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Questions and Answers
What initiates the withdrawal reflex?
What initiates the withdrawal reflex?
- Mechanical stimulation of the skin
- Motor neuron activation
- Stretch receptor signals
- Nociceptor activation (correct)
What happens to the motor neurons of extensor muscles during the withdrawal reflex?
What happens to the motor neurons of extensor muscles during the withdrawal reflex?
- They are excited by interneurons
- They are activated
- They remain unchanged
- They are inhibited (correct)
How do crossed extensor reflexes differ from withdrawal reflexes?
How do crossed extensor reflexes differ from withdrawal reflexes?
- They occur at the same time and involve opposite limbs (correct)
- They do not involve excitatory interneurons
- They are slower in response than withdrawal reflexes
- They are triggered by non-painful stimuli
What is the role of the sensorimotor cortex in transcortical stretch reflexes?
What is the role of the sensorimotor cortex in transcortical stretch reflexes?
Which type of reflex involves more complex circuits than simple withdrawal responses?
Which type of reflex involves more complex circuits than simple withdrawal responses?
What might happen to voluntary actions in the presence of reflex abnormalities?
What might happen to voluntary actions in the presence of reflex abnormalities?
What influences reflex sensitivity in relation to postural stability?
What influences reflex sensitivity in relation to postural stability?
What is the role of 'preparatory set' in postural control?
What is the role of 'preparatory set' in postural control?
In the experiments assessing reflexes, how did reflex amplitude change?
In the experiments assessing reflexes, how did reflex amplitude change?
What experimental setup was used to examine reflex responses to instability?
What experimental setup was used to examine reflex responses to instability?
What type of reflexes are believed to contribute to postural stability in complex 3D situations?
What type of reflexes are believed to contribute to postural stability in complex 3D situations?
How do reflexes respond to non-symmetric stability situations?
How do reflexes respond to non-symmetric stability situations?
What early changes occur in response to postural errors?
What early changes occur in response to postural errors?
Which variable does NOT influence the modulating of reflex responses?
Which variable does NOT influence the modulating of reflex responses?
What distinguishes transcortical reflexes from their spinal equivalents?
What distinguishes transcortical reflexes from their spinal equivalents?
Which strategy is least suitable for correcting standing posture during small perturbations on stable surfaces?
Which strategy is least suitable for correcting standing posture during small perturbations on stable surfaces?
What is a key feature of anticipatory postural adjustments (APAs)?
What is a key feature of anticipatory postural adjustments (APAs)?
Which of the following best describes automatic reactions in postural control?
Which of the following best describes automatic reactions in postural control?
What role does the brainstem play in reactive postural control strategies?
What role does the brainstem play in reactive postural control strategies?
How does the cortex influence the stretch reflex circuit during voluntary actions?
How does the cortex influence the stretch reflex circuit during voluntary actions?
What has been demonstrated regarding pre-movement changes in neural activity?
What has been demonstrated regarding pre-movement changes in neural activity?
In the context of postural stability, what role does preparatory set play?
In the context of postural stability, what role does preparatory set play?
What was concluded regarding the impact of motor cortex inhibition on reflex modulation?
What was concluded regarding the impact of motor cortex inhibition on reflex modulation?
What happens to stretch reflex sensitivity when stability is reduced?
What happens to stretch reflex sensitivity when stability is reduced?
How does co-contraction relate to environmental stability?
How does co-contraction relate to environmental stability?
Which region showed larger long latency stretch reflexes without TMS in an unstable situation?
Which region showed larger long latency stretch reflexes without TMS in an unstable situation?
What did the hypothesis regarding co-contraction suggest?
What did the hypothesis regarding co-contraction suggest?
What effect does TMS have on reflex responses in relation to postural stability?
What effect does TMS have on reflex responses in relation to postural stability?
What is suggested about reflex role in stability with regards to upper limbs?
What is suggested about reflex role in stability with regards to upper limbs?
Which hypothesis concerning motor cortex inhibition and reflex modulation is proposed?
Which hypothesis concerning motor cortex inhibition and reflex modulation is proposed?
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Study Notes
Reflexes
- Reflexes are automatic responses to stimuli, involving neural circuits within the spinal cord.
- Examples include the withdrawal reflex and the crossed extensor reflex.
- The withdrawal reflex is initiated by pain receptors (nociceptors) and causes the withdrawal of a limb from a painful stimulus.
- The crossed extensor reflex is a simultaneous response where the opposite limb extends to provide stability during the withdrawal reflex.
Reflex Modulation
- Reflexes can be modulated by various factors, including the context of movement and the level of voluntary control.
- Transcortical stretch reflexes involve signals from stretch receptors reaching the sensorimotor cortex and modifying the reflex response.
- Preparatory set refers to the readiness of the motor system to generate a desired action or response, potentially influencing reflex expression.
- Changes in co-contraction, or the simultaneous activation of opposing muscle groups, are important for postural stability, with levels increasing as environmental stability decreases.
Automatic Postural Reactions
- Automatic postural reactions are complex responses to postural perturbations, involving multiple muscles and occurring too late to be reflexes.
- These reactions are generated in the brainstem and are likely driven by feedback or feedforward mechanisms.
- Anticipatory postural adjustments (APAs) are feed-forward responses to expected perturbations, occurring before a movement to enhance stability.
Reflex & Voluntary Interactions
- The cortex can regulate lower motor circuits and modulate reflexes.
- Voluntary muscle activation can inhibit reflexes, demonstrating cortical-spinal interactions.
- Muscle synergies, the coordinated activation of muscle groups, may simplify the complex control of movement.
Reflex Abnormalities
- Spasticity, an involuntary increase in muscle tone, often results from reduced inhibition of stretch reflexes due to reduced cortical input.
- This hyper-reactive stretch reflex leads to velocity-dependent resistance to movement and can cause pain.
- Abnormal reflexes are often the result of damage to the central nervous system, disrupting the normal regulation of reflex pathways.
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