Spinal cord anatomy (ascending and desc tracts) Flashcards
How many pairs of spinal nerves are there?
31 pairs
Name the two enlargements of the spinal cord and their significance
- CERVICAL enlargement - brachial plexus, accomodate upper limbs
- LUMBAR enlargement - lumbar plexus, accomodate lower limbs
Spinal cord ends at which vertebral level?
L1-L2
Describe the formation of spinal ROOTS
Rootlets emerge from the anterior (ventral) and posterior (dorsal) surfaces of the spina cord
Ventral and dorsal rootlets coalesce to form roots
Describe the formation of spinal nerves and where they are located
Ventral and dorsal roots traverse SA till they reach vertebral foramina
Here they fuse to form mixed spinal nerve (2 modalities)
What information do the anterior and posterior spinal roots carry? Where do they enter the CNS?
Posterior root:
sensory information TO dorsal horn of spinal cord
Anterior root:
Motor information FROM ventral horn of spinal cord
Name the two branches of a spinal nerve
Anterior and posterior rami
What is the termination of the spinal cord called?
Conus Medullaris
What are the spinal meninges?
Dura
Arachnoid
Pia
What is the significance of the epidural space of the spinal cord?
Contains adipose tissue and venous plexuses used for epidural anaesthesia
CSF is found in which spinal meningeal layer?
SA space
What is the function of denticulate ligament?
Anchors spinal cord to the vertebral canal. Formed from pia and arachnoid mater
List the contents of white matter (outer) of spinal cord
fibres - longitudinal orientation
blood vessels
glial cells
List the contents of grey matter (h-shaped) of spinal cord
4 horns - L & R anterior and posterior Neuronal soma Glial cells Blood vessels Cell processes
List arterial supply of the spinal cord
- Longitudinal arteries - one ant, 2 posterior
- Segmental arteries
- Radicular arteries
Name the two ascending spinal pathways
- Spinothalamic - pain, temperature, deep pressure
2. Dorsal column/medial leminiscus - fine touch, proprioception, vibration
Describe course of first order neuron of dorsal column pathway, where does it synapse?
Enters dorsal column of spinal cord via dorsal horn
Ascends spinal cord
Synapses at nucleus gracilis of medulla
Describe of second order neurone, where does it synapse?
Ascends the brainstem as MEDIAL LEMNISCUS
Synapse at thalamus - ventral posterolateral nucleus
Where does the SENSORY DECCUSSATION occur? Which spinal tract is it a part of?
Sensory decussation occurs in the medulla by second order neurons of the dorsal column/medial leminiscus pathway
Describe course of the 3rd order neurons of the medial lemniscus, where does it synapse?
Ascends through medial 1/2 of the posterior limb of the internal capsule
Synapses in the sensory cortex
Describe course of first order neuron of spinothalamic tract and where it synapses
Begins in dorsal root ganglion and enters spinal cord
Synapses in posterior horn at the substantia gelatinosa
Describe the course of second order neuron of spinothalamic tract and where it synapses
Decussates anterior to the spinal canal
Ascends the spinal cord
Synapses at the ventral posterolateral nucleus of thalamus
Describe the course of the 3rd order neuron of the spinothalamic tract and where it synapses
Ascends from thalamus to cortex, synapses at primary cortex
Name the descending spinal pathways
- Corticospinal tract - fine, precise movements
- Tectospinal tract - mediate reflex head and neck movements towards auditory and visual stimuli
- Reticulospinal tract - control of breathing, cardiac control and consciousness
- Vestibulospinal tract - excitatory input to antigravity muscles
Describe the course of first order neurons of the corticospinal tract and where it decussates
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
What is the tectospinal tract?
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
What is reticulospinal tract?
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)
What is vestibulospinal tract?
Excitatory input to “antigravity” extensor muscles
• Origin – vestibular nuclei of pons and medulla – these receive input from vestibular apparatus and cerebellum
Which spinal tract is responsible for ‘decerebrate rigidity’ and ‘paraplegia in extension’?
Vestibulospinal tract
What is Brown-Sequard Syndrome?
Motor and sensory deficits as a result of hemisection of spinal cord
What are the motor consequences of a true brown sequard syndrome?
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
What are the sensory consequences of a true brown sequard syndrome?
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
