Spinal cord anatomy and Ascending & Descending pathways

Question 1

How many spinal nerves are there?

Answer 1

31

Question 2

In the spinal cord, does the grey matter lie on the outer aspect or the core

Answer 2

The inner core (forms an H shape)

Question 3

What is in the white matter?

Answer 3

Axons, glial cells and blood vessels

Question 4

What is in the grey matter?

Answer 4

Neuronal soma, cell processes, synapses, glial cells and blood vessels

Question 5

Describe the blood supply to the spinal cord

Answer 5

A. Three major longitudinal arteries: one anterior and two posterior that originate from the vertebral arteries. These run the length of the cord.
B. Segmental arteries derived from vertebral, intercostal and lumbar arteries.
C. Radicular arteries that travel along the dorsal and ventral roots.

Question 6

Where is the primary somatosensory cortex?

Answer 6

Postcentral gyrus

Question 7

How does the information from the periphery reach the somatosensory cortex?

Answer 7

Travel through the spinal cord (NB not face and scalp)

Question 8

Which ascending tract sends the signals allowing us fine touch and propriception?

Answer 8

The dorsal column/Medial lemniscus system

Question 9

Where do the signals carried in the dorsal column/Medial lemniscus system cross over?

Answer 9

Medulla

Question 10

What spinal tract carries the sensations of pain, temperature and deep pressure?

Answer 10

Spinothalamic tract

Question 11

Where is the primary motor cortex?

Answer 11

Precentral gyrus

Question 12

What spinal tract allows fine, precise movement?

Answer 12

Corticospinal tract

Question 13

Where do most of the fibres of the corticospinal tract cross over?

Answer 13

Decussation of the pyramids

Question 14

What spinal tract mediates reflex head and neck movement due to visual stimuli?

Answer 14

Tectospinal tract

Question 15

What is the reticular formation?

Answer 15

A network of nerve pathways in the brainstem connecting the spinal cord, cerebrum, and cerebellum, and mediating the overall level of consciousness. Forms the central core of the brainstem

Question 16

Where do the fibres of the reticular formation originate?

Answer 16

Pons and medulla

Question 17

Do reticular fibres originating in the pons tend to facilitate extensor or flexor movements?

Answer 17

Extensor (Inhibit flexor)

Question 18

Do reticular fibres originating in the medulla tend to facilitate extensor or flexor movements?

Answer 18

Flexor (inhibit extensor)

Question 19

What tract provides excitatory input to antigravity muscles?

Answer 19

Vestibulospinal tract

Question 20

Where do the fibres of the vestibulospinal tract originate?

Answer 20

Vestibular nuclei of the pons and medulla.

Question 21

Is the dorsal column a motor or sensory pathway?

Answer 21

Sensory

Question 22

What two fasiculi make up the dorsal column pathway?

Answer 22

Graclie

Cuneate

Question 23

What does the dorsal column sense?

Answer 23

Fine touch and proprioception

Question 24

What four nerve endings sense fine touch?

Answer 24

Meisners corpuscles
Pacinian corpuscles
Rufini endings
Merkel endings

Question 25

Where do the cell body’s of sensory nerves sit? (this is before they enter the spinal cord!)

Answer 25

Dorsal root ganglion

Question 26

Do axons from the lower limb travel in the gracile or cuniform fasiculus?

Answer 26

Gracile

Question 27

Do axons from the upper limb travel in the gracile or cuniform fasiculus?

Answer 27

Cuneate

Question 28

What is a nucleus?

Answer 28

Collection of cell bodies within the CNS

Question 29

Explain the dorsal column medial lemniscus pathway

Answer 29

1. Sensation of fine touch/proprioception perceived by sensory neurones. The cell bodies of these neurones are in the dorsal root ganglion.
2. Travels up on the ipsilateral side in the dorsal column (either gracile of cuneate fasiculus)
3. Reaches the gracile or cuneate nucleus in the Medulla.
4. After this is crosses over at the pyramids of the medulla (after this is is referred to as medial lemniscus)
5. Travels from here to the ventral posterolateral nucleus in the thalamus.
6. Travels from the thalamus to the post central gyrus (primary somatosensory cortex)

Question 30

What is the decussation point in the spinal cord (the fibres of the spinothalamic tract cross here) called?

Answer 30

Anterior white commissure

Question 31

What is lissaure’s fasiculus?

Answer 31

The fasiculus in which the fibres of the spinothalamic ascend for 1 - 2 levels before crossing.

Question 32

Explain the spinothalamic tract

Answer 32

1. Sensory neurones pick up sensations of temperature and crude touch. The cell bodies of these neurones are located in the dorsal root ganglion.
2. Travels up in lissaure’s fasiculus on the ipsilateral side for 1 - 2 levels of the spinal cord.
3. Decussates at the anterior white commisure.
4. Travels to the thalamus
5. Travels from thalamus to the post central gyrus.

Question 33

Describe the corticospinal tract.

Answer 33

1. Arises in the primary motor cortex of the pre central gyrus.
2. Axons exit through white matter and pass through the internal capsule.
3. Travel down through the midbrain and the pons before crossing over at the pyramids of the medulla.
4. Then enter the lateral funiculus of the spinal cord to become the lateral corticospinal tract.
   (The fibres which don’t cross at the medulla continue as the ventral corticospinal tract and they cross segmentally at the spinal cord)
5. Exit the spinal cord

Question 34

What would a stroke causing ischaemia to the internal capsule result in?

Answer 34

Loss of control of the corticospinal tract (spastic paralysis/decorticate posturing)