15 Questions
What is the primary function of upper motor neurons?
To control lower motor neurons and their activity
Where are the somas of upper motor neurons primarily found?
In the cerebral cortex
What is the corticospinal tract?
A collection of axons that travel from the cerebral cortex to lower motor neurons in the spinal cord
What is a sign of upper motor neuron dysfunction?
Hypertonia
What is the result of dysfunction of the corticospinal tract on one side of the spinal cord?
Weakness on the same side of the body
Which of the following statements about upper motor neurons is true?
Information flows from the cerebral cortex down the axons to lower motor neuron somas and then to skeletal muscle cells.
What is the primary difference between the corticospinal tract and the corticobulbar tract?
The corticospinal tract innervates lower motor neurons in the brain stem, while the corticobulbar tract innervates lower motor neurons in the spinal cord.
What is the result of dysfunction of the corticobulbar tract?
Different patterns of weakness.
What can occur with or without weakness as a result of upper motor neuron dysfunction?
Upper motor neuron signs.
Dysfunction of which neurons can cause weakness?
Either lower motor neurons or upper motor neurons.
In which part of the central nervous system do the axons of upper motor neurons primarily synapse?
Brain stem or spinal cord
A person exhibits weakness on the left side of their body. If the dysfunction is in the corticospinal tract, where is the likely location of the lesion?
Right side of the brain
What is the term for rhythmic contraction of antagonist muscles, often seen in upper motor neuron dysfunction?
Clonus
A patient exhibits hypertonia and clonus in their legs. What is the likely site of the lesion?
Cerebral cortex
What is the direction of information flow in the corticospinal tract?
From the cerebral cortex down to lower motor neurons
Study Notes
Upper Motor Neurons
- Different from lower motor neurons, which have somas in the brain stem or spinal cord and send axons to skeletal muscle cells
- Upper motor neurons control lower motor neurons and their activity
- Somas of upper motor neurons are found mainly in the cerebral cortex
- Axons of upper motor neurons descend to synapse on lower motor neurons in the brain stem or spinal cord
- Information flows from the cerebral cortex down the axons to lower motor neuron somas and then to skeletal muscle cells
Corticospinal Tract
- A collection of axons that travel from the cerebral cortex to lower motor neurons in the spinal cord
- Most axons cross over to the other side of the spinal cord before synapsing on lower motor neurons
- Dysfunction of the corticospinal tract on one side of the spinal cord usually results in weakness on the same side of the body
- Dysfunction of the corticospinal tract on the other side of the brain results in weakness on the opposite side of the body
Corticobulbar Tract
- A collection of axons that travel from the cerebral cortex to lower motor neurons in the brain stem
- Upper motor neuron axons often innervate lower motor neurons on the same side of the brain stem
- Dysfunction of the corticobulbar tract can result in different patterns of weakness
Upper Motor Neuron Signs
- Hyperreflexia: an increase in muscle stretch reflexes
- Clonus: rhythmic contraction of antagonist muscles
- Hypertonia: increased tone of skeletal muscles
- Extensor Plantar Response (Babinski Sign): abnormal extension of the toes in response to scraping the bottom of the foot
Dysfunction
- Dysfunction of either lower motor neurons or upper motor neurons can cause weakness
- Upper motor neuron signs can occur with or without weakness, and can help distinguish between upper and lower motor neuron dysfunction
Upper Motor Neurons
- Upper motor neurons control lower motor neurons and their activity
- Found mainly in the cerebral cortex
- Axons descend to synapse on lower motor neurons in the brain stem or spinal cord
- Information flows from the cerebral cortex down the axons to lower motor neuron somas and then to skeletal muscle cells
Corticospinal Tract
- Collection of axons from the cerebral cortex to lower motor neurons in the spinal cord
- Most axons cross over to the other side of the spinal cord before synapsing on lower motor neurons
- Dysfunction on one side of the spinal cord results in weakness on the same side of the body
- Dysfunction on the other side of the brain results in weakness on the opposite side of the body
Corticobulbar Tract
- Collection of axons from the cerebral cortex to lower motor neurons in the brain stem
- Upper motor neuron axons often innervate lower motor neurons on the same side of the brain stem
- Dysfunction results in different patterns of weakness
Upper Motor Neuron Signs
- Hyperreflexia: increased muscle stretch reflexes
- Clonus: rhythmic contraction of antagonist muscles
- Hypertonia: increased tone of skeletal muscles
- Extensor Plantar Response (Babinski Sign): abnormal extension of the toes in response to scraping the bottom of the foot
Dysfunction
- Dysfunction of either lower motor neurons or upper motor neurons can cause weakness
- Upper motor neuron signs can occur with or without weakness, and help distinguish between upper and lower motor neuron dysfunction
Upper Motor Neurons
- Upper motor neurons control lower motor neurons and their activity
- Found mainly in the cerebral cortex
- Axons descend to synapse on lower motor neurons in the brain stem or spinal cord
- Information flows from the cerebral cortex down the axons to lower motor neuron somas and then to skeletal muscle cells
Corticospinal Tract
- Collection of axons from the cerebral cortex to lower motor neurons in the spinal cord
- Most axons cross over to the other side of the spinal cord before synapsing on lower motor neurons
- Dysfunction on one side of the spinal cord results in weakness on the same side of the body
- Dysfunction on the other side of the brain results in weakness on the opposite side of the body
Corticobulbar Tract
- Collection of axons from the cerebral cortex to lower motor neurons in the brain stem
- Upper motor neuron axons often innervate lower motor neurons on the same side of the brain stem
- Dysfunction results in different patterns of weakness
Upper Motor Neuron Signs
- Hyperreflexia: increased muscle stretch reflexes
- Clonus: rhythmic contraction of antagonist muscles
- Hypertonia: increased tone of skeletal muscles
- Extensor Plantar Response (Babinski Sign): abnormal extension of the toes in response to scraping the bottom of the foot
Dysfunction
- Dysfunction of either lower motor neurons or upper motor neurons can cause weakness
- Upper motor neuron signs can occur with or without weakness, and help distinguish between upper and lower motor neuron dysfunction
Upper Motor Neurons
- Upper motor neurons control lower motor neurons and their activity
- Found mainly in the cerebral cortex
- Axons descend to synapse on lower motor neurons in the brain stem or spinal cord
- Information flows from the cerebral cortex down the axons to lower motor neuron somas and then to skeletal muscle cells
Corticospinal Tract
- Collection of axons from the cerebral cortex to lower motor neurons in the spinal cord
- Most axons cross over to the other side of the spinal cord before synapsing on lower motor neurons
- Dysfunction on one side of the spinal cord results in weakness on the same side of the body
- Dysfunction on the other side of the brain results in weakness on the opposite side of the body
Corticobulbar Tract
- Collection of axons from the cerebral cortex to lower motor neurons in the brain stem
- Upper motor neuron axons often innervate lower motor neurons on the same side of the brain stem
- Dysfunction results in different patterns of weakness
Upper Motor Neuron Signs
- Hyperreflexia: increased muscle stretch reflexes
- Clonus: rhythmic contraction of antagonist muscles
- Hypertonia: increased tone of skeletal muscles
- Extensor Plantar Response (Babinski Sign): abnormal extension of the toes in response to scraping the bottom of the foot
Dysfunction
- Dysfunction of either lower motor neurons or upper motor neurons can cause weakness
- Upper motor neuron signs can occur with or without weakness, and help distinguish between upper and lower motor neuron dysfunction
Learn about the structure and function of upper motor neurons, their role in controlling lower motor neurons, and their significance in the nervous system.
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