Motor Function of spinal cord Human Reflexes

What is a reflex? Functional unit of CNS, involuntary response to a stimulus -example/pinprick

Reflex Arc -Bell-Magendi law -DIF/ - formed of : -Sense organ (receptor). -An afferent neuron. -One or more synapses (CNS). -An efferent neuron. -An effector organ -Bell-Magendi law

Components of reflex arc

**- Interneurons (excitatory or inhibitory). **-Afferent neuron - Afferent neurons undergo: 1- Divergence WHY? 2- Convergence WHY? **- Interneurons (excitatory or inhibitory). - (Two types of circuits formed by inter neurons (parallel and reverberating circuits).

Reverberating circuits 1- Parallel 2-Reverbrating

Reverberating circuits -Function - In brain and spinal cord - Respiration&Wakefulness

Renshaw cells - located in anterior horn with motor neurons. -inhibitory (presynaptic inhibition, negative feedback fashion) & lateral inhibition to nearby neurons.

Efferent neuron - alpha motor neurons Gamma motor neurons

Types of reflexes

Stretch reflex

Stretch reflex -Components:- Receptor : Afferent AHC Efferent Effector

Stretch Reflex/ example Knee jerk

Stretch reflex receptor ( Muscle Spindle) Structure of Muscle Spindle:- Two types of intrafusal fibres: .

Muscle Spindle Fibers

Innervation of the muscle spindle 1-Sensory Afferent fibres: 2-Efferent fibres to spindle

Reaction time/ Central delay/ -Number of synapses

Functions of muscle spindle:-

Types of responses Component of stretch reflex 1-Dynamic stretch reflex (dynamic or phasic response) 2- Static stretch reflex( static response

Muscle Tone:- Static 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

alpha-gamma linkage(coactivation) Muscle can contract by:- alpha-gamma linkage(coactivation)

Reciprocal inhibition IN KNEE JERK/ contraction of EXTENSOR of thigh >>>>>>> relaxation of FLEXORS

Physiological Tremor :-.

Higher control on gamma efferent discharge :- 1-Cortical areas. 2-Basal ganglia.

3-Brain stem. Facilitatory Inhibitory: 4-The cerebellum.

Facilitatory supra spinal centers

Inhibitory supra spinal centers

Factors influence stretch reflex ) Enhances Inhibits

Jendrassik’s Maneuver :

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

The Golgi tendon reflex (inverse stretch reflex)

Lengthening Reaction:- response of spastic muscle to lengthening Clonus:- as Ankle clonus

Clinical significance of stretch reflex:- -Tendon jerks

Centers of some reflexes Clinical significant

Centers of some reflexes Clinical significant

Withdrawal reflex (flexor reflex) -Properties of withdrawal R - crossed extensor reflex

Crossed extensor reflex

Importance of withdrawal reflex:- Other examples of polysynaptic reflexes