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Questions and Answers
The motoneurons in the ventromedial portion of the spinal cord are responsible for the flexor muscles of the limbs.
The motoneurons in the ventromedial portion of the spinal cord are responsible for the flexor muscles of the limbs.
False (B)
Short propriospinal interneurons connect motor neurons located in adjacent spinal cord segments.
Short propriospinal interneurons connect motor neurons located in adjacent spinal cord segments.
True (A)
The Ia inhibitory interneuron is not involved in the stretch reflex.
The Ia inhibitory interneuron is not involved in the stretch reflex.
False (B)
Long propriospinal interneurons facilitate communication between the cervical and sacral segments of the spinal cord.
Long propriospinal interneurons facilitate communication between the cervical and sacral segments of the spinal cord.
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Interneurons play a minimal role in modulating the signals within the spinal cord.
Interneurons play a minimal role in modulating the signals within the spinal cord.
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The corticospinal system allows for purposeful use of the hand and arm under the control of the spinal cord.
The corticospinal system allows for purposeful use of the hand and arm under the control of the spinal cord.
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In cats, 40% of the frontal lobe is dedicated to the primary motor functions.
In cats, 40% of the frontal lobe is dedicated to the primary motor functions.
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The layer that originates corticospinal fibers is predominantly the 4th layer of the cerebral cortex.
The layer that originates corticospinal fibers is predominantly the 4th layer of the cerebral cortex.
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The majority of corticospinal fibers in primates are uncrossed.
The majority of corticospinal fibers in primates are uncrossed.
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In humans, corticospinal fibers directly interact with all motor neurons, including axial muscles.
In humans, corticospinal fibers directly interact with all motor neurons, including axial muscles.
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Termination of the corticospinal tract in goats occurs mainly in the lumbar region.
Termination of the corticospinal tract in goats occurs mainly in the lumbar region.
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The largest termination of the corticospinal fibers occurs in the thoracic region.
The largest termination of the corticospinal fibers occurs in the thoracic region.
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Sherrington emphasized the role of the cortex in reflex actions, stating that reflexes can only be controlled by spinal mechanisms.
Sherrington emphasized the role of the cortex in reflex actions, stating that reflexes can only be controlled by spinal mechanisms.
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The Ib interneuron is positioned directly between Ib fibers and sensory neurons.
The Ib interneuron is positioned directly between Ib fibers and sensory neurons.
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Autogenic inhibition operates with increased intensity as muscle force increases, preventing over-exertion.
Autogenic inhibition operates with increased intensity as muscle force increases, preventing over-exertion.
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Renshaw cells are excitatory interneurons responsible for enhancing motoneuron activity.
Renshaw cells are excitatory interneurons responsible for enhancing motoneuron activity.
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Humans possess a unique descending system that enables them to perform voluntary movements with high precision.
Humans possess a unique descending system that enables them to perform voluntary movements with high precision.
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All mammals exhibit the same dexterity and voluntary movement capabilities as humans.
All mammals exhibit the same dexterity and voluntary movement capabilities as humans.
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Independent movements of fingers in humans are solely dependent on anatomical structures.
Independent movements of fingers in humans are solely dependent on anatomical structures.
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The first step in assessing hand function after a stroke is to check for independent finger movements.
The first step in assessing hand function after a stroke is to check for independent finger movements.
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The precision grip in humans is facilitated by the anatomical independence of hand muscles.
The precision grip in humans is facilitated by the anatomical independence of hand muscles.
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The motor neurons communicate only with short proprio spinal neurons.
The motor neurons communicate only with short proprio spinal neurons.
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The circuitry for locomotion is entirely independent of any brain modulation.
The circuitry for locomotion is entirely independent of any brain modulation.
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The spinal cord does not play a role in organizing voluntary movements.
The spinal cord does not play a role in organizing voluntary movements.
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Motor neurons are the final common path to skeletal muscles.
Motor neurons are the final common path to skeletal muscles.
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The cortex operates at a low organizational level compared to the brainstem.
The cortex operates at a low organizational level compared to the brainstem.
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The muscle's force production is the same at all lengths regardless of motor neuron discharge frequency.
The muscle's force production is the same at all lengths regardless of motor neuron discharge frequency.
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The stretch reflex involves direct signaling from Ia fibers to motoneurons.
The stretch reflex involves direct signaling from Ia fibers to motoneurons.
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The spinal cord's motoneuron pools are disorganized without somatotopic arrangement.
The spinal cord's motoneuron pools are disorganized without somatotopic arrangement.
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The brain cannot modulate the force exerted by muscle fibers through the frequency of discharge.
The brain cannot modulate the force exerted by muscle fibers through the frequency of discharge.
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Ib fibers have a role in preventing excessively high force by causing muscle relaxation.
Ib fibers have a role in preventing excessively high force by causing muscle relaxation.
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The ventral horn of the spinal cord is comprised solely of a dorsolateral section.
The ventral horn of the spinal cord is comprised solely of a dorsolateral section.
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The sensor and motor systems do not need to communicate for proper movement functioning.
The sensor and motor systems do not need to communicate for proper movement functioning.
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The diencephalon and telencephalon do not communicate with the spinal cord.
The diencephalon and telencephalon do not communicate with the spinal cord.
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The ventral corticospinal tract accounts for 20% of the corticospinal system and is homolateral.
The ventral corticospinal tract accounts for 20% of the corticospinal system and is homolateral.
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The primary motor cortex is exclusively responsible for sensory input in the brain.
The primary motor cortex is exclusively responsible for sensory input in the brain.
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Macaques are chosen as animal models for research on the corticospinal system due to their close proximity to human brain functions.
Macaques are chosen as animal models for research on the corticospinal system due to their close proximity to human brain functions.
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The lateral corticospinal tract does not decussate before innervating the spinal cord.
The lateral corticospinal tract does not decussate before innervating the spinal cord.
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The extended limbic system plays no role in driving human behaviors related to survival.
The extended limbic system plays no role in driving human behaviors related to survival.
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Neurons retrogradely labeled can show projections from various cortical areas to the corticospinal tract.
Neurons retrogradely labeled can show projections from various cortical areas to the corticospinal tract.
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The cingulate cortex does not contribute to the corticospinal tract in humans.
The cingulate cortex does not contribute to the corticospinal tract in humans.
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The somatosensory cortex has no descending pathways to the anterior horn of the spinal cord.
The somatosensory cortex has no descending pathways to the anterior horn of the spinal cord.
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The primary motor cortex is located in area 4 of the frontal lobe.
The primary motor cortex is located in area 4 of the frontal lobe.
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Study Notes
Cortical Control of Movement
- Voluntary movement is controlled hierarchically, involving the cortex, brainstem, and spinal cord. No single part is more essential.
- Lou Gehrig's disease highlights the crucial role of motor neurons. Without them, the spinal cord cannot organize movements, either reflexive or voluntary. Motor neurons are the final pathway to skeletal muscles.
- The cortex is the highest level, but this isn't because it's physically dominant. It controls lower levels (brainstem and spinal cord) to orchestrate movement.
Spinal Cord Organization
- The spinal cord is part of the central nervous system (CNS), while nerves are peripheral.
- The brain directly controls muscle force through two primary mechanisms:
- Firing frequency of motor neurons
- Number of motor units recruited (size principle)
- Muscles also have inherent length-dependent force production. A change in muscle length alters the force produced at the same firing frequency.
- Reflexive actions, like the stretch reflex, bypass higher brain centers for faster response. Ia fibers directly adjust excitability of motoneurons based on muscle length.
- Ib fibers provide feedback from tendon organs to regulate force. Excessive force causes muscle relaxation.
- Motor neurons synapse in lamina IX of the anterior horn. They are organized into pools and typically involve multiple segments.
- Sensory and motor systems communicate in the same way, with a shared language. Dysfunction can occur if they don't communicate correctly.
Descending Systems
- Descending systems from the cortex and brainstem control movement in the spinal cord in both contralateral and ipsilateral ways, mediating the body's posture and movements.
- Ventral corticospinal tract is homolateral, but works bilaterally through spinal cord commissure, controlling epaxial and proximal muscles.
- Lateral corticospinal tract is the major decussating (crossing over), portion controlling 80% of movements.
- Medial descending pathways come from the brainstem (tectum, reticular formation, vestibular nuclei) controlling medial parts, for posture & balance.
- Lateral pathways are from the red nucleus (rubrospinal tract) and control distal parts of limbs.
- Medial pathways control epaxial and proximal muscles; lateral pathways control distal limb muscles.
- There are two families of systems: medial and lateral. Medial systems control primarily posture, axial, and proximal movements. Lateral systems control more specific and distal movements.
Brainstem Descending Pathways
- Multiple pathways exist, besides corticospinal. They are responsible for both voluntary and involuntary actions. The rubrospinal tract originates from the red nucleus mimicking the lateral corticospinal tract in function.
- Other brainstem pathways are for emotional motor control, including communication with segments of the autonomic nervous system. These systems can modulate spinal cord activity beyond simple movement.
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Description
This quiz examines the hierarchical control of voluntary movement, focusing on the roles of the cortex, brainstem, and spinal cord. It also covers the impact of motor neurons and conditions like Lou Gehrig's disease on movement organization. Test your understanding of these complex interactions in the nervous system.
