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Human Body - Reflex Actions

Grade 7ICSE

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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A Reflex Action is a sudden, involuntary, and spontaneous response to a stimulusstimulus that occurs without the involvement of the conscious brain.

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The structural and functional unit of a reflex action is the Reflex Arc, which involves a specific pathway for nerve impulses.

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Reflex actions are primarily controlled by the Spinal Cord to ensure a rapid response, although the signal is eventually transmitted to the brain for processing.

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The StimulusStimulus is any change in the environment (like heat, pressure, or light) that initiates a nerve impulse.

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Reflexes are categorized into Natural Reflexes (inborn, e.g., blinking of eyes) and Conditioned Reflexes (acquired through experience, e.g., typing or playing a musical instrument).

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The EffectorEffector organ is usually a muscle or a gland that carries out the final response.

📐Formulae

Pathway:Stimulus→Receptor→Sensory Neuron→Spinal Cord→Motor Neuron→Effector→ResponsePathway: Stimulus \rightarrow Receptor \rightarrow Sensory\ Neuron \rightarrow Spinal\ Cord \rightarrow Motor\ Neuron \rightarrow Effector \rightarrow Response

TypeReflex={Naturalif InbornConditionedif LearnedType_{Reflex} = \begin{cases} Natural & \text{if Inborn} \\ Conditioned & \text{if Learned} \end{cases}

💡Examples

Problem 1:

Identify the components of the reflex arc when a person's hand touches a sharp pin.

Solution:

StimulusStimulus: Pain from pin; ReceptorReceptor: Skin receptors; PathPath: Sensory neuron →\rightarrow Spinal Cord →\rightarrow Motor neuron; EffectorEffector: Muscles of the arm.

Explanation:

The sensory neuron carries the 'pain' signal to the spinal cord, which immediately relays a command through the motor neuron to the arm muscles to withdraw the hand.

Problem 2:

How does a conditioned reflex like Pavlov's dog experiment differ from a simple reflex?

Solution:

In a simple reflex, the response to a stimulus is innate (Food→SalivationFood \rightarrow Salivation). In a conditioned reflex, a neutral stimulus is linked (Bell+Food→SalivationBell + Food \rightarrow Salivation).

Explanation:

Conditioned reflexes require LearningLearning and MemoryMemory, involving the cerebral cortex, whereas simple reflexes are SpinalSpinal or AutonomicAutonomic.

Problem 3:

Explain the 'Knee-jerk' reflex in terms of the nervous pathway.

Solution:

Tapping Patellar Tendon→Sensory Neuron→L2−L4 (Spinal Segments)→Motor Neuron→Quadriceps MuscleTapping\ Patellar\ Tendon \rightarrow Sensory\ Neuron \rightarrow L_2-L_4\ (Spinal\ Segments) \rightarrow Motor\ Neuron \rightarrow Quadriceps\ Muscle.

Explanation:

This is a monosynaptic reflex where the sensory neuron synapses directly with the motor neuron in the spinal cord, leading to the instantaneous extension of the lower leg.