Spinal cord tracts Flashcards
What holds the spinal cord in place
- Held in place by spinal rooots, the denticulate ligaments and strands of Pia mater
◦ Denticulate ligament is along the lateral sides fo the spinal cord and an extension of the Pia
What connects the spinal cord to the coccygeal ligaments?
◦ Filum terminale is an extension fo the Pia mater that is attached to the coccygeal segments
Where does the spinal cord end
L1-L2
Where does the Arachnoid and dura mater extend to in the spinal colum before ceasing
S2
Cervical and lumbar enlargements of the spinal cord between what zones?
◦ C4 - T1
◦ L2 - S3
What is the dorsal horn of the spinal cord divided into?
Rexed lamina - 10 llayers
Lamina 1 + 4 and 5 received fast pain fibres and sensory afferents
Substantia gelatinosa or Lamina 2 received C fibre input
Fibres 7-9 contain motor nuerons and interneurons
What % of spinal cord cells are interneurons?
97%
Blood supply of the spinal cord
Single anterior spinal artery supplying anterior 2/3
2x posterior spinal arteries
Where does the anterior spinal artery get feeder branches from
Subclavian
Thyrocostal
Costocervical
Where does the anteiror spinal artery run
Anterior median fissure
What happens of the anterior spinal artery is damaged
‣ Paraplegia as a result of corticospinal and vestibulospinal tract damage
‣ Loss of pain, pressure and deep touch - spinothalamic
‣ Preservation of light touch, proprioception and vibration
Where do the posterior spinal arteries arise from
◦ Arise from posterior inferior cerebellar armies descend medial to the posterior nerve roots and supply the posterior 1/3 of the spinal cord
Where is a common watershed zone in the spinal cord
T4/5
Largest feeder artery is the anterior radicalar artery (radicularis magna) from low thoracic and lumbar artery (left posterior intercostal)
In the corticospinal tract where are the sacral fibres relative to the cervical
Sacral outside, cervical inside (medial)
In the spinothalamic tract where is the sacral fibres in reference to the cervical fibres?
Sacral outside, cervical inside
With reference to the dorsal column is the sacral fibres medial or lateral?
Medial
Cervical lateral
Label this diagram
What are the two divisions of the dorsal colum
Cuneatus - lateraland cervical
Gracilis - medial and reflecting sacral roots
What do the origins of the corticospinal tract descend from after passing through the corona radiata?
anterior 2/3 of the posterior limb of the internal capsule
How does the corticospinal tract fibres descned through the midbrain and brainstem
Crus cerebri middle 3/5
Anterior part of the midbrain (behind which is the tegmentum and then the tectum dorsally/posterior)
Paired cerebral peduncles – located anteriorly and laterally.
Internally, the cerebral peduncles are further separated by the substania nigra into the crus cerebri (anterior) and the tegmentum (posterior).
Hemiparesis =
Weakness of one side
Hemiplegia
No movement of one side
Where do corticospoinal tract decussate
Pyramids - 90% of fibres decussate in the caudal medulla
Where is collateral corticospinal supply
Collaterals to cortex to provide feedback
Collaterals to basal ganglia which adjust tone
Collaterals to red nucleus of the midbrain which gives off the rubrospinal tract
Vestibulospinal tract offshoots to the vestibular nucleus
Offshoots to the reticular system (more alert afer movement)
Cerebellar connections
*Corticonuclear fibres to pons, corticobulbar and corticomesencephalic
What are subcortical descending tracts
Tectospinal
Rubrospinal
Reticulospinal
Vestibulospinal
Tectospinal tract
Decussates - from superior and inferior colliculus in dorsal midbrain (Tectum)
Rubrospinal tract origin? Action>
Red nucleus of the midbrain
Enahnce flexor tone
What is a pyramidal tract
Pass through the pyramids of the medulla
The CORTICOSPINAL tract is the ONLY one to do this, functionally corticonuclear fibres are included all others are extrapyramidal
Reticulospinal tracts come in two varietics
Medullary (flexor)
Pontin (extensor)
Do not decussate
Descend in anteroir white matter column
All ascending pathways have what structure
1st order neuron - primarya fferent approahc CNS< cell bodies in DRG or spinal cord ganglia
2nd order neuron in SC or brainstem receiving signal from >1 afferent and transmit to thalamus CONTRALATERALLY after decussating in the relay nuclei in the SC
3rd order - in the relay nuclei of the thalamus signals ascend to cortex
How does spasticiity work
Hypersensitive intrafusal muscle fibres
Extreme resistance that is velocity sensitive
Tension breaks when golgi tendon organ feeds back
Lead pipe rigidity occurs because of?
Lost UMN inhibition of extrapyramidal tract activity - weaker response than UMN loss of corticospinal/pyramidal tract
Where do the 2nd order neurons of the dorsal column originate from
Just above the pyramids in the medulla is the nucleus gracillis (medial fibres), and nucleus cuneatus (lateral fibres) which are the synapse of 1st and 2nd order neurons and the site of the cell bodies. 2nd order neurons immediately decussate and maintain spatial relationship (lateral = cervical) ascending to thalamus where 3rd order synapse
1st order neuron path of the dorsal colum
First order cell body in dorsal root ganglion
Cell fibres ascend in ipsilateral dorsal column
Fibres from lower limb medial (gracilis), upper limb lateral (cuneatus = >T6)
Ascned to meet nuclei of 2nd order neurons in lower medulla
What do the 2nd order neurons of the dorsal colum ascend through the brainstem in
The medial leminiscus
Spinothalamic first order neurons path
Peripheral reception
Cell body in dorsal root ganglion
Synapse in dorsal horn of spinal cord with 2nd order neuron
Ecah first order neuron gives ascending and descneding branches 1-2 levels creating a local tract called DORSOLATERAL TRACT OF LISSAURE) before synapsing to 2nd order neuron
Path of 2nd order neurons in the spinothalamic tract
Decussate across anterior commisure to anterior or lateral spinothalamic tract
Sacral lateral part of the tract, medial upper
Ascend contralateral to afferent detection
Through spinal leminiscus to pass posterior in the brainstem
Synapse in the thalamus
3 minor ascending tracts
Spinotectal - 2nd order decussate at level in the SC and go to tectum
Spinoolivary - 2nd order decussates in SC at level and goes to olivary nuceli near medulla. Then to cerebrellum
Spinoreticular - fibre of 2nd order goes ipsilateral to reticular formation
Spinocerebellar pathways
Ipsilateral
Ascends in posterior/lateral area (dorsal tract) behind the spinothalamic but in front of the dorsal horn; ventrospinocerebellar passes anterior to the corticospinal tract
Passes to the cerebellum
What is the nucleus of Clarke
SPinocerebellar nucleus in the dorsal grey area extending from C8 - L3 (fibres below L3 pass up to L3), and C7 and above instead go to the accessory cuneate nucleas as the cuneocerebellar pathway
C6 transection has what consequence on respiratory function
- Mechanical efficacy
- Reduced lung volumes
- Postural effects
- Cough weaker
How is mechanical efficacy of respiration affected y C6 transection?
Paralysed chest wall inspiratory and expiratory muscles + stabilissing abdominal muscles
DIaphragm contraction cause reduced inferior chest wall diamtte and inward movement of the chest wall so bucket handle mechanism lost. Work of breathing increased
Expiratory muscles - paralysed
Forced inspiratory muscles intact - SCM, scalenes, pectoralis major, trapezius
How are lung volumes affected by transection of the spinal cord at T6
Reduced TLC by 50-80% of usual values
FVC and FEV1 reduced in a restricted pattern
VC reduced to 1500mls or 50-80% loss
Reduced ERV (most markedly reduced) and reduced FRC with airway closure, atelectasis and V/Q low
Reduced VT by 60%
Both hypoxia and hypercapnoea likely
How does posture affect someones respiratory status post T6 transection
Supine position may AID respiration due to increased intra-abdominal pressure to exert some pressur eon the diaphragm moving the diaphragm to a position of improved mechanical advantage
How is the ability of the lung to respond to threats reduced by T6 transection
Unable to cough effectively due to expiratory muscle paralysis
Rapid respiratory fatigue
What are the cardiovascular consequences of a T6 spinal cord injury
Early massive symapthetic surge and outflow
Followed by loss of sympathetic tone to zones below T6 including skin, muscle blod vessels and dilation of venous capacitance vessels. Signifiant reduction in compensatory mechanisms for postural change/homeostatic reflexes
Neurogenic shock
- Reduced PVR and vasodilation with decreased muscle tone especially if above T6. Decreased preload, bradycardia with unapprosed vagal stimulus if above T1-4 and cardiac output becomes fixed if this is the case
Over weeks to months reflex activity may return below the elvel of the lesion in a patchy and disorganised pattern, excessive response to vasopressors and autonomic dysreflexia
How is the GIT affected by spinal cord syndromes at T6?
Decreased gastric transit, with diltation
PSNS overactivity
Lax lower oeosphageal sphincter
Paralytic ileus with intestinal oedema pooling in the lowr body
Stress ulceration
Metabolic and endocrine consequences of T6 spinal cord injury
Inappropriate ADH secretion with loss of sympathetic innervation and ongoing RAAS activation
Hyperaldosteronism (hypokalaemia, hypernatraemia)
Insulin resistance with muscle wasting and adipositiy, with lost hypoglycaemic response
Bone wasting and hypercalcaemia
Lost body temperature regulation
What is the consequence of a hemisection fo the spinal cord in the thoracic level
Motor - ipsilateral loss below the level of the lesion
Sensory
1. Ipsilateral loss of pain/temperature at the level transected
2. Contralateral loss of sensation from pain and temperature beginning a few levels below the lesion
3. Ipsilateral dorsal colum
Autonomic
1. Ipsilateral loss of PSNS from sacrum
2. Ipsilateral loss of SNS from near level of injury (horners if above T1)
Anterior spinal artery syndrome effects
- Sensory loss bilaterally 2 levels below the level of injury - pain, temperature
- Motor loss bilaterall at level of injury
- Preserved 2 point discrimination, light touch, vibration, proprioception
- ANS - affected
Conus medulllaris effects
Mild motor deficits
Symmetrical
Impaired pain and temperature ssaddle with intact light touch
Achieles tendon reflex present
Sphincters impaired EARLY
Onset sudden and bilateral
Cauda equina
Severe motor deficits
Assymetry common
Saddle sensory loss complete - no dissociative loss
Absent reflexes
Spinchters impaired later
Onset gradual and often unilateral
How does cauda equina difffer from conus medularis
Cauda equina
1. Motor more severe and early
2. Reflexes lost earlier and more obviously
3. Assymetry more common
4. Sphincters a late sign
5. More gradual onset is characteristic
6. Sensory changes complete with no dissociatve loss - conus medularis pain and temperature lost and light touch preserved
7. LMN only for cauda equina whereas mixed UMN and LMN for conus medullaris
