control circuits Indirect activation pathway Final common pathway. Direct activation pathway Largest, best-defined motor pathway
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Corticobulbar fibers occupy a more anterior location in the posterior limb than the corticospinal
Knowledge of the clinical manifestations of the diseases affecting the direct activation pathway comes from experimental studies and from observation of clinical disorders.
Disturbances of the corticospinal system may be irritative (positive) or paralytic (negative).
Clinical Correlations: irritative vs. paralytic
Jacksonian seizures – focal motor seizures starting from the distal upper extremity spreading proximally
Weakness – fine movements, skilled movements (distal muscles); no atrophy; presence of Babinski sign and primitive reflexes (upper motor neuron manifestations)
learned, automatic behavior
preparing and maintaining the background support or posture needed for voluntary motor activity
Anatomy and Physiology
caudate nucleus, lentiform nucleus (putamen, globus pallidus), substantia nigra, subthalamic nucleus
striatum=caudate nucleus + putamen
striatum neurotransmitters: acetylcholine, dopamine (produced in the substantia nigra and transported to striatum via the nigrostriatal pathway)
excess discharge slowing (hypokinesia)
lack of discharge hyperactivity (involuntary movements)
hypokinetic – quiet, weak, monotonous voice, poor articulation, short rushes of words, breathy quality
hyperkinetic – bursts of loudness, elevation of pitch, voice stoppages, distortion of vowels, disintegration of articulation
coordination and correction of movement errors of muscles during active movements
neurotransmitters: glutamate, GABA
Flocculonodular lobe connected with the vestibular nuclei through the inferior cerebellar peduncle
Controls and coordinates axial musculature and movements of the head and eyes
Made up of vermis and paravermis
Its primary input is from dorsal spinocerebellar tract (via the inferior cerebellar peduncle) and the ventral spinocerebellar tract (via the superior cerebellar peduncle) which provide information about motor performance and motor neuron excitability, respectively.
Made up of the lateral portions of the cerebellar hemispheres and receives inputs from pontine nuclei via the middle cerebellar peduncle
The output is from the dentate nucleus through the superior cerebellar peduncle
This subdivision is important in initiation of movement and in coordination of muscles (specifying direction, pattern, and intensity of movement)
Motor unit – a lower motor neuron (ventral horn cell/CN nucleus) + muscle fibers under its control
alpha motor neuron
Final common pathway – many motor units through which all activities in the motor system must act