Upper Motor Neurons: Primary Lateral Sclerosis

Question 1

each lobe of the cerebral cortex is defined by what fissures / sulci?

Answer 1

• frontal lobe: anterior to central sulcus & superior to lateral fissure
• parietal lobe: posterior to central sulcus & anterior to parietooccipital fissure, & superior to lateral fissure
• temporal lobe: anterior to parietoccipital fisure & inferior to latearl fissure
• occipital lobe: posterior to parietoccipital fissure

Question 2

the frontal lobe can be subdivided into what gyri?

what forms these subdivisions?

Answer 2

• on each side, two sulci run perpendicular to the central sulcus: the inferior frontal sulcus & superior frontal sulcus. this devides the frontal lobe - from medial to lat:
  
  • superior frontal gyrus
  • middle frontal gyrus
  • inferior frontal gyrus

Question 3

describe the locations of the motor cortex:

Answer 3

• recall that the motor cortex = precentral gyrus + caudal frontal lobe
  
  • primary motor cortex: located in precentral gyrus (gyri ant to central sulcus)
  • premotor cortex: portions of caudal frontal lobe. specifically, the
    
    • posterior most portion of the _middle frontal gyr_i
    • posterior most portion of the inferior frontal gyri
• supplemental motor cortex: caudal-most portion of the superior frontal gyrus

Question 4

what gyri form the premotor cortex component of the motor cortex?

Answer 4

the posterior most portions of two frontal lobe gyri: middle, inferior

Question 5

define & explain the homunculus

Answer 5

is a spatial segregation of the primary motor cortex (precentral gyrus) based on the portion of the body that they innervate

• going from medial to lateral and also dorsal (superior) to ventral (inferior):
  
  • MEDIAL: lower body - distal to proximal
  • MIDDLE: 1. trunk / head / neck + upper body - distal to proximal to distal
  • LATERAL: face + thoat - superior to inferior

Question 6

label & note important trends.

Answer 6

• going from medial to lateral and also dorsal (superior) to ventral (inferior):
  
  • MEDIAL: lower body - distal to proximal
  • MIDDLE: 1. trunk / head / neck + upper body - distal to proximal to distal
  • LATERAL: face + thoat - superior to inferior
• THE HIP: transition from medial to middle (also dorsal / superior) primary motor cortex

Question 7

the portion of the primary motor cortex with nuerons that intervate the HIP serves as a transition from what two primary cortex regions?

Answer 7

transition from the medial premotor cortex (genitals + LE from D-P) to the middle / superior / dorsal premotor cortex (trunk + UE)

Question 8

the parikaryons (neuron cell bodies) that make up the primary motor cortex send signals through axons that travel where?

Answer 8

give off the axons (white matter) that comprise the corona radiata.

will travel through the:

• association fibers
• corpus collosum
• internal capsule

to get to

• subcortical brain centers

Question 9

review the components of the internal capsule and their bordering anatomy.

Answer 9

• in a transverse cut
  
  • anterior crus:
    
    • caudate nucleus is medial
    • lentiform nucleus (globus pallidus + putamen) is lateral
  • genu
  • posteior crus
    
    • thalamus is medial
    • lentiform nucleus (globus pallidus + putamen) is lateral

Question 10

genu

• is what kind of neural tissue?
• carries what signals? and
  
  • from where?
  • to where?

Answer 10

• is axons (white matter) forming part of the IC
  
  • specifically, contains the corticobulbar tract axons, which:.
    
    • extend from primary motor cortex perikaryons (grey matter) located in the:
      
      • lateral (& most inferior) region. i.e:
        
        • head & neck:
          
          • ​eyes-nose-face-lips
          • teeth-gums-jaw
          • tongue-pharynx
    • carry motor info to: LMNS in the brainstem (cranial nerves)

Question 11

posterior crus

• is what kind of neural tissue?
• carries what signals? and
  
  • from where?
  • to where?

Answer 11

• is axons (white matter) forming part of the IC
  
  • specifically, corticospinal tract axons, which:
    
    • extend from primary motor cortex perikaryons (grey matter) located in the:
      
      • medial & middle (& most superior / dorsal) region
        
        • LE - distal to proximal
        • trunk-head-neck
        • UE -proximal to distal
    • rearrange info from: anterior-posterior: arm-trunk-leg
    • carry motor info to: spinal cord LMNS (ventral horn, gray matter)

Question 12

explain how the posterior crus “rearranges” the signals it carries from the motor cortex

Answer 12

• in medial & middle motor cortex perikaryocns:
  
  • LE: distal-prox I-S
  • trunk-head-neck
  • UE: prox-distal M-L/S-I
• in posterior crus axons (corticobulbar tract):
  
  • anterior-posterior: arms-trunk-legs (a for arms)

Question 13

compare contrast the genu and _posterior cru_s. note the

• fibers they carry
• their origins and destinations

Answer 13

both: extend from perikaryons in the primary motor cortex & synapse onto LMNs.

genu

• corticobulbar tracts
• lateral / inferior motor cortex
• brainstem LMNS (cranial nerves)

posterior crus

• corticospinal tract
• medial / middle motor cortex
• spinal cord LMNS (ventral horn)

Question 14

the neurons that feed axons into the corticobulbar tract & corticospinal tract come from WHAT kind of neurons?

Answer 14

UPPER MOTOR NEURONS

(perikaryons in the primary motor cortex)

Question 15

after the coritospinal tracts travel thru the posterior crus, where do they go next?

Answer 15

the brainstem: midbrain -> pons -> medulla

Question 16

through what part of the midbrain does the corticospinal tract travel?

explain.

Answer 16

• the crus cerebri: the most superficial / inferior / anterior component of the tegmentum (ventral midbrain) specifically,
  
  • through central 1/3 of the crus cerebri
  • with fibers rearranged medial-lateral: arms-trunk-leg

Question 17

through what part of the pons do the corticospinal tracts travel?

explain.

Answer 17

• through the basis pontis
  
  • perpendicular to pontine nuclei
  • near ventral edge of pons

Question 18

what interactions pontine nuclei have with axons?

explain

Answer 18

• corticospinal tracts - run thru ventral pontine nuclei at a perpendicular angle
• middle cerebellar peduncle - formed from pontine nuclie that extend of lateral pons

Question 19

through what part of the medulla do the corticospinal tracts travel?

explain.

Answer 19

• pyramids
  
  • after exiting the pons, they converge venterally & medially
  • then form / travel through the medullary pyramids
  • within the median fissure (between the pyramids), they dessucate

Question 20

review the ventral anatomy of the medulla oblongota

Answer 20

• pyramids (corticospinal tracts): most ventral
• median fissure: divides pyramids
• anterolateral sulcus: border pyramids
• inferior olives: lateral to pyramids

Question 21

discuss the dessucation of corticospinal tract

• where does it occur?
• what occurs after?
• clinical relevance?

Answer 21

• occurs in the median fissure (between pyramids)
• 90% of corticospinal tracst with dessucate:
  
  • if they dessuccate -> lateral corticospinal tract
  • if they dessuccate -> vertical corticospinal tract
• clinical:
  
  • stroke prior to dessucation = contralateral
  • stroke after dessucation = iupsilateral

Question 22

describe the architecture of the white matter in the spinal cord

Answer 22

• divided into large regions called funiculi:
  
  • dorsal funiculus: medial to (im between) dorsal horns
  • ventral funiculus: medial to (in between) ventral horns
  • lateral funiculus: lateral to dorsal & ventral horns

Question 23

how do the corticospinal tracts move through the spinal cord?

what does it do here?

Answer 23

• the corticospinal tracts runs through the gray matter of the spinal cord as two different tracts, where they synapse onto LMNs in the ventral horn:
  
  • lateral corticospinal tract:
    
    • ​DID dessucate
    • in the lateral funiculus
    • synapses onto lateral ventral horn: distal appendages
  • ventral corticospinal tract:
    
    • ​did NOT dessucate
    • in the ventral funiculus
    • synapses onto medial ventral horn: proximal appendages + TRUNK

Question 24

summarize the path of the corticospinal tract.

Answer 24

1. perikaryons (UMNs) in medial + middle primary motor cortex give of axons that
2. enter posterior crus (IC), arranged ant-post: arms-trunk-leg
3. travel through brainstem:
   
   • midbrain: central crus cerebri, arranged med-lat: arms-trunk=leg
   • pons: pontine nuclei
   • medulla: pyramids, dessucate in median fissure
4. enters white matter of spinal cord:
5. synapse onto LMNS in the ventral horn
   
   1. ventral corticalspinal tract -> median ventral horn: trunk + proximal appendages
   2. latearl corticospinal tract -> lateral vental horn: distal appendges

Question 25

what does disruption the corticospinal tract lead to?

explain.

Answer 25

hemipeglia: paralysis on one side of the body.

• a corticospinal lesion that is:
  
  • superior to dessucation (median fissure) -> contralateral hemiplegia
  • inferior to dessucation (median fissure) -> ipsilateral hemiplegia

Question 26

what does damage to UMNS result in?

explain.

Answer 26

• in the absence of UMNs, LMN activation is primary regulated by sensory input.
  
  • remember that LMNS can receive input from: UMNs, interneurons, sensory.
    
    • ​negative feedback from the spindle apparatus / GTO will activate LMNs, will result in constant LMN contraction

Question 27

damage to UNNs of the

• corticospinal tract
• extrapyramidal tracts

leads to what presentation?

Answer 27

• corticospinal tracts (legs, trunk, arms): hyperreflexia
• extrampyramidal tracts (extensors m/c): rigid paralysis

Question 28

what is hoffman’s test?

what is a positive hoffman’s test, and what is it diagnostic of?

Answer 28

• an UE assessment used to dx corticospinal tract UMN injury
• tapping/flicking 3rd finger terminal phalanx: + test = thumb flexion/adduction
  
  • indicates hypereflexia -> UMN injury

Question 29

constrast the clinical presenattion / physical exam see in LMN damage vs LMN damage.

Answer 29

• LMN damage: no input from ANYTHING.
  
  • flaccid paraylsis: hypotonia, hyporeflexia
  • clinical: no DTRs, no babinski
• UMN damage: LMN intput only SENSORY (spindle, GTO)
  
  • rigid paralysis - hyperreflexia, hypertonia:
  • clinical: + Banbinski, + hoffman test

Question 30

primary lateral sclerosis

• pathogenesis
• presentation
• histology

Answer 30

• pathogenesis: corticospinal neuron (UMN) damage
• presentation: hyperreflexia, hypertonia of appendanges + dysphagia
• histology: lateral sclerosis: hardening of lateral funiculus d/t damage of the lateral corticospinal tract running through

Question 31

other than the corticospinal tract, what major component forms the medullary pyramids?

Answer 31

the corticobulbar tract

Question 32

review the path of the corticobular tract

Answer 32

• perikaryons in lateral portion of primary motor cortex: head, neck
• genu of internal capsule
• medullary pyramids
• synapse onto cranial nerve LMNs:
  
  • facial nerve (VII)
  • accessory nerve (XI)

Question 33

what is the extramedullary pyramidal system?

Answer 33

a system of tracts that, like ones in the pyramids, are made of upper motor neurons

but, the run outside the pyramids

Question 34

what are the tracts that form the of the extrapyramidal system?

briefly, where are their perikyarons (origins?)

Answer 34

• tectospinal - superior colliculi (midbrain)
• rubrospinal - red nuclei (midbrain)
• medial longitudinal fasciulus - vesticular nuclei & superior colliculi
• reticulospinal - reticular formation (midbrain)
• vestibulospinal - vestibular nuclei

Question 35

which of the extra- pyramidal tracts dessucate?

where?

Answer 35

• both dessucate in the ventral midbrain (tegmentum):
  
  • tectospinal: in dorsal tegmentum
  • rubrospinal: in ventral tegmentum

Question 36

tectospinal tract

• originates from?
• carries what info?
• decussates where?
• synapses where?

Answer 36

extrapyramidal tract

• origin: colliculi (tectum) - i.e., “tecto”
• carries: visual info (superior colliculi) and auditory info (inferior colliculi):
  
  • to drive reflexive movements of the head / neck
• decussates where: dorsal tegmentum - comes from tectum, which is dorsal to tegmentum
• synapses: onto LMNs in the ventral horn of spinal nerves to cervical segments

Question 37

rubrospinal tract

• originates from?
• carries what info?
• decussates where?
• synapses where?

Answer 37

(extrapyramidal tract)

• originates from: red nucleus (tegmentum)
• carriers: info that mediates postural tone
• dessucates: ventral tegmentum
• synapses onto: LMNS in medial ventral horn - trunk (postural muscles)