569 Neuroscience Mt III

569 Neuroscience Mt III True/False statements about spinal cord and muscle function: 1. Spinal cord: general function: The spinal cord has fundamental circuitry for activating muscles, regulating muscle activity with feedback, and coordinating basic muscle patterns. It provides direct control over muscle function. (True) 2. Motor cortex/brainstem: general function: These regions provide the brain with access to spinal control for both voluntary and automatic movements, thereby exerting direct control over muscles. (True) 3. Basal ganglia: general function: The basal ganglia reinforce patterns of activity in the motor cortex related to purposeful actions. However, they do not exert direct control over muscles; their function is modulatory. (False) 4. Cerebellum: general function: The cerebellum implements internal models that optimize movement control by correcting errors. Like the basal ganglia, its function is modulatory and does not involve direct control over muscles. (False) 5. In adulthood, a single motor neuron: Originates in the motor neuron pool, exits the ventral root, and innervates a muscle fiber. This process is characteristic of motor unit function and is true. (True) 6. Proximal muscles in the ventral horn: Are more medial, while distal muscles are more lateral. This anatomical arrangement is true. (True) 7. All muscle fibers in a motor unit: Have the same fiber type. This uniformity is true for motor units. (True) 8. Steady force-generating capacity of a muscle fiber: Depends on the firing rate of an alpha motor neuron. This statement accurately reflects the control mechanism of muscle force production. (True) 9. Fast motor units: Produce more force and reach steady-state force production more quickly compared to slow motor units. This statement is true regarding the different properties of motor units. (True) T/F: fast motor units are less responsive to neural input ️false T/F: fiber type is the only factor that influences contraction speed ️false (e.g. Ca2+ reuptake) as development occurs, what happens to muscle contraction time? what functional implication does this have (in the study we learned about)? what is the likely physiologic reason for this? ️muscle contraction time decreases (muscle gets faster) allows improved dynamic manipulation (squishing spring) likely due to Ca2+ reuptake mediated by the protein parvalbumin T/F: according to the size principle, smaller motor units are activated first ️true increases in muscle force come from what two things? ️increased recruitment (greater # of MUs) increased firing rate of a motor unit 5HT in the spinal cord ️when awake, 5HT is released onto a-MNs to set the overall excitability of the cell 5HT binding results in persistent inward currents (Ca2+, Na+) with low 5HT input, what happens to the a-MN? what about with high 5HT input? ️cell depolarizes, but doesn't reach threshold or fire spikes cell depolarizes, reaches threshold, and spikes; additionally, once 5HT is removed, the cell continues to spike without descending input from the brain= *plateau potential* paralysis after SCI is due in part to what? ️depriving motor neurons of 5HT spasticity after SCI is likely due to what? ️motor neurons adapt to increase their activity by expressing a different isoform of 5HT receptors this promotes constitutive activity (activity even if 5HT is not present) T/F: blocking constitutive activity reduces spasticity, but baclofen, a GABA agonist, is more effective ️false (blocking constitutive activity does reduce spasticity, GABA part is wrong) why do alpha and gamma MNs need to be stimulated together for muscle spindle function? ️gamma MN stimulation keeps intrafusal fibers taught and responsive to changes in length