Ia afferent monosynaptic collateral (stretch reflex arc)
Second-order tract · detail · segmental
Before the muscle spindle's Ia axon ascends in the dorsal column it gives a collateral in its own segment that synapses directly on the anterior horn cells of the same muscle: the monosynaptic deep tendon reflex. Descending corticospinal and reticulospinal input normally damps this arc, which is why reflexes rise when the descending tracts are cut.
Traced from the start
- Proprioceptors (muscle spindle, Golgi tendon organ, joint receptors)
- Ia afferent monosynaptic collateral (stretch reflex arc)
Detail
- Synapse
- Monosynaptic, glutamate, onto the homonymous alpha motor neurone
- Reflex levels
- Biceps C5/6, brachioradialis C6, triceps C7, knee L3/4, ankle S1
- Modulation
- Tonic inhibition from descending tracts
When it goes wrong
UMN lesion removing descending inhibition
Hyperreflexia, clonus and spasticity below the lesion
Lesion of the afferent or efferent limb (radiculopathy, peripheral neuropathy, anterior horn cell disease)
Absent or diminished reflex at that segment
Practise this structure
1 question in the bank tagged Reflexes.