1. 08b Direct (Pyramidal) Motor Systems (Associated with material in Chapter 16) 08b Direct (Pyramidal) Motor Systems (Associated with material in Chapter 16)

2. Overview of the motor systems Extrapyramidal systems Extrapyramidal systems –Brainstem to spinal cord (indirect activation) –Feedback loop to direct system via basal ganglia Cerebellar system Cerebellar system –Feedback loop to direct system via cerebellum Pyramidal systems (direct activation) Pyramidal systems (direct activation) –corticospinal –corticonuclear (corticobulbar)

3. Structural components of motor system Cerebral cortex Cerebral cortex Subcortical nuclei of the cerebrum: Basal ganglia Subcortical nuclei of the cerebrum: Basal ganglia –putamen, caudate, globus pallidus, subthalamic nucleus and substantia nigra Brainstem (  PNS) Brainstem (  PNS) Cerebellum Cerebellum Spinal cord (  PNS) Spinal cord (  PNS)  PNS  Peripheral mechanism  PNS  Peripheral mechanism

4. Component of motor system: Cortex Pre-frontal association cortex (“executive function”= planning, reasoning, problem solving) Responsible for deciding when to move/act, and when not to. Pre-frontal association cortex (“executive function”= planning, reasoning, problem solving) Responsible for deciding when to move/act, and when not to. Limbic association cortex (emotion) provides input to pre-frontal cortex Limbic association cortex (emotion) provides input to pre-frontal cortex Posterior parietal cortex synthesizes two inputs, to make sense of where body is relative to other objects. Input from Posterior parietal cortex synthesizes two inputs, to make sense of where body is relative to other objects. Input from –Primary somato-sensory cortex –Visual cortex of occipital lobe Output of posterior parietal cortex and pre- frontal cortex sent to pre-motor cortex, so details of the desired movement can be programmed there. Output of posterior parietal cortex and pre- frontal cortex sent to pre-motor cortex, so details of the desired movement can be programmed there. Output of pre-motor cortex goes to primary motor cortex, where the direct motor pathway starts (cell bodies of start of efferent pathway are here) Output of pre-motor cortex goes to primary motor cortex, where the direct motor pathway starts (cell bodies of start of efferent pathway are here)

5. Cranial nerves (PNS) have associated nuclei in the brainstem (CNS), which are organized in columns/clusters in the brainstem. Nuclei are groups/clusters of _____________ in the ______________. This is where _____________ occur. Cranial nerves are made of axons. In the motor system, the cell bodies associated with these axons are found in the _________________ of the brainstem. The motor neuron is the final common pathway for motor impulses to the muscles (effectors) of the face/head. Component of motor system: Brainstem and associated cranial nerves

6. Components of the motor system: Spinal cord and associated spinal nerves The central gray matter of the spinal cord is made up of _____________. This is where _____________ occur. Spinal nerves are made of axons. In the motor system, the cell bodies associated with these motor neurons are found in the _________________ of the spinal cord, ____________ horns. The motor neuron (alpha motor neuron) is the final common pathway for motor impulses to the muscles (effectors).

7. Now that we’ve looked at (re- visited) the structural components that make up the direct, pyramidal motor systems, let’s look more closely at these systems. Remember: Contrast the direct system with the indirect pathways and basal ganglia feedback look (which are extra pyramidal) and the cerebellar feedback loop, which were covered in the previous lecture.

8. Pyramidal systems (direct) Corticospinal Corticospinal Corticonuclear (corticobulbar) Corticonuclear (corticobulbar)

9. Whole bundles of axons course together in pathways, like those you see in the illustration above. Do you see the locations of synapses? Where is the efferent (motor) pathway? How many synapses are there in this pathway? How many bundles/groupings of neurons make up the pathway? Example of pathways

10. In pyramidal (direct activation) pathways, the pathway is generally made up of two sets of neurons that convey the efferent impulses caudally Upper motor neurons (1 st order neurons of the motor pathway) Upper motor neurons (1 st order neurons of the motor pathway) –multipolar neuron which functions as interneuron –cell bodies are in primary motor cortex (pre-central gyrus) –axons descend ….synapse to lower motor neurons (2 nd order neurons of the motor pathway): Multipolar neurons which function as motor neuron (alpha motor neuron) ….synapse to lower motor neurons (2 nd order neurons of the motor pathway): Multipolar neurons which function as motor neuron (alpha motor neuron) –In efferent pathways to head, pharynx, larynx, and muscles of shoulder shrugging and head turning, cell bodies are in nuclei of the brainstem, and axons are in the cranial nerves –In efferent pathways to body, cell bodies are in the central gray matter, and axons are in the spinal nerves

11. Major motor system/group: Pyramidal system Pyramidal systems Pyramidal systems –Primary, direct activation pathway from cortex to muscles, under voluntary control Corticospinal system Corticospinal system Corticonuclear system (formerly corticobulbar system) Corticonuclear system (formerly corticobulbar system) –Precise control for small groups of muscles *, primarily contralateral (some ipsilateral) –Rapid and precise movement (direct innervation) * Small group of muscles does not necessarily mean that the muscles in that group are small!

12. Cortical origins of pyramidal system Majority of fibers begin in primary motor cortex (pre- central gyrus) Majority of fibers begin in primary motor cortex (pre- central gyrus) Location in the primary motor cortex depends on which structure they control (see homunculus), e.g. Location in the primary motor cortex depends on which structure they control (see homunculus), e.g. –legs/feet –hands –face and tongue

15. Pyramidal tracts originate in cortex and consist of upper motor neurons (1 st order) and lower motor neurons (2 nd order) Example of corticospinal Example of Corticonuclear (cranial nerve VII=facial nerve) Do you see how fibers of upper motor neuron descend in corona radiata, then through internal capsule? The facial nerve (cranial nerve VII) contains the fibers of the lower motor neuron of the corticonuclear (cortical bulbar) pathway for facial movement

16. Pyramidal tracts originate in cortex and consist of upper motor neurons (1 st order) and lower motor neurons (2 nd order) Example of corticospinal Example of Corticonuclear (cranial nerve VII =facial nerve) During the descent, the axons of the upper motor neuron send off collaterals to the cerebellum (via the pons), as input for coordination of movement. In medulla, corticospinal UMN courses through the pyramids (in medulla), crossing at pyramidal (motor) decussation (to cerebellum)

17. Pyramidal innervation primarily contralateral, with some ipsilateral innervation Contralateral Ipsilateral Fibers cross Upper face: Mostly contralateral, some ipsilateral Fibers don’t cross Lower face: Contralateral only