Structure and function of the spinal cord

Question 1

What does the spinal cord narrow to form

Answer 1

• Conus medullaris

Question 2

What is the terminal filum

Answer 2

• Is a delicate strand of tissue, about 20 cm in length, proceeding downward from the apex of the conus medullaris

Question 3

What is the cauda equina

Answer 3

• Is a bundle of spinal nerves and spinal nerve rootlets, consisting of the second through fifth lumbar nerve pairs

Question 4

What are the four divisions of the spinal cord

Answer 4

Cervical division - C1-C7
Thoracic division - T1-T12
Lumbar division - L1-L5
Sacral division - S1-S5

Question 5

What is the conus medullaris

Answer 5

• The conus medullaris (Latin for “medullary cone”) or conus terminalis is the tapered, lower end of the spinal cord. It occurs near lumbar vertebral levels 1 (L1) and 2 (L2), occasionally lower. The upper end of the conus medullaris is usually not well defined.

Question 6

What type of fibres do the ventral roots contain

Answer 6

Efferent fibres

Question 7

What type of fibres do the dorsal roots contain

Answer 7

Afferent fibres

Question 8

What does the inner core, gray matter of the spinal cord contain

Answer 8

• Neuronal cell bodies
• H shaped
• Ventral, lateral and dorsal horn

Question 9

What does the outer, white matter of the spinal cord contain?

Answer 9

• Myelinated axons

- White columns/tracts or funiculi

Question 10

What part of the spine are the lateral horns specific to

Answer 10

• Thoracic region

Question 11

Where is there extra gray matter

Answer 11

• At levels that supply the limbs

Question 12

What type of neurons are present in the dorsal horn

Answer 12

• Neurons receiving sensory input

Question 13

What type of neurons are present in the lateral horn

Answer 13

• Preganglionic sympathetic neurons

Question 14

What type of neurons are present in the ventral horn

Answer 14

• Motor neurons

Question 15

What type of white matter tracts carry afferent(sensory) impulses

Answer 15

• Long ascending tracts carry afferent(sensory) impulses to centres within the brain

Question 16

What type of white matter tracts carry efferent(motor) impulses from centres within brain

Answer 16

• Long descending tracts carry efferent(motor) impulses from centres within brain

Question 17

What happens to tracts that go to/from cerebral hemispheres

Answer 17

• Cross

- ie left cerebral hemisphere controls right side of body

Question 18

What column are the ascending white matter tracts located

Answer 18

• Dorsal column

Question 19

What column are the descending white matter tracts located

Answer 19

• Lateral column = descending + ascending tracts

Question 20

What does the ventral column contain?

Answer 20

• mainly descending tracts

Question 21

What is proprioceptive information

Answer 21

• info originating from inside the body(from muscles, joints, tendons)

Question 22

What is exteroceptive info

Answer 22

• info originating from outside the body(pain, temp, touch)

Question 23

What is a first order(primary sensory) neuron

Answer 23

• Enters spinal cord via dorsal root

Question 24

What is a second order neuron

Answer 24

• Ascends spinal cord or brainstem

Question 25

What is a third order neuron

Answer 25

• Projects to the cerebral cortex

Question 26

What is detected by the dorsal column-medial lemniscus pathway

Answer 26

• Fine touch(from cutaneous mechanoreceptors)
• Proprioception(from muscle spindles, golgi tendon organs, joints
• Provides brain with positional information

Question 27

Where do first order neurons enter in the dorsal column-medial lemniscus pathway

Answer 27

• Enter spinal cord and ascend dorsal column on the same side within the

1) fasciculus gracilis(medial)
2) fasciculus cuneatus(lateral)

Question 28

Where do first-order neurons synapse on second-order neurons in the dorsal column-medial lemniscus pathway

Answer 28

• In the medulla

Question 29

Where does the fasciculus gracilis terminate and what limbs does it carry info from

Answer 29

• Terminates in nucleus gracilis(gracile)

- Info from lower limb

Question 30

Where does the fasciculius cuneatus terminate and what limbs does it carry info from

Answer 30

• Terminates in nucleus cuneatus(cuneate)

- Info from upper limb

Question 31

What is the path of the second-order neurons in the dorsal column-medial lemniscus pathway

Answer 31

• Cross in medulla and ascend to thalamus

- Form medial lemniscus(ribbon)

Question 32

What is the path of third-order neurons in the dorsal column-medial lemniscus pathway

Answer 32

• Project from thalamus to somatosensory cortex

Question 33

What happens when there is a lesion on one side of the spinal cord in the dorsal-column medial lemniscus pathway

Answer 33

• Lesion on one side of spinal cord
• eg. in multiple sclerosis
• loss of tactile discrimination + proprioception on same side

Question 34

What are the symptoms of a lesion compromising the dorsal root medial lemniscus pathway

Answer 34

• Sensory ataxia - loss of coordination and balance without visual cues(ie no positional info)

Question 35

What is romberg’s sign

Answer 35

• Severe swaying on standing with eyes closed/feet together

- Indicative of a lesion affecting the dorsal root-medial lemniscus pathway

Question 36

What does the spinothalamic tract detect

Answer 36

• Pain, temp and crude touch(from nociceptors)

Question 37

Path of first-order neurons in spinothalamic tracts

Answer 37

• Enter dorsal horn and form tract of lissauer
• Collateral branches given off at the tip of dorsal horn
• Run up or down 1-2 segments
• Synapse in dorsal horn with second-order neurons

Question 38

Path of second-order neurons in the spinothalamic tracts

Answer 38

• Cross in dorsal horn at each level
• Ascend in anterolateral column to thalamus
• Fibres from lower limb - lateral
• Fibres from upper limb - medial

Question 39

Path of third-order neurons in spinothalamic tracts

Answer 39

• Project from thalamus to somatosensory cortex