Stretch reflex and Golgi Tendon ReflexStretch reflex and Golgi Tendon Reflex

Dr. Faten zakareiaDr. Faten zakareiaPhysiology Department , College of Medicine ,Physiology Department , College of Medicine ,

King Saud UniversityKing Saud University

What is the Stretch Reflex? •It is reflex contraction of muscle resulting from stimulation of the

muscle spindle ( which is the receptor that is located inside muscle & detects changes in muscle length )by stretch

.

Stretch reflexStretch reflex

1-Deep-monosynaptic reflex 1-Deep-monosynaptic reflex

2-sudden stretch of a muscle 2-sudden stretch of a muscle >>>>>reflex contraction of the >>>>>reflex contraction of the stretched musclestretched muscle

-Components:--Components:-

Receptor Receptor : : muscle spindlemuscle spindle

Afferent (annulospiral+flower spray)Afferent (annulospiral+flower spray)

AHC( center)AHC( center)

Efferent Efferent ( motor nerve (alpha fibers70%)to ( motor nerve (alpha fibers70%)to extrafusal muscle fibers +gamma efferent extrafusal muscle fibers +gamma efferent 30% to muscle spindle intrafusal fibers)30% to muscle spindle intrafusal fibers)

Effector/muscleEffector/muscle

Stretch Reflex/ example Knee jerkStretch Reflex/ example Knee jerk

Stretch reflex receptor ( Stretch reflex receptor ( Muscle Spindle)Muscle Spindle) - - Structure of Muscle SpindleStructure of Muscle Spindle-:-:

- - Muscle spindle consists of 3-12 small muscle Muscle spindle consists of 3-12 small muscle fibres (fibres (intrafusal fibresintrafusal fibres))within CT capsulewithin CT capsule..

- - parallel to extrafusal fibres & attached to it parallel to extrafusal fibres & attached to it or to tendonsor to tendons..

--Each intrafusal fibre hasEach intrafusal fibre has::- - CentralCentral non-contractile area ( non-contractile area (receptorreceptor))

- - Peripheral contractilePeripheral contractile on sides of central zone on sides of central zone has actin& myosinhas actin& myosin . .

Muscle Spindle(cont)Muscle Spindle(cont)

Two types of intrafusal fibresTwo types of intrafusal fibres::

11--Nuclear bag fibres Nuclear bag fibres : (2 / spindle): (2 / spindle)

- -central area is dilated with group of nucleicentral area is dilated with group of nuclei

22--Nuclear chain fibresNuclear chain fibres: (4 /spindle: (4 /spindle)) -Thinner& shorterThinner& shorter- -

---one line of nuclei in a chain in the receptor zoneone line of nuclei in a chain in the receptor zone

-- bind to nuclear bag on each sidebind to nuclear bag on each side

Muscle Spindle Fibers

Innervation of the muscle spindleInnervation of the muscle spindleIt has afferent & efferent nerve fibersIt has afferent & efferent nerve fibers

11--Sensory Afferent fibresSensory Afferent fibres:: --Central receptor area of the intrafusal muscle fibres is Central receptor area of the intrafusal muscle fibres is

supplied by supplied by TWOTWO types of afferent fibres types of afferent fibres::

11--Primary (annulospiral) endings (Ia fibres):Primary (annulospiral) endings (Ia fibres): fast, fast, encircle encircle receptor areas of receptor areas of bothboth nuclear bag and nuclear chain nuclear bag and nuclear chain fibresfibres

--When does it dischargeWhen does it discharge??

--discharge most discharge most rapidlyrapidly if the muscle is if the muscle is suddenlysuddenly stretchedstretched

--the the Dynamic response as in tendon jerksDynamic response as in tendon jerks))

22--Secondary (flower-spray) (Secondary (flower-spray) (GGroup II) sensory endingsroup II) sensory endings::--

--supplying receptor area of the supplying receptor area of the nuclear chain fibresnuclear chain fibres ONLYONLY.. --Discharge throughout the period of (Discharge throughout the period of (sustained stretchsustained stretch))((

- -The The Static responseStatic response

N.B/Nuclear bagN.B/Nuclear bag fibres are supplied by primary endings only, fibres are supplied by primary endings only, & responsible for the & responsible for the dynamic responsedynamic response..

Nuclear chainNuclear chain fibres are supplied by both primary and fibres are supplied by both primary and secondary endings & responsible for the secondary endings & responsible for the static responsestatic response..

Motor Efferent fibres to spindleMotor Efferent fibres to spindle- - gamma motor neurons >>>>gamma efferent>>>>> to the gamma motor neurons >>>>gamma efferent>>>>> to the

peripheral contractileperipheral contractile parts of the intrafusal muscle fibres , parts of the intrafusal muscle fibres ,of of two typestwo types::

11--Plate endingsPlate endings / end mainly on the nuclear bag fibres / end mainly on the nuclear bag fibres ( ( Dynamic gamma efferentDynamic gamma efferent))..

22--Trail endingsTrail endings / end mainly on nuclear chain fibres / end mainly on nuclear chain fibres

((Static gamma efferent)Static gamma efferent) ..

Effect of gamma efferent discharge -:

-gamma efferent increase sensitivity of muscle spindle to stretch

a- dynamic gamma efferent (plate endings which end mainly on the nuclear bag fibres , increase sensitivity of muscle spindle to rate of change of stretch.)

B-Static gamma efferent(Trail endings which end mainly on the nuclear chain fibres , increase sensitivity of muscle spindle to steady maintained stretch

Stretch reflexStretch reflex

- - Stretching extrafusal muscle fibers >> Stretching intrafusal Stretching extrafusal muscle fibers >> Stretching intrafusal peripheral contractile fibers>>>>>> peripheral contractile fibers>>>>>> ++ stretch receptor stretch receptor zone (central)zone (central) in intrafusal fibre >> + in intrafusal fibre >> +stimulation of stimulation of

sensorysensory afferent endings encircling receptor area afferent endings encircling receptor area . .--Afferent impulses >> spinal cord >> stimulateAfferent impulses >> spinal cord >> stimulate::

11--alpha motor neuronsalpha motor neurons,(70%) >>,(70%) >>muscle to contractmuscle to contract . .22--gamma motorgamma motor neuronsneurons (30%) causing (30%) causing contraction of the contraction of the

peripheral contractileperipheral contractile

Functions of muscle spindle:-Functions of muscle spindle:-1-1-keep CNS informed about muscle keep CNS informed about muscle length & rate or velocity of change in length & rate or velocity of change in muscle lengthmuscle length..2-muscle spindle act to maintain 2-muscle spindle act to maintain muscle length against rupturemuscle length against rupture:-:-- if muscle is stretched>> muscle if muscle is stretched>> muscle spindle discharge>> reflex spindle discharge>> reflex shortening of muscle by contraction shortening of muscle by contraction to keep its lengthto keep its length

Types of responsesTypes of responses Component of stretch reflexComponent of stretch reflex

.1.111--Dynamic stretch reflex (Dynamic stretch reflex (dynamic or phasic dynamic or phasic response)response)

-Sudden Sudden rapid stretchrapid stretch of a muscle >> of a muscle >> Nuclear bagNuclear bag fibers fibers respond to rate or velocity of stretch>>>>discharge respond to rate or velocity of stretch>>>>discharge SynchronousSynchronous strong impulses from spindles >>>>primary strong impulses from spindles >>>>primary ending >>>alpha motor neuron >>>motor ending >>>alpha motor neuron >>>motor nerve>>>>causing nerve>>>>causing sudden contractionsudden contraction of muscle of muscle extrafusal fibers extrafusal fibers ssynchronouslyynchronously ( (jerk movementjerk movement))

---

--Basis of Basis of tendon jerk tendon jerk ( ( contraction followed bycontraction followed by ))relaxation) (knee,biceps,triceps)relaxation) (knee,biceps,triceps)

When muscle contract, it shortens, muscle spindle relax>>> no discharge of 1ry endings, and muscle relaxWhen muscle contract, it shortens, muscle spindle relax>>> no discharge of 1ry endings, and muscle relax

22 - -Static stretch reflex( static response)Static stretch reflex( static response) - -MaintainedMaintained stretch of muscle>>> stretch of muscle>>> Nuclear chain Nuclear chain

fibersfibers discharge with increased rate discharge with increased rate >>>Impulses in the >>>Impulses in the secondary sensory nervesecondary sensory nerve >>>>alpha motor neuron >>> motor >>>>alpha motor neuron >>> motor nerve>>> contraction of muscle fibers nerve>>> contraction of muscle fibers AsynchronouslyAsynchronously)>>>>>> resulting in )>>>>>> resulting in mildmild sustainedsustained contraction of muscle extrafusal contraction of muscle extrafusal fibers as long as it is stretchedfibers as long as it is stretched

--Basis of Basis of muscle tonemuscle tone

Muscle Tone( Static stretch reflex)Static stretch reflex)

Dif/ resistance of muscle to stretch-Stimuli for muscle tone / Stretch of skeletal muscle between origin and insertion

-Present in antigravity muscle (extensors of LL, back, neck, flexor of UL, muscle of abdominal wall and elevator of mandible

-if lost >>>>>hypotonic or flacidity

-if increased >>>>>>hypertonic,spastic muscle

Muscle can contract by-:

1 -stimulation of alpha motor neurons by muscle stretch::

2 -stimulation of gamma motor neurons

..

3-Best contraction by stim of both alpha&gamma neurons

Reciprocal inhibitionReciprocal inhibition with stretch with stretch reflexreflex

IN KNEE JERK/

Contraction of EXTENSOR of thigh >>>>>>>

Relaxation of FLEXORS

--Reflex contraction of an Reflex contraction of an agonisticagonistic muscle is muscle is accompanied by accompanied by inhibitioninhibition of the of the antagonistantagonist ( contraction of biceps + inhibition of the triceps)( contraction of biceps + inhibition of the triceps)..

--impulses from stretched muscle>>>> SC impulses from stretched muscle>>>> SC to to causecause-:-:

11--stimulatestimulate the motor neurons of the the motor neurons of the stimulated muscle stimulated muscle ( by what?)( by what?)

22 - -send collaterals >>>> send collaterals >>>> inhibitory inhibitory interneuronsinterneurons synapse on the AHCs of the synapse on the AHCs of the antagonistic muscle & inhibit them (antagonistic muscle & inhibit them (( by ( by what?)what?)))

Facilitatory supra spinal centersFacilitatory supra spinal centers

Inhibitory supra spinal centersInhibitory supra spinal centers

The Golgi tendon reflex (inverse The Golgi tendon reflex (inverse stretch reflex)stretch reflex)