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128 Cards in this Set
- Front
- Back
What transmits information from higher brain regions to the spinal cord?
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The descneing spinal cord tracts
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Where do descending spinal cord tracts aris from and terminate?
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Descending tracts arise in the cerebral cortezx and brainstem and descend to terminate in the spinal cord.
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What are most of the descending pathways concerned with control of?
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Motor function
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Name three descending pathway motor functions.
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1. Execution of voluntary movements
2. Maintenance of posture and equilibrium 3. Regulation of spinal cord motor reflex activity |
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Other than motor function what are the two jobs of the descending pathways?
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1. Control autonomic function
2. Regulate processing and transmission of somatic sensory information |
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Lower or Upper motor neurons: Neurons whose axons directly innervate skeletal muscle.
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Lower motor neurons (LMNs)
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Where are the alpha motor neurons located in (which lamina and horn)?
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Lamina IX and the ventral horn
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Where do axons of the alpha motor neurons exit the spinal cord?
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in the ventral roots
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Where are brainstem LMNs located?
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in the motor nuclei of cranial nerves
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Where do the axons of brainstem LMNs course to innervate skeletal muscle of the head & neck?
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With cranial nerves
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What are the final common pathway from the CNS to skeletal muscle fibers, meaning that the only way the CNS can change a muscle's activity is by chanign the firing rate of the LMNs that innervate it.
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Lower Motor neurons
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What are the three sources of direct input to LMNs?
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1. Descending pathway neurons (upper motor neurons) synapse directly on LMNs.
2. Dorsal root ganglion (primary afferent) fibers representing the afferent limb of the myotatic reflex. 3. Excitatory and inhibitory spinal cord interneurons (htese neurons relay information to LMNs from most of the descending pathways and from primary afferent fibers for polysynatpic reflexes). |
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What determines the firing rate of the LMN?
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The spatial and temporal integration by the LMN of its inputs.
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How are LMNs organized somatotopically in the ventral horn
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Somatotopically
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Where are LMNs that innervate the trunk (axial) muscles and proximal muscles of the extremities located?
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In the medial part of the ventral horn
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Where are the LMNs that innervate the distal muscles of the extremities located?
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In the lateral part of the ventral horn.
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Where are the LMNs for extensor muscles located?
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In the ventral part of the Ventral horn
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Where are the LMNs for flexor muscles located?
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In the dorsal part of the Ventral horn
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What are neurons in the cerebral cortex or brainstem whose axons form named descending fiber tracts and innervate lower motor neurons?
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Upper motor neurons.
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True/False: Some upper motor neurons synapse directly on LMNs in lamina IX of the psinal cord?
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True
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True/False: Some upper motor neurons synapse on excitatory or inhibitory interneurons lcoated in laminas V-VIII, which in turn synapse on LMNs in lamina IX.
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True
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True/False: Upper motor neurons synapse direclty only on LMNs in lamina IX of the spinal cord?
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False, they may also synapse on excitatory or inhibitory interneusons located in laminas V-VII, which in turn synapse on LMNs in lamina IX.
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What are the clinical signs of a lesion of lower motor neurons?
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Denervation of skeletal muscle
Flaccid paralysis |
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What characterizes flaccid paralysis (3)?
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Reduced muscle tone (hypotonia)
Reduced or absent myotatic relex Rapid atrophy of the affected muscle(s) |
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What are the two clinical signs of a lesion of upper motor neurons (particularly the lateral corticospinal tract)?
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Does not denervate skeletal muscle
Produces spastic paralysis |
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Describe why a lesion of upper motor neurons results in spasstic paralysis.
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The LMNs that receive input from the damaged UMNs are still connected to their corresponding muscle(s).
In the absence of supraspinal control from the UMNs, the LMNs display abnormally enhanced activity. The increased LMN actavitiy produces spasticity in the affected muscle(s). |
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What are the five characteristics of muscle spasticity?
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1. increased resting muscle tone (hypertonia)
2. increased resistance to passive movement 3. hyperactive myottatic reflexes 4. Return of primitve reflexes that ar e normally inhibited by supraspinal input (e.g. Babinski sing= dorsiflexion of big toe and spreading of the other toes in response to scraping the sole of the foot) 5. Slow muscle atrophy (>1 yr) - Due to disuse, not denervation |
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Where do tracts of the medial descending system course?
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in the anterior funiculus of the spinal cord.
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What is the funciton of the medial descending system?
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Controls axial and proximal musculatur to maint posture and blance
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Where do Medial descening system axons synapse on LMNs or via a interneuron (most commonly)?
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In the medial portion of the ventral horn
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Where does the lateral descending system course?
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In the lateral funiculus.
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Where do the lateral descending system axons synapse (directly or via an interneuron)?
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In the lateral portion of the ventral horn
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What is the function of the lateral descending system?
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Control of fine fractionated movements of the distal extremities
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True/False: The lateral corticospinal tract (LCST) is considred part of the corticospinal tract?
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True
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Which two tracts have the same origin and intial course and are therefore indistinguishable at tleves above the spinal cord?
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The anterior corticospinal tract
and lateral coticospinal tract |
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Where is the origin of the UMN cell bodies of the corticospinal tract?
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Cerebra; cprtex
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What occurs at the spinomedullary junction in the Lateral Corticospinal Tract (LCST)?
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90% of the fibers cross the midline and pass doroslaterally to form the lateral cortical spinal
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Where does the LCST descend in the spinal cord?
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Within the lateral funiculus
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Where do fibers of the LCST synapse with?
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Directly on alpha moto neurons and with interneurons in the lateral part of the vnetral horn, at all levels of teh spinal cord.
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What is the funciton of of the LCST?
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It mediates fine, fractionated movements of the distal extremitites.
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What tract is the the tract primarily repsponsible for controlling our volutnary movements?
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The LCST
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The clnical signs of upper motor neuron lesions are due to damage to which tract?
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LCST
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What will occurr in terms of degeneration follwoing lesio of the LCSt?
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Anterograde degeneration (demyelinatino of the LCST in the contralateral lateral funciulus of the spinal cord
Chromatolysis of neurons in the ipsilateral cerbral cortex |
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What will happen to a lesion of the LCST within the spinal cord?
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Anterograde degeneration of the LCST in ipsilateral spinal cord below the level of the lesion
Chromatolysis of neurons in the contralateral cerebral cortex |
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Where are the UMN cell bodies of the rubrospinal tract (RST) located?
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In the red nucleus of the midbrain
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True/False: Axons do not corss at the site of origin in the midbrain to form the contralateral rubruspinal tract. They proceed farther and decussate within the medulla.
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False. Axons cross at the site of origin in the midbrain to form the contralateral rubrspinal tract.
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Where does the RST descend in the spinal cord?
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In the lateral funiculus
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Where does the RST terminate?
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The later portion of the ventral horn and it only extends to the cervical spinal cord levels
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What is the funciton of the rubrospinal tract?
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Facilitates activity of LMNs of the flexors of the upper extremity.
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True/False: Are lesions ofht eRST associated with clinically significant motor deficits?
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No, since the RST's functions are also carried out by the LCSt.
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Wjere os tje progom pf tje I<M ce;; bpdoes pf tje Amteropr Cprtocps[oma; Tract )ACST)?
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Primary motor corex
Premotor cortex Somatosensory cortex |
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What happens to the 10% of fibers which do not cross the midline at the spinomedullary junction (the 90% went to form the LSCT)?
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The non-crossing fibers continue descending in the ipsilaterla spinal cord as the ACSt.
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What tract is located in the ventromedial portion of the anterior funiculus?
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ACST
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Where doe the ACST extend to?
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Cervical levels of the spinal cord.
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True/False: ACST fibers cross in the anterior white commissure of the cervical spinal cord.
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True
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What happens after ACST fibers cross through the anterior white commissure?
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the Fiber terminate in the medial part of the ventral horn.
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What system is the lateral vestibulospinal tract part of?
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The medial descending system
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In the Lateral Vestibulospinal Tract (LVST) where are the UMN cell bodies located?
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The lateral vestibular nucleus (part of a complex of vestibular nuclei located in the pons & medulla).
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Describe teh course of the LVST.
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The LVST descends ipsilaterally to the spinal cord, where it courses in the ventrolateral portion of the anterior funiculus
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Where do fibers for the lateral vestibulospinal Tract (LVST) terminate?
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Fibers terminate in the medial portion of the ventral horn at all levels of the spinal cord
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Which tract has following functions? Facilitates activity of extensor muscles of the upper and lower extremities
- Important for maintain balance (part of the "righting" reflex). |
Lateral Vestibulospinal Tract (LVST)
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Define: A condition caused by transection of brainstem near the pons/midbrain disrupts almost all of the descending upper motor neuron pathways, but spares the LVST sinces the lateral vestibular nucleus is located in the upper medulla/lower pons.
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Decerebrate rigidity
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________________ is characterized by exaggerated extensor posuring(tone) of the upper and lower extremities due chiefly to the unopposed action of the LVST.
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Decerebrate rigidity
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Which tract is spared in Decerebrate rigidity and why?
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Spares the LVST since the lateral vestibular nucleus is lcoated in the uper medullar/lowerpons.
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What is the origin of the Medial Vesitbulospinal Tract?
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UMN cell bodies are located in the medial and inferior vestiublar nuclei (parts of a complex of vestirbular nuclei located in the pons & medulla).
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True/False: The medial longitudinal fasciculus (MLF) is a composite fiber bundle.
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True
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Where in the spinal cord is the medial longitudinal fasciculus (MLF) found?
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Located near the midline, in the posterior part of the anterior funiculus.
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Describe the course of the medial vestibulospinal tract.
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Descends bilaterally to the spinal cord. In its descent to and within the spinal cord the MVST course in the medial longitudinal fasciculus and extends only to the cervical spinal cord.
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Where does the Medial Vestibulospinal tract terminate?
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To the cervical spinal cord
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What is the origin of the Pontine Reticulospinal tract?
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UMN Cell bodies are loated in the reticular formation of the pons.
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Describe the course of the Pontine Reticulaospinal tract.
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Descends ipsilaterally in the MLF long with the MVST
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Where does the Pontine Reticulospinal Tract Terminate?
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PRST extends to all levels of the spinal cord.
The fibers terminate in the medial portion of the ventral horn |
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What is the function of the PRST (Pontine Reticulospinal tract)?
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Facilitates axial and proximal musculature for postural tone and adjustments.
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Besides the LVST natme one other tract spared in decerebrate rigidity.
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PRST thought to play a minor role in producing the exaggerated extensor posturing
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Where is the origin of the Medulalry Reticulospinal Tract?
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UMN Cell bodies are located in the reticular formation of the medulla
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Describe the course of the Medullary Reticulospinal Tract.
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Descends bilaterally in the dorsolateral portion of the anterior funiculus
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Where does the MRST (Medullary Reticulospinal Tract terminate?
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MRST extends to all levels of the spinal cord
Fibers terminate in the medial portion of the ventral horn |
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What is the function of the MRST (Medullary Reticulospinal Tract)?
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Has an inhibitory influence on axial and proximal limb musculature
(may be involved in producing muscle atonia during sleep) |
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The ANS is characterized by a ___ ________ ______ from the CNS to the effector tissue.
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Two Neuron Pathway
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What is the Neuron #1 in the ANS system?
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Preganglionic neuron
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Sympathetic/Parasympathetic: All preganglionic neurons are located int eh Intermediolateral nucleus of the spinal cord the IML is lcoated in LA VII, from T1-L2.
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Sympatehtic Nuerons
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Sympathetic/Parasympathetic: Mostly involved in "fight or flight" functions (e.g. increases heart rate & sweat secretion, dilates pupils, mobilizes stored energy).
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Sympathetic Nervous system
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Sympathetic/Parasympathetic: controls more "sedentary" functions (decreases heart rate, constricts pupils, increasez gastric movement and secretion).
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Parasympathetic
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Sympathetic/Parasympathetic: Preganglionic neurons are located in some cranial nerve nuclei in the brainstem and in the sacral ___________ nucleus which located in LAM VII from S2-S4
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Parasympathetic
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What is Neuron #2 called in the autonomic nervous system?
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PostGanglionic Neuron
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Where is the origin of the descending autonomic pathway?
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Several cell gropus in the hypothalamus and brainstem
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Describe the course of the Descending autonomic pathway.
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Fibers descend ipsilaterally through the brainstem and spinal cord.
Within the spinal cord, the descending autonomic fibers are located in the medial portion of the lateral funiculus, adjacent to the intermediate zone of the gray matter of the spinal cord. |
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Where does the descending autonomic pathway terminate (Two places)?
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Synapses on preganglionic sympathetic neurons in the intermediolateral nucleus from T1-L2
Preganglionic parasympathetic neurons located int he S2-S4 levles |
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What is the function of the function of the descending autonomic system?
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Cotnrol sympathetic outflow to the entire body
Control parasympathetic outflow to the lower abdominal/pelvic region by regulation the activity of the sacral preganglionic parasympathetic neurons. |
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True/False: There are preganglionic sympathetic fibers in the cranial nerves.
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False. There are no preganglionic sympathetic fibers in the cranial nerves
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Where does sympathetic outflow to the head & neck originate from?
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The preganglinoic sympathetic neurons located int he superior portion of the IML (From T1-T4)
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Where do axons of these preganglionic sympathetic fibers which are the outflow of the head & neck enter?
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T1-T4 ventral roots
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After entering the T1-T4 where do the head/neck sympathetic fibers coruse?
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The preganglionic fibers ascend to the cervical sympathetic trunk an synapse on postganglionic neurons in the superior Cervical ganglion
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What is the most superior ganglion o fht esympathetic trunk called?
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Superior Cervical Ganglion
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What course to structures in the head and neck to control:
- smooth muscle that plays a minor role in rasiing the eylid - vasoconstriction of blood vessels in the face - smooth msucle in the floow of the orbit - Pupillary dilation - Sweat glands of the face |
Postganglionic sympathetic fibers from the superior cervical ganglion
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What are the five clinical signs of HOrner's Syndrome?
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Pseudoptosis-drooping of eyelid
Redness - flushing of the face Enophthalmos - sinking of eye into the orbit Miosis- Constriction of the pupil Dryness (anhydrosis)- lack of sweating in face |
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What general lesion produces Horner's syndrome?
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LEsion of descending autonomic fibers above T1
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Is the descending autonomic pathway crossed?
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NO
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Will a unilateral or a bilater lesion of the descending autonomic pathway result in Horner's syndrome?
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Unilateral
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Name that tract! Origin: Motor,premotor& somatosensory cortex
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LCST (lateral corticospinal tract)
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Name that tract! Origin: Motor, Premotor&somatosensory cortex
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ACST (anterior corticospinal tract0
LCST |
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Name that tract! Origin: Red nucleus
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Rubrospinal tract (RST)
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Name that tract! Origin: Lateral vestibular nucleus
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Lateral vestibulospinal tract (LVST)
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Name that tract! Origin: Medial Vestibular nucleus.
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Medial vestibular nucleus (MVST)
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Name that tract! Origin: Reticular formation of Pons
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PRST or Pontine Reticulospinal tract
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Name that tract! Origin: Reticular formation of medulla
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MRST (Medullary reticulospinal tract)
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Name that tract! Origin: Hypothalamus and brainstem
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Descending autonomics
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List the two pure crossed descending spinal cord fiber tracts.
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LCST
RST |
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Name the two purely bilateral spinal tracts.
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MVST (Medial vestibulospinal tract)
MRST (Medullary reticulospinal tract) |
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Name the three purely uncrossed spinal tracts.
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LVST (Lateral vestibulospinal tract)
PRST (Pontine reticulospinal tract) DA (descending autonomics) |
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Name this tract: descends uncrossed - fibers then cross in spinal cord where they terminate.
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ACST (Anterior corticospinal tract)
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List the two fiber tracts that are part of the lateral descending system.
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LCST
RST |
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Name the five tracts that are part of the medial descending system.
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ACST
LVST MVST PRST MRST |
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Name the trract which is neither lateral medial descending because it is not s omatic motor pathway.
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Descending autonomics
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Name that tract: Termination!
Lateral part of ventral horn at ALL levels. |
LCST
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Name that tract: Termination! Medial Part of Ventral Horn at Cervical levels.
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ACST (Anterior Corticospinal Tract)
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Name that tract: Termination! Lateral Part of Ventral Horn at Cervical Levels.
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RST (Rubrospinal tract)
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Name that tract: Termination! MEdial Part of Ventral Horn at All Levels (3).
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LVST
PRST MRST |
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Name that tract: Termination! Medial Part of Ventral Horn at cervical levels
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MVST
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Name that tract: Termination! IML (LAM VII from T1-T4)
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Descending Autonomics
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Name that tract: Function!
Ractionated movements of individual muscles of distal extremity |
LCST
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Name that tract: Function! Controls neck & proximal muscles of upper limb for postureal adjustments
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ACST
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Name that tract: Function! Supplements LCST for Distal Upper extermity flexors
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RST
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Name that tract: Function! Facilitates extensors for righting reflex
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LVST
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Name that tract: Function!Head positioing and coordinating with eye movements
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MVST
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Name that tract: Function! Facilitates axial and proximal muscles for postural tone
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PRST
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Name that tract: Function! Muscle Atonia of Sleep
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MRST
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Name that tract: Function! Sympathetic innervation of Head & neck structures.
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Descending autonomics
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