Motor Systems Flashcards
Dorsal horn neurons
Sensory neurons
Ventral horn neurons
Alpha and gamma motor neurons
Preganglionic sympathetic fibers
Alpha motor neurons
Extrafusal (fast)
Gamma motor neuros
Intrafusal neurons (slow)
Ia sensory neurons
Muscle spindles (fast)
Ib sensory neurons
Golgi tendon organ (fast)
Spinal cord motor neurons have an somatotropic arrangement Anterior Posterior Medial Lateral
Anterior: Extensor muscles
Posterior: Flexors
Medial: Proximal muscle
Lateral: Distal limb muscles
Safety factor of motor neurons
1
In increase in force\contraction is caused by
Recruitment of more motor units
Three types of muscle fibers
Red (Type I)
White (Type II)
Intermediate
Which fibers fatigue easily
White fibers
Which fibers are fatigue resistant
Red fibers
Which fibers hold the greatest tension
White
Which fibers have the greatest contraction speed
White
Which fibers have the greatest aerobic metabolism
Red
Fatigue resistant white fibers are called
Intermediate fibers
As demand on a muscle increases, what order are muscle fibers recruited
Red, White & Intermediate
Function of deep tendon reflex
Triggers muscle contraction when a muscle is excessively stretched
At the same time, muscles that are antagonistic to the contraction are inhibited to allow contraction to take place
Deep tendon reflex pathay
1a sensory fiber travels to dorsal horn
Synapses with motor neuron that will result in contraction of overstretched muscle
Describe reciprocal inhibition pathway in the deep tendon reflex pathway
1a sensory fiber travels to dorsal horn
Synapses with a interneuron in the integration center
Interneuron synapses and inhibits a motor neuron that causes contraction in antagonistic muscle
2 mechanisms to activate intrafusal muscles
- Muscle contraction
2. Direct gamma motor neuron activation (gamma loop)
Muscle contraction mechanism
Muscle contraction results in gamma motor neuron contraction because muscle spindle will reach a new set point to match extrafusal muscle contraction
Gamma loop
activate just a few gamma motor neurons that will activate afferents that will then activate the other intrafusal muscle fibers
Function of inverse myotatic reflex\golgi tendon reflex
Relax (inhibitory) a muscle in response in response to excessive contraction
At the same time, muscles that are antagonistic to the contraction are stimulated to allow contraction in order to prevent contraction in the muscle undergoing excessive contraction
Pathway of inverse myotonic reflex
Sensory 1b neuron travels to dorsal horn
Synapses with an interneuron
The interneuron hyperpolarizes (inhibits) the motor neuron responsible for excessive contraction
Describe reciprocal excitatory pathway in the deep tendon reflex pathway
Sensory 1b neuron travels to dorsal horn Synapses with the interneuron Interneuron depolarizes (activates) the motor neuron of the antagonistic muscle
Function of the withdrawal reflex
Flexion in one limb is accompanied in the contralateral limb
Polysynaptic
Spacticity
Overactive gamma motor neuron
