Definition Classification Properties of Reflex Action

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Presentation transcript:

Definition Classification Properties of Reflex Action

Reflex Action Definition Automatic involuntary motor response to a sensory stimulus based on a reflex arc is called reflex action The arc consists of an afferent part – receptor ( superficial or deep )and an afferent neurone Center – usually in the spinal cord or brain stem Efferent part – efferent nerve and an effector organ – usually a skeletal muscle , may be a muscle – ( smooth, cardiac or skeletal ) or gland ( exo or endocrine ). Usually it is skeletal muscle response which is considered. Example

Classification 1.Based on the number of synapses involved – Monosynaptic – Deep or Stretch reflex –Knee jerk Disynaptic – negative stretch reflex, reciprocal innervation Polysynaptic - Flexor or withdrawal reflex Asynaptic – local axon reflex

2.Based on development – phylogeny Unconditioned Present at Birth Number Few Due to Existing Reflex arc Abolished with difficulty, permanent Function protective, Instinctive example touching a hot stove species specific Predictable Training not required

2.Based on development – phylogeny Conditioned reflex Acquired Many superimposed easily some good some bad Salivation at thought of food Based on past Experience on existing arcs individual specific Learned Habits and learning Unpredictable

Classification 3.Based on clinical importance and site of presence of receptors – Superficial – flexor reflex – Plantar reflex Babinski’s response , conjunctival, corneal and abdominal Deep – stretch reflex Visceral – Urinary bladder actions

Classification 4.Segments of spinal cord involved segmental – one segment of same side involved Intersegmental – segments of both sides or more than one segment involved Suprasegmental – higher segments involved

Classification 5.Depending on the purpose – functional a.Protective – flexor reflex b.Postural – antigravity – extensor reflex c.Righting reflex d.Conditioned reflex e.Sexual reflex f.Locomotor g.Systemic – CVS, respiratory etc.

Classification 6.Response confined to one or more muscle groups a.Simple – b.coordinated c.Convulsive

Classification 7.Depending on site of centre a.Spinal b.Bulbar c.Mesencephalic d.Diencephalic e.Cortical

Properties of reflex action Reflex action combines the properties of both synapse and receptors – demonstrated in spinal and better in decerebrate animal. Most of the properties apply to flexor or withdrawal reflexes as there are multisynaptic.

Properties of reflex action 1.Specificity – A sensory stimulus always give rise to a specific response – eg. Showing light in to the eye gives rise to constriction of the eye etc .Specificity of the reflex action makes the predictability of the response .However, super imposed conditioned reflexes may mask them

Properties of reflex action 2.Synaptic delay – reflex time is the time between the stimulus and response and is dependant on number of synapses and the delay of conducting the impulses across it .

Properties of reflex action 3.Unidirectional conduction – Impulses are transmitted in one direction only – from the receptors towards to the center in the sensory and from the centre towards periphery in motor nerves . 4.Excitation – some reflexes are excitatory 5.Inhibition- some reflexes are inhibitory in nature

Properties of reflex action 6.Reciprocal Innervation – Muscle contracts reflexly with the contraction of agonist and relaxation of an antagonists . In knee jerk – contraction of extensor of knee is accompanied by inhibition of flexor of the knee. Basis - due to an inter neuron placed in the reflex arc branch of the afferent connects to the excitator (develops EPSP) to the agonist and another to a Golgi bottle neuron or Renshaw cell neurone which it stimulates . This in turn inhibits the antagonist by forming IPSP due to release of an inhibitory transmitter to the neuron supplying the antagonists . This ensures the smooth contraction of the agonist Diagram

Properties of reflex action 7.Irradiation A feeble stimulus gives rise to weak contraction and a strong stimulus gives rise to a strong contraction due to inclusion of adjacent motor neurone .A small pin prick – only finger withdrawn. A bold cut , entire hand is withdrawn.

Properties of reflex action 8.Recruitement and after discharge – When a muscle contracts to direct stimulation there is a quick simple muscle twitch. When it is reflexly contracting instead of quick and short lived contraction, it builds momentum and is sustained with a slow decline. This is due to recruitment and after discharge . Basis- Parallel circuits in the reflex arc of varying length. Diagram

Properties of reflex action 9.Rebound – For a short time following the elicitation of a reflex action ,the excitability of the agonist is reduced and that of antagonist is increased.

Properties of reflex action 10.Summation – both Spatial and Temporal summations are seen in the reflex actions. When two relax actions give the same effect , elicitation of both of the simultaneously gives a greater response – spatial summation . When the stimuli are given repeatedly also the response is more. – temporal summation

Properties of reflex action 11.Due to convergence and divergence in the reflex pathways subliminal fringe and occlusion are seen similar to synapse ) 12.Facilitation 13.Fractionation 14.Fatigue – Repeated elicitation of reflexes leads to reduced response due to fatigue .

Functions 1.Major functions of CNS and ANS are reflex in nature. For eg. posture, equilibrium, locomotion, visceral activities. 2.In CNS itself , learned activities may become patterned for reflex performance .For eg.walking – learned becomes a locomotor reflex only command for start and stop are actually voluntary. Human beings are given the capacity to convert reflex to delibration- intelligence .The response can be stopped, altered , augmented. Brain development ensures that more and more actions come under delibration so that there is coordination and the organism is elevated from lower to higher status ( wisdom )

Functions 3.Economy of energy as spinal cord itself takes care of most of the actions 4.Homeostasis – 5.Clinical application for diagnosis – When elicited with properly- absence indicates LMN lesion and exaggeration UMN Lesion Role of higher centres . Release phenomenon . Site of lesion can be located. Abnormal plantar – Babinski’s – Pyramidal lesion