Section 1. Back

A 48-year-old man goes to his physician because of pain and paresthesia along the lateral aspect of the leg and the dorsum of the foot. The patient's symptoms suggest impingement of the L5 spinal nerve resulting from a herniated intervertebral disc. The L5 spinal nerve most likely exits between which of the following vertebrae?

L3–L4 vertebrae

L4–L5 vertebrae

L5–S1 vertebrae

S1–S2 vertebrae

Spinal nerves in the thoracic and lumbar vertebral region exit the vertebral canal below their associated vertebra. Therefore, the L5 spinal nerve exits below L5, between L5 and S1.

The muscles of the posterior aspect of the thigh, or hamstring musculature, are responsible for flexing the knee joint. Beginning with the motor neuron cell bodies in the gray matter of the spinal cord, identify the most likely pathway that axons would travel from the spinal cord to the hamstring muscles?

Ventral horn, ventral root, ventral ramus

Ventral horn, ventral root, dorsal ramus

Lateral horn, ventral root, ventral ramus

Lateral horn, dorsal root, dorsal ramus

Dorsal horn, dorsal root, ventral ramus

Dorsal horn, dorsal root, dorsal ramus

The ventral horn of the spinal cord gray matter houses motor neuron cell bodies and conveys motor neurons out through the ventral root into the spinal nerve. All muscles of the limbs and body wall are innervated by ventral rami. Although the muscles are present along the posterior aspect of the thigh, muscles are still innervated by the ventral rami. Dorsal rami innervate the skin of the back and the deep back muscles, such as the erector spinae.

A 27-year-old man is brought to the emergency department after being involved in an automobile accident. Radiographic imaging studies indicate that he has sustained a fracture of the L1 vertebral arch and has a partially dislocated bone fragment impinging upon the underlying spinal cord. Which spinal cord level is most likely compressed by this bone fragment?

C1

L2

S3

T4

In an adult, the caudal end of the spinal cord is at the L1–L2 vertebral level. Therefore, a bone fragment from the L1 vertebra would have the potential of touching the caudal end of the spinal cord, not the L1 spinal cord level. C1, L2, and T4 are spinal cord levels superior to the fracture.

A 50-year-old man is diagnosed with flaccid paralysis limited to the right arm, without pain or paresthesias. No sensory deficits are noted. Laboratory studies reveal that the patient is infected with West Nile virus. The target that the virus has infected resulting in this patient's symptoms is most likely the

Ventral horn of spinal cord gray matter

Ventral rami of spinal nerves

Dorsal horn of spinal cord gray matter

Dorsal rami of spinal nerves

The patient has no sensory deficits and presents with only motor deficits. Therefore, the virus affects the ventral horn of the gray matter because that is the location of the motor neuron cell bodies.

A 6-year-old boy is stung by a wasp between his shoulder blades. Identify the pain sensation pathway the axons would travel to course from the skin of his back to the spinal cord.

Ventral horn, dorsal root, dorsal ramus

Ventral horn, dorsal root, ventral ramus

Ventral horn, ventral root, dorsal ramus

Ventral horn, ventral root, ventral ramus

Dorsal ramus, dorsal root, dorsal horn

Dorsal ramus, dorsal root, ventral horn

Dorsal ramus, ventral root, ventral horn

Dorsal ramus, ventral root, dorsal horn

All skin of the back is segmentally innervated by the dorsal rami branches of spinal nerves. Sensory information is then conducted through the dorsal root into the dorsal horn of the gray mater of the spinal cord.

Which of the following paired muscles of the back is primarily responsible for extension of the vertebral column?

Iliocostalis

Latissimus dorsi

Levator costarum

Rhomboid major and minor

Trapezius

The paired iliocostalis muscles, part of the erector spinae musculature, are postural muscles that help to extend the vertebral column and thus keep the spine erect. The latissimus dorsi, rhomboids, and trapezius muscles act primarily on the upper limb. The levator costarum muscles help to elevate the ribs during inspiration but will not extend the vertebral column.

A 44-year-old woman is suspected of having meningitis. To confirm the diagnosis, a lumbar puncture is ordered to collect a sample of the cerebrospinal fluid (CSF). Identify the last layer of tissue the needle will traverse in this procedure before reaching CSF.

Arachnoid mater

Dura mater

Ligamentum flavum

Pia mater

Skin

A lumbar puncture collects cerebrospinal fluid and, therefore, the needle has to enter the subarachnoid space, which is located between the arachnoid and pia mater. Therefore, the last layer of tissue the needle would traverse to enter the subarachnoid space is the arachnoid mater.