Lecture 27: Major neuroanatomical pathways I: Central Pathways

Question 1

what is the anatomical result of upper motor neuron damage

Answer 1

axons from lesioned upper motor neurons no longer synapse on lower motor neuron cell bodies

Question 2

what are some clinical signs from damage to upper motor neurons

Answer 2

spastic paralysis, hyperreflexia, clonus (rapid uncontrollable rhythmic muscle contractions)

Question 3

does upper or lower motor neuron damage affect large groups of muscles may be affected such as entire limbs or entire side of body

Answer 3

upper motor

Question 4

what is the anatomical result of damage to lower motor neurons

Answer 4

axons from lesioned lower motor neurons no longer synapse on motor endplates of muscles

Question 5

what are some clinical signs of lower motor neuron damage

Answer 5

flaccid paralysis, hyporeflexia, atrophy of muscle

Question 6

is it upper or lower motor neuron when there are peripheral nerve lesions that are localized

Answer 6

lower motor neuron

Question 7

what are central pathways

Answer 7

axon tracts to and from the brain that carry motor commands or sensory information

Question 8

what are sensory tracts

Answer 8

carry information on stimuli ascending the spinal cord to brainstem to cortex

Question 9

what are motor tracts

Answer 9

leave the cortex, descend through the spinal cord carrying motor commands

Question 10

what are local circuits and what is an example

Answer 10

paths of local control in the spinal cord
ex: reflexes

Question 11

what is the order of a local circuit

Answer 11

sensory neuron–> interneuron–> motor neuron

Question 12

motor neurons in the ventral horn are upper or lower motor neurons?

Answer 12

lower motor neurons

Question 13

motor tracts are upper or lower motor neuron

Answer 13

upper motor neuron

Question 14

what are the two primary motor tracts

Answer 14

pyramidal and extrapyramidal

Question 15

what is the pyramidal system/corticospinal tract and where does it originate

Answer 15

finely adjusted movements, originates in the cortex

Question 16

what is the extrapyramidal system/rubrospinal tract and where does it originate

Answer 16

coarser movements especially during stereotyped locomotion, originates in the brainstem

Question 17

motor tracts are made of _____ which deliver motor impulses from the brain through the spinal cord. UMN synapse on ___ whose cell bodies are in the ____ of the spinal gray matter. _____ innervate muscle tissue via neuromuscular synapses

Answer 17

upper motor neurons, lower motor neurons whose cell bodies are in the ventral horn of the spinal gray matter. Lower motor neurons innervate muscle tissue via neuromuscular synapses

Question 18

what motor neurons contribute to reflexes

Answer 18

lower motor neurons

Question 19

cell bodies that are located in the cortex, largely in the primary motor area are lower or upper motor neurons

Answer 19

upper motor neurons

Question 20

where do the pyramidal/corticospinal tracts begin

Answer 20

motor cortex

Question 21

where do the pyramid/corticospinal tracts decussate

Answer 21

medualla at the pyramids

Question 22

where does the extrapyramidal/rubrospinal tract begin

Answer 22

midbrain at red nuclei

Question 23

where does the extrapyramidal/rubrospinal tract decussate

Answer 23

while descending to the pons

Question 24

are pyramidal tracts lower or upper motor neuron

Answer 24

upper motor neuron

Question 25

what do pyramidal tracts synapse on

Answer 25

decussate and synapse on lower motor neurons in gray matter

Question 26

where do upper motor neurons originate and where do they synapse

Answer 26

cerebral cortex and brainstem synapse in spinal cord and ventral horn

Question 27

where do lower motor neurons originate and where do they synapse

Answer 27

ventral horn of spinal cord and synapse on motor endplate

Question 28

what is the final common path/motor unit

Answer 28

one lower motor neuron and skeletal muscle fiber