Descending/Ascending Spinal Cord Tracts

Question 1

What are the two enlargements in the spinal cord and what do they mean?

Answer 1

Cervical - related to upper limb

Lumbar - related to lower limb

Question 2

At what level does the spinal cord end?

Answer 2

L1/L2

Question 3

What is the end of the spinal cord called?

Answer 3

Conus medullaris

Question 4

What projects from the conus medullaris?

Answer 4

Thin connective tissue called filum terminale, which is anchored to the dorsum of the coccyx

Question 5

Are the cranial meninges continuous with the cranial meninges?

Answer 5

Yes, via the foramen magnum

Question 6

How is the spinal cord suspended in the spinal canal?

Answer 6

Denticulate ligament - ribbon of tissue on the lateral aspects of the cord

Question 7

What is the denticulate ligament made of?

Answer 7

Pia and arachnoid tissue and attaches to the dura at points along the length of the cord

Question 8

What fills the subarachnoid space?

Answer 8

CSF - just like the brain

Question 9

What is the central canal?

Answer 9

Extension of the 4th ventricle - extends the length of the canal

Question 10

What is the white matter of the spinal cord made up of?

Answer 10

Posterior, Lateral and Anterior fasciculi

Question 11

What is the grey matter in the spinal cord divided into?

Answer 11

4 
Left and Right
Posterior and Anterior 
Horns
Make up letter H

Question 12

What does the horizontal bit of the grey matter H represent?

Answer 12

Dorsal and ventral commisures which surround the central canal

Question 13

Arterial Supply of the spinal cord

Answer 13

3 major longitudinal arteries
Segmental arteries
Radicular arteries

Question 14

Describe the 3 major longitudinal arteries

Answer 14

one anterior and two posterior that originate from the vertebral arteries. These run the length of the cord.

Question 15

What are the segmental arteries derived from?

Answer 15

Vertebral, intercostal and lumbar arteries

Question 16

How do radicular arteries travel?

Answer 16

Along the dorsal and ventral roots. Arteries follow roots

Question 17

Describe venous drainage of the spinal cord?

Answer 17

The venous drainage of the cord follows a similar pattern to the supply, with both longitudinal and segmental veins.
Venous drainage also occurs in spaces around the dura. The dura mater in cranial cavity is adherent to cranial bones, in vertebral canal typically epidural fat pad which separates canal and dura, in fat pad is venous plexus - epidural anaesthetic occurs here as bathes outer layers or roots at exit intervertebral foramen.

Question 18

Where is the first stop for sensory information?

Answer 18

Postcentral gyrus

Question 19

Where in the brain is the sensory area for left sided sensation of the body

Answer 19

Right cortex - postcentral gyrus

Question 20

Where is there least white matter in the length of the spinal cord?

Answer 20

White matter occupies a smaller proportion of the cord as you descend the cord.

Question 21

Which are the ascending tracts of the spinal cord? Name 2

Answer 21

• Dorsal column; fasciculus gracilis and fasciculus cuneatus

- Spinothalamic tract

Question 22

Which are the descending tracts of the spinal cord? Name

Answer 22

• Lateral and ventralcorticospinal
• Medial longitudinal fasciculus
• Rubrospinal
• Reticulospinal (pontine and medullary)
• Vestibulospinal

Question 23

What does the dorsal column/medial lemniscus system do?

Answer 23

Fine touch and proprioception (particularly from upper limb)

Question 24

Describe the ascending action potential after stubbing your toe

Answer 24

stub toe, action potential into dorsal posterior column until reach lower portion of medulla where they synapse, one neuron, one synapsis - until reaches brainstem is ipsilateral - crosses midline at medulla. The second order neutron they synapse onto cross midline and join white matter track on OTHER side called the medial lemniscus (“ribbon like” white matter) then ascends rest of brainstem to internal capsule and enters thalamus. 3rd order neutron will then send its axon into internal capsule to appropriate part of primary somatosensory cortex.

in medulla…..2 nuclei - represent lower input (from lower limb) and upper (upper limb) - nucleus gracilis is receiving information from lower limb and nucleus cuniatus from upper limb/upper half of body. Gracilis is medial as fibres from leg enter and go in and as they ascend other fibres are coming in.

Question 25

Dorsal Column - do fibres cross/where

Answer 25

YES cross in medulla

Question 26

What does the spinothalamic tract do?

Answer 26

Pain, temperature, deep pressure

Question 27

Spinothalamic tract - do fibres cross/ where

Answer 27

YES fibres cross segmentally

Question 28

Describe the action potential journey when someone steps on your foot

Answer 28

anterolateral tract
stamp on toe - pain carried into spinal cord - immediately synapses, 2nd order neutrons send axon across midline and join anterolateral tract on other side, segmentally crossing. Track upwards to brainstem, join spinal lemniscus (white matter track )taking them all the way up to thalamus and 3rd neuron synapses to appropriate primary cortex.

Question 29

Where is the primary motor cortex?

Answer 29

PRE central gyrus

Question 30

Where will the signal to move your right arm come from?

Answer 30

Left cortex - pre central gyrus

Question 31

What does the corticospinal tract do?

Answer 31

Fine precise movement - particularly of distal limb muscles eg digits

Question 32

What is the decussation of the pyramids?

Answer 32

Corticospinal tract - Tract forms visible ridges referred to as the ‘pyramids’ on the anterior surface of the medulla, so also called the pyramidal tract. About 85% of fibres cross in the caudal medulla at the decussation of the pyramids.

Question 33

Where do fibres from the corticospinal tract cross to the other side?

Answer 33

Medulla

Question 34

Describe what happens if a CVA of the internal capsule results in a lack of descending control of the corticospinal tract

Answer 34

Spastic paralysis with hyperflexion of the upper limbs - decorticate posturing
Not paralysed as other tracts can take over

Question 35

What are pyramidal and extrapyramidal tracts?

Answer 35

Corticospinal tracts = pyramidal

All other motor systems collectively called = extrapyramidal

Question 36

What does the tectospinal tract do?

Answer 36

Mostly cervical segments - mediates reflex head and neck movements due to visual stimuli eg watching bus go past head moves

Question 37

What does the reticulospinal tract do?

Answer 37

Voluntary movement

Question 38

Fibres originating in which parts of the brain cause extension/flexion

Answer 38

PONS = EXTENSOR
MEDULLA = FLEXOR

Question 39

What does the vestibulospinal tract do?

Answer 39

Detects falling and activates anti gravity extensors eg arms and legs out to balance

Question 40

Where do fibres of the vestibulospinal tract originate?

Answer 40

Vestibular nuclei of the pons and medulla (these in turn receive input from vestibular apparatus and cerebellum)