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Biology: Human Physiology, Health, and Response - Nervous Coordination (Neurons, Synapses, Receptors, and Reflexes)

Grade 8IB

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

🔑Concepts

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The Central Nervous System (CNS) consists of the brain and spinal cord, acting as the control center for processing information.

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The Peripheral Nervous System (PNS) consists of all the nerves outside the CNS that connect the body to the brain and spinal cord.

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Neurons are specialized cells that transmit electrical impulses. They consist of a cell body, dendrites (which receive signals), and an axon (which carries signals away).

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Myelin sheath is an insulating layer around axons that increases the speed of electrical impulse conduction.

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Receptors are groups of specialized cells that detect changes in the environment (stimuli), such as light (photoreceptors), sound (phonoreceptors), and temperature (thermoreceptors).

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Effectors are muscles or glands that produce a response to a stimulus.

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A synapse is a tiny gap between two neurons. Since electrical impulses cannot jump the gap, chemical messengers called neurotransmitters diffuse across the synapse to trigger a new electrical impulse in the next neuron.

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The Reflex Arc is the pathway of a reflex action: Stimulus→Receptor→Sensory Neuron→Relay Neuron (CNS)→Motor Neuron→Effector→Response\text{Stimulus} \rightarrow \text{Receptor} \rightarrow \text{Sensory Neuron} \rightarrow \text{Relay Neuron (CNS)} \rightarrow \text{Motor Neuron} \rightarrow \text{Effector} \rightarrow \text{Response}.

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Reflexes are involuntary, rapid, and automatic responses that help protect the body from harm.

📐Formulae

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

t=2hgt = \sqrt{\frac{2h}{g}}

💡Examples

Problem 1:

Calculate the speed of a nerve impulse if it travels 1.2 meters1.2 \text{ meters} in 0.015 seconds0.015 \text{ seconds}.

Solution:

v=1.2 m0.015 s=80 m/sv = \frac{1.2 \text{ m}}{0.015 \text{ s}} = 80 \text{ m/s}

Explanation:

To find the speed (vv), divide the distance (dd) by the time (tt) taken for the impulse to travel.

Problem 2:

In a ruler-drop test to measure reaction time, a student catches a ruler after it has fallen a height h=20 cmh = 20 \text{ cm}. Calculate the reaction time (tt) using g=9.8 m/s2g = 9.8 \text{ m/s}^2.

Solution:

First, convert height to meters: 20 cm=0.2 m20 \text{ cm} = 0.2 \text{ m}. Use the formula t=2×0.29.8t = \sqrt{\frac{2 \times 0.2}{9.8}}. t=0.49.8≈0.0408≈0.202 st = \sqrt{\frac{0.4}{9.8}} \approx \sqrt{0.0408} \approx 0.202 \text{ s}

Explanation:

The reaction time can be derived from the physics equation of motion for a falling object, where the height fallen relates to the time taken under gravity.

Problem 3:

Identify the sequence of neurons involved when a person accidentally touches a hot stove and pulls their hand away.

Solution:

Sensory Neuron→Relay Neuron→Motor Neuron\text{Sensory Neuron} \rightarrow \text{Relay Neuron} \rightarrow \text{Motor Neuron}

Explanation:

The heat is detected by receptors in the skin, which send an impulse via the sensory neuron to the spinal cord. In the spinal cord, the relay neuron passes the signal to the motor neuron, which stimulates the arm muscle (effector) to contract.