L46 Spinal Reflexes Flashcards
Define reflexes
predictable stereotyped response to a specific stimulus (specific muscular rnxs to stretch)
Define monosynaptic reflex
afferent and efferent limbs are directly connected (deep tendon reflex)
one single synapse
Define polysynaptic reflex
afferent and efferent limb are interconnected with one or more interneurons (pupillary light reflex, cutaneous reflex)
what are the components of the reflex arc?
sensory receptor (muscle spindle, golgi tendon organ) afferent neuron synapse on efferent neuron (LMN) NMJ muscle
what are examples of reflexes
- deep tendon (myotactic) reflex
- golgi tendon (inverse myotactic) reflex
- flexion crossed extension reflex
what is the afferent limbs?
muscle spindle and Ia fibers
golgi tendon organ and Ib fibers
free nerve endings and Adelta fibers
what make up efferent limbs?
alpha motor neuron
homonymous muscle
synergist muscle
antagonist muscle
what is the nature and purpose of the deep tendon reflex?
when a muscle is passively stretched, it reflexively contracts
the reflex dictates muscle tone under regulation by UMN
what segments are involved in inspiration using the diaphragm
C3,4,5
what segments are involved in shoulder abduction using the deltoid?
C5
what segments are involved in elbow flexion involving the biceps brachi and brachialis
C5,6
what segments are involved in wrist extension using ECRL and ECRB
C6,7
what segments are involved in elbow extension using triceps?
C7,8
what segments are involved in finger flexion using FDS and FDP
C8
what segments are involved in finger abduction and adduction using interossei
C8, T1
what segments are involved in thigh adduction using AL and AB
L2,3,4
what segments are involved in knee extension using quads
L3,4
what segments are involved in great toe extension using EHL
L5, S1
what segments are involved in ankle plantar flexion using gastroc and soleus
S1,2
what segments are involved in anal contraction using sphincter ani externus
S2,3,4
what is the landmark for the ankle jerk reflex
S1
what is the landmark for the knee jerk reflex
L2,3,4
what is the landmark for the biceps and brachioradialis reflex
C5,6
what is the landmark for the triceps reflex
C7
describe the scale for reflex testing
pretty subjective... 0 no response 1+ low normal 2+ average normal 3+ high normal 4+ hyperactive with clonus
- normal responses vary widely within a range
- differences between sides = DISEASE!
define clonus
a series of involuntary, rhythmic, muscular contractions and relaxations. They are not like fasciculations because they are not small twitches, they are large motions usually initiated by a reflex
the stretch (myotactic) reflex works as a _____ to maintain muscle length at a desires value
negative feedback loop
what is the function of the gamma motor neurons in the myotactic reflex?
Are responsible for contracting the ends of the muscle spindle to keep its length identical to the muscle fibers in an effort to maintain monitoring of the muscle length at all times
why are inverse myotactic reflexes slower than myotactic reflexes?
because Ib fibers are small diameter and because the inverse myotactic reflex is polysynaptic and myotactic reflex is monosynaptic
what is the function of the inverse myotactic reflex?
protect muscle and tendon when stimulated constantly
maintain posture
Describe the flexion reflex or the “withdrawal reflex”
In response to painful (nociceptive) stimuli, causing ipsilateral rapid flexion
a protective mechanism
ipsilateal extensor responses are suppressed
Pain afferents (A-delta and C-fibers) will stimulate excitatory interneurons (present at each spinal segment) that synapse on alpha motor neurons to flex the necessary muscle
describe the flexor crossed extensor reflex
The Flexion Reflex is often associated with this Flexion Crossed Extension Reflex in the contralateral limb
This will support the contralateral leg to maintain balance if the flexion reflex causes the ipsilateral leg to lift when you step on a pin
c. SUMMARY
i. Ipsilateral flexor stimulation and extensor inhibition
ii. Contralateral flexor inhibition and extensor stimulation
Summary of the flexor crossed extensor reflex
- ipsilateral flexor _____ and extensor ____
- contralateral flexor _____and extensor ___
stimulation, inhibition
inhibition, stimulation
what type of reflex is the plantar reflex?
polysynaptic
what does a normal adult plantar reflex look like?
toes all flex
what does an abnormal plantar reflex look like?
toes fan out and big toe extends
why do newborns to 1 yo have +babinski sign or abormal plantar reflex (toes are fanning)? (non-pathological positive plantar reflex)
because their pyramidal (corticospinal) tract is immature and not completely myelinated yet
what does a positive babinski sign in adults indicate?
cortical, axonal disruptions, demyelination etc.
what are causes of hyporeflexia (diminished or absent reflexes)?
- lesion of spinal cord segment
- leison of the efferent limb (LMN lesion)
- disease of the NMJ
- lesion of the muscle
- peripheral n. lesion
- lesion of afferent limb (sensory loss)
what does hyperreflexia suggest?
UMN lesion
clonus confirms it
where can UMN damage be located?
in motor center (precentral gyrus etc.) or somewhere along motor tracts
what does hyperreflexia usually follow
spinal shock in spinal cord transections!
describe spinal shock
acute transection of the spinal cord leads to this
during this period (right after accident), spinal reflexes below the lesion are suppressed and it may take several weeks until spinal reflexes truetn
poorly understood
