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128 Cards in this Set

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