Motor Systems Flashcards
What do lower motor neurons innervate?
skeletal muscles (provide motor innervation to the contractile elements in the muscle
Where are the lower motor nueron cell bodies located in?
1) ventral horn of spinal cord gray in lamina IX of rexed
2) brainstem in motor nuclei of cranial nerves
Where do lower motor neurons send axons out of the CNS in?
1) Ventral rootlets of all spinal nerves
2) All cranial nerves except I, II & VIII
What do the lower motor neurons innervate?
skeletal muscle cells
What do lower motor neurons serve as a link between?
CNS and somatic effector cells
What are lower motor neurons known as?
final common pathway neurons
In general, what controls lower motor neurons?
Motor control areas of the brain and the brain stem by various kinds of sensory inputs that come in at sensory segmental levels
What are the parts of the brain and brainstem that influence lower motor neurons known as?
supranuclear motor control areas
Where do some of the supranuclear motor control areas send axons to terminate on?
Lower Motor Neurons
What do the fibers of the supranuclear motor control areas that send axons to terminate on lower motor neurons form?
Descending motor control pathways
What are the pathways of the neurons of the descending motor control called?
Upper motor Neurons
What do Upper Motor Neurons exert influence on?
Lower Motor Neurons
What can influence the activity of the lower motor neurons?
Direct sensory input at a segmental level
In the spinal cord what can modify the activity of lower motor neurons?
somatosensory and visceral information that enters the cord segmentally
What do the modification of lower motor neuron activity by somatosensory and visceral information form?
form the basis of spinal cord reflexes
Can sensory input to the brain areas from cranial nerves active reflex responses involving lower motor neurons of cranial nerves?
yes
What are the two major types of lower motor neurons?
Alpha motor neurons
Gamma motor neurons
What do the major types of lower motor neurons comprise in the spinal cord?
Cell bodies that comprise lamina IX in the spinal cord and cranial nerve motor nuclei in the brainstem
what fibers are part of the alpha motor neurons?
A-alpha fibers
Where are the alpha motor neuron axons found?
Spinal cord or brainstem in spinal or cranial nerves
What do alpha motor neurons provide innervation to?
Extra fusal muscle fibers in skeletal muscle
Do alpha motor neurons innervate one or several extra fusal fibers?
Many extra fusal fibers are innervated by a single alpha motor neuron
What make up a motor unit?
An alpha motor neuron and the muscle fibers it supplies
What type of neurons are gamma motor neurons?
Fusimotor neurons
Which are larger, alpha motor neurons or gamma motor neurons?
Alpha motor neurons
What type of axon fibers are gamma motor neurons?
Group A gamma fibers
What do gamma motor neuron fibers exit and via what means?
Exit spinal cord and brain via spinal & cranial nerves
What do gamma motor neurons provide innervation to?
Intrafusal muscle fibers in a neuromuscular spindle
Where are neuromuscular spindles found?
in skeletal muscle
How are alpha and gamma motor neurons arranged in the ventral horn?
Somatopically arranged
Where are Lower motor neurons that innervate muscles of the trunk located?
Medially in the ventral horn
Where are Lower motor neurons that innervate extremity located?
Positioned laterally in the ventral horn
List the pathway of motor neurons
Upper motor neurons -> descending motor control pathways -> influence lower motor neurons (as ventral spinal tract, medial lateral fasciculus, tectospinal and tectobulbar tracts) -> skeletal muscle cells (via spinal nerves of certain cranial nerves
