Neuro Exam 4.6

• flexor reflexes
• DTR/myotactic/stretch reflex
• GTO reflex/inverse reflex/tendon reflex

Type III and IV fibers (acute and chronic fibers)

flexor mm

protection

to LMNs which allow mm to contract

• contraction of agonistic and synergistic mm following stretching of agonistic mm
• stretch m -> it (along w/ synergist) contracts

DTR/myotactic/stretch reflex

type Ia

dorsal root to synapse w/ LMN that returns to same mm that was stretched

mm tone and upright posture

2 neuron pathway

muscle spindle (neuromuscular bundle [3-4mm in length])

measure length and rate of change of length in extrafusal fibers

proprioceptive reflex (involves skeletal mm)

intrafusal fibers

extrafusal fibers

parallel to the extrafusal fibers

• dynamic nuclear bag (Ia)
• static nuclear bag (II)
• nuclear chain fiber (II)

dynamic nuclear bag

all function to differentiate b/w static and dynamic change in length and rate of change in length of skeletal mm

middle of intrafusal fiber that doesn't contral

wrapped around noncontractile portion of the intrafusal fibers

part of Ia fiber (dynamic nuclear bag)

register length and change (receptor organ of Ia fiber)

proprioceptive

mechanical stretch receptors

• located laterally on either side of the annulospiral ending
• around contractile portion on either side of noncontractile

• endings of secondary fibers (type II -- nuclear chain fibers and static nuclear bag) of intrafusal fibers
• secondary endings

Ia fibers

type Ia fibers (dynamic nuclear bag w/ annulospiral ending) become primary fiber and monosynaptically synapse in SC w/ alpha motor neuron which innervate the same extrafusal fibers of the mm or synergistic mm (no interneuron involved)

type II fibers (static nuclear bag or nuclear chain fiber w/ flower spray endings) become secondary fiber and only synapse w/ alpha motor neurons that attach to extrafusal fibers of the same mm

alpha motor neurons

ventral horns

extrafusal fibers

using Renshaw cells (reciprocal inhibition)

inhibitory neurons in gray matter of SC and associated with alpha motor neuron; choose to inhibit 1 mm and exite 1

extrafusal fibers

proprioceptive reflex (deals w/ skeletal mm)

encapsulated receptor at junction b/w muscle and tendon

separately arranged in a series, however muscle spindles are parallel

autogenic inhibition

type Ib fibers (afferent)

prevents tearing of mm when maxing out

measure tension and rate of change of tension in tendon

• adjust m activity in concert w/ info from muscle spindle and descending controls (suprapinal input)
• prevents tearing of mm by keeping antagonistic m from being excessively stretched or contracted

type Ib synapse w/ Renshaw cells (inhibitory interneurons) to inhibit alpha motor neuron activity

loss of mm tone and sometimes functionally gives way (muscle collapses)

• sometimes doesn't work
• i.e., Achilles tendon or gastroc tears