L7 Spinal cord and ascending pathways of the Nervous System Flashcards
Segments of the Spine
Vertebrae
8 cervical
12 thoraci
5 lumbar
5 sacral
1 coccygeal
End of spinal cord
L1/2
Enlargements of the Spinal cord
Cervical enlargement: around C6
Lumbar enlargement: around L3
Ventral horns are enlarged at these points, due to limb muscles being supplied near here.
Sensory informations
enters via:
Dorsal horn
Dorsal root ganglion - contains primary sensory neuron cell bodies
- carries sensory information into the CNS
Motor information
Goes out via:
Ventral Horns
Motor neurones loacated here
enlarged at cervical and lumbar regions due to many limb muscles to innervate
Organisation of WHITE/GREY matter in CNS
Grey Matter:
- inside in CNS (outside in brain)
- cell bodies
White Matter:
- Outside in CNS (inside in Brain)
- Myelinated Axons
CSF
(Dura & Arachnoid are stuck together)
Dura - toughest
Arachnoid - spider web like
CSF: found in the sub-arachnoid space
- In between the Pia Mater & Arachnoid Mater
Lumbar puncture :
CSF removed around the Cauda Equina area
usually done in L3/4 or L4/5
Proprioception
Unconscious preception of movement and spatial orientation arising from stimuli within the body
Nociception
Neural process of encoding & processing noxious stimuli.
Afferent activity produced in peripheral & CNS by stimuli that have potential to damage tissue
Ascending Pathways
3 main ones (1 alternative slower pathway)
- Dorsal Column-medial Lemniscus Pathway
- Spinothalamic Pathway
- (Spino-reticulothalamic pathway: alternative)
- Spinocerebellar pathways
- dorsal
- ventral
Dorsal column-medial lemniscus Pathway
- Fine discriminative touch
- Vibration
- Proprioception (V IMP!!)
All using Mechancoreceptors as their modality
Gracile Fasciculus (medial area)
- exits below level of T6 as well as above
Cuneate Fasciculus (more lateral)
- ONLY above T6; joins with the Gracile Fasciculus
Spinothalamic Pathway
Fast; has few synapses
- Pain (“fast” pain) - nocioceptors
- Temperature - thermoreceptors
- Crude touch - mechanoreceptors
N.B. Pain and Temperature are the two main ones here, crude touch to a lesser extent
(Spino-reticulothalamic Pathway)
- Evolutionarily “older”
- “slow” dull aching pain
- many synapses
Spinocerebellar Pathways
- Dorsal
- Ventral
2 of these and they lie on the lateral aspects of the spinal cord
- Proprioception
- Touch
N.B: spinocerebellar pathways are important on putting sensory information together with vestibular information i.e. posture and balance etc
Ascending Pathway
Direction if Information Flow:
Skin -> 1st order ->2nd order ->3rd order->Cortex
1st order:
- 2 axons; considered as one axon which branches
- Cell body: in Dorsal Root Ganglion
- goes into Dorsal Horn
Somatosensory Cortex: interprets sensory information
Dorsal Column-Medial Pathway:
- discriminative touch, proprioception, vibration sense
contralateral pathway! Info from one side of the body is recieved by the other side of the brain
1st order neurones:
- Gracile tract: enter below level of T6; travel up the Fasciculus Gracilis (medially)
- Cuneate Tract: enter above level of T6; travel up the Fasciculus Cuneatus (lateral to the Fasciculus Gracilis which it travels with)
Synapses and then dessucate at the Cuneate and Gracile Nuclei (in the dorsal medulla at the bottom of the 4th ventricle) where the cell bodies of the 2nd order neurones lie
2nd order neurones:
- Travel up the Medial Lemniscus pathway into the Thalamus where they synapse with the 3rd order neurones
3rd order neurones:
- Travel up through the Internal Capsule to the Somatosensory Cortex
INTERNAL CAPUSLE
- where huge motorway of axons that go up and down lie
-
primary stroke site:
- area served by extremely small vessels
- can easily be an embolism or haemorrhage at this site
Spinothalamic Pathway
- Pain; temperature; crude touch
contralateral pathway! Info from one side of the body is recieved by the other side of the brain
1st order neurones:
- Synapses immediately in the spinal cord
2nd order neurone
- Axon crosses the midline
- Done at a slight slope; therefore a lesion here would probably produce a defect a few spinal segments BELOW the lesion
- Travels up to the Thalamus (VPL) in the Spinothalamic Tract
3rd order neurone:
- travels from the VPL up to the Somatosensory cortex via the Internal Capsule
Spinothalamic verus Spino-reticulo-thalamic Pathway
Spinothalamic:
- A-delta mechanical nociceptors; small myelinated fibres
- Terminates in the VPL of the Thalamus
- Cortical Terminations in S1
- Functions to localise sharp “fast” pain
Spino-reticulo-thalamic pathway:
- C-polymodal nociceptors; unmyelinated nerve fibres
- Terminates in medial thalamus and hypothalamus
- Cortical terminations in frontal lobe and limbic lobe
- Functions in cortical arousal and affect
Somatosensory Cortex
behind central sulcus
destination for sensory information
Homunculus
Somatosensory
Representation of the body in the somatosensory cortex
Amount of sensory information from different body regions varies, hence the representation is not anatomically proportional.
Body map represents the amount of sensory information relayed back to the somatosensory cortex
Effects of Lesion to Dorsal Columns
- loss of fine touch, proprioception and vibration sense
-
location: below the lesion ipsilaterally
- since the axons come straight up
Effects of lesion to Medial Lemniscus in the Brainstem
- Location: below the lesion contralaterally*
- this crosses the midline*
same as dorsal column, loss of fine touch, proprioception and fine touch
Effect of Lesion to SPinothalamic Tract
Loss of crude touch, pain and temperature sense
Location: several spinal segments below the lesion (since it crosses the spinal cord at a slope) CONTRALATERALLY
2nd order neurons cross the midline to go up
Clinical lesions: Dorsal Columns
Tabes dorsalis:
- late manifestation of Tertiary syphilis - degeneration of dorsal spinal roots & dorsal columns
- Loss of proprioception - high step, unsteady gait - sensory ataxia
- Romberg’s sign - worse with eyes shut; can fall over backwards (sensory ataxia - can’t make the small movements to stay upright)
Subacute combined degeneration of the cord :
- B12 - cyanocobalamin deficiency- pernicious anaemia
- Degeneration of dorsal columns. Also lateral columns (“combined ” ) - weakness and spasticity of limbs
Multiple sclerosis:
- Many effects in CNS
- Fasciculus cuneatus - loss of prioception in hands and fingers
- Loss of dexterity; inability to identify shape & nature of objects - astereognosis
Clinical Lesions:
Spinothalamic Tract
Syringomyelia:
- Central canal enlarged by gelatinous syrinx
- Decussating 2nd order pain/temperature neurons anteriorly compressed
- Dissociated cutaneous loss of pain and temperature – light touch preserved
Cordotomy /tractotomy:
- Elective surgical lesion of tracts for the relief of intractable pain
Clinical lesions - Spinocerebella System
N.B. Cerebellum acts as a comparator between incoming information spinocerebellar, vestibulocerebellar and corticocerebellar systems to refine motor programmes
Cerebellar damage:
Ataxia; incoordination; intention tremor
Ipsilateral effect
Friedreich’s ataxia:
Inherited degeneration of system; congenital disorder
Brown Sequard Syndrome
hemisection of the spinal cord
leads to:
- ipsilateral spastic paralysis below the lesion
- ipsilateral loss of fine touch, proprioception, vibration below the lesion
- contralateral loss of pain and temperature sense several segments below the lesion
Syringomyelia
tubelike enlargement of spinal canal – usually cervical/thoracic
leads to -
- ipsilateral flaccid paralysis if ventral horns are affected – weakness and atrophy of hand muscles
- spinothalamic tract may be first affected due to proximity of crossing fibres to central canal – loss of pain and temperature sense bliaterally in arms and shoulders
