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Coordination and Response - Nervous control in humans

Grade 11IGCSEBiology

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 (CNS) - the brain and spinal cord - and the Peripheral Nervous System (PNS).

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Neurons are specialized cells: Sensory neurons transmit impulses from receptors to the CNS; Motor neurons transmit impulses from the CNS to effectors (muscles or glands); Relay neurons connect sensory and motor neurons within the CNS.

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The Reflex Arc is an involuntary, rapid response to a stimulus. The pathway follows: Stimulus →\rightarrow Receptor →\rightarrow Sensory Neuron →\rightarrow Relay Neuron (in spinal cord) →\rightarrow Motor Neuron →\rightarrow Effector →\rightarrow Response.

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Synapses are junctions between neurons. Signal transmission involves the release of neurotransmitters from vesicles, which diffuse across the synaptic cleft and bind to receptor proteins on the postsynaptic membrane.

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The Pupil Reflex protects the retina. In bright light, circular muscles contract and radial muscles relax (pupil constricts). In dim light, radial muscles contract and circular muscles relax (pupil dilates).

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Accommodation is the process of focusing on objects at different distances. For near objects, ciliary muscles contract, suspensory ligaments become slack, and the lens becomes more convex (rounder).

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Nerve impulses involve the movement of ions such as Na+Na^+ and K+K^+ across the axon membrane to create an action potential.

📐Formulae

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

Reaction Time (s)=2hg\text{Reaction Time (s)} = \sqrt{\frac{2h}{g}}

💡Examples

Problem 1:

During a ruler drop test to measure reaction time, a student catches a ruler after it has fallen a distance of h=0.2h = 0.2 meters. Calculate the reaction time tt, assuming g≈9.8 m/s2g \approx 9.8 \text{ m/s}^2.

Solution:

t=2×0.29.8≈0.202 st = \sqrt{\frac{2 \times 0.2}{9.8}} \approx 0.202 \text{ s}

Explanation:

The reaction time is calculated using the physics formula for a falling object, where the distance fallen relates to the time taken for the nervous system to process the visual stimulus and trigger a motor response in the fingers.

Problem 2:

Explain the movement of a nerve impulse across a synapse involving calcium ions (Ca2+Ca^{2+}).

Solution:

When an impulse reaches the presynaptic knob, Ca2+Ca^{2+} ions enter the neuron, causing vesicles to fuse with the membrane and release neurotransmitters into the synaptic cleft.

Explanation:

The concentration gradient of Ca2+Ca^{2+} is essential for converted electrical signals into chemical signals (neurotransmitters) to cross the gap.

Nervous control in humans - Revision Notes & Key Diagrams | IGCSE Grade 11 Biology