motor control: reflexes Flashcards
what is the purpose of a reflex
protection
corrective action w/o conscious thought
infants – need to feed, not voluntary
characteristics of reflexes
involuntary
rapid
short acting
precise – must be in order to be effective
purpose of myotatic reflex
prevent tearing of muscle due to stretch
what initiates the myotatic (stretch) relfex
muscle spindle
monosynaptic, segmental reflex
charcteristics of the sensory portion of a muscle spindle
not contractile
sensitive to length
composed of 2 fiber types(both innervated by 1a fiber)
nuclear bag fibers
nuclear chain fibersthe 1a fiber (primary afferent) innervating both the nuclear bag and chain is sensitive to
length of m
how fast length is changing
what type of fiber is the secondary afferent of the muscle spindle
what does it innervate
what is it sensitive to
group II fiber
innervates chain fiber only
sensitive only to length of m
motor portion of the intrafusal fibers are innervated by
gamma motorneuron (both bag and chain) control length of sensory portion controls sensitivity of sensory portion of intrafusal fibers
in a myotatic reflex, why is the antagonist m also stretched
primary afferent fibers (1a fibers) synapse on alpha motor neurons of agonist to contract, but also an interneuron that synapses with an alpha neuron for the antagonist m preventing its contraction
purpose of golgi tendon reflex
protect muscles from damage due to excessive force
what initiates the golgi tendon reflex
golgi tendon organ
polysynaptic, segmental reflex
what type of fiber innervates the golgi tendon organ
type 1b fiber
APs increase w/ tension
how does relaxation of contracting m occur in the golgi tendon reflex
type 1b fibers synapse w/ inhibitory interneurons which synapse w/ alpha motorneurons of contracting muscle
–> fewer APs/less tension in m
what stimulates the myotatic reflex vs golgi tendon reflex
myotatic - passive stretch of a m.
golgi - active contraction of a m.
decerebrate posture –
spasticity vs rigidity
spasticity - resists motion in a given direction
continual activation of gamma motorneurons
rigidity - resists motion in all directions
continual activation of alpha motorneurons
brainstem fascilitory region
activates gamma motorneurons to make muscle spindle more sensitive to stretch
spontaneously active
brainstem inhibitory region
inhibits gamma motorneurons making muscle spindle less sensitive to stretch
needs cortical regions to activate
spasticity reflex
with loss of cortex, brainstem (-) region is not activated leading to unopposed brainstem (+) region activation –> spasticity and decerebrate posture?
spinal shock
transection of SC
all reflexes gone
due to hyperpolarization of neurons from lack of
excitatory input from cortex
decorticate posture
motor control - reflexes ppt
flex UE, extend LE
can be bilat or unilat
loss of cortical inputs - most common by lesion of IC
decerebrate posture
motor control - reflexes ppt
contract all anti-gravity m. – ext. UE and LE
lesion caudal to red nucleus, but rostral to
reticulospinal and vestibulospinal nuclei
usually indicative of severe brain injury
