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Human Physiology - Stimulus-Response and Sensory Receptors

Grade 9IB

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

🔑Concepts

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A Stimulus is any detectable change in the internal or external environment. Common stimuli include light, sound, temperature, and chemicals. The body's reaction to this change is called a Response.

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Sensory Receptors are specialized cells that detect specific stimuli. Major types include: Photoreceptors (light in eyes), Chemoreceptors (chemicals in tongue/nose), Mechanoreceptors (pressure/movement in skin/ears), and Thermoreceptors (temperature in skin).

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The Stimulus-Response Model follows a specific pathway: Stimulus→Receptor→Coordinator(CNS)→Effector→ResponseStimulus \rightarrow Receptor \rightarrow Coordinator (CNS) \rightarrow Effector \rightarrow Response.

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A Reflex Arc is a rapid, involuntary response that bypasses conscious thought to protect the body. The pathway involves: SensoryNeuron→RelayNeuron(inSpinalCord)→MotorNeuronSensory Neuron \rightarrow Relay Neuron (in Spinal Cord) \rightarrow Motor Neuron.

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Neurons are nerve cells that transmit electrical impulses. They consist of a cell body, Dendrites (to receive signals), and an Axon (to transmit signals). The speed of these impulses can be affected by the presence of a Myelin Sheath.

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The Synapse is the microscopic gap between two neurons. Electrical impulses are converted into chemical signals called Neurotransmitters to cross this gap.

📐Formulae

v=dtv = \frac{d}{t}

t=2dgt = \sqrt{\frac{2d}{g}}

Speed of Impulse=Distance traveled (m)Time taken (s)\text{Speed of Impulse} = \frac{\text{Distance traveled (m)}}{\text{Time taken (s)}}

💡Examples

Problem 1:

During a reaction time experiment (ruler drop test), a student catches a ruler after it has fallen a distance of d=0.15 md = 0.15\text{ m}. Calculate the reaction time tt given that the acceleration due to gravity is g=9.8 m/s2g = 9.8\text{ m/s}^2.

Solution:

t=2×0.159.8t = \sqrt{\frac{2 \times 0.15}{9.8}} t=0.39.8t = \sqrt{\frac{0.3}{9.8}} t≈0.0306t \approx \sqrt{0.0306} t≈0.175 st \approx 0.175\text{ s}

Explanation:

The formula for reaction time based on falling distance is derived from the equations of motion where d=12gt2d = \frac{1}{2}gt^2.

Problem 2:

A nerve impulse travels from a receptor in the foot to the brain, covering a distance of 1.8 m1.8\text{ m}. If the impulse travels at a speed of 120 m/s120\text{ m/s}, calculate the time taken in seconds.

Solution:

v=dt  ⟹  t=dvv = \frac{d}{t} \implies t = \frac{d}{v} t=1.8120t = \frac{1.8}{120} t=0.015 st = 0.015\text{ s}

Explanation:

To find the time taken for the stimulus to reach the coordinator, we divide the distance by the transmission speed of the neuron.