(S1W4) Neurophysiological Control part 1

Question 1

What are reflexes?

Answer 1

• A reflex is an involuntary, or automatic, action that your body does in response to something- without giving conscious thought.
• They are essential fundamental constructs in the neuromuscular system
• Typically a stimulus gives a single response
• Simple reflexes have no CNS control; action-reaction cannot stop it.
• More complex reflexes involve many more interneurons, some can be mediated by descending signals.

Question 2

What are oscillators?

Answer 2

● Reflexes trigger more complex oscillators for responses
● Neural oscillations are rhythmic or repetitive patterns of neural activity in the central nervous system.
● Brains waves are large scale neural oscillations.
● Stimulus rhythm does not equal the motor rhythm; it can be self sustaining so it does not need external or descending tract input, such as cardiac pacemaker cells
● With an oscillator there can be one stimulus, leading to a pattern of output

Question 3

What are central pattern generators?

Answer 3

• A conceptual term which describes a group of neurons that produce a movement, without any sensory feedback.
• A type of oscillator
• Much more complex than a reflex
• There is a CPG for most movements; such as walking, standing, sneezing, sucking, chewing etc. (these are endogenous activites)
• When you’re walking, there is no consistent movement as there is always something affecting the way that you move, such as the level of ground, or if you’re carrying a weight. So the CPG, while it does not require sensory feedback, it is fine-tuned by sensory feedback.
• Most research into CPGs has been carried out on animals instead of humans.

Question 4

Spinal wipey frog example

Answer 4

• The spinal cord of frogs were cut across the cervical vertebrae so brain and conscious control not involved
• Then, an acid soaked tissue was placed on its back.
• It was found that, the frog’s legs will wipe it off with a specific movement pattern depending where on the back the tissue is
• If you block a joint in the leg it will still achieve the task first time
• Shows the frog can do a complex action without brain
• Also shows even without a motor program, if you restrict how it can do it, it still does it
• No control as per the motor programme theory
• Shows motion is not joint control orientated
• So it must have a selection of central pattern generated movements which have some level adaptability

Question 5

decerebate cat gait example

Answer 5

• The spinal cord of cats was cut across the brain stem so no brain involvement
• Then, a harness was attached to support cat’s body weight
• There was input from the feet to the spine
• Different gait patterns were exhibited with treadmill speed
• No conscious control from brain as per the motor programme theory
• So shows that cats still have various walking patterns depending on speed, with no brain input

Question 6

Proof of central pattern generators in humans

Answer 6

• Use humans who are already paralysed
• Use electrical sensitisation of spinal cord to stimulate just below spinal cord injury
• Use manual therapy (physically move the leg) giving sensory input from leg to spinal cord
• Movements and basic walking patterns restored with no brain input
• Showing there is some form of oscillatory nervous system that isn’t controlled at the brain level