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Coordination and Response - Nervous control in humans

Grade 12IGCSEBiology

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

🔑Concepts

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The human nervous system consists of the Central Nervous System (CNSCNS), comprising the brain and spinal cord, and the Peripheral Nervous System (PNSPNS).

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Nerve impulses are electrical signals that travel along neurones. There are three types: Sensory neurones (receptors to CNSCNS), Relay neurones (within CNSCNS), and Motor neurones (CNSCNS to effectors).

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The Reflex Arc is an involuntary, rapid response to a stimulus. The pathway follows: Stimulus→Receptor→SensoryNeurone→RelayNeurone→MotorNeurone→Effector→ResponseStimulus \rightarrow Receptor \rightarrow Sensory Neurone \rightarrow Relay Neurone \rightarrow Motor Neurone \rightarrow Effector \rightarrow Response.

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Synapses are junctions between neurones. Signal transmission involves the release of neurotransmitters (e.g., acetylcholine) from vesicles, diffusion across the synaptic cleft, and binding to receptors on the post-synaptic membrane.

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Accommodation is the process of changing the shape of the lens to focus on objects at different distances. For near objects: Ciliary muscles contract, suspensory ligaments slacken, and the lens becomes thick/convex.

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The Pupil Reflex protects the retina. In bright light, circular muscles of the iris contract and radial muscles relax, causing the pupil to constrict (miosismiosis).

📐Formulae

Speed of nerve impulse=Distance traveled (m)Time taken (s)Speed\ of\ nerve\ impulse = \frac{Distance\ traveled\ (m)}{Time\ taken\ (s)}

Reaction time=2×dgReaction\ time = \sqrt{\frac{2 \times d}{g}}

💡Examples

Problem 1:

Calculate the speed of a nerve impulse if a person reacts to a stimulus 1.2 m1.2\ m away from the brain in 0.015 s0.015\ s.

Solution:

Speed=1.2 m0.015 s=80 m/sSpeed = \frac{1.2\ m}{0.015\ s} = 80\ m/s

Explanation:

The speed of the impulse is determined by dividing the distance traveled along the neurone by the time taken for the electrical signal to reach the destination.

Problem 2:

Describe the state of the eye components when focusing on a distant object.

Solution:

Ciliary muscles relax →\rightarrow Suspensory ligaments pull tight →\rightarrow Lens becomes thin and less convex.

Explanation:

To focus on distant objects, light rays enter the eye nearly parallel and require less refraction. A thinner lens provides the lower refractive power needed to focus the image onto the retinaretina.

Problem 3:

In the pupil reflex, what happens to the muscles of the iris when moving from a dark room to a bright environment?

Solution:

The Circular muscles contract and the Radial muscles relax.

Explanation:

This antagonistic muscle action reduces the diameter of the pupil to limit the amount of light entering the eye, preventing damage to the light-sensitive cells in the retinaretina.

Nervous control in humans - Revision Notes & Key Diagrams | IGCSE Grade 12 Biology