Structure and function of the spinal cord part 2 Flashcards
What can damage to anteriolateral column as a result of a lesion on one side of spinal cord cause
- Loss of pain, temperature and crude touch on opposite side
What does outside compression of cord and therefore damage to anterolateral column cause
- Loss of lower limb pain first(fibres sit laterally)
What can an inside grey matter tumour affecting the anterolateral column cause
- Loss of upper limb pain first(fibres sit medially)
What do the spinocerebellar tracts detect
- Unconscious muscle proprioception(from muscle spindles, golgi tendon organs)
- For smooth motor coordination
What do the spinocerebellar tracts consist of
- Two neurons only(only 1st order and 2nd order)
- Four tracts
Do the fibres of the spinocerebellar tracts cross
- No they remain uncrossed(note that second order neurons of anterior tract cross to other side and then cross back)
- Left cerebellum controls left side of the body
Path of first-order neurons in the spinocerebellar tracts
- Synapse in dorsal horn
Path of second-order neurons in the spinocerebellar tracts
- Ascend in lateral column to cerebellum
- Very fast axons
What is the effect of a lesion on one side of spinal cord affecting the spinocerebellar tracts
- Uncoordinated lower limb muscular activity on same side
- Although rarely damaged in isolation(other tracts are normally affected)
What is the corticospinal tract responsible for
- Great voluntary motor pathway
What type of neurons does the corticospinal tract contain
- Upper motor(premotor) neuron - from cerebral cortex to ventral horn
- Lower motor neuron - From ventral horn to skeletal muscle
Path of pyramidal tract joining primary motor cortex to the lateral/anterior corticospinal tract
Primary motor cortex –> posterior limb on internal capsule –> cerebral peduncle –> pons –> pyramids of medulla –> lateral/anterior corticospinal tract
Where do the fibres of the corticospinal tract cross
- Cross at the pyramids of decussation
- 80% cross - lateral corticospinal tract
- 20% on same side - anterior corticospinal tract
What happens to the fibres of the anterior corticospinal tract
- Supply deep neck muscles and cross in spinal cord
Topographical organisation of fibres of the corticospinal tract in ventral horn
- Medial - trunk
- Anterolateral - Proximal limb segments
- Posterolateral - distal limb segments
segments - muscles
How does motor neuron disease occur
- Disruption of the corticospinal tract
How does upper motor neuron disease occur
- Degeneration of upper motor neurons
- Spastic paralysis(increased muscle tone)
- Overactive tendon reflexes
- No significant muscle atrophy
How does localisation of loss of axons affect each side in upper motor neuron disease
- Loss of axons above pyramids will result in effects on the opposite side as will cross over
- Loss of axons below pyramids result in effects on the same side
How does lower motor neuron disease occur
- Degeneration of lower motor neurons in ventral horn
- Flaccid paralysis(no muscle tone)
- Muscle atrophy
Defects in what gene causes spinal muscular atrophy
- Caused by defects in the SMN1 gene
- SMN1 gene is vital for survival of motor neurons
What is amyotrophic lateral sclerosis
- Selectively affects lower and upper motor neurons
- Progressive muscle weakness and atrophy but mind intact
Prognosis of amyotrophic lateral sclerosis
- Symptoms initially in limbs or bulbar signs(speech and swallowing difficulties)
- Spasticity present when upper motor neurons affected
- Short life span(-5 years - due to respiratory failure)
What gene has been identified that has a link with development of amyotrophic lateral sclerosis
- eg SOD1 gene
What are extrapyramidal tracts
- Do not pass through the pyramids
- Descending tracts from basal ganglia, cerebellum and pons
What is the reticulospinal tract
- From reticular formation(pons) to spinal cord
- Regulates ventral horn motor activity/reflexes
- Facilitates and inhibits lower motor neurons
- Important for posture and locomotion
