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Questions and Answers
What primarily connects motoneurons and central pattern generator neurons during early development?
What primarily connects motoneurons and central pattern generator neurons during early development?
- Gap junctions and synapses (correct)
- Hormonal signals and feedback loops
- Electrical impulses and sensory feedback
- Synapses and chemical signals
Which of the following best describes the role of central pattern generators (CPGs) in locomotion?
Which of the following best describes the role of central pattern generators (CPGs) in locomotion?
- They inhibit motoneurons for fine motor control.
- They provide sensory feedback to the brain.
- They exclusively control arm movements.
- They coordinate rhythmic movements such as walking. (correct)
Which neuronal types are specified by the gene PAX6?
Which neuronal types are specified by the gene PAX6?
- Inhibitory interneurons and motoneurons
- Motoneurons in the spinal cord and V1 interneurons (correct)
- Corticospinal neurons and sensory feedback neurons
- Renshaw cells and glutamatergic interneurons
What role does sensory feedback play in motor control mechanisms?
What role does sensory feedback play in motor control mechanisms?
Which pathway is crucial for high-level movements requiring precision?
Which pathway is crucial for high-level movements requiring precision?
In which way do descending pathways influence motoneurons?
In which way do descending pathways influence motoneurons?
Which neuronal type is predominantly associated with inhibitory functions in the spinal cord?
Which neuronal type is predominantly associated with inhibitory functions in the spinal cord?
What is the primary activity of rhythm-generating neurons during limb alternation?
What is the primary activity of rhythm-generating neurons during limb alternation?
Which tract is primarily responsible for voluntary control of distal musculature?
Which tract is primarily responsible for voluntary control of distal musculature?
What is the main function of the reticulospinal tracts?
What is the main function of the reticulospinal tracts?
Which tract primarily facilitates maintaining head position in response to visual stimuli?
Which tract primarily facilitates maintaining head position in response to visual stimuli?
The vestibulospinal tracts are primarily responsible for which of the following functions?
The vestibulospinal tracts are primarily responsible for which of the following functions?
Which descending pathway provides voluntary control to proximal musculature?
Which descending pathway provides voluntary control to proximal musculature?
Which of the following statements about the rubrospinal tract is correct?
Which of the following statements about the rubrospinal tract is correct?
What happens to voluntary movement following stroke damage to the motor cortex?
What happens to voluntary movement following stroke damage to the motor cortex?
What allows the reticulospinal tract to activate spinal cord neurons on both sides of the spinal cord?
What allows the reticulospinal tract to activate spinal cord neurons on both sides of the spinal cord?
What role do descending pathways generally serve in the spinal cord?
What role do descending pathways generally serve in the spinal cord?
Which structure provides direct synapses onto motoneurons for fine motor control in primates?
Which structure provides direct synapses onto motoneurons for fine motor control in primates?
What type of neurotransmitter is primarily released by the locus coeruleus?
What type of neurotransmitter is primarily released by the locus coeruleus?
Which structure does the cerebral cortex project directly to, influencing motor control?
Which structure does the cerebral cortex project directly to, influencing motor control?
Which type of activity can agonists elicit in spinal cord injury victims?
Which type of activity can agonists elicit in spinal cord injury victims?
What role does the corticospinal tract primarily play in motor control?
What role does the corticospinal tract primarily play in motor control?
How do reticulospinal neurons facilitate movements following injury?
How do reticulospinal neurons facilitate movements following injury?
What distinguishes the development of corticothalamic and spinal cord circuits in humans and rodents?
What distinguishes the development of corticothalamic and spinal cord circuits in humans and rodents?
What is the primary function of the dorsal column nuclei in the spinal cord?
What is the primary function of the dorsal column nuclei in the spinal cord?
Which descending pathway is primarily responsible for voluntary motor control?
Which descending pathway is primarily responsible for voluntary motor control?
How do descending inputs affect spinal cord circuitry?
How do descending inputs affect spinal cord circuitry?
What role do reticulospinal tracts play in locomotion?
What role do reticulospinal tracts play in locomotion?
Which component is NOT considered part of the ascending pathways in the spinal cord?
Which component is NOT considered part of the ascending pathways in the spinal cord?
What is the primary purpose of reflex arcs in the spinal cord?
What is the primary purpose of reflex arcs in the spinal cord?
What is the significance of corticospinal input during spinal cord development?
What is the significance of corticospinal input during spinal cord development?
What is a key characteristic of motor control mechanisms in the spinal cord?
What is a key characteristic of motor control mechanisms in the spinal cord?
What is the role of long propriospinal interneurons (PINs) in locomotion?
What is the role of long propriospinal interneurons (PINs) in locomotion?
Which spinal cord regions do long propriospinal interneurons connect?
Which spinal cord regions do long propriospinal interneurons connect?
In the context of reflex arcs, what primarily distinguishes multisynaptic pathways?
In the context of reflex arcs, what primarily distinguishes multisynaptic pathways?
What function do descending pathways serve in spinal cord reflexes?
What function do descending pathways serve in spinal cord reflexes?
What type of information do long propriospinal interneurons relay to central pattern generators (CPGs)?
What type of information do long propriospinal interneurons relay to central pattern generators (CPGs)?
Which of the following statements about reticulospinal tracts is correct?
Which of the following statements about reticulospinal tracts is correct?
What is primarily mediated by the crossed extensor reflex?
What is primarily mediated by the crossed extensor reflex?
Which characteristic is essential for the functioning of central pattern generators (CPGs)?
Which characteristic is essential for the functioning of central pattern generators (CPGs)?
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Study Notes
Spinal Circuits and Sensorimotor Development
- The motor system functions hierarchically, evolving from simpler to more complex levels.
- Central Pattern Generators (CPGs) are integral for rhythmic movements like locomotion and swimming.
- CPGs are influenced by both sensory feedback and descending inputs, particularly from the corticospinal tract.
Neonatal and Embryonic Development
- Motoneurons and CPG neurons become active before complete sensory reflex arcs.
- Gap junctions and synapses facilitate the spread of activity among these developing neurons.
- Alternating limb movements are maintained by rhythm-generating neurons that excite motoneurons on the same side of the spinal cord.
Axon Projections in the Embryonic Spinal Cord
- Class V0 interneurons are commissural and inhibitory.
- Class V1 interneurons have origins involving PAX6 and NKX6.2, connecting to both sides of the spinal cord.
- Class V2 interneurons consist of excitatory (V2a) and inhibitory (V2b) types, projecting caudally and ipsilaterally.
- Class V3 interneurons are commissural and excitatory, ensuring robust interconnectivity.
Pathways into the Spinal Cord
- Lateral corticospinal tract controls voluntary movements of distal musculature.
- Anterior corticospinal tract manages voluntary control for proximal muscles.
- Reticulospinal tracts initiate and regulate complex reflex patterns such as locomotion.
- Rubrospinal tract primarily enables motor control through excitation of flexor muscles.
- Tectospinal tract helps in orienting movements in response to visual stimuli.
Organizing Motor Control
- Normal motor control involves input from multiple brain regions to spinal cord motoneurons.
- After a unilateral motor cortex lesion, recovery of function is observed over time due to compensation by surviving corticospinal fibers and other pathways like the reticulospinal tract.
- Enhanced bilateral functions are attributed to reticulospinal projections activating bilateral spinal cord neurons.
Sensory Pathways and Reflexes
- Flexor reflex involves multisynaptic pathways that initiate limb withdrawal from harmful stimuli, often coordinated with CPG circuitry.
- Crossed extensor reflex complements flexor responses by stabilizing posture during limb withdrawal.
Long Propriospinal Interneurons
- Long propriospinal interneurons (PINs) connect cervical and lumbar spinal cord regions to coordinate locomotor patterns.
- They relay and process information within the spinal circuit, critical for smooth, coordinated movements.
Neurotransmitter Modulation
- Neurotransmitters like noradrenaline and serotonin fine-tune motor output and pain modulation in the spinal circuits.
- Different receptors mediate inhibitory or excitatory responses to facilitate varied motor activities, especially in response to injury.
Developmental Stages
- In early human and rodent development, sensorimotor cortices and spinal circuits mature independently, leading to complex motor functionalities later.
Recommended Reading
- Explore resources covering descending pathways and spinal circuits for enhanced understanding of motor control and development.
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