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Term
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Definition
| Tract initiates in the red nucleus, which inhibits extensors and is therefore a lateral system. |
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Term
| Pontine (medial) Reticulospinal Tract |
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Definition
| Originates in the nucleus pontis caudalis and nucleus reticularis pontis. Excites both extensors and flexors, but MAX EXCITATION ON EXTENSORS. So, this is a medial system. |
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Term
| Medullary (lateral) Reticulospinal tract |
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Definition
| Opposite effect of pontine. Inhibits both flexors and extensors with MAXIMUM INHIBITION ON EXTENSORS. So, this is a lateral system. |
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Term
| Lateral Vestibulospinal Tract |
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Definition
| Cells originate in the lateral vestibular nucleus and results in powerful excitation of extensors. This is a medial system because it plays an important role in the maintenance of posture. Think vestibular system. |
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Term
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Definition
| Originates in cervical spinal cord and controls neck muscles involved in head control. |
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Term
| What happens when the spinal cord is cut (spinal transection)? |
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Definition
1) Complete loss of voluntary movements below the lesion.
2) Loss of conscious sensations below the lesions (sensory information can not reach higher centers)
3) Initial loss of reflexes (limbs become flaccid)- this is called spinal shock and is due to removal of alpha and gamm activity
Above C3 you stop breathing. Around C7 bradycardia and hypotension occur |
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Term
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Definition
The pontine reticular formation and the lateral vestibular nucleus both excite extensors in order to maintain posture.
The pontine is normally modulated by central projections. If the spinal cord is cut above the pontine reticular formation, this inhibition is lost and the extensors are stimulated even more. This results in deceribate rigidity.
Cutting the dorsal root with get rid of the deceribate rigidity because is disconnects the Ia afferents. This shows that deceribate rigidity is caused by hypersensitivity of the muscle spindle and is therefore considered gamma rigidity.
The lateral vestibular nucleus is normally modulated by the cerebellum. If you cut the spinal cord above the lateral vestibular nucleus, it will increase excitation of extensors and restore the deceribate rigidity. This is considered alpha rigidity.
Deceribate animals can show the walking reflex if their weight is supported.
They also have tonic neck and tonic labyrinth reflexes. |
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Term
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Definition
| Transection above the red nucleus does not result in deceribate rigidity because of the inhibitory influence on extensor muscles by the red nucleus. These animals will have the righting reflex |
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