Podcast
Questions and Answers
Which type of neuron in the descending pathway is also referred to as the final common pathway?
What is the location of the cell body of a 2nd order neuron in the descending pathway?
What type of contraction occurs in the quadriceps muscle when the patellar tendon is tapped using a neuro hammer?
Which nerve carries the impulse from the stimulated muscle spindle to the spinal cord?
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What is the location of the cell body of a 1st order neuron in the descending pathway?
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What is the function of the 3rd order neuron in the descending pathway?
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What type of reflex arc is shown in the knee jerk/patellar tendon reflex?
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What is the location of the Ventral CST in the spinal cord?
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What is the result of occlusion of the vessel supplying the area where CST fibers are closely packed together?
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What is the location of the Lateral CST in the spinal cord?
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What is the characteristic of a lacunar syndrome?
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What is the effect of a spinal cord lesion on the body?
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What is the result of occlusion of the posterior limb of the internal capsule?
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What is the result of occlusion of a bigger vessel in the brain?
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Where do the rubrospinal tract fibers cross immediately?
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What is the function of the rubrospinal tract in the spinal cord?
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In which Rexed laminae do the rubrospinal tract terminate?
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What is the origin of the tract that forms part of the MLF and is uncrossed?
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Which tract terminates in the anterior horn of upper cervical levels of the spinal cord?
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What is the characteristic of the fibers of the tract originating from the interstitial nucleus of Cajal?
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In which part of the spinal cord do the rubrospinal tract fibers enter?
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What is a characteristic of a patient with a left-sided LMN lesion?
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What is a characteristic of a patient with a right UMN lesion?
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What is the location of the lesion in a patient who is unable to move the left lower half of the face but can still wrinkle both eyebrows?
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What is a characteristic of a patient with a right LMN lesion?
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What is the difference between a left UMN lesion and a left LMN lesion?
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What is the characteristic of a patient with Bell's palsy on the right side?
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Which nucleus is the origin of the Rubrospinal tract?
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Where do the fibers of the Interstitiospinal tract terminate?
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What is the function of the Tectobulbar tract?
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In which part of the spinal cord do the fibers of the Tectospinal tract terminate?
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What is the course of fibers of the Rubrospinal tract?
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What is the origin of the Tectospinal tract?
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Where do the fibers of the Rubrospinal tract terminate?
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Study Notes
Descending Pathway
- Consists of 1st order, 2nd order, and 3rd order neurons
- Originates from cerebral cortex, anterior gray column of the spinal cord, and anterior gray column of the spinal cord
- Axons of 1st order neurons can terminate directly on 3rd order neurons, such as in reflex arcs
Corticospinal Tract (CST)
- AKA Pyramidal Tract
- Originates from cerebral cortex
- Fibers are closely packed together, making them susceptible to damage from occlusion of a single vessel
- Spinal cord lesions can produce paralysis on the ipsilateral side of the body
- Ventral CST is located at the anterior funiculus, while lateral CST is located at the lateral funiculus of the spinal cord
Clinical Correlation
- Lacunar syndrome: small infarcts in the subcortical areas of the brain, resulting in motor or sensory deficits
- Occlusion of a larger vessel can cause both motor and sensory deficits
Rubrospinal Tract
- Originates from the red nucleus in the midbrain
- Fibers cross immediately in the ventral tegmental decussation and descend to the lateral funiculus of the spinal cord
- Terminates in synapses with internuncial neurons in all spinal cord levels
- Modulates reflex postural movements in response to visual and auditory stimuli
Tectospinal and Tectobulbar Tracts
- Originates from the interstitial nucleus of Cajal
- Fibers are uncrossed and form part of the MLF
- Terminates in the anterior horn of upper cervical levels of the spinal cord
- Modulates reflex postural movements in response to visual and auditory stimuli
Bell's Palsy
- AKA Facial Nerve Palsy
- Caused by LMN lesion
- Presents with weakness on one side of the face, including the eyebrow, nose, and mouth
- Prognosis is good, with >85% of patients experiencing spontaneous recovery within 1-2 months
Hypoglossal Nucleus
- Originates from the hypoglossal nucleus in the midbrain
- Modulates reflex postural movements of the head and neck in response to visual and vestibular stimuli
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Description
Test your understanding of neurons in the descending pathway, including 1st, 2nd, and 3rd order neurons, their origins, and functions in monosynaptic reflex arcs.