lecture 10-spinal cord, brainstem, cortex control of motor function Flashcards
describe anterior motor neurons (efferents)
alpha motor neurons give rise to A alpha (A-alpha) fibers
describe interneurons
30X as numerous as anterior motor neuron. small and highly excitable. capable of spontaneous activity. responsible for most of spinal cord integrative function
describe a motor unit
composed of a single motor neuron and the muscle fibers it innervates. composed of extrafusal fibers
describe motor neuron pool
group of motor neurons that innervate fibers within the same muscle
describe recruitment in a motor neuron
refers to the increase in tension of muscle contraction by the activation of additional motor units (size principle)
describe small motor neurons
innervate a few muscle fibers, lowest threshold, fire first, generate smallest force
describe large motor neurons
innervate many muscle fibers, highest threshold, fire last, generate largest force
define renshaw cells
inhibitory cells in anterior horns of spinal cord
where do renshaw cells receive collateral branches from
alpha motor neurons
what does the transmission of inhibitory signals to surrounding motor neurons by renshaw cells result in
results in lateral inhibition and enhance fluidity of limb movement.
describe the muscle spindle
group Ia and II afferents. arranged in parallel with extrafusal fibers. detect both dynamic and static changes in muscle length
describe golgi tendon organ (muscle sensor)
group Ib afferents. arranged in series with extrafusal fibers. detect muscle tension.
describe pacinian corpuslces as muscle sensors
group II afferents. detect vibration
describe free nerve ends (muscle sensors)
groups III and IV afferents. detect noxious stimuli
what are muscle spindles innervated by
small gamma motor neurons (group II afferents)
how do muscle spindles run in comparison to extrafusal fibers
run parallel to them
describe the central region of spindle
has no contractile fibers; functions as a sensory receptor
what does stretching of central region of intrafusal fires stimulate
sensory fibers
what do muscle spindles detect
changes in muscle length
describe nuclear bag fibers
detect rate of change in muscle length. innervated by group Ia afferents and dynamic gamma efferents. multiple nuclei located in a central bag-like configuration
describe nuclear chain fibers
detect static change in muscle length. Innervated by group II afferents and static gamma efferents. more numerous than nuclear bag fibers. multiple nuclei arranged in a single row
what does stimulation of muscle spindle sensory fibers result from
lengthening of entire muscle. contraction of ends of itnrafusal fibers
what are muscle spindle gamma motor neurons coactivated with
alpha motor neurons
descirbe A gamma motor nuerons
supply small intrafusal fibers in middle of muscle spindle
descrie gamma-dynamic motor neurons
excite nuclear bag intrafusal fibers
describe gamma static motor neurons
excite nuclear chain intrafusal fibers
what brain areas control gamma fibers
bulboreticular region of brain stem, cerebellum, basal nuclei, cerebral cortex
describe the dynamic stretch reflex
signals transmitted from primary nerve endings, elicited by rapid stretch/unstretch, opposes sudden changes to muscle length
describe static reflex
transmitted by both primary and secondary endings, causes degree of muscle contraction to remain relatively constant
how are golgi tendon organs arranged in respect to extrafusal fibers
in series with them
what do golgi tendon organ detect
muscle tension
describe the circuitry of golgi tendon organ
type Ib afferent –> inhibitory interneuron –> anterior motor neuron
what does the anterior part of the premotor cortex develop
a motor image of the total muscle movement that is to be performed
what does the posterior motor cortex send signals to
primary motor cortex, basal nuclei and thalamus, primary motor cortex
where are pyramidal cells located in the motor cortex
5th layer
where are input signals located in the motor cortex
layers 2-4
where do upper motor neurons originate
cerebral cortex, cerebellum, brainstem
where do lower motor neurons begin
in CNS from anterior horns of spinal cord and from brainstem cranial nerve nuclei
