motor 2: specific tracts

Question 1

reticulospinal tract

Answer 1

mostly extensor-biased tract

• cell bodies located in medial column of caudal pontine and rostral medullary reticular formation
• the tract descends ipsilaterally and bilaterally to ventral column
• serves postural gait adjusments (balance) during mvmt by acting on anti-gravity muscles
• is central for bilateral and coordinated gross mvmt of the limbs (e.g locomotion)
• gross mvmt during reaching
• reticulospinal tract is highly myelinated and fast acting

Question 2

reticulospinal tract imput

Answer 2

tectospinal tract, vestibulospinal tract, basal ganglia, motor cortex, cerebellum

Question 3

vestibulospinal tracts

Answer 3

nuclei of medial and lat. nuclei of medulla contribute (even though there are 4)

Question 4

lateral vestibulospinal tract

Answer 4

generates muscle tone in deep back and limb extensors

Question 5

medial vestibulospinal tract

Answer 5

stabilizes head during mvmt - esp. rotation

Question 6

tectospinal

Answer 6

cell bodies in sup. colliculi, fibres cross in midbrain to the contralat. and terminate at motoneurons in cervical spinal cord to act on neck and shoulders

• small portion of the tectospinal tract remains ipsilat. to inhibit muscles on one side while the contralat. muscles are excited, therefore acts bilateraly
• controls rflx mvmt of the head, neck and upper limbs in response to all relevant sensory stimuli (visual, auditory, tectile, temperature, pain, etc)

Question 7

tectospinal imputs

Answer 7

visual from retina, auditory for inferior colliculi, sensory input for SC) > superior colliculi > tectospinal tract > neck and shlder muscles

Question 8

tectospinal - 2

Answer 8

controls rflx mvmt of head, neck and upper limbs in response to all relevant sensory stimuli.
important for steering the body (change of direction) during gait as we navigate our visual axis in the direction of mvmt

Question 9

rubrospinal tract (flxor - biased tract)

Answer 9

originates in red nuc. and splts near its origin at midbrain level

• tract descends contralat. and accompanies the lateral corticospinal tract (lat. motor pathways)
• passes through lat. column of SC and ends at lvl of cervical cord
• tract innervates all flxr muscles of UL
• receives input from motor cortex
• acts unilat. and complements the function of the lat. corticospinal tract (alt. mtr pathways)

Question 10

immature or destroyed pyramidal systm.

Answer 10

if rubrospinal tract imput removed, rubrospinal tract acts as a tonic flxr of the arm muscles
-babies, fetuses and stroke patients display strong flxr tone in the UL owing to disinhibition of the rubro. tract

Question 11

topographical organization of alpha and beta-motoneurons in ventral horn

Answer 11

both pyram. and extrapy. target alpha and beta motorneurons of the SC

• alpha and beta motorneurons located in ventral horn
• at brachial and lumbosacral plexus, alpha and beta motorneurons supply the axial muscles are located in the medial ventral horn (medial motoneuron pool) whereas those that suuply limb muscles are located lateral giving rise to lat. motorneuron pool

Question 12

medial motoneuron pool

Answer 12

control axial muscles/axial

Question 13

lat. motoneuron pool

Answer 13

control muscles of the limbs/appendicular

Question 14

lat. motor pathways (in lat column)

Answer 14

contains lat. corticospinal and rubrospinal tracts
- synapse with neurons of lat. motoneuron pool
fine voluntary mvmt of limb muscles
- flxor-biased mvmt of UL
acts unilaterally

Question 15

med.. motor pathways (in ventral column)

Answer 15

cotaints anterior corticospin., reticulospin., vesitbulospin. and tectospin.

• synapse with neurons of med.. motoneuron pool
• postural and rflx mvmt of axial muscles
• mostly acts biilaterally

Question 16

medial descending motor system (mostly extrapy. tratcs)

Answer 16

phylogenetically older than the lateral descending motor system
- controls coordinated whole-body postural and orienting mvmts

Question 17

lat. descending motor system (

Answer 17

phylogenetically younger than all descending motor tracts and highly dvlped in humans
- concerned with mvmts of the limbs

Question 18

Upp. motor neuron lesions

Answer 18

rubrospinal tract is flxr-biased upp. motor neurones in UL

- reticulospinal and vestibulospinal tracts are extensor-biased UMNS in LL

Question 19

Upp. motor neuron lesions - decorticate rigidity

Answer 19

above midbrain = removal of the influence of the corticospinal tracts on rubro., reticulo. and vestibulo. tracts
FLX UL AND EXT. LL

Question 20

Upp. motor neuron lesions - decerbrate rigidity

Answer 20

EXT BOTH LIMBS DUE TO UNOPPOSED EXTENSOR-BIASED UMNS ACTIVITY
- blw midbrain results in removal of rubo. tract in addition to reomval of influence of corticospinal tract on retic. and vestib. tracts