Spinal Cord - Neurology - Medbullets Step 1

Overview

Snapshot

A 26-year-old male presents with lower back pain that radiates down the side of his right leg and into his right foot. The pain started after he was recently lifting furniture into his new home. On physical exam, there is notable weakness on dorsiflexion of the foot and extension of the toe. Sensory loss is noted between the first and second digit of the foot. Knee and ankle reflexes are normal. There is no saddle anesthesia, and anal wink is appreciated. When raising the extended leg while in the supine position, pain radiates from the lower back, down the leg, and into the foot. (L5 radiculopathy due to disc herniation)

Introduction

Spinal nerves
- 31 pairs
  - 8 cervical
  - 12 thoracic
  - 5 lumbar
  - 5 sacral
  - 1 coccygeal
- vertebral exit
  - C1-C7 exit via intervertebral foramina above corresponding vertebra
  - all other nerves exit via intervertebral foramina below corresponding vertebra
Spinal cord termination
- adults
  - spinal cord ends at L1-L2
    - becomes cauda equina
  - subarachnoid space extends to lower border of S2
  - see Lumbar puncture topic
Pathology
- vertebral disk herniation
  - nucleus pulposus herniates posteriolaterally through annulus fibrosis
  - most commonly occurs between L5 and S1
  - cauda equina affects S2-S5 nerve roots

Spinal Cord Pathways

Sensory pathways
- dorsal columns
  - function
    - ascending pressure, vibration, discriminative touch, and proprioceptive sensation
  - subdivisions
    - fasciculus cuneatus
      - upper body and extremities
    - fasciculus gracilis
      - lower body and extremities
  - pathway
    - 1st order neuron
      - sensory nerve ending → dorsal root ganglion (location of cell body) → spinal cord → ipsilateral ascent in dorsal column → synapse in ipsilateral nucleus in medulla (cuneatus or gracilis)
    - 2nd order neuron
      - ipsilateral nucleus in medulla → decussates in medulla → contralateral ascent in medial lemniscus → synapse in VPL of thalamus
    - 3rd order neuron
      - VPL of thalamus → sensory cortex
- Spinothalamic tract
  - function
    - ascending pain and temperature sensation
  - pathway
    - 1st order neuron
      - sensory nerve ending → dorsal root ganglion (location of cell body) → spinal cord → synapse in ipsilateral gray matter of spinal cord
    - 2nd order neuron
      - ipsilateral gray matter of spinal cord → decussates at anterior white commissure → contralateral ascent in spinothalamic tract → synapse in VPL of thalamus
    - 3rd order neuron
      - VPL of thalamus → sensory cortex
Motor pathways
- lateral corticospinal tract
  - function
    - descending voluntary motor control of contralateral limbs
  - pathway
    - 1st order neuron (upper motor neuron)
      - cell body in primary motor cortex → ipsilateral descent through internal capsule → decussation at caudal medulla (pyramidal decussation) → contralateral descent in lateral corticospinal tract → synapse at cell body of anterior horn in spinal cord
    - 2nd order neuron (lower motor neuron)
      - leaves anterior horn of spinal cord → synapses at neuromuscular junction

Blood, Plasma, Serum	Reference Range
ALT	8-20 U/L
Amylase, serum	25-125 U/L
AST	8-20 U/L
Bilirubin, serum (adult) Total // Direct	0.1-1.0 mg/dL // 0.0-0.3 mg/dL
Calcium, serum (Ca²⁺)	8.4-10.2 mg/dL
Cholesterol, serum	Rec: < 200 mg/dL
Cortisol, serum	0800 h: 5-23 μg/dL //1600 h: 3-15 μg/dL 2000 h: ≤ 50% of 0800 h
Creatine kinase, serum	Male: 25-90 U/L Female: 10-70 U/L
Creatinine, serum	0.6-1.2 mg/dL
Electrolytes, serum
Sodium (Na⁺)	136-145 mEq/L
Chloride (Cl^-)	95-105 mEq/L
Potassium (K⁺)	3.5-5.0 mEq/L
Bicarbonate (HCO₃^-)	22-28 mEq/L
Magnesium (Mg²⁺)	1.5-2.0 mEq/L
Estriol, total, serum (in pregnancy)
24-28 wks // 32-36 wks	30-170 ng/mL // 60-280 ng/mL
28-32 wk // 36-40 wks	40-220 ng/mL // 80-350 ng/mL
Ferritin, serum	Male: 15-200 ng/mL Female: 12-150 ng/mL
Follicle-stimulating hormone, serum/plasma	Male: 4-25 mIU/mL Female: premenopause: 4-30 mIU/mL midcycle peak: 10-90 mIU/mL postmenopause: 40-250
pH	7.35-7.45
PCO₂	33-45 mmHg
PO₂	75-105 mmHg
Glucose, serum	Fasting: 70-110 mg/dL 2-h postprandial:<120 mg/dL
Growth hormone - arginine stimulation	Fasting: <5 ng/mL Provocative stimuli: > 7ng/mL
Immunoglobulins, serum
IgA	76-390 mg/dL
IgE	0-380 IU/mL
IgG	650-1500 mg/dL
IgM	40-345 mg/dL
Iron	50-170 μg/dL
Lactate dehydrogenase, serum	45-90 U/L
Luteinizing hormone, serum/plasma	Male: 6-23 mIU/mL Female: follicular phase: 5-30 mIU/mL midcycle: 75-150 mIU/mL postmenopause 30-200 mIU/mL
Osmolality, serum	275-295 mOsmol/kd H₂O
Parathyroid hormone, serume, N-terminal	230-630 pg/mL
Phosphatase (alkaline), serum (p-NPP at 30° C)	20-70 U/L
Phosphorus (inorganic), serum	3.0-4.5 mg/dL
Prolactin, serum (hPRL)	< 20 ng/mL
Proteins, serum
Total (recumbent)	6.0-7.8 g/dL
Albumin	3.5-5.5 g/dL
Globulin	2.3-3.5 g/dL
Thyroid-stimulating hormone, serum or plasma	.5-5.0 μU/mL
Thyroidal iodine (¹²³I) uptake	8%-30% of administered dose/24h
Thyroxine (T4), serum	5-12 μg/dL
Triglycerides, serum	35-160 mg/dL
Triiodothyronine (T3), serum (RIA)	115-190 ng/dL
Triiodothyronine (T3) resin uptake	25%-35%
Urea nitrogen, serum	7-18 mg/dL
Uric acid, serum	3.0-8.2 mg/dL

Hematologic	Reference Range
Bleeding time	2-7 minutes
Erythrocyte count	Male: 4.3-5.9 million/mm³ Female: 3.5-5.5 million mm³
Erythrocyte sedimentation rate (Westergren)	Male: 0-15 mm/h Female: 0-20 mm/h
Hematocrit	Male: 41%-53% Female: 36%-46%
Hemoglobin A1c	≤ 6 %
Hemoglobin, blood	Male: 13.5-17.5 g/dL Female: 12.0-16.0 g/dL
Hemoglobin, plasma	1-4 mg/dL
Leukocyte count and differential
Leukocyte count	4,500-11,000/mm³
Segmented neutrophils	54%-62%
Bands	3%-5%
Eosinophils	1%-3%
Basophils	0%-0.75%
Lymphocytes	25%-33%
Monocytes	3%-7%
Mean corpuscular hemoglobin	25.4-34.6 pg/cell
Mean corpuscular hemoglobin concentration	31%-36% Hb/cell
Mean corpuscular volume	80-100 μm³
Partial thromboplastin time (activated)	25-40 seconds
Platelet count	150,000-400,000/mm³
Prothrombin time	11-15 seconds
Reticulocyte count	0.5%-1.5% of red cells
Thrombin time	< 2 seconds deviation from control
Volume
Plasma	Male: 25-43 mL/kg Female: 28-45 mL/kg
Red cell	Male: 20-36 mL/kg Female: 19-31 mL/kg

Cerebrospinal Fluid	Reference Range
Cell count	0-5/mm³
Chloride	118-132 mEq/L
Gamma globulin	3%-12% total proteins
Glucose	40-70 mg/dL
Pressure	70-180 mm H₂O
Proteins, total	< 40 mg/dL

Sweat	Reference Range
Chloride	0-35 mmol/L
Urine
Calcium	100-300 mg/24 h
Chloride	Varies with intake
Creatinine clearance	Male: 97-137 mL/min Female: 88-128 mL/min
Estriol, total (in pregnancy)
30 wks	6-18 mg/24 h
35 wks	9-28 mg/24 h
40 wks	13-42 mg/24 h
17-Hydroxycorticosteroids	Male: 3.0-10.0 mg/24 h Female: 2.0-8.0 mg/24 h
17-Ketosteroids, total	Male: 8-20 mg/24 h Female: 6-15 mg/24 h
Osmolality	50-1400 mOsmol/kg H₂O
Oxalate	8-40 μg/mL
Potassium	Varies with diet
Proteins, total	< 150 mg/24 h
Sodium	Varies with diet
Uric acid	Varies with diet
Body Mass Index (BMI)	Adult: 19-25 kg/m²