Exam 2 week 8 ppt 8 Intro to Somatic Motor System Flashcards
What are motor systems defined as?
–All structures of the central and peripheral nervous systems (CNS and PNS) that contribute to motor activity
Define Upper motor neuron
–Upper motor neuron
- Projects to lower motor neuron
- Located in motor cortex or brainstem
- Indirectly in Cerebellum & basal nuclei
As discussed previously Upper motor neuron are those motor system neurons that Project to lower motor neurons. These are located in motor cortex, Also as previously discussed upper and lower motor neurons are defined by their connections not their position in the nervous system. For instance upper motor neurons of the pontomedullary junction (vestibular nuclei) can innerate lower motor neurons of the midbrain (oculomotor nucleus neurons)
Define lower motor neuron
–Lower motor neuron
- §Projects directly to skeletal muscle
As discussed previously Upper motor neuron are those motor system neurons that Project to lower motor neurons. These are located in motor cortex, Also as previously discussed upper and lower motor neurons are defined by their connections not their position in the nervous system. For instance upper motor neurons of the pontomedullary junction (vestibular nuclei) can innerate lower motor neurons of the midbrain (oculomotor nucleus neurons)
Components/paths (general) of motor systems & pathways: (4)
- Origin from the upper motor neurons
- Descending pathway – with decussation in some pathways
- Synapse on a lower motor neuron
- The efferent fibers of the lower motor neuron are the only connection between the CNS and PNS
Two things that Motor systems include;
Include
- Neuromuscular junction
- Circuitry to plan, program, coordinate, and modulate the descending motor pathways
More about UMNs (2)
- •Projections that descend to converge on alpha lower motor neurons
- •Originate from many higher motor centers
What are the higher motor centers that UMNs originate from?
- Cerebral Motor Cortex
- Brainstem nuclei
As a higher motor center where UMNs orgiginate, what is the cerebral motor cortex responsible for?
§Responsible for voluntary movement
As a higher motor center where UMNs orgiginate, what are the brainstem nuclei responsible for? (4)
- Influencing voluntary movement,
- Posture
- Muscle tone
- Regulation of reflexes
Name the motor tracts that are included in the prominent motor descending pathways? (5)
- Corticospinal
- Reticulospinal
- Vestibulospinal
- Tectospinal
- Rubrospinal
another name for corticospinal tract
pyramidal tract
do motor tracts go ipsilaterally or contralaterally?
–Some decussate,
some ipsilateral &
some bilateral
In descending Decussated pathways: are s/s contralateral or ipsilateral if the damage is rostral to the decussation?
Contralateral
In descending Decussated pathways: are s/s contralateral or ipsilateral if the damage is caudal to the decussation?
ipsilateral s/s
What are two distinct types of LMNs?
- –Alpha (a) motor neurons – cause voluntary muscle contraction
- –Gamma (g) motor neurons – specialized to control gain of muscle receptor (muscle spindle)
what type of LMN is considered the final common pathway?
•alpha-motor neurons - the final common pathway
–ONLY connection to skeletal muscle
Where are cell bodies of LMNs?
•Cell bodies in CNS nuclei
- –Anterior horn of spinal cord
- –Cranial nerve nuclei of brainstem
Where do LMN axons go?
•Axons leave CNS to innervate striated skeletal muscle cells
can a single motor neuron innervate more than one muscle cell?
yes
Single motor neuron can innervate multiple muscle cells
what is the term used for a single lower motor neuron and all of the muscle cells it innervates?
Motor Unit
What is the pattern of LMN activity and muscle contraction dependent on?
the pattern of excitatory & inhibitory inputs to LMNs
What is a neuromuscular junction?
A speciallized synaptic ending where LMN communicates with the muscle cell
also called hte motor end plate
what happens at a Neuromusclular junction? (two more specific steps)
- –Cholinergic receptors produce end-plate potentials
- –Creates action potentials in skeletal muscle cells to produce contraction
Somatic Motor Systems: Complexity (3)
- •Modulation of UMN systems by thalamus, basal ganglia, and cerebellum
- •Topographical organization of cortical motor areas, descending fibers, and nuclei
- •Parallel operations – UMNs exert simultaneous influences on the final common pathway
Modulation of UMN systems can occur by the action of thalamus, basal ganglia, and cerebellum. Just as we saw in sensory systems, there is a Topographical organization of cortical motor areas, descending fibers, and lower motor nuclei. There are Parallel operations of upper motor neurons exert simultaneous influences on the final common pathway of the lower motor neurons
