Spinal Cord Anatomy and Function

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Questions and Answers

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?

Baclofen

Riluzole (correct)

Dantrolene

Digoxin

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?

Pulmonary aspiration Signup and view all the answers

How does succinylcholine affect ALS patients?

Leads to lethal hyperkalemia Signup and view all the answers

What is the primary function of the second-order neuron in the spinothalamic tract?

To cross to the contralateral side in the medulla Signup and view all the answers

Which of the following fibers is associated with transmitting 'first' pain?

A-delta fibers Signup and view all the answers

Which structure do third-order neurons synapse with in the spinothalamic pathway?

Ventral posterolateral nucleus Signup and view all the answers

What type of sensory information is transmitted by the spinothalamic tract?

Pain and temperature Signup and view all the answers

What characteristic distinguishes the spinothalamic tract from the dorsal column pathway?

Type of fibers utilized Signup and view all the answers

In which part of the spinal cord do pain neurons synapse with second-order neurons?

Substantia gelatinosa Signup and view all the answers

What is the primary function of the lateral spinothalamic tract?

Transmits pain and temperature Signup and view all the answers

Where do second-order neurons synapse with third-order neurons?

Reticular activating system and thalamus Signup and view all the answers

Which tract is responsible for transmitting crude touch and pressure?

Anterior spinothalamic tract Signup and view all the answers

Which of the following statements accurately describes the ventral corticospinal tract?

Crossover occurs in the spinal cord Signup and view all the answers

What role do upper motor neurons play in the nervous system?

Synapse with lower motor neurons in the ventral horn Signup and view all the answers

Where do most tactile signals relay to after passing through the thalamus?

Postcentral gyrus Signup and view all the answers

What best describes the function of the corticospinal tract overall?

Voluntary fine motor control Signup and view all the answers

Which laminae of the spinal cord are primarily involved in sensory functions?

Laminae 1-6 Signup and view all the answers

What is the function of the lateral spinothalamic tract?

Pain and temperature Signup and view all the answers

Which area of the spinal cord contains the cell bodies for neurons supplying the lower extremities?

Lumbar enlargement (L3 - S2) Signup and view all the answers

Which type of neuron is the first-order neuron in the Dorsal Column tract?

A-beta nerve fiber Signup and view all the answers

What characteristic does the Dorsal Column tract enable in terms of sensory information?

Two-point discrimination Signup and view all the answers

Which laminae reside in the ventral grey matter and are primarily motor?

Laminae 7-9 Signup and view all the answers

Which sensory function is NOT transmitted by the Dorsal Column tract?

Crude touch Signup and view all the answers

What type of fibers does the Dorsal Column consist of?

Myelinated, rapidly conducting fibers Signup and view all the answers

What characterizes neurogenic shock compared to hypovolemic shock?

Bradycardia, hypotension, and pink, warm extremities Signup and view all the answers

Which treatment is effective for managing neurogenic shock?

Norepinephrine and volume expansion Signup and view all the answers

What should be avoided within 24 hours following a spinal cord injury due to neurogenic shock?

Succinylcholine Signup and view all the answers

What is the triad of symptoms associated with neurogenic shock?

Bradycardia, hypotension, and hypothermia Signup and view all the answers

What happens to the sympathetic nervous system following spinal shock?

It becomes overactive below the level of injury leading to autonomic hyperreflexia. Signup and view all the answers

Which of the following is a major cause of morbidity and mortality in cervical and upper thoracic spinal cord lesions?

Ineffective alveolar ventilation and inability to clear pulmonary secretions Signup and view all the answers

What effect does injury below T6 have on autonomic hyperreflexia risk?

It decreases the risk compared to injuries above T6. Signup and view all the answers

What is commonly associated with autonomic hyperreflexia?

Stimulation of hollow organs like the bladder and bowel Signup and view all the answers

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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Description

Dive into the structure and functions of the spinal cord with our quiz on laminae, enlargements, and sensory-motor tracts. Explore how sensory information is processed and transmitted, as well as the anatomical distinctions of the cervical and lumbar enlargements. Test your knowledge on the dorsal column and spinothalamic tracts!