Structure and Function of the Spinal Cord Flashcards
The spinal cord is the connection between the
brainstem and the spinal nerves
The spinal cord is protected by
the vertebral canal
Spinal Cord
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Meninges
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Lumbar punctures
involve sampling of CSF from the subarachnoid space
Epidurals
involve the injection into the space outside the sac (epidural space)
Spinal Cord:
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CNS of spinal cord ends at
L1-2
after that is an extension of dura mater that is filled with CSF in the dural sac
A motor neurons cell body/soma is located in the
CNS
A sensory neurons cell body/soma is located in the
PNS
Spinal Cord: Distribution of Grey and White Matter:
centrally located grey matter and peripherally located white matter
What are the three parts of the grey matter of the spinal cord?
- posterior horn of grey
- lateral horn of grey
- anterior horn of grey
What are the three parts of the white matter of the spinal cord?
- posterior funiculus
- lateral funiculus
- anterior funiculus
Pathway of sensory information into the PNS:
- sensory neuron will bring info from the
environment - sensory neuron will synapse in the posterior
horn of the grey matter of the spinal cord - information is passes to an interneuron,
medial to the lateral horn of grey - interneuron will pass information to the
motor neuron in the anterior horn of grey
which then travels out of the spinal cord - cell body of sensory = out of spinal cord
- cell body of motor = in the spinal cord
Which horns of grey matter of the spinal cord are generally larger? (Orientation)
the ventral/anterior horns
Spinal Cord:
- sensory in dorsal root ganglion
- dorsal root
- then enters posterior horn
- sent to brain via a tract up spinal cord
- comes down from brain
- information synapses in the ventral horn at
a motor neuron - information travels via motor neuron out of
ventral horn - mixed spinal nerve carries both motor and
sensory information
Peripheral Nerves:
- how many?
- divisions?
- 31 pairs
- 8 cervical
- 12 thoracic
- 5 lumbar
- 5 sacral
- 4 coccygeal
Divisions of Vertebrae:
- 7 cervical
- 12 thoracic
- 5 lumbar
- 5 sacral
- 1 coccygeal
(30 vertebrae but 31 pairs of spinal nerves)
Thoracic spinal nerves and correlation to vertebrae:
- 12 thoracic spinal nerve pairs
- 12 vertebrae
- spinal nerve is named according to the
vertebrae above it
Cervical spinal nerves and correlation to vertebrae:
- 8 pairs of cervical nerves
- 7 vertebrae
- each spinal nerve is named according to the
vertebrae below it - spinal nerves will exit above the cervical
vertebrae (extra nerve in space between
skull and C1 vertebrae)
Lumbar spinal nerves and correlation to vertebrae:
- 5 pairs of lumbar spinal nerves
- 5 vertebrae
- each spinal nerve is named according to the
vertebrae above it
Sacral spinal nerves and correlation to vertebrae:
- 5 sacral spinal nerve pairs
- 5 vertebrae
- each spinal nerve is named according to the
vertebrae above it
Cervical Nerve Roots:
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Why are there enlargements of the spinal cord in certain areas?
- cervical and lumbar region
- more neural tissue needed in the areas for
upper limb and lower limb innervation - plexi present
What is the conus medularis?
the end of the spinal cord which tapers
Label the conus medularis and the cauda equina and filum terminale.
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What is the Cauda Equina?
The peripheral spinal nerves at the top of the spinal cord exit horizontally, however further down begin to angle downwards
Below L1/2 - not CNS - the spinal nerves bunch together forming the cauda equina
What is the filum terminale?
connective tissue that anchors the spinal cord in place - NOT NERVOUS TISSUE
What vertebral level for a lumbar puncture and why?
- L3/4
- don’t damage the spinal cord
- peripheral nerves will simply be pushed
away by the needle
Lumbar and Sacral Region:
Why is the spinal cord shorter than the vertebral column in adults?
when developing, this is not the case
bones develop quicker and hence the spinal cord is shorter than the vertebral column
Spinal Cord: Blood Supply:
- anterior spinal artery (one) is a branch of the
vertebral arteries - posterior spinal arteries (two) branch off the
vertebral arteries more laterally (smaller
than anterior) - the anterior and posterior spinal arteries are
not enough to supply the whole cord, so are
reinforced by the radiculospinal arteries
which are derived from arteries of the body
wall
Blood Supply to the Spinal Cord:
- opening in cervical vertebrae is the
transverse foramen through which the
vertebral artery comes up to supply the
brain
Venous Drainage of the Spinal Cord:
- 3 anterior spinal veins
- 2-3 posterior spinal veins
Spinal Cord: Distribution of Grey and White Matter at different divisions:
- thoracic = lateral horns = autonomic nervous
system = T1-L2
Spinal Cord: Grey Matter Organisation:
lateral horn only visible in T1-L2 possibly sacral region
Spinal Cord: White Matter Organisation:
- dorsal column contains ascending tracts
- lateral column contains both ascending and
descending tracts - ventral column contains descending tracts
Spinal Cord: White Matter Organisation: Label the tracts:
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Name the ascending tracts of the spinal cord:
spinothalamic tract
Name the descending tracts of the spinal cord:
- fasciulus cuneatus (lateral)
- fasciculus gracilis (medial)
Name the lateral spinal tracts:
the spinocerebellar tracts
Name the spinal cord tracts and direction.
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Ascending Spinal Cord Tracts:
- carry what type of info
- what types of information
- how many steps in the process
first order into spinal cord
second order takes info up to thalamus
third order takes info from thalamus to relevant somatosensory cortex
Spinothalamic Tract:
- what type of pathway
- where does it cross over
- involved in
- detailed pathway
- ascending pathway
- decussation/crossing over in the spinal cord
before reaching the thalamus
spino->thalamic - transmitting sensations of crude touch, pain
and temperature from the spinal cord to the
thalamus - enters spinal cord on the same side via first
order neuron into posterior grey horn - crosses over to the spinothalamic tract on
the opposite side via second order neuron at
the level just above information entry level
eg enters spinal cord at T3, crosses over into
spinothalamic tract at T2 - 2nd order neuron takes information to the
thalamus - 3rd order neuron takes information to
cortical functional area
Detailed pathway of how information travels via the spinothalamic tract:
The first order neuron transmits the sensation along the spinal nerve and travels via the dorsal root into the spinal cord.
In the spinal cord the first order neuronsynapses with the second order neuron in the dorsal horn of grey
The second order neuron then decussates to reach the contralateral spinothalamic tract
The second order neuron travels via the spinothalamic tract up to the thalamus
In the thalamus the secondary order neuron synapses with the third order neuron
The third order neuron travels
Clinical Presentation: Lesion high up on neck:
- loss of pain, temperature, crude touch on
the contralateral (opposite) side to lesion - lesion stops transmission after decussation
Dorsal Column Medial Leminscus:
- what type of pathway
- located in which tract
- function
- ascending tract
- fasciculus cuneatus for upper limb, gracilis
for lower limb - transmitting sensations of vibration,
proprioception and discriminative touch
from the periphery to the brain via the
dorsal columns and medial lemniscus
Dorsal Column Medial Lemniscus:
detailed pathway:
- first order neuron transmits the sensation
along the spinal nerve and travels via the
dorsal root into the posterior grey horn - the first order neuron does not synapse but
runs into the dorsal column (fasciculus
cuneatus from upper limb, fasciculus gracilis
from lower) - the first order neuron ascends in the spinal
cord along the ipsilateral (same side) dorsal
column to enter the medulla - in the medulla the first order neuron
synapses with a second order neuron within
the cunate or gracile nucleus respectively
and then decussates to reach the medial
lemniscus - the second order neuron travels via the
medial lemniscus to reach the thalamus - in the thalamus the second order neuron
synapses with the third order neuron - the third order neuron travels via the
internal capsule to the primary
somatosensory cortex
Clinical Presentation: Lesion high up on neck: DCML:
- disruption in pathway leads to ipsilateral
loss of proprioception.vs.discriminative
touch on the same side as lesion - bilateral dorsal column loss leads to severe
ataxia - possible causes: MS, B12 deficiency
Spinocerebellar Tract: Function:
transmitting sensations of subconscious proprioception (position in space) from the spinal cord to the cerebellum
Spinocerebellar Tract: Ascending Pathway:
- the first order neuron transmits the
sensation along the spinal nerve and travels
via the dorsal root into the spinal cord - in the spinal cord the first order neuron
synapses in the dorsal horn of grey - the second order neuron enters the
ipsilateral spinocerebellar tract and ascends
to the cerebellum - no decussation
Where are the corticospinal tracts located?
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Corticospinal Tracts:
- function
- direction
- two parts
- transmits motor signals from the cortex to
the spinal cord - descending pathway
- upper motor neuron within CNS and lower
motor neuron within PNS
Corticospinal Tract: Descending Pathway:
- the first order neuron has its cell body in the
primary motor cortex and the axon projects
along the internal capsule to reach the
brainstem - the first order neurons run anteriorly in the
brainstem, and enter the medullary
pyramids - in the pyramids the majority of fibres
decussate to enter the corticospinal tract - from the corticospinal tract the first order
neurons descend to the level of innervation,
enter the ventral horn of grey and synase
with the second order neurons - the second order neuron travel out of the
spinal cord via the ventral root and into the
spinal nerve to reach skeletal muscle
upper and lower motor neuron
Motor Neuron Disease:
- affects upper and lower motor neurons
- degenerative condition
- progressive
- causes weakness
- life expectancy about 3-5 years
Upper Motor Neuron Disorders: disruption of corticospinal tract:
lesion above medulla
opposite side affected (corticospinal tract decussates at the medulla)
Upper Motor Neuron Disease: disruption of the corticospinal tract:
lesion below the medulla
same side affected (corticospinal tract decussates at the medulla)
Lower Motor Neuron Disorders: Signs:
- degeneration of lower motor neurons in
ventral horn of grey - flaccid paralysis no muscle ton e
- no tendon reflexes
- muscle atrophy
Extrapyramidal Spinal Tracts are involved in
involuntary motor control
maintain posture, regulate involuntary movement
Where do extrapyramidal tracts originate from?
the brainstem
Rubrospinal Tract:
- originates
- travels
- function
- originates from red nucleus in brainstem
- travels to ventral horn of grey
- facilitates the action of upper limb flexor and
extensors - extrapyramidal
- descending
What pathway is show below?
the rubrospinal tract (extrapyramidal) (descending)
Tectospinal Tract:
- originates
- travels
- function
- superior colliculus
- ventral horn of grey
- modulates postural movement in response
to visual stimuli
extrapyramidal, descending
Vestibulospinal Tract:
- stabalises when head is tilted
extrapyramidal, descending
A complete spinal cord injury will result in
complete loss of sensory and motor information below the level of the lesion
An anterior spinal cord injury will result in
bilateral loss of pain and temperature
bilateral muscle spasticity
usually vascular issue, will affect the anterior spinal artery
affects corticospinal, spinocerebellar, spinothalamic
DCML still working so crude touch, temperature, pain and sensation still there
Posterior Spinal Cord Injury will result in
only affecting DCML
bilateral loss of proprioception, vibration and fine touch
other tracts intact so crude touch, pain, temperature and sensation still present
When do incomplete spinal cord injuries occur?
when the spinal cord is compressed or injured but the brains ability to send signals below the site of the injury is not completely removed
Patient presents with upper limb weakness, sensory loss below the level of injury
upper extremities more affected than lower
motor function more severely impaired than sensory function
what type of spinal cord injury?
central cord injury of corticospinal, part of spinothalamic, part of DCML
Brown-Sequard Syndrome:
- half the spinal cord is affected
- paralysis and loss of proprioception,
vibration, discriminative touch on the
ipsilateral side as injury - loss of pain, temperature and sensation on
the contralateral side to injury
Extrapyramidal tracts are ascending tracts.
True or False?
False
descending tracts like corticospinal tracts
DCML, Spinothalamic and spinocerebellar tracts are ascending tracts.
True or False?
True
