Neural Control of Posture and Locomotion Flashcards
What do anticipatory postural control systems do?
Anticipatory postureal control systems prepares the body in advance for changes in body position via the reticulospinal tract, vestibulospinal tract, and uncrossed corticospinal tract
What sensory input do feedback mechanisms respond to?
Feedback mechanisms respond to motion that has already occured–sensory information includes muscle spindles and Golgi tendon organs.
Describe the somatotopic organization of the lateral motor system.
The lateral motor system involves the lower motor neurons, spinal interneurons, crossed corticospinal tract, and the rubrospinal tract.
The more lateral the motor neuron is located, the more lateral the muscle it innervates.
Describe the somatotopic organization of the medial motor system.
The medial motor system consists of lower motor neurons, spinal interneurons, uncrossed corticospinal tract, and reticulospinal/vestibulospinal tract.
Which regions of the brainstem are responsible for influencing posture and balance?
The vestibular nuclei via the vestibulospinal tract
The pontine and medullary reticular formation motor nuclei via the reticulospinal tract
Their projections converge onto many of the same spinal interneurons that participate in spinal reflex actions
What is the purpose of feedforward and feedback circuits with respect to postural stability?
Feedforward circuits help anticipate a postural change by contracting relevant muscle groups before the change occurs. Feedback circuits respond to an unanticipated change to regain postural stability.
What are the two phases of the step cycle? Which muscle groups contract during each? Can contraction of muscles of the same type overlap either temporally or in a simultaneous pattern? Do opposite limbs show an overlapping pattern during either phase?
The extensors contract during the stance phase and the flexor muscles contract during the swing phase. Muscles of the same type that cause contraction at the three leg joints contract in a temporally overlapping but not simultaneous pattern. The opposite limbs show an overlapping pattern only during the stance phase.
What control of locomotion occurs at the level of the spinal cord? What kind of supra-spinal cord control exists?
The central pattern generator is a rhythmic motor network that generates locomotion and is located in the same spinal segments that contain the motor neurons that innervate limb muscles. The CPG can function in the absence of descending and ascending inputs.
Descending projections from the brainstem regulates the CPG (initiation, modulation, termination) by reticulospinal pathways (as well as by sensory feedback from sensory structures). This input is not rhythmic but it induces rhythmic output from the CPG.
Give the important feature of CPG circuitry organization (hint: interneurons)
CPG organization involves reciprocal inhibition betweeh functional antagonists (i.e. extensor and flexor CPG modules)
Where is the locomotor CPG in the spinal cord?
Medial aspect of the intermediate zone
Describe the pathway for descending control of the spinal locomotor CPG.
The cortex signals to the Mesencephalic Locomotor Region (MLR) which projects to the pontine and medually reticular formation where they activate neurons that project down the spinal cord in the reticulospinal tract. These RST neurons activate spinal locomotor CPG to generate the rhythmic pattern for walking.
The motor cortex also projects to the cerebellum about intended movements while the spinal cord projects back to the cerebellum regarding actual movements. This leads to adjustment of activity as necessary.
How is the speed and pattern of CPG output regulated?
The spinal locomotor CPT self organizes to generate the appropriate pattern based on the intensity of unpatterned input from the mesencephalic locomotor region. Increase in stimulus strength leads to stronger activation of neurons in the pontine and medullary reticular formation and therefore increased signaling to CPG.
How is visual input processed during locomotion?
Visual information projects to the motor cortex which projects down through the corticospinal tract. This acts in parallel with descending locomotion activating systems to regulate the strength of steps in response to visual input.
