Anencephalic children (no brain=no supraspinal input) do have patterned flexion/extension movement while just lying there (genetic hardwiring):
anencephaly: cephalic disorder that results from neural tube defect that occurs when cephalic (head) of neural tube fails to close; resulting in the absence of a major portion of the brain, skull and scalp
still make walking movements b/c of CPG
Normal infants make walking movements even though they have never experienced walking before:
inherited CPGs allow this!
So why can't people with SC injuries above the lumbar spine walk?
more complex to walk on 2 extremities instead of 4 (integration issues w/ equilibrium and balance)
most central pattern generators are learned, but gait is innate
humans require more supraspinal input
Are spinal cord reflexes segmental in nature?
yes; may involve 1 segment or several adjacent segments
Spinal cord reflexes may involve propriospinal loops or circuits (neural circuitry):
located close to midline of SC
communicate b/w different levels
located in gray matter
Spinal cord reflexes can be modulated by supraspinal influences:
rubrospinal tract (bias flexor activity)
reticulospinal tract (bias extensor activity)
Both influence LMN going to mm
What are the 4 fundamental anatomical parts to a SC reflex?
receptor organ on distal end of sensory organ
afferent sensory neuron w/ receptor at distal end
efferent motor neuron w/ effector organ at distal end
effector organ (NMJ)
Where must damage occur to lose reflex?
damage to any part of the fundamental anatomical parts can cause pt to lose reflex