Spinal Cord Flashcards
Describe the structure of the spinal cord
> Roughly cylindrical in shape
Cervical enlargement: C4-T1 (nerves to upper limb)
Lumbar enlargement: L2-S3 (nerves to lower limb)
tapers to Conus Medullaris at L1-L2 (thin thread extends to Co1 = filum terminale: anchors spinal cord)
After conus medullaris = nerves = fully formed running like loose hair up to exit from vertebral column = Cauda Equina
Describe the protection of spinal cord
> Surrounded by 3 meninges
- dense irregular CT
- cerebrospinal fluid to prevent mechanical damage
- provide framework for cerebral + cranial vasculature
- cover spinal nerves until point of exit
- denticulate ligament holds spinal cord in place within the meninges
1. Dura mater - under bones of skull + vertebral column
- highly vascularised
2. Arachnoid mater - middle layer
- avascular + no innervation - Under arachnoid = sub-arachnoid space = full of cerebrospinal fluid: nutrition/protection/waste removal
3. Pia mater - tightly adhered to brain + spinal cord
- thin + highly vascularised (supply to CNS)
Describe the X section of the spinal cord
> H shaped - grey matter (neuronal cell bodies)
- Anterior horn = mostly motor neurons
- Lateral horn = nerves that innervate visceral + pelvic organs
- Posterior horn = somatosensory neurons - transmit info to brain
Central canal = filled with cerebrospinal fluid
White matter = axons
Dorsal roots: ganglion (swelling) that houses the cell bodies of afferent neurons
Ventral roots = efferent (motor)
Name the sensory/ascending pathways:
Dorsal Column
Spino-thalamic tract
Spinocerebellar tract
Describe the Dorsal column pathway
> Found in dorsal white matter
2 sections: cuneatus + gracilis
Carries info to cortex from skin receptors: touch
+ muscle joint receptors: position/vibration/weight distribution
Pathway:
- 1st order neuron - Receptor to Gracilis(LL)/ Cuneatus(UL) (here synapses with 2nd order neuron)
- 2nd order neuron - gracilis/cuneatus to thalamus (crossing to contralateral side at medulla)
- 3rd order neuron - thalamus to primary somatosensory cortex (front of parietal lobe)
> Locate on diagram
- posterior aspect between stalks of H
Describe the Spino-thalamic tract
> 2 sections:
- Lateral: pain + temperature signals
- Anterior: Itch/tickle/pressure/vibration/poorly localised touch sensations
Pathway:
- 1st order neuron: receptor to spinal column (synapses at level of entry)
- 2nd order neuron: Crosses to opposite side of spinal cord and ascends to thalamus (synapses here)
- 3rd order neuron: thalamus to primary somatosensory cortex
On a diagram
- surrounds the anterior stalks of the H - lateral is bigger than anterior
Describe the spinocerebellar tract
> Receives info around balance via joint position receptors
2 sections
- Anterior: doesn’t cross
: enters cerebellum via inferior peduncle
- Posterior: some fibres don’t cross, those that do cross twice (level of entry then before entering cerebellum)
: Enter via superior peduncle
On a diagram
- Outer edge of spinal cord white matter (lateral edges)
Name the descending pathways
Corticospinal tract (pyramidal) Reticulospinal tract Vestibulospinal tract Tectospinal tract Rubrospinal tract
Describe the Corticospinal (pyramidal) tract
> cortex to spinal cord directly
2 sections:
Lateral: control of extremities
Anterior: control of axial skeleton
Pathway
- Starts at motor/pre-motor areas of cortex (cell bodies)
- axon descends ipsilaterally via cerebral peduncle
- converge into axon bundles at medulla oblongata (pyramidal shaped bundles = hence name)
- 80-90% cross to contralateral side and descend as lateral corticospinal tract to respective exit level
- 10-20% descend as anterior corticospinal tract then cross over at level of exit
On a diagram
- Anterior is larger section between anterior stalks of h
- Lateral is pyramid on lateral sides of posterior stalks of h
Describe the reticulospinal tract
> originates as reticular formation in brainstem (Pons + Medulla)
indirect tract travels down spinal cord - controls reflexes
2 paths: Lateral = flexor reflexes
: Medial = extensor reflexes
On a diagram:
Medial = smaller path in between anterior stalks of h
Lateral = medial to lateral pyramidal tract (just lateral to outer mid section of h
Describe the Vestibulospinal tract
> Originates at lateral vestibular nucleus (near pons)
controls position of head/neck/trunk
controls reflexes + balance
uncrossed tract
> On a diagram
: anterior edge of spinal cord - medial to both anterior corticospinal and tectospinal tracts
Describe the tectospinal tract
> Arises at superior colliculus in midbrain
carries body’s response to visual stimuli
tract finishes at cervical level - more synapses to reach lower body
Crossed tract
> On a diagram
- anterior edge of spinal cord - anterior to anterior corticospinal tract
Describe the rubrospinal tract
> Originates at red nucleus - ends at spinal cord
helps fine motor control of movement
fastest conducting neurons (may not play a huge role in humans)
Crosses at origin
potential for reflex movement (indirect control)
On a diagram:
- anterior to widest edge of lateral corticospinal tract (posterior to lateral spinothalamic tract)
Why are spinal cord injuries so bad?
> Lesion may impair motor/sensory/autonomic functions
(to what degree is dependent on level + extent)
- 84% = traumatic (typically = fracture that dislocates)
- Non-traumatic = degenerative disc disease/ infarct (blood clot)/ tumour/ inflammation/ viral infection
What are the vulnerable areas of the spine
Cervical spine - C5-C7 (55%)
Thoracic Spine - T4-T7
Thoracolumbar - T12
