Spinal cord anatomy (ascending and desc tracts)

Question 1

How many pairs of spinal nerves are there?

Answer 1

31 pairs

Question 2

Name the two enlargements of the spinal cord and their significance

Answer 2

1. CERVICAL enlargement - brachial plexus, accomodate upper limbs
2. LUMBAR enlargement - lumbar plexus, accomodate lower limbs

Question 3

Spinal cord ends at which vertebral level?

Answer 3

L1-L2

Question 4

Describe the formation of spinal ROOTS

Answer 4

Rootlets emerge from the anterior (ventral) and posterior (dorsal) surfaces of the spina cord

Ventral and dorsal rootlets coalesce to form roots

Question 5

Describe the formation of spinal nerves and where they are located

Answer 5

Ventral and dorsal roots traverse SA till they reach vertebral foramina

Here they fuse to form mixed spinal nerve (2 modalities)

Question 6

What information do the anterior and posterior spinal roots carry? Where do they enter the CNS?

Answer 6

Posterior root:
sensory information TO dorsal horn of spinal cord

Anterior root:
Motor information FROM ventral horn of spinal cord

Question 7

Name the two branches of a spinal nerve

Answer 7

Anterior and posterior rami

Question 8

What is the termination of the spinal cord called?

Answer 8

Conus Medullaris

Question 9

What are the spinal meninges?

Answer 9

Dura
Arachnoid
Pia

Question 10

What is the significance of the epidural space of the spinal cord?

Answer 10

Contains adipose tissue and venous plexuses used for epidural anaesthesia

Question 11

CSF is found in which spinal meningeal layer?

Answer 11

SA space

Question 12

What is the function of denticulate ligament?

Answer 12

Anchors spinal cord to the vertebral canal. Formed from pia and arachnoid mater

Question 13

List the contents of white matter (outer) of spinal cord

Answer 13

fibres - longitudinal orientation
blood vessels
glial cells

Question 14

List the contents of grey matter (h-shaped) of spinal cord

Answer 14

4 horns - L & R anterior and posterior 
Neuronal soma
Glial cells
Blood vessels 
Cell processes

Question 15

List arterial supply of the spinal cord

Answer 15

1. Longitudinal arteries - one ant, 2 posterior
2. Segmental arteries
3. Radicular arteries

Question 16

Name the two ascending spinal pathways

Answer 16

1. Spinothalamic - pain, temperature, deep pressure

2. Dorsal column/medial leminiscus - fine touch, proprioception, vibration

Question 17

Describe course of first order neuron of dorsal column pathway, where does it synapse?

Answer 17

Enters dorsal column of spinal cord via dorsal horn

Ascends spinal cord

Synapses at nucleus gracilis of medulla

Question 18

Describe of second order neurone, where does it synapse?

Answer 18

Ascends the brainstem as MEDIAL LEMNISCUS

Synapse at thalamus - ventral posterolateral nucleus

Question 19

Where does the SENSORY DECCUSSATION occur? Which spinal tract is it a part of?

Answer 19

Sensory decussation occurs in the medulla by second order neurons of the dorsal column/medial leminiscus pathway

Question 20

Describe course of the 3rd order neurons of the medial lemniscus, where does it synapse?

Answer 20

Ascends through medial 1/2 of the posterior limb of the internal capsule

Synapses in the sensory cortex

Question 21

Describe course of first order neuron of spinothalamic tract and where it synapses

Answer 21

Begins in dorsal root ganglion and enters spinal cord

Synapses in posterior horn at the substantia gelatinosa

Question 22

Describe the course of second order neuron of spinothalamic tract and where it synapses

Answer 22

Decussates anterior to the spinal canal
Ascends the spinal cord
Synapses at the ventral posterolateral nucleus of thalamus

Question 23

Describe the course of the 3rd order neuron of the spinothalamic tract and where it synapses

Answer 23

Ascends from thalamus to cortex, synapses at primary cortex

Question 24

Name the descending spinal pathways

Answer 24

1. Corticospinal tract - fine, precise movements
2. Tectospinal tract - mediate reflex head and neck movements towards auditory and visual stimuli
3. Reticulospinal tract - control of breathing, cardiac control and consciousness
4. Vestibulospinal tract - excitatory input to antigravity muscles

Question 25

Describe the course of first order neurons of the corticospinal tract and where it decussates

Answer 25

Begins at the premotor cortex and descends through internal capsule

Passes through crus cerebri of midbrain

At medulla oblongata, tract bundles up on itself to form “PYRAMID”

• 80% of fibres deccusate –> MOTOR DECUSSATION –> Lateral corticospinal tract
• 20% of fibres continue along the ipsilateral side –> ventral corticospinal tract

Synapse of the descending spinal tract - alpha and gamma neurons via interneurons

Question 26

What is the tectospinal tract?

Answer 26

mediate reflex head and neck movement towards visual and auditory stimuli

• Begins in tectum – posterior portion of midbrain
• Crosses midline and projects down into spinal cord
• Occurs in anterior column

Question 27

What is reticulospinal tract?

Answer 27

Control of breathing, cardiac control, consciousness

• Reticular formation – central core of the brainstem
• Contains many nuclei, receives input from all over the CNS
• Origin – areas of reticular formation in pons (fibres originating here facilitate extensor movements and inhibit flexor movement) and medulla (opposite of pons)

Question 28

What is vestibulospinal tract?

Answer 28

Excitatory input to “antigravity” extensor muscles

• Origin – vestibular nuclei of pons and medulla – these receive input from vestibular apparatus and cerebellum

Question 29

Which spinal tract is responsible for ‘decerebrate rigidity’ and ‘paraplegia in extension’?

Answer 29

Vestibulospinal tract

Question 30

What is Brown-Sequard Syndrome?

Answer 30

Motor and sensory deficits as a result of hemisection of spinal cord

Question 31

What are the motor consequences of a true brown sequard syndrome?

Answer 31

o Motor fibers: cross in the medulla, therefore a lesion in the right side will interrupt the right descending corticospinal tract  weakness if not paralysis in right lower leg

Question 32

What are the sensory consequences of a true brown sequard syndrome?

Answer 32

o Sensory fibers: dorsal column climbs in the ipsilateral side of the spinal cord and has not crossed till medulla – therefore, you lose the sensation in the same side as the lesion.

o Spinothalamic tract – crosses immediately in the spinal cord – right sided lesion interrupts fiber entering from left side of the body – contralateral loss of sensation