REFLEX ( Physiology)

REFLEX
Dr. Anita Choudhary
Professor & HOD
Physiology Department
R.D.Gardi Medical
College
Ujjain

DEFINATION
 Reflex is an involuntary response to a stimulus
 Depends on integrity of reflex arc
Sensory impulse
CNS
Motor effect
4/11/2020Dr. Anita Choudhary

Components of reflex arc
Afferent limb
 Receptor
 Sensory nerve
Center
Efferent Limb
 Motor nerve
 Efector organ

Afferent limb
 Carry sensory input from receptor to the centre.
The afferent neuron enter CNS via dorsal root or
cranial nerves and have their cell bodies in dorsal
root ganglia

CENTER
 Part of CNS( spinal cord or brain)
 Afferent limb ends
 Synapse directly with efferent limb
Or via interneuron

EFFERENT LIMB
Consist of -
 Motor nerve – transmit motor impulse from the
centre to effector organ
 Effector organ – in form of muscle or gland which
show response to the stimulus

Classification of Reflexes
 Depending upon No. of synapse
 Anatomical classification
 Physiological classification
 Clinical classification
 Inborn/ acquired

Depending upon No. of synapse
 Asynaptic
 Monosynaptic
 Disynaptic
 Polysynaptic

ASYNAPTIC REFLEX
 No synapse between afferent & efferent neuron
 Also known as axon reflex arc
 Not a true reflex arc

MONOSYNAPTIC REFLEX
 One synapse present between afferent & efferent
neuron
E.g. Stretch reflexes
 Biceps
 Triceps
 knee

DISYNAPTIC REFLEXES
 One interneuron is placed between present
between afferent & efferent neuron
 E.g. Inverse stretch reflex or golgi tendon reflex

POLYSYNAPTIC REFLEX
 More than one interneuron's present
E.g.
1. Withdrawal Reflex
2. Crossed flexor reflex
3. Crossed extensor reflex

Anatomical Classification
 Depending upon the location of reflex arc
centre ..
1. Cortical reflexes
2. Cerebellar reflexes
3. Midbrain reflexes
4. Bulbar or medullary reflexes
5. Spinal reflexes

ANATOMICAL CLASSIFICATION
(location of reflex arc center)
 Cortical reflex: center in cerebral cortex
 Cerebellar reflexes : in cerebellum
 Mid brain reflexes : in mid brain
 Bulbar /medullary reflex: in Medula oblongata
 Spinal reflexes: in spinal cord

Clinical classification
Clinically reflexes are classified into-
 Superficial
 Deep
 Visceral
 Pathological reflexes

CLINICAL CLASSIFICATION
 Superficial reflex – conjuctival, corneal
 Deep reflex- tendon reflexes
 Visceral reflex eg.- micturation reflex
 Pathological reflex eg- Babinski sign, mass reflex,
clonus, pendular movement

Physiological Classification
 Flexor reflexes.
 Extensor reflexes.
a. Flexor reflexes occur in response to pain
b. Extensor reflexes( antigravity reflexes) – all
stretch reflexes are extensor reflexes. These
are the basis of muscle tone & posture

PHYSIOLOGICAL
CLASSIFICATION
Flexor Reflexes –
 Responds to painful stimuli
 Flexion of joints
 Also called withdrawal reflex

Extensor reflex –
 Stretch reflex …….(with muscle tone )
 Basis of muscle tone and posture
 Also called anti gravity reflex

Spinal cord reflexes
According to the receptor from which they
originate
 Muscle reflexes- Stretch reflex
- Golgi-tendon reflex
 Cutaneous reflexes- withdrawal reflex

Depending upon the segment
involved
 Segmental Reflexes: efferent neuron begins
in the same segment of spinal cord where
afferent neuron ends
 Intersegmental Reflexes: afferent neuron end
in one segment and efferent neuron begins in
other segment
 Suprasegmental Reflex: center lies above
the spinal cord

INBORN/ ACQUIRED
CLASSIFICATION
INBORN OR UNCONDITIONAL REFLEXES
 Present since birth
 No learning/ training required
 Eg: salivation when object in mouth

Acquired or Conditional Reflex
 Develop after birth
 Learning & training required
Eg- salivation by sight, smell and thought

Monosynaptic reflex( Stretch
reflex)
 When a skeletal muscle with intact nerve
supply is stretched ,it contracts
 Stimulus: stretch to the muscle
 Receptor : Muscle spindle
 NT: Glutamic acid( at central synapse)
 Reaction Time: application of stimulus and
the response
 Central delay: 0.6 to 0.9 msec (to traverse the
spinal cord)

2. INVERSE STRETCH REFLEX
(disynaptic reflex)
 Also called Golgi tendon reflex .
 Receptor involved – Golgi tendon organs
 Located in tendons & musculoapeurotic junction
 Placed in series
 Supplied by Ib type sensory nerve
 When muscle contract it stretched

 Receptor – Golgi tendon organ
 Afferent – Ib myelinated nerve fibers
 Centre- spinal cord , end in inhibitory
interneuron that in turn end directly on the
motor neurons
 Efferent – alpha motor neurons to muscle fiber

Pathway & activity of reflex
Contraction of muscle
Increase muscle tension
Golgi tendon detect tension
Send impulse through Ib fibre
Enter spinal cord through dorsal root

Cont….
In spinal cord stimulate
inhibitory interneuron
Release inhibitory
mediator glycine(IPSP)
Inhibit ᾳ motor neuron
Relaxation of muscle that
was originally
contracted

Function of Golgi tendon
reflex
 Protective function: reflexily inhibit muscle
contraction
 Regulation of tension during normal muscle
activity:

Role of gamma motor neuron
Stretching of muscle
Increase firing rate of Ia fibres
Increase ᾳ motor neuron activity
Reflex contraction of muscle

Cont…
Contraction of extrafusal fiber
Makes muscle spindle slack
Decrease firing rate of Ia fibers
(Unloading of muscle spindle)
Once it occur CNS will not receiving the rate &
extend of muscle shortening

Higher control of stretch reflex
 Facilitator
y
↑ϒ-motor
neuron
discharge
 Inhibitory
↓ ϒ motor
neuron
discharge

3. Withdrawal reflex (
polysynaptic)
Definition :Also known as flexers reflex, Is an
cutaneous reflex in response to painful stimuli
Receptors: nociceptors in free nerve endings of Aδ &
C fibres
Pathway : As it is poly synaptic reflex consisting of
following pathway:

Withdrawal reflex
 Also known as flexor reflex
 Cutaneous reflex
 Occur in response of painful stimuli
 Characterized by removal of body parts from the
region

Reflex arc of withdrawal
reflex
Pain fibers carry impulse
Enter spinal cord
Synapse with many interneuron's
A B C

 A : projects on ᾳ- motor neuron on same side ,
that stimulate the flexers cause withdrawal of
limb.
 B: forms inhibitory pathway & : projects on ᾳ-
motor neuron supplying the extensors on same
side brings their relaxation.

 C : some of IN cross to opposite side of spinal cord
end on ᾳ- motor neuron supplying the extensors of
contralateral side – extension of opposite limb
Crossed Extensor Response(2 limb
response)

Flexor Response
Painful stimuli
Contraction of flexors & Inhibition of extensors
Leading to
Flexion of stimulated limb & its withdrawal from
painful stimuli

FUNCTION OF WITHDRAWAL REFLEX
 When associated with crossed extensor reflex it
helps to support the body and regulate the posture

Properties of reflexes
1.Adequate stimulus
2.Delay - Synaptic delay, minimum in mono
synaptic reflexes
3 .One way conduction -
Bell Magendie law

4. Bell Magendie law
Impulse
Receptor
Center
Effector organ

5.Recruitment
Stimulus of constant strength applied for long time
Progressive increase in response
Increase activation of motor neurons

Application of strong stimulus
Impulse spread to neighboring neurons through
collaterals or interneurons
Gives wider response

6.After discharge
Reflex action is elicited continuously
Stop stimulation
Even then reflex response may continue
( internucial neuron continue to transmit signals to
center)

7.Final Common Pathway
All excitatory / Inhibitory neuronal influences
Funnel through ᾳ Motor neuron
Affect muscular contraction
+ stimulation of ᾳ Motor neuron – contraction
- ve stimulation of ᾳ Motor neuron – relaxation

8.Rebound Phenomenon
Inhibition of reflex activity for some time
Once inhibition is over
Reflex activity reappear and become more powerful

cont…
9.Summation
10. Inhibition
11. Occlusion
12. Habituation : reflex response is stereotyped
but with experience it can be modified this is
habi…
13. Senstization : when stimulted repeatedly
decrease response of target neuron

THANK YOU

REFLEX ( Physiology)

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