lecture 17

Questions and Answers

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?

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?

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?

It helps regulate and adjust movements. Signup and view all the answers

Which pathway is crucial for high-level movements requiring precision?

The corticospinal tract Signup and view all the answers

In which way do descending pathways influence motoneurons?

They provide input and modulation of motoneuron activity. Signup and view all the answers

Which neuronal type is predominantly associated with inhibitory functions in the spinal cord?

V0 interneurons Signup and view all the answers

What is the primary activity of rhythm-generating neurons during limb alternation?

They excite motoneurons on the same side. Signup and view all the answers

Which tract is primarily responsible for voluntary control of distal musculature?

Lateral corticospinal tract Signup and view all the answers

What is the main function of the reticulospinal tracts?

Initiate patterned activity and regulate reflexes Signup and view all the answers

Which tract primarily facilitates maintaining head position in response to visual stimuli?

Tectospinal tract Signup and view all the answers

The vestibulospinal tracts are primarily responsible for which of the following functions?

Controlling antigravity muscles and regulating balance Signup and view all the answers

Which descending pathway provides voluntary control to proximal musculature?

Anterior corticospinal tract Signup and view all the answers

Which of the following statements about the rubrospinal tract is correct?

It is involved in excitation of flexor muscles Signup and view all the answers

What happens to voluntary movement following stroke damage to the motor cortex?

Severe loss of voluntary movement unilaterally Signup and view all the answers

What allows the reticulospinal tract to activate spinal cord neurons on both sides of the spinal cord?

It receives inputs from the undamaged cerebral hemisphere and projects bilaterally. Signup and view all the answers

What role do descending pathways generally serve in the spinal cord?

Regulate voluntary and reflex motor control Signup and view all the answers

Which structure provides direct synapses onto motoneurons for fine motor control in primates?

Lateral corticospinal tract Signup and view all the answers

What type of neurotransmitter is primarily released by the locus coeruleus?

Noradrenaline Signup and view all the answers

Which structure does the cerebral cortex project directly to, influencing motor control?

Brainstem and spinal cord Signup and view all the answers

Which type of activity can agonists elicit in spinal cord injury victims?

Central pattern generator (CPG) activity Signup and view all the answers

What role does the corticospinal tract primarily play in motor control?

Coordination of fine voluntary movements Signup and view all the answers

How do reticulospinal neurons facilitate movements following injury?

They utilize inputs from undamaged hemispheres to activate both sides. Signup and view all the answers

What distinguishes the development of corticothalamic and spinal cord circuits in humans and rodents?

They develop independently in humans but not in rodents. Signup and view all the answers

What is the primary function of the dorsal column nuclei in the spinal cord?

Processing sensory information Signup and view all the answers

Which descending pathway is primarily responsible for voluntary motor control?

Corticospinal tract Signup and view all the answers

How do descending inputs affect spinal cord circuitry?

They refine motor output and coordination. Signup and view all the answers

What role do reticulospinal tracts play in locomotion?

They modulate spinal reflexes and locomotion patterns. Signup and view all the answers

Which component is NOT considered part of the ascending pathways in the spinal cord?

Corticospinal tract Signup and view all the answers

What is the primary purpose of reflex arcs in the spinal cord?

To mediate involuntary responses to stimuli. Signup and view all the answers

What is the significance of corticospinal input during spinal cord development?

It influences the formation and maintenance of spinal circuits. Signup and view all the answers

What is a key characteristic of motor control mechanisms in the spinal cord?

They integrate both descending and ascending signals for coordination. Signup and view all the answers

What is the role of long propriospinal interneurons (PINs) in locomotion?

They facilitate interlimb coordination and relay information to central pattern generators. Signup and view all the answers

Which spinal cord regions do long propriospinal interneurons connect?

Cervical and lumbar spinal cords. Signup and view all the answers

In the context of reflex arcs, what primarily distinguishes multisynaptic pathways?

Engagement of multiple interneurons between sensory and motor neurons. Signup and view all the answers

What function do descending pathways serve in spinal cord reflexes?

They regulate reflex responses and coordinate motor activity. Signup and view all the answers

What type of information do long propriospinal interneurons relay to central pattern generators (CPGs)?

Sensory feedback related to limb position and movement. Signup and view all the answers

Which of the following statements about reticulospinal tracts is correct?

They encompass both excitatory and inhibitory pathways to regulate muscle tone. Signup and view all the answers

What is primarily mediated by the crossed extensor reflex?

Extension of the contralateral limb to support balance. Signup and view all the answers

Which characteristic is essential for the functioning of central pattern generators (CPGs)?

Ability to generate rhythmic outputs independently of sensory input. Signup and view all the answers

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.

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Description

Explore the intricate mechanisms underlying spinal circuits and their role in sensorimotor development. This quiz covers topics such as Central Pattern Generators, motoneuron activity in early development, and the different classes of interneurons in the spinal cord. Test your understanding of how these elements contribute to rhythmic movements and motor functions.