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TABLE OF CONTENTS
- Overview of Spinal Cord and Spinal tracts
- Two neuron chain - UMN vs LMN
- Two neuron chain - Stretch Reflex Arch
- Pyramidal Tracts - Anterior and Lateral Corticospinal Tracts
- Pyramidal Tracts - Corticobulbar Tracts and Trigeminal Motor Pathway
- Pyramidal Tracts - Facial Nerve Pathway
- Pyramidal Tracts - Nucleus Ambiguus and Hypoglossal Nerve Pathways
- Extrapyramidal Tracts - Rubrospinal Tract
- Extrapyramidal Tracts - Reticulospinal Tracts
- Extrapyramidal Tracts - Vestibulospinal Tracts
- Extrapyramidal Tracts - Tectospinal Tracts
- Overview of Sensation and First, Second, and Third Order Neurons
- Dorsal Column Medial Lemniscus Pathway
- Anterior and Lateral Spinothalamic Pathways
- Spinocerebellar Pathways
Spinal Cord
Tracts
OUTLINE
- White Matter vs Grey Matter
- Ascending Vs Descending Tracts ○ Motor vs Sensory
- Ascending Sensory Tract Localization ○ Anterolateral Pathways - Spinothalamic Tracts ○ Dorsal Column Medial Lemniscal Tracts ○ Spinocerebellar Tracts
- Descending Motor Tract Localization ○ Anterior Corticospinal Tract ○ Lateral Corticospinal Tract ○ Rubrospinal Tract ○ Reticulospinal Tract ○ Vestibulospinal Tract
Overview of
Spinal Cord
and Spinal
Tracts
REVIEW
Ascending vs Descending White Matter Tracts
Ascending Sensory Tract Localization
Dorsal Column Medial Lemniscal Pathways ○ Fasciculus Gracilis ○ Fasciculus Cuneatus Anterolateral Pathways ○ Anterior Spinothalamic Tract ○ Lateral Spinothalamic Tract Spinocerebellar Pathways ○ Dorsal/Posterior Spinocerebellar Tract ○ Ventral/Anterior Spinocerebellar Tract
References
References: ● Page 2: OpenStax, CC BY 4.0, via Wikimedia Commons ● Page 3: Polarlys and Mikael Häggström, CC BY-SA 3.0, via Wikimedia Commons ● Page 4-5: Polarlys (File:Medulla spinalis - Querschnitt - Bahnen - German.svg), translation by Selket, CC BY-SA 3.0, via Wikimedia Commons
OUTLINE
- White Matter vs Grey Matter
- Ascending Vs Descending Tracts ○ Motor vs Sensory
- Ascending Sensory Tract Localization ○ Anterolateral Pathways - Spinothalamic Tracts ○ Dorsal Column Medial Lemniscal Tracts ○ Spinocerebellar Tracts
- Descending Motor Tract Localization ○ Anterior Corticospinal Tract ○ Lateral Corticospinal Tract ○ Rubrospinal Tract ○ Reticulospinal Tract ○ Vestibulospinal Tract
Overview of
Spinal Cord
and Spinal
Tracts
REVIEW
Upper Motor Neurons (UMN):
● Cell bodies are located in higher cortical areas
○ Motor cortex & brainstem
● Axons will synapse with a LMN in the brainstem or
spinal cord
Lower Motor Neurons (LMN):
● Cell bodies are located in the
○ ventral horn of the spinal cord
○ brainstem motor nucleus
● Axon terminate at NMJ and stimulates Skeletal
muscle
Upper Motor Neurons vs Lower Motor Neurons
Lower Motor Neurons
Lower Motor Neurons (LMN):
In the brainstem:
- LMN cell bodies form cranial nerve nuclei
- axons form cranial nerves which travel to their target muscles in the face
In the spinal cord:
- LMN cell bodies are located in the ventral horns
- axons travel out the ventral root, spinal nerve, dorsal or ventral ramus, peripheral nerve to reach their target muscle
- Atrophy: loss of neurotransmitter signaling to stimulate muscle resulting in muscle fiber deterioration and decrease muscle mass.
- Ipsilateral weakness: results in muscle weakness, or paralysis if ALL its LMN are damaged.
- Hyporeflexia: reduced or absent reflex due to lack of LMN stimulating muscle fibers.
- Fasciculations: damage causes spontaneous firing of action potentials leading to twitching of the muscles fibers
- Hypotonia: Decreased muscle tone due to the lack of stimulation from LMN efferents.
Lower Motor Neuron Lesions
- No atrophy: no atrophy because of intact LMN (may result over time from disuse)
- Weakness: graded weakness of movement (paresis)can be ipsilateral or contralateral (depending on location)
- Hyper-reflexia: increased reflexes due to lack of inhibition from UMN
- No fasciculations: no fasciculations because of intact LMN
- Hypertonia/ Spastic paralysis: affected limb will have increased muscle tone, tested by passive stretch of the limb
- Babinski’s sign
Upper Motor Neuron Lesions
References
References:
● Page 5 & 6: https://assets.coursehero.com/study-guides/lumen/images/cuny-csi-ap-1-2/reflexes/Nerv_151.jpg
● Page 8:
○ Babinski’s demonstration: <a
href="https://commons.wikimedia.org/wiki/File:Babinski%27s_sign_(de).png">derivative work:
Roxbury-de (talk)Objaw_babinskiego.png: The original uploader was Malki at Polish Wikipedia., <a
href="https://creativecommons.org/licenses/by-sa/2.5">CC BY-SA 2.5, via Wikimedia Commons
href="https://creativecommons.org/licenses/by-sa/4.0">CC BY-SA 4.0, via Wikimedia Commons
OUTLINE
1. Upper Motor Neurons (UMN)
2. Lower Motor Neurons (LMN)
3. Stretch Reflex Arch
4. LMN Lesions
5. UMN Lesions
6. Babinski Sign
Two-Neuron
Chain
REVIEW
Lateral Corticospinal Pathway: ● cortex → corona radiata → internal capsule → crus cerebri → medullary pyramids (Decussation) → lateral corticospinal tract → ventral horn LMN → skeletal muscle ● Controls muscles of the distal limbs (hands and feet) ● Responsible for precise, highly skilled movements ○ Ie. playing a piano
Anterior Corticospinal Pathway: ● cortex → corona radiata → internal capsule → crus cerebri → medullary pyramids ( not decussation) → anterior corticospinal tract → ventral horn LMN → skeletal muscle ● Controls muscles neck, trunk, and proximal limbs
90% of corticospinal axons decussate at pyramids (LCS tract) 10% of corticospinal axons do NOT decussate (ACS tract)
Corticospinal Pathways
LMN Lesions ● In the CST have ipsilateral effects ● This is including lesions of LMN axons/spinal nerves and ventral horn cell bodies ● Note: in CBT this is not always the case
UMN lesions ● In the CST, UMN lesions can have ipsilateral or contralateral effects ● This depends on location of lesion relative to point of decussation ● It's important to understand decussations
Corticospinal Tract Lesions
