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Questions and Answers
What is the primary effect of lower motor neuron involvement in ALS?
What is the primary effect of lower motor neuron involvement in ALS?
- Sensory loss in the extremities
- Joint pain and inflammation
- Cognitive decline and memory loss
- Muscle weakness, fasciculations, and atrophy (correct)
Which drug is known to reduce mortality in ALS?
Which drug is known to reduce mortality in ALS?
- Baclofen
- Riluzole (correct)
- Dantrolene
- Digoxin
What is the most common cause of death in ALS patients?
What is the most common cause of death in ALS patients?
- Respiratory failure (correct)
- Cancer complications
- Septic shock
- Cardiac arrest
What is a significant risk associated with bulbar muscle dysfunction in ALS patients?
What is a significant risk associated with bulbar muscle dysfunction in ALS patients?
How does succinylcholine affect ALS patients?
How does succinylcholine affect ALS patients?
What is the primary function of the second-order neuron in the spinothalamic tract?
What is the primary function of the second-order neuron in the spinothalamic tract?
Which of the following fibers is associated with transmitting 'first' pain?
Which of the following fibers is associated with transmitting 'first' pain?
Which structure do third-order neurons synapse with in the spinothalamic pathway?
Which structure do third-order neurons synapse with in the spinothalamic pathway?
What type of sensory information is transmitted by the spinothalamic tract?
What type of sensory information is transmitted by the spinothalamic tract?
What characteristic distinguishes the spinothalamic tract from the dorsal column pathway?
What characteristic distinguishes the spinothalamic tract from the dorsal column pathway?
In which part of the spinal cord do pain neurons synapse with second-order neurons?
In which part of the spinal cord do pain neurons synapse with second-order neurons?
What is the primary function of the lateral spinothalamic tract?
What is the primary function of the lateral spinothalamic tract?
Where do second-order neurons synapse with third-order neurons?
Where do second-order neurons synapse with third-order neurons?
Which tract is responsible for transmitting crude touch and pressure?
Which tract is responsible for transmitting crude touch and pressure?
Which of the following statements accurately describes the ventral corticospinal tract?
Which of the following statements accurately describes the ventral corticospinal tract?
What role do upper motor neurons play in the nervous system?
What role do upper motor neurons play in the nervous system?
Where do most tactile signals relay to after passing through the thalamus?
Where do most tactile signals relay to after passing through the thalamus?
What best describes the function of the corticospinal tract overall?
What best describes the function of the corticospinal tract overall?
Which laminae of the spinal cord are primarily involved in sensory functions?
Which laminae of the spinal cord are primarily involved in sensory functions?
What is the function of the lateral spinothalamic tract?
What is the function of the lateral spinothalamic tract?
Which area of the spinal cord contains the cell bodies for neurons supplying the lower extremities?
Which area of the spinal cord contains the cell bodies for neurons supplying the lower extremities?
Which type of neuron is the first-order neuron in the Dorsal Column tract?
Which type of neuron is the first-order neuron in the Dorsal Column tract?
What characteristic does the Dorsal Column tract enable in terms of sensory information?
What characteristic does the Dorsal Column tract enable in terms of sensory information?
Which laminae reside in the ventral grey matter and are primarily motor?
Which laminae reside in the ventral grey matter and are primarily motor?
Which sensory function is NOT transmitted by the Dorsal Column tract?
Which sensory function is NOT transmitted by the Dorsal Column tract?
What type of fibers does the Dorsal Column consist of?
What type of fibers does the Dorsal Column consist of?
What characterizes neurogenic shock compared to hypovolemic shock?
What characterizes neurogenic shock compared to hypovolemic shock?
Which treatment is effective for managing neurogenic shock?
Which treatment is effective for managing neurogenic shock?
What should be avoided within 24 hours following a spinal cord injury due to neurogenic shock?
What should be avoided within 24 hours following a spinal cord injury due to neurogenic shock?
What is the triad of symptoms associated with neurogenic shock?
What is the triad of symptoms associated with neurogenic shock?
What happens to the sympathetic nervous system following spinal shock?
What happens to the sympathetic nervous system following spinal shock?
Which of the following is a major cause of morbidity and mortality in cervical and upper thoracic spinal cord lesions?
Which of the following is a major cause of morbidity and mortality in cervical and upper thoracic spinal cord lesions?
What effect does injury below T6 have on autonomic hyperreflexia risk?
What effect does injury below T6 have on autonomic hyperreflexia risk?
What is commonly associated with autonomic hyperreflexia?
What is commonly associated with autonomic hyperreflexia?
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Study Notes
Spinal Cord Laminae
- Laminae 1-6 (dorsal grey matter): Sensory functions.
- Laminae 7-9 (ventral grey matter): Motor functions.
- Lamina 10: Surrounds central canal; includes anterior and posterior commissures.
Spinal Cord Enlargements
- Cervical enlargement (C5-C7): Cell bodies for upper extremity neurons.
- Lumbar enlargement (L3-S2): Cell bodies for lower extremity neurons.
Spinal Cord Tracts and Function
- Sensory:
- Dorsal column (cuneatus and gracilis): Fine touch, proprioception.
- Spinothalamic:
- Lateral: Pain, temperature.
- Ventral: Crude touch, pressure.
- Motor:
- Ventral corticospinal: Posture.
- Lateral corticospinal: Limb movement.
Dorsal Column Tract
- Transmits: Fine touch, proprioception, vibration, pressure.
- Allows two-point discrimination.
- Composed of large, myelinated, fast-conducting fibers.
- Faster transmission than spinothalamic tract.
Dorsal Column Tract Anatomy
- First-order neuron: A-beta fiber, enters dorsal root ganglion, ascends ipsilaterally, synapses in medulla (cuneate and gracile nuclei).
- Second-order neuron: Cuneate/gracile nuclei, crosses contralaterally, ascends via medial lemniscus, synapses in thalamus (VPL/VPM).
- Third-order neuron: VPL/VPM nuclei, passes through internal capsule, to somatosensory cortex (postcentral gyrus).
Spinothalamic Tract
- Transmits: Pain, temperature (lateral), crude touch, pressure (ventral).
- Composed of smaller, myelinated/unmyelinated, slower-conducting fibers.
- Slower transmission than dorsal column tract.
- Lacks two-point discrimination.
Spinothalamic Tract Anatomy
- First-order neuron: A-delta (first pain), C-fibers (slow pain), cell body in dorsal root ganglion, may ascend/descend in Lissauer's tract, synapses in substantia gelatinosa (Rexed's lamina II).
- Second-order neuron: Crosses contralaterally, ascends via lateral (neospinothalamic, pain/temperature) or anterior (paleospinothalamic, crude touch/pressure) tracts; synapses in reticular activating system and thalamus.
- Third-order neuron: Primarily in thalamus (ventrobasal complex), passes through internal capsule, to somatosensory cortex.
Corticospinal (Pyramidal) Tract
- Primarily involved in voluntary fine motor control of limbs and posture coordination.
Corticospinal Tract Pathway
- Motor neurons originate in precentral gyrus, pass through internal capsule and medullary pyramids.
- Lateral corticospinal: Innervates limbs, crosses contralaterally in medulla.
- Ventral corticospinal: Innervates axial muscles, crosses contralaterally at spinal cord level.
Upper Motor Neurons
- Originate in cerebral cortex, synapse with lower motor neurons in ventral horn.
Neurogenic Shock
- Sympathectomy below injury level, decreased sympathetic tone, vasodilation.
- Venous pooling, reduced cardiac output, hypotension.
- Cutaneous heat loss, hypothermia.
- Impairment of cardioaccelerator fibers (T1-T4), unopposed vagal tone, bradycardia, reduced inotropy.
- Triad: Hypotension, bradycardia, hypothermia.
Differentiating Neurogenic and Hypovolemic Shock
- Neurogenic: Bradycardia, hypotension, hypothermia, pink/warm extremities.
- Hypovolemic: Tachycardia, hypotension, cool/clammy extremities.
Treating Neurogenic Shock
- Norepinephrine to restore systemic vascular resistance and inotropy.
- Volume expansion.
Succinylcholine and Neurogenic Shock
- Avoid succinylcholine, especially within 24 hours of injury due to risk of worsening outcomes.
Major Causes of Morbidity/Mortality in Cervical/Upper Thoracic Lesions
- Ineffective alveolar ventilation, inability to clear pulmonary secretions.
Chronic Spinal Cord Injury
- After spinal shock phase (1-3 weeks): Return of spinal sympathetic reflexes below injury; overreactive sympathetic nervous system, risk of autonomic hyperreflexia (mass reflex), more likely with injuries above T6, less likely below T10.
Common Events Causing Autonomic Hyperreflexia
- Stimulation of hollow organs (bladder, bowel, uterus).
Amyotrophic Lateral Sclerosis (ALS)
- Lower motor neuron involvement: Muscle weakness, fasciculations, atrophy; starts in hands, spreads to tongue, pharynx, larynx, chest; ocular muscles unaffected.
- Autonomic dysfunction: Orthostatic hypotension, resting tachycardia.
- Sensation remains intact.
ALS Treatment and Mortality
- Riluzole (NMDA receptor antagonist) reduces mortality.
- Respiratory failure is the most common cause of death.
Neuromuscular Blockers in ALS
- Succinylcholine: Risk of lethal hyperkalemia due to proliferation of postjunctional receptors.
- Nondepolarizing neuromuscular blockers: Increased sensitivity.
ALS Patient Considerations
- Risk of pulmonary aspiration (bulbar muscle dysfunction).
- Reduced vital capacity and minute ventilation (muscle weakness).
- Consider postoperative mechanical ventilation.
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