3.19 Spinal Region 2 Flashcards
spinal reflexes involve
interneurons
withdrawal reflex allows
capacity of interneuronal circuits to generate complex movements
What can elicit withdrawal movements?
afferent info from
- skin
- muscles
- joints
reflexes: local sign
- determines specificity of the movement pattern
- response depends on the site of stimulation
In withdrawal reflexes, why do the interneurons and collaterals of primary afferents relay information to other cord segments?
because muscles removing the part from the stimulation aren’t usually innervated by the same segment that received the afferent input
Inhibitory interneurons provide
- reciprocal inhibition
- recurrent inhibition
Interneurons in inhibitory circuits contribute to
spinal cord motor function
reciprocal inhibition separates muscles into
agonists and antagonists
What prevents unwanted activity in antagonists when agonists are voluntarily recruited?
reciprocal inhibition interneurons
recurrent inhibition
opposite to reciprocal inhibition
- inhibits agonists and synergists
- disinhibition of antagonists
Renshaw cells
interneurons that produce recurrent inhibition
Renshaw cells are stimulated by
a recurrent collateral branch from the alpha motor neuron
What do Renshaw cells inhibit?
inhibit alpha motor neurons of synergists (and alpha motor neurons that give rise to collateral branches)
Renshaw cells do what to motor activity?
focus motor activity
loss of descending influence on Renshaw cell activity
may cause difficulty with fine motor control
What factors allow for bladder filling?
- frontal cortex inhibits pontine urination center
- sacral SC urination center (sympathetic and somatic signals)
- may need corticospinal input with a powerful urge to urinate
bladder filling and sympathetic signals
- relax bladder wall
- constrict internal sphincter
bladder filling and somatic signals
constrict external sphincter
corticospinal input with bladder filling
to LMN: cause contraction of pelvic floor muscles and external sphincter
bladder emptying: factors
- frontal cortex allows pontine urination center to activate
- parasympathetic signals from sacral spinal cord urination
parasympathetic signals from sacral spinal cord urination center
- contraction of bladder wall
- relaxation of internal sphincter
What is the signal to empty the bowels?
stimulation of stretch receptors in the wall of the rectum
What part of the SC vital for sexual function?
lower spinal cord
erection of penis or clitoris controlled by
parasympathetic fibers from S2-S4
ejaculation elicited by
- sympathetic nerves from L1-L2
- pudendal nerve
pudendal nerve cell bodies in
S2-S4
lesions in spinal region may interfere with these:
- segmental function
- vertical tract function
- both
segmental function: lesions
lesions interfere with neural function only at the level of the lesion
vertical tract function: lesions
loss of function below the level of the lesion
segmental signs
include
- abn or lost sensation in a dermatomal distribution and/or
- LMN neuron signs in a myotomal distribution
ascending tract signs
problems with regulation of
- BP
- sweating
- bowel/bladder control
descending tract signs include
- paralysis
- spasticity
- muscle hypertonia
What happens if the lateral CST is interrupted?
Babinski’s sign
All signs of damage to vertical tracts occur here
below level of the lesion
peripheral region lesions produce
deficits in peripheral nerve distribution
peripheral nerve lesions cause
- altered or lost sensation in peripheral nerve distribution
- decrease or loss of muscle power in peripheral nerve distribution
Are there vertical tract signs in peripheral region lesions?
NO
spinal region segmental signs occur when
nerve roots and/or spinal nerves are compromised
spinal region segmental signs include
- altered or lost sensation in a dermatome
- decreased/lost muscle power in a myotome
- decreased/lost phasic stretch reflex
spinal region vertical tract signs include:
- altered/lost sensation below lesion level
- altered/lost descending control of BP, pelvic viscera, and thermoregulation
UMN signs include
- decrease/loss in muscle power
- spasticity
- hypertonia
- positive babinski/clonus (if lateral CST is involved)
