functional hierarchy of the motor system

Question 1

how are muscles directly controlled?

Answer 1

via alpha motoneurones

Question 2

what controls spinal reflexes?

Answer 2

brainstem nuclei

Question 3

what are spinal reflexes integrated into?

Answer 3

higher order reflexes

Question 4

what do higher order reflexes control?

Answer 4

posture and balance

Question 5

what do trunk and limb muscles involved with higher order reflexes receive input from?

Answer 5

vestibulospinal and reticulospinal tracts

Question 6

what controls brainstem nuclei?

Answer 6

cerebral cortex
basal ganglia
cerebellum

Question 7

what 4 systems control movement?

Answer 7

descending control pathways
basal ganglia
cerebellum
local spinal cord and brainstem circuits

Question 8

what do LMNs do?

Answer 8

directly innervate muscles to initiate reflexes and vountary movements

Question 9

what would a LMN lesion cause?

Answer 9

flaccid paralysis and muscle atrophy

Question 10

where are LMNs located?

Answer 10

cranial and spinal levels

Question 11

where are UMNs located?

Answer 11

brainstem or cortex?

Question 12

what do UMNs do?

Answer 12

synapse with multiple lower circuit neurones to regulate alpha motoneurone activity
control complex spatiotemporal skilled movements

Question 13

what wold an UMN lesion cause?

Answer 13

spasticity

some paralysis

Question 14

what would happen if there were many lesions in posture regulating pathways?

Answer 14

spastic paralysis

Question 15

what would corticospinal lesions cause?

Answer 15

weakness rather than paralysis

Question 16

what is the mediolateral map of the spinal cord?

Answer 16

proximal muscles are mapped to medial motoneurones and distal muscles are mapped to much more lateral motoneurones

Question 17

where does the spinal cord receive descending input from?

Answer 17

brainstem

Question 18

where does the spinal cord receive direct cortical input?

Answer 18

pyramidal tract

Question 19

what level does sensory input enter the nervous system?

Answer 19

all levels

Question 20

what does damage to sensory input result in?

Answer 20

paralysis as if the motoneurones had been damaged

Question 21

what type of sensory input would occur at the spinal cord?

Answer 21

proprioceptors
touch
pain

Question 22

what type of sensory input would occur at the brainstem?

Answer 22

vestibular systems inform about balance

Question 23

what is the simplest segmental reflex?

Answer 23

stretch reflex

Question 24

what crucial cord segments make up the biceps and triceps jerk?

Answer 24

C6 and C7 respectively

Question 25

what crucial cord segment makes up the patellar tendon reflex?

Answer 25

L4

Question 26

what crucial cord segment makes up the achilles tendon reflex?

Answer 26

S1

Question 27

what is the significance of testing reflexes?

Answer 27

helps to detect level of spinal cord damage. can evoke reflexes above but not below the level of damage

Question 28

what may impaired reflexes be a sign of?

Answer 28

nerve damage

Question 29

in the flexor withdrawal reflex, how does sensory information ascend to the brain?

Answer 29

ascends in the contralateral spinothalamic tract

Question 30

why is the flexor withdrawal reflex much slower than the stretch reflex?

Answer 30

1. because there are several interneurons in the pathway each of which have a small synaptic delay
2. nociceptive sensory fibres have smaller diameter than muscle spindle afferents and so conduct more slowly

Question 31

what reflex activates in the case of an excess load being placed on a muscle?

Answer 31

golgi tendon organ reflex

Question 32

can reflexes be consciously over ridden?

Answer 32

yes

Question 33

what causes alpha motoneurones to override the inhibition from the golgi tendon organs?

Answer 33

descending voluntary excitation of said alpha motoneurones

Question 34

how can the stretch reflex be overridden?

Answer 34

strong descending inhibition hypepolarizes aplha motoneurones and the stretch reflex cannot be evoked

Question 35

what does the activity of gamma motoneurones depend on?

Answer 35

entirely on descending pathways

Question 36

what does high gamma motoneurone activation of muscle spindles result in?

Answer 36

it causes muscles to become extremely resistant to stretch and thus become spastic

Question 37

what does facilitation do?

Answer 37

increases the effects of sensory inputs

Question 38

what is the babinski sign?

Answer 38

when damage or disruption to the corticospinal tract causes extension of the toes when the lateral aspect of the sole is stroked

Question 39

when can the babinski sign be seen when nerves are not damaged?

Answer 39

in children less than 1 year old - motor system not fully developed
after epileptic seizures - transient cortical function disruption

Question 40

what happens in spinal transection?

Answer 40

immediate loss of sensory and autonomic effects- loss of bowel, bladder and sexual regulation

Question 41

what is spinal shock?

Answer 41

loss of supraspinal excitation and reflexes not evoked for 2-6 weeks - then gradual return of reflexes

Question 42

what often happens in spinal shock when reflexes return?

Answer 42

reflexes are very exaggerated - light touch evokes powerful withdrawal reflex of the whole limb

Question 43

what is clonus?

Answer 43

stretch causes oscillatory muscle contraction/relaxation, very distressing