The Spinal Cord and the Periphery Flashcards
What are the three columns that the white matter is arranged into?
Posterior, later and anterior
What are three important tracts in the white matter?
- Corticospinal (pyramidal) tract
- Posterior (spinal) tract
- Lateral spinothalamic tract
Describe the corticospinal (pyramidal) tract
Carried motor impulses from the motor cortex to the skeletal muscle via the spinal cord
Describe the posterior (dorsal) columns
Carries general sensation such as touch, tactile localisation, vibration sense, proprioception (everything except pain and temperature)
Describe the lateral spinothalamic tract
Sensory fibres from the spinal cord to the thalamus - pain and temperature
Describe the pathway of the corticospinal (pyramidal) tract
- Pathway starts from the motor cortex (area 4)
- Projection fibres enter the posterior limb of Internal Capsule (blood supply from MCA)
- Corticobulbar fibres enter the brainstem via the cerebral peduncles
- Corticospinal fibres mostly cross in decussation of pyramids
- In the spinal cord they sit in the lateral corticospinal tract and synapses in the ventral horn at exits at that level into the periphery
What are the two types fibres in the descending spinal tracts?
- Upper motor neurone: starts in area 4 and travels through brainstem and crosses at the decussation to continue down lateral corticospinal tract and synapses in the ventral horn
- Lower motor neurone: synapses in ventral horn and travels to muscles in periphery
What are the different types of fibres in the ascending spinal tracts?
- 1st order neurone: receptor and synapses either in the spinal cord or nucleus in the medulla
- 2nd order neurone: always the one that crosses over and travels to the thalamus
- 3rd order neurone: starts in the thalamus and goes through the internal capsule and then radiates out to the parietal cortex
Describe the pathway of the posterior (dorsal) column
- 1st order neurone starts in periphery and ends by synapsing with 2nd order neurone in the dorsal horn of lower part of medulla, in the nuclei called gracile and cuneate nuclei
- 2nd order neurone enters posterior column and decussates to enter the tract now called lemniscus to enter the thalamus
- 3rd order neurone starts in the thalamus and passes through the internal capsule and radiates to the post-central gyrus (area 1, 2, 3), the primary sensory area
Describe the pathway of the lateral spinothalamic tract
- 1st order neurone enters grey matter and ends at the same level
- 2nd order neurones crosses over at the level of entry (decussates) to reach the lateral spinothalamic tract, travelling to the thalamus
- 3rd order neurone picks up the impulse and passes through the IC, radiation to reach post-central gyrus
In what instances does sensory information not need to be sent to the brain?
Where an immediate response is needed, the spinal cord or other lower centres themselves can make these decisions. These make up some of our reflexes.
What is a reflex?
An involuntary stereotyped pattern of response brought about by a sensory stimulus
They are all dependent of Lower Motor Neurones in the pathway
How are reflexes affected in UMN lesions if the LMN is not affected?
UMN lesion will cause paralysis, but reflexes are still present. However, there is not control from the UMN, the LMN over fires and so reflexes are exaggerated and have increased tone (spasticity)
How is tone affected in UMN and LMN lesions?
UMN lesion: tone is increased (spasticity) and hyperreflexia
LMN lesion: decreased tone (flaccidity), paralysis with absent reflexes
What are the effects of a left UMN lesion at inter capsule (above level of decussation)?
- R sided paralysis
- Hyperreflexia
- Increased tone
