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Human Physiology - The Nervous System

Grade 9IB

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

🔑Concepts

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The Nervous System is divided into the Central Nervous System (CNS), consisting of the brain and spinal cord, and the Peripheral Nervous System (PNS), consisting of nerves outside the CNS.

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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 transmits signals).

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

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Synaptic transmission is the process where a signal passes between neurons across a gap called the synaptic cleft. It involves the release of chemicals called neurotransmitters (e.g., acetylcholine).

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The resting potential of a neuron is typically around −70 mV-70\ mV, maintained by the sodium-potassium pump (Na+/K+-ATPaseNa^+/K^+\text{-ATPase}), which pumps 3Na+3Na^+ out for every 2K+2K^+ in.

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An action potential occurs when a stimulus causes the membrane potential to reach a threshold (usually −55 mV-55\ mV), leading to depolarization as Na+Na^+ channels open.

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Myelination involves the fatty myelin sheath produced by Schwann cells, which insulates the axon and allows for saltatory conduction, significantly increasing impulse speed.

📐Formulae

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

t = \sqrt{ rac{2h}{g}}

ΔV=Vinside−Voutside\Delta V = V_{inside} - V_{outside}

Percentage Change=Final−InitialInitial×100\text{Percentage Change} = \frac{\text{Final} - \text{Initial}}{\text{Initial}} \times 100

💡Examples

Problem 1:

In a reaction time experiment using the ruler-drop method, a student catches a ruler after it has fallen a vertical distance of h=15 cmh = 15\ cm. Calculate the reaction time tt given g=9.8 m/s2g = 9.8\ m/s^2.

Solution:

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

Explanation:

To find the time, we convert distance to meters (0.15 m0.15\ m) and use the kinematic equation h=12gt2h = \frac{1}{2}gt^2, rearranged to solve for tt.

Problem 2:

Explain the movement of ions during the depolarization phase of an action potential.

Solution:

Voltage-gated Na+Na^+ channels open, allowing Na+Na^+ ions to rush into the neuron.

Explanation:

Depolarization is characterized by a rapid change in membrane potential from negative toward positive. This is caused by the influx of positively charged sodium ions (Na+Na^+) following their electrochemical gradient.

Problem 3:

If a nerve impulse travels 1.2 meters1.2\ meters in 0.02 seconds0.02\ seconds, what is the speed of the impulse?

Solution:

v=1.20.02=60 m/sv = \frac{1.2}{0.02} = 60\ m/s

Explanation:

Speed is calculated using the formula v=dtv = \frac{d}{t}, where dd is distance in meters and tt is time in seconds.

The Nervous System - Revision Notes & Key Formulas | IB Grade 9 Science