NEUROSCIENCE: Somatic Motor System


A. Functions

1. Posture: maintain appropriate body position against external forces
2. Movement: change of body position to accomplish desired act
3. Coordination: control pattern and sequence of muscle contraction for smooth, effective action

B. Initiation of Function

1. Involuntary: motor act, initiated by specific internal or external stimulus, generally stereotyped, need not involve conscious volition

2. Voluntary: sometimes initiated without any obvious stimulus, often complex and varied, requires conscious volition

Note: voluntary and involuntary are not separate systems, since they involve shared effector organs and pathways and interact with each other

C. Effector Structures

1. skeletal muscle: regular (extrafusal, ordinary) skeletal muscle fibers

D. Vocabulary

tone: muscle tension in the absence of voluntary activity
hypertonia: increased muscle tone compared to normal
hypotonia: reduced muscle tone compared to normal
dystonia: tonically rigid posture (also called "rigidity")

asthenia: weakness, loss of strength
paresis: partial loss of voluntary control
paralysis: complete loss of voluntary control
-plegia: paralysis (suffix)
paraplegia: paralysis of the lower half of the body
hemiplegia: paralysis of one side of the body
quadriplegia: paralysis from the neck down

apraxia: loss of fine movement control

hyperreflexia: increased reflex response compared to normal ("brisk")
hyporeflexia: reduced reflex response compared to normal ("sluggish")

areflexia: no reflex response
clonus : oscillating response (contractions & relaxations) of a somatic reflex

tremor: small, involuntary oscillatory movement