Spinal Cord Flashcards
what are the 3 principal planes of reference
- coronal
- sagittal
- horizontal
what are the 3 meningeal layers?
- dura matter
- arachnoid matter
- pia matter
what is the dura mater?
- outermost of the meninges
- completely surrounds brain + spinal cord
what are the characteristics of the dura mater?
- dense
- inelastic membrane
what is the cranial dura mater?
- surrounds the brain
- firmly adhered to inner surface of the skull
what is the extradural/epidural space?
-potential space between dura + skul
what is the subdural space?
-potential space between dura + arachnoid mater
what is the subarachnoid space?
-space below the arachnoid mater
what is an extradural hematoma?
bleeding in the extradural space
how do extradural hematomas form?
- damage to branches of the middle meningeal artery (+ vein)
- form slowly
- due to tight attachment of dura to skull
how can subdural hematomas form?
- form in subdural space
- if bridging veins are torn in head trauma
what is a subarachnoid hemorrhage?
-commonest type of intracranial bleeding
-
how many ventricles are there?
4
what are the 4 ventricles?
- 2 lateral ventricles
- 1 third ventricle
- 1 fourth ventricle
what are the lateral ventricles?
-each follows long C-shaped course through all the lobes
what is the third ventricle?
-occupies most of the midline region of the diencephalon
what is the fourth ventricle?
-sandwiched between the cerebellum posteriorly + the pons + rostral medulla anteriorly
the fourth ventricle is continuous with the ____ via the ______
third ventricle, cerebral aqueduct (aqueduct of sylvius)
the fourth ventricle is also continuous with the ____ via _____
subarachnoid space
through 3 openings and channels
do hematomas have immediate symptoms?
-no, there can be a lucid period + delay
what is the first most noticeable sign of a hematoma?
-extreme headache (due to irritation of dura matter)
what is the most feared event of a hematoma?
- occurs in the transentorial (uncal herniation)
- results in respiratory arrest when medullary structures are compressed
what can cause bleeding into the subarachnoid space?
- hemorrhagic strokes
- ruptured arterial aneurysms
- venous damage
what is the source of CSF?
chroid plexus
what are the qualities of CSF?
- clear, colorless liquid
- low in cells + proteins
- similar to plasma
What are the 2 major functions of CSF?
- CSF in subarachoid space: buoyant function + buffering zone
- regulation of extracellular environment of neurons
where is CSF ultimately returned to?
veins + venous circulation
how does CSF enter the veins?
-through arachnoid villi/arachnoid granulations (tiny vessels)
how is CSF brought back to the heart?
- system of veins:
- dural sinuses
- superficial veins
- deep veins
what can lead to the accumulation of CSF in the ventricular system? (enlargement of ventricles, hydrocephalus)
- overproduction of CSF
- decline of CSF return to venous system
- developmental abnormalities in cerebellomedullary region
- obstruction of intra and extraventricular circulations
how does the brain receive blood supply?
- from 4 arteries
1. two internal carotid arteries (ICA)
2. two vertebral arteries
what are the 4 components of the arch of the aorta?
- right common carotid artery (external + internal)
- left common carotid artery (external + internal)
- right vertebral artery
- left vertebral artery
what do the two vertebral arteries unite to form?
The basilar artery
What does the basilar artery bifurcate into?
two posterior cerebral arteries
what are the 3 principal branches of the internal carotid artery?
- anterior cerebral artery
- middle cerebral artery
- anterior choroidal arter
through the 3 branches of the internal carotid artery, the ICA supplies _______
- cortical
2. subcortical structures of the brain
what does the ICA (internal corotid artery supply)?
- cortical
2. subcortical structures of the brain
what are the other 2 branches of the ICA?
- ophthalmic artery (rise to central artery of retina
2. posterior communication artery
does the occlusion of the ICA have any symptoms?
no
what can the occlusion of the ICA cause?
- transient ischemic attack (TIA) or minor stroke
2. multilobar infarction + serious injury, major stroke
why can the occlusion of the ICA go symptomless?
the Circle of Willis
what is the main function of the Circle of Willis?
-provides opportunities for collateral circulation
how is the Circle of Willis formed?
- posterior communication artery on either side joins
- internal carotid artery
- posterior cerebral artery - an anterior communication artery joins
- two anterior cerebral arteries
what does the Circle of Willis illuminate about blood supply?
-ICA and basilar artery share the blood supply to each hemisphere
where do the opposing streams of the ICA and the basilar artery meet in the circle of willis?
-dead point in Posterior Communication artery
what does the dead point in the Posterior Communication artery result in?
-if one ICA is occluded, collateral circulation from vertebral artery + other ICA can compensate
When can problems arise in the Circle of Willis?
when you have an abnormal Circle of Willis
what is the consequence of blocking the ICA?
massive stroke
what does the anterior cerebral artery supply?
- the paracentral lobule
- containing cortical centers for movement + sensation of lower limbs - ventromedial Prefrontal cortex (short term memory, planning, decision making)
what are 3 clinical symptoms of occlusion of the anterior cerebral artery?
- paralysis of opposite foot and leg
- sensory impairments over opposite toes, foot + leg
- cognitive impairments (short term memory + decision-making)
what does the middle cerebral artery supply?
- primary sensory + motor areas for face and arm
- left side: speech areas including Broca’s
what are 3 clinical symptoms of the occlusion of the middle cerebral artery?
- paralysis of opposite face and arm
- sensory impairments over opposite face and arm
- aphasia if on left side. if on right, cognitive impairments related to emotion processing
- anosagnosia
the is the principal branch of the vertebral artery?
- Posterior Inferior Cerebellar Artery (PICA)
what does the Posterior Inferior Cerebellar Artery (PICA) supply?
- lateral aspect of medulla
- parts of cerebellum
what are 2 other branches of the Vertebral artery?
- anterior branch (forms anterior spinal artery)
2. posterior branch (forms posterior spinal artery)
what do the vertebro-basilar arteries supply?
-medulla, pons, cerebellum, midbrain, parts of cerebral cortex
what can the occlusion of 1 vertebral artery cause?
- no symptoms at all
why can the occlusion of 1 vertebral artery cause no symptoms at all?
- compensation of blood flow from many sources like
1. the other vertebral artery
2. influx from Circle of Willis
3. other lower neck arteries
what happens if the anatomy of arteries providing collateral circulation is abnormal?
-occlusion of 1 vertebral artery can cause damage like minor to major strokes
what branch maybe affected by a minor/major stroke from the occlusion of one vertebral artery?
PICA
what are cerebellar damage signs from the occlusion of the PICA?
A-HAND-T Ataxia Hypotonia Asynergia Nystagmus Dysmetria Tremor
What does the basilar artery terminate into?
- two posterior cerebral arteries:
- branches mostly to visual cortex
what are signs of occlusion in the basilar artery?
-visual impairments in contralateral visual field
what does the basilar artery give off before terminating?
- two superior cerebellar arteries
- two anterior inferior cerebellar arteries (AICA)
- 4-6 branches of small pontine for ventral portions of pons
- Labryinthine artery
what are signs of occlusion of of the cerebellar arteries?
cerebellar signs
A-HAND-t Ataxia Hypotonia Asynergia Nystagmus Dysmetria Tremor
what are signs of occlusion of the four to six branches of small pontine for ventral portions?
-some motor signs due to motor tracts passing in the region
what is the labyrinthine artery?
- can arise from basilar or IACA
- supplies labyrinth of inner ear
what are signs of occlusion of the Libyrinthine artery?
- deafness
- vestibular dysfunction (VAN)
1. vertigo/vomit
2. ataxia
3. nystagmus/nausea
what does a complete basilar artery syndrome comprise?
- bilateral long tract signs (sensory + motor)
- cerebellar signs
- cranial nerve signs
- severe brainstem lesion signs
what is a severe brainstem lesion sign?
- if tegmentum of midbrain + rostral pons affected (Coma)
- if ventral half of pons affected (Locked-in syndrome)
what is locked in syndrome?
- patient looks very comatosed
- very conscious
- can’t move a single muscle
what are the only spared movement of locked-in syndrome?
- vertical gaze
- blinking
what is similar to locked in syndrome?
- during anesthesia when administering curare
- blocks neuromuscular junction
what is the anterolateral system (spinothalamic tract)
-pathway for pain and temperature
in the spinothalamic tract, what enters the spinal cord?
dorsal root afferents
what is Lissauer’s tract?
-bundle of fibers traveling up or down before spinal cord
what are the 4 components to the spinothalamic tract?
- origin - lamina I, II, IV, V
- cross - anterior white commisure
- ascend - antero-lateral funiculus
- somatotopy - lower body lateral and upper body medial
where is the lateral reticular formation (RF)?
-in medulla
-where is the dorsal to medial leminiscus (MI)
midbrain
where is the termination of the spinothalamic tract?
-VPL nucleus of thalamus
where does the spinothalamic tract project?
-to somatosensory areas of cortex
what does a lesion in the spinothalamic tract in the spinal cord result in?
-loss of pain and temperature on contralateral side of body below level of the lesion
what does a lesion in the anterior white commissure result in?
-bilateral segmental loss of pain and temperature below the level of the lesion
what is the dorsal column-medial leminscus system?
-pathway for touch-pressure, vibration, and position sense
what is touch
experience of light stimulation of skin
what is vibration
oscillating, vibrating experience
what are the 2 types of position sense?
- static position sense: posutral sense, knowing the position of a limb space
- kinesthesia: knowing the direction of movement of a limb
What are the 2 dorsal columns?
- fasciculus gracilis
2. fasciculus cuneatus
what does the fasciculus gracilis do?
- carry signals for fine analysis of tactile stimuli (2 point discrimination)
- lower extremities + lower part of trunk
is the fasciculus gracilis crossed or uncrossed? where does it synapse?
- uncrossed in spinal cord
- synapse in nucleus gracilis in medulla
what happens to the fasciculus gracilis after it synapses in the medulla?
-crosses and joins ML
where/how dos crossing of the fasciculus gracilis occur?
-via Arcuate Fibers at Decussaation of ML just above pyramidal decussation
what does the fasciculus cuneatus do?
-carry signals for fine analysis of tactile stimuli (two-point discriminatino) for upper exremities + upper part of trunk
is hte fasciculus cuneatus crossed or uncrossed? where does it synapse?
- uncrossed in spinal cord
- synapses in nucleus cuneatus in medulla
what happens after the fasciculus cuneatus synapses?
-crosses and join ML
where does crossing of the fasciculus cuneatus occur?
-via Arcuate Fibers at Decussation of ML, just above pyramidal decussation
where is the medial lemniscus?
-in medulla, located medially
what does the medial lemniscus do?
- moves laterally
- ascends to VPL
- projects to somatosensory areas of cortex
what does a lesion of the posterior column of white matter of the spinal cord result in?
- ipsilateral loss in body segments below level of lesion
- movements are clumsy, uncertain, poorly coordinated
in the somatosensory system, where are second-order neurons for the spinothalamic tract located?
- spinal cord
- cross there
where are the second-order neurons for the posterior column-lemniscus pathway locatedd?
medulla
what would damage to one side of the spinal cord cause?
- less touch on ipsilateral side to lesion
- less pain on contralateral side of lesion
what would damage rostral to the medulla cause?
-loss of both touch and pain on contralateral side of lesion
what are the two types of pathways in the motor system?
- direct pathways
2. indirect pathways
what is the direct pathway of the motor system?
-corticospinal (pyramidal)
what are the 3 indirect pathways?
- reticulospinal
- mesencephalospinal
- vestibulospinal
all motor pathways are subject to modulation by which 2 structures?
- cerebellum
2. basal ganglia
what is the origin of the corticospinal tract?
cerebral cortex
in the posterior limb of internal capsule, how are the motor fibers arranged?
rostral level: motor fibers are in anterior half of posterior limb
caudal level: motor fibers move more posterior
in the cerebral peduncle, where do the motor fibers occupy?
middle part
in the upper medulla how are the motor fibers arranged?
- motor fibers continue through basilar part of pons
- form the pyramids
what do the motor fibers do in the lower medulla?
70-90% of fibers cross
- crossing fibers = pyramidal decusation
- crossed fibers = lateral corticospinal tract
how is the lateral corticospinal tract arranged?
-descend in lateral funiculus
what is somatotopy?
- lower body is lateral
- upper body is medial
what is the significance of somatotopy in the lateral corticospinal tract?
- disease from outside affects lower body first
- disease from inside affects upper body first
where do corticospinal fibers terminate?
- on interneurons in ventral horn
2. others synapse directly on motor neurons of the VH that control hand + finger movements
what is the significance of where the corticospinal fibers terminate/synapse?
-lesions in humans of lateral corticospinal tract affect mostly the voluntary control of finely tuned finger movements
what are 3 qualities of the ventral corticospinal tract?
- descend in ventral funiculus
- terminate bilaterally on VH interneurons
- innervate axial msuculature
what is the function of the lateral corticospinal pathway?
- motor pathway
- innervates skeletal musculature
- skilled movements of distal extremities
what is the result of a lesion of the lateral corticospinal tract in the spinal cord?
-ipsilateral loss of voluntary movement below the level of the lesion that is most marked in the distla extremities
what is characteristic of lesions affecting the anterior horn cells or nerve roots?
- lower motor neuron lesions
- produces LMN syndrome sings and symptoms
what are 7 upper motor neuron signs of damage?
- loss or diminution of movement
- increase in muscle tone
- hyperreflexia
- clonus
- abnormal superficial reflexes
- babinski sign
(all are ipsilateral when lesion in spinal cord and below the level of the spinal cord lesion)
what are 5 signs of lower motor neuron damage?
- loss or diminuation of movement
- decrease in muscle tone
- increase or absence of deep tendon reflexes
- fibrillations/fasciculations of muscle fibers at rest
- muscle atrophy
