34 Questions
Which type of neuron in the descending pathway is also referred to as the final common pathway?
3rd order neuron
What is the location of the cell body of a 2nd order neuron in the descending pathway?
Anterior gray column of the spinal cord
What type of contraction occurs in the quadriceps muscle when the patellar tendon is tapped using a neuro hammer?
Jerk-like muscle contraction
Which nerve carries the impulse from the stimulated muscle spindle to the spinal cord?
Femoral nerve
What is the location of the cell body of a 1st order neuron in the descending pathway?
Cerebral cortex
What is the function of the 3rd order neuron in the descending pathway?
To stimulate skeletal muscles
What type of reflex arc is shown in the knee jerk/patellar tendon reflex?
Monosynaptic reflex arc
What is the location of the Ventral CST in the spinal cord?
Anterior funiculus
What is the result of occlusion of the vessel supplying the area where CST fibers are closely packed together?
Dense manifestation of symptoms, including paralysis or weakness of arms, trunk, and legs
What is the location of the Lateral CST in the spinal cord?
Lateral funiculus
What is the characteristic of a lacunar syndrome?
Small infarcts in the subcortical areas of the brain
What is the effect of a spinal cord lesion on the body?
Paralysis on the ipsilateral side of the body
What is the result of occlusion of the posterior limb of the internal capsule?
Purely motor deficit
What is the result of occlusion of a bigger vessel in the brain?
Both motor and sensory deficit
Where do the rubrospinal tract fibers cross immediately?
Ventral tegmental decussation
What is the function of the rubrospinal tract in the spinal cord?
Modulation of reflex postural movements in response to visual and auditory stimuli
In which Rexed laminae do the rubrospinal tract terminate?
Rexed laminae V, VI, VII
What is the origin of the tract that forms part of the MLF and is uncrossed?
Interstitial nucleus of Cajal
Which tract terminates in the anterior horn of upper cervical levels of the spinal cord?
Tract originating from the interstitial nucleus of Cajal
What is the characteristic of the fibers of the tract originating from the interstitial nucleus of Cajal?
They are uncrossed
In which part of the spinal cord do the rubrospinal tract fibers enter?
Lateral funiculus
What is a characteristic of a patient with a left-sided LMN lesion?
Inability to move the left half of the face
What is a characteristic of a patient with a right UMN lesion?
Inability to move the left lower half of the face
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?
Left UMN
What is a characteristic of a patient with a right LMN lesion?
Inability to move the right lower half of the face
What is the difference between a left UMN lesion and a left LMN lesion?
Location of the lesion, with UMN lesions affecting the upper motor neurons and LMN lesions affecting the lower motor neurons
What is the characteristic of a patient with Bell's palsy on the right side?
No creases on the right side of the face, and nose is skewed to the left side
Which nucleus is the origin of the Rubrospinal tract?
Red nucleus
Where do the fibers of the Interstitiospinal tract terminate?
Internuncial neurons of all spinal cord levels
What is the function of the Tectobulbar tract?
Mediate reflex postural movements of head and neck in response to visual stimuli
In which part of the spinal cord do the fibers of the Tectospinal tract terminate?
Anterior horn of upper cervical spinal cord
What is the course of fibers of the Rubrospinal tract?
Cross in ventral tegmental decussation
What is the origin of the Tectospinal tract?
Superior colliculus
Where do the fibers of the Rubrospinal tract terminate?
Internuncial neurons of all spinal cord levels
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
Test your understanding of neurons in the descending pathway, including 1st, 2nd, and 3rd order neurons, their origins, and functions in monosynaptic reflex arcs.
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