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Dr. SaadKlemanAbd
]MOTOR SYSTEMS, POSTURE, SOMATIC SENSATION, [
2. Voluntary: sometimes initiated without any obvious stimulus, often complex and varied,
requires conscious will.
Note: voluntary and involuntary are not separate systems, since they involve shared
effectorsorgans and pathways, and interact with each other
C. Effector Structures
1. skeletal muscle: regular skeletal muscle fibers
2.neurons innervating skeletal muscle fibers:
 spinal cord: alpha motor neuronsin ventral horn, innervating muscles of movement
andposture
 cranial nerves: motor nuclei in the brainstem controlling;
1) Eye movement
2) Mastication (chewing)
3) Muscles of facial expression
4) Muscles of the soft palate and larynx
5) Muscles supporting the head
6) Tongue muscles
D. Influences on Motor Neurons (Motoneurons);
1. Reflexes: simple, stereotyped, involuntary movements (e.g. flexion reflex, myotatic
reflex)
2. Brain stem nuclei (tone)
3. Brain stem pattern generators: more complex movements, oftenvoluntarily initiated (e.g.
chewing, swallowing, walking)
4. Motor cortex; essential for voluntary activity
5.cerebellum(coordination, balance, posture/tone)
6. Basal ganglia (elaboration of movement & suppression of unwanted movements)
SPINAL CONTROL OF MOVEMENT
There are three inputs to alpha motor neurons
1. Upper motor neurons from the cortex or brainstem
are important mediators of voluntary movements and
are mainly inhibitory in nature.
2. Spinal interneurons may be excitatory or inhibitory .
3. Sensory neurons from muscle proprioceptors
provide feedback about muscle length and tension.
PROPRIOCEPTORS:
 Sensory information about body position and its relationship to the environment is
relayed from the vestibular, visual, and auditory systems, and is conveyed via three
major tracts:
2