NBL 356-656 Module 2 Study Guide Review Q-A Spring Study Guide PDF

NBL 356-656 Module 2 Review Q&A 1. *What is the extrapyramidal (indirect) system? Briefly describe the four extrapyramidal tracts (EPTs), where they originate, where they travel and what their functions are. Which EPTs are involved in involuntary/unconscious movements and which are inv...

NBL 356-656 Module 2 Review Q&A 1. *What is the extrapyramidal (indirect) system? Briefly describe the four extrapyramidal tracts (EPTs), where they originate, where they travel and what their functions are. Which EPTs are involved in involuntary/unconscious movements and which are involved in voluntary/conscious movements.* The extrapyramidal tracts originate in specific nuclei in the brain stem and travel to the spinal cord (and a few travel to other regions of the brain stem). The rubrospinal tract is the only extrapyramidal tract involved in control of voluntary movements. All the rest of the extrapyramidal tracts function predominantly in the unconscious control of balance, posture, coordination, locomotion and reflexes. These tracts include the reticulospinal tract, the vestibulospinal tract, and the tectospinal tract, which are all involved in the unconscious control of posture, balance, locomotion, reflexes and coordination of the head and body movements. From Wikipedia: "These tracts are in turn modulated by various parts of the CNS, including the motor cortex, nigrostriatal pathway, the basal ganglia/nuclei, the cerebellum, the vestibular nuclei, and different sensory areas of the cerebral cortex. Reticulospinal Tract Origin: Reticular formation (located in the midbrain, pons and medulla). The reticular formation is a region located in the core of the brainstem that extends from the midbrain to the medulla, includes ascending pathways to the cortex and descending pathways to the spinal cord and is involved in the control of many responses. You may have learned about the ascending reticular activating system (ARAS), which play a crucial role in maintaining behavioral arousal and consciousness. The reticulospinal tracts are descending tracts that are responsible primarily for postural control and locomotion. There are two tracts called the pontine and medullary reticulospinal tracts, which originate in the pons or medulla, respectively. The somatic axons in these tracts synapse on both local interneurons and lower motor neurons. Although we are focusing on the somatic motor system in this module, it should be noted that the reticulospinal tracts also contain autonomic neurons. Vestibulospinal Tract Origin: vestibular nuclei in pons and medulla. From Wiki "The vestibular nuclei receive information through the vestibulocochlear nerve about changes in the orientation of the head. The nuclei relay motor commands through the vestibulospinal tract. The function of these motor commands is to alter muscle tone, extend, and change the position of the limbs and head with the goal of supporting posture and maintaining balance of the body and head." Tectospinal Tract Origin: tectum (superior colliculus) in midbrain. Involved in reflex postural movements of the head in response to visual and auditory stimuli. The tectospinal tract coordinates head and eye movements. The portion of the midbrain from where this tract originates is the superior colliculus (which is called the tectum in birds and other non-mammalian vertebrates), which receives afferent inputs from the visual nuclei (primarily the oculomotor nuclei complex), then projects to cranial nerve motor nuclei in the midbrain and pons and to the first cervical segments of the spinal cord. Thus the tectospinal tract can control head and neck movements. Since the tracts terminate in the cervical regions, lower segments of the spinal cord would not contain this tract. Rubrospinal Tract Origin: magnocellar red nucleus in midbrain. Involved in voluntary muscle control of limbs. The rubrospinal tract originates in the neurons present in the red nucleus and terminates by synapsing with the interneurons in the spinal cord. The tract is responsible for large muscle movement regulation flexor and inhibiting extensor tone as well as fine motor control. It terminates primarily in the cervical and thoracic portions of the spinal cord, suggesting that it functions in upper limb but not in lower limb control.It is small and rudimentary in humans. For the EPTs upper motor neurons are located in nuclei in the brainstem, and they extend axons, form tracts in the spinal cord and synapse on spinal interneurons and lower motor neurons in the spinal cord ventral horns. A few axons of the EPT (particularly the tectospinal tract) extend to other regions of the brainstem where they synapse on local circuit neurons and lower motor neurons in motor brainstem nuclei. 2. *In some texts, the two main motor systems are divided into the lateral system and the ventromedial system based on the location of the tracts in the spinal cord white matter. What tracts do the lateral and ventromedial systems contain?* Lateral: lateral corticospinal tract and rubrospinal tract 3. *Identify the overall anatomy of the spinal cord. Where and what are the dorsal root ganglia, dorsal horns and dorsal roots, the ventral horns and ventral roots, and general location in the white matter of the lateral and anterior corticospinal tracts, and extrapyramidal tracts? What do the dorsal and ventral horns contain, and what are their general/overall functions? Where do the motor and sensory axons exit and enter the spinal cord? How are the spinal cord gray matter regions (horns) mapped for sensory and motor functions?* The dorsal and ventral roots lie on the outermost lateral dorsal and ventral regions of the spinal cord, and are the regions where the sensory axons enter (dorsal-posterior) or motor axons exit (ventral-anterior) the spinal cord. The dorsal (posterior) and ventral (anterior) horns are the gray matter regions, which contain neuronal cell bodies, dendrites, synapses, gray matter astrocytes and blood vessels. Gray matter: dorsal/posterior=sensory, ventral/anterior=motor. The white matter includes the ascending/sensory tracts (afferents) and descending/motor tracts (efferents) that contain myelinated axons, oligodendrocytes, white matter astrocytes and blood vessels. 4. *What are the [five] major regions/levels/segments of the spinal cord along the A/P (R/C) axis? What are the functions of the vertebral column and spinal meninges? What are the cervical and lumbar enlargements and why are they enlarged?* 5. *Upper motor neurons send axons (descending tracts-corticospinal tracts and extrapyramidal tracts) and synapse on two different types of spinal interneurons and two different types of motor neurons in the spinal cord. What are these?* 6. *The two main types of lower motor neurons are alpha and gamma motor neurons. Where are these neurons located? Where do their axons go? What type of muscles do they innervate? What is the main function of each type of motor neuron?* 7. *What is a muscle and a muscle fiber? What is the motor unit?* 8. *What are flexion, flexors, extension and extensors? What does it mean that some muscles work in antagonistic pairs? Explain why some movement would involve coordinated contraction and relaxation?* 9. *What is a motor pool? Describe the general types and organization of neurons in the ventral horn spinal gray matter. Briefly describe the maps of the motor pools in the ventral horn. (Consider the relative locations of neurons that control axial/distal, and flexor/extensor muscles.) Which descending motor tracts control which types of muscle groups? (Try to specify axial/distal and voluntary/involuntary.)*