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Neuroanatomy Outlined
Amy Dodds
Created on December 19, 2023
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Transcript
Created by Amy Dodds
Click on each bullet point below to reveal the learning outcomes:
Describe the function(s) of the 3 main spinal pathways
Draw and label each of the 3 main spinal pathways
Apply your knowledge to explain the effects of lesions
Describe the function(s) of the 3 main spinal pathways
Draw and label each of the 3 main spinal pathways
Apply your knowledge to explain the effects of lesions
Hover over each button to learn about its function:
SPINOTHALAMIC PATHWAYS
Ascending pathways from the body to the cerebrum. Consists of two pathways, each carrying a different modality of sensation:
Anterior spinothalamic pathway: carries crude touch & pressure
Lateral spinothalamic pathway: carries pain & temperature
Q1: What is the function of the anterior spinothalamic tract?
Sensation of crude touch & pressure
Sensation of pain & temperature
Sensation of fine touch & vibration
Sensation of proprioception
Sensation of pressure & pain
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The anterior spinothalamic tract carries sensory (afferent) information about crude touch & pressure from the body to the cerebrum.
Q2: Where do primary neurons of the spinothalamic tract synapse?
Cuneate nucleus
Cuneate nucleus
Substantia gelatinosa
Ventral posterolateral nucleus
Gracile nucleus
Ventral posterolateral nucleus
Gracile nucleus
Substantia gelatinosa
Ventral horn of grey matter
Ventral horn of grey matter
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Primary neurons of the spinothalamic tract enter the spinal cord via the dorsal root and synapse with their secondary neuron at the substantia gelatinosa of the dorsal horn of grey matter.
Q3: Briefly describe the clinical effects of a total spinal cord transection at the T10 level
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A total cord transection affects the descending and ascending pathways on both sides, but the cranial nerves remain intact. Here, this will present with complete loss of sensory and motor functions below the T10 level, but intact function above this level.
Q4: Where do secondary neurons of the spinothalamic tract synapse?
Cuneate nucleus
Cuneate nucleus
Substantia gelatinosa
Ventral posterolateral nucleus
Gracile nucleus
Ventral posterolateral nucleus
Gracile nucleus
Substantia gelatinosa
Ventral horn of grey matter
Ventral horn of grey matter
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Secondary neurons of the spinothalamic tract ascend via the spinal lemniscus to the thalamus, where they synapse with tertiary neurons at the ventral posterolateral nucleus.
Q5: Which spinal pathway is most likely to be affected by occlusion of the posterior spinal arteries?
Anterior corticospinal
Cuneate nucleus
Substantia gelatinosa
Anterior spinothalamic
Dorsal columns-medial lemniscus
Ventral posterolateral nucleus
Gracile nucleus
Lateral corticospinal
Ventral horn of grey matter
Lateral spinothalamic
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The posterior spinal arteries, which arise from the posterior inferior cerebellar artery (PICA), supply the posterior 1/3rd of the spinal cord.
The DCML pathways run along the dorsal aspect of the spinal cord and, therefore, are most at risk.
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CORTICOSPINAL PATHWAYS
Descending pathways from the cerebrum to the body. Consists of two pathways, each carrying motor signals to different regions:
Anterior corticospinal pathway: carries motor information to trunk
Lateral corticospinal pathway: carries motor information to limbs
Q1: What is the function of the lateral corticospinal tract?
Somatic afferents from limbs
Somatic afferents from trunk
Somatic efferent to trunk
Somatic efferent to face
Somatic efferent to limbs
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The lateral corticospinal tract carries voluntary motor (somatic efferent) information to the muscles of the upper and lower limbs.
Q2: Where do 90% of the corticospinal tract fibres decussate?
Anterior white commissure
Cuneate nucleus
Substantia gelatinosa
Cerebral peduncle
Internal capsule
Ventral posterolateral nucleus
Gracile nucleus
Medulla oblongata
Ventral horn of grey matter
Substantia gelatinosa
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90% of the descending motor fibres decussate at the pyramidal decussation of the medulla oblongata, where they enter the lateral corticospinal tract.
Q3: Briefly describe the clinical effects of spinal cord hemisection (Brown-séquard syndrome)
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Brown-Séquard syndrome affects both the descending and ascending pathways. Typical presentation includes:
- Contralateral loss of pain & temperature sensation (spinothalamic)
- Ipsilateral loss of fine touch sensation (DCML)
- Ipsilateral loss of movement (corticospinal)
Q4: Where do 10% of the corticospinal tract fibres decussate?
Anterior white commissure
Cuneate nucleus
Substantia gelatinosa
Cerebral peduncle
Internal capsule
Ventral posterolateral nucleus
Gracile nucleus
Medulla oblongata
Ventral horn of grey matter
Substantia gelatinosa
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10% of the descending motor fibres decussate at the ventral (anterior) white commissure of the spinal cord, where they leave via the ventral root.
Q5: A patient has suffered a stroke in their internal capsule on the left side. How would this patient likely present?
Bilateral weakness and loss of sensation
Cuneate nucleus
Left-sided loss of crude touch and right-sided weakness
Substantia gelatinosa
Left-sided weakness and bilateral numbness
Ventral posterolateral nucleus
Gracile nucleus
Right-sided loss of fine touch
Right-sided weakness and right-sided loss of sensation
Ventral horn of grey matter
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The internal capsule contains fibres of both the ascending and descending tracts. The patient will present with right-sided weakness and right-sided loss of sensation.
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DCML PATHWAY
Ascending pathways from the body to the cerebrum.Two pathways carrying sensory signals about fine touch & proprioception from different regions:
Gracile fasciculus: carries fine touch & proprioception from T7 downwards
Cuneate fasciculus: carries fine touch & proprioception from T6 upwards
Q1: What is the function of the DCML pathway?
Fine touch & proprioception
Crude touch & pressure
Pain & temperature
Motor control to limbs
Motor control to trunk
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The DCML pathway consists of two pathways, each carrying sensory signals about fine touch & proprioception from different regions.
Q2: Briefly describe the clinical effects of a lesion in the left gracile fasciculus at the L1 spinal cord level.
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The patient will present with loss of fine touch, vibration & proprioception sensation in the left lower limb.
Q3: Which neuron synapses at the gracile nucleus?
Lower motor neuron
Cuneate nucleus
Substantia gelatinosa
Primary sensory neuron
Secondary sensory neuron
Ventral posterolateral nucleus
Gracile nucleus
Tertiary sensory neuron
Ventral horn of grey matter
Upper motor neuron
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The primary sensory neuron enters the spinal cord via the dorsal root and passes into the gracile fasciculus where it ascends. At the medulla oblongata, it forms a synapse with the secondary neuron in the gracile nucleus.
Q4: Which spinal pathways are most likely to be affected by occlusion of the anterior spinal artery?
Corticospinal & Spinothalamic
Cuneate nucleus
Substantia gelatinosa
Corticospinal & DCML
Cuneate fasciculus & Corticospinal
Ventral posterolateral nucleus
Gracile nucleus
Gracile fasciculus & Spinothalamic
Ventral horn of grey matter
Spinothalamic & DCML
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The anterior spinal artery, which arises from the vertebral arteries, supplies the anterior 2/3rd of the spinal cord. The corticospinal and spinothalamic pathways run in this region of the spinal cord and, therefore, are most at risk.
Q5: A patient suffers a right-sided midbrain lesion affecting the DCML pathway. Which part of the DCML pathway is most likely to be affected?
Gracile fasciculus
Cuneate nucleus
Cuneate fasciculus
Substantia gelatinosa
Internal arcuate fibres
Ventral posterolateral nucleus
Gracile nucleus
Medial lemniscus
Ventral posterolateral nucleus
Ventral horn of grey matter
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The secondary neurons of the DCML pathway decussate in the medulla oblongata via the internal arcuate fibres and enter the medial lemniscus. They ascend in the medial lemniscus through the pons and midbrain, before synapsing at the thalamus in the cerebrum.
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Damage to the ascending pathways at this point has occurred after their decussation, so the patient presents with loss of sensation on the contralateral side to the lesion – in this case, on the right side.
In this case, the lesion has occurred below the level of the decussation, so symptoms will present on the ipsilateral side to the lesion.
Fibres that decussate in the medulla oblongata will enter the lateral corticospinal tract, so fibres in the anterior corticospinal tract decussate lower down, in the spinal cord white matter!
Just remember...
Lateral = Limbs
So the lateral corticospinal tract supplies somatic motor information to the Limbs!
Damage to the corticospinal tracts at this point has occurred prior to their decussation, so the patient presents with weakness on the contralateral side to the lesion – in this case, on the right side.