Mayo Clinic I - 07 - Spinal Cord Anatomy

Question 1

Where do you find alpha and gamma motor neurons?

Answer 1

In the anterior section of the cord gray matter, referred to as the ventral horn

Question 2

What is a motor unit?

Answer 2

Single motor neuron and all the muscle fibers it supplies

Question 3

What is the role of gamma motor neurons?

Answer 3

Provide innervation to muscle spindles, which are stretch receptors in the muscle

Question 4

What is the role of the Clarke column?

Answer 4

Mediate information from muscle spindles and other receptors to the cerebellum

Question 5

Where in the spinal cord do you find the corticospinal tract?

Answer 5

Lateral funiculus; leg fibers originate in the medial cortex, arm and face fibers in the lateral cortex

Question 6

Path of upper motor neurons in the corticospinal tract?

Answer 6

Originate in layer 5 of the primary motor cortex. Descend through the corona radiata, internal capsule, and ventral aspect of the brainstem, and decussate at the caudal medulla. Continue as the lateral corticospinal tract in the spinal cord.

Question 7

An upper motor neuron lesion in the corticospinal tract will result in?

Answer 7

Ipsilateral weakness below the level of the lesion

Question 8

Role of the vestibulospinal tract?

Answer 8

These tracts synapse on interneurons or alpha motor neurons for maintenance of erect posture relative to head and eye motion; medial - cervical spine, lateral - project to neurons innervating muscles in the trunk and lower extremities

Question 9

Origin of tectospinal tract?

Answer 9

Superior colliculus of the midbrain

Question 10

Where does the superior colliculus receive information from?

Answer 10

Oculomotor nuclei and intergrates other sensory information to respond to the environment

Question 11

Pathway of the tectospial tract?

Answer 11

It crosses and projects to the cranial nuclei involved in extraocular movement and the cervical spinal cord to coordinate movements of the head, neck and eyes in response to sensory stimuli

Question 12

Main function of fibers in the rubrospinal tract?

Answer 12

To influence flexion, primarily in the upper extremities

Question 13

The dorsal column-medial lemniscal system conveys what information?

Answer 13

Information regarding vibration, joint posiition sense, and discriminative touch

Question 14

Fasciculus gracilis receives input from where?

Answer 14

Dorsal root ganglion neurons from below T6; it lies medial to fasciulus cuneatus in the dorsal funiculus at the level of the spinal cord; this information enters the fasciculi and ascends to nucleus gracilis at the level of the caudal medulla

Question 15

Fasciculus cuneatus receives input from where?

Answer 15

The dorsal root ganglion neurons from T6 and above; this information enters the fasciculi and ascends to nucleus cuneatus at the level of the caudal medulla

Question 16

What information is is carried in the spinothalamic tract?

Answer 16

Pain and temperature sensation

Question 17

Pathway of the spinothalamic tract?

Answer 17

Axons from the DRG neurons enter the spinal cord dorsally, synapse in the dorsal horn at or slightly above entry level; second-order neurons decussate and ascend in the ventral funiculus as the anterior spinothalamic tract and in the lateral funiculus as the lateral spinothalamic tract

Question 18

What information is carried in the spinocerebellar tract?

Answer 18

Information about unconscious proprioception to the cerebellum

Question 19

Origin of the dorsal spinocerebellar tract?

Answer 19

Clarke column (C8-L2) ; carries information regarding unconscious proprioception from the lower extremity and trunk

Question 20

Upper extremity unconscious proprioception is carried in what?

Answer 20

The cuneocerebellar tract; it courses through the lateral funiculus

Question 21

Characteristics of Brown-Séquard syndrome

Answer 21

Upper motor neuron weakness and loss of vibration/proprioception below the level of the lesion ipspilaterally and contralaterally loss of sensation to pain and temperature; at the level of the lesion, the patient may have a small area of loss of all sensory modalities

Question 22

Commissural syndrome is due to?

Answer 22

Interruption of the segmental crossing of the spinothalamic tract. Because a central lesion does not affect the spinothalamic tract and affects only the decussating segmental fibers, patients have symptoms only at the level surrounding the lesion

Question 23

The anterior spinal artery typically supplies what?

Answer 23

The ventral two-thirds of the spinal cord

Question 24

Anterior spinal artery syndrome?

Answer 24

Ischemia of the anterior spinal artery generally causes weakness and loss of sensation to pain and temperature below the lesion but often spares the dorsal columns