Spinal Cord Flashcards
At what vertebral level does the spinal cord end?
L1/L2
What is the denticulate ligament?
Connective tissue derived from pia and arachnoid mater that anchors the spinal cord at each vertebral level
What is the conus medullaris?
End of the spinal cord that becomes cauda equina
What is the name of thin tissue that anchors the spinal cord to the coccyx?
Filum terminale
What is the difference between the dura mater on the brain and on the spinal cord?
On the brain the Dura mater attaches directly to the bone like a periosteum but that does not occur in spinal cord
What lies between the vertebrae and the dura mater of the spinal cord?
Epidural fat (called the epidural space) (allows movement)
What are the respective names of the dips in the spinal cord anteriorly and posteriorly?
Anterior: ventral median fissure
Posterior: dorsal median sulcus and septum
Where does the central canal begin and end?
Begins from 4th ventricle of brain and is blind ending
From what arteries do the 3 major longitudinal arteries of the spine originate?
Vertebral arteries
Longitudinally, there are 2 anterior arteries and 1 posterior. True/false?
False. 1 anterior and 2 posterior
Called anterior and posterior spinal arteries
What 3 arteries do the segmental arteries arise from?
- vertebral
- intercostal
- lumbar
What is the name of the arteries that travel along the dorsal and ventral roots?
Radicular arteries
In which layer does the anterior and posterior internal vertebral venous plexus sit?
Epidural space
Where is the primary somatosensory cortex on the brain?
On the postcentral gyrus in the parietal lobe
The size of the somatosensory cortex is proportionate to the level of sensitivity of the body part and not to the size of the body part, i.e. arranged somatotopically. True/false?
True
What are the two areas of the body that’s somatosensory nerves don’t travel in the spinal cord?
- Face
- Scalp
Why is the spinal cord thickened at the cervical and lumbar region?
Because there is more grey matter to supply motor nerves to upper and lower limbs
What system carries most of the fine touch, pressure, conscious proprioception and vibration nerves?
Dorsal column (AKA funiculus)-medial lemniscus system
What is the difference between the nucleus gracilis and nucleus cuneatus in the medulla?
- nucleus gracilis receives presynaptic sensory fibres from lower portion of body
- nucleus cuneatus receives presynaptic sensory fibres from thoracic/upper limb portion of body
What is the medial lemniscus?
It’s a band of white matter in the brain
Where specifically do the 2nd order sensory fibres synapse to the 3rd order sensory fibres to bring info to cortex?
Ventral posterior lateral nucleus of the thalamus
What tract carries info relating to pain, temperature, itch, tickle and deep pressure?
Spinothalamic tract (or anterolateral tract)
Where do the fibres cross the spinal cord in the spinothalamic tract?
Fibres cross segmentally i.e. at the level of the vertebrae they enter
Outline the pathway of neurons in the spinothalamic tract.
First order neurons enter posterior roots and posterior horn, synapse in dorsal horn -> second order neurons, cross over spinal cord to other side to anterolateral portion, ascends spinal cord then synapses into third order neurons at thalamus which takes info to primary somatosensory cortex.
What is the name of the white matter within which the spinothalamic tract neurons travel?
Spinal Lemniscus
Where is the primary motor cortex located specifically in the brain?
On the precentral gyrus
What tract carries motor info on fine, precise movement?
Corticospinal tract
Outline the pathway of the corticospinal tract axons from the cerebral motor cortex.
Pass from motor cortex through internal capsule, then through basis pedunculi (white matter tract on anterior surface of midbrain), through pyramidal tract on medulla - here most fibres cross to other side AKA decussation & splits into lateral CST and ventral CST
What is the difference between lateral CST and ventral CST?
- Lateral CST fibres cross at medulla (decussation of the pyramids)
- Ventral CST fibres continue down same side until they cross segmentally at level at which they are carrying out action
What is decussation of the pyramids?
Where the axons in the corticospinal tract split into lateral CST and ventral CST. Most axons cross spinal cord into opposite (lateral CST) and rest stay and cross segmentally (ventral CST)
What is decorticate posturing?
Spastic paralysis with hyperflexion of the upper limbs that can occur with CVA of internal capsule
What is the tectospinal tract? (Type of tract, Where it starts & what it mediates)
Extrapyramidal tract that starts in midbrain and mediates reflex head and neck movement due to visual stimuli
What is the reticulospinal tract? (Type of tract, where it starts and what it mediates)
- extrapyramidal tract
- starts in reticular formation in pons and medulla
- reticular formation mediates a lot including influencing of voluntary movement and tone of muscles
What is significant about vestibulospinal tract descending axons?
ipsilateral - don’t decussate
What is the main role of vestibulospinal tract axons?
Excitatory input to antigravity extensor muscles i.e. stops you from falling over if someone pushes you
Why do lesions on tracts lead to spasticity and contraction?
Because reflex motor activity at synapse level is unopposed and takes over
What is Brown-Sequard’s syndrome and describe motor and sensory presentation?
Lateral hemisection of the cord
Motor-> leads to ipsilateral paralysis because cuts fibre before it crosses
Sensory -> leads to ipsilateral loss of vibratory sense & proprioception because cuts fibre before it crosses BUT leads to contralateral loss of pain and temperature sense because that sides fibres have crossed over
Why does the cauda equina exist?
Because during growth the vertebral column grows much quicker than the spinal cord so the spinal nerves have to grow long to reach out of vertebral column
What passes through middle third of the basis pedunculi of midbrain?
corticospinal tract
Each spinal nerve pair supplies everything in one segment of the body wall. What are the 4 different functions supplied by these nerves?
- somatic general sensory
- motor functions: somatic and sympathetic
- reflex functions
Ataxia (loss of co-ordination and balance) is both a somatic general sensory and somatic motor symptom. True/false?
True
Testing each spinal nerve segment’s reflexes tests for what functions?
Both motor and sensory functions simultaneously
Where does the synapse occur in the monosynaptic reflex arc?
occurs in anterior horn in spinal cord where sensory axons synapse with LMN axons that supply muscle
What is the explanation for normal muscle tone?
every time skeletal muscle is stretched the monosynaptic reflex arc occurs
What controls the power of the reflex muscle contractions?
Descending pathways
What symptom does an Upper motor neuron lesion cause?
spasticity
What symptom does an Lower motor neuron lesion cause?
flaccidity
In spasticity the muscle can’t contract and has reduced tone. True/false?
False. That is paralysis, in spasticity the muscle has intact functioning motor nerve but descending controls from brain malfunctioned. Muscle will have increased tone
What is Meralgia paraesthetica?
Compression of the lateral cutaneous nerve often as it passes under inguinal ligament
What is the name of the ten distinct sections that the spinal cord is subdivided into?
Laminae of Rexed
Nociceptors (pain & temp) are in which laminae of the spinal cord?
I and II
Low threshold mechanoreceptors are in which laminae of the spinal cord?
III - VI
Proprioceptors are in which laminae of the spinal cord?
VII - IX
Which axons of the dorsal column-medial lemniscus decussate and where do they do this?
- 2nd order neurones decussate
- in the medulla
Where do first and second order neurones of the dorsal column-medial lemniscus pathway synapse?
In the nucleus gracillis/nucleus cuneatus in the medulla oblongata
DCML primary afferent sensory axons enter the dorsal horn and travel up the same side of the spinal cord they entered on before crossing to other side of brain. True/false?
True
In DCML, first order neurones travel up the spinal cord on the contralateral side they enter.
In spinothalamic tract, second order neurones travel up the spinal cord on the ipsilateral side they enter.
True/false?
False
DCML - first order - ipsilateral
Spinothalamic - second order - contralateral
Spinothalamic tracts axons decussate altogether at the medulla. True/false?
False.
They decussate segmentally at same spinal level they enter
Is the gracile tract medial or lateral to the cuneate tract?
Medial gracile tract and lateral cuneate tract
Up to which vertebral level does gracile tract carry sensory info? This is also the level that cuneate tract begins to carry sensory info
T6
What part of the brainstem do the 2nd order neurones of DCML pathway travel through to get to the thalamus?
Medial lemniscus
What part of the brain do the 3rd order neuron axons in the DCML pathway travel through to get to the somatosensory cortex?
Posterior internal capsule
Primary sensory afferent axons in the DCML pathway send a short branch to neurones deeper into dorsal horn as well as a long axon that goes up spinal cord. True/false?
True
What is lateral inhibition?
When one neurone is activated, it inhibits its neighbouring neurons activity through inhibitory interneurons
What is the reason for lateral inhibition AKA contrast enhancement?
basically blocks out other stimuli to enhance stimulus perception
What are the lateral descending tracts? (2) what part of CNS controls them?
- lateral corticospinal tract
- rubrospinal tract
- cerebral cortex
What are the ventromedial descending tracts? (4) what part of CNS controls them?
- pontine reticulospinal tract
- medullary reticulospinal tract
- lateral vestibulospinal tract
- tectospinal tract
- ventral corticospinal tract
- brainstem
What general function are lateral descending tracts responsible for?
conscious voluntary movement of distal musculature
What general function are ventromedial descending tracts responsible for?
posture and locomotion
Where specifically in spinal cord do corticospinal tract motor axons synapse when they get to the vertebral level of action?
dorsolateral region of ventral horn
What does rubrospinal tract have control over?
flexor limb muscles
Where do rubrospinal tract axons decussate?
ventral tegmental decussation in the midbrain
Lesion on which group of descending tracts (lateral/ventromedial) presents as:
- loss of fractionated movements (not being able to move limb joints one at time)
- impairment of voluntary movements
- normal posture
lateral descending tracts
Patients can make full recovery with corticospinal tract lesions. However recovery is not possible with lesions of both corticospinal and rubrospinal descending tracts. True/false?
True
What is the role of the superior colliculus?
integrating visual world and head orientation - makes a map of the external environment
Where are the cell bodies for the tectospinal tract?
superior colliculus in midbrain
