W9 - Control Gait Flashcards
What are the current theories on Bipedal walking?
- To allow foraging on the savannah when the sun is overhead and quadrupeds must seek shade
- To make the bipedalist appear taller to intimidate predators and antagonists
- To fulfil the locomotor needs of scavengers; migratory scavengers following ungulate herds; endurance hunters & game stalkers
- Due to prolonged flooding our ancestors were driven out of the remaining forest and into the sea, where there was an abundance of accessible food
- all of which are said to be as a result of central pattern generators in the spinal cord
What are the adaptations associated with bipedalism?
- The foramen magnum (hole in the bottom of the skull) allows us to hold our heads up, not hang forward
- We do not have an opposable toe to hand onto things, for faster walking
- our vertebral column is less stiff, has curvature allowing humans to stand-up tall and straight
- increased hip/knee angle for larger strides and optimal walking technique
Label and describe the basic stepping pattern?
- Stance phase about 60% and swing phase about 40%
- Gait cycle starts with a heel strike = the beginning of a cycle
- Constant braking and propulsion
- initial-double limb support, single-limb support, second double-lime support, initial swing, mid swing and terminal swing
Describe the animal model preparation for classic locomotion studies:
The cat rhythmic activity of walking (Graham Brown,1911)
- transecting mid brain = decerebrate (no brain)
- Transecting the spinal cord & cut dorsal roots = animals have no sensory feedback
- recorded from tendon in gastrocnemius & tibialis anterior of cat
= stepping pattern comes from neural circuits in the SC, but also brain –> from sensory & limb proprioception
What were the 4 conclusions from the (Graham, 1911) study?
- Supraspinal structures are not necessary for producing the basic motor patterns of stepping.
- The basic rhythmicity of stepping is produced by neuronal circuits contained entirely within the spinal cord.
- The spinal circuits can be activated by tonic descending signals from the brain, stimulating areas of the brain.
- The spinal pattern generating networks do not require sensory input but nevertheless are strongly regulated by input from limb proprioceptors.
What is the stretch & flexor reflex afferents (FRA)?
Which study investigated the Half-center hypothesis by
A) stimulating flexor reflex afferents
B) half-center organisation
- Stretch reflex concept - Excites 1a inhibitory neuron that inhibits the antagonist
- Knee jerk is important for preventing slipping and falling over (Jankoswska et al., 1967)
- Half-centre hypothesis (Graham brown)
- Stimulating the contralateral FRA excites the extensor interneuron which excites a flex motor neurone (Exciting eachother)
- With time the extensor interneuron fatigues = flex interneuron to work fully(or visversa) -> allows us to rely on reciprocal inhibition. All in spinal cord, but is initiated/stopped by brain
How and who evolved the half-centre hypothesis into the central pattern generator (CPG) hypothesis in Lamprey:
- (Grilner, 1960) used Lamprey fish(moving through water by a sinusoidal wave pattern of each body segment, propelling it through the water)
- rhythm isolated in the spinal cord can still be achieved by cut parts
- all sensory input is formed by a set of neurons in the SC alternating (flex & ext), (excit & inhib neurons), sent to the brain stem. - made up of sensory neurons(detect stretching), interneurons and motor neurons.
- Dorsal and ventral motor neurons innervate to propelling muscles rhythmically.
What is the mesencephalic locomotor region?
the centre in the brainstem can trigger locomotion and change the speed and pattern of movement by changing the level of activity delivered to the spinal cord.
What were the 2 studies to determine if CPGs exist in humans?
- (Yang et al., 1998) studied inflants, where an infant that was lowered onto a treadmill at 3 months old, could generate a somewhat walking pattern. However this pattern could have been coming from anywhere in the body, as the baby was not cerebrate
- (Dimitrijevic et al., 1998) studied spinal cord injury patients. The electrode implanted in T12 of the SC and stimulated it to replicate a tonic input. An got locomotor like activity, however this might have been produced by the brain not the SC
What are the supraspinal functions:
Supraspinal functions:
- activate CPG (initiate walking)
- control speed
- refine motor pattern in response to afferent feedback
- guide limb movement in response to visual stimuli
How is walking adaptively controlled?
- muscles = afferent signals -> cerebellum in brain stem cause corrections
- vision = excites the visual cortex -> motor cortex allowing for visual guidance of locomotion e.g.: stepping onto a curb
Describe the study by (Petersen et al., 2012)
EG-EMG coherence during walking provides evidence for motor cortex control of TA
- Treadmill walking that monitored muscle activity with electrodes
- Used frequency spectrum, for strength of the activity at different freq
- The brain is responsible for the locomotion pattern
How can we investigate cortical control of walking?
- using transcranial magnetic stimulation
- It creates an electrical stimulus to excite the motor cortex to get tibialis anterior muscle to contract
- Very repeatable signal
- Navigated TMS ensures we can stimulate the area of the motor cortex for the tibialis anterior muscle
- (Zuur et al., 2009)
What is the difference seen by short-latency intracortical inhibition (SICI)
- uses TMS
1) conditioning stimulus 2s before test stimulus (control not felt as it at threshold)
2) test stimulus - shows descending drive to the muscles in humans = more important than the central pattern generators (from brain) & shows inhibition during walking
Describe the study by (Winter, 1992):
- Control of toe clearance during swing phase is critical for bipedal walking
- Brain is more important to prevent tripping because of the descending control
