Spine Flashcards
Questions covering required knowledge of spinal anatomy for the primary FRCA exams, particularly relevant for the SOE and OSCE. There is considerable overlap with neurophysiology in past spinal anatomy stations for the OSCE, and this is reflected in these flashcards.
For a lumbar epidural block, what volume of local anaesthetic is required per segment to be blocked?
1.5 - 2.0 ml
What is the total cerebrospinal fluid (CSF) volume in the adult?
100 - 200 ml
What is the normal spinal CSF pressure in the supine patient?
7 - 20 cm H2O (5-15 mm Hg)
In a transverse section of the spinal cord, of what is the grey matter composed?
Nerve cell bodies and unmyelinated axons
What does the dorsal root ganglion contain?
Cell bodies of the afferent neurons
Describe the neurological pathway followed after stimulation of a nociceptor by a painful stimulus from the point of entry into the spinal cord
Enters the spinal cord via the posterior nerve root, synapses in the dorsal horn, crosses the midline to ascend in the lateral spinothalamic tract. After synapsing in the thalamus, impulses are relayed to the sensory cortex
Identify the lateral spinothalamic tract on the diagram
Area marked A
What modality is carried by the anterior spinothalamic tract?
Touch (coarse touch & pressure)
Which spinal tracts are represented by the area marked B?
Spino-cerebellar tracts (anterior and posterior).
These tracts are responsible for proprioceptive signals, obtained from the golgi tendons and muscle spindles.
What does the area marked C on the diagram represent and what modalities are carried by it?
Dorsal/posterior columns.
Proprioception from skin and joints, fine touch, vibration, two-point discrimination
What is the specific gravity of CSF?
1003-1009 (1.003-1.009)
Which spinal tracts are represented by area E
Anterior corticospinal tracts (innervate axial muscles)
Which spinal tract is represented by Area D?
Lateral corticospinal tract (limb muscles)
What type of nerve impulses travel in the corticospinal tracts and how do the fibres terminate?
Descending motor impulses.
They synapse with motor neurones in the anterior horn.
Within the spinal cord, where are ascending pain and temperature fibres carried?
Lateral spinothalamic tract
What vessels contribute to the arterial blood supply of the cord?
Anterior spinal artery
Posterior spinal artery (arises from vertebrals or PICA)
Spinal branches of the vertebral, intercostal, lumbar and sacral arteries
*Great anterior medullary artery (Artery of Adamkiewicz) - this usually arises on the left from a posterior intercostal artery between level T9-12
What is the origin of he anterior spinal artery?
Branch from each of the vertebral arteries
What is the clinical effect of thrombosis of the anterior spinal artery?
Loss of motor and most sensory modalities, with sparing of proprioception, fine touch and vibration (dorsal columns)
What are the extrapyramidal tracts responsible for?
Control of posture and muscle tone
Where are the lateral horns found and what do they contain?
The lateral horns are only found in the thoracic segments of the spinal cord, and they contain the preganglionic sympathetic neurons
What structure attaches the spinal cord to the coccyx, and what is derived from?
The fiulm terminale. This is formed by merged layers of pia and dura mater
What is the conus medullaris?
The tapering caudal end of the spinal cord
What deficiencies result from anterior spinal artery syndrome?
Paraplegia
- α motor neurons in anterior horn damaged (LMN injury)
- descending (UMN) axons in corticospinal tracts disrupted
Sensory Loss
- Loss of coarse touch, pressure (anterior spinothalamic tracts)
- Loss of temperature and pain sensation (lateral spinothalamic tracts)
- n.b. there is sparing of the dorsal columns, so fine touch, proprioception and vibration is usually intact
Autonomic dysfunction
- Disruption of sacral parasympathetic neruons
Where does the spinal cord terminate in adults and in neonates?
L1/2 and L3
What are the main sensory receptor classes?
proprioceptors
- limb position
nociceptors
- tissue damage
thermoreceptors__
- temperature
mechanoreceptors
- touch
Describe the basic sensory afferent pathway
Sensory receptors
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1st order neuron
- cell bodies in dorsal root ganglia
- synapse with 2nd order neuron in cord
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2nd order neuron
- ascending tracts
- synapse in thalamus
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3rd order neuron
- relay action potentials to central cortex via internal capsule
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Primary somatosensory cortex
- located in postdentral gyrus of parietal lobes
- somatotropically organised (sensory homunculus)
What are the different ways to describe/classify an acute spinal cord injury?
Level of injury
- cervical and thoracic injuries most common
Stability of vertical columns
- anterior column - anterior longitudinal ligament → first 2/3rds of veterbrae and intervertebral discs
- middle column - last 1/3 of the verterbrae and IV discs → posterior longitudinal ligament
- posterior column - PLL → supraspinal ligament
Extent of injury
- 50% will be complete transections
Describe the course of the major descending tract (CST)
Upper motor neurons leaves the motor cortex (located in the precentral gyrus) and track along the posterior limbs of the internal capsules to the medullary pyramids.
90% of the fibres decussate in the medullary pyramids and descend in the lateral corticospinal tracts (to innervate limb muscles), and 10% descend in the ipsilateral anterior corticospinal tracts (to innervate truncal axial muscles) where the fibres cross at the level they innervate.
The upper motor neurons synapse in the anterior/ventral horns with the lower motor neurons which exit via the ventral roots and merge with the dorsal roots as part of the spinal nerves, terminating at the motor end plates of the muscles they innervate.
What is lateral medullary (Wallenburg) syndrome? What symptoms and signs will be evident?
Occlusion of the posterior inferior cereballar artery causes infarction of the lateral medulla oblongata. This disrupts the spinothalamic tracts which transit through the lateral medulla, as well as the trigeminal nerve nuclei.
Presentation therefore inlcudes:
vestibulocerebellar symptoms - vertigo, loss of balance (towards side of lesion), diplopia, nystagmus
autonomic dysfunction - ipsilateral Horner’s, hiccoughs
sensory symptoms - loss of pain and temperature sensation to contralateral side of body; stabbing-like pain to ipsilateral side of face
ipsilateral bulbar weakness - hoarseness, dysphagia, dysarthria, decreased gag reflex
What is syringomyelia? What modality does it tend to affect first, and why?
Progressive dilation/expansion of the central canal of the cord (a syrinx) which causes destruction of surrounding tissue.
Loss of temperature and pain sensation due to disruption of axons passing through anterior commisure to the lateral spinothalamic tract.
What are the deficits in Brown-Sequard syndrome?
Ipsilateral paralysis below level of lesion
Ipsilateral loss of fine touch, vibration and position sense below the level of the lesion
Contralteral loss of pain and temperature sensation 1 or 2 levels below lesion
What is dissociated sensory loss?
The loss of one or more sensory modalities with the preservation of one or more others, usually a sign of a very focal lesion in the cord.
Describe the primary course of pain and temperature sensation from stimulus to cortex.
(Spinothalamic tract)
Pain and temperature stimuli are received by nociceptors and thermoreceptors in the skin, joints or viscera inducing action potentials in primary order neurons.
The axons of the primary order nerves enter the spinal cord via the dorsal nerve roots (their cell bodies lie in the dorsal root ganglia) and ascend or descend one or two levels in Lissauer’s tract before synapsing with second order neurons in the dorsal horn.
The axons of the second order neuron cross the spinal cord at this level in the anterior commisure, before ascending in the contralateral spinothalamic tract to the thalamus, where they synapse with third order neurons which convey the impulse to the post-central gyrus, which forms the sensory cortex.
Describe the primary course of fine touch (two-point discrimination), vibration and position sense (proprioception) from stimulus to cortex.
(The dorsal column-medial lemniscus pathway (DCML))
The first order neuron enters the dorsal root and ascends in the dorsal column.
Specifically neurons from the lower body (below T6-8) ascend the cord in the more medial fasciculus gracilis and neurons from the upper trunk and limbs (above T6-8) ascend in the more lateral fasciculus cuneatus.
In the medulla the neurons of each fascicle synapse with second order neurons in the gracile and cuneate nuclei, which together are known as the dorsal column nuclei.
Second order neurons, ascending as the internal arcuate fibres, decussate above the nuclei and continue their ascent as the medial lemniscus to the thalamus, where they synapse with 3rd order neurons destined to terminate in the post-central gyrus (sensory motor cortex).
What effect on respiration would an injury at level C3 or above have?
Complete paralysis of all respiratory muscles. Artificial ventilation must commence immediately or the patient will die.
What effect would an injury above T8 have on respiration?
Intercostal muscle paralysis would result, thereby abolishing the ‘bucket-handle’ mechanism responsible for the outward ‘spring’ or force of the chest wall. As a consequence FRC will be reduced, as the elastic recoil forces of the lungs will be relatively unopposed.
Ventilation will be dependant on the diaphragm and abdominal muscles alone.
What cardiovascular effect/s would result from a spinal cord lesion above the level T1?
Bradycardia. The sympathetic supply to the heart is disrupted leaving parasympathetic innervation unopposed.
CO is reliant on pre-load alone, and the patient will not be able to tolerate hypovolaemic states which would cause significant cardiovascular decompensation.
How does a spinal cord injury affect the peripheral nervous system?
Motor
- Initially flacid paralysis & loss of reflexes (spinal shock)
- In the first few weeks there is onset of spastic paralysis and brisk reflexes develop
Somatic and visceral sensory loss
How does a complete spinal cord injury affect the gastrointestinal system?
Because the vagus nerve continues to modulate the semi-autonomous enteric nervous system the injury results in:
- delayed gastric emptying and paralytic ileus
- gastric ulceration without PPI
- constipation due to loss of sensations of defaecation (necessating regular laxatives)
What metabolic effects result from complete spinal cord injury?
Loss of thermoregulation
- vasodilation increases risk of hypothermia
- active warming can lead to hyperthermia due to an inability to sweat appropriately
Hyperglycaemia
Secondary to stress response of injury
Describe patterns of incomplete spinal cord injury
Anterior spinal artery syndrome
Paraplegia, loss of coarse touch, temperature and pain sensation, and autonomic dysfunction
Central cord syndrome
Hyperextension of the neck (particularly in elderly or high speed collisions) results in limb paralysis/weakness, autonomic dusturbances and varying degree of sensory loss
Brown-Séquard syndrome
Contralateral loss of temperature and pain sensation (1 or 2 levels below lesion) and ipsilateral paralysis and loss of proprioception, vibration and fine touch.
Cauda-equina
Leg weakness, saddle anaesthesia and urinary retention (autonomic)
Describe the princpiples of management for an acute spinal cord injury (SCI)
The key goal is to avoid secondary cord injury
cABCDE approach according to ATLS principles
Spine immobilsation principles
Catastrophic haemorrhage - stop bleeding
Airway - jaw thrust, early intubation, fast-acting opioid to obtund stress repsonse to intubation, avoidance of suxemethonium >24 hours
Breathing - maintain PaO2 >10 kPa, normocapnia
Circulation - R/O internal bleeding, Rx CV effects of SCI, give IVI fluids and blood products to maintain normovolaemia
Disability - CT head if < GCS
Everything else - Treat hypoglycaemia and electrolyte disturbances, re-warm patient, thorough secondary survey with MILS and log-roll.
