The Spinal Cord and Periphery Flashcards
What are tracts?
Tracts – bundle of myelinated axons – each bundle is carrying one modality – e.g. touch goes through one tract
These tracts have set pathways
Cross from one side to another at different levels
Where are sensory and motor fibres found?
The axons of sensory fibres enter through the dorsal root into the dorsal horn of grey matter
Motor neurons have their cell bodies in the ventral horn
How is white matter arranged?
The white matter is arranged in 3 columns – posterior, lateral & anterior
Each column has various bundles (tracts) of axons
Ascending pathways are sensory, descending pathways are motor
What is the Corticospinal/pyramidal tract?
carries motor impulses from motor cortex to skeletal muscles
What is the Posterior/dorsal column?
carries touch, tactile localisation, vibration sense, proprioception
What is the Lateral spinothalamic tract?
carries pain and temperature
What are 3 importnt tracts?
Corticospinal/pyramidal tract
Posterior/dorsal column
Lateral spinothalamic tract
What does the corticospinal/pyramidal tract do?
Control of voluntary skilled movements (i.e. motor pathway)
What is the pathway of the corticospinal/pyramidal tract?
Pathway starts from the motor cortex (Area 4)
Posterior limb of Internal Capsule (blood supply middle cerebral artery)
Corticobulbar fibres go to contralateral cranial n nucleii
Corticospinal fibres mostly cross in decussation of pyramids (Lateral corticospinal tract)
Where do corticospinal/pyramidal fibres cross over (decussation)?
in the lower part of the medulla
How many neurons are there in the corticospinal/pyramidal pathway?
2
they are called upper and lower neurons
What horn are the lower motor neurons of corticospinal/pyramidal neurons in
ventral horn
What is the difference between ascending spinal tracts/sensory pathways and motor pathways
There are 3 neurons between peripheral receptor and cortex
goes to area 3, 1, 2 of the brain
the crossing over occurs in the second neuron this time
What does the posterior/dorsal column carry?
Carries sensations of fine touch, tactile localisation, vibration sense, proprioception
What is the course of the posterior/dorsal column
1st order neuron ends by synapsing with the cell body of the 2nd neuron. This is situated in the lower part of the medulla
2nd order neuron crosses over (decussates) in the medulla
The tract now is called medial lemniscus and passes through the medulla, pons and midbrain to reach the thalamus
The third order neuron starts from the thalamus and axons pass through the IC and radiate to the post-central gyrus (Area 2,1,3)
What is the tract called when the second neuron crosses in the medulla?
medial lemniscus
What does the lateral spinothalamic tract carry?
pain and temperautre
What is the course of the lateral spinothalamic tract?
First order neuron enters into the grey matter and ends at the same level
2nd order neurons cross over to reach the lateral column and is now called lateral spinothalamic tract
2nd order neuron ends in thalamus and 3rd order passes through IC, radiation to reach post-central gyrus
Where does decussation occur in the lateral spinothalamic tract?
decussation is occurring at the level of entry!!
Name what each picture is showing from left to right?
corticospinal/pyramidal tract
posterior/dorsal column
lateral spinothalmic tract
Does all sensory information need ot be sent to the brian for decisions to be made?
no
in certain instances where an immediate response in needed, the spinal cord or other lower centres themselves can take these decisions
these make up some of our reflexes
What are reflexes?
a reflex is an involuntary stereotyped pattern of response brought about by a senssory stimulus
many reflexes are mediated at the level of the spinal cord (spinal reflexes)
anatomically they may be monsynaptic (strech reflex) or polysynaptic (flexor reflex)
Describe the strech reflex?
strech reflex is important in contorl of msucle tone and posture. if the tendon is streched the the muscle contracts in order to prevent falling and reserve balance
sensory receptors in muscle carry strech impulses and tells the nerve in the ventral horn to contract the muscleand at the same time also tells the antagonistic muscle to relax
one muscle always contracts and one always relaxes
What is the flexor (and crossed externsor) reflex?
flexor reflex helps protect the body from painful stimuli
sensory neuron goes to spinal cord and causes motor neurons to contract the muscle to cause withdrawl from the painful stimulus
at the same time it also causes a crossed extensor response to the other limb to compensate for the loss of support of the other limb
Do UMN or LMN mediate reflexes?
LMN
If LMN is not affected in a UMN lesion that causes paralysis then what happens to reflexes?
Reflexes are exaggerated - UMN tells your LMN how much of a reflex to give but if it is not working then this cannot happen
What controls tone of a muscle?
requires LMN
How does a UMN and LMN lesions affect tone?
UMN lesions cause increased tone (spasticity) but if it was a LMN then this would cause flaccidity
Corticospinal/pyramidal tract:
what would happen if someone had a left UMN lesion at the internal capsule (top arrow)
right sided paralysis - contralateral
hyper-reflexia
incresed tone - spasticity
Corticospinal/pyramidal tract:
what would happen if someone had a left UMN lesion at the upper cervical spinal cord (middle arrow)
left sided paralysis - below the level of decussation so it is ipsilateral paralysis
hyper-reflexia
increased tone - spasticity
Corticospinal/pyramidal tract:
what would happen if someone had a left LMN lesion (bottom arrow)
left sided paralysis - ipsilateral
absent reflexes - arreflexia
flaccid
What is motor neuron disease (lower motor neuron)
Group of diseases affecting the lower motor neuron in the ventral horn of spinal cord
The neuron dies and as a result muscle supplied by it atrophies
Progressive, incurable disease
What is the posterior/dorsal column responsible for?
fine touch
tactile sensation
vibration sensation
proprioception
posterior/dorsal column?
what lesion is the top arrow pointing at and what effect would it have?
Lesion above decussation at IC – contralateral (right sided) sensory loss
posterior/dorsal column?
what lesion is the bottom arrow pointing at and what effect would it have?
Lesion at L cervical spinal cord (below decussation) – L sided (ipsilateral) sensory loss
What does the lateral spinothalamic tract sense?
pain and temperature
What would lesions at the areas show by the arrows cause?
Lesion at L IC – R sided (contralateral) pain and temperature loss
Lesion at L cervical spinal cord – R sided (contralateral) sensory loss
Both lesions are above the decussation, so pain and temperature sensation lost on the opposite side
Would a lesion above decussation cause signs and symptoms on the same or opposite side and would a lesion below decussation cause signs and symptoms on the same or opposite side?
If lesion is above level of decussation then signs and symptoms are C/L
If lesions is below the level of decussation then signs and symptoms are ipsilateral
Is the strech and flexor reflex monosynaptic or polysynaptic?
monosynaptic (strech reflex)
polysynaptic (flexor reflex)
