Motor Function of spinal cordMotor Function of spinal cord

Human ReflexesHuman Reflexes

What is a reflex?What is a reflex?

Functional unit of CNS, involuntary Functional unit of CNS, involuntary response to a stimulusresponse to a stimulus

-example/pinprick-example/pinprick

Reflex ArcReflex Arc--DIFDIF//

- -formed offormed of ::

--Sense organ (receptor)Sense organ (receptor)..

--An afferent neuronAn afferent neuron . .

--One or more synapses (CNS)One or more synapses (CNS) . .

--An efferent neuronAn efferent neuron . .

--An effector organAn effector organ

--Bell-Magendi lawBell-Magendi law

Components of reflex Components of reflex arcarc

****-Afferent neuron-Afferent neuron

- Afferent neurons undergo:- Afferent neurons undergo:

1- 1- DivergenceDivergence WHY? WHY? 2-2- ConvergenceConvergence WHY? WHY?

**- Interneurons**- Interneurons ( (excitatoryexcitatory or or inhibitoryinhibitory). ).

- (Two types of circuits formed by inter neurons- (Two types of circuits formed by inter neurons

(parallel and reverberating circuits).(parallel and reverberating circuits).

Reverberating circuitsReverberating circuits

1- Parallel 1- Parallel 2-Reverbrating 2-Reverbrating

Reverberating circuitsReverberating circuits--Function-Function-- In brain and spinal cord- In brain and spinal cord--- RespirationRespiration&&WakefulnessWakefulness

Renshaw cells

- - located in anterior horn with motor neuronslocated in anterior horn with motor neurons . .

--inhibitoryinhibitory ((presynaptic inhibitionpresynaptic inhibition,, negative negative feedback fashion)feedback fashion)

& & lateral inhibitionlateral inhibition to nearby neurons to nearby neurons..

Efferent neuronEfferent neuron

--

1.1. alphaalpha motor neurons motor neurons

2.2. GammaGamma motor neurons motor neurons

Types of reflexesTypes of reflexes

Stretch reflexStretch reflex

Stretch reflexStretch reflex

-Components:--Components:-

Receptor Receptor ::

AfferentAfferent

AHCAHC

EfferentEfferent

EffectorEffector

Stretch Reflex/ example Knee jerkStretch Reflex/ example Knee jerk

Stretch reflex receptor ( Muscle Spindle)Stretch reflex receptor ( Muscle Spindle)

Structure of Muscle SpindleStructure of Muscle Spindle-:-:

Two types of intrafusal fibresTwo types of intrafusal fibres:: . .

Muscle Spindle Fibers

Innervation of the muscle spindleInnervation of the muscle spindle11--Sensory Afferent fibresSensory Afferent fibres::

22--Efferent fibres to spindleEfferent fibres to spindle

Reaction timeReaction time//

Central delayCentral delay//

--Number of synapsesNumber of synapses

Functions of muscle spindle:-Functions of muscle spindle:-

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

.1.111--Dynamic stretch reflex (Dynamic stretch reflex (dynamic or phasicdynamic or phasic

responseresponse))

22 - -Static stretch reflex( static responseStatic stretch reflex( static response

Muscle Tone:- Static stretch reflexStatic stretch reflex

Dif/ resistance of muscle to stretch-Stimuli for muscle tone

-Present in ?

-hypotonic or flacidity

-hypertonic,spastic muscle

Effect of gamma efferent discharge-:

a- dynamic gamma efferent

B-Static gamma efferent

Muscle can contract by-:

alpha-gamma linkage(coactivation)

Reciprocal inhibitionReciprocal inhibition

IN KNEE JERK/

contraction of EXTENSOR of thigh >>>>>>>

relaxation of FLEXORS

Physiological TremorPhysiological Tremor-: -: . .

Higher control on gamma efferent Higher control on gamma efferent dischargedischarge-: -:

1-Cortical areas.

2-Basal ganglia.

3-Brain stem. Facilitatory

Inhibitory:

4-The cerebellum.

Facilitatory supra spinal centersFacilitatory supra spinal centers

Inhibitory supra spinal centersInhibitory supra spinal centers

Factors influence stretch reflexFactors influence stretch reflex)

EnhancesEnhances InhibitsInhibits

JendrassikJendrassik’’s Maneuvers Maneuver: :

The Golgi tendon reflex (inverse stretch reflex- (AUTOGENIC INHIBITION))

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

Lengthening Reaction:-Lengthening Reaction:- response of spastic muscle to response of spastic muscle to lengtheninglengthening

Clonus:- Clonus:- as as Ankle clonusAnkle clonus

Clinical significance of stretch Clinical significance of stretch reflex:-reflex:---Tendon jerksTendon jerks

Centers of some reflexes Centers of some reflexes Clinical significantClinical significant

Centers of some reflexes Centers of some reflexes Clinical significantClinical significant

Withdrawal reflexWithdrawal reflex(flexor reflex)(flexor reflex)

--Properties of withdrawal RProperties of withdrawal R - -crossed extensor reflexcrossed extensor reflex

Crossed extensor reflexCrossed extensor reflex

Importance of withdrawal reflexImportance of withdrawal reflex-:-:Other examples of polysynaptic reflexesOther examples of polysynaptic reflexes