What is the Nervous System?
The nervous system is the body's communication network, made of the brain, spinal cord and nerves. Its basic functional unit is the neuron, a specialized cell that transmits electrical and chemical signals.
The nervous system controls the body using neurons — cells with dendrites, a cell body and an axon — that carry electrical impulses and communicate through chemical synapses.
- 1↓DendritesBranch-like extensions that receive signals from other neurons.
- 2↓Cell body (soma)Contains the nucleus and organelles; integrates incoming signals.
- 3↓AxonLong fiber that conducts the electrical impulse (action potential) away from the soma.
- 4↓Myelin sheathFatty insulation around the axon that speeds up signal conduction.
- 5Axon terminalsEnd branches that release neurotransmitters to the next cell across a synapse.
Step-by-step worked examples
A myelinated neuron conducts an impulse at about 100 m/s, while an unmyelinated one conducts at about 1 m/s. How many times faster is the myelinated neuron?
Speed ratio = myelinated speed ÷ unmyelinated speed Ratio = 100 / 1 = 100 The myelinated neuron conducts the signal 100 times faster.
The human brain has roughly 86 billion neurons, and each neuron can form about 1,000 to 10,000 synaptic connections. Using 7,000 as an average, roughly how many total synapses exist?
Total synapses ≈ neurons × average connections Total ≈ 86,000,000,000 × 7,000 Total ≈ 6.02 × 10¹⁴ (about 600 trillion synapses)
A sciatic nerve signal travels 1 meter at 100 m/s. How long does it take to reach its destination?
time = distance / speed time = 1 m / 100 m/s = 0.01 s That is 10 milliseconds for the impulse to travel 1 meter.
Flashcards
Quick quiz
Q1.Which part of a neuron receives incoming signals?
Q2.What does the myelin sheath do?
Q3.Which division of the nervous system includes the brain and spinal cord?
Q4.Which neuron type carries signals from sense organs to the CNS?
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Common mistakes
Thinking all nerve cells are identical. — Correct: Neurons vary widely in shape and function — sensory, motor and interneurons all play different roles.
Believing glial cells transmit signals like neurons. — Correct: Glial cells support, insulate and protect neurons but don't typically transmit electrical impulses themselves.
Assuming signals always travel at the same speed. — Correct: Conduction speed varies a lot — myelinated axons can conduct over 100x faster than unmyelinated ones.
Confusing the nerve (a bundle of axons) with a single neuron. — Correct: A nerve is a cable-like bundle of many neuron axons; a neuron is a single cell.
FAQ
What is the nervous system?
The nervous system is the body's network of neurons, spinal cord and brain that senses stimuli, processes information and controls responses.
What is a neuron?
A neuron is a specialized cell with dendrites, a cell body and an axon that transmits electrical and chemical signals throughout the nervous system.
What are examples of neurons?
Sensory neurons (detect touch or light), motor neurons (control muscle movement) and interneurons (relay signals within the brain and spinal cord).
How is neuron signal speed calculated?
Conduction speed = distance traveled ÷ time taken; myelinated neurons can reach speeds around 100 m/s, versus about 1 m/s for unmyelinated ones.