Neuromotor System Flashcards
The basal ganglia is involved in voluntary motor movements and procedural learning, as well as forming habits, emotion, and cognition - to where does it almost exclusively project its signals?
thalamus
type of muscle fiber that is innervated by alpha motor neurons and generates tension by contracting, thereby moving skeletal elements
extrafusal muscle fiber
a collection of all motor neurons that innervate a single
muscle is called a what?
motor pool
type of muscle fiber that is embedded in main muscle fibers that is involved in proprioception and facilitating muscle tone
intrafusal muscle fiber (muscle spindle)
these neurons terminate on the contractile end portions of muscle spindle fibers and take part in the process of muscle contraction, representing about 30% of fibers going to muscle
gamma (γ) motor neurons (fusimotor system)
muscle spindle fiber that contains cell nuclei jumbled together in the middle, and in response to stretch encodes the rate of change (velocity) of muscle length
nuclear bag fiber
muscle spindle fiber that contains cell nuclei aligned in a single row, and in response to stretch conveys information about static length of the muscle
nuclear chain fiber
what type of information do type Ia afferent spindle fibers provide the CNS?
muscle length and velocity (they wrap around both nuclear chain and nuclear bag fibers)
what type of information do type II afferent spindle fibers provide the CNS?
only immediate muscle length information (they do not innvervate nuclear bag fibers, which convey information about muscle velocity)
restoring tautness to muscle spindles following stretch is achieved via coactivation of alpha and gamma neurons by what system?
corticospinal system (and other supraspinal systems)
Muscle tone is fine-tuned by tonic discharge of
gamma motor neurons activated by what brainstem pathways?
reticulospinal and vestibulospinal
states that increases in the rate of action potentials of
motor neurons allows for as much as a 4-fold increase in muscle force (from single twitch to fused tetanic contraction)
rate code
states that with increasing strength of input, motor neurons are recruited from smallest (fewer ion
channels) to largest (most ion channels).
size principle
_____ sized neurons innervate fast-twitch, fatigue resistant fibers (for normal movements)
medium
____ sized neurons innervate fast-twitch, fatigable
fibers (for bursts of energy)
large
____ sized neurons innervate slow-twitch fibers (for
postural control)
small
in the ventral horn, ____ groups of motor neurons innervate flexors while _____ groups innervate extensors.
dorsal; ventral
in the ventral horn, _____ groups of motor neurons innervate axial (proximal) muscles while ______ groups
innervate more distal muscles
medial; lateral
the intermediate zone of the spinal cord is heavily populated by propriospinal neurons, which are the major players in these networks, responsible for complex stereotypic movements involving multiple muscle groups
central pattern generators
True or false: in most spinal cord injuries involving central pattern generators, the problem is degradation of the CPG network.
False. usually the problem is loss of command signal by supraspinal inputs (ie, corticospinal system) necessary to voluntarily activate pattern generators for stereotypic movements
regulate stereotypic movements of the head (ie, swallowing, respiration, chewing, saccadic eye movements)
brainstem central pattern generators
maintenance of upright posture by constant, automatic corrections of axial and limb muscles is based on control of what kind of neurons that increase tone?
gamma motor neurons
descending motor pathway whose fibers pass through the posterior limb of the internal capsule; involved in individual muscle control, facilitation of flexors, and CPG command
corticospinal system
descending motor pathway whose fibers pass through the genu of the internal capsule; primary function is to control voluntary movements of the eyes, jaw muscles of facial expression, swallowing and voice modulation, and tongue mobility
corticobulbar system
True or false: most fibers of the corticospinal/bulbar systems contact alpha motor neurons directly.
False. Only 20% directly contact alpha motor neurons; the rest contact interneurons in the intermediate zone (corticospinal) and pontine/medullary reticular formation (corticobulbar)
Why is it that unilateral corticobulbar lesions usually produce no clinical effect?
Most CN motor nuclei receive bilateral corticobulbar inputs (with the exception of the facial and hypoglossal nuclei, which receive mainly crossed input from the opposite motor cortex)
descending pathway that originates in the red nucleus, whose presence and function is only clinically significant during decerebrate and decorticate rigidity
rubrospinal system
descending pathway that is involved in postural control, regulation of muscle tone, and CPG coordination
reticulospinal system
the pontine (medial) reticulospinal tract facilitates extensor muscle activity to _______ muscle tone, while the medullary (lateral) reticulospinal tract suppresses extensor activity to ____ muscle tone.
increase; decrease
While the corticospinal tract is thought to activate CPGs,
this tract is heavily involved in integrating the motor systems for coordination of automatic locotomor movements.
reticulspinal tract
the descending system that is involved in reflexive head turn toward or away a visual or auditory stimulus
tectospinal tract
descending lateral and medial pathways that target intermediate zone and medial motor neurons that maintain upright posture (vestibulo-spinal reflex) and maintain head in upright position (vestibulo-collic reflex; ends at T1)
vestibulospinal tracts
two systems that together function in postural control through facilitation of extensors, as well as coordination of head, neck, and axial spine movements
vestibulospinal and tectospinal systems
