CHAPTER 16 Pyramidal systems direct activation corticospinal corticonuclear corticobulbar Structural components of motor system Cerebral cortex o Prefrontal association cortex executive function planning reasoning problem solving responsible for deciding when to move act and when not to o Limbic association cortex emotion provides input to prefrontal cortex o Posterior parietal cortex synthesizes two inputs to make sense of where body is relative to other objects Input from Primary somateosensory cortex Visual cortex of occipital lobe o Output of posterior parietal cortex and prefrontal cortex sent to premotor cortex so details of the desired movement can be programmed there o Output of premotor cortex goes to primary motor cortex where the direct motor pathway starts Brainstem PNS o Cranial nerves PNS have associated nuclei in the brainstem CNS where are organized in columns clusters in the brainstem o 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 impuses to the muscles efferent of the face head o Components of the motor system spinal cord and associated spinal Spinal cord PNS nerves The grey matter of the spinal cord is made of ganglia This is where the synapses happen Spinal nerves are made of In the motor system the cell bodies associated with motor neurons are found in the of the spinal cord dorsal horn The alpha motor neuron is the final common pathway for the motor impulses to the muscles effectors Pyramidal systems direct Corticospinal and corticonuclear In the pyramidal direct activation pathways the pathway is generally made up of 2 sets of neurons that convey the efferent impulses caudally pyramidal system Primary direct activation pathway from cortex to muscles under voluntary control Precise control for small groups of muscles Upper motor neurons 1st order neurons of the motor pathway o Multipolar neuron which functions as interneuron o Cell bodies are in primary motor cortex precentral gyrus o Axons descend o Synapse to lower motor neurons 2nd order neurons of the motor pathway Multipolar neuron which function as motor neuron o In efferent pathways to head pharynx larynx and muscles of shoulder shrugging and head turning cell bodies are in nuclei of brainstem and axons are in the cranial nerves o In efferent pathways to body cell bodies in the central grey matter and the axons are in the spinal nerves Cortical origins of pyramidal system majority of fibers being in primary motor cortex precentral gyrus location of the primary motor cortex depends on which structure they control homunculus The facial nerve CN7 contains fibers of lower motor neuron of the corticonuclear pathway for facial movement 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 curves through pyramids crossing at pyramidal decussation Strictly book notes Efferent impulses from the primary motor cortex PMC activate spinal and brainstem motor LMN neurons and induce contraction of specific muscles The cortical motor projections regulate a series of movements that are complex discrete precise and skilled Anatomy Primary motor cortex is in the precentral gryus of the frontal lobe rostral to the central sulcus PMC has Betz cells important in voluntary motor movement The motor neural impulses that travel in the pyramidal tract originate from the 3 cortical regions PMC PreMC and primary sensory cortex o 25 30 of pyramidal tract fibers arise from PMC Motor cortex is organizes contralateral to output and input The short corticonuclear corticobulbar and long corticospinal efferent prjections from the motor cortex cross the midline to innervate contralateral cranial nerve and spinal output motor nuclei Lesion of the motor fibers above the point of decussation caudal medulla for ling fibers and multiple brainstem points for short fibers produces clinical signs contralateral to significant damage Descending pathways Descending efferents to the LMN s travel on one of two pathways either corticospinal tract or corticonuclear tract All fibers cross midline before synapsing on their LMN Corticospinal tract 30 of motor fibers Mediates voluntary movement through spinal neurons LMN Upper 2 3 of the PMC PreMC and SMC Travel through corona radiate and descend through all this shit UMN fibers of the lateral corticospinal tract terminate on the interneurons and alpha motor neurons in the spinal anterior grey horn to initiate movement Corticonuclear tract 70 of motor fibers Short fibers Controls the facial oral and others through CN nuclei in brainstem Control skilled and fine movements Exclusively control skeletal muscles of the face and head Contralateral and bilateral fibers Fibers from left motor cortex innervate both left right motor nuclei Cranial nerves Spinal Nerves Spinal nerves and cranial nerves Mixed nerves afferent and efferent trunk and limbs Spinal peripheral nerves Sensory posterior o Dorsal root connects to dorsal horn of gray matter o GSA and GVA Motor anterior o Ventral roots connect from ventral horn of gray matter beginning of final common pathway of somatic motor system Contains lower motor systems o GSE and GVE Cranial nerves compared to spinal nerves Cranial nerves Some cranial nerves are motor only Some are sensory only Some cranial nerves do not carry both somatic autonatomic nerve systems All have some relation to speech hearing swallowing language and communication Spinal nerves Spinal nerves are mixed Spinal nerves carry both somatic autonomic nervous syste s Largely voluntary Cranial nerves 12 PAIRS Roots connect to CNS o Brainstem o Uppermost spinal cord Exit brain and pass through the skull to reach sense organs or muscles of head and neck Susceptible to damage All 12 relevant to speech language hearing or swallowing When cranial nerves are damaged causes can be o Dysarthria speech motor disorder o Dysphagia swallowing disorder Nerve 1 2 3 4 5 6 7 8 9 Name Olfactory Optic Oculomotor Trochlear Trigeminal Abducens Facial Vestibular Glossopharyngeal Function Smell taste Vision Eye eyelid movement Eye movement Sensation of face motor palate Eye movement Sensation tongue motor facial Balance and hearing Sensation of soft palate motor pharynx Motor to larynx Motor to larynx shoulder Motor to tongue 10 11 12 How to remember the order On