FCP
The lower motor neuron system
Motor nerves contain alpha motoneurons and....?
Gamma motoneurons
What are other names for the direct activation pathway?
Pyramidal tract
Direct motor system
Upper motor neuron system (UMN)
What are other names for the indirect activation pathway?
Extrapyramidal tract or indirect motor system
The relationship between alpha motoneurons involving synapses at the level of the spinal cord and brainstem
T/F: The FCP is the last link in the chain of neural events that lead to movement.
True
What is the stretch reflex?
In response to external forces, the gamma motor neurons induce an involuntary reflexive movement
What are the three characteristics of motor cortex organization (warning long answer)
1. Striated muscles are represented in an upside down fashion along motor strips
2. Number of motoneurons devoted to striated muscle is allocated according to degree to which fine control of voluntary movement is required
3. Motor cortex is organized in columns of neurons extending vertically from surface to deeper lays of cortex
What is the motor function role of the reticular formation?
Field of scattered cells lying between large nuclei & fiber tracts in the medulla, pons, and midbrain. It mediates consciousness and ascending sensory information & has complex effects on LMNs
Annoying questions... describe some effects of damage to a motor unit
Damage to a nerve may lead only to weakness/paresis if all the alpha motoneurons supplying the muscle are not damaged
Loss of innervation leads to atrophy
excess or spontaneous motor unit activity may be seen on surface of skin as brief localized twitches called fasciculations
muscles deprived of LMN input will generate slow repetitive action potentials and contract regularly; fibrillation
DAMAGE OF THE FCP (LMN LEVEL) LEADS TO FLACCID DYSARTHRIA
Where is the direct origin of the LMN (alpha motoneurons)
Brainstem or anterior horns of the spinal cord
The activity of gamma motoneurons is strongly influenced by...
cerebellum, basal ganglia, and indirect activation pathways
(in contrast to activities of alpha motoneurons which are more strongly tied to the Directions activation pathway)
T/F: Near the basal ganglia & thalamus, corona radiate converges into compact band known as the internal capsule (contains all afferent & efferent fibers projecting to and from the cortex)
True
What is the motor function role of the vestibular?
Located in floor of fourth ventricle in pons and medulla, receives sensory input from the vestibular apparatus of ear and from cerebellum. Project to brainstem, cerebellum and spinal cord.
Paired CN that supply muscles involved in phonation, resonance, articulation, and prosody
Paired spinal nerves involved in respiratory activities
What are motor units?
Muscle fibers innervated by LMN
Gamma motoneuron is the efferent component of the gamma motor system; how does firing react with the muscle spindle?
the contractile parts of the muscle spindle to contract (shorten) which lengthens the elastic part of the muscle spindle
What are the three major divisions of the internal capsule?
Anterior limb, genu, and posterior limb
What is the motor function role of the red nucleus?
Overall mass of cells in midbrain tegmenjtum (corticorubral tract & rubrospinal tract)
Describe the effects of damage of the UMN (DAP)
Unilateral UMN lesions can produce a relatively mild dysarthria (unilateral UMN dysarthria)
Bilateral UMN lesions produce spastic dysarthria
How do Alpha motoneurons (LMN) also innervated interneurons (Renshaw cells)?
Through collateral fibers from the axons of alpha motoneurons
Tell me what happens to the spindle if a muscle is stretched by movement (warning long answer)
This stretch of the spindle is detected by the sensory ending (annulospinal ending) and a signal is transmitted to the spinal cord/brainstem where the alpha motoneuron is led to fire
This stimulates extrafusal muscle fibers to contract. This process of contraction resists the stretch on muscle. (basis for normal muscle tone)
DAP originating in the left hemisphere innervates CN and SN on the right (contralateral side) or both sides of the body. DAP innervation of the speech CN is primarily bilateral except for....?
Tongue (CN XII) and lower face (CN VII) ~ they are innervated primarily by contralateral (opposite side) corticobulbar fibers
What is the function of the indirect activation pathway?
Regulate reflexes and maintain posture, tone and associated activities to support direct activation pathway in speech movements of smooth speech, range and direction.
What are the effects of damage to the IAP?
Lesions affect muscle tone and reflexes