Reflex Pathways Flashcards
Any involuntary action or response evoked by a stimulus
reflexes
preprogrammed (knee jerk, inverse stretch, crossed extensor)
innate reflexes
walking, speaking, and writing are examples of what types of reflexes
learned reflexes
direct meeting of receptor to effector
stretch reflex is the only example
monosynaptic reflexes
interneurons found between receptor and effector
all reflexes BUT knee jerk
polysynaptic reflexes
connections involving one layer of the spinal cord
unisegmental
involvement of several segments of the spinal cord
multisegmented
response of the same side of body as receptor signal
ipsilateral
response on opposite side of body of receptor
contralateral
bind muscles together
facia capsules
bulk of contractile elements in muscles
extrafusal fibers
nerves that stimulate extrafusal contraction
alpha motor efferents
Intrafusal Fibers
sensory unit, found in the center of muscle spindles, striated at ends
contain Annulospiral endings
lowest threshold for response
Type 1A A Primary Afferent signals
Nuclear Bag Fibers
Flower Spray Organs
higher firing threshold than Nuclear Bag
Type 2 afferent fibers, Type 1A afferent fibers
Nuclear Chain Fibers
Stimulate contraction of intrafusal fibers for tensioning of spindle “sensor unit”
Gamma Motor Efferent
the 4 motor reflex pathways
- Myotatic, Stretch, or Knee Jerk Reflex
- Inverse Stretch Reflex
- Withdrawal Reflex
- Crossed Extensor Reflex
as a muscle or tendon is stretched, increased firing of sensory afferent fibers, motor efferent fibers stimulated in the spinal cord, prevents overstretch of muscle
Myotatic, Stretch, or Knee Jerk Reflex
this stimulated contraction against antagonist muscle
submaximal stretch
at the same time as a stimulated contraction there is an inhibition of antagonistic muscle
large stretch
response to contraction of extrafusal fibers
efferent signal set to spindle for retensioning
activation causes intrafusal fibers to shorten
increases spindle activity
initiates impulses from 1a fibers
allows spindle to contract and catch up to contracted extrafusal fibers
role of Gamma Motor Efferents
polysynaptic reflex invoked when movement required excessive muscle strength, activates receptor called Golgi Tendon Organ, inhibits contraction of the actively contracting muscle and stimulates contraction of the antagonistic muscle
Inverse stretch Reflex
removal of limb from noxious stimulus, stimulatory for ipsilateral flexors, inhibitory for ipsilateral extensors,
Withdrawal reflex
if posture is involved in a withdrawal reflex, stimulatory for contralateral extensors, inhibitory for contralateral flexors
Crossed Extensor Reflex
reaction time
time between stimulus and response
Central delay =
reaction time - conduction velocity
minimum synaptic delay
.5 msec
reverberating circuits
stimulatory: found esp in respiration control loops
Renshaw cells: create reverberating inhibitory circuits that shut down reflexes
Jendrassik’s Maneuver
clasped hands during knee jerk reflex
facilitates knee jerk reflex
increased gamma efferent discharge
brain stem functions
blood pressure, respiration rate, wakefulness, posture and walking
Reticular formation
posture
if severed, decerebrate rigidity
Lesion between the brain and spinal cord produces
Spinal shock, loss of all reflexes, then hyperactive reflexes
