week 3- reflexes Flashcards
what are 2 other names for deep tendon reflex
muscle stretch reflex myotatic reflex
outline what occurs during a muscle reflex
the muscle spindle detects muscle stretch and sends information to the dorsal horn via II and 1a afferents, which then sends information to alpha motor neurons (LMN) in the ventral horn to contract in response to the stretch. This is modified by the Y motor neurons (gain control which innervates the contractile ends of the intramural fiber). This is controlled at the level of the reticular formation in the brainstem.
differentiate between the two types of muscle spindle afferents
1a- dynamic, cares about the changing situation II- static -increases with total Length, only cares about the total
what occurs in the antagonist and synergistic muscles during a DTR
Spindle afferents indirectly contact motor neurons of antagonist muscle by synapsing on inhibitory interneurons [multi-synaptic pathway!] … which decreases contraction of the antagonist muscle Spindle afferents also synapse directly on motor neurons to synergistic muscles …and cause those muscles to contract, too
describe alpha-gamma co-activation
regulates how tightly the feedback needs to be regulated depending on situation and posture
what aspects need to be intact to ensure a reflex
sensory, motor output pathway, brainstem do not need UMN to reflex, but since the UMN does modulate you can see hyperrflexia with damage
what is the grading for DTR
dynamic portion 0 = none + = hyporeflexive (1+) ++ = normal (2+) +++ = generally considered brisk, but normal (3+) ++++ = hyperactive (with clonus) (4+) can also look at muscle tone for static portion
what does a change in muscle tone indicate
If muscle tone changes (decrease or increase) Sensory limb has changed, Motor limb has changed, or UMN modulation of reflex has changed
name the two ways in which sensory neurons can detect duration
1- constant input coding- good for pressure detection 2- on and off coding (beginning and end) good for vibration
explain the difference in receptive fields
can vary throughout the body determined by somatosensory cortex pinpricks only 2 mm apart can be detected separately on the fingertips while pinpricks 0.5 cm apart may be perceived as a single touch in the middle of the back.
differentiate between small and large fiber axons
Large
A- beta- fine touch, vibration
type 1a, 1b, II- proprioception
Expect peripheral demyelinatingdisorders to affect these modalities disproportio
small
a delta- small myelinated, 12-37C, sharp fast localized pain
C fibers- smaller unmyelinated, 25-45 C, delayed aching burning, diffuse pain
what is the difference between deep and superficial reflexes
superficial- decrease with UMN damage
deep- does not need, but they assist in modulation so may see hyperreflexia
what tract is damaged with if there is a + babinksi sign
If the corticospinal tract is damaged, we see “up-going toes” (i.e. the Babinski sign)
superficial reflex (others include abdominal and cremaster scrotum)
which is actually the re-emergence of the primitive extensor plantar reflex
how does a chronic versus a acute UMN lesion present
