Spinal cord and periphery Flashcards
Describe the pathway of the dorsal/posterior column
- First neurone enters into the spinal cord and moves up the cord to the lower part of the medulla where it synapses
- Second neurone decussates in the medulla
- At this point the tract is known as the medial lemniscus
- From medial lemniscus to the thalamus
- Thalamus acts as triage centre
- Third neurone from the thalamus to the post-central gyrus
Describe the pathway of the lateral spinothalamic tract
Only for pain and temperature receptors
1st neurone ends at level where the it enters the spinal cord
Decussation occurs at the level of entry to spinal cord
2nd neurone ends at the level of the thalamus- enters into the lateral spinothalmic tract
3rd neurone from thalamus to post-central gyrus
Whats are corticobulbar vs corticospinal tracts?
Tracts of white matter, spefically UMNs. Corticobulbar fibres terminate in the brainstem, in cranial nerve nuclei. Corticospinal fibres terminate in the spinal cord
Most motor fibres descend by the corticospinal tract, describe its passage:
- > UMN starts in Primary Motor Cortex
- > Passes through the posterior limb of the internal capsule
- > Passes through cerebral peduncle to the brainstem (Here corticobulbar fibres split off and synapse in contralateral cranial nerve nuclei)
- > Most corticospinal fibres decussate in the pyramids and enter the lateral corticospinal tract (Some stay on the same side travelling as the anterior corticospinal tract)
- > When they get to the level they supply the fibres synapse in the grey matter of the spinal cord and exit through the ventral horn as spinal nerves
What do fibres of the corticospinal tract do?
They are involved in voluntary (So skeletal) skilled movements
How do Upper & Lower motor neurons affect reflexes?
Reflexes occur through LMNs and are dampened by UMN. Hence an UMN lesion would lead to hyperreflexia and increased tone
Whats different about the set up of ascending spinal tracts (i.e. sensory) vs descending?
Sensory tracts have 3 neurons rather than 2, called:
- 1st order neurons
- 2nd order neurons
- 3rd order neurons
There are two main sensory tracts, what are they and what do they do?
- Posterior/dorsal Column Rsponsible for fine touch, tactile localisation, vibration and proprioception
- Spinothalamic Tract Responsible for pain & Temp and crude touch
Whats the structural difference between the posterior/dorsal column and the lateral spinothalamic tract?
- Both have 3 neurons - Both 3rd order neurons connect a nucleus in the thalamus to the Post Central Gyrus of the parietal lobe. - In both the 2nd order neuron does the crossing over However, in the dorsal column the 1st order neuron travels up the dorsal column and synapses in the medulla Whereas, in the lateral spinothalamic tract they synapse in the grey matter at the level they enter.
Define a reflex?
An involuntary stereotyped pattern of response brought about by a sensory stimulus
What happens if there is damage to the UMN above the level of decussation
- Contralateral paralysis
- Hyperreflexia
- Increased tone
What happens if there is damage to the LMN
- Ipsilateral flaccidity
- Absent reflexes
What is an UMN and an LMN
1-UPPER MOTOR NEURONE: generates in area 4 and carries the impulse all the way down into the ventral horn where it synapses
2- LOWER MOTOR NEURONE: starts at synapse of ventral horn and carries impulse to the muscle
What are the two splits of the spinothalmic tract
Lateral: carries temperature and pain
Anterior: carries crude touch
How do reflexes work??
Sensory neurone enters in through dorsal horn
Synapses with interneurones
Synapse with motor neurones in the ventral horn which carry out a response
