Motor 1 Describe the overall organization of neural structures involved in the control of movement EXAM THREE MATERIAL a CONFUSED WITH THIS b first need to locate the baseball through eyes and the visual cortex pathway I think there are connections between V1 and M1 then through corticospinal tract or cerebellum for motor movement then lower MNs c Local spinal cord and brainstem circuits d Descending modulatory pathways e Upper motor neurons send input to the LMNs and their circuits They receive input from the cerebellum and the basal ganglia They are responsible for voluntary control posture balance and proprioception f Basal Ganglia involved with gating proper initiation of movement via sending the go signal g Cerebellum sensory motor coordination of ongoing movement h Lower motor neurons send axons out of the brainstem and spinal cord to innervate the skeletal muscles of the i error signal head and body i Local circuit neurons receive sensory inputs as well as descending projections from higher centers j major source of synaptic input to the lower motor neurons 1 Ventral Horn Organization are on the lateral part of the VH a The most proximal part of the limb is located most centered in the ventral horn of the spinal cord Distal limbs 2 Motor cortex composed of They all send input to the Each responsible for a The medial and lateral premotor cortexes and the motor cortex b All send input down the lateral corticospinal tract c The medial premotor cortex internal stimuli and cues d The lateral premotor cortex the external stimuli and cues e The motor cortex more of the voluntary movements 3 The lateral corticospinal tract a First goes down the midbrain pons crosses over in the medulla down the ventral horn of the spinal cord goes to the LMNS a Start in the motor cortex mibrain pons crossover in the medulla use the cranial nerves to move the facial 4 The corticobulbar tract muscles 5 Want to link the muscle movements and the motor cortex a Use monkey have the monkey perform a certain movement and use electrodes to record from the muscle and also from the area of the motor cortical neuron associated with that muscle b Have the monkey perform the task and record the EMGs c d Find that there is a fixed latency between the AP in the muscle and also in the single cortical neuron Direct connection between the motor cortex and the muscle doing action 6 Finer motor control due to the a More synapses not a larger number of MNs 7 Want to see the responses of cortical neurons to muscle movements a give a monkey a joystick and record from a single cortical neuron as the monkey moves the joystick in different directions see that there a preferential AP firing increases and decreases depending on the direction find that different cortical neurons have different amounts of AP firing rates depending on direction overall have a population vector that will have an overall direction similar to the direction of the joystick movement see that when the monkey moves all the cortical neurons have some kind of response whether it be excitatory or inhibitory population of neurons in response to any movement the motor cortex is organized more based on the movement of the muscle not simply by muscle organization b c d e f 2 What are the two major systems that modulate the flow from upper motor neurons to lower motor neurons resulting in the activation of skeletal muscles a Cerebrum acts to correct errors of movement by comparing movement commands from the cortex with sensory feedback b Basal ganglia involved in planning and initiation of complex movements 3 Describe how motor neurons are organized a Each lower motorneuron innervates a single muscle called a motorneuron pool are grouped together into rod shaped clusters that run parallel to the long axis of the cord for one or more spinal cord segments 4 What are the different types of motor units Describe the order in which they are recruited a Slow fatigue resistant motor units slower very resistant to fatigue generate very little force i last the longest able to keep going for long periods of time walking b Fast fatigue resistant motor units can generate more force than slow fatigue resistant motor units but can not do so for a long time i more force but fatigue faster gallop i Tire very fast sprint c Fast fatigable motor units generate a lot of force but can only act for a very short period of time d Motor units are recruited in order increasing size force for some movements so that slow fatigue are recruited first then fast fatigue resistance then fast fatigable i Recruitment is inversely related to force to give a gradual build up of force ii Allows a smooth precise control for a wide range of forces to be generated 5 How does the nervous system control muscle contraction a Recruiting the right types of motor units for a task i Recruitment is based on the necessary force that needs to be generated b Varying the action potential frequency within those motor units by controlling the rate of AP s firing in the motor neurons 6 Describe the series of events that happen when you lift up a mug with an increased load a The sensory receptor initiates the stretch reflex b Stretching a muscle spindle leads to increased activity in afferents and an increase in the activity of alpha motor c Afferents also excite the motor neurons that innervate synergistic muscles and inhibit the motor neurons that neurons that innervate the same muscle innervate antagonists d The stretch reflex operates as a negative feedback loop to regulate muscle length e y motor neurons innervate specialized muscle fibers that in combination with the nerve fibers that innervate them are actually sensory receptors called muscle spindles i regulate sensory input by setting the intrafusal muscle fibers to an appropriate length f Muscle spindles are embedded within connective tissues capsules in the muscle g The muscle fibers are also innervated by sensory axons that send information to the brain and spinal cord about h the length and tension of the muscle alpha motor neurons innervates the extrafusal muscle fibers which are the striated muscle fibers that actually generate the forces needed for posture and movement 8 Mug reflex unexpected tension a Have the mug get a little more filled the afferent sensory fibers have mechanoreceptors that sense this change in tension send signal to the ventral horn of the spinal cord make synapses with the alpha fibers direct and depolarize muscle contracts and