L6

Question 1

posture and locomotor control

• righting reflex in decerebrated frog vs spinally-transected
• scratch reflex

Answer 1

present i D but not s-t

scratch = pressent in both = brainstem mediated.

Question 2

function of postural and locomotor control

Answer 2

control positions of body segments in stable relation to each other and to move the body over varying terrain

Question 3

main postural reflexes: 
stretch
placing
hopping
vestibular
righting
neck

Answer 3

s = muscle stretch
p - object in way, move foot around and place
h - shift in centre of gravity, catch self w foot.
v - head acceleration
r- gravity and pressure on body
n - head movements

Question 4

response to stretch reflex? integrated?

Answer 4

resist stretch

spinal cord

Question 5

placing - response? integrated?

Answer 5

lift and place foot forward

spinal cord

Question 6

hooping response? integrated?

Answer 6

step to catch self

spinal cord, brainstem

Question 7

vestibular response? integrated?

Answer 7

stabilize head, extend limb in reaction to acceleration

- midbrain

Question 8

righting response? integrated?

Answer 8

right body

brainstem

Question 9

neck

Answer 9

think yoga moves
head back, open arms and chest
head forward = contract, close chest.
head left = extend ipsilateral side.

brainstem

Question 10

context-dependence and adaptation of postural stretch-reflexes: maintain postural stability

Answer 10

ankle extensor stretch = reduce body sway if foot is displaced horizontally, so CNS augments = less sway.
toe-up rotation = destabilizing. CNS attenuates in successive trials. more sway.

Question 11

context -dependence and adaptation controlled by?

postural muscles activated involuntarily because voluntary movement of limbs

Answer 11

controlled by cerebellum and brainstem reticular fromation. - back actviated before grab something with hand.

Question 12

stable, variable-speed movement across unpredicatble terrain

solution?

Answer 12

complex cyclical coordination of muscles
adaptation w vision, proprioception, skin receptor feedback
automaticity to “free” higher centers in CNS

Question 13

locomotor step cycle & muscle activity

Answer 13

stance - extensor
swing = flexor
transition: bi-functional muscles

Question 14

digitigrade gait

vs plantigrade

Answer 14

walk on toes

walk on flat foot

Question 15

first basic question:

Answer 15

neural network that sequences muscles in mammalian locomotion in the spinal cord or supraspinal centres?

Question 16

clinical conditions evidence for supraspinal pattern generation

Answer 16

stroke: poor, absent flexion of hip.
spinal cord injury: paralysis below level of spinal transection
PD: inability to initiate locomotion, suffling steps
cereballar ataxis: unsteady gait, scissoring, high-stepping.

Question 17

graham browns experiment in cats

Answer 17

anesthetized cats decerebrated, abolishing consciousness.
- leg flexor, extensor could still generate alternating, rhtyhmic movments in response to strong sensory input & elec stim of brainstem.
CPG - in spinal cord

Question 18

experimental evidence supporting spinal pattern generation

Answer 18

• activating spinal cord below complete transection can elicit locomotr rhyth,
  = needs descending drive

Question 19

clinical evidence support spinal pattern generation

Answer 19

locomotor rhyth, elicited in parapalegic with spinal cord transections with e.stim, clondifine, cyproheptidine.
clondidine- mediate presynatpic inhibition, reduce spasticity and facilitate locomotion.
recovery from cerebellar damage, cortical damage can walk normal.

Question 20

experimental evidence that descending drive in important

Answer 20

high decerebrate cats - intact midbrain adapt to speed. caudal transections cannot.
- e. stim in MLR of midbrain of decerebrate promotes locomotion. can increase step cycle rate and locomotor velocity.
TMS affects leg flexor more than extensor
neurons rhythmically co-activated with leg muscles, indicating pattern generation role.

Question 21

second basic question:

Answer 21

locomotor CPG entirely within CNS or sensory afferents part of it?

hypothesis: intrinsic mechanism capable of generating locomotor pattern without sensory input.
- command neurons = activity spontaneously bursts in rhyth,. elicit and coordinate rhythmical activity of neurons controlling limb muscles in absence of sensory input.

Question 22

experimental evidence for basic rhythm generator in CNS

Answer 22

• rhythmical activity of leg muscles elicited in de-afferented animals.

Question 23

experimental evidence for CPG being entirely in spinal cord

Answer 23

fictive locomotion: rhythmic activity in decerebrated animals. require IV drugs or steady electrical stimulation of sensory nerve roots to provide generalized CNS excitation.

Question 24

clinical evidence that sensory contributes to locomotor pattern generation

Answer 24

gait in de-afferented abnormal. incorrect timing, muscle sequencing

Question 25

experimental evidence that sensory afferent contributes

Answer 25

stretch reflexes - sensory. affect muscle activation
reflex responses modify locomotor pattern
bule-based phase swtiching = phase transitions between swing and stance phases triggered by sensory input

Question 26

if-then sensory-triggered rules for gait

Answer 26

swing onset: if stance, extensor force low, leg extended, contralateral foot on ground THEN flex and swing
stumble: IF in swing, skin stimulus THEN swing forward and place.
BUT IF in stance and skin stimulus THEN maintain ground contact

backward gait: IF stance, extensor force low, hip flexed forward and contralateral foot on ground THEN flex and swing back.

Question 27

third basic Q

answer?

Answer 27

is spinal locomotor CPG localized or distributed along several segments?
generated by single segment of lumbar and sacral spinal cord, even half of single segment. rostral segments set rhythm generated by caudal segments.

Question 28

overall conclusions of control system

Answer 28

CPG in spinal cord. strong modulation from descending and sensory inputs.
gait initiated by descending drive from BG and hypothalamus.

Question 29

desired velocity of body may be basic descending command signal.

-

Answer 29

decerebrate locomotive cats. highly cerebrate, walk spontaneously if treadmill starts = increased stimulation of midbrain = increase speed.

gait velocity command from BG and hypo, mediated by MLR. different CPG neurons, force feedback.

Question 30

different neurons in CPG responsible for?

Answer 30

speed of movement, duration of phases.

which muscles activated, how strongly activated.