Anatomy
At what vertebral level does the spinal cord typically end in adults?
L1–L2 , forming the conus medullaris
What is the typical resting membrane potential of a neuron?
-70 mV
Which root contains the cell bodies of sensory neurons?
Dorsal root =dorsal root ganglion
A patient with multiple sclerosis presents with slowed nerve conduction. Why?
Demyelination reduces membrane resistance, increases ion leakage, blocks saltatory conduction, → slowed/failed action potentials
Which ligament connects the tips of the spinous processes along the vertebral column?
Supraspinous ligament
Which ion channels open first to initiate depolarization during an action potential?
Voltage-gated Na ion channels
Name the two enlargements of the spinal cord and their corresponding spinal levels.
Cervical enlargement C4–T1 + Lumbosacral enlargement T11–S1
A lesion of the left spinothalamic tract at T8 would cause what sensory deficit?
Loss of pain and temperature sensation on the contralateral (right) side
Labeled
A - spinous Process
B - Transverse process
C - Body
D - Vertebral foramen
Which type of nerve fibers carry dull, aching, poorly localized pain?
C fibers = unmyelinated, slow-conducting
Where do fibers of the dorsal column–medial lemniscus cross (decussate)?
Medulla
A patient with lesion at L4 causes loss of the knee jerk reflex.
Which muscle group is most affected?
Quadriceps femoris
Labeled
A
B
C
D
What is the mechanism of referred pain in the spinal cord?
Convergence of visceral and somatic sensory neurons onto the same ascending pathway → brain interprets visceral pain as somatic
Which muscle group prevents pelvic drop during mid-stance?
Hip abductors - Gluteus medius and minimus
A patient’s pelvis drops on the left when standing on the right leg.
What is this gait pattern, and which nerve is affected?
Trendelenburg gait +superior gluteal nerve lesion
Labeled
A- Fasciculus Cuneatus
B- Fasciculus gracilis
C- Lateral Corticospinal tract
D- Anterior Corticospinal tract
E- Spinothalamic tract
Differentiate between the absolute and relative refractory periods of the action potential.
Absolute = Na⁺ gates closed, no AP possible
Relative = membrane hyperpolarized by K⁺ efflux, stronger stimulus needed for AP
Name all layers in order for the lumbar puncture needle to reach CSF.
Skin → subcutaneous tissue → supraspinous ligament → interspinous ligament → ligamentum flavum → epidural space → dura mater → arachnoid mater → subarachnoid space
A 60-year-old with chronic low back pain, worse at night, weight loss, and fever.Which serious underlying cause must be ruled out and how?
Malignancy or spinal infection; investigate with MRI, blood tests (WBC, ESR, CRP)