1. Introduction to motor systems
Domina Petric, MD

2. Introduction
Sceletal muscles are the effector systems for somatic motor system.
Lower motor neurons innervate sceletal muscles.
Upper motor neurons exist in the motor cortex and the brainstem.
The motor cortex is the posterior part of the frontal lobe: executive functions are integrating sensory, emotion, mnemonic signals and plans for the production of behavior.

3. Basal ganglia are concerned with gating proper initiation of movement.
Introduction
Upper motor neurons in the brainstem are involved in setting the stage for the execution of the voluntary movement.
Basal ganglia are concerned with gating proper initiation of movement.
Cerebellum is concerned with sensory motor coordination and ongoing movement.

4. Upper motor neurons (descending systems):
Basal ganglia: gating proper initiation of movement
Upper motor neurons (descending systems):
Motor cortex (planing, initiating and directing voluntary movements)
Brainstem centers (basic movements and postural control)
Cerebellum: sensory motor coordination and ongoing movement
Local circuit neurons: lower motor neuron integration
Motor neuron pools: lower motor neurons
Sensory inputs
Sceletal muscles

5. Ventral horn of the spinal cord
Laminae VII-IX: lower motor neurons.
Cervical enlargement: upper extremities.
Lumbosacral enlargement: lower extremities.
There is somatotopy in the ventral horn: in more medial parts of the ventral horn are the neurons that are supplying more proximal muscles of the extremity (for example, shoulder muscles of the hand).
More lateral in the ventral horn are neurons that supply more distal muscles of the extremity (for example, hand muscles).

6. Somatotopic organisation of the ventral horn

7. single alfa motor neuron
Motor unit
single alfa motor neuron
muscle fibers innervated by that sigle alfa motor neuron

8. Three types of motor units are:
Slow motor unit: generate less force slowly.
Fast fatigue resistant: generate significant amount of force more quickly.
Fast fatigable: generate much larger amount of force very rapidly.

9. Types of motor units
Slow motor unit can maintain its maximum amount of force production for a very long period of time.
Fast fatigue resistant motor unit can maintain its amount of force production for several minutes.
Fast fatigable motor unit generate the most force very quickly, but fatigue rapidly.

10. Fast fatigue resistant
The size principle
Fast fatigable
motor units are
the largest.
Slow motor unit
Standing
Fast fatigue resistant
Walking
Running
Fast fatigable
Jumping
Runing fast
Sequential progression

11. Literature
Leonard E. White, PhD, Duke University